Microstructure, Intermetallic Growth, and Reliability of Rapidly Solidified Pb-Free Solder Joints Formed via Solder Ball Jetting

Abstract

The majority of research on Pb-free solders has been done with reflow times sufficient to allow significant intermetallic growth at the liquid solder/pad interface. With the need for small, fine-pitched solder joints and to avoid damage to heat-sensitive read/write sensors, the hard disk drive industry predominantly uses solder jet bonding for electrical connections of the heads. This technique does not use flux and has solidification times on the order of a millisecond, four orders of magnitude smaller than that of conventional solder technology. Therefore, the intermetallic formation is highly nonequilibrium and is localized near the pad interface. Surface finish thicknesses and composition have a significant influence on intermetallic growth and composition of solder joints. The intermetallic microstructure, along with voids, can significantly impact joint reliability. In this paper, results of wettability and mechanical solder ball shear measurements on as-plated and aged samples are reported and correlated with microstructure and growth of intermetallic compounds (IMCs) at the solder/pad interface. A wide range of Au-Sn IMCs are found at the pad interface, and Au-embrittlement effects are not found until Au exceeds 7 wt.%.

Evaluation of laser solder ball jetting for solder ball attachment process

“…The EDX analysis on the showed a layer of highly variable Au-Sn di concentrations at the solder/bond pad inter Figure 5(a). Very thin and uneven platelets observed, which was resulted by the rapid h of the solder when reflowed by the inherentl [1,6,17]. On the contrary, an uneven layer Cu 6 Sn 5 IMC was determined by EDX ana based reflowed bump.…”

“…mps would experience a much ux-based reflowed bumps. The in fine crystal grains and r jetted bumps, as compared to lting from the gradual cooling owed bumps [1,5]. As the laser ains and higher volume of grain obstructions against the shear he bump.…”

“…Electronic packages head towards a trend of miniaturization for greater portability, improved performance and more functionality [1]. With the continuous shrinkage in the size of electronic packages, the density of input/output (I/O) counts is rising, and the pitch between solder interconnections is decreasing within a given area [2][3].…”

“…As a result, a robust metallurgical bonding was formed between the solder ball and the metal bond pad. As the activation energy of the IMC layer is low, the IMC layer would continue to grow via solid-state diffusion mechanism, even after the solder ball has fully solidified at room temperature [1,3]. However, IMCs are inherently brittle in nature, and excessive thickness is undesirable.…”

Nanoindentation properties of as-soldered low-Ag SAC-Bi-Ni/Cu

“…The sizes of the common solder balls are about 100μm to 760μm in the electronic industry [4][5][6][7] . Due to the extremely tiny sizes of the solder balls, it is hard to evaluate their mechanical properties by traditional method.…”