Diemat, Inc. | Advances in Thermoplastic Adhesive Technology for High Power and Reworkability Applications

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ADVANCES IN THERMOPLASTIC ADHESIVE TECHNOLOGY FOR HIGH POWER AND REWORKABILITY APPLICATIONS

ABSTRACT

Today's emerging markets in the electronic packaging industry require some unique properties in adhesives, especially in die attach applications. In multichip module (MCM) applications, for example, the low temperature reworkability of die bonds is of primary importance, particularly if known good die (KGD) are not employed. Large area die on organic substrates, which is key to the more portable, high power computers, requires a very compliant adhesive to absorb the high mismatch in expansions. Other requirements for an adhesive in today's demanding applications include good rheology for dispensing or stenciling, fast and low temperature cures, high thermal/electrical conductivity, and a low modulus of elasticity, for low-stress component attachment.

More recently, the emerging higher density, higher frequency, higher power active devices are putting increasingly difficult demands on device packaging. Substrate materials with high thermal conductivities are replacing the traditional ceramics in hermetic, high power packages. Thermally enhanced plastic molded and laminate packages more frequently feature heat sinks embedded in the package or a metal base for direct attachment of the power devices. This increased use of highly conductive substrates makes the die attach material a critical element in the heat flow path.

This paper describes the development of a novel reworkable thermoplastic adhesive paste with thermal conductivities as high as 40 W/mK, an order of magnitude higher than traditional Ag epoxies with a typical thermal conductivity of 3 W/mK. The key material variables in a silver-loaded organic die attach are isolated and studied for their impact on thermal conductivity. These variables include the polymer type, shape and size of the filler, and the volume fraction of filler. The relationship between bulk electrical and thermal conductivities was also demonstrated with over 100 data points of thermal conductivities. A summary of the properties of the new thermally enhanced thermoplastic adhesive is compared with other material technologies.

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