IC Component Level Failure Induced By Intermetallic Layer Structural Defects of Solder Joint
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IC Component Level Failure Induced By Intermetallic Layer Structural Defects of Solder Joint Ming Sun, Mike Loo, and Lily Zhao ATO-Innovation, Philips Semiconductors San Jose, CA95131, U.S.A. ABSTRACT Solder joint has been widely used in microelectronics industry as an interconnect of Integrated Circuit (IC) chip and Printed Circuit Board (PCB). Frequently, a functional failure of the component on the system is a result of solder joint damage. Eutectic 63Sn/37Pb solder joint mechanical behaviors on Ni/Au plated copper pad and bare copper pad were experimentally investigated to address the effect of pad surface cleanness on the formation of intermetallic compound. The joints with thinner intermetallic compound layer resulted in a poor solder ball shear strength. Microstructural analysis revealed that the oxidations of Ni and Cu during substrate manufacturing contributed to the improper growth of intermetallic compound during assembly and reliability tests. In additions, the experimental results showed that the growth of the intermetallic compound layer were dependent not only on the time and temperature of solder reflow and testing, but also on the cleanness of the pad surfaces and available area for the diffusion of Ni in the case of Ni/Au plated copper pad, Cu in the case of bare copper pad and Sn in the joint area. INTRODUCTION Increasing reliability requirement for solder joint serving as an interconnect between high pin count integrated circuit (IC) component and printed circuit board has drawn more and more attention on the intermetallic compound (IMC) layer structure between the solder and metallic pad on substrate. Intermetallic compound forms instantaneously when eutectic 63Sn/37Pb solder melts on the copper pad or Au/Ni plated copper pad. Thickness of intermetallic layer in the solder joints may depend not only on the time and temperature of reflow, testing or operation, but also on the surface cleanness of copper pad and Au/Ni plated copper pad before the soldering. Any unwanted formation of oxides on the pads surface induced during pad etching, plating or assembly related process will initiate an interface failure of solder joint. Although many mechanism studies have been done on the formation of solder joint and its effects on reliability of printed circuit board (PCB) level, previously reported studies and developed models on the joints behavior are more focus on the solder alloys instead of intermetallic alloys interface, which results in many difficulties to understand solder joint failure phenomena and failure roots during product development and manufacturing. Furthermore, the most discussions of solder joint failure are either based on solder material’s resistance or based on intermetallic compound without considering its structural defects induced during component assembly and process [1]. The aim of this paper is to introduce an experimental result showing that the oxidation-induced defect between the intermetallic compound layer and metallic pads (Ni/Au plated or bare copper) results i
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