Prefluxing in Wave Soldering for Board Assembly
A jiggling component, a dangling wire or a loose screw can easily throw off the entire functionality of a circuit board. That’s why, after layout design and fabrication, a board needs to be assembled correctly. Fortunately, automated services such as pick-and-place machines help to reduce costs and human error during at-scale production.
But, the question remains: what are the best methods for board assembly? Whether your board requires conventional leaded through hole components or surface mount ones, there are many assembly techniques to choose from. One of the more traditional is wave soldering. Wave soldering is less common today than other methods such as infra-red reflow, which is more suitable for the smaller pitch surface mount components found on modern PCBs.
Wave soldering is a process where a wave of hot molten solder passes across the underside of a printed circuit board. This allows solder to flow from pin to pad, creating a solid bond between them. The heat from the molten solder also melts the flux and pre-heats the board.
In a typical setup, a conveyor transports the board through a heated tunnel where the pre-heat and activation of the flux takes place. The board is then transferred to a machine which produces the wave of molten solder. The board is then cooled as it moves through the machine and the wave height can be adjusted by adjusting the pump pressure on the machine.
The Role of Prefluxing in Wave Soldering for Board Assembly
The first turbulent wave in the wave soldering process provides wash action to remove residual liquid flux, and flushes away organic layers that may have formed on the surface of the board. The second smooth laminar wave forms the solder fillet and prevents bridging. The board is then quenched at a slower rate than the heat transfer process to protect the boards from warpage and allow time for the solder joints to reflow and solidify.
When you’re working with a manufacturer that offers PCB assembly services, make sure they’re using the right equipment. The quality of your finished product depends on it. The soldering stage of board assembly, which includes techniques like reflow soldering and wave soldering, is highly dependent on precise temperature control:
In this process, solder paste is applied to the PCB pads, and components are placed on top. The board then passes through a reflow oven, where it is heated to melt the solder paste and create electrical connections. The temperature profile in the reflow oven must be meticulously controlled to ensure the solder melts correctly without damaging the components. Excessive temperatures can cause component warping or failure, while insufficient temperatures can lead to poor solder joints and unreliable connections.
Used primarily for through-hole components, this process involves passing the PCB over a wave of molten solder. The temperature of the molten solder must be carefully regulated to ensure it flows properly and forms solid joints. Too high a temperature can cause solder bridging and damage to the PCB, while too low a temperature can result in weak solder joints.
