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September 6, 2011

Stencil Life

Is there a recommended usage rate for stencils? Is there a way to determine when it's time to replace a squeegee or a stencil?

K. B.

Experts Comments

For the stainless steel type of stencils commonly used for solder paste application, they will typically outlive the product lifecycle as long as they are well taken care of and not damaged. Some common forms of stencil damage that may occur involve improper handling of the stencil (bending, twisting, scratching etc), and improper set up of the machine (i.e. damage caused by the metal squeegee).

Also, exposure to high heat can degrade a stencil, not adhering to proper cleaning techniques, or using incompatible chemicals for the cleaning can have a negative impact as well. Stencils with tighter pitch components tend to wear at a faster rate than those that have larger webs between openings.

Visual inspection of the stencil before use and inspection of the solder paste deposit should give an indication of any degradation of the stencil quality.

The same applies for a squeegee as far as possible causes of degradation and quality.

Matt Stevenson
Director of Marketing
Sunstone Circuits
Matt Stevenson has over 20 years experience in the PCB industry. Serving in roles as a Chemical Lab Technician, Process Engineer, Quality Engineer, Quality Manager, and Marketing Manager. He has proven himself to be an invaluable resource.

Oversimplified recommendation:

When you can't get a clean paste wipe at any pressure--replace the blades

When the stencil is loose enough that you can't a clean snap-off (stencil deflects downward when separating from board) -- replace stencil.

Bill Coleman
Vice President Technology
Photo Stencil
For over 18 years, Dr. Coleman has been the vice president of technology for Photo Stencil, working closely with customers to understand their printing requirements. His efforts have resulted in several new stencil products.

The simple answer to usage rates is No...

The easiest way to tell if the stencil is end of life is simple to look for reduced tension around the artwork, if it looks/feels "baggy" then the stencil should be replaced.

High pressure, damaged squeegees poor tooling are some of contributing factor to stencil killers...

Clive Ashmore
Global Process Manager
Dek Printing Machine
Mr. Ashmore is responsible for the Global Applied Process Engineering group for DEK. Clive specializes in all aspects of manufacturing engineering, with special emphasis on mass imaging technologies.
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