Hi Steve!

I don't know if you caught my epilog reply, but the mask coming off had
nothing to do with the XJN...the fab vendor didn't do a pumice scrub before they
applied the mask. Their production paperwork, or lot traveler had been
signed-off that it had been done. We do tape tests at incoming receiving inspection,
and nothing was noted with these fabs. Only until themally shocking the fab at
wave solder (with a bunch of expensive parts loaded), and then washing, did the
mask lose adhesion because of the bad surface prep.


As far as specifying the type of soldermask used, I sure wish I could! But
many of our customers that use dry-film are DoD suppliers, and they either; A.)
Dry-film is what they've been using since they started, and aren't going to
change now, or; B.) To switch to a LPI means either changing the drawing or
having to requalify the assembly, something they say is just too much trouble.

It's hard to convince them to change, because they don't feel the pain. All
they want is assembled product built to their spec's using the materials they
specify. They don't have to deal with the scrap that we have to deal
with...that's our problem, not theirs.

Sometimes you can get the fab vendor to eat the cost of the assembly when a
step is skipped when they built the fab, sometimes you can't. When you can, it
still takes a lot of time and effort to build your case against them, time
that's being taken away from your primary purpose, which is to build
product...unless your company has deep pockets and has a staff specifically for that
purpose.

-Steve Gregory-


> Steve,
>
> I had related problems with several types of dryfilm soldermasks when I
> used SSA back in the 1990's, which is a precursor to XJN. The solvent,
> IMHO, is active enough to attack the acrylic portion of the dryfilm mask
> under the correct conditions, time, temp, spray pressure, proper cure of
> soldermask, proper board prep, etc... This was also true when we used 1,1,1
> trich, and should also be true of n-propyl bromide. I've cleaned off more
> acrylic conformal coated boards in my time than I care to admit. Acrylic is
> weak stuff.
>
> Repeated washing, typical in hi-rel environments, adds to the problem.
>
> WE stopped using dryfilm soldermasks on our designs as a whole because we
> could not find them superior to LPI's and could not justify the risks.
> As a contract manufacturer, we stipulated the use of LPI's, regardless of
> original design requirements, as part of the contract, which superceded the
> drawing package. I believe you will continue to be plagued by "occasional"
> failures of this type. If you upgrade from your batch machine to an inline,
> you will see a increase in the failure rate.
>
> Last, let me say that the purpose of the soldermask was to act as a
> manufacturing aid. Therefore, selection of the soldermask should be left to
> the manufacturer, and should be selected for performance in the factory.
> Therefore, you should specify the soldermask to the design\customer and
> stop the madness.
>
> Good Luck
> Steve Mikell
> [log in to unmask]
>


---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------