You might try to protect them in the wave with a masking pallet. We do quite
a few of those to solve that very problem. You can give me a buzz, Chuck
Smith @ GSC 972-494-1911.

----- Original Message -----
From: Jim Kittel <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, December 14, 2000 2:28 PM
Subject: [TN] Solder Failure During SMT/Wave Solder


> Hi,
> I am encountering solder failures I have never seen before on some type II
> SMT assemblies.  These are about 8 x 16 inch mixed technology boards with
> misc SMT parts including some 0.020 inch pitch QFP's and some thru hole
> connectors.  The cards are 0.062 and about 8 layers of 1 ounce copper.
> Paste is 63/37 eutectic.
>
> We paste, populate the primary side with SMT, reflow solder, clean,
inspect,
> and then send the board to wave solder area.  In wave solder they install
> the thru hole connectors on the primary side and then wave solder.  From
> what I know this is an industry standard process.
>
> The problem is that on two QFP's (always the same) the leads can be easily
> lifted right out of the solder fillet after wave solder.  (Board has
> cooled.) Sometimes the solder stays on the lead, sometimes it stays on the
> pad.  Solder is always fine before wave solder.  We attached thermocouples
> to leads on these QFP's and ran the boards back thru the wave solder.
Found
> a lead that peaked below melt temperature and another lead peaked above
> solder melt.  The leads between these are the ones that can be easily
pulled
> out of the solder after cooling.  In some cases the solder appears dull
and
> grainy, but in other cases it still looks shiny.
>
> Is it possible the solder in these connections is reaching the plastic
> stage, crystallizing and then loosing it's strength?  If so, why doesn't
> this happen to others in the industry running this process?  We have to
run
> about 3 feet/minute to solder the thru hole connectors to the 1 ounce
> planes.  Is the remedy to go even slower to reflow all the top
connections?
> Ran EDX on the solder in the failed connections and saw nothing unusual.
> Any help would be appreciated.  I am stumped.
>
> Thanks,
>
> Jim Kittel
> L-3 Communications
>
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