INTRODUCTION 2 

The function of a heat sink is to increase the surface area available for the heat transfer or heat from a component or device thereby increasing the amount of heat that can be dissipated.

The following products/services are available:

1 A range of Standard heat sinks and accessories
which permit optimum flexibility in the design of Electrical and Electronic equipment requiring heatsink applications.

2 Custom designed heatsink's.
We have facilities available which enable us to provide design and manufacture of custom and specialised Heat Sinks to your requirements.

HEAT SINK SELECTION

The main factors to consider when selecting a Heat Sink are:-

1 Geometry

2 Thermal Resistance

3 Cost

Defining the necessary Heat Sink performance.
In order to calculate the maximum acceptable thermal resistance for the Heat Sink so that the device being cooled does not overheat it is first necessary to define the thermal parameters under which it is to operate.

The basic equation for thermal equilibrium is:-

  Temperature difference
across the system
Power dissipated =
  Sum of all the thermal
resistance in the heat
flow path
EQUATION 1
Thus PD = Tj - Ta
   
    Øjc + Øcs + Øsa
Where PD  = Power dissipation (W)
  Tj    =  Max allowable junction temp (°C)
(specified by device manufacturer)
  Ta   = Ambient Tempreature (°C)
  Øjc  = Thermal resistance junction to case (°C/W)
(Specified by device manufacturer)
  Øcs = Thermal resistance, case to Heat Sink (°C/W)
  Øsa = Thermal resistance, Heat Sinks to ambient air (°C/W)
The maximum value for thermal resistance heat sink to air (sa) is usually determined by rearranging equation 1 to the following:
EQUATION 2
Øsa = Tj - Ta  
- (Øjc + Øcs)
  PD  

The result of the above equation provides a thermal resistance value which must be equalled or bettered by the Heat Sink selected.
EXAMPLE
A semi-conductor device is to be operated with its junction temperature not exceeding 80ºC whilst dissipating 16 watts to ambient air at a temperature of40ºC. The thermal resistance, junction to case, is specified by the manufacturer as 1.25ºC/W and the thermal resistance, case to sink (using an insulating washer and thermally conductive compound) is taken as 0.50ºC/W.

Øsa = 80 - 40 - (1.25 + 0.50)
  16
        = 0.75°C / W  

The heat sink therefore must have a thermal resistance which does not exceed 0.75ºC/W.
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