Die Cast Heat Sinks for Power Electronics
Reading the conductivity number correctly
Our heat sink die castings are specified with a thermal conductivity in the range of 72 to 100 W/m·K. That figure describes the bulk metal, not the finished assembly. Heat leaving a power device crosses several resistances in series: the mounting face, whatever interface material sits between device and casting, the fin structure itself, and finally the air moving across it. The metal is only one of those resistances, and rarely the dominant one. A poorly flattened mounting face with a thick interface gap can easily cost more than choosing between two alloys, which is why seeing the whole chain matters.
That is why we treat the mounting face as a machined feature rather than an as-cast surface. After casting, parts move to our five-axis CNC centres, where general tolerances of ±0.05 mm can be held where they are specified on the drawing. Flatness across the contact area decides how much interface material remains in the joint, and therefore how much thermal resistance stays permanently built into the assembly. Tell us at enquiry stage which surface mates to the device, so that face is machined and inspected rather than left at standard casting tolerance and then polished by hand in your own workshop.
Fin geometry: what casting will and will not give you
Die casting fills fins well up to a point. Every fin needs draft to release from the tool, so very tall and very thin fins either will not fill or will not eject cleanly, and pushing fillspeed alone usually makes matters worse rather than better. Our process applies vacuum die casting and uses mold-flow simulation during tooling design to push that boundary outward, because trapped gas at the fin tip is the usual reason a thin rib arrives short. Even so, there is a practical aspect ratio beyond which the tool rather than the machine sets the limit.
The common answer is a hybrid. Cast the base plate with moderate fins where convection is useful anyway, then machine the genuinely critical surfaces afterwards on five-axis CNC centres - mounting pads, sealing faces, connector windows. This keeps the casting cycle short while putting precision only where it pays for itself instead of spreading it across the whole part. If your thermal budget genuinely needs taller fins than can be cast, ask us to quote both the as-cast version and the machined-fin version; the difference in unit cost is frequently smaller than expected once assembly labour is included.
Finishing, environment and verification
Our heat sink castings are supplied with an anodised finish. Anodising is not only corrosion protection: it changes surface emissivity and therefore how effectively the fins radiate heat away, and it changes electrical behaviour where the housing also serves as a ground path. Powder coating gives far more colour choice and film thickness but adds another layer between metal and air. State the operating environment - indoor enclosure, under-hood, coastal installation - rather than merely naming a finish that somebody upstream happened to prefer.
Verification runs through our QC laboratory, covering CMM inspection, salt-spray testing and batch traceability, and we issue full batch reports under ISO 9001 and IATF 16949 documentation alongside RoHS and REACH compliance. Send STEP, IGES or DXF drawings together with the dissipated power, available airflow and any maximum case temperature you have to meet. Our engineers return a DFM review free of charge with a quotation inside 24 hours, then samples in about 7 days and volume production in 30 to 45 days after approval.
FAQ
What thermal conductivity should I expect?
Heat sink castings are specified in the 72 to 100 W/m·K range. Delivered performance also depends on mounting flatness, interface material and available airflow, so those boundary conditions matter as much as the alloy itself when you model the thermal budget for the finished assembly rather than for the raw casting.
How tall can cast fins be?
Fin height is limited by the draft needed for ejection and by fill behaviour at the tip. Vacuum assistance and mold-flow simulation during tooling design extend what is achievable, but beyond a certain aspect ratio machined fins or a hybrid cast-and-machine construction is the realistic route rather than simply raising injection speed.
Which finish should I specify?
Anodising is commonly used for heat sink castings and changes both corrosion behaviour and surface emissivity; powder coating gives thicker coverage but adds a resistive layer. Give us the operating environment and tell us whether the surface has to remain electrically conductive, because that often decides the question before appearance does.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.