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 have no recommended technique for verifying machine paste mixing as we do not recommend the use of paste mixing equipment.

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.

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
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.

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
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.

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
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.

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
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.

Reader Comment

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).

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.

Jasbir Bath, Koki Solder America

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