Homebrew_PCBs

Been using the Seno 100 photo resist applicator to sensitize some pcb board stock. Main problem I find is getting an even coating.  The applicator sponge is fed from a valve in the main body when you push down. If that happens you get flooded in resist but just before you are starved, so the coating tends to be very variable in thickness from board to board and also on a single board as the stuff tries so quickly it does not level very well.
Only trick I found so far is to keep the resist in the fridge to slow down the evaporation process as much as possible.

Anybody got any other tips or tricks on how to get a good uniform, preferable thin, coating using this system?

Thanks

Alex





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

On 02/04/2013 13:50, Alex Hun wrote:

> Been using the Seno 100 photo resist applicator to sensitize some pcb
> board stock. Main problem I find is getting an even coating. The
> applicator sponge is fed from a valve in the main body when you push
> down. If that happens you get flooded in resist but just before you are
> starved, so the coating tends to be very variable in thickness from
> board to board and also on a single board as the stuff tries so quickly
> it does not level very well.
> Only trick I found so far is to keep the resist in the fridge to slow
> down the evaporation process as much as possible.
>
> Anybody got any other tips or tricks on how to get a good uniform,
> preferable thin, coating using this system?

How about using a squeegee on it.

Leon
--
Leon Heller
G1HSM

Alex,

I just bought some spray on photo resist. They say to spray on a thin coat
and then put the board, resist side down, on a piece of tissue paper for
around 8 minutes. This absorbs the excess. Then, if necessary, put down a
second coat. Have not tried it yet but hope to do so today.

Rick

-----Original Message-----
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
On Behalf Of Alex Hun
Sent: Tuesday, April 02, 2013 5:50 AM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] Seno 100 photo resist applicator

Been using the Seno 100 photo resist applicator to sensitize some pcb board
stock. Main problem I find is getting an even coating.  The applicator
sponge is fed from a valve in the main body when you push down. If that
happens you get flooded in resist but just before you are starved, so the
coating tends to be very variable in thickness from board to board and also
on a single board as the stuff tries so quickly it does not level very well.
Only trick I found so far is to keep the resist in the fridge to slow down
the evaporation process as much as possible.

Anybody got any other tips or tricks on how to get a good uniform,
preferable thin, coating using this system?

Thanks

Alex





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



------------------------------------

Be sure to visit the group home and check for new Links, Files, and Photos:
http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links

Pardon my ignorance, but are you using a liquid resist?
If so, can you tell me what it is, and where you get it?

Thanks

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

On 4/2/2013 5:50 AM, Alex Hun wrote:
>
> Been using the Seno 100 photo resist applicator to sensitize some pcb
> board stock. Main problem I find is getting an even coating. The
> applicator sponge is fed from a valve in the main body when you push
> down. If that happens you get flooded in resist but just before you
> are starved, so the coating tends to be very variable in thickness
> from board to board and also on a single board as the stuff tries so
> quickly it does not level very well.
> Only trick I found so far is to keep the resist in the fridge to slow
> down the evaporation process as much as possible.
>
> Anybody got any other tips or tricks on how to get a good uniform,
> preferable thin, coating using this system?
>
> Thanks
>
> Alex
>
> [Non-text portions of this message have been removed]
>
>



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

On 02/04/2013 16:37, Roland Harriston wrote:

> Pardon my ignorance, but are you using a liquid resist?
> If so, can you tell me what it is, and where you get it?

It's a liquid supplied in an applicator. Mega Electronics sells it in
the UK:

http://www.megauk.com/pcb_chemicals.php

Leon
--
Leon Heller
G1HSM

Leon:
Thanks for the information.

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

On 4/2/2013 8:53 AM, Leon Heller wrote:
>
> On 02/04/2013 16:37, Roland Harriston wrote:
> > Pardon my ignorance, but are you using a liquid resist?
> > If so, can you tell me what it is, and where you get it?
>
> It's a liquid supplied in an applicator. Mega Electronics sells it in
> the UK:
>
> http://www.megauk.com/pcb_chemicals.php
>
> Leon
> --
> Leon Heller
> G1HSM
>
>



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

Thanks to all responders!
I'll give the squeegee a try on the next batch.

As Leon kindly clarified, it is a liquid resist, supplied in an applicator similar to some shoe polish ones: a small tube with a sponge on the end. As you push on the sponge a small valve allows an amount of liquid resist into the sponge to be distributed on the board.

The challenge is to get the resist distributed on the board in a nice even way, without building up too much of a layer. The stuff has a tendency to form ridges and dry very quickly, leaving little time for it the settle to an even coat.

Alex

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

I'm using the spray bottle version from MG Chemicals. After two tries and no
luck, I'm now waiting for an answer from their help line.

Rick

-----Original Message-----
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
On Behalf Of alexhun19
Sent: Tuesday, April 02, 2013 1:26 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] Re: Seno 100 photo resist applicator


Thanks to all responders!
I'll give the squeegee a try on the next batch.

As Leon kindly clarified, it is a liquid resist, supplied in an applicator
similar to some shoe polish ones: a small tube with a sponge on the end. As
you push on the sponge a small valve allows an amount of liquid resist into
the sponge to be distributed on the board.

The challenge is to get the resist distributed on the board in a nice even
way, without building up too much of a layer. The stuff has a tendency to
form ridges and dry very quickly, leaving little time for it the settle to
an even coat.

Alex

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

------------------------------------

Be sure to visit the group home and check for new Links, Files, and Photos:
http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links

Thanks for the information.

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

On 4/2/2013 8:53 AM, Leon Heller wrote:
>
> On 02/04/2013 16:37, Roland Harriston wrote:
> > Pardon my ignorance, but are you using a liquid resist?
> > If so, can you tell me what it is, and where you get it?
>
> It's a liquid supplied in an applicator. Mega Electronics sells it in
> the UK:
>
> http://www.megauk.com/pcb_chemicals.php
>
> Leon
> --
> Leon Heller
> G1HSM

If you check further down the page at Mega.UK you will find 600-031 Seno 1000 Photoresist 1Ltr £91.90...

Read; -
Seno 1000 Photoresist
A professional ready-to-use positive working liquid Photoresist which shows a very strong contrast in developing and has very good adhesion and spreading properties -ideal for the finest circuit board application. The Photoresist can be applied to uncoated PCB laminate by spray, dip and spin coat-ing machines.

The last application quoted "dip and spin-coating machines.
When first started makeing my own PCB's as a spotty Teen, I modified a old Philips 33/45 Record Turn-Table with a small electric motor connected directly to the T/Table shaft.

Mounting the bare, clean Copper clad mounted with sticky-tape to the Table center and turning the motor on.
When motor has run-up to running speed, drop a measured amount of Photoresist onto the center of the spinning board. Centrifical Force will spread an even layer of Resist over the board, any excess will spin of the edge of the board on to the T/Table
Spin times and Measured amount would have to be experimented with to achive desired Resist thickness.
I used this method when Positiv 20 became available in a spray can!
Just spraying onto a board laying on old Newspaper (Horizontal or Vertical) produced poor results; - Horizontal caused "pools" of resist and Vertical caused a ridge of resist flowing to the lower edge. These inital attempts at this "new fangled Hocum" almost drove me told me  mental, until one of the RF Boys in Tech revealed his home-made "spin coating Machine"

Thats all folks!...these ramblings may solve the problems at hand or perhaps spark up an idea in someone's thoughts.
chester

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

alexhun19:

>
> Depending on the viscosity of the liquid, perhaps a spin-coating
> technique would work.
>

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

> Thanks to all responders!
> I'll give the squeegee a try on the next batch.
>
> As Leon kindly clarified, it is a liquid resist, supplied in an
> applicator similar to some shoe polish ones: a small tube with a
> sponge on the end. As you push on the sponge a small valve allows an
> amount of liquid resist into the sponge to be distributed on the board.
>
> The challenge is to get the resist distributed on the board in a nice
> even way, without building up too much of a layer. The stuff has a
> tendency to form ridges and dry very quickly, leaving little time for
> it the settle to an even coat.
>
> Alex
>
> >
> > Alex
> >
> >
> >
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
>

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

If the boards are 5" x5" or less then you could spin coat the boards, it gives a fairly nice coating.

see: https://picasaweb.google.com/115378886522213655693/DYIPCBs?authuser=0&feat=directlink

Craig

--- In Homebrew_PCBs@yahoogroups.com, Alex Hun <alexhun19@...> wrote:
>
> Been using the Seno 100 photo resist applicator to sensitize some pcb board stock. Main problem I find is getting an even coating.  The applicator sponge is fed from a valve in the main body when you push down. If that happens you get flooded in resist but just before you are starved, so the coating tends to be very variable in thickness from board to board and also on a single board as the stuff tries so quickly it does not level very well.
> Only trick I found so far is to keep the resist in the fridge to slow down the evaporation process as much as possible.
>
> Anybody got any other tips or tricks on how to get a good uniform, preferable thin, coating using this system?
>
> Thanks
>
> Alex
>
>
>
>
>
> [Non-text portions of this message have been removed]
>

I used a similar spin machine when I worked for a university research lab.
Worked great!

Todd K7TFC

On Apr 2, 2013 3:24 PM, "Roland Harriston" <rolohar@...> wrote:
>
>
>
> alexhun19:
> >
> > Depending on the viscosity of the liquid, perhaps a spin-coating
> > technique would work.
>
> >
>
> Roland F. Harriston, P.D.
> ***********************
>
> > Thanks to all responders!
> > I'll give the squeegee a try on the next batch.
> >
> > As Leon kindly clarified, it is a liquid resist, supplied in an
> > applicator similar to some shoe polish ones: a small tube with a
> > sponge on the end. As you push on the sponge a small valve allows an
> > amount of liquid resist into the sponge to be distributed on the board.
> >
> > The challenge is to get the resist distributed on the board in a nice
> > even way, without building up too much of a layer. The stuff has a
> > tendency to form ridges and dry very quickly, leaving little time for
> > it the settle to an even coat.
> >
> > Alex
> >
> > >
> > > Alex
> > >
> > >
> > >
> > >
> > >
> > > [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]

--- In Homebrew_PCBs@yahoogroups.com, "designer_craig" <cs6061@...> wrote:

>
> If the boards are 5" x5" or less then you could spin coat the boards, it gives a fairly nice coating.
>
> see: https://picasaweb.google.com/115378886522213655693/DYIPCBs?authuser=0&feat=directlink
>
> Craig
>

Why just 5" x 5"? Are you saying that Spin Coating will not work on a larger than 5" x 5" board? I if so, Why?


Ben

Ben,

I think he was referring to the capacity of the spin machine he showed in
the photos. I used to use spin coating, and there's no reason it can't be
bigger.

73,

Todd
------------------------------------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
------------------------------------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design

On Sat, Apr 6, 2013 at 8:17 PM, Ben L <bhleavi@...> wrote:

> **
>
>
>
>
> --- In Homebrew_PCBs@yahoogroups.com, "designer_craig" <cs6061@...> wrote:
> >
> > If the boards are 5" x5" or less then you could spin coat the boards, it
> gives a fairly nice coating.
> >
> > see:
> https://picasaweb.google.com/115378886522213655693/DYIPCBs?authuser=0&feat=directlink
> >
> > Craig
> >
>
> Why just 5" x 5"? Are you saying that Spin Coating will not work on a
> larger than 5" x 5" board? I if so, Why?
>
> Ben
>
>
>


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

On 07/04/13 15:58, Todd F. Carney / K7TFC wrote:

> Ben,
>
> I think he was referring to the capacity of the spin machine he showed in
> the photos. I used to use spin coating, and there's no reason it can't be
> bigger.

How fast does it have to spin? The velocity of the outside edge of the
board would be getting quite high I imagine as you increased the board
size.

I know spin coating has been used commercially but it always bothered me
since I do not understand how it can be a uniform coating. Basically there
is zero centrifugal force in the center and lots at the edges. How can that
create a uniform coating?



Decades ago I used to coat PCBs by SLOWLY withdrawing them from a skinny
rectangular tank which left a uniform coating except the bottom edge.
Placing the PCB still vertically on a tissue paper drained off the excess at
the edge.

Bertho



From: James Sent: Sunday, April 07, 2013 00:15

On 07/04/13 15:58, Todd F. Carney / K7TFC wrote:
> Ben,
>
> I think he was referring to the capacity of the spin machine he showed in
> the photos. I used to use spin coating, and there's no reason it can't be
> bigger.

How fast does it have to spin? The velocity of the outside edge of the
board would be getting quite high I imagine as you increased the board
size.



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

*I didn't ever know the speed of what I used to use, but in comparing it in
my memory with a 45 rpm record (also from memory), I'd guess it was about
twice that fast. One certainly kept one's fingers away. While it's true the
perimeter would be moving much faster than the center as measured in
inches/second (or some other linear unit), I think in this application it's
angular velocity that matters and that's the same at all points. At 90 rpm
that would be 32,400�/minute. *
*
*
*We used to mount the pcb material, start it spinning, and then carefully
pour a small amount of emulsion at the center. Since "center" is really
only a theoretical concept, it was always off center enough that the
emulsion was flung across the board, hitting the sides of the open
enclosure the thing was mounted it. It don't think we ever cleaned up that
mess. It got pretty thick after a while.*

73,

Todd
------------------------------------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
------------------------------------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design

On Sat, Apr 6, 2013 at 9:14 PM, James <bitsyboffin@...> wrote:

> **
>
>
> On 07/04/13 15:58, Todd F. Carney / K7TFC wrote:
> > Ben,
> >
> > I think he was referring to the capacity of the spin machine he showed in
> > the photos. I used to use spin coating, and there's no reason it can't be
> > bigger.
>
> How fast does it have to spin? The velocity of the outside edge of the
> board would be getting quite high I imagine as you increased the board
> size.
>
>
>


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

Spin coating is uniform enough that it is also used in the manufacturing of
silicon wafers for integrated circuits. You want to talk about holding fine
lines? Try 50 nanometers. That is 500 Angstroms, 0.000002 inches.
Spinning works.



From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
On Behalf Of Boman33
Sent: Saturday, April 06, 2013 10:48 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: RE: [Homebrew_PCBs] Re: Seno 100 photo resist applicator





I know spin coating has been used commercially but it always bothered me
since I do not understand how it can be a uniform coating. Basically there
is zero centrifugal force in the center and lots at the edges. How can that
create a uniform coating?

Decades ago I used to coat PCBs by SLOWLY withdrawing them from a skinny
rectangular tank which left a uniform coating except the bottom edge.
Placing the PCB still vertically on a tissue paper drained off the excess at
the edge.

Bertho

From: James Sent: Sunday, April 07, 2013 00:15

On 07/04/13 15:58, Todd F. Carney / K7TFC wrote:
> Ben,
>
> I think he was referring to the capacity of the spin machine he showed in
> the photos. I used to use spin coating, and there's no reason it can't be
> bigger.

How fast does it have to spin? The velocity of the outside edge of the
board would be getting quite high I imagine as you increased the board
size.

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





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

Todd,
I am not arguing, just thinking.....
It helps when discussing concepts to emphasize for better clarity, so:
If the resists is added an inch off center, I cannot see it moving toward
the center to coat that area. Presumably the pour was sloppy enough to
actually cover the center section.

Similarly thinking about a very small drop sitting at the center, I would
expect very little force to move it away and spread out.

Finally, resist added in the center and spreading outwards has to cover a
larger and larger area and therefor presumably be a thinner coating further
out.

Now, after writing all that there might be a completely different
explanation:
There might be a microscopic layer that attaches itself to the surface with
a thin high boundary friction force and the excess just slides off, so as
long as sufficient amount is added that thin surface layer stays constant.
I do not know.
Bertho

-----Original Message-----
From: Todd F. Carney / K7TFC Sent: Sunday, April 07, 2013 01:52

*I didn't ever know the speed of what I used to use, but in comparing it in
my memory with a 45 rpm record (also from memory), I'd guess it was about
twice that fast. One certainly kept one's fingers away. While it's true the
perimeter would be moving much faster than the center as measured in
inches/second (or some other linear unit), I think in this application it's
angular velocity that matters and that's the same at all points. At 90 rpm
that would be 32,400°/minute. *
*
*
*We used to mount the pcb material, start it spinning, and then carefully
pour a small amount of emulsion at the center. Since "center" is really only
a theoretical concept, it was always off center enough that the emulsion was
flung across the board, hitting the sides of the open enclosure the thing
was mounted it. It don't think we ever cleaned up that mess. It got pretty
thick after a while.*

73,

Todd

As I wrote, I know it works but the question is why.

Bertho



From: Andrew Volk Sent: Sunday, April 07, 2013 02:08



Spin coating is uniform enough that it is also used in the manufacturing of
silicon wafers for integrated circuits. You want to talk about holding fine
lines? Try 50 nanometers. That is 500 Angstroms, 0.000002 inches.
Spinning works.

From: Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs%40yahoogroups.com>
[mailto:Homebrew_PCBs@yahoogroups.com
<mailto:Homebrew_PCBs%40yahoogroups.com> ]
On Behalf Of Boman33
Sent: Saturday, April 06, 2013 10:48 PM
To: Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs%40yahoogroups.com>
Subject: RE: [Homebrew_PCBs] Re: Seno 100 photo resist applicator

I know spin coating has been used commercially but it always bothered me
since I do not understand how it can be a uniform coating. Basically there
is zero centrifugal force in the center and lots at the edges. How can that
create a uniform coating?

Decades ago I used to coat PCBs by SLOWLY withdrawing them from a skinny
rectangular tank which left a uniform coating except the bottom edge.
Placing the PCB still vertically on a tissue paper drained off the excess at
the edge.

Bertho

From: James Sent: Sunday, April 07, 2013 00:15

On 07/04/13 15:58, Todd F. Carney / K7TFC wrote:
> Ben,
>
> I think he was referring to the capacity of the spin machine he showed in
> the photos. I used to use spin coating, and there's no reason it can't be
> bigger.

How fast does it have to spin? The velocity of the outside edge of the
board would be getting quite high I imagine as you increased the board
size.






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

On Sat, Apr 6, 2013 at 11:53 PM, Boman33 <boman33@...> wrote:

>
> As I wrote, I know it works but the question is why.

Mine is not to reason why, mine is but to do or . . . hey, wait a minute!

Actually, I suspect the viscosity and surface tension of the emulsion has
something to do with how the spin-coating method works. It may also be that
it does end up thinner the farther it gets from the center, but that it
doesn't matter given the use and the pretty-course image resolution
required. Back then, I found myself more concerned about the thickness of
the copper than of the emulsion.

The engineers I worked for had always used 2oz copper clad, and that's what
they wanted me to use. I wanted to use 1oz copper because a) I could get
more yield from the etchant, b) it etched faster, and c) because it etched
faster I could preserve fine lines much easier than with the thick 2oz
stuff. If etching takes too long, it begins to undercut the traces and then
the resist flakes off on the edges of the traces for that reason. Thin
traces, such as dogbones or "sneak-throughs," would just get torn up. But
it didn't matter how much data or how many calculations of current vs. temp
rise of traces of thinner clad, they insisted on 2oz. Neither did it matter
that industry standard by that time (1984) was 1oz except for special
applications. Even Coombs the Revered (author of the standard text on pcb
design) could not move them.

I was able to ramrod the abandonment of the spinner/liquid emulsion hassle
and we started using laminated dry film. In that small industrial setting,
spun-and-flung liquid emulsion was a real bother, but for the hobbyist I
think it's not a bad idea, as long as you can put a spinner together for
next-to-nothing. At some point, the cost of the apparatus (along with the
minor hassle) and the emulsion chemistry makes presensitized pcbs a much
better value (and much easier, too!).

Just curious: is that a real panda in your avatar picture?

73,

Todd
------------------------------------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
------------------------------------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design


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

Todd,

The panda is real. I had an opportunity to play with and feed seven of them
in China.

Bertho



From: Todd F. Carney / K7TFC Sent: Sunday, April 07, 2013 04:54



On Sat, Apr 6, 2013 at 11:53 PM, Boman33 <boman33@...
<mailto:boman33%40vinland.com> > wrote:

>
> As I wrote, I know it works but the question is why.

Mine is not to reason why, mine is but to do or . . . hey, wait a minute!

Actually, I suspect the viscosity and surface tension of the emulsion has
something to do with how the spin-coating method works. It may also be that
it does end up thinner the farther it gets from the center, but that it
doesn't matter given the use and the pretty-course image resolution
required. Back then, I found myself more concerned about the thickness of
the copper than of the emulsion.

The engineers I worked for had always used 2oz copper clad, and that's what
they wanted me to use. I wanted to use 1oz copper because a) I could get
more yield from the etchant, b) it etched faster, and c) because it etched
faster I could preserve fine lines much easier than with the thick 2oz
stuff. If etching takes too long, it begins to undercut the traces and then
the resist flakes off on the edges of the traces for that reason. Thin
traces, such as dogbones or "sneak-throughs," would just get torn up. But
it didn't matter how much data or how many calculations of current vs. temp
rise of traces of thinner clad, they insisted on 2oz. Neither did it matter
that industry standard by that time (1984) was 1oz except for special
applications. Even Coombs the Revered (author of the standard text on pcb
design) could not move them.

I was able to ramrod the abandonment of the spinner/liquid emulsion hassle
and we started using laminated dry film. In that small industrial setting,
spun-and-flung liquid emulsion was a real bother, but for the hobbyist I
think it's not a bad idea, as long as you can put a spinner together for
next-to-nothing. At some point, the cost of the apparatus (along with the
minor hassle) and the emulsion chemistry makes presensitized pcbs a much
better value (and much easier, too!).

Just curious: is that a real panda in your avatar picture?

73,

Todd
----------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
----------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design





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

Wow! That was quite a thing!

73,

Todd
------------------------------------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
------------------------------------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design

On Sun, Apr 7, 2013 at 2:14 AM, Boman33 <boman33@...> wrote:

> **
>
>
> Todd,
>
> The panda is real. I had an opportunity to play with and feed seven of them
> in China.
>
> Bertho
>
> From: Todd F. Carney / K7TFC Sent: Sunday, April 07, 2013 04:54
>
>
> On Sat, Apr 6, 2013 at 11:53 PM, Boman33 <boman33@...
> <mailto:boman33%40vinland.com> > wrote:
> >
> > As I wrote, I know it works but the question is why.
>
> Mine is not to reason why, mine is but to do or . . . hey, wait a minute!
>
> Actually, I suspect the viscosity and surface tension of the emulsion has
> something to do with how the spin-coating method works. It may also be that
> it does end up thinner the farther it gets from the center, but that it
> doesn't matter given the use and the pretty-course image resolution
> required. Back then, I found myself more concerned about the thickness of
> the copper than of the emulsion.
>
> The engineers I worked for had always used 2oz copper clad, and that's what
> they wanted me to use. I wanted to use 1oz copper because a) I could get
> more yield from the etchant, b) it etched faster, and c) because it etched
> faster I could preserve fine lines much easier than with the thick 2oz
> stuff. If etching takes too long, it begins to undercut the traces and then
> the resist flakes off on the edges of the traces for that reason. Thin
> traces, such as dogbones or "sneak-throughs," would just get torn up. But
> it didn't matter how much data or how many calculations of current vs. temp
> rise of traces of thinner clad, they insisted on 2oz. Neither did it matter
> that industry standard by that time (1984) was 1oz except for special
> applications. Even Coombs the Revered (author of the standard text on pcb
> design) could not move them.
>
> I was able to ramrod the abandonment of the spinner/liquid emulsion hassle
> and we started using laminated dry film. In that small industrial setting,
> spun-and-flung liquid emulsion was a real bother, but for the hobbyist I
> think it's not a bad idea, as long as you can put a spinner together for
> next-to-nothing. At some point, the cost of the apparatus (along with the
> minor hassle) and the emulsion chemistry makes presensitized pcbs a much
> better value (and much easier, too!).
>
> Just curious: is that a real panda in your avatar picture?
>
> 73,
>
> Todd
> ----------------------------------------------------------
> K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
> ----------------------------------------------------------
> QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design
>
> [Non-text portions of this message have been removed]
>
>
>


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

Ben,
As the board get larger and larger it's harder to keep it balanced on the spin table so it doesn't fly off. Also it's harder to get a good coat without streak out towards the outer edges. It's not that you can't do a 6"x6 or even an 8"x *" but it may take several trys to get it to get a coating that will work out.

Craig

--- In Homebrew_PCBs@yahoogroups.com, "Ben L" <bhleavi@...> wrote:
>
>
>
> --- In Homebrew_PCBs@yahoogroups.com, "designer_craig" <cs6061@> wrote:
> >
> > If the boards are 5" x5" or less then you could spin coat the boards, it gives a fairly nice coating.
> >
> > see: https://picasaweb.google.com/115378886522213655693/DYIPCBs?authuser=0&feat=directlink
> >
> > Craig
> >
>
>
> Why just 5" x 5"? Are you saying that Spin Coating will not work on a larger than 5" x 5" board? I if so, Why?
>
>
> Ben
>

Andrew Volk:

You are quite right. I also worked in the semiconductor fabrication
domain for a while,
and we used spin-coating with the old Kodak KPR, and other resists which
were
applied using a professional spin-coat machine.

The wafer was placed on the turntable. A drop of resist was applied to
the center (approx)
or the wafer. The motor was turned on, and the resist was thrown across
the surface of
the wafer very, very evenly.

The turntable rotated at high RPM for only a second or two.
Yes, sometimes the resist splashed out onto the wall of the spin-coater.


The "dip tank" method is very successful for coating large PCB panels.
The size of the panel is only limited by the capacity of the dip tank.
Usually, the "pro" machines have a controlled withdrawal mechanism
which assures even coating.

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

On 4/6/2013 11:08 PM, Andrew Volk wrote:
>
> Spin coating is uniform enough that it is also used in the
> manufacturing of
> silicon wafers for integrated circuits. You want to talk about holding
> fine
> lines? Try 50 nanometers. That is 500 Angstroms, 0.000002 inches.
> Spinning works.
>
> From: Homebrew_PCBs@yahoogroups.com
> <mailto:Homebrew_PCBs%40yahoogroups.com>
> [mailto:Homebrew_PCBs@yahoogroups.com
> <mailto:Homebrew_PCBs%40yahoogroups.com>]
> On Behalf Of Boman33
> Sent: Saturday, April 06, 2013 10:48 PM
> To: Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs%40yahoogroups.com>
> Subject: RE: [Homebrew_PCBs] Re: Seno 100 photo resist applicator
>
> I know spin coating has been used commercially but it always bothered me
> since I do not understand how it can be a uniform coating. Basically there
> is zero centrifugal force in the center and lots at the edges. How can
> that
> create a uniform coating?
>
> Decades ago I used to coat PCBs by SLOWLY withdrawing them from a skinny
> rectangular tank which left a uniform coating except the bottom edge.
> Placing the PCB still vertically on a tissue paper drained off the
> excess at
> the edge.
>
> Bertho
>



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

I alos found that it helps to first wet the entire board with the resist a brush or finger then pour more resist in the center and start it spinning. My spinner is built from a garden variety 12V 4" computer fan. Don't remember the fan's rpm but my rpm control system consist of holding down the button till the rpm seems good then pulsing it button to maintain it. One can tell by sight what works good for RPM you can see the puddle of resist spread out. I start out just a little slow but within a couple of seconds I go to high speed.
It gives a very nice even coating that is not too thick. I do thin out out the resist I am using just a little.

Unfortunately sourcing finished boards from China has become so economical that I out sourced my last two project boards rather tha doing them my self.

Craig

--- In Homebrew_PCBs@yahoogroups.com, "designer_craig" <cs6061@...> wrote:
>
> Ben,
> As the board get larger and larger it's harder to keep it balanced on the spin table so it doesn't fly off. Also it's harder to get a good coat without streak out towards the outer edges. It's not that you can't do a 6"x6 or even an 8"x *" but it may take several trys to get it to get a coating that will work out.
>
> Craig
>
> --- In Homebrew_PCBs@yahoogroups.com, "Ben L" <bhleavi@> wrote:
> >
> >
> >
> > --- In Homebrew_PCBs@yahoogroups.com, "designer_craig" <cs6061@> wrote:
> > >
> > > If the boards are 5" x5" or less then you could spin coat the boards, it gives a fairly nice coating.
> > >
> > > see: https://picasaweb.google.com/115378886522213655693/DYIPCBs?authuser=0&feat=directlink
> > >
> > > Craig
> > >
> >
> >
> > Why just 5" x 5"? Are you saying that Spin Coating will not work on a larger than 5" x 5" board? I if so, Why?
> >
> >
> > Ben
> >
>

>The "dip tank" method is very successful for coating large PCB panels.

The size of the panel is only limited by the capacity of the dip tank.
Usually, the "pro" machines have a controlled withdrawal mechanism
which assures even coating.
That's what I was thinking. Maybe a stepper motor and simple control
would do the job.
Charlie


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

M. Guy:

If you can go back and find some information on the Kepro company, you
might be able to see some photos of the dip-coat tank that they sold
many years ago.

The beauty of the Kepro setup was that it was made of rather "generic"
hardware parts and could be easily duplicated in any modestly equipped
home workshop.

The only problem with any form of dip coating is that there is always a
"wedge" or a slightly thicker coating at the very end of the coated PC
panel. That would be the last edge emerging from the dip tank.
But this problem is of no consequence if the size of the panel is
slightly longer
that the actual PC pattern, and you don't actually use the very end of the
panel.

Too bad that Kepro went out of business when reliable, low-cost dry film
resist
became widely used in the PC fab industry.

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

>
> >The "dip tank" method is very successful for coating large PCB panels.
> The size of the panel is only limited by the capacity of the dip tank.
> Usually, the "pro" machines have a controlled withdrawal mechanism
> which assures even coating.
> That's what I was thinking. Maybe a stepper motor and simple control
> would do the job.
> Charlie
>
> [Non-text portions of this message have been removed]
>
>

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

On Sun, Apr 7, 2013 at 4:56 PM, Roland Harriston <rolohar@...>
wrote:

>
> Too bad that Kepro went out of business when reliable, low-cost dry film
> resist
>
> became widely used in the PC fab industry.
>
>

Kepro as company is gone, but at least some of its product line was taken
taken over by Dalpro. Now, Dalpro has been taken over by
CamCon Chemicals. Here's what they say on their home page:

*If you ordered from DalPro or Kepro in the past, we are now your supplier!*


Here's their url: http://www.camconchemical.com/kepro-equipment/

They have at least one page devoted to Kepro equipment:

*We buy, sell, repair and sell parts

>
> for all Kepro etching equipment. We also *

*sell the boards and chemicals you need to make your circuit boards. *

*We are the leading supplier to colleges and universities around the

> country!*

Here's the link for that page:

http://www.camconchemical.com/kepro-equipment/

73,

Todd
------------------------------------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
------------------------------------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design





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

Roland & Todd,

That's interesting info. Also good detective work Todd!
Thanks for the links!

Charlie
Missouri Guy

On Sun, 7 Apr 2013 18:11:49 -0700 "Todd F. Carney / K7TFC"
<k7tfc@...> writes:


On Sun, Apr 7, 2013 at 4:56 PM, Roland Harriston <rolohar@...>
wrote:

>
> Too bad that Kepro went out of business when reliable, low-cost dry

film

> resist
>
> became widely used in the PC fab industry.
>
>

Kepro as company is gone, but at least some of its product line was taken
taken over by Dalpro. Now, Dalpro has been taken over by
CamCon Chemicals. Here's what they say on their home page:

*If you ordered from DalPro or Kepro in the past, we are now your
supplier!*

Here's their url: http://www.camconchemical.com/kepro-equipment/

They have at least one page devoted to Kepro equipment:

*We buy, sell, repair and sell parts

>
> for all Kepro etching equipment. We also *

*sell the boards and chemicals you need to make your circuit boards. *

*We are the leading supplier to colleges and universities around the

> country!*

Here's the link for that page:

http://www.camconchemical.com/kepro-equipment/

73,

Todd
----------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
----------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design

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




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

Todd:


Thanks for the Kepro update information.

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

>
>
> Kepro as company is gone, but at least some of its product line was taken
> taken over by Dalpro. Now, Dalpro has been taken over by
> CamCon Chemicals. Here's what they say on their home page:
>
> *If you ordered from DalPro or Kepro in the past, we are now your
> supplier!*
>
> Here's their url: http://www.camconchemical.com/kepro-equipment/
>
> http://www.camconchemical.com/kepro-equipment/
> <http://www.camconchemical.com/kepro-equipment/>
>

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

It bugged me so I researched it and found that the evaporation of the solvent as it spreads across the board thickens the resist just enough to match the increasing centrifugal force. For silicon wafers they control the viscosity, speed and acceleration very closely. It's apparently much less critical with PC boards.

Boman33 <boman33@...> wrote:

>Todd,
>I am not arguing, just thinking.....
>It helps when discussing concepts to emphasize for better clarity, so:
>If the resists is added an inch off center, I cannot see it moving toward
>the center to coat that area. Presumably the pour was sloppy enough to
>actually cover the center section.
>
>Similarly thinking about a very small drop sitting at the center, I would
>expect very little force to move it away and spread out.
>
>Finally, resist added in the center and spreading outwards has to cover a
>larger and larger area and therefor presumably be a thinner coating further
>out.
>
>Now, after writing all that there might be a completely different
>explanation:
>There might be a microscopic layer that attaches itself to the surface with
>a thin high boundary friction force and the excess just slides off, so as
>long as sufficient amount is added that thin surface layer stays constant.
>I do not know.
>Bertho
>
>-----Original Message-----
>From: Todd F. Carney / K7TFC Sent: Sunday, April 07, 2013 01:52
>
>*I didn't ever know the speed of what I used to use, but in comparing it in
>my memory with a 45 rpm record (also from memory), I'd guess it was about
>twice that fast. One certainly kept one's fingers away. While it's true the
>perimeter would be moving much faster than the center as measured in
>inches/second (or some other linear unit), I think in this application it's
>angular velocity that matters and that's the same at all points. At 90 rpm
>that would be 32,400°/minute. *
>*
>*
>*We used to mount the pcb material, start it spinning, and then carefully
>pour a small amount of emulsion at the center. Since "center" is really only
>a theoretical concept, it was always off center enough that the emulsion was
>flung across the board, hitting the sides of the open enclosure the thing
>was mounted it. It don't think we ever cleaned up that mess. It got pretty
>thick after a while.*
>
>73,
>
>Todd
>
>

Interesting!

Thanks Laurence.

Bertho



From: Laurence Hand Sent: Monday, April 08, 2013 01:16



It bugged me so I researched it and found that the evaporation of the solvent as it spreads across the board thickens the resist just enough to match the increasing centrifugal force. For silicon wafers they control the viscosity, speed and acceleration very closely. It's apparently much less critical with PC boards.

Boman33 <boman33@... <mailto:boman33%40vinland.com> > wrote:

>Todd,
>I am not arguing, just thinking.....
>It helps when discussing concepts to emphasize for better clarity, so:
>If the resists is added an inch off center, I cannot see it moving toward
>the center to coat that area. Presumably the pour was sloppy enough to
>actually cover the center section.
>
>Similarly thinking about a very small drop sitting at the center, I would
>expect very little force to move it away and spread out.
>
>Finally, resist added in the center and spreading outwards has to cover a
>larger and larger area and therefor presumably be a thinner coating further
>out.
>
>Now, after writing all that there might be a completely different
>explanation:
>There might be a microscopic layer that attaches itself to the surface with
>a thin high boundary friction force and the excess just slides off, so as
>long as sufficient amount is added that thin surface layer stays constant.
>I do not know.
>Bertho
>
>-----Original Message-----
>From: Todd F. Carney / K7TFC Sent: Sunday, April 07, 2013 01:52
>
>*I didn't ever know the speed of what I used to use, but in comparing it in
>my memory with a 45 rpm record (also from memory), I'd guess it was about
>twice that fast. One certainly kept one's fingers away. While it's true the
>perimeter would be moving much faster than the center as measured in
>inches/second (or some other linear unit), I think in this application it's
>angular velocity that matters and that's the same at all points. At 90 rpm
>that would be 32,400°/minute. *
>*
>*
>*We used to mount the pcb material, start it spinning, and then carefully
>pour a small amount of emulsion at the center. Since "center" is really only
>a theoretical concept, it was always off center enough that the emulsion was
>flung across the board, hitting the sides of the open enclosure the thing
>was mounted it. It don't think we ever cleaned up that mess. It got pretty
>thick after a while.*
>
>73,
>
>Todd
>

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

> Here's their url: http://www.camconchemical.com/kepro-equipment/
>
>

Be nice if they had pricing information. Anyone know what their prices are like?

Ben

>
> Be nice if they had pricing information. Anyone know what their prices are
> like?

That's strange, huh? I just sent them an email asking about this. I
indicated the links I posted went to over 6,000 group members. I also
ventured to guess that not having prices listed was a deal breaker for most
homebrewers. It certainly is for me.

I'll post their reply when it arrives.

73,

Todd
------------------------------------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
------------------------------------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design

On Mon, Apr 8, 2013 at 7:01 PM, Ben L <bhleavi@...> wrote:

> **
>
>
>
> > Here's their url: http://www.camconchemical.com/kepro-equipment/
> >
> >
>
> Be nice if they had pricing information. Anyone know what their prices are
> like?
>
> Ben
>
>
>


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

> > Be nice if they had pricing information. Anyone know what their prices are
> > like?
>
>
> That's strange, huh? I just sent them an email asking about this. I
> indicated the links I posted went to over 6,000 group members. I also
> ventured to guess that not having prices listed was a deal breaker for most
> homebrewers. It certainly is for me.
>
> I'll post their reply when it arrives.
>

Did you ever get a reply back from them?

Ben