Rod -

In my opinion, going to dry film is like taking a step backwards. I do not
know whether or not your are using SMT or No Clean, but I could tell you
some stories. First, dry film does not have the resolution that LPI has for
having the solder mask close to the pads for fine pitch assembly. Secondly,
stencil printing over the thicker dry film mask for SMT components is very
difficult because the mask's thickness impedes solder paste contact with the
pad for a good deposition. Thirdly, if not properly cured you can end up
with contamination problems and, if you are wave soldering, you can have
lots of solder balls on the bottom side of the boards. Depending on your via
hole sizes, some LPI's can fill or partially fill the vias. Lastly, what is
the problem with conformal coating going into the via holes?

Another item to consider is: I do not know what level of reliability your
boards require, but I would have much more confidence cleaning and
contamination testing my boards in house before conformal coating, than I
would have in the PCB fabricator fully cleaning the boards in the via holes
prior to masking them over and maybe entrapping contaminants in the vias.
Good Luck!

Ed Valentine
Electronics Manufacturing Solutions
8612 Mourning Dove Road, Raleigh, NC 27615
Phone: (919) 270-5145, Fax: (919) 847-9971
Email: [log in to unmask]
Website: http://www.ems-consulting.com

----- Original Message -----
From: "Rod Simon" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, October 30, 2000 10:38 AM
Subject: [DC] Soldermask


> I am looking for some information on dry film soldermask vs. LPI
> soldermask.
>
> Manufacturing wants to change all boards to dry film mask and tent all via
> holes so that when conformal coating is applied to the boards the coating
> does not drip through the holes.
>
> About 2-3 years ago I remember reading an article on problems with dry
film
> and alternatives to using dry film. Since I had only used dry film once or
> twice a long time ago I did not save the information and can


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----



?t find it in
any back issues of Printed Circuit Design or SMT that I have.

It is my understanding that our main supplier has the facilities to dry
film and is encouraging the dry film solution. (In my opinion more $ and
less Competition) Cost is not a big issue since we do not produce large
quantities of our products.

Any help would be greatly appreciated.

Rod Simon

[log in to unmask]   Flight Vision Inc.       Sugar Grove IL 60554
630-466-2119

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