Abstract
Department of Electronic Engineering, and *Department of Physics and Materials Science,City University of Hong Kong, Hong Kong, People’s Republic of China(Received May 18, 2000)(Accepted in revised form August 18, 2000)Keywords: Solder joint; Intermetallic; Aging; Kinetics; FatigueIntroductionAs the trend in requirements of electronic packaging is toward higher I/O, greater performance, higherdensity, and lighter weight, the use of area array packaging technology is expected to increase. The typeof packaging, such as ball grid array (BGA), chip scale package (CSP), and Flip Chip, provides theultimate in high I/O-density and count with superior electrical performance, and very small size. Themechanical properties of solder joint are recognized as one of the critical factors that determine theirreliability and lifetime [1–5]. During soldering, the formation of intermetallic compounds (IMCs) atsolder/substrate interface is inevitable and ensures a good metallurgical bond. However, during storageand field service, the growth of IMCs will influence the strength of solder joints and result inmechanical failure of the joints [6–10]. Our recent research result shows that the fatigue lifetime ofsolder joint decreases linearly with the increasing square root of IMCs layer thickness [11]. Since theintermetallic is responsible for the solder joint failures, attention has to be paid to the effect of IMCsgrowth on the lifetime and reliability of microelectronic assemblies.This paper discusses the Ni-Sn/Cu-Sn IMCs layer growth kinetics in the joint soldered on platedAu/Ni FR-4 printed circuit board (PCB), which is one of the most commonly used substrate for finepitch area array packaging. The kinetic model describing and predicting the IMC thickness can be usedto estimate the solder joint reliability and lifetime, according the relationship of the IMC thickness withvibration fatigue failure and cyclic bend fatigue.Experimental ProceduresIn this experiment, the chip scale package CSP46-T.75 with Sn/Pb-eutectic solder ball was placed andsoldered on FR-4 printed circuit boards using a high-speed flexible mounter (CASIO YCM-5500V) anda 5-zone N
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