Study on the Reliability of Sn–Bi Composite Solder Pastes with Thermosetting Epoxy under Thermal Cycling and Humidity Treatment

Abstract

In this study, a Sn–Bi composite solder paste with thermosetting epoxy (TSEP Sn–Bi) was prepared by mixing Sn–Bi solder powder, flux, and epoxy system. The melting characteristics of the Sn–Bi solder alloy and the curing reaction of the epoxy system were measured by differential scanning calorimeter (DSC). A reflow profile was optimized based on the Sn–Bi reflow profile, and the Organic Solderability Preservative (OSP) Cu pad mounted 0603 chip resistor was chosen to reflow soldering and to prepare samples of the corresponding joint. The high temperature and humidity reliability of the solder joints at 85 °C/85% RH (Relative Humidity) for 1000 h and the thermal cycle reliability of the solder joints from −40 °C to 125 °C for 1000 cycles were investigated. Compared to the Sn–Bi solder joint, the TSEP Sn–Bi solder joints had increased reliability. The microstructure observation shows that the epoxy resin curing process did not affect the transformation of the microstructure. The shear force of the TSEP Sn–Bi solder joints after 1000 cycles of thermal cycling test was 1.23–1.35 times higher than the Sn–Bi solder joint and after 1000 h of temperature and humidity tests was 1.14–1.27 times higher than the Sn–Bi solder joint. The fracture analysis indicated that the cured cover layer could still have a mechanical reinforcement to the TSEP Sn–Bi solder joints after these reliability tests.

Board Level Drop Test for Evaluating the Reliability of High-Strength Sn–Bi Composite Solder Pastes with Thermosetting Epoxy

“…The results showed that the peak temperature of the epoxy resin system was 151.4 • C, and the curing reaction was completed close to 200 • C [22]. An optimized reflow profile was applied to the solder TSEP Sn-Bi-x solder pastes, while the original reflow profile was used to solder the Sn-Bi solder paste in order to allow the epoxy resin system to complete the curing reaction [20,22]. The reflow profiles of the Sn-Bi solder paste and TSEP Sn-Bi solder pastes are shown in Figure 3.…”

“…The Sn-Bi composite solder paste with thermosetting epoxy with different proportions (3 wt.%, 5 wt.%, and 7 wt.%) (TSEP Sn-Bi-x, x = 3, 5, 7) was used to print on the PCB side, forming the hybrid Sn-Bi/TSEP Sn-Bi-3, Sn-Bi/TSEP Sn-Bi-5, and Sn-Bi/TSEP Sn-Bi-y solder joints. The TSEP Sn-Bi solder paste was prepared using Sn-Bi solder powder (particle size 25-45μm), flux, and epoxy system, and the epoxy resin system consisted of thermosetting epoxy resin and a curing agent, which can be seen in previous studies regarding the preparation of TSEP Sn-Bi solder paste [20,22]. Figure 2 illustrates a two-part schematic diagram of the drop test specimen's preparation process.…”

“…An optimized reflow profile was applied to the solder TSEP Sn-Bi-x solder pastes, while the original reflow profile was used to solder the Sn-Bi In the previous study, the epoxy resin system curing reaction of TSEP Sn-Bi-x solder pastes was analyzed with a differential scanning calorimeter (DSC). The results showed that the peak temperature of the epoxy resin system was 151.4 • C, and the curing reaction was completed close to 200 • C [22]. An optimized reflow profile was applied to the solder TSEP Sn-Bi-x solder pastes, while the original reflow profile was used to solder the Sn-Bi solder paste in order to allow the epoxy resin system to complete the curing reaction [20,22].…”

“…After the thermal cycling test and temperature and humidity test, the TSEP Sn-Bi solder joints demonstrated better mechanical characteristics. The addition of the epoxy system could provide good protection for the solder joints, and reduce fatigue damage from environmental influence [22].…”

Microstructure and Shear Behaviour of Sn-3.0Ag-0.5Cu Composite Solder Pastes Enhanced by Epoxy Resin

“…The research result indicated that the appropriate addition of epoxy resin could notably improve the spreadability and shear properties of Sn-Bi solder pastes. Moreover, the thermal reliability and drop characteristics of Sn-Bi epoxy solder joints were enhanced, which could mainly benefit from the mechanical refinement of epoxy resin [ 17 , 18 ].…”