> Dupont call their product Valu.

> Regards,
> Bob Metcalf

> >>> Jerry Cupples <[log in to unmask]> 04/16/96 05:22pm >>>
> Steve Quinn asked:
> 
> >We have just started using a dry film mask(Vacrel), which is about
> .003"
> >thick.  We are using a .006" stencil and printing .020" pitch parts, and
> are
> >measuring paste thickness of about .009".


I have used Vacrel Dry Film in my designs. I am now using LPISM of different
sorts.  I have also had a really good chat with DuPont re their Valu system
(wet&dry) a few years ago.

I think that your problem with Vacrel may be stemming from the fact that it is
about 0.003" thick all the way accross the board. This is in addition to the
height of tracks on the board. It will rise up over tracks somewhat (I imagine
it may thin out to some degree but I don't believe much) creating a bit of a
well where the pads are (also a void where it lifts off the board going up over
a track).  This is why Dry film has never been recommended for screening solder
paste.

My understanding is that Valu is a two part system.  A liquid fills the gaps
between tracks, up to the height of the tracks, & then a thin (0.001)" dry film
is placed over the top.  In an SMOBC situation, it is likely that the final
height of the pads will be as high or > than the surrounding soldermask, making
contact of the screen much more complete that you are trying to do now.

DuPont offered to do a small run of boards, for free, (5-10) to see if 
1. we liked it 
&
2. our board stuffers (good term ;-) liked it to solder with.

Maybe they'll do the same for you.


Good luck.  Let us know what you decide.

-- 
Regards,                                         JNA Telecommunications Limited
                                  ___  _____     16 Smith Street
Dom Bragge    (VK2YAK)        __ / / |/ / _ |    Chatswood NSW 2067
PWB Designer                 / // /    / __ |    AUSTRALIA
Tel: (+61 2) 9935 5792       \___/_/|_/_/ |_|
Fax: (+61 2)  417 3862                           http://www.jna.com.au


-- 
Regards,                                         JNA Telecommunications Limited
                                  ___  _____     16 Smith Street
Dom Bragge    (VK2YAK)        __ / / |/ / _ |    Chatswood NSW 2067
PWB Designer                 / // /    / __ |    AUSTRALIA
Tel: (+61 2) 9935 5792       \___/_/|_/_/ |_|
Fax: (+61 2)  417 3862                           http://www.jna.com.au