EPOXY FLUX MATERIAL AND PROCESS FOR ENHANCING ELECTRICAL INTERCONNECTIONS

摘要

There are two main drivers that are causing electronic device manufacturers to look into methods other than solder paste to form electrical interconnection on area array devices. The first driver is the move to smaller and smaller pitch. On hand-held devices it is very common to see 0.5mm and 0.4mm pitch CSPs, with 0.3mm pitch WLCSPs becoming more prevalent. While there are solder paste materials that can be used to print these fine features, these materials (and the accompanying stencil thickness) are not always suitable for the other components on the assembly. The other driver is the stacking of CSPs. Package on package (PoP) process has been well studied and documented over the past few years [3-5], here once again, printing solder paste for the second level interconnect is not practical. In both cases there have been studies looking at tacky flux and/or dipping solder paste in order to form the solder joints. Both of these methods can be used to produce good solder joints, but due to the end nature of these devices these solder joints typically need to be enhanced against drop and vibration by the use of an additional underfill process. In this paper we outline the material and the processes used to produce devices with a novel epoxy based fluxing system. This material provides the wetting and activity to create a solder joint as well as providing some reliability enhancement due to the epoxy adhesive portion without the use of harmful solvents. In addition, we will also discuss the process capability of this material with respect to repeatability.