In PCBA production, applying flux is an indispensable part. There are many kinds of flux coating methods, such as foam coating method, spray coating method, brush coating method, dip coating method and jet coating method. Today we mainly introduce the foam coating method and spray coating method.

1. Foam coating method

The foam coating device is generally composed of a flux tank, a nozzle, and a porous foam tube immersed in the flux. The foam tube should be immersed in the flux, about 50mm away from the liquid surface, when a certain pressure of pure air is fed into the porous tube, a stable flux foam flow will be formed above the nozzle. The PCB passes through the peak of the foam wave, and coats a layer of flux with a uniform thickness and a controllable thickness on the soldering surface of the PCB. In this device, the density control of the flux is very important. The quality of the flux peak formation depends largely on the density of the flux, the pressure of the gas and the level of the flux above the foam tube.

2. Spray coating method

The spray coating method is divided into direct spray method, rotary spray method and ultrasonic spray method. The direct spray method is also called the spray method and is only suitable for coating liquid flux with low solid content. Direct spray coating system usually consists of flux storage tank, spray head, air flow regulator and so on. The rotary spray method is also called the rotary screen spray method, which mainly uses a rotary screen made of stainless steel or other flux-resistant materials, and part of it is immersed in a flux container. When the PCB adopts the long insertion method, the height of the component leads extending out of the PCB surface can reach 5cm, which is the most suitable method. In the foam wave coating method, the height of the lead exposed on the PCB surface is usually limited to less than 1.5 cm. Rotary spray system usually consists of flux, rotating screen, slotted stainless steel pipe, air flow regulator and so on. The flux stuck in the holes of the rotating screen meets the high-speed airflow sprayed from the slot on the top of the stainless steel tube, forming a coating on the lower surface of the PCB and the component area. The ultrasonic spray method uses the cavitation effect of ultrasonic energy to turn the liquid flux into an atomized form and apply it to the soldering surface of the PCB.

The above is about the commonly used flux coating methods in PCBA production, do you understand?