You may be using the wrong media with your microblaster.  Did you talk to
them and ask for a more aggressive media.   I have seen this done,  to
remove solder mask and done pretty well, but cannot remember what they used
as a media to remove it.   You know by the time you get all these answers
you will have these done and I am sure all future orders of this board will
be fixed or you will have someone by the throat and shaking them pretty
vigorously to remove all the solder mask at that time.    Good luck



                      Stephen Gregory
                      <Stephen.Gregory@L        To:       [log in to unmask]
                      ABARGE.COM>               cc:
                      Sent by: TechNet          Subject:  [TN] Selective LPI soldermask removal...
                      <[log in to unmask]>


                      03/30/05 12:24 PM
                      Please respond to
                      TechNet E-Mail
                      Forum; Please
                      respond to
                      Stephen.Gregory






Happy "Hump-day"!

I might have asked the list about this over a year ago, I can't remember.
But I have this
assembly that goes into a Radar system. There's a device on the assembly
that has to
be sitting over the metal of the top layer plane, with no solder mask on
the board beneath
the footprint of the device for it to work properly. Unfortunately, the
solder mask file in the
gerbers didn't reflect this. So at the time (over a year ago), I reworked
the boards that we
had to correct the problem...and let me tell you, it's a REAL PIA!

Go to: http://www.stevzeva.homestead.com and look at "Mask Removal", and
"After Tinning"
to see what I'm trying to do.

I did this over a year ago, and we got an order for these assemblies
again...but the gerber never
got corrected, and I get to do this again. WHOOPEE!

I have to remove the solder mask beneath where the device is going to be
installed, and then
I solder coat the area to cover the exposed copper. I'm removing the solder
mask very, very
carefully with a Dremel and a very fine abrasive tip, and I'm using an
exacto knife with various
blades. This is all being done tediously under a microscope to prevent the
copper from being
removed from the plane. We have a micro-blaster here to remove conformal
coating, but it can't
get down to the bare copper. That's why I'm using the Dremel and exacto
knife. This time when
the board house did their micro-etch or pumice scrub just prior to applying
the solder mask, they
really did a good job! That mask is on there, and meant to stay put! I'm
really having a hell of a
time doing this on these latest fabs.

Is there any other way to remove this coating in the area that I need to?
I'm thinking maybe a
laser. Does anybody know where I would go to get this done, and about what
it would cost?
There's only 5-boards that I need this done to, but it takes me a couple of
hours with each board
to complete the job.

Kind regards,

-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX
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