Introduction: In an IGBT or power semiconductor module, the baseplate is clamped to a heat sink, the gap varies across the footprint, and every screw hole, standoff, and edge must line up on the first build.
IGBT and power module assemblies combine tight stack tolerances with creepage and clearance rules, so die-cut parts usually outperform trimmed sheet stock. Geometry, thickness, hardness, and insulation determine the drawing and drive the inputs for a custom die-cut quote.
Heat inside a power module travels from the junction through the package, out through the baseplate, across the interface, and into the heat sink. Package thermal metrics such as junction-to-case resistance describe what happens inside the package, while the interface is the part controlled by the pad. A pad that leaves air pockets raises interface resistance and pushes junction temperature up, and the usual cause is poor fit rather than poor material. The insulation job runs alongside the thermal one. In a module that switches at high voltage, the pad is the barrier between a live baseplate and a grounded heat sink. That barrier has to cover the full contact area, extend past the mounting hardware where creepage distance matters, and stay in position during assembly. A rectangular sheet cut by hand on the line can leave ragged edges, exposed burrs, and inconsistent overhang, all of which change how the pad behaves under clamping force and how much of the gap it actually fills. Die-cut geometry solves the fit problem directly. The outline matches the baseplate footprint, punched holes sit around the mounting screws instead of being crushed by them, and slots or notches clear standoffs, busbars, and terminal posts. Compression ends up even because the pad is the same shape everywhere it needs to be. When the part drops in without trimming or repositioning, the assembly team gets a repeatable stack height and the thermal engineer gets a contact area that matches the design.
Four inputs decide most power module pad drawings: thickness, hardness, dielectric strength, and volume resistivity. They are not independent. Thickness and hardness determine how much the pad compresses under the clamping load the housing applies, and that compression changes final stack height and how much of the gap is genuinely filled. Dielectric strength and volume resistivity determine whether the pad can stand off the voltage the module sees.
These four values only work as a set. A very soft pad fills an uneven gap well, but it compresses more, so installed thickness differs from the nominal figure used in a thermal calculation. A thick pad forgives machining tolerance, but it adds resistance to the heat path. A pad in this range is a ceramic-filled silicone elastomer with 1.0–8.0 W/m·K thermal conductivity and a -50°C to 200°C operating range, so its mechanical and electrical behavior holds across the temperature swings a power module sees in service. Ask for thickness, hardness, compression data, and insulation figures together before the drawing is finalized.
A drawing is the fastest route from “we need a pad” to “we have a pad. ” Send the module footprint outline with hole positions and diameters, the keep-out areas around busbars and terminals, the overhang required beyond the baseplate edge for creepage, and the target thickness with its tolerance. A DXF or native CAD file removes most ambiguity, and a dimensioned PDF works when the geometry is simple. The drawing review checks that the outline clears the mounting hardware, that punched holes will not tear once the pad is compressed, and that corners will not lift during assembly. Adhesive backing is the next decision. Single-sided PSA anchors the pad to the heat sink so it stays in place while the module is lowered on top. Double-sided PSA holds both faces and suits assemblies that get flipped or moved before fastening. Adhesive adds a thin layer, so state which side is coated and confirm the total stack height on the sample. The pad keeps its thermal and insulation behavior; the tape is part of the mechanical stack. Samples are where the drawing gets proven. A die-cut sample, usually within a few working days of drawing release, lets the assembly team check hole alignment, edge quality, drop-in fit, compression at the actual bolt torque, and how the adhesive behaves on the real heat sink surface. Die-cutting practice shows that part tolerance depends on material thickness, hardness, and geometry, so the practical answer comes from the sample and the fit check rather than from a tolerance figure quoted in advance. Working with a custom silicone thermal pad manufacturer shortens this loop because drawing review and material choice happen together. Die-cutting, material compounding, and adhesive selection run in the same production flow, so thickness, hardness, and PSA choices on the drawing can be checked against the material that goes into production. RoHS and REACH compliance covers the chemical side, and a UL 94 V-0 flame-retardant design direction is available where a housing standard calls for it. Where a module switches at very high voltage or follows unusual creepage rules, final clearance is signed off through the module’s own electrical safety review.
A die-cut thermal silicone pad for a power semiconductor module is a geometry problem and a material problem at the same time. The drawing has to match the mounting pattern and creepage needs, while the material has to deliver the thickness, hardness, and insulation the stack requires. Locking thickness, Shore OO hardness, dielectric strength, and volume resistivity before you submit a drawing saves a revision cycle, and a die-cut sample confirms fit before production tooling is committed. If you have a module footprint, a target thickness, and a preferred adhesive side, send them together with your CAD or DXF file and ask for a sample and quote in the same pass.
A：Thickness depends on the gap you need to close. The 0.3–5.0 mm range covers most power module assemblies, and the best choice is usually the thinnest pad that still fills the gap across the entire footprint, since extra thickness adds thermal resistance. Dielectric strength of ≥5 kV/mm gives the insulation margin per millimeter of compressed pad, so multiply it by the compressed thickness to estimate the standoff under clamping force and compare that with the voltage the module switches.
A：Die-cutting lets the pad match the baseplate footprint exactly, with punched holes around mounting screws, notches for busbars and standoffs, and controlled overhang where creepage distance matters. The pad then drops in without trimming, compresses evenly, and produces a repeatable stack height. Hand-cut edges leave variable overhang and uneven compression, which shows up as higher interface resistance and inconsistent assembly results from unit to unit.
A：Yes. Single-sided PSA is the common choice because it holds the pad to the heat sink while the module is lowered on top. Double-sided PSA suits assemblies that get flipped or moved before fastening. Adhesive adds a thin layer to the stack height, so confirm which side is coated and verify the total height with a sample. The pad keeps its thermal and insulation behavior throughout; the tape is part of the mechanical build.
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