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Date: | Thu, 13 Jul 95 17:04:40 EST |
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In response to Dave Hoover's request concerning pcb warpage during BGA
repair:
Our analysis of BGA rework processes involved use of a 10"x12", 10
layer, .062" thick FR4 test board containing (12) PBGA 225 OMPAC
devices. Several manufacturers' rework systems were evaluated,
allowing comparison of rework processes utilizing both highly focused
and wide area bottom side heating methods.
We also experienced the problem of severe local area warpage during
the reflow process, particularly where highly focused bottom heat was
used. In some instances, the board surface at the center of the BGA
dropped more than .015".
Our best success dealing with the local warpage problem was achieved
with the use of controlled wide area convective bottom side heating
combined with adequate board support. The entire pc assembly was
bottom heated prior to and during reflow with a fairly gentle thermal
profile not exceeding 1.5 degrees C/sec. ramp rate. The profile's
thermal events were precisely controlled with thermocouple feedback
from the pcb, BGA, and top & bottom heat sources. The entire
preheat/reflow cycle averaged 6 minutes, followed by cool down at room
temperature. This process eliminated any significant local warping,
but keep in mind it was a controlled test using a single side test pcb
with only BGA's attached.
Dave, I hope this info helps. Sounds like your customer is headed in
the right direction.
Dennis Measor
Senior Manufacturing Engineer
Allen-Bradley Co, Cleveland, Ohio
[log in to unmask]
Ph: 216.487.6170
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