1 memory chips are flip chip mounted on the back side of a printed wiring board consisting of a copper plane (5 m m thick) sandwiched between two layers of FR4 (see Figure 2.1). Each of the components dissipates a total power of 1 W. The face area of the PWB is 10 cm 2 and the back side is insulated. The three layers making up the composite structure are each 0.1 mm thick. Heat is removed from the exposed face of the PWB via natural convection to ambient air at 25 o C.(Suppose there are 10 chips mounted on the PWB. 6 showing in the following figure though) 1) Draw the thermal circuit network; 2) Calculate the average temperature of the back surface of the printed wiring board. FIGURE 2.1 Populated PWB cooled by natural convection TABLE 6.4 Thermal properties of commonly used electronics packaging materials. TABLE 6.5 Representative values of heat transfer coefficient [11].