Reliability prediction for TFBGA assemblies

One of the key hot topics in dense LSI packaging technologies is to reduce the thermo-mechanical stress caused by a mismatch of coefficients of thermal expansion among material employed. In this paper, results obtained by accelerated thermal and power cycling tests, by using thin fine pitch BGA (TFBGA) packages, are reported. Power-cycling stands for a life-time acceleration method which is close to the real environmental conditions of many electronics product. For this purpose a set of TFBGA thermal test packages was designed and manufactured for reliability assessment of solder joint interconnections. The assemblies consisted of an array of polysilicon resistors surrounding a sensing diode for accurate temperature measurements. The package uses qualified bill of materials including a 36 mm² dummy die. Each assembly was designed to reproduce perfectly the thermo-mechanical behavior of the mass production packages by several semiconductor manufacturers. Both experiments and simulations were carried out to locate the position of the most critical parts. The complexity of the structural package characteristics was examined by using FEM modeling methodology. A strain energy based model was employed to locate the most vulnerable parts in the package and predict failure rates.