Rich,
first, make sure you have an initial overlap of let's say 25 mils on each
pad. Secondo, you may want to check if it happens with other manufacturers
than Kemet & AVX. Is the push-pull effect occured in the oven due to the
plating of the parts? You mentioned that the parts were well centered. Also,
validate the direction of your misalignment and check if it is always the
same. It may be helpful to find the root cause.

Having to choose between a good solder joint on a misaligned part and a bad
solder joint on a centered component I would choose the first. As you can
see on Fig. 12-31, the solder paste didn't wet at all. But this is not your
case. You may want to perform a shear test to raise your confidence level
that your shippable products are within specifications.

Good luck in your finding,

Eric

-----Original Message-----
From: Rich Lasko [mailto:[log in to unmask]]
Sent: Monday, February 16, 2004 9:14 AM
To: [log in to unmask]
Subject: [TN] SMT Chip Components End Overlap (Section 12.2.2.8)


Greetings everyone,



Let me first start off with a little background information.  I am currently
investigating a random issue on one of our SMT assemblies.  The issue
revolves around four (4) 0805 chip components.  (Kemet C0805C824K8RAC & AVX
VC080505A150DP)  During initial placement of the components (pre reflow) the
part is centered directly between the lands and there is good component to
pad overlap.  However, during post reflow we are noticing that occasionally
(on only these four components) the parts shift so that the component to pad
overlap is now being questioned.  Please note, the end overlap looks pretty
close to Figure 12-31 however on my products there is a good solder joint
that meets both the minimum fillet height and end joint width criteria.  So
my question is, if the component is soldered but is borderline and
questionable as to the amount of end overlap should this be reworked?  I
have always felt that if you have a good solder joint to begin with that
touching it to move this component less than 0.015" is running the risk of
doing more damage than good.  Thoughts?



Thanks in advance for your feedback.



Regards,



Rich Lasko

BEI, LLC


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