Not every IGBT design needs a power module. Below a few tens of kilowatts, discrete IGBTs in TO-247, TO-220, and TO-263 packages carry the load with lower cost, simpler sourcing, and a flexible layout—provided the package’s thermal, mounting, and insulation realities are respected. This article covers the discrete side of IGBT selection: how the packages compare, how mounting and insulation change the thermal result, and where a discrete part is the right answer instead of a module.
Discrete vs Module: Where the Line Sits
The module offers an integrated, low-inductance layout with matched die, diode, and thermal design; the discrete part offers cost and flexibility. The crossover is practical rather than fixed:
| Consideration | Discrete IGBT (TO-247 etc.) | Power module |
|---|---|---|
| Current range | Typically up to 40–75 A per device | Higher, with paralleled dies inside |
| Layout | Designer controls the commutation loop | Module provides a controlled loop |
| Thermal path | Package to heatsink via pad or case | Baseplate and heatsink design |
| Cost and flexibility | Lower cost, easier sourcing | Higher cost, higher integration |
| Paralleling | Multiple discretes, layout-dependent | Integrated or designed for parallel |
The screening heuristic: for currents up to roughly 40–75 A and designs that want to control the layout, discrete IGBTs are the economical answer; above that, or where loop inductance and thermal integration dominate, the module wins. The companion articles on 650 V and 1200 V IGBTs cover the device selection; this article covers the package and the mounting.
The TO-247 Package and Its Family
TO-247 is the standard discrete power IGBT package: a through-hole package with a large tab (the collector in most parts), three leads, and a mounting hole for a heatsink screw. The family around it:
| Package | Typical use | Thermal path | Mounting |
|---|---|---|---|
| TO-220 | Low to medium power | Tab to heatsink or PCB | Through-hole or clip |
| TO-247 | Medium to high power | Tab to heatsink | Screw to heatsink |
| TO-263 (D2PAK) | Medium power, SMT | Tab to PCB copper | Surface mount |
| TO-264 | Higher current | Tab to heatsink | Screw to heatsink |
The TO-247 is the workhorse because it balances tab area, current capability, and a proven field history. The tab is both the collector connection and the heat path; the mounting hardware and the insulation between the tab and the heatsink decide how much of the package’s capability is realized.
Package current comparison. The practical current capability tracks the tab area and the thermal path more than the package name: a TO-220 part in a clipped mount may carry 20–30 A where a screw-mounted TO-247 carries 40–75 A, and a TO-263 on a good copper pad sits between them. The datasheet’s current ratings assume defined thermal conditions; the package comparison table above is a screening map, and the real capability comes from the thermal budget at the operating ambient.
The SMT option. The TO-263 (D2PAK) trades the heatsink screw for a PCB-mounted tab, which suits medium-power SMT lines but moves the heat into the board—the same copper-and-via discipline as the TO-252 article in this series. Choosing between TO-247 and TO-263 is choosing between a heatsink-centric and a board-centric thermal design; the package-thermal guide carries the method for both.
Mounting and Insulation: Where Thermal Designs Fail
The datasheet’s Rth(j-c) ends at the case; the case-to-heatsink path is the designer’s responsibility, and three details dominate it:
- The insulation layer. The TO-247 tab is usually the collector, so it is electrically live. Isolating the tab from the grounded heatsink requires a thermal pad, mica, or a silicone insulator with the right thickness and thermal conductivity. The insulator’s Rth adds directly to the thermal chain; a thick, cheap insulator can double the case-to-heatsink resistance.
- Screw torque and interface pressure. The mounting screw torque sets the contact pressure, which sets the interface resistance. Too little torque leaves air gaps; too much risks cracking the package or the insulator. The torque specification in the package drawing is a design input, not a suggestion.
- Thermal interface material (TIM). Grease or a phase-change pad fills the microscopic air gaps between the tab and the heatsink. The TIM’s rated temperature and aging behavior matter at high power; the companion article on high-temperature SiC reliability covers the material-verification discipline that applies here too.
A practical mounting check: measure the case temperature at the tab and the heatsink temperature at full load, and compare the difference with the insulator’s expected Rth times the power. A larger than expected drop means the interface is not working, and no device change will fix it.
A TO-247 Thermal Budget Example
Consider a TO-247 IGBT switching 30 A at a 50% duty in a motor drive: 2.0 V saturation voltage, 30 W conduction plus 15 W switching loss, a 60 °C ambient, and a target junction temperature below 125 °C.
- Total loss: 45 W.
- Allowable rise: 125 − 60 = 65 K.
- Required total Rth: 65 / 45 ≈ 1.44 K/W.
- The chain: Rth(j-c) near 0.5 K/W, the insulator and TIM near 0.4–0.6 K/W, leaving about 0.4–0.5 K/W for the heatsink-to-ambient path—a small extruded heatsink with airflow, and no margin for a poor interface.
The figures are method illustrations. The example shows why the interface dominates: a thick, low-quality insulator can consume the entire case-to-sink budget, and the same IGBT with a poor mount runs at its limit or beyond.
Fault and SOA context. The discrete IGBT’s short-circuit withstand time and the reverse-bias SOA are read from the datasheet and matched to the protection scheme; the companion IGBT articles carry the selection detail. The package adds its own boundary: a TO-247’s pin spacing and the board’s creepage must suit the voltage, and the mounting hardware must not stress the package body.
The Installation Interface in Detail
The mounting interface deserves its own detail, because it is where discrete IGBT designs most often fail:
- Tab electrical potential. The TO-247 tab is the collector in most parts and is electrically live. The isolation pad must carry both the dielectric rating for the operating voltage and the thermal conductivity for the heat path; a pad that satisfies one and not the other fails the design.
- Mounting torque window. The datasheet’s recommended torque range sets the contact pressure. Below the window, air gaps raise the interface resistance; above it, the package body or the insulator cracks. The torque specification is a design input, and a torque-controlled driver is the production control.
- Heatsink flatness. The interface assumes the heatsink surface is flat within the package’s expectations. A bowed or warped heatsink concentrates the pressure at the edges and leaves the center of the tab floating; the flatness check belongs in the mechanical review.
- Clip versus screw. A clip applies a defined force without a screw, simplifying assembly and improving consistency for TO-220-class parts; the screw gives higher force and a controlled torque for TO-247. The choice trades assembly speed against interface control.
- Creepage and clearance. The tab-to-heatsink path and the lead-to-tab spacing must respect the working voltage and pollution degree; the insulator’s shape and the board’s slotting contribute to the required distances.
- Parallel layout symmetry. When multiple TO-247 IGBTs are paralleled, the gate drive, the power loop, and the mounting must be symmetric; one device with a different torque or a longer gate trace carries the transient current and ages first.
Each item is a measurable specification—the dielectric rating, the torque window, the flatness, the creepage—and the package drawing plus the mechanical review carry them. The generic thermal-chain method belongs to the package-thermal guide; this page owns the interface details.
The Freewheeling Diode and the Discrete Pair
An IGBT in a switching stage needs a freewheeling diode across it. In a module, the diode is co-packaged and matched; in a discrete design, the pair is chosen by the designer:
- Co-packaged discrete IGBTs. Many TO-247 IGBTs include the diode in the same package (the “F” suffix on some families); the diode’s current, recovery, and thermal data are in the same datasheet.
- Separate discrete diode. If the IGBT is not co-packaged, select a diode rated for the load current, the recovery behavior, and the shared heatsink. The diode’s loss adds to the heatsink budget, so the pair’s total, not the IGBT alone, is the thermal input.
The reverse-recovery behavior of the freewheeling diode directly stresses the IGBT at turn-on; the diode and IGBT are a system, and the selection should treat them as one.
A Selection Path for Discrete IGBTs
- Fix the electrical requirement: bus voltage, current, frequency, and the overload duty.
- Choose the package by current and thermal budget: TO-220 for low power, TO-247 for the mainstream, TO-263 for SMT.
- Design the mounting and insulation: insulator, TIM, screw torque, and the case-to-heatsink Rth budget.
- Size the freewheeling diode with the IGBT as a pair.
- Check the short-circuit and SOA data against the protection scheme.
- Verify the thermal path on the real assembly at full load.
The insulation system deserves its own line: the insulator’s voltage rating, the creepage between the tab and the heatsink, and the board’s clearance at the operating voltage are part of the package selection, not an afterthought. The 1700 V article’s insulation discipline applies at the discrete level too, scaled to the voltage class.
For the discrete families and packages in this class, the product catalog on the Good-Ark site is the entry point; to compare discrete IGBT options for your current and package, contact Good-Ark.
Frequently Asked Questions
When should I use a discrete IGBT instead of a module? For currents up to roughly 40–75 A where cost, sourcing, and layout flexibility matter more than the module’s integrated loop and thermal design. Above that range, the module usually wins.
Does the TO-247 tab need to be isolated from the heatsink? Yes, if the tab is the collector and the heatsink is grounded. Use a rated insulator and TIM; the insulator’s thermal resistance is part of the thermal budget.
Can I parallel TO-247 IGBTs? Yes, with matched saturation voltage and symmetric gate drive and layout. The parallel discipline from the IGBT selection articles applies: individual gate resistors and thermal coupling.
Where can I check the package outline and mounting data? The Documents section carries the package outlines and thermal data, and the contact page connects you to the team for mounting-specific support.
The Package Is Half the Thermal Design
The discrete IGBT’s electrical ratings come from the die; its real performance comes from the mounting. Choose the package by current and budget, design the insulator and TIM into the thermal chain, pair the freewheeling diode with the IGBT, and verify the case-to-heatsink path at full load. When the mounting is right, the discrete IGBT is one of the most economical power switches available; when it is wrong, no datasheet number saves the design.