SMTA International Conference Proceedings

Solder-Joint Reliability of a 0.65mm Pitch Molded Array Package for Automotive Applications

Authors: Burton Carpenter, Mollie Benson, A. R. Nazmus Sakib, Andrew Mawer, Paul Galles, Abdullah Fahim
Company: NXP Semiconductors, Inc.
Date Published: 9/22/2019   Conference: SMTA International

Abstract: BGA components used in high reliability automotive microprocessor applications have historically been 0.8mm pitch or larger. Recently, emerging market requirements have pushed BGA pitches down to 0.65mm. However, industry expectations of solder-joint reliability remain constant; customers expect cyclical thermal fatigue lifetimes to be the same as, or in some cases more robust than prior generations of packages.

The paper reports experimental board level temperature cycle results of a 0.65 pitch, 10x10mm MAPBGA (molded array plastic BGA) package test vehicle that could be used as an automotive radar microprocessor. Thermal fatigue life was assessed per IPC-9701A using AATS (air-to-air thermal shock) between -40ºC and +125ºC.

A 13 cell DOE (design of experiments) examined various combinations of package BGA pad surface finishes (electroplated Ni/Au and OSP [organic solderability preservative]) and five package solder ball alloys (SnAg, SAC105, SAC105N, SAC405, and SAC-Bi [a Bi containing SAC derivative]). NanoIndentation on solder-joint cross-sections were used to correlate localized hardness and microstructure to the solder-joint lifetimes.

Good wetting occurred on the BGA pad OSP surface. The solder-joint lifetimes followed clear trends. The Ni/Au BGA pad surface finish outperformed OSP. SAC-Bi was the best performing alloy, followed by SnAg, SAC405 and SAC105/SAC105N, in that order. No differences were observed for the OSP surface finish provide by different substrate suppliers.

Key Words: 

Solder-joint reliability, SnAg, SAC, temperature cycle, thermal fatigue, NanoIndentation, OSP

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