Bonded vs extruded heatsinks?

Extruded heatsinks are produced by pushing aluminum through a die. Maximum fin height-to-gap ratio (aspect ratio) is about 8:1. Bonded fin heatsinks assemble individual fins into a base, achieving aspect ratios of 20:1 to 40:1 with fin heights up to 150 mm. This provides 2-3x more surface area per footprint, enabling lower thermal resistance. Bonded fins cost more but are necessary for high-power-density applications.

Epoxy bonding: thermally conductive adhesive (1-3 W/m-K) fills the fin-to-base joint. Lowest cost but highest joint thermal resistance. Brazing: furnace brazing with aluminum filler (150-200 W/m-K joint). Better thermal performance. Swaging: mechanical crimping of fins into grooves. No thermal interface material. Best thermal performance (direct metal-to-metal contact). Choice depends on thermal requirements and budget.

When to use bonded fin?

When extruded heatsinks cannot provide sufficient cooling due to height or aspect ratio limitations. Typical applications: RF power amplifier chassis (500+ W), radar transmitters, base station equipment, LED lighting, and power converters. Also when mixed materials are needed: copper base (for spreading) with aluminum fins (lightweight, cost-effective). Not justified for low-power applications where extruded or stamped heatsinks suffice.

Power & Thermal

Bonded Fin Heatsink

A Bonded Fin Heatsink uses individually manufactured fins inserted and bonded into grooves machined into a base plate. This construction achieves fin aspect ratios of 20:1 to 40:1 (vs 8:1 for extrusions), fin heights up to 150 mm, and enables mixed materials (copper base + aluminum fins). Bonding methods include epoxy, brazing, and swaging. Used for high-power RF amplifiers, radar transmitters, and power electronics dissipating 500-5000+ watts.

Category: Power & Thermal

Aspect Ratio: Up to 40:1

Understanding Bonded Fin Heatsinks

The key advantage is surface area density. More fins per unit footprint, taller fins, and thinner fins all increase the total surface area available for convective heat transfer. A bonded fin heatsink can provide 2-3× the surface area of an equivalent-footprint extruded heatsink.

For RF power amplifiers in outdoor enclosures, bonded fin heatsinks with natural convection are common because fans reduce reliability. The high aspect ratio maximizes passive cooling. For indoor rack-mount equipment with forced air, the dense fin spacing takes full advantage of the available airflow.

Heatsink Thermal Resistance

R_th = 1 / (h·A_fin·η_fin)
h = convection coefficient (W/m²·K)
A_fin = total fin surface area
η_fin = fin efficiency (0.5-0.95)

Taller fins: more area but lower η_fin
Optimal: balance height vs efficiency

Heatsink Technology Comparison

Type	Max Aspect	Max Height	Cost	Performance
Extruded	8:1	75 mm	Low	Good
Bonded fin	40:1	150 mm	Medium	Very good
Skived	25:1	80 mm	Medium	Good
Vapor chamber	N/A	Flat	High	Excellent

Common Questions

Frequently Asked Questions

Bonded vs extruded?

Extruded: max 8:1 aspect, 75 mm. Bonded: 40:1, 150 mm, 2-3× surface area. Bonded costs more but needed for high power.

Bonding methods?

Epoxy (cheap, higher R_th), brazing (better thermal), swaging (best, direct metal contact). Choice = performance vs cost.

When needed?

500+ W RF PAs, radar, base stations, power converters. When extrusions can't provide enough cooling in the footprint.

Related Terms

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