D2PAK and TO-220 are both capable 30–40 A rectifier packages, but they embody two different thermal philosophies: the D2PAK turns the PCB into the heatsink, while the TO-220 bolts to an external one. The right choice follows the product’s mechanical architecture—dense board or chassis-level cooling. This article compares the two heat paths and maps them to application profiles.
Two Thermal Philosophies: Board Copper vs Bolt-On Heatsink
A rectifier’s junction temperature is set by the total loss times the total thermal resistance from junction to ambient. The package determines which part of that chain is practical: a D2PAK’s exposed pad spreads heat into PCB copper, so the board design is the heatsink; a TO-220’s tab is made to be clamped to an external heatsink, so the mechanical assembly is the heatsink. Both can carry 30 A continuously only if the board copper or the heatsink assembly actually removes the conduction loss; the package’s nominal current rating is not a system capability.
The philosophy shows up in the datasheet numbers. The AMBRB3045CT, a 30 A, 45 V dual Schottky in D2PAK, lists 2.0 °C/W junction-to-case; the AMBR40250S, a 40 A, 250 V Schottky in TO-220AB, also lists 2.0 °C/W. Identical device-level resistance, completely different system-level heat paths.
The comparison is therefore never about the packages’ datasheet numbers alone; it is about which heat path the product can actually build. A chassis with room for a heatsink favors the TO-220; a sealed board with no access favors the D2PAK—and the boundary moves with the mechanical design, not the electrical rating.
The same philosophy appears at the system level: a D2PAK design spends board area and copper weight, a TO-220 design spends a mounting step and a heatsink—so the choice is also a manufacturing and BOM decision, not only a thermal one.
The D2PAK Path: Copper, Vias, and Solder
For the D2PAK, the exposed pad is the thermal exit, and everything after it is board design. The pad needs a matching copper area on the PCB, thermal vias into inner planes, and a solder joint that actually connects—a voided solder joint adds resistance no external heatsink can recover. The board copper then spreads the heat to the enclosure or airflow.
The practical limits: the heat path grows with copper area, so the D2PAK rewards boards with room to spare; in a dense board with a small pad, the effective resistance climbs toward the junction-to-ambient figure and the 30 A capability shrinks. D2PAK suits sealed, board-level modules where an external heatsink is mechanically impossible—automotive ECUs, compact power stages, and lighting modules.
Solder quality is the hidden variable: a voided joint under the exposed pad can add several °C/W that no copper area recovers, so the D2PAK decision includes an inspection plan—X-ray or cross-section on first builds and a thermal check of the pad temperature. Via density is the other design lever: a pad with a generous copper area but no vias leaves the heat in the top layer, where it cannot reach the far side of the board. The path also scales with current: at 30 A the copper requirement is substantial; at 10 A a modest pad suffices—another reason the package decision is current-dependent.
The TO-220 Path: TIM, Torque, and Airflow
For the TO-220, the tab is the thermal exit, and the mechanical assembly takes over: a thermal interface material fills the air gaps between tab and heatsink, screw torque sets the contact pressure, and the heatsink’s size and airflow set the ambient-side resistance. The path is predictable and powerful—a chassis with a properly sized heatsink can remove far more heat than a board pad—but it costs assembly steps, space, and a mounting system.
The tradeoff inside the TO-220 world: the same part can run at 40 A on a large heatsink and at a fraction of that on a poorly mounted tab. Mounting quality is the thermal design, which is why the TO-220 mounting guide treats torque, TIM, and insulation as engineering parameters rather than assembly details.
A typical 30 A stack shows the leverage: with an effective forward drop near 0.9 V, the load dissipates about 27 W, and at 2.0 °C/W junction-to-case that is roughly 54 °C from case to junction before the heatsink is even in the chain. The TO-220 wins exactly when the heatsink can carry that 27 W to the airflow; the numbers make the assembly the center of the design.
Current, Space, and Cost Tradeoffs
| Decision factor | D2PAK (board mount) | TO-220 (bolt-on) |
|---|---|---|
| Heat path | PCB copper and vias | External heatsink via TIM |
| Thermal ceiling | Limited by board area and airflow | Limited by heatsink size |
| Assembly | SMT, reflow | Through-hole + screw/TIM |
| Board space | Modest footprint, needs copper | Larger hole pattern, tab clearance |
| Mechanical robustness | Good under vibration | Tab must be secured |
| Isolation | Pad isolated on the board | Tab may be live; insulation pad needed |
| Typical fit | Sealed board-level modules | Chassis power with real heatsink |
The cost comparison is system-level: a D2PAK saves the heatsink but needs a copper-heavy board; a TO-220 needs the heatsink but can use a simpler board. At volume, the board-area cost of the D2PAK and the assembly cost of the TO-220 usually decide.
The isolation decision also belongs on the cost sheet: a D2PAK pad is isolated by the board, while a TO-220 tab may need an insulation pad and bushing that add thermal resistance and a small extra cost. The two packages end up with different system BOMs even when the die and ratings are equivalent.
Airflow availability is part of the same tradeoff: a chassis with forced air makes the TO-220’s heatsink far more effective, while a passively cooled product may have no airflow to push through fins at all.
Choosing by Application Profile
Three profiles cover most decisions. First, the sealed board-level module—automotive ECU, lighting driver, compact adapter: the D2PAK fits because there is nowhere to bolt a heatsink, and the board can be designed with copper and vias. Second, the chassis-level power supply—OBC, server power, industrial drive: the TO-220 fits because a real heatsink with airflow removes the continuous 30–40 A heat that a board pad cannot. Third, the hybrid: a TO-220 with a small, well-vented heatsink in a mid-power adapter, where the assembly cost is justified by a lower board cost.
One more variable is the production line: a plant already set up for SMT pays less to add a D2PAK than to introduce a through-hole, torque-controlled assembly step, and vice versa. The manufacturing footprint is part of the application profile, not an afterthought.
When the current class and mechanical architecture are settled, the comparison reduces to one number: the total system thermal resistance from junction to ambient that the product can actually achieve—then pick the package whose path you can build.
Engineering note. The comparison above follows the datasheet rating structure of the AMBRB3045CT and AMBR40250S—both 2.0 °C/W junction-to-case, with the D2PAK path completed by board copper and the TO-220 path by TIM, torque, and heatsink. RθJA figures (50–62.5 °C/W on the datasheet-published parts) assume defined mounting conditions; the achievable system resistance depends on the actual board or heatsink design, so confirm with a case-temperature measurement on the prototype.
Frequently Asked Questions
Which package carries more current, D2PAK or TO-220?
Both can carry 30–40 A with the right heat path; the D2PAK needs generous board copper and vias, the TO-220 needs a properly mounted heatsink. The system thermal design, not the package name, sets the limit.
Is the TO-220 always better for high power?
Not automatically. A TO-220 with a large heatsink and airflow can remove more heat than a board pad, but if the product cannot accommodate a heatsink, the D2PAK with a copper-heavy board is the practical answer.
Do I need thermal vias for a D2PAK?
Usually yes, for 30 A-class currents: the exposed pad connects to a copper pad, and vias into inner planes spread heat through the board. Without them the heat stays in the top layer and the effective resistance rises.
Can the TO-220 tab be electrically live?
Yes, in many circuits the tab connects to the cathode or anode potential. If the heatsink must be grounded or touched, use an electrically insulating pad and bushing rated for the voltage, and accept the added thermal resistance.
How do I decide between the two for a sealed module?
If there is no access for a heatsink, the D2PAK is usually the answer—design the board copper and vias early. If the chassis allows a heatsink and airflow, the TO-220 gives a higher thermal ceiling for continuous current.
Conclusion
D2PAK and TO-220 are two ways to solve the same equation: get the heat from junction to ambient. The D2PAK spends board copper and vias; the TO-220 spends a heatsink and assembly. Match the package to the product’s mechanical architecture, size the real heat-flow route, and confirm with a prototype measurement.
Browse the standard bridge rectifiers category on the Good-Ark site, and contact Good-Ark with your current class and mechanical layout for a package recommendation.