SMTA International Conference Proceedings


EVALUATION OF RELIABILITY AND METALLURGICAL INTEGRITY OF WIRE BONDS AND LEAD FREE SOLDER JOINTS ON FLEX CIRCUIT MODULES

Authors: Daniel T. Rooney, Ph.D. et al.
Company: Flextronics International
Date Published: 9/25/2005   Conference: SMTA International


Abstract: This paper presents a study of the optimization of the gold plating thickness for the use of both wire bonding and soldered interconnects on the same flexible printed circuit board module. Wire bondability is typically better when the gold plating thickness is greater than 30 micro-inches; however, the risk of problems with solder joint embrittlement becomes a concern with thicker gold plating.

In order to better understand the effect of the gold plating thickness on wire bondability and solder joint embrittlement, an evaluation was performed on samples with three ranges of gold plating thicknesses (10 to 20 micro-inches, 20 - 30 micro-inches, and 30 - 45 microinches), on flexible printed circuit board (FPC), substrates. Mechanical shear testing and metallurgical analyses were conducted on chip component solder joints in this three thickness gold study. Thermal shock and drop testing were conducted to evaluate the reliability of the sample modules that were mounted in portable hand held consumer products.

Drop testing is especially critical for determining the reliability of the sample modules, which are used in portable consumer electronics products. Drop testing was performed to characterize the effect of gold embrittlement on the mechanical integrity of the solder joints with gold content ranging from 1 to 4 weight percent.

Key words: gold embrittlement, solder joint, wire bond



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