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March 7, 2016

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.

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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.

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Mitch Holtzer
Global Director of Customer Technical Support
Alpha Assembly Solutions
As the Global Director of Customer Technical Service (CTS) for Alpha, Mitch sets direction and provides coordination for the Alpha CTS group in a global capacity. A major focus of this position is to provide strategic support to OEM, CEM and Automotive customers and target accounts. Mitch joined Alpha in 1998 and has progressed through positions of increasing responsibilities in Marketing, Product Management and R&D. He is a graduate of Purdue University with a degree in Chemistry and holds an MBA from Temple University.

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.

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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.

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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.

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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.