Homebrew PCBs

Hi guys,

I tried my first photo process board this weekend and the process 
failed completely.  I am using the dry film, negative resist from MG 
chemicals.

The failure was in the developing of the resist.  While developing, 
all the resist washed off.  It was developed as I could see the 
traces in the resist, but faintly.

The developer solution was a best guess on dilution so this is 
probably my main failure point.  

I am wondering what actually holds the resist to the board though.  
Per the instructions, I am suppose to peel off the backing, apply 
resist to the board and then run it through a laminator twice.  Is 
this what causes the dry film to stick to the board or is it the 
exposure process?

I also suspect that using vellum for the artwork is not a good 
thing.  Using some scraps, I noticed that exposure is much different 
using transparncy than vellum.  So my next attempt will be using 
transparencies and to carefully measure the developer.

Chris

With a negative film, this sounds more like under-exposure.
Have you tried increasing exposure time ?

--- On Mon, 10/20/08, lcdpublishing <lcdpublishing@...> wrote:

From: lcdpublishing <lcdpublishing@...>
Subject: [Homebrew_PCBs] Dry film- negative resist... First attempt failure
To: Homebrew_PCBs@yahoogroups.com
Date: Monday, October 20, 2008, 3:19 PM










    
            Hi guys,



I tried my first photo process board this weekend and the process 

failed completely.  I am using the dry film, negative resist from MG 

chemicals.



The failure was in the developing of the resist.  While developing, 

all the resist washed off.  It was developed as I could see the 

traces in the resist, but faintly.



The developer solution was a best guess on dilution so this is 

probably my main failure point.  



I am wondering what actually holds the resist to the board though.  

Per the instructions, I am suppose to peel off the backing, apply 

resist to the board and then run it through a laminator twice.  Is 

this what causes the dry film to stick to the board or is it the 

exposure process?



I also suspect that using vellum for the artwork is not a good 

thing.  Using some scraps, I noticed that exposure is much different 

using transparncy than vellum.  So my next attempt will be using 

transparencies and to carefully measure the developer.



Chris




      

    
    
	
	 
	
	








	


	
	

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"lcdpublishing" <lcdpublishing@...> writes:

> While developing, all the resist washed off.

I agree this sounds like underexposure.

If you don't have a step gauge, you can sort of calibrate your
exposure by making a lot of small boards (like 1 in2) with a striped
print on your film.  Mark the back with exposure times in powers of
two - 15s, 30s, 1m, 2m, 4m, 8m, 16m (more if needed).  Expose each for
the marked time and develop.  Note the shortest time that exposes the
clear areas, and the longest time that doesn't expose the covered
areas, and pick a time between those.  You don't have to etch these
boards - just expose and develop, and inspect the film.

If you have a step gauge, one exposure is all you need to calibrate.

> I am wondering what actually holds the resist to the board though.  

Heat.  Try peeling the film off by hand, it should be really hard to
do so.

Also, you need to let the film "rest" for 15 minutes after exposure -
before you peel off the second backing - to let the polymerization
complete, before developing.

On 20 Oct 2008 12:51:07 -0400, you wrote:

>
>"lcdpublishing" <lcdpublishing@...> writes:
>
>> While developing, all the resist washed off.
>
>I agree this sounds like underexposure.
>
>If you don't have a step gauge, you can sort of calibrate your
>exposure by making a lot of small boards (like 1 in2) with a striped
>print on your film.  Mark the back with exposure times in powers of
>two - 15s, 30s, 1m, 2m, 4m, 8m, 16m (more if needed).  Expose each for
>the marked time and develop.  Note the shortest time that exposes the
>clear areas, and the longest time that doesn't expose the covered
>areas, and pick a time between those.  You don't have to etch these
>boards - just expose and develop, and inspect the film.
>
>If you have a step gauge, one exposure is all you need to calibrate.
>
Patience and thinking backwards can replace a step gauge while using a
single board.

Apply the resist, then mark the board into seven sections. Use a piece
of metal as a dark slide (we're pretty sure it won't pass UV 8:)). 

Expose the whole board for 15s, cover the first segment. 
Expose the remainder for another 15s (30s total), cover the first two
segments. Expose for another 30s (1m total), cover the first three
segments. Expose 1m (2m total), cover first four segments. Expose 2m
(4m total), cover first five segments. Expose 4m (8m total), cover the
first six segments. Expose the remaining segment for 8m (16m total).

On Mon, 20 Oct 2008 15:19:41 -0000, you wrote:

>Hi guys,
>
>I tried my first photo process board this weekend and the process 
>failed completely.  I am using the dry film, negative resist from MG 
>chemicals.

Negative resist?  I'm familiar with the positive resist on precoated
boards.
>
>The failure was in the developing of the resist.  While developing, 
>all the resist washed off.  It was developed as I could see the 
>traces in the resist, but faintly.
>
>The developer solution was a best guess on dilution so this is 
>probably my main failure point.  
>

probably not.  For the positive resist it's about 10:1 water to
developer.

>I am wondering what actually holds the resist to the board though.  
>Per the instructions, I am suppose to peel off the backing, apply 
>resist to the board and then run it through a laminator twice.  Is 
>this what causes the dry film to stick to the board or is it the 
>exposure process?
>
>I also suspect that using vellum for the artwork is not a good 
>thing.  Using some scraps, I noticed that exposure is much different 
>using transparncy than vellum.  So my next attempt will be using 
>transparencies and to carefully measure the developer.

Very much so, however, I think you have a different problem.

Assuming that the resist is a negative resist, and if it is
unpolymerized ( which means that just out of the can it washes away in
the developer), it "hardens" from the top down.  Insufficient exposure
causes there to be a layer of hardened resist over the top of a layer
of unexposed resist.

That unexposed resist will wash off.

I'd suggest you do an exposure test, steps of two, or take their
recommended exposure and go around that.  You may see the difference.

The transmission of your media of the UV is very different from velum
to a transparency, so that's possibly a cause of your problems.

Harvey

>
>Chris
>

----- Original Message ----- 

From: "Harvey White" <madyn@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Monday, October 20, 2008 8:05 PM
Subject: Re: [Homebrew_PCBs] Dry film- negative resist... First attempt 
failure


> On Mon, 20 Oct 2008 15:19:41 -0000, you wrote:
>
>>Hi guys,
>>
>>I tried my first photo process board this weekend and the process
>>failed completely.  I am using the dry film, negative resist from MG
>>chemicals.
>
> Negative resist?  I'm familiar with the positive resist on precoated
> boards.
>>
>>The failure was in the developing of the resist.  While developing,
>>all the resist washed off.  It was developed as I could see the
>>traces in the resist, but faintly.
>>
>>The developer solution was a best guess on dilution so this is
>>probably my main failure point.
>>
>
> probably not.  For the positive resist it's about 10:1 water to
> developer.

I use 12g NaOH to 1l of water.

Leon
--
Leon Heller
Amateur radio call-sign  G1HSM
Yaesu FT-817ND transceiver
Suzuki SV1000S motorcycle
leon355@...
http://www.geocities.com/leon_heller

kabowers@... writes:
> Patience and thinking backwards can replace a step gauge while using
> a single board.

True, but a step gauge tells you the *desired* exposure, not just
"something that works".  They're pretty cheap too.

> using transparency than vellum.  So my next attempt will be using 
> transparencies and to carefully measure the developer.

If you are using washing soda for the developer you should not have
any problems with losing exposed traces because it is too strong. 

If you are trying to dilute down NaOH(Drano) then it could be trickier
since NaOH is what is used to strip the resist after etching.

As others have mentioned though, the problem is probably due to
underexposure.

lcdpublishing wrote:
> Hi guys,
> 
> I tried my first photo process board this weekend and the process 
> failed completely.  I am using the dry film, negative resist from MG 
> chemicals.

If you've never done exposures and this was your first PCB then it would 
be almost guarantee a failure. Normally, a calibration step is made to 
determine exposure time with the equipment. Without any preliminary 
tests your just going to cause hours of frustration.
I'd agree with what all points other people have said.

javaguy11111 wrote:

> 
> If you are trying to dilute down NaOH(Drano) then it could be trickier
> since NaOH is what is used to strip the resist after etching.

It would almost be impossible to develop with NaOH because even tiny 
amount will shoot pH too high.

All negative dry film I've come across have specified a developer of 
9~10 g/L sodium carbonate, at 24~27 deg.C. For paint brush style manual 
developing, I find 30 to 35 deg.C better temperature.

--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell <a_seychell@...>
wrote:
>
> javaguy11111 wrote:
> 
> > 
> > If you are trying to dilute down NaOH(Drano) then it could be trickier
> > since NaOH is what is used to strip the resist after etching.
> 
> It would almost be impossible to develop with NaOH because even tiny 
> amount will shoot pH too high.
> 
> All negative dry film I've come across have specified a developer of 
> 9~10 g/L sodium carbonate, at 24~27 deg.C. For paint brush style manual 
> developing, I find 30 to 35 deg.C better temperature.
>
Adam is right, if you dilute in NaOH so your photoresist will pull
away so fast, i develop my dry film photoresist with sodium carbonat
with warm water too

Thanks everyone,

All great advice and information.  I think the next smart step for me is to do an exposure test 
using transparency as opposed to vellum.  Also getting a measure cup of some sort so I can 
mix the developer properly!

Chris

lcdpublishing wrote:
> Thanks everyone,
> 
> All great advice and information.  I think the next smart step for me is to do an exposure test 
> using transparency as opposed to vellum.  Also getting a measure cup of some sort so I can 
> mix the developer properly!
> 

Your best bet is to measure out 100 grams of sodium carbonate and make 
up a 500ml concentrate solution (i.e 200g/L). That way you don't need 
+-1g accuracy. Then to make your developer, just dilute it to 10g/L with 
common kitchen items for measuring liquid volume.