Recently, high speed and smaller electronic devices are demanded with the fast growing of mobile products market. For this reason, 3D - Through Silicon Via (3D-TSV) and ultra-fine pitch interconnection technologies have been rapidly developed in electronic packaging industry. To obtain highly reliable less than $30 \mu m$ fine pitch Cu pillar/Sn-Ag micro bump interconnection, non-conductive films (NCFs), pre-applied type of underfill material, have been investigated. For flip chip bonding processes using ultra-fine pitch Cu-pillar/Sn-Ag bump, there are several processing steps such as flux application, solder reflow, and underfill dispensing processes. However, conventional underfill material and process has several problems such as void between interconnection due to the limitation of capillary flow and flux residue causing interconnection corrosion. However, NCFs can achieve void free underfill function and no flux residue, and also have some advantages of reduced processing steps and lower cost because of the flux function included in NCFs.
In order to realize stable Cu-pillar/Sn-Ag bump joint by the flip chip bonding method, it is necessary to investigate the behavior of solder and NCFs resin during the NCFs bonding processes. Especially, NCFs resin can be trapped on the solder joint during flip chip bonding process. In addition, concave shaped solder bump joint which can be high stress concentration area formed at the metallurgical bonding area between solder and PCB metal pads. Eventually, the poor Cu-pillar/Sn-Ag bump joint morphology can cause crack initiation and early failure during reliability tests. To control precisely NCFs resin flow and solder joint morphology during flip chip bonding process, the curing properties and viscosities of NCFs should be studied. Especially, the material properties of NCFs at the solder melting temperature determine Cu-pillar/Sn-Ag bump joint morphology during flip chip bonding processes. Therefore, it is important to optimize the curing properties and viscosity of NCFs at the solder melting temperature of $221^\circ C$.
In chapter 2, the effect of viscosity and hardening properties of NCFs on Cu-pillar / Sn-Ag solder bump joints on solder joint morphology was studied. The shape of the solder joint was observed by examining the shape change of the solder joint according to the flip chip bonding temperature. In addition, the shape of the solder joint was observed by changing the viscosity of the NCFs according to the silica filler content of the NCFs. In this process, the mechanisms and conditions for the formation of traps and concave-shaped solder joints of NCFs were investigated. Finally, the viscosity approximation was used to derive the change in the hardness and viscosity of NCFs during the flip chip bonding process, and the conditions in which NCFs trap and concave shape solder joints were generated.
In chapter 3, the effect of the viscosity and hardening properties of NCFs on solder bump flip chip joints on solder joint morphology was studied. By controlling the flip chip bonding time, the shape change of the solder joint according to the flip chip bonding temperature was observed to investigate the formation mechanism of the solder bump flip chip joint. And in this study, the degree of cure and Viscosity approximation were derived to derive the curing and viscosity values of NCFs that change within a short bonding time within 5 seconds. Did. Finally, the curing conditions and viscosity conditions of NCFs that generate concave shape solder joints were investigated.
In chapter 4, reliability results of solder joint geometry were evaluated at Cu-pillar / Sn-Ag solder bump joint and solder bump flip chip joint. In addition, the effects of thermo-mechanical properties of NCFs and the shape of solder joints on thermal cycle reliability were compared and analyzed, and what was the dominant factor.
최근, 모바일 제품 시장이 빠르게 성장함에 따라 고속 및 소형 전자 장치가 요구되고있다. 이러한 이유로, 전자 패키징 산업에서 3D-TSV (3D-Through Silicon Via) 및 초 미세 피치 상호 연결 기술이 빠르게 개발되었다. $30 \mu m$ 미만의 미세 피치 Cu 필러 / Sn-Ag 마이크로 범프 상호 연결을 신뢰성있게 확보하기 위해, 미리 도포 된 언더필 재료의 비전 도성 필름 (NCF)이 조사되었다. 초 미세 피치 Cu- 필러 / Sn-Ag 범프를 사용하는 플립 칩 본딩 프로세스의 경우 플럭스 적용, 솔더 리플 로우 및 언더필 디스 펜싱 프로세스와 같은 여러 처리 단계가 있다. 그러나, 종래의 언더필 재료 및 프로세스는 모세관 유동의 제한으로 인한 상호 접속 사이의 공극 및 상호 접속 부식을 야기하는 플럭스 잔류 물과 같은 몇 가지 문제점을 갖는다. 그러나, NCF는 공극이없는 언더필 기능을 달성 할 수 있고 플럭스 잔류물이 없고, NCF에 포함 된 플럭스 기능으로 인해 처리 단계가 감소하고 비용이 적게 든다는 이점도 있다. 플립 칩 본딩 법에 의해 안정적인 Cu- 필러 / Sn-Ag 범프 조인트를 실현하기 위해서는 NCF 본딩 공정 동안 솔더 및 NCF 수지의 거동을 조사 할 필요가 있다. 특히, 플립 칩 본딩 프로세스 동안 NCF 수지가 솔더 조인트에 포획 될 수 있다. 또한, 솔더와 PCB 금속 패드 사이의 야금 결합 영역에서 높은 응력 집중 영역이 될 수있는 오목한 형태의 솔더 범프 조인트. 결국, 불량한 Cu- 필러 / Sn-Ag 범프 조인트 형태는 신뢰성 테스트 중에 균열이 시작되고 조기 고장이 발생할 수 있다. 플립 칩 본딩 공정 동안 정밀한 NCF 수지 흐름 및 솔더 조인트 형태를 제어하려면 NCF의 경화 특성 및 점도를 연구해야한다. 특히, 솔더 용융 온도에서의 NCF의 재료 특성은 플립 칩 본딩 프로세스 동안 Cu- 필러 / Sn-Ag 범프 조인트 형태를 결정한다. $따라서 221 ^\circ C$의 솔더 용융 온도에서 NCF의 경화 특성과 점도를 최적화하는 것이 중요하다.
