Jung-Hwan Bang

Interfacial reactions and mechanical strength of Sn-3.0Ag-0.5Cu/Ni/Cu and Au-20Sn/Ni/Cu solder joints for power electronics applications

Abstract The mechanical strength of Sn-3.0Ag-0.5Cu (SAC305) and Au-20Sn solder joints and their interfacial reaction with a Ni-plated ceramic substrate were evaluated to assess their suitability for use as die attach materials in power module applications. The compatibility between the two solder alloys and the Ni substrate was assessed during isothermal long-term aging, while the mechanical strength of the two solder joints was measured by die shear testing. A higher intermetallic compound (IMC) growth rate and Ni consumption rate was observed in the SAC305 solder joint, with the formation of a thick IMC layer and weak interface resulting in brittle fracture. The Au-20Sn solder joint, on the other hand was found to exhibit superior high temperature interfacial stability and joint strength.

Lead-free Solder for Automotive Electronics and Reliability Evaluation of Solder Joint

Automotive today has been transforming to an electronic product by adopting a lot of convenience and safety features, suggesting that joining materials and their mechanical reliabilities are getting more important. In this study, a Sn-Cu-Cr-Ca solder composition having a high melting temperature (>230℃) was fabricated and its joint properties and reliability was investigated with an aim to evaluate the suitability as a joining material for electronics of engine room. Furthermore, mechanical properties change under complex environment were compared with several existing solder compositions. As a result of contact angle measurement, favorable spreadability of 84% was shown and the average shear strength manufactured with corresponding composition solder paste was 1.9kg/mm 2 . Also, thermo-mechanical reliability by thermal shock and vibration test was compared with that of the representative high temperature solder materials such as Sn-3.5Ag, Sn-0.7Cu, and Sn-5.0Sb. In order to fabricate the test module, solder balls were made in joints with ENIG-finished BGA and then the BGA chip was reflowed on the OPS-finished PCB pattern. During the environmental tests, resistance change was continuously monitored and the joint strength was examined after tests. Sn-3.5Ag alloy exhibited the biggest degradation rate in resistance and shear stress and Sn-0.7Cu resulted in a relatively stable reliability against thermo-mechanical stress coming from thermal shock and vibration.

Study on Joint of Micro Solder Bump for Application of Flexible Electronics

Abst ract In electronic industry, the trend of future electronics will be flexible, bendable, wearable electronics. Until now, there is few study on bonding technology and reliability of bonding joint between chip with micro solder bump and flexible substrate. In this study, we investigated joint properties of Si chip with eutectic Sn-58Bi solder bump on Cu pillar bump bonded on flexible substrate finished with ENIG by flip chip process. After flip chip bonding, we observed microstructure of bump joint by SEM and then evaluated properties of bump joint by die shear test, thermal shock test, and bending test. After thermal shock test, we observed that crack initiated between Cu6Sn5IMC and Sn-Bi solder and then propagated within Sn-Bi solder and/or interface between IMC and solder. On the other hands, We observed that fracture propated at interface between Ni3Sn4 IMC and solder and/or in solder matrix after bending test

Mechanical Behavior of Weldbond Joint of 1.2GPa Grade Ultra High Strength TRIP Steel for Car Body Applications

The effect of weldbond hybrid joining process on the mechanical behavior of single lap and L-tensile joints was investigated for the newly developed 1.2GPa grade ultra high strength TRIP(transformation induced plasticity) steel. In the case of single lap shear behavior, the weldbond joint of 1.2GPa TRIP steel showed lower maximum tensile load and elongation than that of the adhesive bonding only. It was considered to be due to the reduction of real adhesion area, which was caused by the degradation of adhesive near the spot weld, and the brittle fracture behavior of the spot weld joint. In the case of L-tensile behavior, however, the maximum tensile load of the weldbond joint of 1.2GPa TRIP steel was dramatically increased and the fracture mode was change to the base metal fracture which is desirable for the spot weld joint. These synergic effect of the weldbond hybrid joining process in 1.2GPa TRIP steel was considered to be due to the stress dissipation around the spot weld joint by the presence of adhesive which resulted in the change of crack propagation path.

A study of joint properties of Sn-Cu-(X)Al(Si) middle-temperature solder for automotive electronics modules

Joint properties of electric control unit (ECU) module using Sn-Cu-(X)Al(Si) lead-free solder alloy were investigated for automotive electronics module. In this study, Sn-0.5Cu-0.01Al(Si) and Sn-0.5Cu-0.03Al(Si) (wt.%) lead-free alloys were fabricated as bar type by doped various weight percentages (0.01 and 0.03 wt.%) of Al(Si) alloy to Sn-0.5Cu. After fabrications of lead-free alloys, the ball-type solder alloys with a diameter of 450 um were made by rolling and punching. The melting temperatures of 0.01Al(Si) and 0.03Al(Si) were 230.2 and 230.8℃, respectively. To evaluation of properties of solder joint, test printed circuit board (PCB) finished with organic solderability perseveration (OSP) on Cu pad. The ball-type sol- ders were attached to test PCB with flux and reflowed for formation of solder joint. The maximum tem- perature of reflow was 260℃ for 50s above melting temperature. And then, we measured spreadability and shear strength of two Al(Si) solder materials compared to Sn-0.7Cu solder material used in industry. And also, microstructures in solder and intermetallic compounds (IMCs) were observed. Moreover, thickness and grain size of Cu6Sn5 IMC were measured and then compared with Sn-0.7Cu. With increasing the amounts of Al(Si), the Cu6Sn5 thickness was decreased. These results show the addition of Al(Si) could suppress IMC growth and improve the reliability of solder joint.

Technical Trend of TSV(Through Silicon Via) Filling for 3D Wafer Electric Packaging

Through Silicon Via (TSV) technology is the shortest interconnection technology which is compared with conventional wire bonding interconnection technology. Recently, this technology has been also noticed for the miniaturization of electronic devices, multi-functional and high performance. The short interconnection length of TSV achieve can implement a high density and power efficiency. Among the TSV technology, TSV filling process is important technology because the cost of TSV technology is depended on the filling process time and reliability. Various filling methods have been developed like as Cu electroplating method, molten solder insert method and Ti/W deposition method. In this paper, various TSV filling methods were introduced and each filling materials were discussed.

X-선 투과검사를 이용한 저항 점용접부 품질평가기법

For the resistance spot welds of CR1180 and GA1180 TRIP steels, the weld quality evaluation method using the digitalized X-ray transmission imaging apparatus was investigated in comparison with the crosssectional examination method. In the case of the resistance spot welding of CR1180, three circular regions, such as WZ(white zone), GZ(grey zone) and DZ(dark zone), appeared on X-ray image and they corresponded to the diameters of indentation mark, nugget and corona bond, respectively. The variation of X-ray transmission thickness due to the thickness variation of the weld seemed to be mainly responsible for the formation of those contrasts. The X-ray image contrast formed from the variation of transmission thickness at the outer border line of DZ could also enable the inspections of the notch shape, nonuniformity of the welding pressure and spatter from its sharpness, concentricity and the normal straight line, respectively. The X-ray image of the resistance spot weld of galvannealed GA1180 TRIP steel was very similar to that of CR1180 TRIP steel except the crown shaped outer border line of DZ which was considered to be due to the melting behavior of zinc having the boiling temperature even lower than the melting temperature of steel.

Joint Property of Sn-Cu-Cr(Ca) Middle Temperature Solder for Automotive Electronic Module

2 . Also, the thickness of IMC(intermetallic compound) was evaluated with various aging temperature and time in order to understand Cr effect on Sn-0.7Cu solder. Cu6Sn5 IMC was formed between Cu pad and the solder alloy and the average thickness of the Cu6Sn5 IMC was measured about 4um and it was about 50% of thickness of Cu6Sn5 IMC in Sn-0.7Cu. It is expected to have a positive effect on reliability of the solder joint.

Joint reliability of various Pb-free solders under harsh vibration conditions for automotive electronics

Abstract These days, realization of technology for automotive electronics is important for convenience and safety in automobile industries. Although technology development is continuously progressing, various problems associated with the reliability of automotive electronics have arisen. In this study, combined vibration tests were performed to determine the reliability of various solders under harsh environments: Sn-3.0Ag-0.5Cu (SAC305), Sn0.7Cu and Sn-0.5Cu-0.01Al-0.005Si-0.008Ge (SnCuAl(Si)) solder (in wt%). The Pb-free solder balls were used on electroplating nickel finished Cu pads of a fine ball grid array (FBGA) package. The BGA packages mounted with solder balls were set up on electroless nickel-immersion gold (ENIG) finished Cu pads of a daisy-chained printed circuit board (PCB). The combined random vibration test was performed under 2.5 Grms in the range of 400 to 2000 Hz in the temperature range of −45 to 125 °C and was continued until 500 cycles. The reliability of the solder joint was determined by measuring the electrical resistance using a multi-meter. The resistance gradually increased and finally approached infinity. In addition, the IMC thicknesses increased during the combined random vibration test, which affected the fracture behavior. To determine the reliability of the solders, the number of failures of solders and the crack morphology and propagation in each solder were evaluated. Among the three solders, the SnCuAl(Si) solder demonstrated the best reliability.

Intermetallic Compounds and Mechanical Property of Sn-Cu-xCr/Cu Solder Joint by Multiple reflows Conditions

자동차 산업 분야에서 ELV (End of Life Vehicle) 환경 규제로 인하여 자동차 전장품에 Pb를 포함한 4대 중금속의 사용이 제한되고 있다. 열충격 및 진동 조건 에 상대적으로 노출이 적은 자동차 실내 전장품은 Sn3.0Ag-0.5Cu 무연 솔더로 대체하고 있다. Table 1과 같이 자동차 엔진 및 미션 주변의 전장부품은 일반 가 전부품에 비해 주행시 최대 155°C의 고온 환경 및 열 충격, 최대 20G의 고진동등 가혹한 환경에 노출되며, 최 소 15년 이상의 장기 신뢰성이 요구되고 있다. 솔더 접합 소재 측면에서 자동차 전장부품에 사용 가능한 솔더 후보군으로 Sn-Zn계, Sn-Al계, Sn-Ni계, Sn-Au 계, Sn-Bi계, Sn-Ag-Cu계 등이 있다. 하지만 Sn-Zn Multiple reflows에 따른 Sn-Cu-xCr/Cu 접합계면의 금속간화합물 거동 및 기계적 특성 연구