Spalling suppression by Sn-3.5Ag incorporated with Cu particles

C. Y. Liu, S. J. Wang

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

Spalling phenomenon is one of the current urgent reliability issues for the Pb-free solder implementation in flip chip technology. Essentially, spalling was caused by high interfacial energy between intermetallic compound and Cr, which dewetted the layer compound into a spherical compound. In this paper, we report that spalling of Ni thin UBM (Under Bump Metallization) can be prevented during the soldering reaction, if a Cu reservoir is introduced into the structure of C4 (Controlled Collapse Chip Connections) solder joints. Once molten Sn-3.5Ag solder was saturated with Cu atoms, Cu precipitated out as a layer of Cu-Sn compound on Ni thin UBM. Cu-Sn compound layer served as a reaction barrier to retard the consumption of Ni thin UBM. So, spalling is retarded. After prolonged reflowing, Ni thin UBM was converted to ternary Cu-Sn-Ni compounds. Remarkably, we found that Cu-Sn-Ni compound still resided on the Cr surface without spalling. Unlike interfaces of Cu-Sn compound/Cr or Ni-Sn compound/Cr, the interface of Cu-Sn-Ni compound/Cr is very stable and has a low interfacial energy. Hence, spalling effect on Ni thin UBM is prevented.

Original languageEnglish
Title of host publicationProceedings of the 4th International Symposium on Electronic Materials and Packaging, EMAP 2002
PublisherInstitute of Electrical and Electronics Engineers Inc.
Pages366-371
Number of pages6
ISBN (Electronic)078037682X, 9780780376823
DOIs
StatePublished - 2002
Event4th International Symposium on Electronic Materials and Packaging, EMAP 2002 - Kaohsiung, Taiwan
Duration: 4 Dec 20026 Dec 2002

Publication series

NameProceedings of the 4th International Symposium on Electronic Materials and Packaging, EMAP 2002

Conference

Conference4th International Symposium on Electronic Materials and Packaging, EMAP 2002
Country/TerritoryTaiwan
CityKaohsiung
Period4/12/026/12/02

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