problem4-74

# problem4-74 - PROBLEM 4.74 KNOWN Silicon chip mounted in a...

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PROBLEM 4.74 KNOWN: Silicon chip mounted in a dielectric substrate. One surface of system is convectively ooled while the remaining surfaces are well insulated. c F IND: Whether maximum temperature in chip will exceed 85 ° C. SCHEMATIC: ASSUMPTIONS: (1) Steady-state conditions, (2) Two-dimensional conduction, (3) Negligible contact resistance between chip and substrate, (4) Upper surface experiences uniform convection oefficient, (5) Other surfaces are perfectly insulated. c ANALYSIS: Performing an energy balance on the chip assuming it is perfectly insulated from the substrate, the maximum temperature occurring at the interface with the dielectric substrate will be, ccording to Eqs. 3.43 and 3.46, a ( ) ( ) ( ) ( ) 7 3 7 3 2 2 max 2 c q H/4 q H/4 10 W/m 0.003 m 10 W/m 0.003 m T T 20 C 80.9 C. 2k h 2 50 W/m K 500 W/m K = + + = + + = × D D ± ± Since T max < 85 ° C for the assumed situation, for the actual two-dimensional situation with the onducting dielectric substrate, the maximum temperature should be less than 80 ° C. c Using the suggested grid spacing of 3 mm, construct the nodal network and write the finite-difference equation for each of the nodes taking advantage of symmetry of the system. Note that we have chosen to not locate nodes on

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