Heatsink Design-ZZcooler Electronics Company

General Rules for Heat Sink Design
Drive the heat from the component to air within the available volume and temperature difference
Thermal interface material at contacting surfaces
 Area and conductivity for conduction and spreading
 Surface area for convection and radiation
 Surface treatment for convection and radiation
At a minimum in raw material cost
 Least volume / mass of material
 Lowest cost material
At a minimum in manufacturing process cost
 Material compatible with versatile, low cost, low waste processes
 Easy to prototype, cost effective to mass produce
With robust mechanical retention, easy installation

Heat Sink Design Methods
Heat transfer correlations
 Quick back of the envelope calculations
 Rough size of heat sink required
Numerical Design Tools ¨C QFIN
 Combine correlations with numerical conduction calculations
 More robust handling of geometry details, flow bypass, interfaces, ducts, fans ¡­ 
Comprehensive Design Tools
 Icepak CFD software ¨C interface tailored for electronics cooling
 Gambit + Fluent CFD software ¨C full capability tools

Selection Criteria & Metrics
Heat Transfer Performance: W/oC/Volume
 Fin density required
 Type of spreading required
Weight & Cost:
 mass/Volume, mass/W;
 cost/volume, cost/W
Form factor & shape
 Fin aspect ratios ¨C type of fin technology
 Distance for heat transport in the x, y, and z directions
Spreading enhancement
 Need heat pipes?
 How many?

Heat Sink Application Inputs
Natural convection
  Given heat sink temperature delta above air & length of flow path
Forced convection
  Ducted air flow without bypass
    Given fan curve ¨C use limits 0.7*CFM_max & 0.4*P_max
    Given max flow and pressure ¨C use pressure for design then check if CFM is     within limits
 Non-ducted air flow with significant bypass
    Use 1.3X dynamic head of approach flow as driving pressure
    (will need to solve flow bypass network for final design)
 Fan-heat sink
    Use 0.5*CFM_max and 0.5*P_max
Mass limits (x,y,z are dimensions in meters)
    mass < x*y*((z-0.006)*0.25+0.006)*2700 (kg) ¨C extrusion possible
    Otherwise will likely need assembled fin technology heat sink

Fin Density Required
x-y is plane of heat sink base, z is normal to base
Check thermal performance requirement
Separate spreading resistance to get ~fin resistance required
Spreading ¨C from heat source over x-y size & base thickness (Seri Lee Formula)

 
W/oC/cu. in. of Fin Volume ¨C select fin density (Al Fins)
Below 0.03 ¨C Natural Convection possible
Below 0.20 ¨C Low Density Fins, Low DP (gaps >~ 3 mm)
Below 0.40 ¨C High Density Fins, Low DP (<~20 Pa)
Below 0.65 ¨C High Density Fins, High DP (Blowers)
Above 0.80 ¨C Look for liquid or two-phase radiator type HS
If getting close to each limit, consider next higher option or copper
The above performance limits increase by 15% if weight limits allow copper fins.