In a message dated 97-08-16 05:05:31 EDT, Yuan Li writes: << Any restrictions on putting components on the opposite side of the BGA site? My opinion is NO. >> Yuan, Solder joint reliability of leadless assemblies gets degraded significantly when components are mounted back to back. I have seen LCCC test data that showed this effect very clearly (LCCCs were mounted back to back). In a single sided assembly, the board can flex during thermal cycling, thus providing compliance to the assembly and some stress/strain relief. However, when similar components are mounted back to back, the board cannot flex. The assembly stiffness increases by a very large amount and solder joints see much higher stresses and strains. Whether this matters depends on your application, BGA and die size, CTE mismatch between board and BGA, use conditions and expected design life. 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 For SMT / BGA / CSP reliability info, go to: Home page: <A HREF="http://members.aol.com/Epsiinc1/index.html">http://members.aol.com/Ep siinc1/index.html</A> (last updated on June 28, 1997). - click on the above or copy: http://members.aol.com/Epsiinc1/index.html __________________________________________________________________