Ideally one would like a solder joint shape that is slightly hour-glass shaped, because it provides the most uniform strain distribution (see papers by Satoh, Hitachi; Engelmaier, Bell Labs). That is however only obtainable by 'stretching' the joints. Solder joint shape, except for height which is a first-order parameter, is however only a second-order variable compared to other parameters. More barrel-shaped solder joints experience somewhat shorter lives because the thicker sections strain less therefore forcing more strain onto the thinner sections, which also experience strain concentrations, particularly for solder-mask defined (SMD) pads. The difference between SMD and non-SMD (NSMD) solder joints is that NMSD solder joints have fatigue lives between 1.3 to 3 times longer than SMD joints, depending on the severity of loading (more difference for highly accelerated tests) as long as everything else is the same (see papers by Mawer, Motorola). Voids are primarily process indicators. There is experimental evidence that voids retard crack propagation locally around the void on a temporary basis. There is no standard, IPC or otherwise, on voids--nor should there be. See also J-STD-013, Implementation of Ball Grid Array and Other High Density Technology. Werner Engelmaier Engelmaier Associates, Inc. Electronic Packaging, Interconnection and Reliability Consulting 23 Gunther Street Mendham, NJ 07945 USA Phone & Fax: 201-543-2747 E-Mail: [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************