In a message dated 99-01-11 14:01:24 EST, you write:

<< 1)  Does anyone have data showing the effect on solder joint reliability of
 a twice re-flowed BGA?   A client is considering a board design with BGAs on
 both sides and is concerned about the reliability of the solder joints on  a
 BGA placed on the first side because it would be exposed to two reflow
 cycles. >>

For "mirrored" back-to-back components, the solder joint fatigue life will
decrease by 2 to 3X, when compared to "single-sided" assemblies. Reliability
itself will decrease by a larger factor. See, for example, data by Juso et
al., in Proceedings, ECTC'98, p. 525.
The reason for it is mostly mechanical. The assembly loses a lot of compliance
because the board section under the components of a "mirrored" assembly cannot
bend.
This effect has been observed in thermal cycling (for BGAs, CSPs, TSOPs and
others) and is very well captured by life prediction models that account for
board flexing.

Jean-Paul
_____________________________________________________
Jean-Paul Clech
EPSI Inc., P. O. Box 1522, Montclair, NJ 07042, USA
tel: +1 (973)746-3796, fax: +1 (973)655-0815
SMT / BGA / CSP Assembly Reliability Specialists
home page: http://members.aol.com/Epsiinc1/index.html
_____________________________________________________

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################