Guide
Should a Heat Sink Be Die Cast, Extruded or CNC Machined?
A heat sink is a finned metal body that spreads heat from a component into the surrounding air, and the manufacturing process sets how thin the fins can be, how close together they can sit and which alloy they are made from. Those three limits, more than the price of the first part, decide which of the three common routes fits a production run.
By Saola Manufacturing engineering team · Published · Updated
This guide is for thermal and mechanical engineers in electronics, lighting and power equipment who must choose a process for a production run. It uses a published process-capability table for the fin limits, the Aluminum Association alloy registrations for composition, and a trade-press comparison for the qualitative differences. The sources give no conductivity figure, so none is invented here; take that number from the datasheet of the alloy you buy.
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Should a heat sink be die cast, extruded or CNC machined?
Choose extrusion for a straight-finned profile, die casting when the fins must be part of a three-dimensional housing, and machining when the fins must be thin, tall or closely spaced, or the quantity does not support tooling. Many designs combine two routes, such as an extruded profile with a machined base and tapped holes.
A trade-press comparison summarizes the trade-offs in plain terms: die casting allows shapes that extrusion cannot make, is relatively inexpensive and suits high production rates; extrusion is cost-effective for complex cross-sections but is limited in product width; machining offers good design flexibility but is typically more expensive and suits low-volume, premium products (Electronic Specifier, November 2022). That is a starting point. The number that most often decides the question is the fin limit.
What fin thickness and spacing can each process make?
Machining reaches the finest fins and the tallest fin-to-gap ratio, extrusion sits in the middle, and die casting needs the thickest fins and the widest gaps. The published table gives typical limits of 0.5 mm for machined fins, 1 mm for extruded fins and 1.75 mm for die-cast fins.
The figures below come from a process-capability table in an Electronics Cooling article on designing air-cooled ducted heat sinks. They are general capability limits from 2007, not what every shop achieves today, and the article does not give base thickness or thermal conductivity. Use them to see which routes are even possible for a target fin geometry, then ask suppliers what they can hold.
| Process | Minimum fin thickness (mm) | Minimum fin spacing (mm) | Maximum fin height to spacing ratio | Materials listed |
|---|---|---|---|---|
| Extruded | 1 | 6.6 | 8:1 | Aluminum |
| Die casting | 1.75 | 8.3 | 6:1 | Aluminum, zinc alloy |
| Machining | 0.5 | 1 | 50 (as printed) | Aluminum, copper, magnesium |
Two things follow from the table. A forced-air design that needs gaps narrower than the typical extrusion limit of 6.6 mm cannot use an extruded profile and must be machined or built another way. And a tall, tightly pitched fin field that die casting cannot fill is not a casting problem to solve with a bigger tool; it is a sign to change process or to relax the geometry. The article also notes that porosity from gas evolution can degrade the thermal conductivity of cast heat sinks (Electronics Cooling, August 2007), which is why the porosity guide matters for a machined cast base.
Does the alloy change thermal performance?
Yes: die-casting alloys carry several percent silicon and copper, while typical extrusion alloys are close to pure aluminum with small additions, and conductivity falls as alloying content rises. The size of the gap should be read from the datasheet of the alloy actually supplied, because the sources here give no figure.
The composition limits below are the registered ranges. A380.0 is a common die-casting alloy and 383.0 is another, and aluminum die castings are usually ordered to ASTM B85, the specification for aluminum-alloy die castings; 6063 is a typical wrought alloy for extruded profiles and 6061 is common for machined stock. Alloy additions interrupt the aluminum lattice, so the relationship between composition and conductivity is a matter of metallurgy, but the numerical conductivity of each alloy and temper should come from a materials datasheet or the supplier’s lot report, not from a table of nominal values.
| Alloy | Route | Silicon | Copper | Magnesium |
|---|---|---|---|---|
| A380.0 | Die casting | 7.5–9.5 | 3.0–4.0 | 0.10 max |
| 383.0 | Die casting | 9.5–11.5 | 2.0–3.0 | 0.10 max |
| 6063 | Extrusion | 0.20–0.6 | 0.10 max | 0.45–0.9 |
| 6061 | Machined stock, extrusion | 0.40–0.8 | 0.15–0.40 | 0.8–1.2 |
The practical effect is that a die-cast housing with integral fins starts at a disadvantage against an extruded or machined sink of the same geometry, and porosity can widen it. That does not rule casting out: if the housing, the mounting features and the fins can be one part, the system-level saving in parts and assembly may outweigh a lower fin conductivity, but only the thermal model with the real alloy can say. See the zinc versus aluminum guide if zinc is under consideration.
How do shape and volume point to a process?
Shape decides first: straight fins point to extrusion, integral three-dimensional housings to casting, and fine or tall fin fields to machining. Volume decides second, because casting needs a die and machining does not.
At annual volumes in the low tens of thousands, tooling payback has to be checked part by part. The table summarizes the choice. It is qualitative and draws on the sources listed below; it makes no price claim, since cost depends on the part, the alloy and the market.
| If the design is | Lean toward | Watch for |
|---|---|---|
| Straight fins, constant cross-section, one length | Extrusion | Width limits; fin gaps no tighter than the process allows; cut-to-length and base machining |
| Fins integral with a housing, bosses and ribs | Die casting | Wider gaps and thicker fins; lower-conductivity alloy; porosity; draft; tooling investment |
| Very thin or tall fins, pin fields, or low quantity | CNC machining | Machining time per part; best for premium or low-volume parts |
| Standard profile but custom mounting | Extrusion plus machining | Base flatness and hole position as machined features |
For the cast-versus-machined question on its own, the break-even guide works through the tooling payback logic, and the mold cost guide covers what drives the die.
What gets machined on a cast or extruded heat sink anyway?
The base face, the tapped holes and any datum surfaces are normally machined, whichever route makes the fins, because that is where the heat crosses into the sink and where the part is located. The fins can stay as formed.
As typical practice, a thermal interface needs a flat, smooth mounting face, and an as-cast or as-extruded surface is rarely the best one. Machining the base to a flatness callout gives the interface material a controlled gap; the die casting flatness guide and the flatness versus parallelism guide explain how to write it. Tapped holes in cast aluminum are better placed in machined bosses or fitted with inserts, as covered in the thread insert guide.
Saola places die casting and extrusion with partner plants it manages, and the base flatness, holes and datum faces are CNC work at the lead CNC plant, normally milling with turning for round bodies. The die casting page describes how managed casting works. Each quote states the production site for every step.
What should the RFQ say about a heat sink?
State the thermal requirement, the fin geometry that is fixed, the alloy and any datum or flatness callout, and say whether the process is fixed or open. A drawing that fixes the process removes the supplier’s chance to propose a cheaper route.
If thermal resistance at a given airflow is the requirement, say so and give the fin envelope; if the fin geometry is already validated in a thermal model, say it is fixed. Name the alloy family and ask the supplier to confirm what they will use, since the alloy changes the result. Mark the machined faces and the flatness. Ask for a quote on two routes when volume is uncertain, so the break-even is visible, and send the STEP file with the drawing.
Frequently asked
Can a die-cast heat sink match an extruded one thermally?
Only if the geometry and alloy allow it. The table above shows die casting needs thicker fins and wider gaps than extrusion, and the alloy carries more silicon and copper, so a like-for-like fin pattern is usually not reachable. A thermal model with the real alloy decides.
Is the 2007 table still valid?
It is a general capability table from 2007, so treat it as a screening tool. Individual suppliers may achieve finer geometry, and the article notes a modified die-casting route with much finer limits. Confirm with the supplier before fixing a dimension.
Does machining a heat sink from solid cost more?
It is typically the more expensive route per part, according to the trade-press comparison cited above, which is why it suits low volumes or premium designs. Cost still depends on the geometry, so ask for a quote.
Where does the thermal conductivity number come from?
From the datasheet of the alloy and temper being supplied, or the supplier’s material report. The sources used here give composition and process limits but no conductivity value, so none is quoted.
Can an extruded profile be machined into a pin-fin sink?
Cross-cutting a profile is a common way to make pin fins from an extrusion, and it is a machining operation. Confirm the fin limits with the supplier, since the table covers straight fins.
Sources
- Design for manufacturability of forced convection air-cooled fully ducted heat sinks, M. Iyengar, Electronics Cooling, August 2007
- What’s the best heat sink manufacturing process?, Electronic Specifier, November 2022
- Designations and Chemical Composition Limits for Aluminum Alloys in the Form of Castings and Ingot (Pink Sheets), The Aluminum Association, revised August 2025
- International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys (Teal Sheets), The Aluminum Association, revised December 2025
- ASTM B85/B85M-18e1, Standard Specification for Aluminum-Alloy Die Castings, ASTM International, 2018