Abstract: An improved thermal interface between an integrated circuit chip and a heat sink comprises a copper grid embedded in a layer of a solder material that has a fusion temperature higher than the maximum operating temperature of the semiconductor chip, and bonds to the semiconductor chip and the heat sink when heated to the fusion temperature of the solder material in the presence of a soldering flux. The copper grid has high thermal conductivity so that the amount of solder material needed for an efficient thermal interface is reduced and solder materials with less expensive components may be used. The copper grid also tends to mitigate local hot spots by enhancing lateral heat transfer, and inhibits solder spreading during formation of the thermal interface.

Abstract: Performance of a flux in a soldering process is assessed by monitoring the activity of the flux via its electrical conductance measured using a probe having interdigitated metallic traces and a temperature sensor. The measured conductance-temperature time profile provides information useful for selecting a suitable flux formulation and soldering conditions for a given application, for determining the cause of soldering process problems, and for developing improved flux formulations.