μPGA SOCKET AND SOLDER JOINT RELIABILITY STUDY

摘要

Reliability of a Micro Pin Grid Array Socket interposer and interconnect solder joint for μPGA processor are studied. The socket is feature with Zero-Insertion-Force (ZIF) mechanism for the contact connection to the processor. The unique sliding cover and contact fingers design allow the interconnection of μPGA from conventional large force insertion operation to quasi-zero force of solid contact by the compliance of pin and stiffness of finger. The major rationale of design and application are to enhance manufacturability in both insertion assembly and rework. To assess the reliability of the socket and solder joint and identify the process window in the early stage of product development cycle, a test vehicle (TV) with daisy chain (DC) construction, separation header and test via access are designed for failure detection and isolation during the realtime monitoring in Accelerated Temperature Cycling test. This paper will describe the methodology of consolidating the package and board level reliability assessment to facilitate the potential of shortening the product development cycle. Design of Experiment (DOE) is extensively used from process development to package reliability assessment. Various inspection methods are used in the pre-processing IQA stage to assess the package and PCB physical properties. With reflow-emulated thermal process applied on the socket and PCB, the Shadow Moire was also used to monitor the package wrapage on global and μPGA locations. Interconnect Stress Test (IST) will be performed to ensure the via wall strength integrity and trace quality during pre-conditioning and thermal cycle. Fatigue fracture mode and life cycle will be, analysis by 5DX, Dye Penetrant, failure analysis, and Weibull distribution of the failure of the solder joint. Contact resistance will be measured with 4-wire setting and its reliability response in the thermal cycling will be compared to the lognormal accumulative failure of the solder joint in future study. Conjunction with FEM analysis endeavor on stress/strain response of the solder joint under bending load, a mechanical stress emulation approach is proposed to fundamentally look insight of its correlation to the reliability scale and eventually resolve current quasi-brittle solder cracking issue in the electronic industry.