Thermal interface material is a very important element of the BGA solution. Small die sizes and both “exposed” and “lidded” package types, combined with relatively high component power, makes standard double-sided thermal adhesive tape ineffective. Overall thermal conductivity across the thermal interface is determined by a combination of factors. The bulk conductivity of the material is dependent on the chemical composition. Thermal tapes are elastomers with conductive particles added in suspension. The durometer or “hardness” of the material can effect its conformance between the component and heat sink base. Manufacturers sometimes offer various thicknesses to combat this issue. Thicker material will have better compliance, however the added thickness will reduce the thermal conductivity. The final choice is usually the thinnest material that provides the best percentage of contact area. The percentage of contact area is also effected by the surface contours (concave and/or convex). The surface roughness on a micro scale can also be a concern as smooth and shiny doesn’t always mean flat.