Hi Jorge,
>All the thermocouples were directly attached to the component solder joints,
the
>peak temperature reaches 210 degrees Celsius. The time above liquiduos
(183C) is 60 >seconds. The component is  a 0.020" pitch plastic QFP, the body
>measures around 30 mm by 30 mm. I'm quite sure the profile numbers are
>right, it works for everything on the board, but those QFPs. No idea what's
>wrong. Any ideas of what may be happening?
ANSWER: Well, this comes from some of the technically sloppy ideas that float
around in the industry. 60 seconds above 183C is not necessarily enough for
some components, and certainly not with a higher melting solder like you have
on your leads. In order to get reliable reflow you need to be at or higher
than [Liquidus + 20C] for about 5 to 10 seconds. At a peak reflow temperature
of 210C you are nowhere near that. Also for larger components like this you
need to attach the thermocouple to a non-soldered lead notone that is already
attached to the PCB--the component interior is a heat sink.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 386-437-8747, Fax: 386-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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