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Mixed convection is a fundamentally significant heat transfer mechanism that occurs in a selection of industrial and technological applications. For example, it is of great interest to thermal designers in the field of electronic cooling. Given that its occurrence is frequent, there is a necessity to understand the physics of this fundamental mechanism at board level. Therefore, this paper is concerned with the development of optical measurement techniques for mixed convection, in order to try and improve the current understanding of why, where, and when mixed convection occurs. It is motivated both by a desire to gain an understanding the fundamental physics of mixed convection and to solve design problems in electronic cooling applications where mixed convection often occurs. It is focused on heated horizontal ribs, which are two dimensional approximation of a super ball grid array, mounted on a printed circuit board in cross-flow at a low Reynolds number, high Grashof numbers and at the Prandtl number for air. This paper describes two types of data from a series of experiments. Firstly, a physical description of the flow is discussed through interferometric images and Particle Image Velocimetry (PIV) streamlines with the objective of improving the understanding of mixed convection heat transfer from board mounted components. Secondly, explanation is given as to how the mean Nusselt number varies in terms of rib position and power input.