A heat sink is a thermal part before it is a machined part. What governs performance is fin surface area and the thermal path into the base — and what governs cost is how thin and how tall you ask the fins to be. The two are not always aligned, and the aspect ratio is where most designs cross the line into an expensive part.
The same part can be produced several ways, and the choice is decided by volume and geometry rather than preference. We quote whichever is actually cheaper for your quantity.
| Approach | How it works | Best at | Watch out for |
|---|---|---|---|
| Machined from solid | Fins cut into a solid aluminum block with a slitting saw or small end mill | 1–500 pieces; prototypes; complex mounting features in the same part | Fin aspect ratio limited by tool reach; material utilisation 20–40% |
| Skived fins | A blade peels fins up from a solid block, leaving them attached at the base | High aspect ratio (up to 15:1) at production volume | Needs a dedicated blade and setup; not economic for small batches |
| Extruded + machined | Extruded heat sink profile cut to length, then machined for mounting and flatness | 500+ pieces with a standard fin profile | Die cost; extruded base flatness usually needs a machining pass |
| Bonded fins | Separate fins epoxy-bonded or soldered into a grooved base | Very high aspect ratios, or when fin material differs from base | Bond line is a thermal resistance — usually worse than an integral fin |
These are the decisions that account for most of the cost difference between two parts of the same overall size.
| Feature | Recommended | Why it matters |
|---|---|---|
| Fin aspect ratio (height : width) | ≤ 6:1 machined; 8–10:1 with care | Tool reach and deflection; above this, skiving or bonding wins |
| Fin thickness | 1.0–1.5mm machined; 0.5mm skived | Thinner fins save material but deflect and chatter |
| Fin gap | ≥ 1.2× cutter diameter | Narrower gaps force smaller tools, slower feeds and more passes |
| Base thickness | ≥ 3mm below the fin root | Spreading resistance; too thin and the base cannot spread heat to the outer fins |
| Base flatness | 0.05mm typical; 0.02mm for high-power devices | Contact resistance matters more than most buyers expect |
| Surface finish on base | Ra 1.6 or better, or specify a thermal interface | Roughness creates air gaps; thermal paste compensates only partly |
| Mounting hole position | ±0.1mm unless locating a device | Tightening position tolerance on all holes multiplies inspection |
Machining fins is a reach problem. A 1mm wide, 10mm tall fin needs a cutter that can reach 10mm deep in a 1mm slot — at that ratio the tool is thin, slow and prone to deflection, so cycle time climbs and scrap risk climbs with it. On a 100 × 100mm heat sink, going from 4:1 to 8:1 aspect ratio can triple the machining time.
The practical split: up to about 6:1, machined fins are economic at any volume. Above that, skived fins (production volume) or extruded profiles (standard shapes) are usually cheaper per unit of thermal performance. If your design needs 10:1, it is worth checking whether a taller base and shorter fins meets the same thermal target.
| Cost element | Share of price | What to change if it is too high |
|---|---|---|
| Fin machining time | 45–70% of part cost | The dominant cost — driven by aspect ratio and fin count |
| Material | 15–25% | Block size is set by fin height plus base, not by the finished weight |
| Base flattening | 8–15% | A separate finishing operation after fins are cut |
| Setups | 2–3 | Fins on one face, mounting features on the other |
| Inspection | 3–6% | Base flatness and fin integrity |
Thermal performance scales with surface area, but cost scales worse than linearly with fin count and aspect ratio. Ten 1mm fins cost more than six 1.5mm fins for roughly the same surface area, and the thicker fins are far less likely to be damaged in handling or assembly.
Before optimising for the last few percent of thermal resistance, check whether the design is thermally limited at all. Many heat sinks are sized for a worst case that never occurs, and the cost of that margin is paid on every unit.
Anodize is often specified for corrosion resistance and appearance, but the oxide layer is a thermal insulator. On a heat sink the anodize is usually thin enough (5–15 µm) not to matter for the fins, but on the mounting base it adds contact resistance. Where the base contacts a device or a thermal pad, mask the base from anodize.
A heat sink base that is flat to 0.05mm still leaves an air gap at the microscopic level, which is why thermal interface material exists. If the design relies on a pad or paste, specify the flatness the interface material can absorb rather than an arbitrary tight tolerance. If it relies on direct metal contact, flatness and roughness both matter.
Thin tall fins bend. On a 1mm fin at 8:1, a knock during packing or installation can close the gap between two fins and destroy the thermal path. Specify protective packaging and consider whether the outermost fins should be thicker as sacrificial members.
It depends on fin width. Up to about 6:1 height-to-width is comfortable — a 1.5mm fin up to 9mm tall, or a 2mm fin up to 12mm. Beyond that, tool deflection and chatter make the cut slow and the finish poor. Above roughly 8:1, skived fins or an extruded profile are usually the better process.
Machined fins win at low volume and when the part also needs mounting features or a non-standard outline. Skived fins win at production volume with high aspect ratios, because the process forms the fins rather than cutting around them, so material utilisation and cycle time are both better. Below a few hundred pieces the skiving setup usually does not amortise.
For a device mounted with thermal paste or a pad, 0.05mm over the contact area is normally adequate, because the interface material absorbs the remaining gap. For direct metal contact or a large die, 0.02mm or better is worth specifying. The governing number is what the interface material can absorb, not an arbitrary standard.
On the fins, the effect is small — the anodize layer is thin and the fin area is large. On the mounting base it matters more, because the oxide adds contact resistance exactly where heat enters the sink. Mask the base if the design relies on direct contact, or specify chromate conversion instead of anodize.
The usual construction is a separate copper spreader and aluminum fin stack, joined by screws, thermal epoxy or soldering. Machining a single part from two metals is not practical. If the design needs a copper base, plan the joint as a separate assembly step and specify the interface material between the two.
Include the quantity, whether the finish is visible, and which fits or seals are critical. You get a line-item quote within 24 hours and DFM notes on the features driving your price.