SMT Reflow Soldering Oven: How It Work

By Harriett Crosby

When it comes to soldering of electrical components on to printed circuit board (PCB), surface mount technology (SMT) is the most widely used method. The SMT reflow soldering oven is the machine that has greatly contributed to this technology. Highly technical principles in bonding are all put together to ensure optimal functionality of this particular machine that has literally transformed the electronics industry. In addition to precise control of this process, the machine consumes less power than other methods used and produces more products per unit time than any other method.

This is one of the machines that get used more often than any other machines in the electrical line of assembly. Before passing over to the oven, the solder paste made of flux, small solder particles and chemical cleaning agents is used to loosely attach the electrical components on to the printed circuit board (PCB) and then sent to the next step.

It involves joining of electrical components on to contact pads with solder paste and heat. In the process of highly controlled heating that take place in the oven, solder melts in the right position and permanently join the electrical components on PCB in the process.

Through a conveyor belt, the PCB and the mounted components are directed into the oven. This requires time and temperature precision to avoid destroying any of the components. There are four phases that these components pass through in the oven. In starts at preheat zone where time/temperature rate (ramp rate) is determined. This is important to the other zones too as it gives the correct temperature to be used. The melting point of solvent is also set here.

The second zone is the thermal soak zone. Removal of paste volatiles takes place here through a 60 to 120 second heat exposure of the PCB at a predetermined temperature. This is followed by the reflow stage, the stage in which the whole thing happens. Printed circuit board and components are exposed to the highest possible temperatures. The tolerable (liquidus) temperature for each of the component is determined and the maximum temperature is set just below it. This forces reduction between the surface tension between solder particles so that they melt at the point of contact on the pad.

The 4th zone is the cooling stage where control cooling ensures that the components are correctly placed and fixed. In all these stages, both heating and cooling process is keenly controlled to avoid any thermal shock that may damage the components or the PCB.

Most of these ovens use ceramic heaters as the source of heat. The heat flows to the assemblies through hot air using fan (radiation) or just the infrared electromagnetic radiation. As the new models are introduces, the techniques of heat transfers are improved.

These machines have gained favor with electronic assemblers for various reasons. These include simple methods of operating, faster production, high level of accuracy, produces much more component per unit time than any other method. In addition to this, depending on the model, it is possible to attach the components on both sides of PCB and there is efficiency in electricity utilization.

In order to remain relevant in electrical assembly industry, just like any other industry, it is important to use highly efficient and most up-to-date technology. There are latest models SMT reflow soldering oven that offers efficiency level that results to high productivity and profitability to a firm.

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