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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.
Highlights
Since the European Union’s Restriction of Hazardous Substances (RoHS) Directive was introduced in 2001, a great deal of research has been focused on lead-free solder alloys, owing to restrictions on the use of Sn–Pb solder [1,2,3,4]
We focused on the mechanical properties of Sn–Bi and thermosetting epoxy (TSEP) composite Sn–Bi solder joints after thermal cycling test and temperature and humidity test
3, 5, and 7 wt.% epoxy systems were mechanically mixed with Sn–Bi solder paste
Summary
Since the European Union’s Restriction of Hazardous Substances (RoHS) Directive was introduced in 2001, a great deal of research has been focused on lead-free solder alloys, owing to restrictions on the use of Sn–Pb solder [1,2,3,4]. The resistance to thermal cycling and high temperature and humidity and mechanical shock are important properties to characterize the mechanical reliability of solder joints [14,15,16,17]. Various approaches have been attempted to increase the reliability of Sn–Bi solder joints, such as adding trace alloying elements or nanoparticles to Sn–Bi solders, which could inhibit the intermetallic compound (IMC) growth and increase the reliability. We focused on the mechanical properties of Sn–Bi and thermosetting epoxy (TSEP) composite Sn–Bi solder joints after thermal cycling test and temperature and humidity test. By comparing and analyzing the mechanical property evolution of Sn–Bi solder joints with different contents of epoxy resin, the best composition of TSEP Sn–Bi solder paste was determined
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