Hik Seppo,
All the guidelines in IPC-D-279 apply.
>1. Thermal expansion/stress with possibly different PCB substrates across
>40mm. (relatively large).. - Are CGA's any better in this regard?, can
>CGA's come in very low profile (<0.3mm?)
A:  CGAs are ceramic with large delta-CTE with the PWB; inyour case there
should be hardly any delta-CTE. Of course , if you have solder columns low
profile (<0.3mm?) is not possible. However, you  certainly cannot clean
underneath such an arrangement.

>2. Reliability with application board flex/twist and cracking of pads?,
>Possible board warpage problems?
A:  Since your LGA is very thin, PWB flexing should not be a real problem.

>3. Resistance to shock? - has anyone used underfill for LGA's?.
A:  Since your LGA is very thin and light, mechanical shock should not be a
real problem.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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