In this study, solder joints mixed with graphene-nanosheets (GNSs) were investigated for the manufacture of highly reliable electronic devices. In order to analyze the effect of adding GNSs, experiments were performed by adding various amounts of GNSs (0.01, 0.05, 0.1, 0.3, 0.5 wt%). To compare and analyze the properties of the solder joints to which GNSs were added, shear forces were measured, and cross-sectional observation was performed. The bonding strength of the solder joints containing 0.05% GNSs was the highest, and the bonding strength of the solder joints with higher GNSs contents did not increase. This is because, as the content of GNSs increases, the viscosity of the solder paste also increases; therefore, the solder paste detachability from the metal mask was lowered and a sufficient amount was not applied. In addition, due to the high content of GNSs, the fluidity of solder powder and paste decreased, resulting in defects in the shape of the solder joint. Therefore, the optimal GNSs content in this study was 0.05%, and studies for optimal viscosity should be continued.

Bonding properties of epoxy-containing solder joints were investigated by a high temperature aging test. Specimens were prepared by bonding an R3216 standard chip resistor to an OSP-finished PCB by a reflow process with two basic types of solder (SAC305 & Sn58Bi) pastes and two epoxy-solder (SAC305+epoxy & Sn58Bi+epoxy) pastes. In all epoxy solder joints, an epoxy fillet was formed in the hardened epoxy, lying around the outer edge of the solder joint, between the chip and the Cu pad. In order to analyze the bonding characteristics of solder joints at high temperatures, a high-temperature aging test at 150°C was carried out for 14 days (336 h). After aging, the intermetallic compound Cu₆Sn₅ was found to have formed in the solder joint on the Cu pad, and the shear stress on the conventional solder joint was reduced by a significant amount. The reason that the shear force did not decrease much, even though in epoxy solder, was thatbecause epoxy hardened at the outer edge of the supported solder joints. Using epoxy solder, strong bonding behavior can be ensured due to this resistance to shear force，even in metallurgical changes such as those where intermetallic compounds form at solder joints.

We have studied the effects of Ag on the characteristics of Sn₄₃Bi₅₇Ag_x(wt%) lead-free solders for photovoltaic ribbon. Ag atoms in the solder formed an alloy phase of Ag₃Sn after reacting with some part of Sn atoms, while they did not react with Bi atoms, but decreased the mean size of Bi solid phase and the thickness of solder. When Ag atoms of 3.0 wt% was added to eutectic Sn₄₃Bi₅₇(wt%) solder, it showed the optimally useful results that the peel strength of photovoltaic ribbon greatly increased and the sheet resistance of the solder decreased. In the meanwhile, the eutectic Sn₄₃Bi₅₇(wt%) solder showed a low melting temperature of 138.9℃, and showed a very similar result regardless of the added amount of Ag atoms.

The bonding characteristics of MLCCs (multi layer ceramic capacitor, C1608) lead-free solder (SAC305) joints were evaluated through thermal shock test (-40℃~125℃, total 1,800 cycle). After the test, IMCs( intermetallic compounds) growth and cracks were verified, also shear strengths were measured for degradation of solder joints. In addition, The thermal stress distributions at solder joints were analyzed to compare the solder joints changes before and after according to thermal shock test by FEA (finite elements analysis). We considered the effects of IMCs growth at solder joints. As results, the bonding characteristics degradation was occurred according to initial crack, crack propagations and thermal stress concentration at solder-IMCs interface, when the IMCs grown to solder inside.

In this study, the characteristics and error ranges of the mechanical bonding strength were analyzed according to before and after thermal shock test for various chips of automotive application component using Sn-3.0Ag-0.5Cu solder. In the after thermal shock test, the mechanical bonding strengths tend to decrease, meanwhile decreasing rates of mechanical strengths were less then 12% at specimen`s bonding area below 3.5mm2, and were from 17 to 21% at specimen`s bonding area above 12 mm2. On the other hand, Specimen`s mean deviation rates were about 5% at specimen`s bonding area more than 12 mm2. Inversely, at specimen`s bonding area is less then 3.5 mm2, mean deviation rates were increased to about 8%. It means that the smaller device size is, the larger mean deviation rate. In addition, error ranges and deviation rates of the mechanical bonding strengths may differ slightly depending on their bonding area. Furthermore, process conditions as well as method of mechanical reliability evaluation should be established to reduce the error ranges of bonding strength.

Abstract: This study investigated the characteristics of fracture behavior and mode on solder joints before and after thermal shock test for automotive application component using Sn-3.0Ag-0.5Cu solder, which has a outstanding property as lead-free solder. The shear strength was decreased with thermal cycle number, after 432 cycles of thermal shock test. In addition, fracture mode was verified to ductile, brittle fracture and base materials fracture such as different kind fractured mode using SEM and EDS. Before the thermal shock, the fractured mode was found to typical ductile fracture in solder layer. After thermal shock test, especially, Ag was found on fractured portion as roughest surface. Moreover, it occurred delamination between a PCB and a Cu land. Before thermal shock test, most of fractured mode in solder layer has dimples by ductile fracture. However, after thermal shock test, the fractured mode became a combination of ductile and brittle fracture, and it also could find that the fracture behavior varied including delamination between substrate and Cu land.