Hi Steve and All

From experience I'd recommend filling all of the vias which don't ultimately
contain a thru-hole lead with one of the nonconductive via fill compounds
offered by Enthone, McDermid, and others.  I'd also recommend an LPI SMOBC
on those via pads located directly under the CLCC's to help avoid later
metallic growth problems for various and sundry reasons.

Regards - Kelly


-----Original Message-----
From: Stephen R. Gregory <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Monday, June 26, 2000 8:05 PM
Subject: [TN] "The Kobiyahshi Muru", or the no-win scenario...


>This is a weird one...
>
>We've got some boards here that we build for a DOD customer. This board has
>some LCCC's on it (small ones, 32-28-pins). We've been building them and
>masking off certain test via's that are un-masked that wind-up beneath the
>LCCC's because of the concerns (justifably) of cleaning. Now they want to
>expand the test coverage that they've had, and want to un-mask all the
vias!
>
>I know from reading posts from Werner and others that if you have un-masked
>vias, that you need full-fill after wave for reliabilty concerns. I also
know
>that cleaning flux residues from vias beneath an LCCC is a lost cause.
>
>I have heard that the fab vendors can fill vias for you...that to me would
>alleviate the concerns about cleaning. Vias that are filled already would
not
>allow flux to get beneath the part.
>
>My question is; is that very expensive to get done? Getting the via's
filled
>at the fab vendor? I've never asked that be done before...
>
>And no, the design of the board can't be changed...those of you that deal
>with ancient military designs know what I'm talking about...
>
>-Steve Gregory-
>
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