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How to avoid printing faults in SMT processing?
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How to avoid printing faults in SMT processing?

How to avoid printing faults in SMT processing?

In the electronics industry, PCBA processing mostly adopts SMT processing, and there are many common faults in the process of use. According to statistics, 60% of defects are caused by solder paste printing. Therefore, ensuring high quality solder paste printing is an important premise to ensure the quality of SMT patch processing. Next, SMT processing manufacturers will introduce how to avoid printing failures in SMT processing.

The solution of printing fault in SMT patch processing

96 (1)

First, there is no gap between the mold and the PCB printing method, which is called "touch printing". 

All structures require high stability and are suitable for printing high-precision solder paste. After printing, the wire mesh board has good contact with the printed board and is separated from the PCB. Therefore, the printing accuracy of this method is high, and it is especially suitable for fine gap and ultra-fine printing.

1. Printing speed.

When the scraper is pushed up, the solder paste rolls forward. Fast printing is conducive to stencil printing.

The rebound also prevents the solder paste from leaking. In addition, the slurry can not roll in the screen, resulting in low solder paste clarity, which is also the reason for the fast printing speed.

2. Printing method:

Common printing methods are touch printing and non-contact printing, screen printing and blank printing on printed circuit boards. The printing method is "non-contact printing", generally 0.5 × 1.0mm, which is suitable for solder paste with different viscosity. Push the solder paste into the steel mesh with a scraper, punch holes, and contact the PCB board. After gradually removing the scraper, the steel mesh is separated from the PCB, reducing the risk of vacuum leakage in the steel mesh.

3. Scraper type: 

There are two kinds of scraper: plastic scraper and steel scraper. For ics with PITCH≤0.5mm, the use of steel scraper should be used for printing to facilitate the formation of solder paste after printing.

4. Adjustment of scraper

In the welding process, the operating point of the scraper is printed in the direction of 45°, which can significantly improve the non-uniformity of the solder paste opening and reduce the damage of the perforated steel plate. The pressure of the scraper is generally 30N/mm.

Second, the installation should choose the IC installation height of the spacing does not exceed 0.5mm, 0mm or 0~-0.1mm, so as to avoid the installation height is too low to cause the solder paste collapse, short circuit during reflux.

Third, refusion welding.

The main reasons for reflow assembly failure are as follows:

a. The temperature rises too fast; 

b. The heating temperature is too high; 

c. The solder paste heating speed is faster than PCB; 

d. Excessive water flow.

Therefore, when determining the reflow welding process parameters, various factors should be fully considered to ensure that the welding quality is not a problem before batch assembly. Our own SMT processing plant can provide SMT processing services for minimum package 0201 components. The SMT plant is equipped with 3 Fuji high-speed SMT lines, 2 DIP plug-in production lines, equipped with AOI optical detector, automatic solder paste printing machine, semi-automatic solder paste printing machine, lead-free wave soldering, lead wave soldering, upper and lower 8 temperature zone reflow welding, PCBA functional test frame, aging, board loading machine, cleaning tools, etc., at the same time, a professional research and development laboratory is set up. Five professional engineers cooperate with customers to perform general functional testing, test point testing, as well as channel, noise, waveform, drop and temperature testing. 

Shenzhen Kingford Technology Co., Ltd. specializes in providing integrated PCBA electronic manufacturing services, including upstream electronic component procurement to PCB production and processing, SMT patches, DIP plug-ins, PCBA testing, finished product assembly and other one-stop services.

Just upload Gerber files, BOM files and design files, and the KINGFORD team will provide a complete quotation within 24h.