We're currently designing a flexi which will be populated with a micro BGA
device, 0.35 dia balls on a 0.75 pitch.

Someone told me in passing some time ago that joint reliability would be
increased if the holes in the covercoat above the pads were made larger than
the pads. This ensures the solderjoint is not undercut by the covercoat thus
introducing a fatigue sensitive defect.

The trouble is they didn't tell me how much to pull it back by. Does anyone
know?

Regards,




Eric Christison
Mechanical Engineer
VLSI Vision Ltd
Aviation House
31 Pinkhill
Edinburgh
EH12 7BF

Tel:    +44 (0) 131 539 8165
Fax:    +44 (0) 131 539 7141
A company of the STMicroelectronics Group

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