Linda,

I woud be interested to see the information you have that says underfilling
a BGA with Conformal Coating reduces life cycle. I epoxy underfill BGA's at
present, but there are mutterings from bean counters, etc about this extra
process, and why can't we just underfill with coating? I have argued about
his, but from a rather hypothetical standpoint - comparative thermal
conduction properties of the two materials, ease of rework of my underfill
versus difficulty in removing parts stuck down with coating, stated
improved life of BGA joints using epoxy versus "I expect coating underfill
to have no beneficial effect on life cycle". I've had no words of wisdom to
back up my wanting to keep epoxy underfilling and my rejecting coating
underfilling.

I suspect the reason for reducing life cycle is if the coating underneath
the component is thick and hasn't cured properly - after all, it's supposed
to be a thin coating, not a thick filler. The chemisty of uncured coating
is bound to be different from that of cured stuff. Perhaps Graham N. or
Brian E. can step in at this point (?).

Peter



Linda Woody <[log in to unmask]>     20/05/2002 11:53 PM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to Linda Woody

             To: [log in to unmask]
             cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
             Subject: [TN] Conformal coating BGAs








I am searching for any data out in the industry referencing the affects
of conformal coatings on BGA devices? How much coating should be allowed
under the device? Should the underside of the BGA be completely dammed or
underfilled? I have collected data that shows standard spraying of coating
material does not affect life cycle, but allowing complete underfill of the
coating material greatly reduces life cycle. What concerns are there for
leaving exposed adjacent uncoated conductors (BGA balls) under the BGA
devices?

Regards,

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