A thin, flat plate integrated circuit of 5 mm thickness is cooled on its upper surface by a dielectric liquid. The heat dissipation rate from the chip is 20,000 W/m2 and with the coolant flow at a free stream temperature of T?,l =250C, the convective heat transfer coefficient between the chip surface and the liquid is 1000 W/(m2 K). On the lower surface, the chip is attached to a circuit board, where the thermal contact resistance between the chip and the board is 10-4 m2.K/W. The thermal conductivity of board material is 1.0 W/m. K, and its other surface ( away from the chip) is exposed to ambient air at T?,a =200C where it is cooled by natural convection with the heat transfer coefficient of 30 W/(m2 K). (a) Determine the chip surface temperature under steady state condition for the

Question

described conditions. (b) If the maximum chip temperature is not to exceed 750C, determine maximum allowable heat flux hat is generated by the chip. (c) A colleague suggests that in order to improve the cooling, you use a high conductivity bonding base at chip-board interface that would reduce the thermal contact resistance at the interface to 10-5 m2.K/W. Determine the consequent increase in the chip heat flux that can be sustained.



GIVEN



FIND

(a) Chip surface temperature under steady state condition

(b) Maximum allowable heat flux generated by the chip

(c) Consequent increase in chip heat flux if high conductivity bonding is used.

ASSUMPTIONS

Steady state conditions prevail

The thermal conductivity of the wall (k) is constant

One dimensional conduction

Negligible radiation and thermal resistance between chip surface and the liquid.

SKETCH

The thermal circuit of problem is given by

Answer 1

(a) A heat balance in the above problem gives