Introduction To The Welding Process For Printed Circuit Board (PCB)

There are two different selective welding processes: drag welding and dip welding.

The selective drag welding process is performed on a single small tip solder wave. The drag welding process is suitable for welding in very tight Spaces on a PCB.

For example, individual solder joints or pins, single row pins can be used for drag welding process. The PCB moves on the solder wave of the nozzle at different speeds and angles to achieve the best welding quality. In order to ensure the stability of welding process, the inner diameter of the welding nozzle is less than 6mm. After the direction of solder solution is determined, the solder nozzles are installed and optimized in different directions for different welding needs. Manipulator can be from different directions, namely 0° ~ 12° between different angles close to the solder wave, so users can weld various devices on the electronic components, for most devices, the recommended inclination Angle is 10°.

Compared with the dip welding process, the solder solution of drag welding process and the movement of PCB board make the heat conversion efficiency in the welding process better than the dip welding process. However, the heat required to form the weld joint is transferred by the solder wave, but the mass of the solder wave of the single nozzle is small, and only the temperature of the solder wave is relatively high, in order to meet the requirements of the drag welding process.

Example: the solder temperature is 275℃ ~ 300℃, the drag speed of 10mm/s ~ 25mm/s is usually acceptable. Nitrogen is supplied in the welding area to prevent the oxidation of solder waves, which eliminates the oxidation and avoids the generation of bridge defects in the drag welding process. This advantage increases the stability and reliability of the drag welding process.

The machine has the characteristics of high precision and high flexibility, the module structure design system can be fully customized according to the customer’s special production requirements, and can be upgraded to meet the needs of future production development. The radius of motion of the manipulator can cover the flux nozzle, preheat, and solder nozzle, so that different welding processes can be performed on the same equipment. The unique synchronous process of the machine can greatly shorten the single board process cycle. The manipulator has the ability to make this selective welding with high precision and high-quality welding characteristics.

The first is the precise positioning ability of the manipulator height stability (±0.05mm), to ensure that the parameters of each plate production height repeat consistently;

Secondly, the 5-dimensional motion of the manipulator enables the PCB to contact the tin surface at any optimized Angle and orientation to obtain the best soldering quality.

The tin wave height measuring needle installed on the splint device of the manipulator is made of titanium alloy. Under the control of the program, the tin wave height can be measured regularly. The tin wave height can be controlled by adjusting the rotating speed of the tin pump to ensure process stability.

Despite all these advantages, the single-tip wave tow process has its drawbacks: the welding time is the longest of the three processes: flux spray, preheat, and soldering. And because the solder spots are one by one drag welding, with the increase of the number of solder spots, the welding time will increase significantly, in the welding efficiency is not compared with the traditional wave soldering process. But that is changing, and multiple nozzles are designed to maximize production. For example, double nozzles can be used to double production, and double nozzles can be used for flux.

The immersion selective welding system has multiple solder nozzles and is designed one-to-one with the PCB solder spot. Although the flexibility is not as good as the manipulator type, the output is equivalent to the traditional wave soldering equipment, and the equipment cost is lower than the manipulator type. Depending on the size of the PCB, single or multiple plates can be transferred in parallel, and all pending solder joints will be fluxed, preheated, and soldered in parallel at the same time. However, due to the different distribution of solder joints on different PCB, it is necessary to make special solder nozzles for different PCBs. It is important and difficult for the design engineer to keep the size of the weld nozzles as large as possible to ensure the stability of the welding process without affecting the surrounding components on the PCB, because the stability of the process may depend on it.

Using immersion selective welding process, welding joints of 0.7mm ~ 10mm can be welded. The welding process of short pins and small size pads is more stable, and the possibility of bridging is small. The distance between adjacent solder joint edges, devices, and welding nozzles should be greater than 5mm.