Yong-Ho Ko

Controlling Interfacial Reactions and Intermetallic Compound Growth at the Interface of a Lead-free Solder Joint with Layer-by-Layer Transferred Graphene

The immoderate growth of intermetallic compounds (IMCs) formed at the interface of a solder metal and the substrate during soldering can degrade the mechanical properties and reliability of a solder joint in electronic packaging. Therefore, it is critical to control IMC growth at the solder joints between the solder and the substrate. In this study, we investigated the control of interfacial reactions and IMC growth by the layer-by-layer transfer of graphene during the reflow process at the interface between Sn-3.0Ag-0.5Cu (in wt %) lead-free solder and Cu. As the number of graphene layers transferred onto the surface of the Cu substrate increased, the thickness of the total IMC (Cu6Sn5 and Cu3Sn) layer decreased. After 10 repetitions of the reflow process for 50 s above 217 °C, the melting temperature of Sn-3.0Ag-0.5Cu, with a peak temperature of 250 °C, the increase in thickness of the total IMC layer at the interface with multiple layers of graphene was decreased by more than 20% compared to that at the interface of bare Cu without graphene. Furthermore, the average diameter of the Cu6Sn5 scallops at the interface with multiple layers of graphene was smaller than that at the interface without graphene. Despite 10 repetitions of the reflow process, the growth of Cu3Sn at the interface with multiple layers of graphene was suppressed by more than 20% compared with that at the interface without graphene. The multiple layers of graphene at the interface between the solder metal and the Cu substrate hindered the diffusion of Cu atoms from the Cu substrate and suppressed the reactions between Cu and Sn in the solder. Thus, the multiple layers of graphene transferred at the interface between dissimilar metals can control the interfacial reaction and IMC growth occurring at the joining interface.

The effect of intermetallic compound evolution on the fracture behavior of Au stud bumps joined with Sn-3.5Ag solder

The microstructure and joint properties of Au stud bumps joined with Sn-3.5Ag solder were investigated as functions of flip chip bonding temperature and aging time. Au stud bumps were bonded on solder-onpad (SOP) at bonding temperature of 260°C and 300°C for 10 s, respectively. Aging treatment was carried out at 150°C for 100 h, 300 h, and 500 h, respectively. After flip chip bonding, intermetallic compounds (IMCs) of AuSn, AuSn2, and AuSn4 were formed at the interface between the Au stud bump and Sn-3.5Ag solder. At a bonding temperature of 300°C, AuSn2 IMC clusters, which were surrounded by AuSn4 IMCs, were observed in the Sn-3.5Ag solder bump. After flip chip bonding, bonding strength was approximately 220.5mN/bump. As aging time increased, the bonding strength decreased. After 100 h of aging treatment, the bonding strength of the joint bonded at 300°C was lower than that bonded at 260°C due to the fast growth rate of the AuSn2 IMCs. The main failure modes were interface fractures between the AuSn2 IMCs and AuSn4 IMCs, fractures through the AuSn2 IMCs and pad lift. Initial joint microstructures after flip chip bonding strongly affected the bonding strengths of aged samples.

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.

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

Interfacial Microstructure and Mechanical Property of Au Stud Bump Joined by Flip Chip Bonding with Sn-3.5Ag Solder

Abstract The effect of flip chip bonding parameters on formation of intermetallic compounds (IMCs) between Au stud bumps and Sn-3.5Ag solder was investigated. In this study, flip chip bonding temperature was performed at 260℃ and 300℃ with various bonding times of 5, 10, and 20 sec. AuSn, AuSn 2 and AuSn 4 IMCs were formed at the interface of joints and (Au, Cu) 6 Sn 5 IMC was observed near Cu pad side in the joint. At bonding temperature of 260℃, AuSn 4 IMC was dominant in the joint compared to other Au-Sn IMCs as bonding time increased. At bonding temperature of 300℃, AuSn 2 IMC clusters, which were surrounded by AuSn 4 IMC, were observed in the solder joint due to fast diffusivity of Au to molten solder with increased bonding temperature. Bond strength of Au stud bump joined with Sn-3.5Ag solder was about 23 gf/bump and fracture mode of the joint was intergranular fracture between AuSn 2 and AuSn 4 IMCs regardless bonding conditions.Key Words : Au stud bump, Flip chip bonding, Interfacial reaction, Bonding strength

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.

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

A Study on the Electrochemical Corrosion Property of Sn-xSb Solder Alloy

In this study, the electrochemical corrosion property was measured by increasing Sb contents. The corrosion property of Sn-5Sb, Sn-8Sb, Sn-10Sb, Sn-8Sb-3Ag solder alloys was measured using polarization test. The polarization curves were measured in 3.5 wt. % NaCl solution of 25 °C. Ag/AgCl and platinum were used by reference electrode and counter electrode, respectively. Corrosion potential (Ecorr), corrosion current density (Icorr) and linear polarization resistance (LPR, Rp) were estimated from the anodic and cathodic tafel lines. SnSb IMC was more diffused in the β-Sn structure by increasing Sb contents. Also, SnSb and Ag3Sn IMC was diffused in the β-Sn structure at Sn-8Sb-3Ag solder alloy. The corrosion potential (Ecorr) and corrosion current density (Icorr) was increased by increasing Sb contents. But, the linear polarization resistance (LPR) was decreased by increasing Sb contents.