微電子接點之界面微結構改質與強化

Interfacial Microstructure Modification and Mechanical Reinforcement of Microelectronic Joints

熊昱凱(Y.K. Hsiung) ； 謝清順(C.S. Hsieh) ； 李承宇(C.Y. Lee) ； 楊舒評(S.P. Yang) ； 郭蔡同(T.T. Kuo) ； 何政恩(C.E. Ho)

《鑛冶：中國鑛冶工程學會會刊》 66卷4期 (2022/12) Pp. 50-62

https://doi.org/10.30069/MM.202212_66(4).05

摘要

介金屬化合物（intermetallic compound, IMC）微結構與焊接性質（solderability）有著密切關係，一向被視為電子封裝品質的關鍵指標。本文改編自"IMC microstructure modification and mechanical reinforcement of Sn-Ag-Cu/Cu microelectronic joints through an advanced surface finish technique"一文，作者透過新近發展的表面處理（surface finish）技術，其中包括：有機保焊膜（organic solderability preservative, OSP）、化銀（immersion silver, ImAg）、化錫（immersion tin, ImSn）、直接鈀金（electroless palladium/immersion gold, EPIG）、及金鈀金（immersion gold/electroless palladium/immersion gold, IGEPIG）等，來調整介金屬微結構，以增強銲點的機械特性。研究發現，使用OSP表面處理容易生長傳統的扇貝狀（scallop-like）Cu_6Sn_5於Cu/Sn反應界面。相對的，使用其它金屬表面處理則容易生長鬆散的稜柱狀（prismatic）Cu_6Sn_5結構。此一鬆散的Cu_6Sn_5結構，其晶粒間存在許多熔融銲料通道（molten solder channels），可作為Sn與Cu的快速擴散路徑，使Sn較容易接觸到Cu銲墊，而Cu原子藉由通道向外擴散。如此一來，避免了不利銲點特性的Cu_3Sn產生。若進一步透過高速推球（high-speed ball shear, HSBS）測試則可發現，採用新近發展的IGEPIG表面處理技術可顯著提升Sn-Ag-Cu/Cu銲點強度，大幅改善電子封裝之可靠度。

關鍵字

微電子封裝 ； 表面處理技術 ； 介金屬化合物 ； 高速推球測試

並列摘要

Solderability strongly depended on the intermetallic compound(s) (IMC) microstructure between solder and copper (Cu), which has been one of the most crucial factors for microelectronic packaging reliability. This study was conducted to modify the Cu-Sn IMC microstructure and to reinforce the mechanical characteristics of Sn-Ag-Cu/Cu microelectronic joints through surface finish coatings, including organic solderability preservative (OSP), immersion Ag (ImAg), immersion Sn (ImSn), Au/Pd (electroless palladium/ immersion gold, EPIG), and Au/Pd/Au (IGEPIG) multilayer. The research results revealed that the type of surface finish would dominate the Cu-Sn IMC growth morphology and mechanical characteristics, even though these surface finishes were completely eliminated in the early stage of soldering reaction. Specifically, a dense Cu_6Sn_5 layer with a scallop-like appearance was obtained for the traditional OSP case, while a prismatic, loose Cu_6Sn_5 microstructure was produced for the alternative cases (metal films). This loose Cu_6Sn_5 microstructure offered numerous molten solder channels for the in-diffusion of Sn to Cu, retarding undesired Cu_3Sn growth at the Cu_6Sn_5/Cu interface; consequently, a brittle-to-ductile transition in the joint fracture mode with a high shear strength and fracture energy was obtained in the high-speed ball shear (HSBS) test. A significant mechanical reinforcement of the Sn-Ag-Cu/Cu microelectronic joints can be achieved with the replacement of the traditional OSP coating by the newly developed IGEPIG surface finish.

並列關鍵字

Microelectronic package ； Surface finish ； Intermetallic compound(s) ； HSBS

參考文獻

F. Song, S.W.R. Lee, K. Newman, H. Reynolds, S. Clark, and B, Sykes, 9th electronics packaging Technology conference, (2007), 463-470.

C.E. Ho, T.T. Kuo, C.C. Wang, and W.H. Wu, Electron. Mater. Lett., (2012), 8, 495-501.

H. Li, R. An, C. Wang, Y. Tian, and Z. Jiang, Electron. Mater. Lett., (2015), 144, 97-99.

K. Zeng, R. Stierman, T.C. Chiu, D. Edwards, K. Ano, and K. N. Tu, J. Appl. Phys., (2005), 97, 024508.

T. Laurila, V. Vuorinen, and M.P. Kröckel, Mater. Sci. Eng., (2010), 68, 1-38.