of copper or aluminum alloys or other suitable thermally conductive material fig4 illustrates the cross sectional shape of one of the raindrop shaped pin fins 30 wherein the general flow direction is indicted by a vertically oriented arrow the cross section of the pin fin has a large rounded end 35 with a first radius of r 1 at the flow upstream and a small rounded end 38 with a second radius r 2 at the flow downstream straight portions 39 a 39 b interconnect the two radii the distance between the radius center points for the first and second radii is denoted d in the figure and the total length or in vertical orientation of the heat sink the fin height is denoted h the heat sink 1 with the raindrop shaped pin fins is so designed as to minimize the wake at the tail of the fin and correspondingly to minimize the heat sink pressure drop it can be seen in fig4 that the primary difference between a raindrop shaped fin and an elliptical fin is the shape at the fin leading edge with respect to the cooling flow the raindrop shaped fin shown in fig4 has the first radius of r 1 along the fin axis the fin dimension changes sharply to the small second radius of r 2 this structure with one large and one small radius can significantly reduce the drag force generated at the tail of the fin and consequently reduce the pressure drop across the fin thus a raindrop shaped pin fin is characterized by three dimensions the leading first radius r 1 the trailing second radius r.