(1) At normal component spacings, neighboring components should not
significantly affect each others solder joint temperatures--the conductive
heat transfer between component and PWB becomes good only after solder joint
formation. However, for operating use, it is my understanding that Boeing
places the components on the PWAs for commercial aircraft with uniform
operating temperatures in mind.
(2) Modern reflow ovens provide good temperature uniformity, and certainly
experiments need not be done for uniformity.  However, profiles need to be
established for each code to assure that even the slowest heating solder
joint on the most massive component will be about 20C above liquidus for 5 to
10 seconds.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-Mail: [log in to unmask]

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