Key takeaways
- A battery interconnect is a current path, a fuse and a weld interface at the same time, so the drawing has to control all three.
- Copper and aluminium need different sections for the same current, and the joint between them needs its own design and test.
- The fuse neck is the most tolerance-sensitive feature: a small change in width or thickness moves the melting current.
- Volume decides the process: a progressive die for high volume, laser cutting or a simple tool for prototypes and low volume.
What counts as a battery interconnect
A battery interconnect carries current between cells, modules or the pack terminals. In a stamped form it can be a cell connector that joins two cylindrical cells, a module busbar that collects several cells, a flat conductor that links a module to a fuse box, or a plate that carries current through a pack wall. The shapes differ, but they share a set of requirements: low resistance, a controlled fuse behaviour where needed, a reliable weld or bolt interface and a surface that suits the joining process.
Stamping suits these parts because they are flat, thin and produced in volume. A progressive die can blank the outline, pierce the weld windows, coin the fuse neck and form a locating feature in one strip. The same part can also be laser cut from sheet at low volume, which is useful for prototypes and for pack variants that do not justify a die.
The part is rarely just a conductor. It is a mechanical locator, a thermal path and sometimes a sensor connection. The design review should include the pack assembly, the weld process and the service access, not only the electrical rating.
| Part | Function | Material | Critical call |
|---|---|---|---|
| Cell connector | Joins adjacent cells | Copper or aluminium | Weld area and current section |
| Module busbar | Collects several cells | Copper, often nickel plated | Section, flatness and hole position |
| Fuse link | Opens on overcurrent | Copper or copper alloy | Neck width, thickness and edge |
| Sense tab | Voltage or temperature sensing | Copper alloy | Weld or crimp and isolation |
| Pack plate | Carries current through a wall | Copper or aluminium | Sealing face and clearance |
A single part can combine several rows. A module busbar may also carry a fuse neck and a sense tab.
Material and plating
Copper is the default for high current because it has the lowest resistance among the common conductor metals. Aluminium is lighter and cheaper per kilogram, but it needs a larger section for the same current and it forms a resistive oxide that has to be managed at the joint. Copper alloys such as brass or phosphor bronze are used where spring force or strength matters more than pure conductivity.
The temper matters as much as the alloy. A soft temper forms easily but can deform under clamp load. A harder temper holds its shape but cracks at a tight bend. The drawing should state the temper and the bend radius, and the supplier should confirm that the material can take the form without an edge crack.
Plating is a joint decision. Nickel is common for weldability and corrosion resistance, tin is common for bolted joints and solderability, and silver is used where contact resistance matters. The plating thickness and the masked areas should be on the drawing, because a weld window with the wrong plating can change the weld quality. Unplated copper that is handled and stored can oxidise, so the process route and the shelf life matter.
The oxide is the joint
Aluminium forms an oxide within minutes of cleaning. A welded aluminium joint needs a process that breaks or displaces that oxide, and a bolted joint needs a contact surface that stays clean. The plating and the joint design have to be developed together.
Sizing the conductor
The section is set by the current, the allowable temperature rise and the duty cycle. A continuous current needs a larger section than a short pulse, and a part inside a sealed pack may run hotter than the same part in free air. The calculation should use the actual ambient, the cooling path and the terminal temperature, not a generic current density.
A simple illustrative example: a copper conductor 20 mm wide and 1 mm thick has a section of 20 mm squared. At a current density of 5 A per mm squared, that is about 100 A continuous, before any derating for temperature or grouping. These numbers are illustrative and must be checked against the actual thermal and duty conditions.
The shape of the section matters too. A wide, thin conductor has more surface for cooling but less stiffness. A narrow, thick conductor is stiffer and easier to bend in one plane. The current path should be as short and as direct as the pack layout allows, because every extra millimetre adds resistance and heat.
Fuse links and weak points
Some interconnects include a fuse: a narrowed neck that melts when a cell or module draws too much current. The neck is a calibrated weak point, and its behaviour depends on the width, the thickness, the length, the material and the heat sinking around it. A small burr or a rounded corner can change the melting current and the time to open.
The drawing should specify the neck dimensions with a tight tolerance, the material temper and the edge condition. The supplier should control the die wear at the neck station and inspect the neck on a sample basis. If the neck is coined or rolled, the thickness reduction should be measured, not assumed.
Fuse testing is a system test, not a material test. The part has to be tested in the pack or in a representative fixture at the specified current and ambient. A test on a free part in air can give a different result from a part clamped to a busbar or buried in a module. The test plan should match the installation.
Weld tabs, bolt pads and joints
A weld tab needs a flat, clean area with enough material for the weld tool and enough clearance for the tool body. The tab should not sit at the end of a narrow neck where the heat cannot dissipate. The weld schedule should be developed on the actual material and plating, not on a coupon of a different grade.
A bolted joint needs a flat pad, a defined contact area and a fastener that can hold the clamp load. The pad should be stiff enough not to dish under the bolt, and the plating should suit the mating surface. A joint between aluminium and copper needs a bimetallic interface or a plated barrier to avoid galvanic corrosion.
Ultrasonic welding, laser welding and resistance welding each need a different tab design. Laser welding needs a gap-free interface and a clean surface. Ultrasonic welding needs a sonotrode footprint and a support anvil. Resistance welding needs electrode access on both sides. The joining method should be chosen before the tab geometry is frozen.
Insulation, clearance and the pack environment
A bare interconnect in a pack needs clearance to the housing and to other conductors, and the creepage distance depends on the voltage, the pollution degree and the material. A coated part can reduce the clearance, but the coating has to cover the edges and survive the pack temperature and the vibration.
Heat shrink, powder coating, dip coating and laminated film are the common insulation routes. Each adds thickness and changes the bend radius and the fit. The coating should be specified with a thickness, a dielectric strength and a temperature rating, and the drawing should show which areas are masked for welding or bolting.
The pack environment adds condensation, salt mist, vibration and thermal cycling. A part that passes a room-temperature insulation test can still fail after a damp heat cycle. The validation plan should include the environmental sequence that the pack will see, not only a single dielectric test.
Volume and process choice
At prototype volume, laser cutting from sheet is usually the fastest and cheapest route. It needs no die, it can produce a variant in a day and it gives a clean edge. The limitation is the cut speed and the cost per part at volume, and the fact that a laser-cut edge has a different burr and heat-affected zone from a stamped edge.
At high volume, a progressive die is usually the right answer. It can blank, pierce, coin, form and mark in one strip, and the piece price falls as the tooling is amortised. The die needs a stable drawing and a volume that justifies the tool. A part with several variants may suit a family die with interchangeable inserts, or a laser cell that can switch programs.
The volume break is not a single number. It depends on the part size, the number of stations, the material cost and the finishing route. A small interconnect with a simple outline may justify a die at a lower volume than a large plate with several forms. The comparison should be made on total cost per good part, including the scrap value of the copper.
What to inspect
The first article should include the outline, the hole positions, the weld window, the fuse neck, the pad flatness and the plating thickness. The burr on the contact and weld surfaces should be checked, because a burr can hold a weld off the interface or create a high point under a bolt.
Functional checks depend on the part. A fuse link needs a resistance check and a calibration test. A welded assembly needs a pull or shear test and a cross-section. A bolted joint needs a contact resistance or a millivolt drop check. A coated part needs a dielectric test and a coating thickness check.
Traceability should link the part to the coil lot, the die run and the plating batch. For a battery programme, a defect that appears in one lot can often be traced to a material or a process change. The record is part of the quality pack and should be agreed before the first shipment.
Frequently asked questions
Can battery interconnects be aluminium instead of copper?
Yes, where the larger section and the joint design are acceptable. Aluminium is lighter and cheaper per kilogram, but it needs a bigger section for the same current and a joint process that handles the oxide. The choice is usually made on weight, cost and the joining route together.
How tight should a fuse neck tolerance be?
Tight enough to keep the melting current inside the specified band. The exact tolerance depends on the neck geometry and the fuse rating. The drawing should also control the edge condition and the material temper, because both affect the result.
What plating is best for a welded battery interconnect?
Nickel is common because it welds well and resists corrosion. The right choice depends on the welding process and the mating material. The plating thickness and the masked weld areas should be specified and tested on the actual joint.
When does a stamped interconnect need a progressive die?
When the volume is steady and high enough to amortise the tool, and the drawing is stable. At prototype or low volume, laser cutting or a simple tool is usually faster and cheaper. The break-even depends on part size, stations and finishing.
Sources and further reading
- ISO 6469-1, Electrically propelled road vehicles, safety specifications, rechargeable energy storage system
- IEC 60529, Degrees of protection provided by enclosures
- Qumek EV interconnect stamping and DFM notes
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