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November 12, 2019

How To Measure Solder Paste Rolling Diameter

A customer has asked us to measure the rolling diameter of solder paste while printing with our automated stencil printer.

Is there a way to do this? What is the impact if the rolling diameter of solder paste is larger or smaller than some ideal?

S.K.

Expert Panel Responses

The diameter of the solder paste roll height is very important. Too much paste will cause sticking to the squeegee. Too little paste can cause skips.

The paste suppliers Technical Bulletin should give you a recommended diameter and tolerance.

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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.

The rolling diameter of the solder paste affects the fill of the stencil apertures and therefore the printed solder paste quality and consistency.

If the diameter is too small, then partial fill of the apertures may occur which leads to low printed solder paste volumes. Low rolling solder paste diameters are also susceptible to air gaps in the roll which lead to missing solder paste in the print.

If the diameter is too large, then the paste may not roll and may smear/slide across the stencil. This can lead to a smear or blanket of solder paste over the top of the apertures. This smear of solder paste can release to the circuit board creating excessive printed volume or it may hold the solder paste in the apertures creating low printed volume or missing solder paste bricks.

There are automatic solder paste roll monitoring options for screen printers. I recommend that you speak with your equipment supplier for details.

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Tony Lentz
Field Applications
FCT Assembly
Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.

Some brands of stencil printers have an available option to measure the paste roll height. It is worth checking with the vendor of your printer to see if they have this option.

Typically the recommendation for the paste roll height is 1/2" to 3/4", but your solder paste vendor should be able to give specific recommendations to you. The reason to keep the paste roll height in the recommended range is that the solder paste printing behavior and rolling is impacted by the height of the paste.

If the paste roll height is too high, the paste doesn't roll as well and can lead to insufficient aperture fill. And if the paste roll height is too low, there is risk that parts of the board will be starved for paste. In either case, a higher degree of defects is likely to happen if you don't have a way to keep an eye on this through your printer's Paste Roll Height Monitor.

Controlling the height of the paste is an important parameter to drive print quality and keep end-of-line defects to a minimum.Some brands of stencil printers have an available option to measure the paste roll height. It is worth checking with the vendor of your printer to see if they have this option.

Typically the recommendation for the paste roll height is 1/2" to 3/4", but your solder paste vendor should be able to give specific recommendations to you. The reason to keep the paste roll height in the recommended range is that the solder paste printing behavior and rolling is impacted by the height of the paste.

If the paste roll height is too high, the paste doesn't roll as well and can lead to insufficient aperture fill. And if the paste roll height is too low, there is risk that parts of the board will be starved for paste. In either case, a higher degree of defects is likely to happen if you don't have a way to keep an eye on this through your printer's Paste Roll Height Monitor.

Controlling the height of the paste is an important parameter to drive print quality and keep end-of-line defects to a minimum.

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Brian Smith
General Manager - Electronic Assembly Americas
DEK International
Mr. Smith has been supporting customers in the electronics assembly industry since 1994. His expertise is focused on solder paste printing and reducing soldering defects. He holds a BS in Chemical Engineering and an MBA in Marketing. He has authored several papers in trade magazines and at industry conferences. He is an SMTA Certified Process Engineer.

Please see the link below and this may help with your question as it is a common one. However, please understand there are many factors to consider; Paste mesh, squeegee material, squeegee height, squeegee end dams or no dams, automatic squeegee dispensing systems, and sealed squeegee systems.

The squeegee blades should extend beyond the required printing surface by 0.500" inch on each side of the art work/image on stencil. To small of a diameter will tend to plow the paste versus rolling the paste during printing process.

To large a dimeter will do the same especially if paste is on the drier side (old). Ideally the size of your paste diameter would be equal to half of the squeegee height. If the squeegee is 1.00 inch in height your rolling paste should be roughly 0.500 inch (half the squeegee height).

http://www.circuitnet.com/experts/71591.html

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David Cormier
Engineering Manager
Circuit Technology Center, Inc.
Manufacturing Engineer of 20+ years. Involved in Industries relating to all sectors of defense, Commercial product Industries, RF - Microwave and Semiconductor industries. Vast knowledge and experience relating Mil-STD’s, IPC-STD’s, EAI-STD’s, GEIA-STD’s, J-STD’s and MIL-PRF-STD’s.

Solder paste is typically dispensed across the entire squeegee blade length and maintained at a 15mm rolling diameter assuming the use of the most commonly used 500 gram jar of solder paste. This eliminates waste of solder paste from overflowing the sides of squeegee.

Some stencil printers have a rolling diameter measuring system that monitors the rolling diameter in real-time and triggers automatic dispensing of additional paste if the rolling diameter falls below a minimum level, typically 10mm.

This eliminates insufficient solder paste on the stencil and keep the paste rolling speed within optimum range to achieve best printing results.

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Carlos Bouras
General Manager
Nordson SELECT
Carlos Bouras is the General Manager of Nordson SELECT and has over 30 years of experience in the electronics manufacturing industry. Carlos's expertise is in process engineering, product development and manufacturing operations. For the past 15 years Carlos has focused specifically on automated assembly issues and is the holder of several US patents for non-contact dispensing and precision dispensing of adhesives for the packaging of microprocessor devices.

The rolling diameter of the solder paste should be 1 inch optimum. If it is more it will block the screen.

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Amit Bahl
Director of Sales and Marketing
Sierra Circuits
Amit Bahl started to work at Sierra Circuits in 2006 where he formed strong relationships with his customers working with them on flex PCBs, HDI, controlled impedance, etc. In 2009, he was promoted Director of Sales and Marketing.