Designing and manufacturing superior custom batteries

Steatite has extensive experience of manufacturing custom battery packs and we’ve just added extra capability to our remit.

Our engineers have been successfully spot welding and arc welding packs for a number of years. Spot welding is suitable for the vast majority of our cells, where parts are up to 3mm in thickness. The process does not require excessive heat and the energy delivered to the spot can be carefully controlled to produce reliable welds. Our semi-automated production lines are tailored specifically to create the optimum bond for specific cells and applications, and regularly adapted for changing requirements.

We’ve recently installed an Asterion™ wire bonder, manufactured by K&S and provided by Inseto to add wire bonding to our inhouse capabilities.

Compared to traditional methods of interconnecting, wire bonding enables manufacturers to offer custom battery packs with high discharge capabilities and reduced assembly time (in a shorter lead time) which meet even higher levels of reliability and safety. Wire bonding helps to prolong cell life and improve battery performance as a result of lower resistance.

Steatite specialises in creating custom batteries which often need to be built in a particular size and shape for unusual housings, and wire bonding allows us the flexibility to place cells in tailored positions and still maintain strong and dependable connections.

What is wire bonding?

Wire bonding is an interconnect technology used to bond integrated circuits, semiconductors and other electronic devices. The process is used by high quality battery manufacturers for the production of Lithium-ion battery pack assembly.

There are three different types of wire bonding: ball bonding, suitable for small wires only; wedge bonding, suitable for small and wide diameter wires; and compliant bonding.

In addition, different wire bonding techniques can be used:

• Thermocompression (wedge: ball) bonding is the original technique, dating back to 1957. This method requires high force and high temperature – around 300°C – but is
viewed as reliable and robust.

• Ultrasonic (wedge: wedge) bonding relies on pressure and vibrational energy and so is carried out at lower temperatures (around 25°C) and is the most common technique for
Aluminium wires.

• Thermosonic (ball: wedge) bonding is the most prevalent method of wire bonding and is conducted at temperatures between 100°C and 240° High pressures are not required
as the bond is formed through ultrasonic energy.

Gold was originally the material of choice for wire bonding technology but Aluminium has now become increasingly widespread due to its good electrical performance and lower cost. Copper wire is another option and is favoured by some manufacturers due to its inherent stability and similarly low cost.

Steatite’s wire bonder

The Asterion model is a rotary head ultrasonic wedge bonder featuring a graphical bond head setup, advanced bond process diagnostics, integrated pull test & loop control with an optional configurable bond head, segmented bonding, extensive logging capabilities, and advanced vision for component alignment.

This model was selected due to the larger bondable area: the 300 x 300mm working area and 0.1μ resolution is ideal for ultrasonic bonding of large wires and ribbons to batteries. The low operating temperature means that components are less likely to be damaged during the process, making the resultant battery packs robust and reliable. Creating new wires is simple and intuitive using the windows-based graphical user interface.

Close up of cells with wire bonds

Pull testing capability was also particularly important in the selection process to ensure every pack which leaves our manufacturing site is as robust as possible. The process involves positioning a hook underneath the wire and pulling either until the bond breaks (destructive testing) or a pre-defined force is reached (non-destructive testing).

The location of the wire bond on the bond pad is, of course, extremely important for a secure bond, and we are confident that the Asterion bonder maintains excellent control of bond positioning.

Build, test and test some more

To ensure that Steatite battery packs are correctly and safely bonded, they are tested to comply with several standards, including MIL-STD-883. This military-grade standard stipulates the following mechanical tests for electronics:

• Internal visual.

• Destructive bond pull test.

• Non-destructive bond pull test.

• Ball bond shear test.

• Constant acceleration.

• Random vibration.

• Mechanical shock.

• Stabilisation bake.

• Moisture resistance.

Our engineers also have the capability to design and build bespoke test equipment to analyse, program and test many of the custom battery packs that we design and manufacture. For our more advanced batteries that are designed to operate in high temperature environments, we also have a large thermal test chamber.

Additionally, our battery test facility houses a large selection of power supplies and electronic loads to enable automated emulation of customer applications to aid with testing suitability and projected lifetime of battery packs, often before the final application design is completed.

Power failure is not an option in many of the critical applications we manufacture batteries for. With our best-in-class wire bonding facilities and stringent test capability, customers can be assured that our battery packs will deliver consistent power throughout the lifecycle of the pack.

Expert battery engineering

We will now be able to deliver wire bonded battery packs to customers covering a range of applications including medical, industrial, oceanographic, transport and energy.

We know that every cell that leaves our factory having been wire bonded is safe, reliable and robust. This is in addition, of course, to our traditionally bonded battery packs which have been tried and tested over decades.

See more of what we do and how we can support your standard or custom battery pack requirements: