Hi Adam,
Thanks for the reply.
>I've been using tenting method with great success and is one of the few
>operations that have not cause me headaches. My first comment is that
>you have resist adhesion problems. In my experience, dry film tenting
>over holes holds up very well, even for holes large as 3mm. I use a wet
>lamination method so the holes are actually filled with water. I have
>not tried hot roll lamination.
I checked film adhesion, it is rock solid. Actually problem is exactly at the center of the holes. When I look at the film before developing, I see that film sucked in to the hole. Because of that center of the hole is far away from the surface and it gets less light energy. This causes under exposed film at the center and inside developing bath it starts to dissolve from that point.
BTW I'm using LDI to expose the film.
>Forget about pattern plating. I have been down that path and its
>disadvantages outweigh advantages. A tin resist requires difficult to
>maintain alkaline etchants. Also, tin plating solutions become depleted
>by atmospheric oxidation when they are used infrequently. A Sn/Pb
>plating bath may allow use of persulfate or peroxy sulfuric etchants but
>again I believe you'll also have tin(II) oxidation problems.
I agree it is a big hassle.
>Overexposed dry film will become brittle , and could be a source of your
>problem. Are the traces are holding up ok, and you find cracks in the
>dry film covering the hole opening ?
>Is the resist lifting around the outside of the pad ?
If I increase exposure duration further this happens. Traces are always good but you can see cracks on hole openings. I didn't see any resist lifting problem outside the pad.
I think using your wet film method will solve film sucking problem, it will minimize pressure change inside the hole. I need to read your notes first before give a try.
Regards,
Volkan
--- On Sun, 1/10/10, Adam Seychell <a_seychell@...> wrote:
From: Adam Seychell <a_seychell@...>
Subject: Re: [Homebrew_PCBs] Dry film tenting problem & pattern plating
To: Homebrew_PCBs@yahoogroups.com
Date: Sunday, January 10, 2010, 10:18 PM
Volkan wrote:
>
>
> Hi,
> I'm facing dry film tenting problems. It couldn't protect THP holes and
> tents start to break during developing. I did some googling and saw that
> this problem is known and according to Dupont technical articles, it is
> recommended to increase exposure duration to avoid tent break. I tried
> it and I saw great improvement.
> Another recommendation was, to reduce roller pressure to avoid hole
> sharp edge cutting of the film. It is stated that pressure in the holes
> decreases after lamination and it sucks film (film is liquid during
> lamination) to the holes and because of that, sharp hole edges cut the
> film. This cut decreases film strength. Another advise was to decrease
> the lamination temperature. I also tested both, they helped but didn't
> solve the problem completely.
>
> My second try was to use pattern plating method. I tried electroplated
> tin as a resist and ammonium persulfate as an etcher, it didn't act as
> an etch resist and etched away with copper.
>
> Any ideas/suggestions or does anyone faced similar tenting problems?
> Which etcher can be used for tin or nickel etch resist? Is there any
> practical formula for homebrewers?
> I'll appreciate a lot on any guidance.
> Thanks,
>
I've been using tenting method with great success and is one of the few
operations that have not cause me headaches. My first comment is that
you have resist adhesion problems. In my experience, dry film tenting
over holes holds up very well, even for holes large as 3mm. I use a wet
lamination method so the holes are actually filled with water. I have
not tried hot roll lamination.
Forget about pattern plating. I have been down that path and its
disadvantages outweigh advantages. A tin resist requires difficult to
maintain alkaline etchants. Also, tin plating solutions become depleted
by atmospheric oxidation when they are used infrequently. A Sn/Pb
plating bath may allow use of persulfate or peroxy sulfuric etchants but
again I believe you'll also have tin(II) oxidation problems.
Overexposed dry film will become brittle , and could be a source of your
problem. Are the traces are holding up ok, and you find cracks in the
dry film covering the hole opening ?
Is the resist lifting around the outside of the pad ?
Adam
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