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무전해 Ni(P)과 무연솔더와의 반응 중 금속간화합물의 spalling 현상에 관한 연구

Spalling of Intermetallic Compound during the Reaction between Electroless Ni(P) and Lead-free Solders

강성권|유진|이택영|손윤철|D.Y.Shin
한국마이크로전자및패키징학회 (The Microelectronics And Packaging Society)|2004.09|마이크로전자 및 패키징학회지 (Jornal of the Microelectronics and Packaging Society)|제11권 제3호|pp. 37-45

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참고문헌

주제분류재료공학

초록

무전해 Ni(P)는 솔더링 특성과 부식저항성이 우수하고 표면 거칠기가 적으며 원하는 금속 상에 선택적으로 도금이 가능하여 전자패키지에서 반도체칩과 기판의 표면 금속층으로 폭 넓게 사용되고 있다. 그러나 솔더와의 반응 중 금속간 화합물의 spalling과 솔더 조인트에서의 취성파괴 문제가 성공적인 적용의 걸림돌이 되어 왔다. 본 연구에서는 각각 조성이 다른 세가지 Ni(P)막 (4.6, 9, and 13 wt.% P)을 사용하여 솔더와의 반응시 무전해 Ni(P)막의 미세구조 및 상 변화와 금속간화합물의 spalling 거동을 면밀히 조사하였다. Ni3Sn4 화합물 아래로 침투한 Sn과 P-rich layer (Ni3P)와의 반응에 의해 Ni3SnP 층이 형성되며 Ni3SnP 층이 성장함에 따라 Ni3Sn4가 spalling됨이 관찰되었다. Spalling 후에는 Ni(P)막이 용융된 솔더와 직접 접촉하게 되어 Ni(P)막의 결정화가 가속화되고 Ni3P 상이 Ni2P 상으로 변태되었다. 또한 이러한 결정화 과정 중 Ni(P)막의 부피가 감소됨에 따라서 인장응력이 발생하여 막 내부에 크랙이 발생하였다.

Abstract

Electroless Ni(P) has been widely used for under bump metallization (UBM) of flip chip and surface finish layer in microelectronic packaging because of its excellent solderability, corrosion resistance, uniformity, selective deposition without photo-lithography, and also good diffusion barrier. However, the brittle fracture at solder joints and the spalling of intermetallic compound (IMC) associated with electroless Ni(P) are critical issues for its successful applications. In the present study, the mechanism of IMC spalling and microstructure change of the Ni(P) film were investigated with varying P content in the Ni(P) film (4.6, 9, and 13 wt.% P). A reaction between Sn penetrated through the channels among NiSn IMCs and the P-rich layer (NiP) of the Ni(P) film formed a NiSnP layer. Thickening of the NiSnP layer led to NiSn spalling. After NiSn spalling, the Ni(P) film directly contacted the molten solder and the NiP phase further transformed into a NiP phase. During the crystallization process, some cracks formed in the Ni(P) film to release tensile stress accumulated from volume shrinkage of the film.

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