Gaby,
Check the age of the chips and the exposure time verses humidity...
Many times the plating on the leads absorb moisture like the rest of the
package. When heated to reflow temps the moisture vaporizes in microvoids
and blows off small bits of plating and solder as the solder melts in the
presence of the flux..
By baking (low and long) the PLCCs in question in dry nitrogen and
duplicating your reflow process, you can get a measure of whether the
problem you are having is caused by moisture or something else.
Paul Edwards
Process Engineering
[log in to unmask]
Tel: 408-433-4700
FAX: 408-433-9988
Surface Art Engineering
81Bonaventura Dr.
San Jose, CA 95134
DUNS: 944740570
CAGE/NCAGE: 1XZ48
-----Original Message-----
From: Gabriela Bogdan [mailto:[log in to unmask]]
Sent: Friday, September 10, 2004 9:24 AM
To: [log in to unmask]
Subject: [TN] Tin plating on leads HELP!!!
Dear friends,
After assembly, on all circuits there was one fine pitch PLCC from a certain
vendor which had lots of small solder balls between the leads, even on the
solder mask dam between them.
Other PLCC's with the same pitch were clean.
We tried to see the amount of solder balls by X-ray, and found many more
behind the leads.
At first we thought that our solder paste was the culprit, but seeing that
other components were "normal" , we looked closer to the leads by X-ray, and
saw a lot of small voids only along the leads of the bad component, these
voids reaching to the upper end of the leads, where the solder paste did
not reach. Visually, the upper part of the leads was very rough.
I suppose that the tin plating of the leads contained additives which epand
during soldering, even burst out, and "spit" the molten solder all around.
If this is the case,how could I reject such components during incoming
inspection?
Should I do a solderability test for each batch on a printed ceramic plate?
Gaby
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