具有铜—殷钢—铜结构的印制线路板

Printed Wiring Boards Constructed With Copper-Invar-Copper

使用无引线陶瓷芯片载体(LCCC)可以达到高密度封装。普通印制板(PWB)对于无引线陶瓷芯片载体不是满意的基板,因为热膨胀系数(TCE)不匹配能引起铅焊处开裂。解决这个问题的一个方法是把铜一殷钢—铜(CIC)粘到印制板上。铜—殷钢—铜减小了印制板的热膨胀系数,使它与陶瓷的热膨胀系数相匹配。除了起抑制膨胀作用外,铜—殷钢—铜也被用作电源板,或接地板,以及散热片。这个课题的任务是研制具有铜—殷钢—铜结构的多层印制板的生产工艺,支持洛克希德火箭和航天公司(LMSC)的计划。多层板具有以下生产特点:铜—殷钢—铜来自两个供应商,铜—殷钢—铜预先钻孔,聚酰亚胺和环氧树脂作为介质。铜—殷钢—铜或与金属化孔绝缘或与金属化孔(PTH)互联,铜—殷钢—铜表面处理或由生产厂家处理或由用户自己处理。还有,为了暴露出铜—殷钢—铜以便与热传导体接触,使用二氧化碳激光器把绝缘材料从印制板边缘除去。印制板试样必须经过MIL—P—55110标准浮焊试验,然后对金属化孔进行剖视。金相切片实验显示铜—殷钢—铜有良好的内层附着力以及对预钻孔有良好的树脂填充能力。殷钢在化学沉铜线中受化学物质腐蚀引起凹蚀。除了观察到殷钢界面有一些空隙外,铜—殷钢—铜的电镀附着力一般是合格的。改进后的工艺可以减少空隙数量。

High density packaging can he achieved by using leadless ceramic chip carriers (LCCCs). Conventional printed wiring boards (PWBs) are not satisfactory substrates for LCCCs because the mismatch in thermal coefficient of expansion (TCE) causes solder joints to crack. One solution to this problem is to bond copper-Invar-copper (CIC) to PWBs. The CIC reduces the TCE of the PWB to match that of the ceramic. In addition to acting as an expansion restrainer,CIC is also used as a power or ground plane and a heat sink. The objective of this project was to develop processes for fabricating multilayer PWBs constructed with CIC in support of LMSC programs. Multilayer boards were fabricated with the following characteristics;CIC from two vendors,pre—drilled holes in the CIC, poiyimide and epoxy for dielectrics, CIC isolated form or interconnected to piated-through holes (PTHs), and CIC surface-treated in-house and by the vendor. Also,dielectric was removed from the edges of PWBs using a carbon dioxide laser to expose the CIC for attachment of a heat transfer connector. PWB samples were subjected to the solder float test per MIL-P-55110 and then the PTHs were cross—sectioned. Examination of the microsections revealed that the CIC had good inner layer adhesion and good resin backfill in the pre-drilled holes. The Invar was attacked by the chemicals in the electroless line causing it to etch back. Plating adhesion to the CIC was generally acceptable except some voids were observed at the Invar interface. Process refinements can be made to reduce the number of voids.