PS900 Soldering System Reduces Micro Cracking

OK International has launched a soldering system for PV tabbing and bussing applications that reduces micro cracking. The PS900 with specially designed hoof-tip geometry optimises the power delivered to the solder joint, while its temperature-sensitive heater ensures low-temperature soldering, thus minimising thermally induced stresses on cell surfaces. The system incorporates the company's patented Smartheat technology, which will produce and maintain a specific, self-regulated temperature with a heater that does not require calibration and that responds directly to thermal loads.

There are two suitable solder alloys utilised for solar-cell soldering applications: the Sn96Ag4 with a melting point of +221C or the bismuth-containing Bi58Sn42 with a melting point of +138C. Proper soldering will result in an intermetallic layer that is 1-2um, which demands precise time and temperature control during the solder-joint formation. Hoa Nguyen, vice-president of technology, said: 'The ability to solder at low, controlled temperatures within a short time window reduces the stresses on the cells and the likelihood of micro cracking.

'Connection temperatures must be maintained below 300C. 'This new system employs Smartheat technology to produce thermally controlled, high-quality solder joints,' added Nguyen. The micro cracking of delicate solar-cell substrates is a common defect that can occur during PV tabbing and bussing soldering processes. Reducing the soldering temperature to a minimum prevents the cells being subjected to mechanical or thermal stresses. During the soldering operation, the differential thermal expansion of the copper and the silicon elements can occur at temperatures greater than +300C.

This differential can result in the formation of micro cracks that may not be detected during the manufacturing process and result in a reduced field lifespan. The OK Smartheat PS-900 soldering system with a specially designed STV-DRH40 hoof-tip geometry optimises the power delivered to the solder joint, thus providing high-performance efficiency with increased tip life, according to the company. The temperature-sensitive 'T' heater series ensures low-temperature soldering and thus minimises thermally induced stresses on the surface of the solar cells.

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