International Business Machines Corporation

Ping Kwong Seto

Michael A Gaynes

Amit Kumar Sarkhel

Thomas M Culnane

Hussain Shaukatullah

Bao-Tong Ma

Where an electrical connection is needed between an electric circuit on a substrate and a component with very finely spaced leads, pads are formed on the substrate at points where such connections to the circuit are to be made. A solder paste is deposited using a particular, described stencil having a thickness and apertures with specific tolerances. The component is positioned so that its leads to be attached are contiguous with corresponding pads, and the electrical connections are completed by reflowing the solder paste forming consistent and reliable electrical joints of solder alloy.

Method for producing circuit board assemblies using surface mount components with finely spaced leads

An aluminum or copper heat sink is attached to a ceramic cap or exposed semiconductor chip using flexible-epoxy to provide improved thermal performance. The aluminum may be coated by anodizing or chromate conversion or the copper may be coated with nickel. Such structures are especially useful for CQFP, CBGA, CCGA, CPGA, TBGA, PBGA, DCAM, MCM-L, single layer ceramic, and other chip carrier packages as well as for flip chip attachment to flexible or rigid organic circuit boards. These adhesive materials withstand thermal cycle tests of 0.degree. to 100.degree. C. for 1,500 cycles, -25.degree. to 125.degree. C. for 400 cycles, and -40.degree. to 140.degree. C. for 300 cycles; and withstand continuous exposure at 130.degree. C. for 1000 hours without loss of strength. Flexible-epoxies have a modulus of elasticity below 100,000 psi and a glass transition temperature below 250.degree. C., are much stronger than typical silicone adhesives, and do not contaminate the module or circuit board with silicone. The flexible epoxy may contain a material having a low coefficient of thermal expansion (CTE) in order to provide a CTE between that of the silicon die and the metal of the heat sink.

Apparatus for attaching heat sinks directly to chip carrier modules

An aluminum or copper heat sink is attached to a ceramic cap or exposed semiconductor chip using flexible-epoxy to provide improved thermal performance. The aluminum may be coated by anodizing or chromate conversion or the copper may be coated with nickel. Such structures are especilly useful for CQFP, CBGA, CCGA, CPGA, TBGA, PBGA, DCAM, MCM-L, single layer ceramic, and other chip carrier packages as well as for flip chip attachment to flexible or rigid organic circuit boards. These adhesive materials withstand thermal cycle tests of 0.degree. to 100.degree. C. for 1,500 cycles, -25.degree. to 125.degree. C. for 400 cycles, and -40.degree. to 140.degree. C. for 300 cycles; and withstand continuous exposure at 130.degree. C. for 1000 hours without loss of strength. Flexible-epoxies have a modulus of elasticity below 100,000 psi and a glass transition temperature below 25.degree. C., are much stronger than typical silicone adhesives, and do not contaminate the module or circuit board with silicone. The flexible epoxy may contain a material having a low coefficient of thermal expansion (CTE) in order to provide a CTE between that of the silicon die and the metal of the heat sink.

Chip carrier modules with heat sinks attached by flexible-epoxy

Method for producing circuit board assemblies using surface mount

Method for attaching heat sinks directly to chip carrier modules using

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Madison, AL, United States of America

Ping Kwong Seto