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.

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.

Abstract: Lead-free solder compositions suitable for joining electronic devices to printed wiring boards, which comprises by weight 0.2 to 0.9% copper, 0.006 to 0.07% nickel, 0.03 to 0.08% bismuth, less than 0.5% silver, less than 0.010% phosphorus, and a balance of tin and inevitable impurities. A solder composition embodying this invention finds particular application in automated wave-soldering machines where conventional lead-free solders dissolve excessive copper from printed wiring circuitry and component terminations.

Abstract: Method for controlling the deposition of solder on a heat spreader or heat sink is disclosed. The method comprises applying an attaching flux and finishing flux to a heat spreader, placing a preform thereon and subjecting the same to reflow conditions. The finishing flux is applied to solubilize the normally insoluble corrosive residues that would occur when the attaching flux is subjected to reflow conditions with the preform and heat spreader. Alternatively, the attaching flux may be applied to the preform and heat spreader before undergoing reverse reflow conditions and then the finishing flux is applied to the solder deposit and heat spreader and the same subjected to second reflow conditions. After each method, the residues left from the attaching flux which are solubilized by the finishing flux, are cleaned by washing with a typical solvent. The solder deposit can be optionally flattened before coupling with a die.

Abstract: Method for controlling the deposition of solder on a base metal or substrate is disclosed. The method comprises applying an attaching flux and finishing flux to a substrate, placing a preform thereon and subjecting the same to reflow conditions. The finishing flux is applied to solubilize the normally insoluble corrosive residues that would occur when the attaching flux is subjected to reflow conditions with the preform and substrate. Alternatively, the attaching flux may be applied to the preform and substrate before undergoing reverse reflow conditions and then the finishing flux is applied to the solder deposit and substrate and the same subjected to second reflow conditions. After each method, the residues left from the attaching flux which are solubilized by the finishing flux, are cleaned by washing with a typical solvent.