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July 27, 2026 - Updated
March 2, 2016 - Originally Posted

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?

S.R.

Expert Panel Responses
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.

David Bao
David Bao
Director New Product Development, Metallic Resources, Inc
David Bao has more than fifteen years of experience in developing new solder paste, wave soldering fluxes and other SMT consumables. He currently serves as the Director of New Product Development at Metallic Resources Inc. He received a Ph.D. in Chemistry at Oklahoma State University.
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.

Georgian Simion
Georgian Simion
Engineering and Operations Management, Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations Contact me at georgiansimion@yahoo.com.
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.

Edithel Marietti
Edithel Marietti
Senior Manufacturing Engineer, Northrop Grumman
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.
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.

Mitch Holtzer
Mitch Holtzer
Director of Reclaim Business, Alpha Assembly Solutions
I've been in the soldering materials/applications industry for 25 years. Since joining Alpha, Ive been the global product manager for preforms, wave soldering flux, solder paste and more recently the Director of the soldering materials reclaim business.
We have no recommended technique for verifying machine paste mixing as we do not recommend the use of paste mixing equipment.

Kay Parker
Kay Parker
Technical Support Engineer, Indium Corporation
Kay Parker is a Technical Support Engineer based at Indium Corporation's headquarters in Clinton, N.Y. In this role she provides guidance and recommendations to customers related to process steps, equipment, techniques, and materials. She is also responsible for servicing the company's existing accounts and retaining new business.
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