Peter,
  I was unable to access the HOMESTEAD site to view the failure.   Can you
please
send it to my mail box for viewing.

Victor,

-----Original Message-----
From: Peter Lee [mailto:[log in to unmask]]
Sent: Sunday, August 24, 2003 11:11 PM
To: [log in to unmask]
Subject: [TN] Moisture under chip capacitors


Technet,

I have come across a rash of failed assemblies that have 0805 capacitors and
resistors, bottom side glued, wave soldered and washed. Trouble shooter
reported touching up the solder joints on a few areas and the boards would
pass test.

I had a look at one board which was reported to have a 0805 56K resistor
with "drifting" values. I pulled the component off mechanically in order not
to apply any heat and noticed several mini-voids within the adhesive body. I
have seen solder bridge within the glue before but this was the first time I
saw wet residue within the voids.

You can view a sample image from Steve's web site:
http://www.stevezeva.homestead.com/files/SMTAdhesive.jpg

The image showed the bottom side of the cracked resistor after removal
(white), with a portion of solder mask (green) and SMT adhesive (red).

I used a 8mil stencil. The thermal profile was verified and conformed to the
slope/ curing specs.

Has anyone seen this before? Any explanation as to how the void was formed
and how moisture got tapped in? Does anyone re-use their glue on the line or
throw away any left-over to avoid moisture in the glue?



Rgds,
Peter

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