Can you explain the role of prefluxing in wave soldering for Electronic component assembly

prefluxing in wave soldering for Electronic component assembly

The basic principle of wave soldering is quite simple: After the components have been placed on a printed circuit board (PCB), the assembly is placed on a conveyor that moves it across a tank of liquid molten solder. The molten solder forms a ridge that contacts the component leads and PCB circuitry. This is a far more efficient process than manually hand soldering individual components.

But the successful operation of a wave soldering line depends on a huge number of variables, each of which can create serious defects. The most common defects are burrs, bridging shorts, and excess solder. The best way to avoid these problems is to preflux the components. This is a step that the electronic manufacturing company or contract assembly manufacturer takes before putting the parts through the reflow oven on a conveyor belt.

During the prefluxing process, the parts are coated with liquid electronic component assembly. The flux removes oxidation from the metal surfaces of the part and helps the solder to wet them. This helps ensure that the solder will make good contact with the metal and that there will be no bridging or spikes in the electrical conductivity of the joint.

Oxidation is the enemy of good soldering; it prevents the easy movement of electrons between atoms that makes metals the best electrical conductors. The oxidation also creates a rough surface that repels solder, so it won’t easily cling to the metal surface. In a pure state, metals are quite reactive and want to combine with other elements to form compounds that lock the electrons in place, which doesn’t allow them to move freely.

Can you explain the role of prefluxing in wave soldering for Electronic component assembly

In the past, the oxidation on metal surfaces was removed by coating them with glue. This was done on the part before it went into the reflow oven to keep the parts from falling off during reflow. This added cost, equipment maintenance, and time to the process. Glue can also leak and drip onto parts that are not being soldered, which can cause them to fail prematurely.

As technology evolved, and circuit boards became more complex, the skinny symmetrical wave that was originally used in the early days of wave soldering began to prove inadequate. Large components needed to be placed very close together, and this caused small parts to be “shadowed” by larger ones – preventing the solder from reaching them. The high rosin concentrations of the fluxes that were so helpful in preventing excess solder became liabilities in this new situation. Solder skips and trapped air can also interfere with the process, causing failures.

The solution was to introduce a turbulent (“chip”) wave before the original asymmetrical wave. This forced the molten solder to move more aggressively in three dimensions, helping it to overcome the shadowing effects of large components and push aside flux that might otherwise cling to the parts. This helped to eliminate the bridging shorts and excess solder that plagued through-hole assemblies. In some cases, the chip wave can be turned off and only the laminar wave used for soldering.

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