Influence of Cu powders on the wettability and mechanical properties of solderable epoxy composites

A Cu powder-filled solderable epoxy composite (Cu-SEC), in which Cu powders were applied as reinforcement materials, was developed to enhance the mechanical properties of solderable epoxy composite (SEC) joints. To clarify the influence of the Cu powder content on the wettability and mechanical properties of SECs, four types of Cu-SECs with different Cu powder concentrations in the metal fillers (from 0 to 20 vol%) were synthesized, and two types of wetting tests (i.e., planar and line metallization wetting tests), and microhardness tests were conducted. The Cu-SECs for which the Cu powders content less than a certain value (10 vol%) exhibited proper wettability with a reasonable wetting angle and spreading shapes to the Cu metallization in a planar metallization wetting test, and showed excellent selective wetting properties with a uniform and stable selectively wetted conductive path morphologies in a line metallization wetting test. The microhardness of the Cu-SEC joints increased with the increasing Cu powder content due to the strengthening effect of the uniformly distributed Cu powders within the wetted low-melting-point solder (LMS) filler. However, the wettability and selective wetting properties of the molten LMS deteriorated as the Cu powder content increased to more than a certain value because of the partially increased viscosity and reduced fluidity of the fused LMS.