|Ask the Experts|
May 14, 2020
Solder Paste Mixing
How can we confirm that our centrifuge machine is properly mixing jars of solder paste to give us the results as per the standard requirement?
|Expert Panel Responses|
We have no recommended technique for verifying machine paste mixing as we do not recommend the use of paste mixing equipment.
Technical Support Engineer
Mixing solder paste in a centrifuge can cause flux and other ingredients to separate from powder particles and is not recommended by many solder paste manufacturers.
Testing viscosity at multiple shear rates is the only method to confirm if the centrifugal mixing had an adverse effect on the paste.
Global Director of Customer Technical Support
Alpha Assembly Solutions
If the vendor's requirements for handling and storage of solder paste are followed mixing it with a plastic spatula should be enough to maintain its properties. Some solder paste manufacturers do not recommend the use of mechanical equipment.
If you still prefer to use the centrifuge, the goal will be to obtain a nice smooth homogenous mixture without flux separation. A capability study on the mixer can determine if changes in paste's tack & viscosity have occurred.
Senior Manufacturing Engineer
The use of a mechanical (automated) mixing process is recommended to be done in conjunction with a viscometer to understand if the paste viscosity is within the values that the manufacturer recommends for optimal results.
Engineering and Operations Management
We do not recommend using a centrifuge machine to mix solder paste. Unopened refrigerated paste should be allowed to reach room temperature, 19-25 degrees C (4 - 8 hours).
Before putting on the stencil, manually stir the solder paste with a spatula for about one minute to ensure paste homogeneity and proper rolling.
Director New Product Development
Metallic Resources, Inc
In the industry, certain companies do use automatic paste conditioning/mixing equipment to pre-condition the solder paste in the jar and cartridges before use. Companies such as Malcom/ Seika supply mixing equipment such as SPS-10 & SPS-2000 (both jar-type), and SPS-5A (cartridge-type).Jasbir Bath, Koki Solder America
It is typically recommended to return the paste temperature to ambient
room temperature before mixing and mix time should not exceed 1 to 3 minutes to avoid excessive internal friction and heat generation, as it shall lead to adversely affecting the rheology of the paste.
For testing of viscosity, you could follow the tests done by the paste manufacturer which are shown in their data sheets.
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