Since this topic is very hot in Technet, I'd like to drop few
cents of my own.

All we, boneheads know board design and fabrication
processes are contributing factors for flatness of boards.
Hope we all realize that CTE of FR4 material is approx.
130'c.  When the material goes above this temp during board
fabrication, reflow or wavesoldering processes, it expands,
shrinks, warp, bows, and do all kinds of bad things to itself.
So why not a mad chemist invents a board material with CTE
of 250'c or higher?...

Using OSP or Ni/Au surface finish boards provides
consistent flatness because they are not subjected to
thermal stress during board fabrication process, unlike HASL
process.

regards
Matthew Park
Automation Engineer
Norsat International Inc.  BC.

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