Design and characteristics of a newly developed cavity-up plastic and ceramic laminated thin BGA package

The key requirements for a package are high electric and thermal performance, thinness, light weight, small size or high assembly density, and low cost. Plastic packages are superior in terms of electrical performance and cost whereas highly thermally conductive ceramic packages are superior in terms of thermal performance, weight, and size. However, these conventional plastic or ceramic packages cannot simultaneously satisfy all the requirements. A new cavity-up plastic and ceramic laminated package (PCLP) has been developed that not only has superior electrical and thermal characteristics simultaneously without a heat sink, but also a thin profile and small size and is cost-effective. For example, frequency range applicable to the PCLP exceeds 500 MHz, the maximum power dissipation is 4 W under natural convection, and the thickness is less than 2 mm. The PCLP is composed of two substrates: an electrically conductive plastic substrate and a thermally conductive ceramic substrate. The plastic substrate, made of liquid crystal polymer (LCP) and copper, forms a flexible printed circuit (FPC). LCP is a suitable material since it has low water absorption, low dielectric constant, and low dielectric loss. The ceramic substrate is cofired tungsten-metallized aluminum nitride (AlN). It has high thermal conductivity and its coefficient of thermal expansion (CTE) is close to that of silicon. The ALN substrate also supports mechanically both the FPC and the semiconductor chip. The package is made using simple processes: both FPC and AlN substrate are single insulation layers; interconnections technologies are simple, for example, screened bump interconnection and lamination; and a conventional pattern formation is used, for example, screen printing. The measured electrical resistance is 450 m Omega (line length = 14.7 mm, width = 50 mu m), which was about 1/10 of that for a simple ceramic cofired package of the same dimensions with a tungsten conductor. The measured thermal resistance is 10.8 degrees C/W under natural convection without a heatsink. In this paper the PCLP's design concept. Configuration and performance characteristics are reported.