The interactions of lead (Pb) in lead free solder (Sn/Ag/Cu) system

52nd Electronic Components and Technology Conference 2002. (Cat. No.02CH37345) Pub Date : 2002-08-07 DOI:10.1109/ECTC.2002.1008091

C. Key Chung, R. Aspandiar, K. Foo Leong, Cheng Siew Tay

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引用次数: 20

Abstract

The solder interaction of Pb within the Sn/Ag/Cu system was characterized using Differential Scanning Calorimetry (DSC). Components were then assembled with the Pb-free solder. Cross-sectioning and fine polishing were performed on the solder joints at the as-soldered stage and after temperature cycle readouts at 250, 500, 750, and 1000 cycles. The microstructure of the solder joints was examined using Scanning Electron Microscopy (SEM), and solder elements were mapped and identified by Energy-Dispersive X-ray (EDX) analysis. DSC detected Pb reaction with Sn/Ag at 179/spl deg/C and ternary compound formation. SEM/EDX found that Pb diffused into the Sn/Ag/Cu matrix during reflow soldering to form different microstructures, namely CuSn, SnAg, SnPbAg, and Pb-rich phases. The SnAg structure was found as a rod/needle morphology that was detrimental to solder joint reliability. During temperature cycling, this structure loosened its embedding effects due to grain-boundary sliding in the solder matrix, which accelerated solder fatigue crack propagation. Solutions to this problem are discussed.

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铅(Pb)在无铅焊料(Sn/Ag/Cu)体系中的相互作用

采用差示扫描量热法(DSC)表征了Sn/Ag/Cu体系中Pb与钎料的相互作用。然后用无铅焊料组装组件。在焊接阶段和在250、500、750和1000循环的温度循环读数后，对焊点进行横切和精细抛光。利用扫描电子显微镜(SEM)观察了焊点的微观结构，并利用能量色散x射线(EDX)分析对焊点元素进行了定位和鉴定。DSC检测到Pb与Sn/Ag在179℃下发生反应并形成三元化合物。SEM/EDX发现，回流焊过程中Pb扩散到Sn/Ag/Cu基体中，形成CuSn、SnAg、SnPbAg和富Pb相等不同的显微组织。发现SnAg结构为棒状/针状，不利于焊点的可靠性。在温度循环过程中，由于钎料基体晶界滑动，该结构的嵌入效果松动，加速了钎料疲劳裂纹的扩展。讨论了解决这一问题的方法。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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52nd Electronic Components and Technology Conference 2002. (Cat. No.02CH37345)

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