Technical Support

SMT solder paste printing step-by-step process explanation

In order to standardize the SMT shop solder paste printing process and ensure the quality of solder paste printing, SMT has developed the following process guidelines applicable to SMT shop solder paste printing. GT’s engineering department is responsible for the development and revision of the guidelines; it is responsible for setting printing parameters and striving to improve poor processes. GT’s manufacturing and quality departments are then responsible for implementing the guidelines to ensure good print quality. So today, I bring you the SMT solder paste printing steps, take a look!

SMT solder paste printing steps

I. Tools and auxiliary materials used in SMT solder paste printing process.

1, printing machine
2, PCB board
3, stencil
4, Solder paste
5, solder paste stirring knife

Second, SMT solder paste printing steps

1, check before printing

1.1 Check the correctness of the PCB board to be printed.
1.2 check whether the surface of the PCB to be printed is complete and free of defects and dirt.
1.3 Check whether the stencil is consistent with the PCB and whether its tension meets the printing requirements.
1.4 Check whether the stencil is plugged, if there is plugging, the stencil should be wiped with dust-free paper dipped in alcohol and blown dry with an air gun, using an air gun to maintain a distance of 3-5CM from the stencil.
1.5 Check whether the use of solder paste is correct, whether according to the “storage and use of solder paste” use, Remarks: pay attention to the return temperature time, stirring time, lead-free and leaded distinction, etc.

2, SMT Solder Paste Printing

2.1 Fix the correct stencil to the printing machine and debug OK.
2.2 Assemble clean and good squeegee to the printing machine.
2.3 Add the solder paste to the stencil with the solder paste stirring knife, the first time add the solder paste height at about 1CM, width 1.5-2CM, length depending on the PCB length, both sides than the printing area can be about 3CM long, should not be too long or too short; later add solder paste every two hours, the amount of tin about 100G.
2.4 Put into the PCB printing, printing the first 5PCS board requires full inspection, after the printing quality OK, notify IPQC first inspection, confirm the printing quality is not abnormal, notify the production line operator to start production.
2.5 During the normal printing process, the operator should check the printing effect once every half hour to see if there is less tin, even tin, pulling the tip, shift, leakage and other bad phenomena, and focus on the printing effect of overly dense components such as “BGA, QFP, SOP, row of plugs”, etc.
2.6 Every 5PCS printing, need to clean the stencil once, if the PCB board has too dense pin components “BGA, QFP, SOP, row of plugs”, to increase the frequency of cleaning every 3PCS cleaning.
2.7 During the production process, if 3 PCS printing is found to be bad in a row, notify the technician to debug; clean the PCB board with bad printing. When cleaning poorly printed PCB, do not use hard objects to directly scrape the surface of the PCB to prevent scratching the PCB surface lines, PCB with gold fingers, should avoid gold fingers, wipe repeatedly with dust-free paper with a little alcohol, blow dry with a wind gun, check under a magnifying glass, no residual solder paste for OK.
2.8 During the normal printing process, check regularly whether the solder paste is overflowing, and collect the overflowing solder paste.
2.9 after the end of production, to recover solder paste, scrapers, stencils and other auxiliary materials and tools, and cleaning of fixtures, specifically according to the “storage and use of solder paste” and “stencil cleaning operating guidelines” operations.

3, solder paste printing process requirements

3.1 The main printing defects are: less tin, even tin, pull tip, shift, leakage, more tin, collapse, PCB board dirty, etc.
3.2 solder paste printing thickness for the stencil thickness -0.02mm ~ +0.04mm.
3.3 to ensure defect-free soldering effect after the furnace.


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