Mechanical Product Design & Development Partner

Heat Sink Selection Process

With increase in heat dissipation rate and reduction in overall form factor, thermal management of electronics devices is becoming very important part of electronics product design.

Electronics chip/IC/processor  performance, reliability and life are inversely proportional to the its temperature (higher the temperature lower will be the product life). By performing product thermal analysis in initial stage of product design you can save cost and product design life-cycle time can be reduced.

Heat Sinks are required to ensure the proper operation and long term reliability of heat dissipating components. Heat-sinks  provide a means to dissipate the power into the surrounding ambient air and maintain a safe operating temperature.

Heat transfer rate from solid part to air is generally less. Heat sink is used to increase the heat transfer rate by increasing the surface area that is in direct contact with the air/coolant. This allows more heat to be dissipated and/or lowers the device operating temperature. Purpose of a heat sink is to maintain the device temperature below the maximum allowable temperature.

Performance of a heat sink is determined by value of thermal resistance of the heat sink. Higher the value of heat-sink thermal resistance, lower will be the rate of heat dissipation from heat sink to outer environment.

Selection of Heat-Sink For Electronics Chip

First step in the selection of heat sink is find the required value of Heat sink thermal resistance. To calculate heat sink thermal resistance: value of product working temperature, environmental temperature and rate of heat dissipation from electronics chip need to be determined.

Below you can see the thermal circuit of an electronics chip over the PCB and heat sink is thermally attached with the chip  using thermal interface material.

Thermal Circuit

Rja (Total Thermal Resistance) = Thermal Resistance From Junction to Air

Rjc = Thermal Resistance from junction to chip

Rch (Thermal resistance of interface material)= Thermal Resistance from chip to heat sink

Rha = Thermal resistance from heat sink to air

Tj = Junction Temperature

Ta = Ambient air temperature

Q = Maximum Heat dissipated by chip

With the known value of maximum environmental temperature, maximum designed heat dissipation by chip (Q), Thermal resistance of chip & thermal interface material, value of thermal resistance of heat sink can be determined.

After getting the value of the heat sink thermal resistance, Heat sink can be customised or selected in required size and material.


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