In the past, most industrial solder pastes were made using oxidized powder produced by simple air atomization. Pressure to improve the control of the size range of solder pastes, and to avoid the use of corrosive halide fluxes, has led to a demand for lower oxide levels. In addition, increased use of automated oxygen analyzer application systems has led to much more critical specifications for paste heology and stability in storage. In turn, this leads to a demand for a smaller maximum particle size, with limits on fines, especially super-fines (e.g. sub 20 microns).
Resulting from these pressures, ultrasonically atomized solder powder is ideal for this growing market. Ultrasonically atomized solder powder can offer:
The marketplace requires a spread of solder powder sizes, with premium prices paid for good quality solder powder of 50-70 microns. The challenge is to increase the solder powder yield, improve the solder powder quality and reduce the production cost.
The rapid atomizing and cooling of the solder powder requires a specific level of oxidation to form on the surface of the droplet. If there is too much oxygen in the atomizing tower, excess metal oxides form on the surface causing large conglomerations of material and poor yields. If there is too little oxygen, the droplets re-combine as they cool, giving a ‘rain’ like effect in the tower and forming poorly shaped droplets with reduced yields. Controlling the oxygen level in the tower is complicated, as the desired and normal droplet oxidation tends to reduce the oxygen available as the atomizing process proceeds.
Henkel Loctite Adhesives have been working with oxygen analysis specialists Systech Illinois to take a fresh look at the requirements for efficient production of solder powder, with the aim of increasing the efficiency in both their lead and lead-free solder regimes. In order to fully understand the solder powder production process and the level of control required, a Systech Model 9513 automated oxygen controler system was installed. Originally developed to control the oxygen level in a reflow solder oven and reduce purge nitrogen consumption, the Systech Model 9513 with advanced control electronics has proved ideal for monitoring and controlling the oxygen level in Henkel’s atomizing towers. In this application, the Systech Model 9513 continually monitors the oxygen level in the tower, and uses that signal together with the internal program settings and fuzzy logic controller to vary the flow rate of a bleed of compressed air into the system.
Following an extended trial of the system, Henkel engineers determined the oxygen level for optimum yield and production efficiency. Henkel is now using the Systech Model 9513 as its automatic oxygen controller to maintain the levels of oxygen in the atomizing towers, ensuring the best quality production conditions are maintained.
In addition to the improvements in yields, Henkel have also been able to reduce the amount of nitrogen used to inert their towers. This has resulted in direct cost savings of over £8000 per year per tower, offering Henkel an excellent return on investment and minimal payback time.