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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.43  No.8 (2002)  >  pp.1802-1807

<<Previous article Vol.43  No.8 (2002)   pp.1802 - 1807 Next article>>

Mechanical Strength and Microstructure of BGA Joints Using Lead-Free Solders

Masataka Nishiura1), Akihiro Nakayama1), Sigeaki Sakatani2), Yasuhiro Kohara2), Keisuke Uenishi2) and Kojiro F. Kobayashi2)
1) Corporate Quality Administration Group, Matsushita Electronic Components Co., Ltd.
2) Department of Manufacturing Science, Graduate School of Engineering, Osaka University

Au–Ni plated Cu pads were reflow soldered by using lead free solder balls. The microstructure and strength of the as-reflowed solder joints were investigated. For solder joints using Cu-free Sn–Pb and Sn–Ag solder balls, a Ni3Sn4 reaction layer was formed on the boundary between solder and pads. On the other hand, a Cu–Sn based (Cu, Ni)6Sn5 reaction layer (η) was formed in solder joints using Cu-containing solder balls. The growth rate for an η reaction layer during heat exposure at 423 K was much slower than that for a Ni3Sn4 reaction layer. This suppression of an η reaction layer growth can be attributed to the fact that the Cu in solder balls was mostly removed during the formation of the η layer. By ball shear test, cold bump pull and hot bump pull tests, mechanical properties of the obtained BGA joints were investigated. Fracture loads and crack propagation path changed by changing the mechanical tests, the BGA joints using Cu containing Sn–Ag–Cu solder or low P type Ni plating revealed better mechanical properties. We established the mismatch of the boundaries between reaction layers and the P-enriched Ni–P layer, which was caused by the chained voids formed due to the Kirkendall effect, led to low joint strength.

electrolessplating, ball grid array, lead free solder, intermetallic compound, shear strength, tensile strength, Phosphourus enriched Nickel-Phosphorus layer, chained voids, Kirkendall effect

Received: February 27, 2002
Accepted: May 28, 2002 , Published online: September 06, 2005
Copyright (c) 2005 The Japan Institute of Metals



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