Solder paste viscosity measurement is an important step in the electronics manufacturing process, especially in surface mount technology (SMT). The main purpose of this is to ensure the quality and reliability of solder joints, as well as to optimize printing performance and product durability. 

Here are the specific reasons for the role of measuring solder paste viscosity:

1. Control print quality and performance

• Weld uniformity: Viscosity directly affects the ability of the solder paste to pass through the stencil and coat the circuit board. The correct viscosity helps ensure that the solder paste is evenly distributed across each solder point, creating uniform solder joints.
• Prevent printing errors:
  • Viscosity too high: When the solder paste is too thick, it may not fill the gaps in the printed mold, resulting in underprinting, uneven printing, or missed print spots.
  • Viscosity too low: When solder paste is too thin, it can overflow outside the area to be soldered (collapse), causing solder bridges between the component pins, leading to a short circuit. 

2. Ensure the durability and stability of the weld

• Welding accuracy: During reflow, the correct viscosity helps the solder paste maintain its shape and position, preventing it from shifting or splatter. This ensures that components are properly placed and that the solder joints are of high quality.
• Minimize soldering errors: Viscosity control helps reduce common soldering defects such as cold joints or under-soldering, thereby improving the reliability and longevity of electronic devices. 

3. Control the life and condition of the solder paste

• Assessment of quality loss: Solder paste viscosity can increase over time due to chemical reactions between the metal powder and flux, or due to solvent evaporation. Measuring viscosity helps identify solder paste deterioration as it nears its end of life, allowing the manufacturer to make appropriate decisions about continued use or disposal.
• Adjusting the production process: By monitoring viscosity, technicians can adjust process factors such as print speed and wiper pressure to ensure the best performance, regardless of small changes in solder paste properties. 

4. Optimize production parameters

• Customize for each product: Depending on the requirements of each type of circuit board and component, a manufacturer may need a specific viscosity range to optimize the printing and soldering process. Measurement helps determine the most suitable viscosity range for each application.
• Check for consistency: Regular viscosity measurements help check the consistency of solder paste batches. This is especially important to ensure stable and reliable production processes at scale.

The Malcom PCU-285 solder paste viscometer operates on the principle of using a coaxial spiral pump sensor. This method is specially designed to measure the viscosity of materials with non-Newtonian rheological properties, such as solder paste, with high accuracy and repeatability. 

Main components and principles

1. Coaxial spiral sensor:
   • The device uses a sensor consisting of an outer cylinder and an inner cylinder in a spiral shape.
   • The solder paste sample is placed in the space between these two cylinders.
2. Effect of shear force:
   • During the measurement, one of the two cylinders will rotate, creating a shear force acting on the solder paste sample.
   • Solder paste is a non-Newtonian fluid, meaning its viscosity changes depending on the shear force applied to it. This process simulates the behavior of solder paste under stress during screen printing.
3. Torque measurement:
   • The gauge will measure the torque required to maintain the rotational speed of the cylinder.
   • This torque is proportional to the viscosity of the solder paste. If the solder paste is too viscous, it will resist the rotation of the cylinder more strongly, requiring a greater torque.
4. Temperature control:
   • The viscosity of solder paste is very sensitive to temperature. To ensure accurate and comparable measurement results, the PCU-285 incorporates a thermostat to keep the solder paste sample temperature stable throughout the measurement.
5. Calculation and display:
   • The device will automatically calculate the viscosity from the torque and rotational speed data.
   • Measurement results are displayed on the touch screen, and data and graphs can be saved for analysis.
   • In addition to viscosity, the device is also capable of measuring rheological index (TI - Thixotropic Index) and viscosity non-recovery rate (R - Viscosity Non-Recovery Rate) according to JIS Z3284 standard. 

Summary of measurement steps

1. Sample preparation: The solder paste sample is fed into the spiral sensor.
2. Temperature control: The device regulates the temperature of the sample to the level required to ensure accuracy.
3. Creating shear force: The spindle starts to operate, applying cutting force to the solder paste sample.
4. Torque measurement: The sensor measures the torque required to maintain rotational speed.
5. Calculation and display: Integrated software processes data and displays viscosity, TI, and R results.

To use the Malcom PCU-285 solder paste viscosity meter, you need to follow the main steps of preparing the solder paste sample, installing the measuring device and taking the measurement. 

1. Preparation

• Check the device: Make sure the PCU-285 is plugged in, powered on, and booting the built-in Windows operating system.
• Prepare solder paste: Take a sample of solder paste to be tested and stir well to ensure uniformity.
• Install measuring tools: Attach the appropriate stirring paddle and measuring chamber (usually 100ml or 300ml). Place the measuring chamber in position inside the machine. 

2. Touch screen setup

• Select measurement mode: On the touch screen, select the appropriate measurement mode. PCU-285 can measure various parameters of solder paste:
  • Viscosity: Measure the viscosity value of the solder paste.
  • Thixotropic index (TI): Measure the change in viscosity of solder paste when subjected to mechanical stress.
  • Viscosity non-recovery ratio (R): Measure the viscosity recovery ability of solder paste after being subjected to impact.
• Parameter settings: Set measurement parameters such as the rotation speed range of the agitator blade (from 1 to 50 rpm) and other parameters according to JIS Z3284 standard. \

3. Operation and measurement

• Get solder paste sample: Take a sufficient amount of solder paste and put it into the pre-assembled measuring chamber.
• Automatic measurement: Press the button START on the touch screen to start the automatic measurement process. The machine will stir the solder paste according to the set parameters.
• Track results:
  • During the measurement, the device will display the graph and measured values on the screen.
  • When the measurement is finished, the device will automatically save the results.
• Analysis of results:
  • Check the viscosity index, TI, R and compare with the quality standard of the solder paste.
  • Use the results to evaluate the quality of solder paste before putting it into production, especially in SMT (surface mount technology) processes. 

4. Connect and manage data

• Copy data: You can connect a USB memory stick to the PCU-285 to copy saved measurement data.
• LAN connection: The machine can connect to LAN to manage and analyze data on the computer.

To contact Semiki Instrumentation Co., Ltd for advice and purchase of solder paste viscosity meter Malcom PCU-285, you can use the following information: 

General contact information

• Hotline: 0979 761 016
• Email for consultation and sales: [email protected]
• Website: semiki.com