Optimization of Pb-Free Solder Joint Reliability from a Metallurgical Perspective
Source: Journal of Electronic Materials, Volume 41, Number 2, February 2012 , pp. 253-261(9)
Abstract:To obtain the desired performance of Pb-free packages in mechanical tests, while the solder composition should be carefully selected, the influence of metals dissolved from the soldering pad or under bump metallization (UBM) should also be taken into account. Dissolved metals such as Cu can alter the intermetallic compound (IMC) formation, not only at the local interface but also on the other side of the joint. The high rate of interfacial cracking of Sn-Ag-Cu solder joints on Ni/Au-plated pads is attributed to the high stiffness of the solder and the dual IMC structure of (Cu,Ni)6Sn5 on Ni3Sn4 at the interface. Approaches to avoid this dual IMC structure at the interface are discussed. A rule for selecting the solder alloy composition and the pad surface materials on both sides of the joints is proposed for ball grid array (BGA) packages.
Document Type: Research Article
Affiliations: 1: SC Packaging, Texas Instruments Inc., Dallas, TX, USA, Email: firstname.lastname@example.org 2: ASP Packaging, Texas Instruments Inc., Dallas, TX, USA 3: Quality and Reliability Assurance, Texas Instruments Japan Limited, HIJI, Oita, Japan 4: SC Packaging, Texas Instruments Inc., Dallas, TX, USA
Publication date: February 2012