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Shear Strength of Sn–3.5Ag Solder Bumps Formed on Ni/Au and Organic Solderability Preservative Surface-Finished Bond Pads After Multiple Reflow Steps

Published online by Cambridge University Press:  03 March 2011

Jung-Sub Lee ,
Kun-Mo Chu  and
Duk Young Jeon
Jung-Sub Lee
Affiliation:
Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon 305-701, Republic of Korea
Kun-Mo Chu
Affiliation:
Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon 305-701, Republic of Korea
Duk Young Jeon
Affiliation:
Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon 305-701, Republic of Korea
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Abstract

Sn–3.5Ag solder bumps were formed on electroless Ni/immersion Au (Ni/Au) and organic solderability preservative (OSP) surface-finished bond pads, respectively. The shear strength of the solder bumps was measured as a function of reflow steps. Fracture surfaces and interfacial microstructures were investigated by scanning electron microscope. The shear strength of Ni/Au samples increased up to the seventh reflow step and subsequently decreased after the tenth reflow step. Spalling of Ni3Sn4 intermetallic compounds (IMCs) and the P-rich Ni layer strengthened and weakened the bond, respectively. For OSP samples, although Cu6Sn5 IMCs grew as the reflow step was repeated, no remarkable change in shear strength was observed. Interfacial fractures of OSP samples occurred at the interface between Cu6Sn5 IMC and Cu3Sn IMC. Fracture surfaces of OSP samples showed concave pits that consisted of a Cu3Sn bottom and an Sn wall. The pits were formed by separation of Cu6Sn5 IMC from Cu3Sn IMC and the molten Sn channel between the Cu6Sn5 IMC grains.

Keywords

Intermetallic alloysMicrostructureStrength
Type
Articles
Information
Journal of Materials Research , Volume 20 , Issue 11 , November 2005 , pp. 3088 - 3093
Copyright
Copyright © Materials Research Society 2005

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