New epoxy resins for printed wiring board applications

Purpose - This paper seeks to give an overview of problems arising with the change to lead-free soldering and to give guidance on possible counter actions in the context of the chemical structure of the base material. Design/methodology/approach - The paper contains a number of correlations between different physical measurements and their impacts on real life processing conditions. The problem areas are highlighted and the corrective actions that need to be taken on the base materials are described. The impact of the choice of flame retardant on material properties is demonstrated. Findings - Results suggest that conventional resin systems seem to be still suitable for standard FR-4 applications with only a few reflow cycles. Higher thermally resistant products are necessary for more complex structures that require multiple reflow cycles. There are basically two ways to increase the thermal resistance. Replace dicyandiamide by a phenolic hardener or change to a bromine-free flame retardant. Both approaches are successful in raising the decomposition temperature, with the latter having the additional advantage of achieving better electrical performance and lower density. Originality/value - The value of the paper lies in its ability to provide guidance on the critical base material properties. It describes the change in physical properties that laminates will see when moving up in temperature to facilitate lead-free soldering. Selection criteria for base materials are given in order to neutralize the impact of the higher temperature.