We investigate the effect of the modification of cellulose acetate propionate as an organic vehicle for silver paste on solar cell efficiency. For the modification of cellulose acetate propionate, poly(ethylene glycol) is introduced to the hydroxyl groups of a cellulose acetate propionate backbone via esterification reaction. The chemical structure and composition of poly(ethylene glycol) functionalized cellulose acetate propionate is characterized by Attenuated total reflectance Fourier transform infrared, 1H nuclear magnetic resonance, differential scanning calorimetry and thermogravimetric analysis. Due to the effect of structural change for poly(ethylene glycol) functionalized cellulose acetate propionate on the viscosity of silver paste, the solar cell efficiency increases from 18.524% to 18.652 %. In addition, when ethylene carbonate, which has a structure similar to poly(ethylene glycol), is introduced to cellulose acetate propionate via ring opening polymerization, we find that the efficiency of the solar cell increases from 18.524% to 18.622%.

We used an etching process to control the line-width of screen printed Ag paste patterns. Ag paste was printed on anodized Al substrate to produce a high power LED. In general, Ag paste spreads or diffuses on anodized Al substrate in the process of screen printing; therefore, the line-width of the printed Ag paste pattern increases in contrast with the ideal line-width of the pattern. Smudges of Ag paste on anodized Al substrate were removed by neutral etching process without surface damage of the anodized Al substrate. Accordingly, the line-width of the printed Ag paste pattern was controlled as close as possible to the ideal line-width. When the etched Ag paste pattern was used as a seed layer for electroless Ni plating, the line width of the plated Ni film was similar to the line-width of the etched Ag paste pattern. Finally, in pattern formation by Ag paste screen printing, we found that the accuracy of the line-width of the pattern can be effectively improved by using an etching process before electroless Ni plating.

최근 전자 디스플레이에서 각광받고 있는 터치스크린은 급속한 정보화 사회 속에서 비약적인 발전을 거듭하고 있다. 터치패널은 키보드나 마우스와 같은 입력장치를 사용하지 않고, 화면에 나타난 문자나 특정 위치에 사람의 손 또는 물체가 닿으면 그 위치를 파악하여 특정한 기능을 처리하도록 한 패널이다. 이러한 터치스크린에서의 터치패널용 Ag 페이스트는 대부분 열 경화형 페이스트를 사용하고 있다. 이러한 열 경화형 페이스트는 건조공정에 따른 열에너지 소비와 유기용제에 따른 작업환경 개선의 문제점을 가지고 있다. 본 연구에서는 기존에 사용되는 열 경화형 Ag 페이스트가 아닌 친환경적이고 경제적인 UV 경화형 페이스트를 제조하였다. 현재 시판중인 열 경화형 바인더 대신 UV 경화형 올리고머를 사용하였고 유동특성을 부여하기 위해 단관능 모노머를 첨가하여 전도성 Ag paste 패턴형성을 할 수 있었다. 그 결과 열 경화형 Ag 페이스트만큼 접착력, 경도, 내성 등이 우수하였으며 미세패턴의 재현이 가능했으며 스크린 인쇄를 이용한 친환경적인 패터닝 기술로서의 가능성을 확인할 수 있었다.

The current study examined Ag migration from the Ag paste bump in the SABiT technology-applied PCB. A series of experiments were performed to measure the existence/non-existence of Ag in the insulating prepreg region. The average grain size of Ag paste was 30 nm according to X-ray diffraction (XRD) measurement. Conventional XRD showed limitations in finding a small amount of Ag in the prepreg region. The surface morphology and cross section view in the Cu line-Ag paste bump-Cu line structure were observed using a field emission scanning electron microscope (FE-SEM). The amount of Ag as a function of distance from the edge of Ag paste bump was obtained by FE-SEM with energy dispersive spectroscopy (EDS). We used an electron probe micro analyzer (EPMA) to improve the detecting resolution of Ag content and achieved the Ag distribution function as a function of the distance from the edge of the Ag paste bump. The same method with EPMA was applied for Cu filled via instead of Ag paste bump. We compared the distribution function of Ag and Cu, obtained from EPMA, and concluded that there was no considerable Ag migration effect for the SABiT technology-applied printed circuit board (PCB).

본 실험에서는 스크린 인쇄 및 그라비어 인쇄 등 direct printing에 사용가능한 UV 경화형 Ag paste를 제조하였다. Ag 분말은 표면이 극성이므로 분말끼리의 응집력이 강하고, 비극성인 UV경화형 수지와의 친화성이 좋지 못해, 분산성이 좋지 못한 paste를 얻을 수 있다. 따라서 본 실험에서는 Ag 분말 표면을 올레인산 또는 도데칸 티올로 코팅함으로써, Ag 분말 표면을 비극성화하여 UV 경화형 수지와의 친화성을 높이는 것으로 Ag 분말 일차 입경 수준의 paste 분산특성을 얻었다. 제조된 Ag paste의 레올로지 특성을 검토한 결과, 표면 처리된 Ag paste의 경우, 낮은 전단 영역에서 형성된 Ag 분말과 바인더 수지와의 응집구조에 의해 shear thinning 거동을 나타내며, 높은 저장 탄성율을 갖게 되었다. UV 경화한 Ag 도막의 전기적 특성을 측정한 결과, UV 경화가 진행될수록 Ag 분말사이의 접촉이 증가하여 비저항이 감소하였고, 1500mJ/㎠에서는 10-3Ω․㎝의 비저항을 갖는 Ag 도막을 얻을 수 있었다.

Conductive pastes consist of conductive fillers( Au, Ag, Ni, Cu etc.), organic binders, solvents and additives. Meanwhile, there are some metal powders such as copper, nickel etc that are used for pastes which have serious surface corrosion problems. This problem leads to change of the color and decrease in conductivity and affect storage stability of conductive pastes. By using silane coupling agent and dispersion agent, we can ensure both the corrosion stability and long term storage stability, and enhance the high performance electrical and mechanical properties of EMI shielding silicone sealant.