Hi Tuan, hi Pohkh,
Assuming that the chip capacitors are o.k. to begin with, and that they are
not damaged during placement, the cause is in all likelihood a combination of
solder fillets that are too large and a cooling rate after reflow that is too
fast. I would venture to bet, that in both of your cases you have soldering
pads for these components that are large because they were originally
designed for wave soldering. Solution is to make the width of the pads no
wider than the components (that also reduces dombstoning) and to reduce the
length of the pads protruding on either side--lengthwise--of the components.
This will reduce the solder fillets considerably; for reflow soldering, there
really is no need for the solder fillets from a reliability point of view. If
reliability is an issue, glue the components to the board to get an increased
solder joint height.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]

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