LED 패키지 솔더 접합부의 기계적 신뢰성에 미치는 열처리의 영향

고민관 ( Min Kwan Ko ),안지혁 ( Jee Hyuk Ahn ),이영철 ( Young Chul Lee ),김광석 ( Kwang Seok Kim ),윤정원 ( Jeong Won Yoon ),정승부 ( Seung Boo Jung ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.1

We studied the effect of heat treatment on the microstructures and mechanical strength of the solder joints in the Light Emitting Diode (LED) packages. The commercial LED packages were mounted on the a flame resistance-4 (FR4) Printed Circuit Board (PCB) in the reflow process, and then the joints were aged at 125℃ for 100, 200, 300, 500 and 1000 hours, respectively. After the heat treatment, we measured the shear strength of the solder joints between the PCB and the LED packages to evaluate their mechanical property. We used Pb-free Sn-3.0Ag-0.5Cu solder to bond between the LED packages and the PCBs using two different surface finishes, Electroless Nickel-Immersion Gold (ENIG) and Electroless Nickel-Electroless Palladium-Immersion Gold (ENEPIG). The microstructure of the solder joints was observed by a scanning electron microscope (SEM). (Cu,Ni)6Sn5 intermetallic compounds (IMCs) formed between the solder and the PCB, and the thickness of the IMCs was increased with increasing aging time. The shear strength for the ENIG finished LED package increased until aging for 300 h and then decreased with increasing aging time. On the other hand, in the case of an ENEPIG finished LED package, the shear strength decreased after aging for 500 h.

열압착 접합 조건에 따른 경·연성 인쇄회로기판 간 Sn-58Bi 무연솔더 접합부의 기계적 특성

최지나,고민관,이상민,정승부,Choi, Ji-Na,Ko, Min-Kwan,Lee, Sang-Min,Jung, Seung-Boo 한국마이크로전자및패키징학회 2013 마이크로전자 및 패키징학회지 Vol.20 No.2

We investigated the optimum bonding conditions for thermo-compression bonding of electrodes between flexible printed circuit board(FPCB) and rigid printed circuit board(RPCB) with Sn-58Bi solder as interlayer. In order to figure out the optimum bonding conditions, peel test of FPCB/RPCB joint was conducted. The peel strength was affected by the bonding conditions, such as temperature and time. The fracture energies were calculated through F-x (Force-displacement) curve during peel test and the relationships between bonding conditions and fracture behaviors were investigated. The optimum condition for the thermo-compression bonding with Sn-58Bi solder was found to be temperature of $195^{\circ}C$ and time of 7 s. 본 연구에서는 Sn-58Bi 솔더를 이용한 경성 인쇄 회로 기판 (Rigid printed circuit board, RPCB)과 연성 인쇄회로 기판 (Flexible printed circuit board, FPCB) 간의 열압착 접합 시, 접합 조건에 따른 기계적 특성에 대하여 연구하였다. 접합 온도와 접합 시간을 변수로 열압착 접합을 실시하여 $90^{\circ}$ 필 테스트(Peel test)를 통해 접합 강도를 측정하고, 단면과 파단면을 관찰하였다. 접합 온도가 증가할수록 접합 강도가 증가하였으며, 접합 시간에 따른 접합 강도의 변화 또한 관찰할 수 있었다. 접합 시간이 증가하면서 접합부의 파괴에 영향을 미치는 요인이 솔더 층에서 금속간 화합물(Intermetallic compound, IMC) 층으로 변화하는 것을 관찰할 수 있었다. 필 테스트 과정의 F-x(Force-distance) curve를 통해 파괴 에너지를 계산하여 금속간 화합물이 접합 강도에 미치는 영향을 평가하였으며, 본 연구에서 $195^{\circ}C$, 7초 조건이 접합 강도와 파괴 에너지가 가장 높게 나타나는 최적 접합 조건으로 도출되었다.

열압착법을 이용한 경.연성 인쇄회로기판 접합부의 접합 강도에 미치는 접합 조건의 영향

이종근,고민관,이종범,노보인,윤정원,정승부,Lee, Jong-Gun,Ko, Min-Kwan,Lee, Jong-Bum,Noh, Bo-In,Yoon, Jeong-Won,Jung, Seung-Boo 한국마이크로전자및패키징학회 2011 마이크로전자 및 패키징학회지 Vol.18 No.2

We investigated effects of bonding conditions on the peel strength of rigid printed circuit board (RPCB)/ flexible printed circuit board (FPCB) joints bonded using a thermo-compression bond method, The electrodes on the FPCB were coated with Sn by a dipping process. We confirmed that the bonding temperature and bonding time strongly affected the bonding configuration and strength of the joints. Also, the peel strength is affected by dipping conditions; the optimum dipping condition was found to be temperature of $270^{\circ}C$ and time of 1s. The bonding strength linearly increased with increasing bonding temperature and time until $280^{\circ}C$ and 10s. The fracture energy calculated from the F-x (Forcedisplacement) curve during a peel test was the highest at bonding temperature of $280^{\circ}C$. 본 연구에서는 interlayer로 Sn을 사용하여 경성 인쇄 회로 기판(Rigid printed circuit board, RPCB)과 연성 인쇄 회로 기판(Flexible printed circuit board, FPCB) 간의 열압착 접합(Thermo-compression bonding) 조건을 최적화하는 연구를 진행하였다. 접합에 앞서 FPCB를 다양한 온도와 시간조건 하에서 Sn이 용융된 솔더 배스 안에서 침지(Dipping) 공정을 수행하였고, 열압착법을 이용하여 FPCB와 RPCB의 접합을 수행하였다. FPCB/RPCB 접합부의 접합 강도를 $90^{\circ}$ 필 테스트(Peel test)를 이용하여 측정하였다. 그 결과 $270^{\circ}C$, 1s의 침지 조건에서 FPCB의 polyimide(PI)와 Cu 전극 계면에서 파단되고, 이때, 최대 박리 강도를 얻었다. FPCB와 RPCB의 열압착 접합시 주요 변수로는 압력, 온도, 시간이 있으며, 특히 온도의 증가에 따라 접합 강도가 크게 증가하였다. 접합부 계면 관찰 결과, 접합 온도와 시간이 증가함에 따라 접합 면적이 증가하였으며, 이로 인해 접합 강도가 증가하는 것으로 사료된다. 필 테스트 과정에서 나타나는 F-x(Forcedisplacement) 곡선을 토대로 산출한 파괴 에너지와 접합 강도는 $280^{\circ}C$, 10s의 접합 조건에서 가장 높게 나타났으며, 이 조건이 최적 접합 조건으로 도출되었다.

Solder Joint Reliability in Flip Chip Package with Surface Treatment of ENIG under Thermal Shock Test

하상수,윤정원,고민관,김대곤,김성진,홍태환,정승부,하상옥,김종웅 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.4

This study investigated the microstructural evolution and evaluated the thermo-mechanical reliability of a Sn-3.0Ag-0.5Cu (in wt.%) flip chip package during a thermal shock test. The reliability of the flip chip bonded packages was evaluated by means of the thermal shock in the temperature range of 233 K to 398 K. After 250 thermal shock cycles, cracks finally occurred at the corner solder bump joint on the chip side interfacial regions. In that, the crack initiated at the solder region near the intermetallic compound (IMC) layers. For the interpretation of the failure mechanism of the package, finite element analyses were conducted. From the finite element analysis or computational simulation result, the distribution of the plastic work in the corner solder bump was found to be most considerable. This means that the corner solder bump has the highest potential for first crack initiation and growth, because the thermo-mechanical failure of the solder joints is mainly caused by the accumulation of the plastic work. This matched well with the experimental results. This study investigated the microstructural evolution and evaluated the thermo-mechanical reliability of a Sn-3.0Ag-0.5Cu (in wt.%) flip chip package during a thermal shock test. The reliability of the flip chip bonded packages was evaluated by means of the thermal shock in the temperature range of 233 K to 398 K. After 250 thermal shock cycles, cracks finally occurred at the corner solder bump joint on the chip side interfacial regions. In that, the crack initiated at the solder region near the intermetallic compound (IMC) layers. For the interpretation of the failure mechanism of the package, finite element analyses were conducted. From the finite element analysis or computational simulation result, the distribution of the plastic work in the corner solder bump was found to be most considerable. This means that the corner solder bump has the highest potential for first crack initiation and growth, because the thermo-mechanical failure of the solder joints is mainly caused by the accumulation of the plastic work. This matched well with the experimental results.

LED 패키지 솔더 접합부의 기계적 신뢰성에 미치는 리플로우 횟수의 영향

이영철 ( Young Chul Lee ),김광석 ( Kwang Seok Kim ),안지혁 ( Ji Hyuk Ahn ),윤정원 ( Jeong Won Yoon ),고민관 ( Min Kwan Ko ),정승부 ( Seung Boo Jung ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.11

The research efforts on GaN-based light-emitting diodes (LEDs) keep increasing due to their significant impact on the illumination industry. Surface mount technology (SMT) is widely used to mount the LED packages for practical application. In surface mount soldering both the device body and leads are intentionally heated by a reflow process. We studied on the effects of multiple reflows on microstructural variation and joint strength of the solder joints between the LED package and the substrate. In this study, Pb-free Sn-3.0Ag-0.5Cu solder and a finished pad with organic solderability preservatives (OSP) were employed. A Cu6Sn5 intermetallic compound (IMC) layer was formed during the multiple reflows, and the thickness of the IMC layerincreased with an increasing number of reflows. The shear force decreased after three reflows. From the observation of the fracture surface after a shear test, partially brittle fractures were observed after five reflows.