Synth-DIY Yahoo! Groups Archives

Thread

Photo Resist Gelatin Bicromate Process

2010-07-29 by Athar Kaludi

Hi All

I come across a guy making a printing block of Printing press on Zinc Plate by exposing in sunlight by negative film. Then after developing he etch to remove unexposed area of Zinc.

I suppose the same can be applied for PCB. I asked and learned the process there.

The process require to mix 3 table spoon of Gelatin in 250 ml of water slowly gently heating for 20 - 30 minutes. Dissolved gelatin become gel like - upon cooling mix 2 - 4 gms of Ammonium bichromate [yellow orange powder] in gelatin. The byproduct is light sensitive now so use in subdued light only and keep in brown bottle.
Layer the gel on cooper clad and completely dry. Now expose via circuit film for 4 - 5 min in sunlight. Develop in tap water and dry. Etch the Copper clad in etching solution and circuit is ready.

Any one used this process or can any thing better known to users to add to this will be appreciated and helpful.

Athar Kaludi
Karachi, Pakistan
Premium PCB Manufacturing


 



      

[Non-text portions of this message have been removed]

Re: [Homebrew_PCBs] Photo Resist Gelatin Bicromate Process

2010-07-29 by Leon Heller

On 29/07/2010 10:04, Athar Kaludi wrote:
> Hi All
>
> I come across a guy making a printing block of Printing press on Zinc Plate by exposing in sunlight by negative film. Then after developing he etch to remove unexposed area of Zinc.
>
> I suppose the same can be applied for PCB. I asked and learned the process there.
>
> The process require to mix 3 table spoon of Gelatin in 250 ml of water slowly gently heating for 20 - 30 minutes. Dissolved gelatin become gel like - upon cooling mix 2 - 4 gms of Ammonium bichromate [yellow orange powder] in gelatin. The byproduct is light sensitive now so use in subdued light only and keep in brown bottle.
> Layer the gel on cooper clad and completely dry. Now expose via circuit film for 4 - 5 min in sunlight. Develop in tap water and dry. Etch the Copper clad in etching solution and circuit is ready.
>
> Any one used this process or can any thing better known to users to add to this will be appreciated and helpful.


Be careful with ammonium bichromate, chromium compounds are very toxic.

Leon
-- 
Leon Heller
G1HSM

Modifying a Epson Stylus 220

2010-07-29 by Kamal Edirisinghe

Dear Friends,

Has anybody modified a Epson Stylus 220 for PCB printing. I do not have a Epson 
Photo 220 ,so I opened what I have . Almost all the plastic covers are removed 
except the bottom guides.But it looks to me like it is not easy to modify this 
printer for PCB direct printing.

Any idea or help is appreciated.

Thanks
Kamal
Sri Lanka
 
 


      

[Non-text portions of this message have been removed]

Re: [Homebrew_PCBs] Photo Resist Gelatin Bicromate Process

2010-07-29 by James Bishop

Sounds interesting. I did a google search and what you are talking about
seems to be called Dichromated Gelatin. It is used for making holograms.
Apparently it can support very fine detail, so it might be useful as a
photo-resist.

Here is a link:
http://www.holowiki.com/index.php/Dichromated_Gelatin_Chemistry

<http://www.holowiki.com/index.php/Dichromated_Gelatin_Chemistry>Also, it is
called ammonium Dichromate not bichromate.

James.

On Thu, Jul 29, 2010 at 7:04 PM, Athar Kaludi <ceo_premium@...> wrote:

>
>
> Hi All
>
> I come across a guy making a printing block of Printing press on Zinc Plate
> by exposing in sunlight by negative film. Then after developing he etch to
> remove unexposed area of Zinc.
>
> I suppose the same can be applied for PCB. I asked and learned the process
> there.
>
> The process require to mix 3 table spoon of Gelatin in 250 ml of water
> slowly gently heating for 20 - 30 minutes. Dissolved gelatin become gel like
> - upon cooling mix 2 - 4 gms of Ammonium bichromate [yellow orange powder]
> in gelatin. The byproduct is light sensitive now so use in subdued light
> only and keep in brown bottle.
> Layer the gel on cooper clad and completely dry. Now expose via circuit
> film for 4 - 5 min in sunlight. Develop in tap water and dry. Etch the
> Copper clad in etching solution and circuit is ready.
>
> Any one used this process or can any thing better known to users to add to
> this will be appreciated and helpful.
>
> Athar Kaludi
> Karachi, Pakistan
> Premium PCB Manufacturing
>
>
>
> [Non-text portions of this message have been removed]
>
>  
>


[Non-text portions of this message have been removed]

Modifying a Epson Stylus 220

2010-07-29 by Bob Butcher

Modifying the printer is only part of the problem. Have you tested the ink to see if it is waterproof? If you use water based ink, the etchant will dissolve the ink and you will remove all the copper, not just where desired. Most ink jet printers use water based ink, however solvent based ink is made. IMHO the solvent based ink would plug the nozzles on a water based printer, so it is not simple to switch. I have used India Ink applied by hand with some success, but sometimes it comes off as well.

Bob




      

[Non-text portions of this message have been removed]

Re: [Homebrew_PCBs] Modifying a Epson Stylus 220

2010-07-29 by Kamal Edirisinghe

Hi Bob,

Your point is understood. I need to get the printer modified first and then look 
for a suitable ink. 

Hoping somebody will come up with a answer to my questions.

Thanks
Kamal




________________________________

Show quoted textHide quoted text

From: Bob Butcher <bbutcher85@...>
To: Homebrew_PCBs@yahoogroups.com
Sent: Thu, July 29, 2010 8:25:38 PM
Subject: [Homebrew_PCBs] Modifying a Epson Stylus 220

Modifying the printer is only part of the problem. Have you tested the ink to 
see if it is waterproof? If you use water based ink, the etchant will dissolve 
the ink and you will remove all the copper, not just where desired. Most ink jet 
printers use water based ink, however solvent based ink is made. IMHO the 
solvent based ink would plug the nozzles on a water based printer, so it is not 
simple to switch. I have used India Ink applied by hand with some success, but 
sometimes it comes off as well.

Bob

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Re: Photo Resist Gelatin Bicromate Process

2010-07-29 by bebx2000

--- In Homebrew_PCBs@yahoogroups.com, Athar Kaludi <ceo_premium@...> wrote:
>
> Hi All
> 
> I come across a guy making a printing block of Printing press on Zinc Plate by exposing in sunlight by negative film. Then after developing he etch to remove unexposed area of Zinc.
> 
> I suppose the same can be applied for PCB. I asked and learned the process there.
> 

Bichromated  (dichromated) gelatin has a long history in the area of alternative photographic  procrsses.  There is a book entitled, "Photoresist" by W.S. DeForest  (McGraw-Hill, 1975) that outlines the evolution of photoresist as three periods,

	the 1800s natural colloids, gelatin albumen, shellac, gum arabic, glue
	the 1930s polyvinyl alcohol
	the 1950s (onward) polyvinyl  cinnamate, positive Shipley resists, dry film 

He notes that dichromated fish glue forms a highly etch resistant coating after a post bake of 350-500 deg F which is good for plates, but bad for PCBs.  Also, dichromated shellac is mentioned as one of the most successful of the naturally occurring materials for electronic applications with the ability to form fine detail and a comparatively low post bake of 200 deg F.

I think a better emulsion for PCB work can be found in polyvinyl acetate/polyvinyl alcohol formulations by virtue of its water based developing. I have been working on a DIY solder mask following the guidelines of this patent,

IMAGE-FORMING PROCESS 5556735 (Google Patents)

Examples 1 and 2 of this patent give straight forward recipes and processes for making your own solder mask. All of the ingredients are readily available. It is noted in the patent that polyvinyl acetate is only necessary to improve the toughness of the coating

My first attempt failed because I purchased polyvinyl acetate beads and I couldn't get them to dissolve in water.  They will dissolve in a number of solvents like acetone, but I didn't do this because I wanted to stick to the patent recipe. The correct product is a polyvinyl acetate dispersion like CM Bond M-2. Polyvinyl alcohol is hydrolyzed polyvinyl acetate and water soluble with a little work. The thing is, however, that both of these ingredients are the main components of white glue (aka Elmer's Glue-all and School Glue, among others). You can find references to the use of sensitized PVA glue as DIY screen printing emulsions.

I put aside the exact recipes of the cited patent and have been working with Elmer's Glue-All sensitized with ammonium dichromate together with a green pigment. This is a real trial and error process to determine the percentage of dichromate , thickness of coating and exposure time. The glue applies very easily to the circuit board and seems to self level for a uniform coating. I am pretty certain that it includes the flow aid and surfactant ingredients mentioned in the patent. Working with ammonium dichromate introduces the so called "dark reaction" so that you cannot store your sensitized boards for more than a day before exposure. Diazo may be better.

There is another patent,

Solid Photoresist and method of Making Photoresist 4447519

that outlines dipping in a 1% solution of ammonium dichromate before exposure which alleviates the storage problem. But any way you cut it, ammonium dichromate is a nasty substance that just loves to crosslink collagen; of which there is plenty in the human body. So be careful with this stuff.

I have had some success with this process, but not in a uniform manner. I do not have a lot of time to devote to this. I am convinced, however, that it can lead to a DIY solder mask once the kinks are ironed out. 

Baxter

Re: [Homebrew_PCBs] Modifying a Epson Stylus 220

2010-07-30 by Bob Butcher

It appears to me that the Epson Stylus 520 is a roll type printer rather than a flat bed printer. How do you plan to handle rigid PCB material without bending it?

Bob

--- On Thu, 7/29/10, Kamal Edirisinghe <kamediri@yahoo.com> wrote:

Show quoted textHide quoted text

From: Kamal Edirisinghe <kamediri@...>
Subject: Re: [Homebrew_PCBs] Modifying a Epson Stylus 220
To: Homebrew_PCBs@yahoogroups.com
Date: Thursday, July 29, 2010, 9:42 AM

Hi Bob,

Your point is understood. I need to get the printer modified first and then look 

for a suitable ink. 

Hoping somebody will come up with a answer to my questions.

Thanks

Kamal

________________________________

From: Bob Butcher <bbutcher85@...>

To: Homebrew_PCBs@yahoogroups.com

Sent: Thu, July 29, 2010 8:25:38 PM

Subject: [Homebrew_PCBs] Modifying a Epson Stylus 220

Modifying the printer is only part of the problem. Have you tested the ink to 

see if it is waterproof? If you use water based ink, the etchant will dissolve 

the ink and you will remove all the copper, not just where desired. Most ink jet 

printers use water based ink, however solvent based ink is made. IMHO the 

solvent based ink would plug the nozzles on a water based printer, so it is not 

simple to switch. I have used India Ink applied by hand with some success, but 

sometimes it comes off as well.

Bob

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Re: [Homebrew_PCBs] Modifying a Epson Stylus 220

2010-07-30 by Bob Butcher

It seems to me that you might want to find a flat bed ink jet printer, perhaps one that uses solvent based ink, such as the 
PromoJET  Solvent Flatbed Inkjet PrinterIt is designed to print on metal and many other surfaces. I don't know about the price.

See 
http://www.inkcups.com/equipment/inkjet-printers/promojet-solvent-ink-printer/Default.aspx

There are a few other flat bed printers, some fairly cheap, but I am not sure about the ink, probably water based.

Most of the ones I have found are pricey, ranging from $6800 to $64,000 on e-bay. 
I think trying to use solvent based ink in a water based printer will quickly damage or at least plug the print head.
Bob




      

[Non-text portions of this message have been removed]

Re: Modifying a Epson Stylus 220

2010-07-30 by alienrelics

You should ask this on the Inkjet PCB Construction list.

http://tech.groups.yahoo.com/group/Inkjet_PCB_Construction/

James Newton collected some of the more informative posts about inkjet ink as PCB resist from this list and the other and posted them here:
http://techref.massmind.org/techref/pcb/etch/directinkjetresist.htm

Steve Greenfield
PS note from the moderator: please do not start a thread by replying to another message. Even when you erase the other text and change the subject line, hidden header information remains and Yahoogroups links it to the other thread.


--- In Homebrew_PCBs@yahoogroups.com, Kamal Edirisinghe <kamediri@...> wrote:

Show quoted textHide quoted text

>
> 
> Dear Friends,
> 
> Has anybody modified a Epson Stylus 220 for PCB printing. I do not have a Epson 
> Photo 220 ,so I opened what I have . Almost all the plastic covers are removed 
> except the bottom guides.But it looks to me like it is not easy to modify this 
> printer for PCB direct printing.
> 
> Any idea or help is appreciated.
> 
> Thanks
> Kamal
> Sri Lanka
>  
>  
> 
> 
>       
> 
> [Non-text portions of this message have been removed]
>

Photo Resist Gelatin NO Bicromate Process

2010-07-30 by Athar Kaludi

Gary

Thanks for reply. Helpful.

I also want to get rid off the bicromate. As you mentioned can you name the chemical name so that i can also try that.
Secondly the adhesion problem on copper i am also facing - Can i try other things in resin other than Elmer glue. Any idea,.

ATHAR 

--- On Fri, 7/30/10, garydeal <garydeal@...> wrote:

Show quoted textHide quoted text

From: garydeal <garydeal@ucom.net>
Subject: [Homebrew_PCBs] Re: Photo Resist Gelatin Bicromate Process
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 30, 2010, 4:07 PM







 



  


    
      
      
      >But any way you cut it, ammonium dichromate is a nasty substance that just 

>loves to crosslink collagen; of which there is plenty in the human body. 

>So be careful with this stuff.



Yes, quite. If you've seen the "Erin Brockovitch" (sp?) movie, the 

substance that was getting into the groundwater (and ruining people) was 

hexavalent chromium, which is the ammonium, potassium, sodium, etc., 

dichromates.



I believe that the information on chromated gelatin over at the 

holography site includes something regarding mixing waste dichromate 

solutions and wash water containing dichromates with used photographic 

developer, which changes it to an insoluble form. This drastically 

reduces it's impact.



I used to be involved in the corporate use of this process on a 

relatively small scale, and they eventually had to stop and find a 

replacement. An industrial silkscreen-making goop (diazo?) ended up being 

the thing, it dropped right into the process (being sprayed on, resisting 

acetone, coming off with bleach, etc). The toughest part was figuring out 

how to measure it out for amounts much smaller than the one-gallon kit.



In the above process, I was aware that a competing company would add 

Elmer's white glue to the mix when they had adhesion problems with the 

plain gelatin/dichromate mixture. I'm not sure if they realized that the 

glue was also crosslinking.



The green pigment may not be the best choice for sensitizing (the 

base mixture requires UV). Look on the holography site for information on 

red-sensitive DCG - although then you'll have to use a dark green 

safelight, which gives rise to the phrase "working in the green 

darkness". It's probably easier to come up with enough UV, I expose UV 

sensitive resist with a cheap 500 watt halogen with the UV shield glass 

removed (~4 minutes at 18 inches through an old glass-topped photo 

contact printer).





    
     

    
    


 



  






      

[Non-text portions of this message have been removed]

Re: Photo Resist Gelatin Bicromate Process

2010-07-30 by garydeal

>But any way you cut it, ammonium dichromate is a nasty substance that just 
>loves to crosslink collagen; of which there is plenty in the human body. 
>So be careful with this stuff.


     Yes, quite. If you've seen the "Erin Brockovitch" (sp?) movie, the 
substance that was getting into the groundwater (and ruining people) was 
hexavalent chromium, which is the ammonium, potassium, sodium, etc., 
dichromates.

     I believe that the information on chromated gelatin over at the 
holography site includes something regarding mixing waste dichromate 
solutions and wash water containing dichromates with used photographic 
developer, which changes it to an insoluble form. This drastically 
reduces it's impact.

     I used to be involved in the corporate use of this process on a 
relatively small scale, and they eventually had to stop and find a 
replacement. An industrial silkscreen-making goop (diazo?) ended up being 
the thing, it dropped right into the process (being sprayed on, resisting 
acetone, coming off with bleach, etc). The toughest part was figuring out 
how to measure it out for amounts much smaller than the one-gallon kit.

     In the above process, I was aware that a competing company would add 
Elmer's white glue to the mix when they had adhesion problems with the 
plain gelatin/dichromate mixture. I'm not sure if they realized that the 
glue was also crosslinking.

     The green pigment may not be the best choice for sensitizing (the 
base mixture requires UV). Look on the holography site for information on 
red-sensitive DCG - although then you'll have to use a dark green 
safelight, which gives rise to the phrase "working in the green 
darkness". It's probably easier to come up with enough UV, I expose UV 
sensitive resist with a cheap 500 watt halogen with the UV shield glass 
removed (~4 minutes at 18 inches through an old glass-topped photo 
contact printer).

Re: Photo Resist Gelatin Bicromate Process

2012-01-24 by Jeff

Hi Baxter,

I bought some ammonium dichromate and will try the patent you suggested of 1% solution ammonium dichromate sensitizer.  My question is, do you know what the 1% is in reference to?  Is it 1% by weight?  For example, mixing 99 grams of water and 1 gram of ammonium dichromate?

Jeff


--- In Homebrew_PCBs@yahoogroups.com, "bebx2000" <bebx2000@...> wrote:

Show quoted textHide quoted text

>
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, Athar Kaludi <ceo_premium@> wrote:
> >
> > Hi All
> > 
> > I come across a guy making a printing block of Printing press on Zinc Plate by exposing in sunlight by negative film. Then after developing he etch to remove unexposed area of Zinc.
> > 
> > I suppose the same can be applied for PCB. I asked and learned the process there.
> > 
> 
> Bichromated  (dichromated) gelatin has a long history in the area of alternative photographic  procrsses.  There is a book entitled, "Photoresist" by W.S. DeForest  (McGraw-Hill, 1975) that outlines the evolution of photoresist as three periods,
> 
> 	the 1800s natural colloids, gelatin albumen, shellac, gum arabic, glue
> 	the 1930s polyvinyl alcohol
> 	the 1950s (onward) polyvinyl  cinnamate, positive Shipley resists, dry film 
> 
> He notes that dichromated fish glue forms a highly etch resistant coating after a post bake of 350-500 deg F which is good for plates, but bad for PCBs.  Also, dichromated shellac is mentioned as one of the most successful of the naturally occurring materials for electronic applications with the ability to form fine detail and a comparatively low post bake of 200 deg F.
> 
> I think a better emulsion for PCB work can be found in polyvinyl acetate/polyvinyl alcohol formulations by virtue of its water based developing. I have been working on a DIY solder mask following the guidelines of this patent,
> 
> IMAGE-FORMING PROCESS 5556735 (Google Patents)
> 
> Examples 1 and 2 of this patent give straight forward recipes and processes for making your own solder mask. All of the ingredients are readily available. It is noted in the patent that polyvinyl acetate is only necessary to improve the toughness of the coating
> 
> My first attempt failed because I purchased polyvinyl acetate beads and I couldn't get them to dissolve in water.  They will dissolve in a number of solvents like acetone, but I didn't do this because I wanted to stick to the patent recipe. The correct product is a polyvinyl acetate dispersion like CM Bond M-2. Polyvinyl alcohol is hydrolyzed polyvinyl acetate and water soluble with a little work. The thing is, however, that both of these ingredients are the main components of white glue (aka Elmer's Glue-all and School Glue, among others). You can find references to the use of sensitized PVA glue as DIY screen printing emulsions.
> 
> I put aside the exact recipes of the cited patent and have been working with Elmer's Glue-All sensitized with ammonium dichromate together with a green pigment. This is a real trial and error process to determine the percentage of dichromate , thickness of coating and exposure time. The glue applies very easily to the circuit board and seems to self level for a uniform coating. I am pretty certain that it includes the flow aid and surfactant ingredients mentioned in the patent. Working with ammonium dichromate introduces the so called "dark reaction" so that you cannot store your sensitized boards for more than a day before exposure. Diazo may be better.
>  
> There is another patent,
> 
> Solid Photoresist and method of Making Photoresist 4447519
> 
> that outlines dipping in a 1% solution of ammonium dichromate before exposure which alleviates the storage problem. But any way you cut it, ammonium dichromate is a nasty substance that just loves to crosslink collagen; of which there is plenty in the human body. So be careful with this stuff.
> 
> I have had some success with this process, but not in a uniform manner. I do not have a lot of time to devote to this. I am convinced, however, that it can lead to a DIY solder mask once the kinks are ironed out. 
> 
> Baxter
>

MGR Dry Film Photoresist Sold by SRA Solder

2012-01-24 by Rich Osman

I'm sure it's a repack of another vendors product.  Any one have any pro
or con comments. 

I've had good luck with SRA as a vendor.

-- 
mailto:lists@...     http://www.n1oz.net       ARS: N1OZ
Rich Osman;  POB 93167; Southlake, TX 76092 (Near DFW Airport)

Re: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-24 by David

Hi,
I'm not familiar with SRA, but, I have used dry film photoresist and had excellent results, [no mess!!] I've purchased in the past from this seller on Ebay:

http://www.ebay.co.uk/itm/320735056113?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Reliable service and not too expensive!


--- In Homebrew_PCBs@yahoogroups.com, Rich Osman <lists@...> wrote:

Show quoted textHide quoted text

>
> I'm sure it's a repack of another vendors product.  Any one have any pro
> or con comments. 
> 
> I've had good luck with SRA as a vendor.
> 
> -- 
> mailto:lists@...     http://www.n1oz.net       ARS: N1OZ
> Rich Osman;  POB 93167; Southlake, TX 76092 (Near DFW Airport)
>

Re: [Homebrew_PCBs] Re: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-24 by Roland Harriston

David:

Does this  Ebay  seller also sell the developer for this film?
What is the developer for this type of  film?

Thanks for the info.

Roland F. Harriston, P.D.
*******************
>  
>
> Hi,
> I'm not familiar with SRA, but, I have used dry film photoresist and 
> had excellent results, [no mess!!] I've purchased in the past from 
> this seller on Ebay:
>
> http://www.ebay.co.uk/itm/320735056113?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 
> <http://www.ebay.co.uk/itm/320735056113?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649>
>



[Non-text portions of this message have been removed]

Re: Photo Resist Gelatin Bicromate Process

2012-01-24 by bebx2000

Jeff,

I am pretty sure that patent (4447519) is talking about a weight/volume solution. Ammonium dichromate solubility is 36.4g/100g water(1 g water = 1 ml water) at 68F according to the MSDS. So the maximum solution that you can get is ~ 36%. So what I did was make a saturated solution and then dilute it to 1%. The formula for weight percent (w/v) is: [Mass of solute (g) / Volume of solution (ml)] x 100.

The correct procedure is weigh say, 10 grams of ammonium dichromate and dissolve it in 900 ml of distilled water and then bring the final volume up to 1000 ml. I don't think you need to be too precise. More sensitizer will only reduce the exposure time.

Baxter

--- In Homebrew_PCBs@yahoogroups.com, "Jeff" <jeff.heiss@...> wrote:

Show quoted textHide quoted text

>
> Hi Baxter,
> 
> I bought some ammonium dichromate and will try the patent you suggested of 1% solution ammonium dichromate sensitizer.  My question is, do you know what the 1% is in reference to?  Is it 1% by weight?  For example, mixing 99 grams of water and 1 gram of ammonium dichromate?
> 
> Jeff
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, "bebx2000" <bebx2000@> wrote:
> >
> > 
> > 
> > --- In Homebrew_PCBs@yahoogroups.com, Athar Kaludi <ceo_premium@> wrote:
> > >
> > > Hi All
> > > 
> > > I come across a guy making a printing block of Printing press on Zinc Plate by exposing in sunlight by negative film. Then after developing he etch to remove unexposed area of Zinc.
> > > 
> > > I suppose the same can be applied for PCB. I asked and learned the process there.
> > > 
> > 
> > Bichromated  (dichromated) gelatin has a long history in the area of alternative photographic  procrsses.  There is a book entitled, "Photoresist" by W.S. DeForest  (McGraw-Hill, 1975) that outlines the evolution of photoresist as three periods,
> > 
> > 	the 1800s natural colloids, gelatin albumen, shellac, gum arabic, glue
> > 	the 1930s polyvinyl alcohol
> > 	the 1950s (onward) polyvinyl  cinnamate, positive Shipley resists, dry film 
> > 
> > He notes that dichromated fish glue forms a highly etch resistant coating after a post bake of 350-500 deg F which is good for plates, but bad for PCBs.  Also, dichromated shellac is mentioned as one of the most successful of the naturally occurring materials for electronic applications with the ability to form fine detail and a comparatively low post bake of 200 deg F.
> > 
> > I think a better emulsion for PCB work can be found in polyvinyl acetate/polyvinyl alcohol formulations by virtue of its water based developing. I have been working on a DIY solder mask following the guidelines of this patent,
> > 
> > IMAGE-FORMING PROCESS 5556735 (Google Patents)
> > 
> > Examples 1 and 2 of this patent give straight forward recipes and processes for making your own solder mask. All of the ingredients are readily available. It is noted in the patent that polyvinyl acetate is only necessary to improve the toughness of the coating
> > 
> > My first attempt failed because I purchased polyvinyl acetate beads and I couldn't get them to dissolve in water.  They will dissolve in a number of solvents like acetone, but I didn't do this because I wanted to stick to the patent recipe. The correct product is a polyvinyl acetate dispersion like CM Bond M-2. Polyvinyl alcohol is hydrolyzed polyvinyl acetate and water soluble with a little work. The thing is, however, that both of these ingredients are the main components of white glue (aka Elmer's Glue-all and School Glue, among others). You can find references to the use of sensitized PVA glue as DIY screen printing emulsions.
> > 
> > I put aside the exact recipes of the cited patent and have been working with Elmer's Glue-All sensitized with ammonium dichromate together with a green pigment. This is a real trial and error process to determine the percentage of dichromate , thickness of coating and exposure time. The glue applies very easily to the circuit board and seems to self level for a uniform coating. I am pretty certain that it includes the flow aid and surfactant ingredients mentioned in the patent. Working with ammonium dichromate introduces the so called "dark reaction" so that you cannot store your sensitized boards for more than a day before exposure. Diazo may be better.
> >  
> > There is another patent,
> > 
> > Solid Photoresist and method of Making Photoresist 4447519
> > 
> > that outlines dipping in a 1% solution of ammonium dichromate before exposure which alleviates the storage problem. But any way you cut it, ammonium dichromate is a nasty substance that just loves to crosslink collagen; of which there is plenty in the human body. So be careful with this stuff.
> > 
> > I have had some success with this process, but not in a uniform manner. I do not have a lot of time to devote to this. I am convinced, however, that it can lead to a DIY solder mask once the kinks are ironed out. 
> > 
> > Baxter
> >
>

MoRe: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-24 by Rich Osman

SRA sells a 1' x 5' roll of MG 416DFR Negative Dry Film Photo Resist for
$15.95

http://sra-solder.com/product.php?xProd=6652

and MG 4170-500ML Negative Developer for $9.95 (makes 5.5 liters)

http://sra-solder.com/product.php/6659/0

The eBay seller sells slightly more area of film (80 inches vs 60 for
MG) but it's cut up in 6 X 8" pieces for $15 delivered.

He sells resist developer in 20 gram bags which will make 2 Liters of
developer for about $6.25 delivered to US addresses.


On 1/24/2012 1:16 PM, Roland Harriston wrote:
>  
>
> David:
>
> Does this Ebay seller also sell the developer for this film?
> What is the developer for this type of film?
>
> Thanks for the info.
>
> Roland F. Harriston, P.D.
> *******************
> >
>

-- 
mailto:lists@...     http://www.n1oz.net       ARS: N1OZ
Rich Osman;  POB 93167; Southlake, TX 76092 (Near DFW Airport) 






[Non-text portions of this message have been removed]

Re: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-24 by bebx2000

The change of color when exposed is a real plus. I find that determining correct exposure time is a real pain when working with Riston or similar products.

Baxter

--- In Homebrew_PCBs@yahoogroups.com, Rich Osman <lists@...> wrote:

Show quoted textHide quoted text

>
> I'm sure it's a repack of another vendors product.  Any one have any pro
> or con comments. 
> 
> I've had good luck with SRA as a vendor.
> 
> -- 
> mailto:lists@...     http://www.n1oz.net       ARS: N1OZ
> Rich Osman;  POB 93167; Southlake, TX 76092 (Near DFW Airport)
>

Re: [Homebrew_PCBs] Re: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-24 by Roberto

Hello, I use it for a year and sold take that works well in rolls of 2 meters are able to make the RF PCB with high resolution take it good
Roberto

Show quoted textHide quoted text

  ----- Original Message ----- 
  From: David 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Tuesday, January 24, 2012 7:18 PM
  Subject: [Homebrew_PCBs] Re: MGR Dry Film Photoresist Sold by SRA Solder


    
  Hi,
  I'm not familiar with SRA, but, I have used dry film photoresist and had excellent results, [no mess!!] I've purchased in the past from this seller on Ebay:

  http://www.ebay.co.uk/itm/320735056113?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

  Reliable service and not too expensive!

  --- In Homebrew_PCBs@yahoogroups.com, Rich Osman <lists@...> wrote:
  >
  > I'm sure it's a repack of another vendors product. Any one have any pro
  > or con comments. 
  > 
  > I've had good luck with SRA as a vendor.
  > 
  > -- 
  > mailto:lists@... http://www.n1oz.net ARS: N1OZ
  > Rich Osman; POB 93167; Southlake, TX 76092 (Near DFW Airport)
  >



  

[Non-text portions of this message have been removed]

MoRe: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-24 by David

Sorry for delay in replying, had to go out for a while, but i see your question was answered perfectly well, i also use "Chiltern Connections Ltd" [UK company] PCB photoresist developer which is a sodium hydroxide free product, code: CCL/PDSM/25B their contact number in UK is +44 1491 824788 FAX +44 1491 824799. not sure if its available in the US though, its main ingredient is Sodium metasilicate works perfectly well, as does the developer from the ebay dry film supplier.

--- In Homebrew_PCBs@yahoogroups.com, Rich Osman <lists@...> wrote:

Show quoted textHide quoted text

>
> SRA sells a 1' x 5' roll of MG 416DFR Negative Dry Film Photo Resist for
> $15.95
> 
> http://sra-solder.com/product.php?xProd=6652
> 
> and MG 4170-500ML Negative Developer for $9.95 (makes 5.5 liters)
> 
> http://sra-solder.com/product.php/6659/0
> 
> The eBay seller sells slightly more area of film (80 inches vs 60 for
> MG) but it's cut up in 6 X 8" pieces for $15 delivered.
> 
> He sells resist developer in 20 gram bags which will make 2 Liters of
> developer for about $6.25 delivered to US addresses.
> 
> 
> On 1/24/2012 1:16 PM, Roland Harriston wrote:
> >  
> >
> > David:
> >
> > Does this Ebay seller also sell the developer for this film?
> > What is the developer for this type of film?
> >
> > Thanks for the info.
> >
> > Roland F. Harriston, P.D.
> > *******************
> > >
> >
> 
> -- 
> mailto:lists@...     http://www.n1oz.net       ARS: N1OZ
> Rich Osman;  POB 93167; Southlake, TX 76092 (Near DFW Airport) 
> 
> 
> 
> 
> 
> 
> [Non-text portions of this message have been removed]
>

MoRe: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-24 by Roberto

Hello, I use it for a year and sold take that works well in rolls of 2 meters are able to make the RF PCB with high resolution take it good
Roberto

--- In Homebrew_PCBs@yahoogroups.com, Rich Osman <lists@...> wrote:

Show quoted textHide quoted text

>
> SRA sells a 1' x 5' roll of MG 416DFR Negative Dry Film Photo Resist for
> $15.95
> 
> http://sra-solder.com/product.php?xProd=6652
> 
> and MG 4170-500ML Negative Developer for $9.95 (makes 5.5 liters)
> 
> http://sra-solder.com/product.php/6659/0
> 
> The eBay seller sells slightly more area of film (80 inches vs 60 for
> MG) but it's cut up in 6 X 8" pieces for $15 delivered.
> 
> He sells resist developer in 20 gram bags which will make 2 Liters of
> developer for about $6.25 delivered to US addresses.
> 
> 
> On 1/24/2012 1:16 PM, Roland Harriston wrote:
> >  
> >
> > David:
> >
> > Does this Ebay seller also sell the developer for this film?
> > What is the developer for this type of film?
> >
> > Thanks for the info.
> >
> > Roland F. Harriston, P.D.
> > *******************
> > >
> >
> 
> -- 
> mailto:lists@...     http://www.n1oz.net       ARS: N1OZ
> Rich Osman;  POB 93167; Southlake, TX 76092 (Near DFW Airport) 
> 
> 
> 
> 
> 
> 
> [Non-text portions of this message have been removed]
>

Re: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-25 by David

Roland,
My mistake on my last message, I use the Sodium Metasilicate based developer for Positive Photoresist not negative photoresist!!, the product from the dry film ebay supplier is a negative developer, although, I have also used Ilford Perceptol Cat 1960529, primarily used for BW film developing, but does a reasonably good job on PCB's hope this helps

David

--- In Homebrew_PCBs@yahoogroups.com, Roland Harriston <rolohar@...> wrote:

Show quoted textHide quoted text

>
> David:
> 
> Does this  Ebay  seller also sell the developer for this film?
> What is the developer for this type of  film?
> 
> Thanks for the info.
> 
> Roland F. Harriston, P.D.
> *******************
> >  
> >
> > Hi,
> > I'm not familiar with SRA, but, I have used dry film photoresist and 
> > had excellent results, [no mess!!] I've purchased in the past from 
> > this seller on Ebay:
> >
> > http://www.ebay.co.uk/itm/320735056113?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 
> > <http://www.ebay.co.uk/itm/320735056113?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649>
> >
> 
> 
> 
> [Non-text portions of this message have been removed]
>

Re: [Homebrew_PCBs] Re: MGR Dry Film Photoresist Sold by SRA Solder

2012-01-25 by Roland Harriston

David:
Thanks for the good information.

Roland F. Harriston, P.D.
*******************

David wrote:

Show quoted textHide quoted text

>  
>
> Roland,
> My mistake on my last message, I use the Sodium Metasilicate based 
> developer for Positive Photoresist not negative photoresist!!, the 
> product from the dry film ebay supplier is a negative developer, 
> although, I have also used Ilford Perceptol Cat 1960529, primarily 
> used for BW film developing, but does a reasonably good job on PCB's 
> hope this helps
>

Re: Photo Resist Gelatin Bicromate Process

2012-01-29 by Jeff

Hi Baxter,

I was wondering if I could ask you a few details about your comment from the Photoresist book on ammonium dichromate and shellac.  Does the book mention a ratio of dichromate powder to shellac?  What is the dichromate dissolved in before mixing into the shellac?  After the shellac is UV exposed, how is the unexposed shellac removed?  Is there a develop step after exposure like traditional resist?  Is the 200 deg F post bake after board coating and before UV exposure?

Jeff


--- In Homebrew_PCBs@yahoogroups.com, "bebx2000" <bebx2000@...> wrote:

Show quoted textHide quoted text

>
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, Athar Kaludi <ceo_premium@> wrote:
> >
> > Hi All
> > 
> > I come across a guy making a printing block of Printing press on Zinc Plate by exposing in sunlight by negative film. Then after developing he etch to remove unexposed area of Zinc.
> > 
> > I suppose the same can be applied for PCB. I asked and learned the process there.
> > 
> 
> Bichromated  (dichromated) gelatin has a long history in the area of alternative photographic  procrsses.  There is a book entitled, "Photoresist" by W.S. DeForest  (McGraw-Hill, 1975) that outlines the evolution of photoresist as three periods,
> 
> 	the 1800s natural colloids, gelatin albumen, shellac, gum arabic, glue
> 	the 1930s polyvinyl alcohol
> 	the 1950s (onward) polyvinyl  cinnamate, positive Shipley resists, dry film 
> 
> He notes that dichromated fish glue forms a highly etch resistant coating after a post bake of 350-500 deg F which is good for plates, but bad for PCBs.  Also, dichromated shellac is mentioned as one of the most successful of the naturally occurring materials for electronic applications with the ability to form fine detail and a comparatively low post bake of 200 deg F.
> 
> I think a better emulsion for PCB work can be found in polyvinyl acetate/polyvinyl alcohol formulations by virtue of its water based developing. I have been working on a DIY solder mask following the guidelines of this patent,
> 
> IMAGE-FORMING PROCESS 5556735 (Google Patents)
> 
> Examples 1 and 2 of this patent give straight forward recipes and processes for making your own solder mask. All of the ingredients are readily available. It is noted in the patent that polyvinyl acetate is only necessary to improve the toughness of the coating
> 
> My first attempt failed because I purchased polyvinyl acetate beads and I couldn't get them to dissolve in water.  They will dissolve in a number of solvents like acetone, but I didn't do this because I wanted to stick to the patent recipe. The correct product is a polyvinyl acetate dispersion like CM Bond M-2. Polyvinyl alcohol is hydrolyzed polyvinyl acetate and water soluble with a little work. The thing is, however, that both of these ingredients are the main components of white glue (aka Elmer's Glue-all and School Glue, among others). You can find references to the use of sensitized PVA glue as DIY screen printing emulsions.
> 
> I put aside the exact recipes of the cited patent and have been working with Elmer's Glue-All sensitized with ammonium dichromate together with a green pigment. This is a real trial and error process to determine the percentage of dichromate , thickness of coating and exposure time. The glue applies very easily to the circuit board and seems to self level for a uniform coating. I am pretty certain that it includes the flow aid and surfactant ingredients mentioned in the patent. Working with ammonium dichromate introduces the so called "dark reaction" so that you cannot store your sensitized boards for more than a day before exposure. Diazo may be better.
>  
> There is another patent,
> 
> Solid Photoresist and method of Making Photoresist 4447519
> 
> that outlines dipping in a 1% solution of ammonium dichromate before exposure which alleviates the storage problem. But any way you cut it, ammonium dichromate is a nasty substance that just loves to crosslink collagen; of which there is plenty in the human body. So be careful with this stuff.
> 
> I have had some success with this process, but not in a uniform manner. I do not have a lot of time to devote to this. I am convinced, however, that it can lead to a DIY solder mask once the kinks are ironed out. 
> 
> Baxter
>

Re: Photo Resist Gelatin Bicromate Process

2012-01-30 by bebx2000

Hi Jeff,

The book I cited really didn't give any recipes. The reference to shellac was in a chapter devoted to the historical development of resists. Later chapters fell into the nether world of organic chemistry. This patent, 4447519, in examples 4 and 5 gives the proportions. c2h5oc2h4oh is Ethylene Glycol Monoethyl Ether which is a solvent. Union Carbide Corp. trademarked it as Cellosolve. I think it is now marketed as Butyl cellosolve. See,

http://www.chemistrystore.com/Chemicals_A_F-Butyl_Cellosolve.html

I really don't have any further details about shellac. I assume that the above solvent would remove it and its use with the sensitizer is to soften the shellac for better penetration. The post baking is to continue the crosslinking to further harden the resist. A good source for this sort of thing is under the topic of "alternative photographic processes" Look at the APUG Forum: Alternative processes. I think the PVA/PVac/Elmer's glue approach is better than using shellac, or the other glues like fish or rabbit because of the water "developing" step.

While digging through my files I came across a screen printing post for a glue sensitizer formula,

quote:
"An alternative to photo emulsion(the answer)
Wed, March 28, 2007 - 9:15 PM 

1 tsp of Ammonium Dichromate -> 1 oz. Water 
Dissolve and mix with 8 oz. Elmer's Glue 
see below (dry measure equiv.)
	1 tsp = (14.3 gm/3) = 4.76 gm
Fairly flexible open time, decent exposure times 
(10-20 minutes under daylight), rinse with water, and a 
bulletproof stencil is yours."
end quote

Baxter

--- In Homebrew_PCBs@yahoogroups.com, "Jeff" <jeff.heiss@...> wrote:

Show quoted textHide quoted text

>
> Hi Baxter,
> 
> I was wondering if I could ask you a few details about your comment from the Photoresist book on ammonium dichromate and shellac.  Does the book mention a ratio of dichromate powder to shellac?  What is the dichromate dissolved in before mixing into the shellac?  After the shellac is UV exposed, how is the unexposed shellac removed?  Is there a develop step after exposure like traditional resist?  Is the 200 deg F post bake after board coating and before UV exposure?
> 
> Jeff
> 
>

RE: [Homebrew_PCBs] Re: Photo Resist Gelatin Bicromate Process

2012-01-30 by Jeff Heiss

Hi Baxter,

 

I am trying the recipe of ammonium dichromate mixed with Elmers glue and I
am finding two things.  First, the Elmers glue does not dissolve in water
without physical agitation.  Take plain, unmixed Elmers strait from the
bottle, spread it on something, and let it dry.  Once dry, immerse it in
water.  The glue does not dissolve in the water unless rubbed lightly with
your finger.  No rubbing, no dissolving.  I left the glue in water over
night and all was still there the next day.  

 

Second, the glue hardened from UV exposure does not stick to the copper well
enough to avoid coming off during the agitation required to remove the
unexposed glue.  If the unexposed glue could dissolve on it's own in the
water, I don't think this would matter.  I would try real PVA polyvinyl
alcohol to see if it dissolves in water without agitation but I don't have
PVA.  I read that Elmers is polyvinyl acetate, not polyvinyl alcohol and
they are two different things. 

 

Jeff

 

  _____

Show quoted textHide quoted text

From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
On Behalf Of bebx2000
Sent: Sunday, January 29, 2012 11:39 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] Re: Photo Resist Gelatin Bicromate Process

Hi Jeff,

The book I cited really didn't give any recipes. The reference to shellac
was in a chapter devoted to the historical development of resists. Later
chapters fell into the nether world of organic chemistry. This patent,
4447519, in examples 4 and 5 gives the proportions. c2h5oc2h4oh is Ethylene
Glycol Monoethyl Ether which is a solvent. Union Carbide Corp. trademarked
it as Cellosolve. I think it is now marketed as Butyl cellosolve. See,

http://www.chemistrystore.com/Chemicals_A_F-Butyl_Cellosolve.html

I really don't have any further details about shellac. I assume that the
above solvent would remove it and its use with the sensitizer is to soften
the shellac for better penetration. The post baking is to continue the
crosslinking to further harden the resist. A good source for this sort of
thing is under the topic of "alternative photographic processes" Look at the
APUG Forum: Alternative processes. I think the PVA/PVac/Elmer's glue
approach is better than using shellac, or the other glues like fish or
rabbit because of the water "developing" step.

While digging through my files I came across a screen printing post for a
glue sensitizer formula,

quote:
"An alternative to photo emulsion(the answer)
Wed, March 28, 2007 - 9:15 PM 

1 tsp of Ammonium Dichromate -> 1 oz. Water 
Dissolve and mix with 8 oz. Elmer's Glue 
see below (dry measure equiv.)
1 tsp = (14.3 gm/3) = 4.76 gm
Fairly flexible open time, decent exposure times 
(10-20 minutes under daylight), rinse with water, and a 
bulletproof stencil is yours."
end quote

Baxter

--- In Homebrew_PCBs@yahoogroups.com
<mailto:Homebrew_PCBs%40yahoogroups.com> , "Jeff" <jeff.heiss@...> wrote:
>
> Hi Baxter,
> 
> I was wondering if I could ask you a few details about your comment from
the Photoresist book on ammonium dichromate and shellac. Does the book
mention a ratio of dichromate powder to shellac? What is the dichromate
dissolved in before mixing into the shellac? After the shellac is UV
exposed, how is the unexposed shellac removed? Is there a develop step after
exposure like traditional resist? Is the 200 deg F post bake after board
coating and before UV exposure?
> 
> Jeff
> 
> 

[Non-text portions of this message have been removed]

Re: [Homebrew_PCBs] Re: Photo Resist Gelatin Bicromate Process

2012-01-30 by Charles Patton

A few bits of anecdotal experience and personal observations about photo 
resists (mostly from experiences 40 years ago.)

1) I always thought of photo resists as primarily polar (water soluble) 
and non-polar (organic solvent such as Toulene.)   You chose the resist 
to match the need application.  I.e., if you were going to make a silk 
screen to apply paint patterns, you chose a polar resist such as gelatin 
or polyvinyl alcohol because it was essentially immune to the petroleum 
solvents in the paint.  If you were etching a PCB (that uses and aqueous 
solution) you chose a non-polar  resist (Dychem aerosol) that required a 
solvent such as Toluene or Tri-chlor so it was completely immune to the 
aqueous etchant.

2) Having said that, it has already been mentioned the process of making 
printing plates.  I knew nothing of how to make printed circuits so I 
thought of a local platemaking shop and went there to learn how to etch 
metal.  It was an education.  They got around the problem of an aqueous 
resist in a rather nasty fashion.
   a) The resist (I believe it was either dichromate sensitized 
polyvinyl alcohol or egg albumin)  was flowed onto the zinc plate and 
essentially air dried at near room temp.
   b) The plate was then exposed with a negative and an arc lamp.
   c) The plate was washed with warm water to remove the unexposed resist.
   d) The plate was dipped in a chromic acid solution.
   e) The plate was placed on a flame burner and the temperature raised 
until the resist turned a dark chocolate brown color.  At this point the 
resist is so totally cross-linked because of the chromic acid and heat 
so that no solvent, polar or non-polar will touch it.   They etched with 
splash/spray of ferric chloride.    An additional step was to powder the 
surface with "dragon's blood"(?) and by allowing most of it to slide 
off, then setting it with heat(?).  That additional process could pretty 
much control undercutting, even when etching as deep as 0.050" or more.  
As previous posters mentioned however, that heat treatment is well 
beyond what a PCB can handle.

3) Later I learned the proper processes.  We primarily used 
silkscreening with an asphalt like ink and bubble etched with ferric 
chloride.  So the screens were make using di-chromate sensitized 
gelatin  per 1) above being an aqueous resist worked very well with a 
solvent based ink.  No high temperatures needed.  The gelatin was coated 
on paper and we would dip it into ammonia dichromate, roll a plastic 
sheet onto the surface, and expose through a positive  with an arc 
lamp.  Basically the carbon tissue photographic process. Soak in water 
and wash off the paper sheet and unexposed gelatin. The pattern remained 
on the plastic sheet.  Then press the pattern into the silkscreen.   The 
other process was to sensitize polyvinyl alcohol and coat the silkscreen 
with it, dry, and expose, then wash it out.  Either method worked.  
Presentized sheets were available but didn't have a good shelf life for 
our consumption rate.

4) The times we needed one-offs or finer lines we used the aerosol 
Dychem resist that we developed with trichloroethylene .(Tri-Chlor)

The solvent based films were bad news as the solvents 
are/**/carcinogenic and bad for the lungs.  The new films with carbonate 
developers I believe work on the principle  that the developer is 
alkaline and the etchant is acidic so the PH controls whether the film 
stays intact.  (someone more knowledgeable about this could certainly 
clarify this point.)

Anyway, some notes from the dinosaur age.

Regards,
Charles R. Patton


*//* <http://www.google.com/search?lr=&q=carcinogenic&start=0&spell=1>

RE: [Homebrew_PCBs] Re: Photo Resist Gelatin Bicromate Process

2012-01-30 by MIKE DURKIN

Let it dry? Shouldn't you just figure out what one ounce dried out weighs then calc out how much one ounce dry weighs when wet...? Then add to the adjusted value of 8oz ?

If I had some ammonium dichromate I would give it a whirl!!


To: Homebrew_PCBs@yahoogroups.com

Show quoted textHide quoted text

From: jeff.heiss@...
Date: Mon, 30 Jan 2012 00:05:18 -0500
Subject: RE: [Homebrew_PCBs] Re: Photo Resist Gelatin Bicromate Process

      Hi Baxter,

I am trying the recipe of ammonium dichromate mixed with Elmers glue and I

am finding two things.  First, the Elmers glue does not dissolve in water

without physical agitation.  Take plain, unmixed Elmers strait from the

bottle, spread it on something, and let it dry.  Once dry, immerse it in

water.  The glue does not dissolve in the water unless rubbed lightly with

your finger.  No rubbing, no dissolving.  I left the glue in water over

night and all was still there the next day.  

Second, the glue hardened from UV exposure does not stick to the copper well

enough to avoid coming off during the agitation required to remove the

unexposed glue.  If the unexposed glue could dissolve on it's own in the

water, I don't think this would matter.  I would try real PVA polyvinyl

alcohol to see if it dissolves in water without agitation but I don't have

PVA.  I read that Elmers is polyvinyl acetate, not polyvinyl alcohol and

they are two different things. 

Jeff

_____  

From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]

On Behalf Of bebx2000

Sent: Sunday, January 29, 2012 11:39 PM

To: Homebrew_PCBs@yahoogroups.com

Subject: [Homebrew_PCBs] Re: Photo Resist Gelatin Bicromate Process

Hi Jeff,

The book I cited really didn't give any recipes. The reference to shellac

was in a chapter devoted to the historical development of resists. Later

chapters fell into the nether world of organic chemistry. This patent,

4447519, in examples 4 and 5 gives the proportions. c2h5oc2h4oh is Ethylene

Glycol Monoethyl Ether which is a solvent. Union Carbide Corp. trademarked

it as Cellosolve. I think it is now marketed as Butyl cellosolve. See,

http://www.chemistrystore.com/Chemicals_A_F-Butyl_Cellosolve.html

I really don't have any further details about shellac. I assume that the

above solvent would remove it and its use with the sensitizer is to soften

the shellac for better penetration. The post baking is to continue the

crosslinking to further harden the resist. A good source for this sort of

thing is under the topic of "alternative photographic processes" Look at the

APUG Forum: Alternative processes. I think the PVA/PVac/Elmer's glue

approach is better than using shellac, or the other glues like fish or

rabbit because of the water "developing" step.

While digging through my files I came across a screen printing post for a

glue sensitizer formula,

quote:

"An alternative to photo emulsion(the answer)

Wed, March 28, 2007 - 9:15 PM 

1 tsp of Ammonium Dichromate -> 1 oz. Water 

Dissolve and mix with 8 oz. Elmer's Glue 

see below (dry measure equiv.)

1 tsp = (14.3 gm/3) = 4.76 gm

Fairly flexible open time, decent exposure times 

(10-20 minutes under daylight), rinse with water, and a 

bulletproof stencil is yours."

end quote

Baxter

--- In Homebrew_PCBs@yahoogroups.com

<mailto:Homebrew_PCBs%40yahoogroups.com> , "Jeff" <jeff.heiss@...> wrote:

>

> Hi Baxter,

> 

> I was wondering if I could ask you a few details about your comment from

the Photoresist book on ammonium dichromate and shellac. Does the book

mention a ratio of dichromate powder to shellac? What is the dichromate

dissolved in before mixing into the shellac? After the shellac is UV

exposed, how is the unexposed shellac removed? Is there a develop step after

exposure like traditional resist? Is the 200 deg F post bake after board

coating and before UV exposure?

> 

> Jeff

> 

> 

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Re: Photo Resist Gelatin Bicromate Process

2012-01-30 by bebx2000

Hi Jeff,
If you are not having any luck with Elmers's glue, try casein (see patent 4237210). Elmer's glue by the way, is an emulsion of PVA/PVac. The most explicit recipe for PVac and PVA that I could find was in patent 5556735, but you will never be able to make it without a high speed mixing mill which is why I turned to Elmer's glue. Another factor that might be causing problems is your UV source. 5556735 is applying an energy deposition of 800 mJoules/cm**2. There is a relationsip between the rate and the required total energy to crosslink; generally the fastest rate possible. The range of Riston dry film is 35-150 mJoules/cm**2 depending upon the product line. I have a 150 watt metal halide source that is providing 14 mW/cm**2 at 6 inches. Most DIY black light setups are putting out much less than this. My exposure time was of the order of 60 sec.

I am satisfied with toner transfer for PCBs. My original quest was for a DIY solder mask so that it was only necessary to mask the pads. The PVac provides toughness to the coating in this case and it is only necessary rub off (yes, I did have to rub it off under water) the coating on small areas after exposure. For traces, PVA might work just fine. You can buy it here,

http://www.ebay.com/itm/Polyvinyl-Alcohol-PVA-One-Pound-Lab-Chemical-/250983683335?pt=LH_DefaultDomain_0&hash=item3a6fcb1507

and,

http://shop.chemicalstore.com/navigation/detail.asp?MySessionID=167-920303619&CatID=30&id=PVOH7130

Baxter

--- In Homebrew_PCBs@yahoogroups.com, "Jeff Heiss" <jeff.heiss@...> wrote:

Show quoted textHide quoted text

>
> Hi Baxter,
> 
>  
> 
> I am trying the recipe of ammonium dichromate mixed with Elmers glue and I
> am finding two things.  First, the Elmers glue does not dissolve in water
> without physical agitation.  Take plain, unmixed Elmers strait from the
> bottle, spread it on something, and let it dry.  Once dry, immerse it in
> water.  The glue does not dissolve in the water unless rubbed lightly with
> your finger.  No rubbing, no dissolving.  I left the glue in water over
> night and all was still there the next day.  
> 
>  
> 
> Second, the glue hardened from UV exposure does not stick to the copper well
> enough to avoid coming off during the agitation required to remove the
> unexposed glue.  If the unexposed glue could dissolve on it's own in the
> water, I don't think this would matter.  I would try real PVA polyvinyl
> alcohol to see if it dissolves in water without agitation but I don't have
> PVA.  I read that Elmers is polyvinyl acetate, not polyvinyl alcohol and
> they are two different things. 
> 
>  
> 
> Jeff
>

Re: Photo Resist Gelatin Bicromate Process

2012-01-31 by Robert

Hi all,

> There is a book entitled, "Photoresist" by W.S.
 DeForest (McGraw-Hill, 1975)

I was able to find 5 used copies of this title at abebook.com for about $1.00 each and shipping about $3.00 or $4.00

my used copy is on it's way! 


Thanks!
Robert



--- In Homebrew_PCBs@yahoogroups.com, "bebx2000" <bebx2000@...> wrote:

Show quoted textHide quoted text

>
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, Athar Kaludi <ceo_premium@> wrote:
> >
> > Hi All
> > 
> > I come across a guy making a printing block of Printing press on Zinc Plate by exposing in sunlight by negative film. Then after developing he etch to remove unexposed area of Zinc.
> > 
> > I suppose the same can be applied for PCB. I asked and learned the process there.
> > 
> 
> Bichromated  (dichromated) gelatin has a long history in the area of alternative photographic  procrsses.  There is a book entitled, "Photoresist" by W.S. DeForest  (McGraw-Hill, 1975) that outlines the evolution of photoresist as three periods,
> 
> 	the 1800s natural colloids, gelatin albumen, shellac, gum arabic, glue
> 	the 1930s polyvinyl alcohol
> 	the 1950s (onward) polyvinyl  cinnamate, positive Shipley resists, dry film 
> 
> He notes that dichromated fish glue forms a highly etch resistant coating after a post bake of 350-500 deg F which is good for plates, but bad for PCBs.  Also, dichromated shellac is mentioned as one of the most successful of the naturally occurring materials for electronic applications with the ability to form fine detail and a comparatively low post bake of 200 deg F.
> 
> I think a better emulsion for PCB work can be found in polyvinyl acetate/polyvinyl alcohol formulations by virtue of its water based developing. I have been working on a DIY solder mask following the guidelines of this patent,
> 
> IMAGE-FORMING PROCESS 5556735 (Google Patents)
> 
> Examples 1 and 2 of this patent give straight forward recipes and processes for making your own solder mask. All of the ingredients are readily available. It is noted in the patent that polyvinyl acetate is only necessary to improve the toughness of the coating
> 
> My first attempt failed because I purchased polyvinyl acetate beads and I couldn't get them to dissolve in water.  They will dissolve in a number of solvents like acetone, but I didn't do this because I wanted to stick to the patent recipe. The correct product is a polyvinyl acetate dispersion like CM Bond M-2. Polyvinyl alcohol is hydrolyzed polyvinyl acetate and water soluble with a little work. The thing is, however, that both of these ingredients are the main components of white glue (aka Elmer's Glue-all and School Glue, among others). You can find references to the use of sensitized PVA glue as DIY screen printing emulsions.
> 
> I put aside the exact recipes of the cited patent and have been working with Elmer's Glue-All sensitized with ammonium dichromate together with a green pigment. This is a real trial and error process to determine the percentage of dichromate , thickness of coating and exposure time. The glue applies very easily to the circuit board and seems to self level for a uniform coating. I am pretty certain that it includes the flow aid and surfactant ingredients mentioned in the patent. Working with ammonium dichromate introduces the so called "dark reaction" so that you cannot store your sensitized boards for more than a day before exposure. Diazo may be better.
>  
> There is another patent,
> 
> Solid Photoresist and method of Making Photoresist 4447519
> 
> that outlines dipping in a 1% solution of ammonium dichromate before exposure which alleviates the storage problem. But any way you cut it, ammonium dichromate is a nasty substance that just loves to crosslink collagen; of which there is plenty in the human body. So be careful with this stuff.
> 
> I have had some success with this process, but not in a uniform manner. I do not have a lot of time to devote to this. I am convinced, however, that it can lead to a DIY solder mask once the kinks are ironed out. 
> 
> Baxter
>