To be able to exploit the full range of commercially available microchips when making E-yarns it is crucial that separate fine wires can be soldered onto multiple solder pad. Previously, the semi-automated soldering process could only solder a single fine wire to a given component. For two-terminal devices, such as LEDs or thermistors, this wire would be soldered to both solder pads and then cut creating to discrete connections.
The Advanced Textiles Research Group (ATRG) are now able to solder two terminal devices onto insulated copper wires in parallel. This is a critical step towards being able to solder multi-terminal (>2 terminal) chips. The new process is achieved by carefully controlling two parallel, insulated copper wires using stepper motors. A solder paste dispenser is moved over the fine wires using a robotic arm and a predetermined quantity of solder paste is applied to each wire. A pick-and-place machine is then used to place the chip onto the solder paste dots, and an infra-red heat source is used to solder the chip onto the wires using a reflow soldering process.
Not only is this a step towards soldering more complex devices in an automated fashion but the ability to solder components to wires in parallel can be useful when using two-terminal devices as it allows both copper wires to leave one end of the yarn. This simplifies the insertion of the E-yarn into a garment as the other end of the E-yarn does not need to loop back to the hardware module or battery.