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Subject:	Re: Random absence of solder joints - update
From:	"Campbell, William (wcampbel)" <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Fri, 6 Apr 2001 13:05:17 -0400
Content-Type:	text/plain
Parts/Attachments:	text/plain (63 lines)

Ioan-  try running a bare pcb through the wave.  If it shows poor wetting,
then I would reject the lot. If it shows good wetting, you know there's
something in your process that's the problem.  One "wasted" pcb can save a
lot of heartache later on.  -Bill

-----Original Message-----
From: Tempea, Ioan [mailto:[log in to unmask]]
Sent: Friday, April 06, 2001 12:25 PM
To: [log in to unmask]
Subject: [TN] Random absence of solder joints - update

Hi technos,

and big thanks for the interest in my problem. Now, I tried to follow all
the leads, I checked the solder mask, I ruled out the contamination, since
the problem shows on each and every board, checked for oily residues, etc.

To clarify, the problem pads show no sign of having been in contact with the
solder, they are like before waving.

So I still can't put the finger on the cause. However, by hand spraying the
bottoms, or running the foam fluxer at max, we reduced the number of
problems. We even get, from time to time, fully soldered boards.

Maybe the boards have gone through some thermal cycling that made the
intermetallics grow, or the pads are oxidized for some reason. Maybe a bad
batch. I'm sure that a stronger flux would solder very well, but why this
deviation from the regular process, since we are talking regular boards?

So, the follow up question is:
what should I do to avoid that the problem reappear while running a future
job, eventually high volume?

Thanks,
Ioan

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