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March 10, 2015

PCBA Inspection Process Causing Damage

We inspect PCBAs on a relatively hard ESD mat surface. QA claims that during inspection, moving of the PCBAs on the mat will scratch and stress the soldered components (bottom side). Are there any studies on this matter? Are there any dedicated tools in the market designed for this purpose?

T.S.

Experts Comments

I am not aware of any specific studies that were done on the movement of a PCB on a "relatively" hard mat causing damage to bottom side components.. It stands to reason that the use of a mat, properly grounded, is a benefit to the board. Typically any mat being used will have a softer surface than the laminated work surface of the bench.

If your operators are sliding the PCB across the surface then, yes, there is a potential for damage. Just placing a PCB on the surface should not cause any issues. If you have concerns about damage I would suggest switching to a homogeneous vinyl material which is typically a softer surface. Be aware that this type of material cannot be used with a constant monitoring system as there is no conductive layer.
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Jerry Karp
President
JSK Associates
Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.
True. Moving the PCBA on a hard surface will sometimes scratch components, and stress soldered joints. There are many table-top inspection stations on the market designed to avoid damage to the assemblies. The common setup is a stationary rail that holds the PCBA. Other most advanced fixtures come equipped with a camera in order to display the images on a monitor.
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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.
I'd agree that any time we slide a PCBA across a surface, there is some risk. If the surface is clean and smooth, that risk is absolutely minimal unless very sensitive components are involved. If your QA folks can provide quantifiable evidence that there is a risk, then one approach would be to use a carrier to which the PCBA is affixed and inspect while in the carrier. In this way, all contact with the bench is eliminated.

Another benefit is that the PCBA can be held precisely level and at a known height, which might be important if you are inspecting under stereo microscopes. I'm envisioning an adjustable metal frame with feet to support the board off the table.
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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
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