Reliability prediction for TFBGA assemblies

One of the key hot topics in dense large scale integration packaging technologies is to reduce the thermomechanical stress caused by a mismatch of coefficients of thermal expansion among material employed. Nearly all manufacturers of portable electronics products perform several kinds of physical tests in the development cycle to evaluate reliability of the products. In this paper, results obtained by accelerated thermal and power cycling tests by using thin fine pitch gall grid array (TFBGA) packages are reported. Power-cycling stands for a lifetime acceleration method which is close to the real environmental conditions of many electronic products. For this purpose, a set of TFBGA thermal test packages were 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 a qualified bill of materials including a 36-mm/sup 2/ dummy die. Each assembly was designed to perfectly reproduce the thermomechanical behavior of the mass production packages by several semiconductor manufacturers. This package is used in telecom wireless application where it offers high density input/output solution for advanced application-specific integrated circuit (IC) devices a system on chip ICs. Both experiments and simulations were carried out to locate the position of the most critical parts. Complexity of structural package characteristics was examined by using finite-element method modeling methodology. A strain energy based model was employed to locate the most vulnerable parts in the package and predict failure rates.