Free convective heat transfer for the wire-bonded and low powered QFN64b electronic device

The aim of this study is to quantify the natural convective heat transfer concerning the wire-bonded version of the Quad flat non-lead with 64 leads denoted as QFN64b. This active package generates during operation low powers corresponding to the partial operation of the electronic equipments. In this power range, the thermal state of such device is entirely different from that of the higher power conditions corresponding to normal operation. To size the low-powered QFN64b component while increasing its reliability, it is necessary to know the natural convective heat transfer coefficient. This is the main objective of the present survey which presents the details of this parameter in five specific areas of the assembly constituted by a Printed Circuit Board (PCB) on which is welded the active package. It generates a power varying between 0.01 W and 0.1 W by steps of 0.01 W and it may be inclined with respect to horizontal plane by an angle ranging from 0 to 90° corresponding to the horizontal and vertical position respectively, by steps of 15°. The average convective heat transfer is quantified by means of original correlations allowing its determination in any area of the considered assembly, according to the generated power and inclination angle. They allow better sizing of the QFN64b device which is widely used in the modern electronic assemblies for specific applications. They contribute to improve their reliability while saving energy.