Experimental determination of the effect of printed circuit card conductivity on the thermal performance of surface mount electronic packages

Surface mount electronic packages, typically a few millimeters thick, are mounted directly and very close to printed circuit cards. Due to close proximity to the card, the overall thermal performance of the package depends on the thermal conductivity of the circuit cards. For characterizing the thermal performance of surface mount packages, SEMI Specification G42-88 specifies a FR4 card with one layer of circuitry in a fan-out pattern on the package side. To determine the effect of the circuit card conductivity on the thermal performance of surface mount packages, tests were done with a number of different types of packages on two types of cards. The packages were all 28 mm 208-leaded EIAJ/JEDEC type plastic with copper and alloy 42 leadframes, plastic with exposed heat spreader, and metal quad flat packs. One of the test card designs was similar to SEMI Specification card, with only one layer of circuitry in a fan-out pattern on the package side. The other card had two internal copper planes in addition to the fan-out pattern of circuitry on the package side. This paper describes the experimental procedure and discusses the thermal performance of these various surface mount packages on these two types of cards. The data shows that the thermal performance of plastic packages with alloy 42 leadframe is relatively insensitive to the amount of copper in the circuit card. On the other hand, the thermal performance of metal packages shows the most dependence on the amount of copper in the circuit cards