Experimental investigation was performed to find the pressue drop characteristics of parallel plate channels where model packages of various sizes are mounted. For packages without fins, the ratio of channel height to package height is 1.3 to 2.7, and for packages with fins it is 1.2 to 2.0. The ratio of placement pitch to package height is 1.8 to 5.6 for packages without fins, and for packages with fins it is 2.1 to 3.4. A new flow model is proposed which incorporates the three-dimensional nature of wakes behind the packages. The predicted values of pressure drop based on this model for packages with and without fins correlate the experimental results within ±20−30%.