SMT Stencil Printer Setup Guide: 5 Steps to Achieve Precise Solder Paste Deposition

Introduction

In modern electronics manufacturing, solder paste printer is the first key process in the SMT production line, affecting the yield and reliability of the entire product. Among them, the correct setup of SMT stencil printer is crucial for the accurate deposition of solder paste.

In this article, we will discuss the basic working principle of SMT stencil printer, the key parameters affecting the quality of solder paste printing, and provide a set of systematic setup guide to help you improve the accuracy and consistency of solder paste printing, and ultimately improve the overall production efficiency and product quality.

I. The role of the SMT stencil printer and the basic principles

1. Definition of stencil printing

SMT stencil printer is through the stencil will be solder paste accurately printed to the PCB on the pads of the process, the process determines the quality of the solder joints in the subsequent reflow oven process.

2. The workflow of the solder paste printer

2.1. The core part of the SMT stencil printer 

• PCB positioning system: Used to fix and align the PCB
• Stencil clamping device: To fix the stencil and keep it flat
• Squeegee system: To control the solder paste in the stencil coating and pressing
• Visual alignment system: Automatic identification of PCB and stencil deviation between
• Control system: Coordination of the action of various components to achieve automated printing

2.2. Printing steps

PCB is placed and fixed.

Stencil drops down and is in close contact with PCB.

Solder paste is applied to stencil.

Squeegee pushes solder paste through the stencil opening at a set angle and pressure.

Stencil is lifted up, and solder paste stays on PCB pads.

Completes a printing cycle.

II. The main factors affecting the accuracy of solder paste deposition

1. Stencil design and quality

• Hole size and shape: Should be based on the size of the pad, the type of components and solder paste particle size reasonable design.
• Thickness selection: The commonly used thickness of 0.1mm ~ 0.15mm, the thickness of too large will lead to excessive amount of solder paste.
• Material and processing accuracy: Laser cutting stencil more accurate than chemical etching, suitable for high-density fine-pitch printing.

2. Solder paste performance

• Viscosity and thixotropy: Good solder paste should have the right viscosity, which can flow under the action of the squeegee, but also can maintain the shape after printing.
• Particle size and distribution: The finer the solder paste particles, the higher the printing resolution, but too fine may increase costs.
• Storage and use environment: Temperature and humidity need to be controlled to avoid oxidisation or drying out.

3. Printing parameter setting

• Squeegee angle and speed: Usually the recommended angle is 45°~60°, and the speed control is between 20~80 mm/s.
• Squeegee pressure: Too much pressure may lead to stencil deformation or solder paste extrusion; too little will not be able to fill effectively.
• Mould release speed and distance: Too fast mould release may cause solder paste pulling or collapsing; too slow will affect the efficiency.
• Snap-off Distance: The initial distance between the stencil and the PCB, affecting the effect of solder paste release.

4. Equipment Status and Maintenance

• Mechanical Accuracy: Including XY platform repetitive positioning accuracy, Z-axis lifting and lowering accuracy.
• Cleanliness: Stencil, squeegee and PCB carrier need to be cleaned regularly to prevent residue from affecting printing quality.
• Vision system calibration: ensure that the image recognition system can accurately detect alignment errors.

III. How to set up the SMT stencil printer to ensure accurate solder paste deposition?

1. Preparation stage

1.1. PCB and stencil matching check

Verify that the PCB drawing and stencil design are consistent.

Use microscope or AOI equipment to check the stencil openings for blockage or burrs.

Check the PCB board surface for oil, warpage and other problems.

1.2. Solder Paste Status Confirmation

Check whether the solder paste is within the shelf life.

Make sure the solder paste has warmed up to room temperature (usually 4 hours in advance).

Mix well before use.

2. Initial parameter setting

2.1. Vision Alignment Setting

• Start the machine vision system and select the Mark points on the PCB and stencil for alignment.
• Set the offset tolerance range (e.g. ±0.025mm) and alarm or stop when it exceeds the range.
• For complex boards, multi-point alignment function can be enabled to enhance the accuracy.

2.2. Printing Parameter Configuration

• Squeegee Angle: It is recommended to set 45°~60°.
• Squeegee speed: Initially set at 40 mm/s, adjustable according to the flow of solder paste.
• Squeegee pressure: Generally 30 ~ 80N, depending on the thickness of the stencil and pad density adjustment.
• Mould height: Set to 0.05 ~ 0.2mm, to avoid solder paste wire drawing.
• Printing gap: Set to 0.05 ~ 0.1mm, to ensure that the solder paste can be released smoothly.

3. Test printing and debugging

3.1. First sample printing

Use the standard sample plate for the first printing.

Visual inspection of the solder paste is complete coverage of the pad, there is no leakage, bridging, offset phenomenon.

Solder paste inspection machine can be used to measure the volume, height, position and other parameters of the solder paste.

3.2. Parameter Optimisation

• If there is insufficient solder paste, the squeegee pressure can be increased or the squeegee speed can be reduced.
• If there is too much solder paste, reduce the pressure or increase the speed.
• If the edge of the solder paste is blurred, it may be that the mould release is too fast or the viscosity of the solder paste is too low.
• If there is an offset, recalibrate the vision system or check the mechanical accuracy.

4. Formal Production Setup

4.1. Establish SOPs

Save the parameters of successful debugging as templates for the same products.

Write clear operation procedure documents to ensure consistency of execution by operators.

Set up regular reminders to clean the stencil and scraper to prevent contamination.

4.2. Implement online monitoring

Configure SPI system to monitor the quality of solder paste printing in real time.

Set up automatic rejection mechanism for defective products.

Record each printing data for traceability and analysis.

IV. Common Problems and Solutions 

V. Advanced Suggestions for Improving Printing Quality

1. Regular Maintenance and Repair

• Regularly lubricate the guide rails and transmission parts.
• Clean the optical lens and sensor.
• Replace worn squeegees and seals.
• Calibrate XYZ axis movement accuracy.

2. Personnel training and standardised operation

• Provide professional training for operators to master basic principles and troubleshooting skills.
• Implement the ‘one person, one machine’ responsibility system to improve the sense of responsibility.
• Encourage a culture of continuous improvement and collect feedback from the field to optimise the process.

Conclusion

SMT stencil printer as the first step of the SMT process, the subsequent placement, reflow oven and even finished product yield has a decisive impact. Only through a comprehensive and detailed setup of the stencil printer can the accuracy and consistency of solder paste deposition be ensured.

With the development of intelligent manufacturing, SMT printing machine is moving towards higher precision, higher automation, higher intelligence direction. Enterprises should also keep pace with the times, the introduction of advanced equipment and management systems, combined with scientific process parameter settings and strict quality control, to improve production efficiency and product quality.

If you are looking for a high-performance SMT solder paste printer or need a customised SMT solution, please feel free to contact us, we will provide you with professional technical support and service.

Company profile

Zhejiang NeoDen Technology Co., LTD., founded in 2010, is a professional manufacturer specialized in SMT pick and place machine, reflow oven, stencil printing machine, SMT production line and other SMT Products. We have our own R & D team and own factory, taking advantage of our own rich experienced R&D, well trained production, won great reputation from the world wide customers.

We believe that great people and partners make NeoDen a great company and that our commitment to Innovation, Diversity and Sustainability ensures that SMT automation is accessible to every hobbyist on everywhere.