Consider an electronic equipment that has ICs with a maximum junction temperatur
ID: 2995365 • Letter: C
Question
Consider an electronic equipment that has ICs with a maximum junction temperature rating of 125 deg C. The maximum circuit board temperature rise above the outside room ambient is measured to be 35 deg C.
The heat dissipation and the thermal impedance of some of the representative ICs is given below:
IC #1 0.5 W 50 deg C / W
What is the maximum allowable circuit board temperature? And what is the maximum allowable room ambient air temperature that the equipment can operate in?
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Consider a six-layer glass epoxy printed wiring board (PWB), 2mm thick and 10 cm wide.
Calculate the thermal resistance along the plane of the PWB over a length of one cm, assuming the PWB has no copper planes.
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Consider a double-sided PWB, 1.5mm thick.
Calculate the thermal resistance through the thickness of the PWB per square cm of PC board area.
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Calculate the thermal resistance per square cm through the thickness of a glass epoxy board, 1.0mm thick. We would like to reduce this resistance by a factor of 5. This can be achieved by drilling holes and plating them with 1 oz copper. If the hole diameter is 0.25mm, how many holes per square cm need to be drilled?
Explanation / Answer
The effects of EMP on ICs include malfunctions and loss of data, thermal runaway, gate-insulator breakdown, avalanche breakdown, tunnel breakdown, and metalization burnout. The energy required may be provided by the surge itself and/or by other sources (such as the power supply or storage capacitors). As successive generations of electronics pack ever more components into smaller spaces, this increasingly inhibits the ability of the circuit to conduct away the heat that results from the typically intense, short voltage and current flows generated by an EMP.
Tests with EMP simulators have shown that a very short pulse of about 10-7 Joule is sufficient to damage a microwave semiconductor diode, and roughly .05 J will damage an audio transistor, whereas 1 J would be required for vacuum tube damage [ref. 5, pp. 522