Pan Pacific Symposium Conference Proceedings


CONSIDERATIONS FOR HEAT SPREADER ATTACH OPTIMIZATION ON HIGH PERFORMANCE FLIP CHIP BGA PACKAGES

Authors: Mukul Joshi, Kumar Nagarajan, and Nael Zohni
Company: Xilinx, Inc.
Date Published: 2/25/2005   Conference: Pan Pacific Symposium


Abstract: Flip Chip BGA (FCBGA) has become a well known and proven packaging technology in the semiconductor industry. For high-end applications using 'Application Specific Integrated Circuit' (ASIC) or 'Field Programmable Gate Array' (FPGA) chips, a flip chip BGA package incorporating larger die, discrete chip-capacitors on the package and a single piece heat spreader (lid) has become an ubiquitous solution.

Constrained by mechanical boundary conditions as a result of increase in die size coupled with presence of multiple chip-capacitors on the substrate, less space is available for heat spreader seating area (lid foot width) for the same package size. Hence, achieving adequate lid adhesion with the substrate becomes a major challenge and a serious look into 'Design for Manufacturing' (DFM) approach is called for.

This paper discusses the lid and lid adhesive material properties and the lid design considerations that were studied and optimized in a series of systematic experiments. Lid assembly process, material properties of lid adhesive, lid foot and lid cavity dimensions showed a significant impact on lid adhesion strength. Lid adhesion at higher temperatures, especially that above the glass transition temperature (Tg) of the lid adhesive, was proven to be a critical factor in estimating robustness of the lid adhesive in terms of its adhesion with the package.

Effect of board mount assembly, rework and external heat-sink mount processes on lid adhesion was also studied after optimizing the critical design parameters, and it showed minimal or no deterioration of lid adhesion. Finally JEDEC standard reliability testing was performed to ensure robustness of FCBGA with optimized lid design, and it exhibited excellent reliability performance.

Key words: Flip Chip BGA (FCBGA), Single Piece Heat Spreader (Lid), Lid Pull Strength, Lid Adhesion.



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