Busbar Surface Treatment - Battery Design

There are a number of different surface treatments that primarily fall into those designed to insulate and those designed to improve electrical contact resistance. There are some specific thermal properties that can also be improved by surface treament.

Insulation

These coatings include:

Heat-Shrink Tubing
- PVC
- Polyolefin
Epoxy Powder Coating
Solid/Structural Insulators
- Fiberglass-reinforced Plastics: DMC/BMC/SMC
- Ceramic/Porcelain
- Polyester/Thermoplastic
Film Insulation
Silicone

Electrical Contact Resistance

Plating the surfaces of busbars where they connect has a number of functions:

improved surface flatness
reduce oxidation
- Copper Surface Corrosion
create a malleable surface that conforms under pressure

Rachman et al [1] show the contact resistance of copper busbars versus contact pressure for different surface coatings.

The coating/plating materials are:

Gold
- highest corrosion resistance
- high cost
Nickel
- high hardness
- wear resistant
- reasonable corrosion resistance
- base plating – used to improve uniformity of top plating such as gold
Silver
- highest electrical conductivity
- low and stable contact resistance
- enhances solderability
Tin
- reduced friction and wear
- oxide layer is conductive
- malleability improves contact surface area

There are also advantages with dual plating [2]:

Nickel and Tin
- nickel acts as a diffusion and corrosion barrier, which can significantly reduce tin whisker growth
Nickel and Silver
- nickel underlayer acts as a diffusion barrier to prevent copper migration
- low contact resistance
- excellent corrosion and oxidation protection
- superior performance in high-current, high-temperature applications

Thermal Properties

Sometimes copper busbars are painted black to increase the radiative heat loss, the Copper Association [3] give a good pros and cons rationale:

Since the natural emissivity of a copper bar that has been in use for even a short time will be above 0.5 and probably approaching 0.7, the benefit of increasing it to 0.9, although positive, will be small. On the negative side, the paint layer acts as an insulator, reducing the efficiency of the convection process. In general, painting will give little increase and possibly a reduction in the currentcarrying capacity of a busbar for a given working temperature. Painting may be worthwhile for very wide bars (where convection is less effective) operating at large temperature rises (where radiation is more effective).