The 550F temperature used in thermal stress testing is
the same for all laminate materials. BECAUSE they
are all soldered the same - as across a wave solder
machine.  Boards which are vapor phase soldered have
a somewhat lower temperature for solder attachment but
there is rarely a sign on a bare board that says "NOTE:
use solder temp of 475F to solder or barrels will crack"

Soldering iron temps are much higher than the 550, but
the dwell is less than 10 seconds.

The tests run by a laminate mfgr. is on laminate only have
little to do with a final board since there are no holes in it.

The test is designed to determine how the plated through hole
will survive assembly operations and will pick up deficiencies in
plating deposits/laminate combinations.  Tensile/elongation for
a board produced with FR4 may not be adequate for laminates
which expand more during soldering.

The 550 has been the industry standard for at least 15 years and
plating chemistry suppliers are able to meet the requirement
for the various types of laminate.  When it was changed from the
original 500F, the reason was that boards could pass the 500F float
and still have barrel cracks during assembly operations.  There was
a lot of screaming and thrashing initially, but todays product can and
does pass the test.

When boards are purchased to  IPC specifications, the plating
deposit in the hole is assumed to be able to pass the thermal
stress test.  The assembler is then fairly confident that hole
wall plating will withstand typical wave soldering operations,
2 -3 surface mount soldering operations and repair/replacement
of a component 2 times.

My gut reaction is that your board supplier needs to get with
their electrolytic chemistry supplier and beef-up the plating
deposit to withstand the extra z-axis expansion of the laminate
used.

Susan Mansilla
Technical Director
Robisan Lab

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