Nordson EFD has developed a non-contact dispense valve for precision jetting of low viscosity flux onto solar cell bus bars.
Operating at speeds up to 500Hz/sec, the Square Wave 745NC valve meets the photovoltaic industry’s need to deposit continuous lines of microdots on the solder-coated metal ribbons that connect adjoining PV wafers.Flux removes oxidation and contamination to improve solar cell efficiency and power output.
The Square Wave’s innovative solenoid technology delivers a high-speed cycle rate that minimises process variation for repeatable dot-to-dot consistency. A low actuation speed of 2 milliseconds prevents build-up of flux crystals on the valve’s nozzle which could prevent the fluid from being deposited precisely on the bus bar. The pistons’ unique material reduces friction and wear. Tests showed over 880 million cycles of use without any deterioration.
Because of its non-contact design, the Square Wave never touches the delicate and brittle PV wafer; therefore, breakage and rejects are minimised. A special nozzle enables multiple orifice diameters from 100 - 175 microns so deposit sizes and volumes can be easily changed.
“Nordson EFD’s 745NC solves the problems of slow evaporation, excess non-activated flux, flux build-up, clogging of the nozzle, and prevents encapsulation delamination caused by excessive flux application,” explained Terry Dunbar, Nordson EFD market development manager.
“These factors drive up the cost-of-ownership and increase manufacturing down-time. The 745NC uses the least amount of flux and produces the highest utilisation strength of the solar cell strings.”