In order to standardize the solder paste printing process in SMT workshop and ensure the solder paste printing quality, SMT processing factory has formulated the following process guidelines, which are applicable to solder paste printing in SMT workshop. The Engineering Department is responsible for the formulation and modification of the guidelines; Be responsible for setting printing parameters and improving defective processes. The Manufacturing Department and the Quality Department shall implement the guidelines to ensure good printing quality.
1、 Tools and accessories used in SMT solder paste printing process:
1. Printing machine
2. PCB board
3. Steel mesh
4. Solder paste
5. Solder paste mixing knife
2、 SMT Solder Paste Printing Steps
1. Inspection before printing
1.1 Check the correctness of PCB to be printed;
1.2 Check whether the surface of PCB to be printed is complete and free of 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 steel mesh is blocked. If it is blocked, wipe the steel mesh with dust-free paper and alcohol, and dry it with an air gun. When using an air gun, keep a distance of 3-5 cm from the steel mesh;
1.5 Check whether the solder paste used is correct, and whether it is used according to the "Storage and Use of Solder Paste". Note: Pay attention to the temperature recovery time, mixing time, and the distinction between lead-free and leaded solder paste.
2. SMT solder paste printing
2.1 Fix the correct steel mesh on the printing machine and debug it;
2.2 Assemble the clean scraper onto the printing machine;
2.3 Use the solder paste stirring knife to add the solder paste to the steel mesh. The height of the first solder paste is about 1CM, the width is 1.5-2CM, and the length depends on the length of the PCB. The two sides can be about 3CM longer than the printing area, and should not be too long or too short; After that, add solder paste every two hours, and the amount of tin is about 100G;
2.4 Put in PCB board for printing. The first 5 PCS boards to be printed require full inspection. After the printing quality is OK, notify IPQC for first inspection. After confirming that the printing quality is normal, notify the production line staff to start production;
2.5 During the normal printing process, the staff should check the printing effect every half an hour to see if there are any defects such as less tin, tin connection, tip pulling, displacement, missing printing, etc., and focus on the printing effect of pin dense components such as "BGA, QFP, SOP, row plug";
2.6 The steel mesh shall be cleaned every 5PCS printed. If there are components "BGA, QFP, SOP, row plug" with too dense pins on the PCB, the cleaning frequency shall be increased every 3PCS;
2.7 In the production process, if 3 consecutive pcs of poor printing are found, notify the technician for debugging; Clean the PCB board with poor printing. When cleaning the poorly printed PCB, do not scratch the surface of the PCB directly with hard objects to prevent scratching the circuit on the surface of the PCB. For the PCB with gold fingers, avoid the gold fingers. After repeatedly wiping with dust-free paper and a little alcohol, dry it with an air gun, and check under a magnifying glass. It is OK if there is no residual solder paste;
2.8 During the normal printing process, it is necessary to regularly check whether the solder paste is overflowing, and collect the overflowing solder paste;
2.9 After the production is completed, the auxiliary materials and tools such as solder paste, scraper and stencil shall be recovered, and the tooling and fixtures shall be cleaned according to the "Storage and Use of Solder Paste" and "Guidelines for Steel Mesh Cleaning";
3. Solder paste printing process requirements
3.1 The main defects of printing include: less tin, continuous tin, sharpening, displacement, missing printing, more tin, collapse, dirty PCB, etc,
3.2 Solder paste printing thickness is -0.02mm~+0.04mm of steel mesh thickness;
3.3 Ensure that the welding effect behind the furnace is free from defects;
Hongqiao Technology Co., Ltd. is a high-tech enterprise specializing in the research, development and production of cutting fluid, electronic hardware cleaner, surface treatment agent, welding materials: solder paste, tin rod, tin wire, BGA solder ball, SMT tin, electronic flux and thinner, electronic welding equipment and accessories, electroplating anode plate (rod), semi tin ball and other products.