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Laminated Busbar Design Guide – From Specification to Finished Part

08/21

2026

By A&J Link Engineering Team · Last updated August 2026 · 11 min read
The short answer
The laminated busbar design process in one screen.
  • ✓Design starts with the specification. Current, voltage, ambient, mechanical envelope and applicable standard — these five inputs determine every decision that follows.
  • ✓Seven steps, in order. Specification → layer stack → conductor geometry → current and temperature → insulation → terminals → verification.
  • ✓Each step constrains the next. Changing the layer stack moves the insulation, which moves the terminals, which moves the envelope. The design is a whole, not a list.
  • ✓Verify before manufacturing. Electromagnetic and thermal simulation, plus a first-article check, catch most problems before tooling is cut.
Designing a laminated busbar is not a matter of picking a size and drawing an outline. It is a sequence of decisions, each of which constrains the next — and the order matters. This laminated busbar design guide walks through that sequence, from the specification that starts the project to the verification that closes it.
It is written for engineers who need to translate a system requirement into a manufacturable part, and for procurement teams who need to understand what the supplier is actually deciding. Each of the seven steps below states what is decided at that stage, and points to a more detailed article where the calculation or method is covered in full.
Scope: this article covers the design process itself — the sequence of decisions. How to select a standard part from a catalogue is a separate subject, covered in our selection guide. The two are complementary: selection answers "which part", design answers "how is it made".
This guide sits inside our broader laminated busbars technical library, which covers selection, manufacturing, installation and maintenance.

1. Start with the Specification

Every design decision flows from the specification. Before any geometry is drawn, five inputs need to be defined.
1.1 The Five Design Inputs
  • Current. Continuous and peak, with the duty cycle and any fault current requirement.
  • Voltage. System voltage class, which determines creepage, clearance and insulation requirements.
  • Ambient and cooling. Ambient temperature, airflow or cold-plate availability, and the allowable temperature rise.
  • Mechanical envelope. The available space, mounting points, and interface with surrounding components.
  • Applicable standard. IEC 61439-1 for assemblies, or an application-specific requirement for higher-voltage systems.
1.2 Why the Order Matters
These five inputs are not independent. Increasing the current for the same envelope forces a larger conductor, which reduces the available insulation space, which affects both the voltage rating and the achievable inductance. Changing the cooling condition changes the allowable current density, which changes the conductor size, which changes the envelope again.
This is why the specification has to be agreed before design begins. A specification that is still moving will produce a design that is still moving — and the later the change happens, the more expensive it becomes.

2. Define the Layer Stack

With the specification fixed, the first geometry decision is the layer stack — how many conductor layers, and in what order.
2.1 The Layer Count Follows the Topology
The circuit topology determines what layers are needed. A simple DC link uses P–N. A multi-phase converter may use P–N–P or P–N–GND. The designer chooses the topology; the layer stack follows it. What matters at this stage is that the total conductor cross-section — thickness × number of current-carrying layers — will meet the current requirement from the specification.
2.2 Polarity Arrangement and Inductance
How the positive and negative layers are arranged has a direct effect on loop inductance. The closer the opposing conductors, the smaller the loop area and the lower the inductance. This is the reason laminated construction exists — but the specific techniques for translating a topology into a low-inductance geometry are treated separately in our article on inductance reduction.
2.3 Layer Order and Thermal Behaviour
The order of layers also affects heat dissipation. The outer layers have a direct cooling path to the environment; inner layers rely on conduction through the stack. Where the stack has more than two current-carrying layers, the middle layers will run hotter for the same current — a factor that must be accounted for when the conductor cross-section is sized in step 4.

3. Define the Conductor Geometry

With the layer stack set, the next decision is the shape of each conductor — width, thickness and path.
3.1 Width vs Thickness
For the same cross-section, a wider and thinner conductor dissipates heat better than a narrow and thick one, because more of the copper is close to a cooling surface. Thickness beyond about 10 mm gives diminishing returns: the internal thermal path becomes long enough that added copper does not add much capacity. This trade-off is one of the most useful rules of thumb in busbar design.
3.2 Cross-Section and Current
The cross-section sets the raw current capability, but the actual rating depends on cooling. For naturally cooled copper, the usual design band is 1.2 to 2.0 A/mm²; for forced air or cold-plate cooling, higher values are achievable. The full calculation, including derating factors, is covered in a separate article.
3.3 Routing and Bend Radius
The routing of the conductor follows the mechanical envelope. Bends are formed before lamination, and the bend radius has to be large enough to avoid cracking or excessive work-hardening of the copper. Where the conductor must follow a non-planar path, the forming is done as a separate operation before the stack is assembled.

4. Size for Current and Temperature

With the geometry sketched, the next stage is to confirm that it meets the current and thermal requirements — and to adjust if it does not.
4.1 Current-Carrying Check
The first check is whether the conductor cross-section can carry the specified current at the intended cooling condition. A density estimate gives a quick answer; the calculation method and derating factors are covered in our guide to busbar current capacity.
4.2 Temperature Rise Verification
The second check is that the resulting temperature rise stays within the applicable limit — for bare copper under IEC 61439-1, that means a rise of no more than 105 K above ambient. How temperature affects resistance and insulation life, and why the limit is set where it is, is covered in our article on busbar temperature performance.
4.3 When Simulation Is Needed
For simple geometries, the density estimate plus a derating factor is enough. For high-current or tightly enclosed designs, or where the cooling path is not obvious, a full thermal simulation is warranted. Deciding when simulation is needed is part of the design process; the method itself is covered separately.

5. Define the Insulation System

The insulation between layers is what makes the busbar safe at its rated voltage — and it also sets the minimum spacing that determines the achievable inductance.
5.1 Material Selection
Common insulating films are PET, PEN and polyimide. The choice is a balance between dielectric strength, temperature rating and cost. PET is the general-purpose option; polyimide is used where the highest temperature or the thinnest possible layer is required. The selection criteria are covered in our article on insulation materials.
5.2 Creepage and Clearance
The applicable standard sets minimum creepage and clearance distances for the system voltage. These distances determine how far apart the conductors and terminals must be, and they often constrain the physical envelope more than the conductor does — particularly at higher voltages.
5.3 Insulation Class and Temperature
The insulation system has a thermal class — B (130 °C), F (155 °C), H (180 °C) — and its temperature must stay within that class throughout its service life. In most designs, the insulation class is the limiting factor, not the copper. The relationship between temperature and insulation life is covered in our article on busbar temperature performance.

6. Define Terminals and Connections

The terminals are where the busbar meets the rest of the system — and where electrical performance is most often lost.
6.1 Terminal Type
Bolted, welded and press-fit terminals are all common. The choice depends on the current, the serviceability requirement, and the interface with the surrounding components. In many designs, more than one type is used — a bolted terminal where the busbar connects to a removable module, and a welded terminal where it connects to a permanently installed component.
6.2 Contact Resistance
The resistance of the joint is a design parameter, not an afterthought. A poor joint adds localised heating exactly where there is the least material to dissipate it, and the elevated temperature accelerates oxidation of the contact surfaces, raising the resistance further. Design techniques for keeping joint resistance low are covered in a dedicated article on bolted connections.
6.3 Mechanical Interface
The terminal positions and mounting points have to match the surrounding hardware. Bolt-hole spacing, stud size and mounting orientation are fixed by the mating components, not by the busbar design — which means the terminal layout is often the least flexible part of the design.

7. Verify Before Manufacturing

The final stage is verification — confirming that the design as drawn meets the specification before any tooling is cut.
7.1 Electromagnetic Verification
For any application where inductance matters, the loop inductance of the proposed geometry is verified by electromagnetic simulation. The result is compared against the target derived from the switching behaviour of the downstream converter.
7.2 Thermal Verification
Thermal verification confirms that the temperature rise stays within the applicable limit at the intended cooling condition. For most custom designs, this is done by simulation; the method and its limitations are covered in our article on thermal simulation with ANSYS.
7.3 First Article and Production Handoff
A prototype is produced and tested to confirm what simulation cannot fully capture — contact resistance at the terminals, actual temperature rise of the assembled part, and mechanical fit in the real enclosure. Once the first article is approved, the design is handed off to production, where process consistency and traceability determine whether unit ten matches unit one.

Frequently Asked Questions

What is the first step in designing a laminated busbar?
Define the specification: current (continuous and peak), voltage class, ambient and cooling condition, mechanical envelope, and the applicable standard. These five inputs determine every subsequent decision, and they need to be agreed before any geometry is drawn. A specification that is still moving will produce a design that is still moving.
How many layers should a laminated busbar have?
The layer count follows the circuit topology, not a fixed rule. A simple DC link uses P–N; multi-phase converters may use P–N–P or P–N–GND. What matters is that the total conductor cross-section — thickness multiplied by the number of current-carrying layers — meets the current requirement. The arrangement of those layers then determines the loop inductance.
Why is a wide, thin conductor better than a narrow, thick one?
For the same cross-section, a wide and thin conductor has more surface area close to the copper, so heat reaches the surface more easily and is dissipated more effectively. A narrow and thick conductor has a longer internal thermal path. Beyond about 10 mm thickness, the gain from additional copper flattens — the internal path becomes too long to help.
How is the temperature rise checked?
For bare copper under IEC 61439-1, the allowable temperature rise is 105 K above ambient. The design is checked against that limit using either a calculation for simple geometries or a full thermal simulation for high-current or tightly enclosed designs. The insulation class also sets a second limit, and usually the lower of the two controls the design.
When is simulation needed in busbar design?
Simulation is warranted when the geometry is complex, the current is high, the enclosure is tightly sealed, or the cooling path is not obvious. For simple, well-ventilated designs, a density estimate plus a derating factor is sufficient. The two most common simulation types are electromagnetic (for loop inductance) and thermal (for temperature rise).

Summary

This laminated busbar design guide follows seven steps, in order: specification, layer stack, conductor geometry, current and temperature sizing, insulation, terminals, and verification. Each step constrains the next, and the design is coherent as a whole rather than a list of independent decisions. The specification is the foundation; verification before manufacturing is the close.
  • Start with five inputs. Current, voltage, ambient and cooling, mechanical envelope, applicable standard.
  • Layer stack follows topology. P–N, P–N–P or P–N–GND — and the arrangement sets the inductance.
  • Wide and thin beats narrow and thick. For the same cross-section, surface area determines cooling.
  • Verify before tooling. Electromagnetic and thermal simulation, plus a first-article check.
Designing a laminated busbar for a new project?
Send us your specification — current, voltage, envelope and cooling — and our engineering team will confirm the layer stack, conductor geometry and insulation for your application.
Request a Design Review

References & Standards

  1. IEC 61439-1 — Low-voltage switchgear and controlgear assemblies, Part 1: General rules. International Electrotechnical Commission. webstore.iec.ch

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