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April 2004

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Thu, 1 Apr 2004 04:15:08 -0600
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Dear All,
I have seen a few SMT chip resistors images showing a layer of solder
between the component termination and the PCB pad (the termination and the
pad don't seem to touch at any point). I wonder why this is possible (the
suraface tension and the chip weight should force the chip to come into
contact with the pad)? Is it because 1) bubbles trapped between pad and
component, 2)uneven termination and pad creating contact points, 3)solder
trapped under chip, 4)needle-like intermetallics form during reflow, 5)
flux residual, etc etc. I am sure somebody out there has a convinving
answer!
Regards,
Hua
BTW: Solder fillets of these resistors all have concave shape.

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