| Summary: | 碩士 === 國立臺北科技大學 === 材料科學與工程研究所 === 107 === With the rapid development of technology and the miniaturization of electronic components, the size of solder joints continue to shrink. The reliability of electronic components are receiving more attention. Any microscopic defect occurring at the interface between the Sn-based solder and the Cu-bonded solder joint impairs the reliability of solder joints. Kirkendall void formed at the interface of the copper/solder joint is a typical example. Kirkendall void was formed due to the difference in the diffusion rate of copper and tin. In recent years, some literatures report that the pores are generated from additives used in copper electroplating baths and are attributed to impurity residues of the additives in the electroplating process of Cu layer.
We compare copper pillar bumps electroplated with and without additives. Heat treatments including varied cycles of reflow, high temperature cycle test (TCT) and high temperature storage test (HTST) were conducted. The copper/solder interface intermetallic compounds were observed. The residual impurities in the electroplated copper were analyzed by secondary ion mass spectrometry. And the shear strength was measured to understand the effects of Kirkendall void and the intermetallic compounds on solder joint properties. The copper pillar bumps form Cu/Cu3Sn and Cu6Sn5/Sn intermetallic compounds (IMCs) after heat treatments. As the cycle of reflow is increased and heat treatment time is prolonged, the intermetallic compound continues to thicken. The IMCs thickness grows from 1.22~1.68 μm to 4.73~4.76 μm after 1 and 10 reflows, respectively.
The shear strength of the bumps gradually increases with the initial 1-5 reflows from 167~206 to 220~281 N/mm2 after 1 and 5 reflow, respectively. The presence of intermetallic compounds enhances the shear strength between copper and tin. However, further increase in heat treatment time also increases Kirkendall void causing the shear strength to drop after 5 reflows. The shear strength decreases to 125~150 N/mm2 after 10 reflows. The initial ductile fracture changes to brittle fracture.
|
|---|
