고속전단 시험을 이용한 Sn-37Pb BGA solder joints의 기계적 신뢰성 특성 평가
Mechanical reliability of Sn-37Pb BGA solder joints with high-speed shear test
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초록
본 연구에서는 BGA (Ball Grid Array) 솔더 접합부에 high impact가 가해졌을 경우 접합부의 기계적 특성에 대해서 연구하였다. 시편은 ENIG (Electroless Nickel Immersion Gold) 표면 처리된 FR- 4 기판 위에 직경이 500 μm인 Sn-37Pb 솔더볼을 BGA 방식으로 배열하고 리플로우 (Reflow)를 통하여 제작하였다. HTS (High Temperature Storage) 테스트를 위해, 시편을 일정한 온도의 120oC에서 250시간 동안 시효처리 (Aging)를 실시하였다. 시효처리 후, 각각의 시편은 고속 전단 시험기 (Dage-4000HS)를 이용하여 속도 변수는 0.01, 0.1, 1, 3 m/s로 설정하여 고속전단 시험을 실시하였다. 전단시험 후, 솔더 접 합 계면과 파면을 주사전자현미경 (Scanning Electron Microscope, SEM)을 통하여 관찰하였다. 솔더 접 합 계면에는 Ni3Sn4의 금속간 화합물이 성장하였으며, 시효처리 후, 솔더 접합 계면에 생성된 금속간 화 합물의 두께가 증가하는 것을 관찰 할 수 있었다. 전단 시험 결과, 전단 속도가 빨라짐에 따라 전단 강도 값은 증가하는 경향을 나타내었다. 솔더 접합부의 파단은 전단 속도와 시효처리 시간에 따라 다양한 파 괴 모드로 진행됨을 알 수 있었다. 또한, 파괴 모드는 연성파괴 형상을 보이다가 전단속도가 증가함에 따 라 취성 파괴 형상으로 변하는 것을 알 수 있었다.
Abstract
The mechanical shear strength of BGA (Ball Grid Array) solder joints under high impact loading was investigated. The Sn-37Pb solder balls with a diameter of 500 μm were placed on the pads of FR-4 substrates with ENIG (Electroless Nickel Immersion Gold) surface treatment and reflowed. For the High Temperature Storage (HTS) test, the samples were aged a constant testing temperature of 120oC for up to 250h. After the HTS test, high speed shear tests with various shear speed of 0.01, 0.1, 1, 3 m/s were conducted. Ni3Sn4 intermetallic compound (IMC) layer was observed at the solder/Ni-P interface and thickness of IMC was increased with aging process. The shear strength increased with increasing shear speed. The fracture surfaces of solder joints showed various fracture modes dependent on shear speed and aging time. Fracture mode was changed from ductile fracture to brittle fracture with increasing shear speed.
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