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 performanc e, thinness, light weight, small size or high assembly density, and low cos t. Plastic packages are superior in terms of electrical performance and cos t whereas highly thermally conductive ceramic packages are superior in term s of thermal performance, weight, and size. However, these conventional pla stic or ceramic packages cannot simultaneously satisfy all the requirements . A new cavity-up plastic and ceramic laminated package (PCLP) has been dev eloped that not only has superior electrical and thermal characteristics si multaneously without a heat sink, but also a thin profile and small size an d is cost-effective. For example, frequency range applicable to the PCLP ex ceeds 500 MHz, the maximum power dissipation is 4 W under natural convectio n, and the thickness is less than 2 mm. The PCLP is composed of two substra tes: an electrically conductive plastic substrate and a thermally conductiv e 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 l ow dielectric loss. The ceramic substrate is cofired tungsten-metallized al uminum nitride (AlN). It has high thermal conductivity and its coefficient of thermal expansion (CTE) is close to that of silicon. The ALN substrate a lso supports mechanically both the FPC and the semiconductor chip. The pack age is made using simple processes: both FPC and AlN substrate are single i nsulation layers; interconnections technologies are simple, for example, sc reened bump interconnection and lamination; and a conventional pattern form ation is used, for example, screen printing. The measured electrical resist ance is 450 m Omega (line length = 14.7 mm, width = 50 mu m), which was abo ut 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.