多层柔性衬底电路板的低成本丝网印刷

当大批量生产多层聚合物基厚膜电路板时需要低成本的印刷技术.对于有超过6层导电层且不平滑的表面来说,丝网印刷是一个便宜、便捷的选择.为了研究丝网印刷技术的可行性,本研究在不同衬底材料的表面,如聚碳酸酯(PC)、聚酯(PET)、聚酰亚胺(PI)和液晶聚合物(LCP),使用同样的印刷分辨率,常规的厚膜网版印刷,通过丝网的网孔在衬底上形成精细图形.最后,研究在双层PI衬底(拥有2层导体层,在导体层的两侧有1层绝缘层覆盖板基孔)上的印刷.丝网印刷的导体材料是银基纳米颗粒油墨,介质层是聚酰亚胺基材料.许多变量是妨碍这种经济适用技术大规模生产应用的影响因素.例如,如果固化温度超过200℃,聚酰亚胺基板的稳定性就成为大问题.在本实验中,如果印刷面积小,层与层之间的对齐公差是允许的.然而,在印刷进行一段时间后,层与层之间的平整度会变差.测试用纳米粒子油墨是一种很好的导电系统,但是,当固化温度从230℃降低到200℃时,生产效率会受到极大影响.另一种实现多层结构的方法是层压法.本研究选择PET和PC层,重点是处理沉积胶层的PET层和片材的复合过程.多层结构中的板基孔和导线通过常规厚膜网印解决.先打孔,然后采用厚膜网印填补,最后印刷表面.层与层之间的黏合精度和对准精度<±15μm.

Low Cost Printed Flexible Multilayer Substrates

For high-volume products, such as mobile terminals, low cost techniques for multilayer polymer-based thick film wiring board manufacturing are needed. Screen-printing is a cost efficient technology candidate to build up approximately 6 conductor layers on both sides of a flexible substrate, for example. In order to experimentally evaluate the feasibility of screen-printing technique, the printing resolution was tested on different substrate materials, such as, polycarbonate (PC), polyethylene terephtalate (PET), polyimide (PI) and liquid crystal polymer (LCP), Conventional screen printed polymer thick film pastes were characterized on polymer substrates to form multilayer fine-line patterning and through-hole vias.The final demonstrator was a double-sided PI substrate having two conductor layers separated by dielectric layers on both sides of the substrate and through substrate vias. The screen printed conductor material was an Ag-based nano particle ink and the dielectric layer was a polyimide-based material.Several challenges were identified that might hinder the applicability of the technology for mass-production. The stability of the polyimide substrate is a problem if the curing temperature of the printed materials is above 200"C. Layer-to-layer alignment tolerances are feasible if the printed area is small, 5"x5", in our case. The flatness of the substrate, however,is not very good after printing several layers on each other. The tested nano particle ink is a promising conductor system; however, lowering of the curing temperature from 230℃ below 200℃ would have a major impact on production friendliness. Another way to realise multilayer structures is to utilise lamination methods. In this study PET and PC sheets were also used. The focus in the processing development was on the deposition of adhesive layer over the PET sheet and the lamination process. Vias and conductors needed in multilayer structures were realised by utilising conventional thick-film processes. Viaswere punched and then filled by stencil printing and conductors were screen-printed. The lamination parameters were optimised for each material system. Good adhesion was achieved and the alignment accuracy between the layers was <± 15μm.