3D chip stacking packages and 3D-Through Silicon Via (3D-TSV) vertical interconnection have been popular. Usually, Cu-pillar/SnAg micro-bumps have been used for vertical interconnections of 3D-TSV chip stacking. A Thermo-Compression (TC) bonding method using Non-Conductive Films (NCFs) has performed these vertical interconnections. Heat and pressure induced molten solder wetting on the pad, and deforming too during TC bonding process. The deformed molten solder on the sidewall of the Cu-pillar results in the increase of solder and Cu pillar contact interfaces. As a result, faster Sn consumption made the Kirkendall voids at the solder joint. The novel Double layer NCFs (D-NCFs) can solve the solder sidewall wetting problem on the Cu-pillar. D-NCFs have the double layer NCFs structure, which consist of the fast curing speed top NCFs layer and the slower curing speed bottom NCFs layer. The top NCFs layer has the fast cure temperature below the melting temperature of the solder in order to prevent the molten solder movements on the Cu-pillar sidewall. On the other hand, the bottom NCFs layer helped the molten solder wet on the pads, which has the flux ability and slower curing property. In this study, D-NCFs have been investigated for wafer level (WL) processes in 40µm fine-pitch Cu-pillar/SnAg micro bump chip assembly. D-NCFs properties were adjusted for WL capability and then bonding conditions were optimized in terms of solder wetting on Cu-pillar and electrical interconnection. As a result, D-NCFs can significantly increase the remaining Sn solder between the Cu-pillar/SnAg/Cu interconnection and decrease the Sn consumption.In chapter 2, effects of curing agent in the conventional single layer NCFs on Cu-pillar/SnAg/Cu interconnection Chip-on-Chip (COC) assembly were investigated. As a result, the NCFs containing anhydride curing agent can remove the native oxide of SnAg solder well generating carboxyl acid. Finally, the content of the anhydride curing agent were optimized in terms of the NCFs formability and degree of curing after bonding process.In chapter 3, 40 µm pitch Cu pillar/SnAg solder micro-bump assembly using new D-NCFs have been investigated. At first, of the curing speed and the viscosity of the top NCF layer, the curing speed was defined as the effective factor for preventing solder wetting on the Cu-pillar in D-NCFs. Then, the thickness conditions of D-NCFs and the bonding pressure were optimized by evaluating the solder joint morphologies. The optimized thickness of the top NCF layer is 10 µm, which is the same as the thickness of Cu pillar. Finally, after thermal aging, solder joint using D-NCFs show less Sn consumption than the solder joint using conventional single NCF because of no solder sidewall wetting of Cu pillar in D-NCF packages.In chapter 4, 40 µm pitch Cu pillar/SnAg solder micro-bump assembly using wafer level processible (WL processible) D-NCFs have been investigated. WL processability of D-NCFs was optimized in terms of the adhesion and elongation properties of D-NCFs by changing epoxy formulation. Finally no delamination of the D-NCFs at the edge and corner of diced chips was obtained by using the optimized D-NCFs after the dicing process. And the thermo-compression bonding conditions of the optimized D-NCFs were evaluated in terms of, solder sidewall wetting, solder height, and electrical bump contact resistance. As a summary D-NCFs solved the solder wetting on the sidewall of Cu pillars problem, resulting in significant amount of remaining Sn contents at the solder bump joint. After reliability tests, D-NCFs show excellent reliability performance in thermal cycle test and pressure cooker test compared with the conventional single layer NCFs because of no solder sidewall wetting of Cu pillar and resulting plenty of remaining Sn at the solder bump joint.
작으며 고성능의 전자 기계에 대한 필요성이 점차 대두되면서, 전자 패키지에서 3D 패키징 및 적층에 대한 필요성은 증가하게 되었다. 여러 3D 적층 및 패키징 기술 중에 실리콘 칩을 관통하는 Through Silicon Via (TSV)를 통해 칩들을 3차원으로 적층하는 방법이 가장 높은 공간 효율성과 전기적 성능으로 인하여 각광받고 있다. 이러한 TSV 칩의 적층 방법으로 Cu pillar/SnAg micro-bump가 높은 접합 신뢰성, 및 낮은 본딩 온도로 인하여 칩간 접합 방법으로 산업체에서 통상적으로 쓰이고 있다. 하지만 마이크로 범프의 크기가 작아짐에 따라 기존의 본딩 방법으로는 칩간 적층을 할 때 플럭스 잔여물, 언더필의 완전하지 못한 충전 등의 문제가 생겨, Non-Conductive Films (NCFs)를 이용한 본딩이 대두되었다. 하지만 NCFs를 이용한 본딩은 Cu-pillar/SnAg micro-bump가 기판의 패드에 접촉하며 젖을 수 있게 충분한 압력과 온도가 필요하며 이때 SnAg 솔더가 기판의 패드에만 젖는 것이 아니라 Cu-pillar의 측면으로도 젖어 SnAg 솔더와 Cu의 계면 반응 면적이 늘어 SnAg 솔더의 소모가 빨라진다는 문제가 있다. 이것을 방지하기 위한 새로운 NCFs인 Double-layer NCFs(D-NCFs) 연구를 진행하였다. 두개의 NCFs 층으로 되어 있는 D-NCFs의 bottom NCFs layer는 SnAg 솔더를 감싸고 있으며, 산무수물 경화제가 들어가 있는 NCFs로 본딩 공정 중 carboxyl acid의 생성으로 SnAg 솔더 표면의 산화막을 제거할 수 있어 다른 경화제가 들어있는 NCFs보다 솔더 조인트 형성을 가장 잘 할 수 있다. 반면, D-NCFs의 top NCFs layer는 Cu-pillar를 감싸고 있으며, 빠른 경화 특성을 가지고 있어, 본딩 공정 중 SnAg 솔더의 용융보다 빨리 충분히 경화되어 SnAg 솔더의 Cu-pillar 측면으로의 젖음을 방지할 수 있다. D-NCFs를 이용하여 제작한 솔더 조인트에서 Sn 소모가 더 적은 것을 확인 할 수 있었다. 그리고 D-NCFs에서도 기존의 단일층 NCFs와 같이 웨이퍼 단위 프로세스가 가능하며, pressure cooker 신뢰성 실험, thermal cycling 신뢰성 실험을 통해 기존의 단일층 NCFs보다 우수한 특성을 가지고 있는 것을 확인할 수 있었다.
