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Copper MetGraf™ Composite Cores for PCB Thermal Control
Keywords: CTE-controlled, Substrates, Thermal control
Printed circuit boards (PCBs) have become very dense with smaller via sizes, traces, and spaces to support shrinking semiconductor device sizes. In addition to the shrinkage in part geometries, semiconductors need to operate at higher power levels to support faster data rates, increasing overall power dissipation and heat flux. Additionally, silicon carbide and gallium nitride semiconductors require different CTE (coefficient of thermal expansion) values than silicon devices for certain packaging materials. Increased power and heat flux affects device performance and PCB reliability. This presentation reviews process development goals and results of a development program demonstrating manufacturing improvements required to produce thin copper-graphite composite sheets in thicknesses not previously available. Standard PCB manufacturing facilities require panel sizes of 18” x 24” and very minimal thicknesses for materials which may be candidates for use as thermal control cores; copper composite materials have not previously been available in either large panel sizes or the specified thicknesses which meet such requirements. This presentation outlines cooperative development by two suppliers, working with a large potential OEM customer, to improve manufacturing processes to enable production of 12” x 18” panel sizes in the requisite thicknesses to match PCB manufacturing requirements. This presentation will include data for manufacturing requirements needed to develop CTE-controlled multilayer interconnect circuit cards with high density and able to handle increased thermal loads. These improvements enabled production of copper-graphite composite sheets between 0.010”-0.020” in thickness, with 320-680 micron electrolytic copper plating; these sheets have then been incorporated into the new multilayer PCBs, through a development partnership with TTM Technologies (Stafford CT USA). The goal for thermal control PCB development for both suppliers is product and process development, commercialization, and transition into multilayer PCBs designed for missile, aerospace, defense, and high-reliability PCB assemblies where geometry shrinkage, increased power, and increased heat flux demand improvements in PCB capabilities. Current process and packaging requirements for applications will be described, the result of the first phase of this development program. Cost reduction and additional thermal performance testing are the focus for the second phase of the development program, which is now in process.
Robert A. Hay, Vice President, Business Development
Metal Matrix Cast Composites, LLC
Waltham, MA
USA


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