Board-Level Solder Joint Reliability Study of Land Grid Array Packages for RF Applications Using a Laser Ultrasound Inspection System

Abstract

Microelectronics packaging technology has evolved from through-hole, and bulk configuration to surface-mount, and small-profile ones. Today's electronics industry is also transiting from SnPb to Pb-free to meet environmental requirements. Land grid array (LGA) package has been becoming popular in portable electronics in terms of low profile on the printed wiring boards and direct Pb-free assembly process compatibility. With package profile shrinking and operating power dramatically increasing, solder joint quality and reliability has become a major concern. Solder joint failure at the package level or board level will cause electronic devices not to function during service. In this paper, board-level solder joint reliability of the LGA packages under thermal loading is studied with thermal cycling tests. A novel laser ultrasound-interferometric system developed by the authors at Georgia Tech is applied to inspect solder joint quality during the thermal cycling tests. While the laser ultrasound inspection technique has been applied successfully to flip chips and chip scale packages, this study is the first application of this technique to over-molded packages. In this study, it is found out that the LGA packages can withstand 1000 temperature cycles without showing crack initiation or other failure mechanisms in solder joints. The laser ultrasound inspection results match the visual observation and X-ray inspection results. This study demonstrates the feasibility of this system to solder joint quality inspection of over-molded packages. In particular, the devices constituting the object of this study are radio frequency (RF) modules, which are encapsulated through over-molding and are mounted on a typical four-layer FR4 board through LGA terminations.