Huandi Gu

Graduation Semester and Year

2014

Language

English

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Kim Choong-Un

Abstract

Now a day in electronic industry, as the trend of requiring smaller package size with better electronic performance, lead-free solder joints are always required to decrease their sizes. As a result, the reliability of smaller size solder joints has became a critical issue. The primary factor causing the reliability issue of lead-free solder joints is intermetallic compound (IMCs) formation which forming during soldering process and thermal aging process and can significantly affect the mechanical properties of solder joint. In this study, two different size solder joints with same composition (SAC305 with 96.5%Sn, 3.0Ag, 0.5%Cu) are subjected to isothermal aging treatment in 150 ̊C for 0-500 h to evaluate the effect of the solder size on IMC formation. Interfacial reaction in the Cu/Sn and Cu/Ni/Sn interface are observed. Two different phases of IMCs including Cu6Sn5 (η phase) and Cu3Sn (ε phase) were founded in the Cu/solder interface. The morphology of the IMC layer was analyzed by scanning electron microscopy (SEM). Growth thickness and growth kinetics of the intermetallic compound were studied. The result showed that during solid state aging treatment, the IMCs forming in both small and large solder joints are diffusion-controlled. The growth rate of IMCs in small solder joint is faster at early aging period, and then its growth rate decreases and becomes slower than large size solder joint. The different of the IMCs growth rate can be explained by the Cu-Saturation in the solder reflowing process. Furthermore, Ni layer acts as a very effective diffusion barrier which decreases the growth rate of Cu/Solder IMCs.

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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