Influence of process variables on the reliability of microBGATM package assemblies

Chip scale packages (CSP) are being introduced as fine-pitch ball array components offering increased product performance and full compatibility with current surface mount assembly operations. A 0.75 mm pitch CSP aimed at the flash memory market is being produced as an alternative to the standard thin small outline package. The current study evaluates the effects of board surface finish and assembly process parameters on the accelerated thermal cycling life of such assemblies. Both daisy chained and functional flash memory MicroBGA^TM packages are used in a matrix of experiments including high and low solder paste volumes and two surface finishes. In-line solder paste volume measurements are discussed with respect to modern printing technologies and recommendations are made regarding SMT process optimization. Reliability test data are presented following testing at both -40°C to 85°C and 0°C to 100°C conditions