Kelley,
What was wrong with just "simple Dry film tenting"??
And how thick was the product after application?
R. Kubes
Honeywell DAS (Albq)
> ----------
> From: Kelly M. Schriver[SMTP:[log in to unmask]]
> Sent: Thursday, October 01, 1998 7:54 AM
> To: [log in to unmask]
> Subject: [TN] LPI Filled Vias ?
>
> Good morning TechNet!!!!!
>
> Here's a challenge for the board fabrication guys and gals:
>
> Most of our board designs go into severe environment service. For the
> past
> eight ten years or so, we have been tenting vias with thin dry film solder
> mask disks, followed by an LPI overcoat of the entire board (both sides).
> The
> purpose of all of this is to seal up all exposed conductive surfaces,
> particularly those under component bodies, prior to assembly. This leaves
> only the termination pads and plated thru holes which receive thru hole
> leads
> exposed. This has worked out to be a very successful process.
>
> We arrived at this combined mask application after having tried a number
> of
> different via fill approaches and just simple dry film tenting. None of
> these
> were fully satisfactory (bumps, open voids, ruptures, incomplete fill, not
> process durable, too costly, not repeatible, etc.). The dry film plus LPI
> also turned out to be the only approach that ALL of our board vendors
> could
> handle reliably.
>
> Now I am revisiting the process. We have run a few samples using LPI as a
> via
> plug as well as the overall solder mask. These have turned out to be very
> durable in our assembly process. Microsections indicate small voids, less
> than 50% of the via volume, which are not a problem to this application.
> Board thicknesses range from .040" to .080". Finished vias range from
> .008"
> to .016" dia. (This covers multiple designs.)
>
> Now, here's the big question: Could you produce class 2 and 3 boards
> with
> LPI plugged vias which will not rupture or expose metal during my
> soldering
> and cleaning processes? (Assume that worst case will not exceed four
> solder
> and cleaning cycles. Cleaning agents may include DI water, long chain
> alcohols or citric acids) Total mask thickness buildup over pads should
> not
> exceed .0015", in order to not interfere with our stencils.
>
> For anyone who is actively performing this process or assembling CCAs
> using
> this process - I would greatly appreciate your inputs.
>
> Regards - Kelly
>
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