Ed,

UL approvals of materials is different than UL approval given to fabricators.
The materials usually undergo seperate material testing. The fabricators
qualification is after processing of several materials together. An example
would be a particular soldermask on a laminate material. The type soldermask,
it's thickness, the type laminate material and it's thickness will have an
affect on the final flamability rating given to a fabricator.

It is not unusual for a different flame rating to be given for the combination
than that given to the individual material. A case in point would be the use
of polyimide laminate and soldermask. Many thin polyimide materials do not
carry a 94-V0 rating. Especially once a soldermask is applied to it. But given
the correct combination of soldermask and polyimide thickness, it is possible
to receive a 94-V0 rating.

I don't believe that the fabricator actually "fails" to receive a rating, but
would receive a lower rating than he was seeking to achieve. Most fabricators
will submit maerial combinations so as to receive several ratings for a given
set of tests. As another example. They may submit samples of different
laminate thicknesses with a specific soldermask apllied to it. The result
would be a 94-HB on the thinner materials and a 94-V0 on the thicker
materials.

Regards,

Gary Ferrari
Executive Director
IPC Designers Council

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