STRESS RELIEVED BALL GRID ARRAY PACKAGE

摘要

A method and structure for reducing thermally induced strains on the solder joints that couple a ball grid array (BGA) module to a circuit card, so as to improve the fatigue life of the BGA module. The thermally induced strains arise from a mismatch in thermal expansion coefficient between the dielectric substrate of the BGA module and the dielectric board of the circuit card. The method generates void annular regions around portions of the BGA dielectric substrate to which the BGA solder balls are to be attached and/or around portions of the circuit card dielectric material to which the BGA module is to be attached. This results in the formation of dielectric islands or peninsulas that bound the solder balls of the BGA module after installation on the circuit card. The dielectric islands or peninsulas thus formed serve to increase the effective height over which the differential expansion is accommodated, thereby reducing the strains throughout the solder joints. Additionally, the void annular regions provide space for the deformation of the dielectric islands or peninsulas, thereby increasing their compliance and transferring strain from the solder joints to the dielectric islands or peninsulas.