Interfacial reaction study on a solder joint with Sn-4Ag-0.5Cu solder ball and Sn-7Zn-Al (30 ppm) solder paste in a lead-free wafer level chip scale package

Abstract

The interfacial reactions of solder joints between the Sn-4Ag-0.5Cu solder ball and the Sn-7Zn-Al (30 ppm) presoldered paste were investigated in a wafer level chip scale package (WLCSP). After appropriate surface mount technology (SMT) reflow process on the printed circuit board (PCB) with organic solderability preservative (Cu/OSP) and Cu/Ni/Au surface finish, samples were subjected to 150°C high-temperature storage (HTS), 1,000 h aging. Sequentially, the cross-sectional analysis is scrutinized using a scanning electron microscope (SEM)/energy-dispersive spectrometer (EDS) and energy probe microanalysis (EPMA) to observe the metallurgical evolution in the interface and solder buck itself. It was found that Zn-enriched intermetallic compounds (IMCs) without Sn were formed and migrated from the presolder paste region into the solder after reflow and 150°C HTS test.

The effect of Ag content on the formation of Ag3Sn plates in Sn-Ag-Cu lead-free solder

“…The typical reflow time-temperature profile for the lead-free and the lead-based vehicles are as those shown in previous studies. 4,17 The activation temperature and peak temperature for Sn-3Ag-0.5Cu paste are 153.5°C and 243.5°C, respectively, and the reflow cycle is 360 sec. The activation temperature and peak temperature for Pb-bearing vehicles are 152.5°C and 223.5°C, respectively, and the reflow cycle is 380 sec.…”

“…Wafer level chip size package (WLCSP) has been introduced in recent years for increasing density, performance, light weight, thinner and smaller size, and cost effectiveness of the devices in the electronic packaging industry. [1][2][3][4] SnPb alloys have been widely used solders for assembly and packaging of the electronics industry for years because of their low cost and superior properties required for interconnecting electronic components. However, increasing environmental and health concerns over the toxicity of lead, combined with global legislation to limit or ban the use of Pb in manufactured products, 5,6 has led to extensive research and development works in lead-free solder materials.…”