접합 소재에 따른 고출력 플립칩 LED 패키지 특성 연구
Properties of High Power Flip Chip LED Package with Bonding Materials
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초록
고출력 LED 패키지의 열적 경로(thermal path)를 줄이기 위해 플립칩 본딩법에 대한 연구가 활발히 진행되고있다. 본 연구에서는 Au-Sn 열압착 본딩 및 Sn-Ag-Cu(SAC) 리플로우 본딩을 이용하여 본딩 특성 및 열적특성을 비교평가 하였다. Au-Sn 열압착 본딩은 50 N에서 300oC의 접합온도로 본딩하였고, SAC 솔더는 솔더페이스트를 인쇄한 후리플로우법으로 피크온도 255oC에서 30 sec에서 본딩하였다. SAC 솔더를 사용한 LED 패키지의 전단강도는 5798.5 gf/mm2로 Au-Sn 열압착 본딩의 3508.5 gf/mm2에 비해 1.6배 높았다. 파단면과 단면분석 결과 Au-Sn, SAC 솔더 모두 LED칩 내부에서 파단이 일어나는 것을 관찰하였다. 반면 Au-Sn 열압착 본딩 샘플의 열저항은 SAC솔더 접합 샘플에 비해 낮았으며, SAC 솔더 접합부 내부의 기공에 의해 열저항이 커짐을 알 수 있었다.
Abstract
Flip chip bonded LED packages possess lower thermal resistance than wire bonded LED packages becauseof short thermal path. In this study, thermal and bonding properties of flip chip bonded high brightness LED were evaluatedfor Au-Sn thermo-compression bonded LEDs and Sn-Ag-Cu reflow bonded LEDs. For the Au-Sn thermo-compressionbonding, bonding pressure and bonding temperature were 50 N and 300oC, respectively. For the SAC solder reflowbonding, peak temperature was 255oC for 30 sec. The shear strength of the Au-Sn thermo-compression joint was 3508.5 gf/mm2 and that of the SAC reflow joint was 5798.5 gf/mm. After the shear test, the fracture occurred at the isolation layerin the LED chip for both Au-Sn and SAC joints. Thermal resistance of Au-Sn sample was lower than that of SAC bondedsample due to the void formation in the SAC solder.
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