고종횡비 범프 형성을 위한 리버스 옵셋용 무연 솔더 페이스트 제조에 관한 연구

Abstract

Recently, there are many methods of forming bumps in flip chip bond packaging such as evaporation, electroplating, screen printing, solder ball jetting super-juffit, stud. But because I/O (in put/out put) bump is required a miniaturization, high density and uniformity, a need about improved technology is being requested. A reverse offset printing have received much attention as demands for fine patterning have increased in the field of printed electronics. The reverse offset printing that can facilitate fine patterns for integration and miniaturization of electronic devices is suitable for forming fine solder bumps. The advantage of reverse offset printing is the control of uniform thickness. The solder bump printing for flip chip packaging can be a promising application field of printed electronics, if the reverse offset printing which enable uniform and fine patterning is adapted. However, the solder bump printing with high aspect ratio is a challenging goal in reverse offset printing, which definitely hinges on the control of rheological characteristics of paste. In this study, we developed SnAgCu solder pastes of reverse offset type. The viscosity, Thixotropy Index, G' (storage modulus), G" (loss modulus) of paste were evaluated with a rheometer and analyzed their effects on the printability and the formation of thick film by printing. As a result, the paste with high Thixotropy Index and outstanding recovery could form the high aspect ratio of solder bumps in reverse offset printing. In addition, electrical performance by reflow process and possibility of device were evaluated.