SMT solder paste printing step process explanation

In order to standardize the solder paste printing process in SMT workshops and ensure the quality of solder paste printing, SMT has formulated the following process guidelines for solder paste printing in SMT workshops.

SMT solder paste printing steps

1. Tools and accessories used in the SMT solder paste printing process:

1. Printing press

2. PCB board

3. Steel mesh

4. Solder paste

5. Solder paste stirring knife

2. SMT solder paste printing steps

1. Check before printing

1.1 Check the correctness of the PCB to be printed;

1.2 Check whether the surface of the PCB board to be printed is complete without defects and dirt;

1.3 Check whether the steel mesh is consistent with the PCB, and whether its tension meets the printing requirements;

1.4 Check whether the stencil is blocked. If there is any blockage, wipe the stencil with dust-free paper and alcohol, and dry it with an air gun. When using the air gun, keep a distance of 3-5CM from the stencil;

1.5 Check whether the solder paste used is correct and whether it is used in accordance with "Storage and Use of Solder Paste". Note: Pay attention to the temperature recovery time, stirring time, and the distinction between lead-free and lead-containing.

2, SMT solder paste printing

2.1 Fix the correct stencil to the printing press and debug OK

2.2 Assemble a clean and good scraper onto the printing press;

2.3 Add the solder paste to the stencil with a solder paste stirring knife. The height of the solder paste is about 1CM and the width is 1.5-2CM for the first time. The length depends on the length of the PCB. The two sides are about 3CM longer than the printing area. ; After adding solder paste every two hours, the amount of tin is about 100G;

2.4 Put the PCB board for printing, the first 5 PCS boards to be printed require full inspection. After the printing quality is OK, notify IPQC for the first inspection. After confirming that there is no abnormality in the printing quality, notify the production line operator to start production.

2.5 During the normal printing process, the operator needs to check the printing effect every half an hour to see if there are any undesirable phenomena such as less tin, continuous tin, tip drawing, displacement, and missing printing. SOP, row plug" and other key points to check the printing effect.

2.6 The stencil needs to be cleaned once every 5PCS is printed. If there are components with too dense pins "BGA, QFP, SOP, socket" on the PCB, the cleaning frequency should be increased and cleaned once every 3PCS.

2.7 During the production process, if it is found that the continuous 3PCS printing is not good, the technician should be notified to debug it; the PCB board with poor printing should be cleaned. When cleaning poorly printed PCBs, do not use hard objects to scrape the surface of the PCB directly to prevent scratches on the surface of the PCB. PCBs with golden fingers should avoid the golden fingers. After repeatedly wiping with dust-free paper and a little alcohol, use an air gun. Blow dry, check under a magnifying glass, no residual solder paste is OK.

2.8 During the normal printing process, it is necessary to regularly check whether the solder paste overflows, and collect the overflowing solder paste.

2.9 After the production is over, the accessories and tools such as solder paste, scraper and stencil should be recovered, and the fixtures should be cleaned according to the "Storage and Use of Solder Paste" and "Guidelines for Cleaning of Stencils".

3. Solder paste printing process requirements

3.1 The main defects of printing are: less tin, continuous tin, sharpening, displacement, missing printing, more tin, collapse, dirty PCB board, etc.

3.2 The thickness of solder paste printing is -0.02mm～+0.04mm of stencil thickness.

3.3 Ensure that the welding effect after the furnace is free of defects.