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Extruded heat sinks — how to specify one that actually cools
Published 2026-10-29
An extruded heat sink looks like a simple profile with fins on it. Thermally it is a compromise made visible: every fin you add gives heat more surface to leave from, and every fin you add makes the section harder to extrude evenly and the part heavier. Most of the heat sink orders that disappoint do not fail because the extrusion was bad — they fail because the section was specified as if fins were free, or because the face that has to sit flat on a device was never specified at all. This is what to decide before the section goes into tooling.
When extrusion is the right route
Extrusion earns its place when the cross-section stays constant along the length and the volume justifies a die. Power supplies, inverters, LED drivers, motor drives — anywhere the same finned section repeats across hundreds or thousands of parts — are the natural territory. The section is pushed out in one pass, cut to length, and the fins, base and any mounting features that can live in the section come out together.
It stops being the right route when the fin geometry stops being constant: very tall, very thin, very dense fins, or a fin field that changes across the part, push past what a die can hold evenly. Bonded, folded-fin and skived constructions exist for exactly that territory. If your thermal design needs fins your extrusion supplier hesitates over, that hesitation is information — ask what fin geometry they can hold, rather than pushing a section that will come out uneven.
Volume matters commercially too. A custom die is a fixed cost spread across the run. For a one-off prototype, an existing section adapted by machining is usually the honest answer; for a repeating order, the custom section pays for itself in material saved and assembly avoided. That trade-off is covered in the die cost guide linked below.
What sizes the section
Three features do most of the thermal work, and all three are worth calling out separately in the enquiry rather than leaving to a general outline.
Fin height, thickness and pitch. Taller, thinner, more closely spaced fins give more surface area, but they also make metal flow harder to balance across the die. A section that looks good on paper and comes out with wavy or uneven fins has not saved anything. If you have a fin geometry in mind, state it — and if you do not, state the envelope the section has to fit and let the extrusion review propose a fin field that can actually be held.
Base thickness. Heat has to travel from the device into the base and then out along the fins. A base too thin starves the outer fins; a base too thick adds weight and cost for little gain. The base is also the face that usually carries the mounting holes or threads, so its thickness has to serve both jobs at once.
Alloy and temper. The common 6000-series alloys cover most heat sink work, and 6063 is often the starting point for a finned section because it extrudes cleanly into fine detail. The alloy choice is covered properly in the alloy guide linked below — what matters here is stating the full grade and temper on the drawing, because a section quoted in one alloy and produced in another is not the same part thermally or mechanically.
The mounting face decides more than the fins
A heat sink only works if heat actually gets into it, and that happens across the face that sits on the device. A base that is bowed, twisted or rough at the contact area leaves air gaps, and air gaps are insulation exactly where you cannot afford it. So the mounting face deserves its own line on the drawing: how flat it has to be, whether it is milled after extrusion, and what it has to mate with.
Milling the mounting face, drilling and tapping device holes, and cutting the section to finished length are secondary operations — they happen after extrusion, and they are how a raw finned profile becomes a finished heat sink. If your design needs them, say so in the enquiry rather than assuming they are included. A profile quoted as-extruded and a profile quoted as a finished, drilled and tapped part are two different prices for a reason.
Tolerances follow the same logic. The general tolerance class for the section is one thing; the flatness and position of the mounting interface is another. State which dimensions are functional — the ones the device actually sits on — and which are general. The tolerances guide linked below explains what the standard class does and does not control.
Finish: usually black anodize, but say why
Most extruded heat sinks you see are black anodized, and the reasons are practical rather than cosmetic: anodizing protects the surface, and a dark finish radiates better than a bright one. But finish is also a tolerance decision — an anodized layer has thickness, and on a tight mounting interface that thickness has to be accounted for, either by masking the face or by allowing for it in the dimension.
If the heat sink lives outdoors or in a corrosive environment, say so: sealing quality after anodizing is what decides whether the finish lasts, and it is covered in the anodizing guides linked below. If appearance matters — a visible heat sink on a consumer product, for instance — state the colour reference with the enquiry, not after the first batch.
What to send for a quote
A heat sink enquiry that gets a fast, honest quote contains the same set of items every time. Send them together and the review can confirm the section, the operations and the finish in one pass instead of three rounds of questions.
| Send this | Why it matters |
|---|---|
| Section drawing, with fin and base dimensions | Decides whether the section can be extruded evenly and what die work is needed |
| Alloy and temper | Sets extrudability, finish and mechanical behaviour |
| Mounting interface: flatness, holes, threads, milled face | Decides the secondary operations and the real finished-part price |
| Finish and colour reference | Anodizing type and masking change both price and dimensions |
| Quantity, and whether repeats are expected | Spreads the die cost and decides custom section vs adapted stock |
| Delivery destination | Packing and freight start from here |
One last check before you send it
Read the drawing once as if you were the person who has to make it: is every dimension that matters to cooling or assembly actually on there, or is it implied? Fin geometry, base thickness, mounting face, finish — if any of them lives only in an email or a meeting note, write it on the drawing. The parts that come back right are almost always the ones whose drawings left nothing to guess.
Send the drawing and the table above with the enquiry, and the quote that comes back will price the heat sink you actually need — not the nearest catalogue approximation of it.
Related
Profiles in this guide