전해 도금법을 이용한 공정 납-주석 플립 칩 솔더 범프와 UBM (Under Bump Metallurgy) 계면반응에 관한 연구

장세영; 백경욱; Se-Young Jang; Kyung-Wook Paik

Korean Journal of Materials Research, Vol.9, No.3, 288-294, March, 1999

Studies on the Interfacial Reaction between Electroplated Eutectic Pb/Sn Flip-Chip Solder Bump and UBM(Under Bump Metallurgy)

장세영, 백경욱

한국과학기술원 재료공학과

Se-Young Jang, and Kyung-Wook Paik

Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusung-dong, Yusung-gu Taejon, 305-701, Korea

초록

솔더 범프를 사용하는 플립 칩 접속기술에서 범프와 칩 사이에 위치하는 금속 층들의 조합을 UBM (U nder Bump Metallurgy) 라고 부르며 이 UBM 을 어떤 조합으로 사용하는 가에 따라 접속의 안정성이 크게 좌우된다. 본 연구에서는 UBM 중에서 솔더 접착 층으로 사용되는 구리 층의 두께를 1um와 5um로 하는 한편 barrier 층으로 사용되는 금속 충을 Ti, Ni, Pd으로 변화시키면서 이틀 UBM 과 공정 납-주석 사이의 계면반응을 살펴보았다. 이를 위해 100um 크기의 솔더 범프를 전해도금법을 사용하여 제작하고 리플로 횟수와 시효시간에 따른 각 UBM 에서의 금속간 화합물의 성장을 관찰하였다. Cu6S n5 η’ - 상 금속간 화합물이 모든 조건에서 형성되었고 Cu층의 두께가 5um로 두꺼운 경우에는 Cu3Sn ε- 상도 관찰되었다. Pd을 사용한 UBM 구조에서는 시효처리 시에 Cu6Sn5 상아래쪽에 PdSn4 상이 형성 되었다. 또한 이들 계면에서의 금속간 화합물의 성장은 솔더 범프의 접속강도 값과 밀접한 관계를 가진다.

In the flip chip interconnection using solder bump, the Under Bump Metallurgy (UBM) is required to perform multiple functions in its conversion of an aluminum bond pad to a solderable surface. In this study, various UBM systems such as AI 1μm / Ti 0.2μm / Cu 5μm, Al 1μm / Ti 0.2μm / Cu 1μm, AI 1μm / Ni 0.2μm / Cu 1μm and AI 1μm / Pd 0.2μm / Cu 1μm for flip chip interconnection using the low melting point eutectic 63Sn-37Pb solder were investigated and compared to their metallurgical properties. 100μm size bumps were prepared for using an electroplating process. The effects of the number of reflows and aging time on the growth of intermetallic compounds(lMC) were investigated. CusSn5 and Cu,Sn IMC were observed after aging treatment in the UBM system with thick copper (AI 1μm/Ti 0.2μm/Cu 5μm) However only the Cu6Sn6 was detected in the UBM systems with l JLffi thick copper even after 2 reflow and 7 dayaging at 150 ℃. Complete Cu consumption by Cu-Sn IMC growth gives rise to a direct contact between s이der inner layer such as Ti, Ni and Pd, and hence to possibly cause reactions between two of them. In this study, however, only for the Pd case, IMC of PdSn4 was observed by Cu consumption. UBM interfacial reactions with solder aftected the adhesion strength ot solder balls after solder reflow and annealing treatment.

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