Key takeaways
- Start from a thermal resistance budget: R = ΔT ÷ P.
- The interface (flatness, TIM, clamping) can cost as much as the fins save.
- Natural convection needs wider fin gaps than forced convection.
- Tapered fins and moderate fin ratios make heat sinks extrudable and efficient.
- Black anodizing raises emissivity — useful in passive designs.
An extruded heat sink is simple to make but easy to get wrong. The goal is a profile that meets a thermal target at the lowest weight and cost while staying comfortably inside what the die can extrude.
Step 1 — Set the thermal budget
Heat flows from the component through a chain of thermal resistances: junction to case, case to heat sink (the interface) and heat sink to air. For the heat sink you need:
Rsa ≤ (Tcase,max − Tambient) ÷ P − Rinterface
Worked example. A 30 W module may run at a maximum case temperature of 85 °C in 40 °C ambient air. The total allowed resistance is (85 − 40) ÷ 30 = 1.5 K/W. With a thermal interface material contributing about 0.1 K/W, the heat sink itself must achieve 1.4 K/W or better in the actual airflow and orientation.
Step 2 — Choose the cooling mode
- Natural convection — no fan, silent and reliable, but needs more surface area and wider fin gaps. Orient fins vertically so warm air rises freely.
- Forced convection — a fan allows denser fins and a much smaller heat sink, but adds noise, power and a failure point. Direct the airflow along the fin channels.
Step 3 — Size the base
The base spreads heat from the component to all fins. Small, concentrated sources need a thicker base; sources that cover most of the base need less. A base that is too thin leaves outer fins cold; one that is too thick adds weight without benefit.
Step 4 — Design the fins
- Height: taller fins add area, but efficiency falls toward the tips.
- Thickness and taper: a thicker root carries heat into the fin and strengthens the die tongue; a thinner tip saves weight.
- Spacing: wide enough for air to flow — especially in natural convection — and for the die to be robust.
- Fin ratio: very tall fins with narrow gaps are hard to extrude. Discuss the ratio with your extruder early.
Step 5 — Finish and interface
- Flatness at the contact face is essential; face-mill it if needed.
- Thermal interface material fills microscopic gaps — specify type and thickness.
- Mounting pressure matters: clips or screws must clamp evenly.
- Black anodizing raises emissivity from a few percent (bare aluminum) to well above 0.8, improving radiation in passive designs. Mask the contact area.
Step 6 — Validate
Estimate with correlations or CFD, then test a prototype in the real enclosure, orientation and airflow. Extrusion makes prototypes easy: cut a sample from a standard section or the first trial of a custom die.
Standard or custom?
Start with our standard heat sink profiles — no die cost — and move to a custom section if you need a specific envelope or integrated mounting features. Learn more about extruded heat sinks or send your thermal requirements.
Frequently asked questions
What is the best fin spacing for a natural convection heat sink?
It depends on fin height, length and temperature difference. Natural convection needs gaps wide enough that the warm boundary layers on adjacent fins do not merge; as a rough rule, passive heat sinks use noticeably wider gaps than forced-air designs. Validate with calculation or testing.
Is a thicker base always better?
No. A thicker base spreads heat from a small source better, but beyond a point it adds weight and cost with little benefit. The best thickness depends on the source size relative to the heat sink.
Should heat sinks be anodized?
Often yes. Anodizing protects against corrosion, and black anodizing raises emissivity, which improves radiation in natural convection. Mask or machine the component contact area.