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Drop Test Performance of BGA Assembly Using SAC105Ti Solder Sphere

Presenter: Ning-Cheng Lee, Ph.D.
Company: Indium Corporation
Date Published: 6/28/2012

Description: Assembled BGA/CSP devices with SnAgCu (SAC) solder joints are vulnerable upon drop due to the fragility of solder joints. Although reducing the Ag content of SAC alloy does help, the crack resistance upon drop is still considerably poorer than eutectic SnPb system, thus new alloy with improved drop test performance is greatly desired. In this work, SAC105 doped with Ti (SAC105Ti) as BGA/CSP sphere was studied for its drop test reliability. Four different solder combinations were evaluated: 1) SnPb paste with SnPb balls, 2) SnPb paste with SAC105Ti balls, 3) SAC305 paste with SAC105Ti balls, and 4) SAC305 paste with SAC105 balls. The number of completely fractured interconnects was counted for each type of component after a total 100 drops. Presence of Ti improved the drop test performance significantly, despite the voiding side effect caused by its oxidation tendency. It is anticipated that the voiding can be prevented with the use of a more oxidation resistant flux. Wide pasty range of SAC105 with SnPb paste was reported to cause significant voiding. In view of this, use of SAC105 BGA with SnPb solder paste is not recommended, with or without Ti addition. High reflow temperature drove fracture to shift to interface at package side, presumably through building up IMC thickness beyond the threshold value. A lower reflow temperature is recommended. Electrical response is consistent with complete fracture data. But, complete fracture trend is inconsistent with that of partial fracture trend, and neither data can provide a full understanding about the failure mode. By integrating complete fracture and partial fracture into "Virtual Fracture," the failure mechanism becomes obvious and data sets become consistent with each other.

You will learn about (1) what new BGA solder sphere alloy will yield a superior drop test performance, (2) how to analyze the dye and pry reliability drop test data, (3) how the process and package design affect the reliability.

Key Words: 

BGA, CSP, Drop Test, Ti Solder, virtual fracture

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