Hi Technetters:

Thermal stress test per IPC 6013 calls out for 3 different temperatures
(288C, 260C, 232C) at which the test could be performed to determine whether
the flex circuit will withstand assembly and repair heat excursions. The
procedure is meant to encompass a wide variety to flex circuits - from
double sided to complex rigid-flex and made with a wide variety of materials
- from polyester to polyimide.

The question I have is regarding the rigid section of a typical rigid-flex
contruction. This section can be built up with all polyimide materials and
prepreg, typical FR-4 epoxy and adhesiveless material, epoxy adhesive
instead of prepreg or acrlyic adhesives instead of prepregs.

How would one go about determining the correct temperature to use when
performing thermal stress test if the construction is typical FR-4 (Tg 140C)
and acrylic adhesive for bonding as well as coverlay, so that the test
truely represents the reliability of the construction and not induce failure
due to higher temperature excursion which the construction may not
withstand? The part has to go through a typical rigid-flex reflow process in
the assembly twice.

Thanks for your help in advance.

Chetan Shah

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