Ioan -
A couple of possibilities on the "dull grainy" joints:
- Check the plated thru hole barrels of several bare boards - any signs of
debris, process residues, etc.? I had a condition where we found holes with
"trash" that floated to the top of the solder column and drove us wild for a
while. It had no pattern, and sure made for some ugly top side fillets.
- Solder which remains liquified for a prolonged period will form crystaline
clumps which take on a definite grainy appearance. Does this condition in
any way correlate with high thermal mass solder connections such as ground
plane hookups, heavy leads, etc.? Reprofiling to produce an earlier
sollidification of the solder can solve this, if you can do so without
increasing your overall defect rate. As an alternative, a supplemental
cooling system to solidify the molten solder can also help solve the
problem.
Even though these type joints are acceptable, they can sure be a darned
nuisance to try to explain to the personnel examining them or to customers,
who in many cases don't have the background to understand the rationale for
their acceptability.
Have a good day - hope this helps.
Regards - Kelly
PS/Watch out for the green tea/grog/boiled milk concoctions of Ingemar and
PK!
-----Original Message-----
From: Tempea, Ioan <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Wednesday, October 06, 1999 7:32 AM
Subject: [TN] Cold solder epilogue... maybe
>Thanks for the interest and thoughtfulness.
>
>There are three things I would like to clarify:
>
>- first, my identity, the name is IOAN, starts with an I, the letter after
>H. Some of you passed this test;
>
>- second: tea, grog, etc is not exactly my kind of stuff; where I come from
>we go for strong licors;
>
>- third: looks like the hours I spend reading through e-mails are very
>precious. Being in contact with people of your expertise is a big chance
for
>me.
>
>So, after getting some of the hints on the Technet, I realized that, indeed
,
>it's not cold solder, but the dull, grainy joints that IPC-610 accepts for
>this kind of boards.
>
>Did this solve my problem? Maybe. Now I have this phenomenon labeled as
>process indicator by the QA. This adds to the other process indicator, the
>solder joints that don't have 100% filling. The same IPC-610 accepts 50%,
so
>we are going to make some cross sectioning.
>
>The thing is I have two process indicators that are getting worse. More
>grainy joints, more not-so full joints. I wonder where will this lead.
>
>Why do we do two passes? We couldn't avoid damaging the board with only one
>pass, simply, the board wouldn't preheat enough to avoid the thermal shock
>when hitting the wave. If we set the preheaters higher, the passive
>components will go out of spec.
>
>Thanks again,
>
>Ioan
>
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