Cu pad위에 무전해 도금된 UBM (Under Bump Metallurgy)과 Pb-Sn-Ag 솔더 범프 계면 반응에 관한 연구

나재웅; 백경욱; Jae-Woong Nah; Kyung-Wook Paik

Korean Journal of Materials Research, Vol.10, No.12, 853-863, December, 2000

Studies on the Interfacial Reaction between Electroless-Plated UBM (Under Bump Metallurgy) on Cu pads and Pb-Sn-Ag Solder Bumps

나재웅, 백경욱

한국과학기술원 재료공학과

Jae-Woong Nah, and Kyung-Wook Paik

Department of Materials Science and Engineering, Korea Advanced Institute of Sceince and Technology, 373-1, Kusung-dong, Yuseong-gu, Taejeon 305-701, Korea

초록

Cu 칩의 Cu 패드 위에 솔더 플립칩 공정에 응용하기 위한 무전해 구리/니켈 UBM (Under Bump Metallurgy) 층을 형성하고 그 특성을 조사하였다. Sn-36Pb-2Ag 솔더 범프와 무전해 구리 및 무전해 니켈 충의 사이의 계면 반응을 이해하고, UBM의 종류와 두계에 따른 솔더 범프 접합(joint) 강도 특성의 변화를 살펴보았다. UBM의 종류에 따른 계면 미세 구조, 특히 금속간 화합물 상 및 형태가 솔더 접합 강도에 크게 영향을 미치는 것을 확인하였다. 무전해 구리 UBM의 경우에는 솔더와의 계면에서 연속적인 조가비 모양의 Cu 6 Sn 5 상이 빠르게 형성되어 파단이 이 계면에서 발생하여 낮은 범프 접합 강도 값을 나타내었다. 무전해 니켈/무전해 구리 UBM에서는 금속간 화합물 성장이 느리고, 비정질로 도금되는 무전해 Ni의 륵성으로 인해 금속간 화합물과의 결정학적 불일치가 커져 다각형의 Ni 3 Sn 4 상이 형성되어 무전해 구리 UBM의 경우에 비해 범프 접합 강도가 높게 나타났다. 따라서 무전해 도금을 이용하여 Cu 칩의 Cu pad 위에 솔더 플립칩 공정에 응용하기 위한 UBM 제작시 무전해 니켈/무전해 구리 UBM을 선택하는 것이 접합 강도 측면에서 유리하다는 것을 확인하였다.

In this study, a new UBM materials system for solder flip chip interconnection of Cu pads were investigated using electroless copper (E-Cu) and electroless nickel (E-Ni) plating method. The interfacial reaction between several UBM structures and Sn-36Pb-2Ag solder and its effect on solder bump joint mechanical reliability were investigated to optimife the UBM materials design for solder bump on Cu pads. Fer the E-Cu UBM, continuous coarse scallop-like Cu 6 Sn 5 , intermetallic compound (IMC) was formed at the solder/E-Cu interface, and bump fracture occurred this interface under relative small load. In contrast, Fer the E-Ni/E-Cu UBM, it was observed that E-Ni effectively limited the growth of IMC at the interface, and the Polygonal Ni 3 Sn 4 IMC was formed because of crystallographic mismatch between monoclinic Ni 3 Sn 4 and amorphous E-Ni phase. Consequently, relatively higher bump adhesion strength was observed at E-Ni/E-Cu UBM than E-Cu UBM. As a result, it was fecund that E-Ni/E-Cu UBM material system was a better choice for solder flip chip interconnection on CU PadS.

Keywords:solder;UBM;electroless plating;IMC;flip chip

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[2] Greer S, 1996 Proceedings of 46 th Electronic Components and Technology Conference, ECTC96/ pp.546, 1996 (1996)

[3] Warrior M, 1990 Proceedings of 40 th Electronic Components and Technology Conference, ECTC90/ pp.460, 1990 (1990)

[4] Inaba M, Yamakawa K, Iwase N, IEEE Transactions on Components, Hybrids and Manufacturing Technology,CHMT/ v.13, no.1, pp.119, 1990 (1990)

[5] Kloeser J, Ostmann A, Gwisasda J, Belchtold F, Zakel E, Reichl H, ISHM '96 Proceeding, 93 (1996)

[6] Adema GM, Berry CJ, Koopman NG, Rinne GA, Yung EK, Turlik I, International Journal of Microcircuits and Electronic Packaing, IJMEP/ v.17, no.4, pp.352, 1994 (1994)

[7] Rutter EW Jr., Moyer ES, Harris RF, Frye DC, Joer VL, Oaks FL, Proceedings of 1st International Conference on Multichip Module, ISHM/IEPS/ pp.394, 1992 (1992)

[8] 장세영, 백경욱, 한국재료학회지, 9(3), 288 (1999)

[9] Bader S, Gust W, Hieber H, Acta Metall. Mater., 43(1), 329 (1995)

[10] The properties of electrodeposited Metals and Alloys, Safranek WH, Amer. Electroplaters surface Finishers Soc.(2nd ed.)/ 1986 (1986)

[11] Mei Z, Callery P, Fisher D, Hua F, Glaser J, Advances in Electronic Packaging,ASME 1997/ v.2, pp.1543, 1997 (1997)

[12] Jeon YD, Paik KW [private communication]

[13] Massalski TB, Binary Alloy Phase Diagram(2nd ed.)/ v.2, pp.1481, 1986 (1986)

[14] Kim HK, Tu KN, Phys. Rev. B, 53(23), 16027 (1996)

[15] Bartels F, Morris JW Jr., Dalke G, Gust W, J. Electron. Mater., 23(8), 787 (1994)

[16] Mahoney MW, Dynes PJ, Scriptta Metallurgia, 19, 539 (1985)

[17] Lee CY, Lin KL, Thin Solid Films, 249(2), 201 (1994)

[18] Kim HK, Tu KN, Appl. Phys. Lett., 66(14), 2002 (1995)

[19] Poter DA, Easterling KE, Phase transformation in Metals and Alloys(2nd ed.)/ Champman & Hall, pp.142-171, 1992 (1992)

[20] Zhang C, Shang JK, Liu P, 2000 Proceedings of 50 th Electronic Components and Technology Conference,ECTC2000/ pp.138, 2000 (2000)

[21] Lin KW, Liu YC, IEEE Transaction on Advanced packaging, 22(4), 568 (1999)

[22] Jang SY, Paik KW, 2000 Proceedings of 50^{th} Electronic Components and Technology Conference, ECTC2000/ pp.64, 2000 (2000)