Abstract
The thermal resistance θ_<ja> of a plastic ball grid allay (P-BGA) mounted on a low thermal conductive PCB was measured in two different environments; a wind tunnel and an enclosure. The gap between the PCB and the bottom wall in the enclosure is 1 mm, and those in the wind tunnel are 1mm and 30mm. The measured θ_<ja> of the P-BGA in the enclosure indicated that it depended on the number of fans but did not depend on the location of the fans. The thermal resistance of P-BGA was 18.6℃/W with one fan active, 16.0℃/W with two fans active, and 14.7℃/W with three fans active. The measured upstream air velocity in the enclosure was 0.25〜0.3 m/s per fan. It was found by comparing θ_<ja> in the enclosure with that in the wind tunnel that the cooling effect in the enclosure was not equivalent to that for the gap of 1 mm in the wind tunnel, but to that for 30 mm.
