PCB Technical - Techniques for controlling solder paste printing in PCBA

The techniques for controlling solder paste printing in PCBA are introduced as follows:

Paste printing is very important for PCBA. It directly affects the overall soldering effect of PCBA. In the process of PCBA processing, how to do solder paste printing has become a problem that must be considered by production managers. The effect of solder paste printing consists of four parts: stencil, solder paste, printing process, and detection method.

1. Steel mesh

The opening of the stencil must be appropriately enlarged or reduced according to the layout of the electronic components on the PCBA board to determine the amount of tin on the pad, so as to achieve the best soldering effect, avoid the occurrence of tin connection, less tin, etc., which requires craftsmanship The engineer conducts a rigorous evaluation. In addition, the material of the steel mesh is also critical, which affects the tension of the steel mesh and the life of repeated use.

In addition, the cleaning and storage environment before feeding the steel mesh is particularly critical. Strict cleaning must be carried out each time before going online, and check whether the vias are blocked or there is tin dross. Some PCBA manufacturers recommend purchasing a stencil tension meter, and perform a tension test of the stencil before each feeding.

Two, solder paste

Solder pastes need to be selected from mid-to-high-end brands, such as Senju, Vitero, etc., and it is better to contain active ingredients such as gold or silver. The solder paste must be stored strictly in a refrigerator at 2 to 10 degrees Celsius, and relevant statistics must be made for each storage and delivery. The recovery of solder paste must be strictly controlled within the scope of the IPC standard, and the tin paste must be strictly implemented before going online. Paste mixing program.

Three, solder paste printing

At present, manufacturers are using fully automatic solder paste printers, whose equipment can well control the printing strength and speed and other parameters, and has a certain automatic cleaning function. The operator only needs to set the parameters in strict accordance with the regulations.

In the mass production process, it is particularly important to detect the phenomenon of blocked holes and deviations of the stencil, especially when some defects detected by SPI after printing show an upward trend, it is necessary to stop the machine to check the operating conditions of the stencil itself.

Four, SPI printing effect detection

After the solder paste printing machine, it is particularly important to configure the SPI solder paste detector, which can effectively detect many defects such as small tin, continuous tin, gap, wire drawing, offset and so on in the solder paste printing process. So as to maximize the overall welding PPM value.

It is not a secret to manage the effect of solder paste printing. It requires managers to carefully implement every management method in the PCBA processing process. And design a set of closed-loop mechanism that can find and detect defects.