Tombstone

We have that problem only when the components are not properly centered between the solder paste pads before the PCB is sent to the furnance. Like you mentioned, its not a constant problem, it only happens every now and again.

I'd double check the pickup location and the placement location on your application system first.

John

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Check the fine SMTnet archives. There's hundreds of postings on tomston* and tomb ston* there.

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If it's inconsistent, reflow and part cleanliness is most likely OK. Check you stencil printing process. How do you perform post-print inspection? What is the stencil-life of your paste? How often is the stencil underwiped? Do you track paste additions during production? Look for stuff like this first.

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Hello Everyone,

Mountains and mountains of data in the archives. As a contractor the variables in your production lots don't help I'm sure.

On a larger scale, one suggestion maybe to first look at when and where your tomb stoning is occuring.

1. Is it occuring on only certain types of components?

2. Are there different pastes being run? Therefore, is this more consistent with any single paste material?

3. Is this issue primarily occuring with certain sized boards, thick boards or boards loaded with heat sinks or other large heat drawing components?

4. Are there significant changes in the reflow parameters between lots?

5. How well is the control of your environment in your production facility? If you logged temp & Humidity each day would you find a higher incident rate tied to these factors? Do you have any large (Shipping) doors to other rooms or outside not evironmentally controled near your line? Can opening a door create temp shifts that are significant to effect air flow and temp around the oven etc...

On a more specific note......

1. Do you have stencil wipe capability on your Screen printer? If so, are you systematically using it? If you have an MPM with this option feel free to contact tech support and question them about appropriate use, you may just need to increase frequency of use. You can email them a question from the website http://www.speedlinetechnologies.com

2. Do you use an ultrasonic cleaner for your stencils? Hand cleaning stencils is more prone to create print issues as there is an operator dependence on performance to address PMR Systems can provide a low cost ultrasonic cleaner with filtration to extend your chemical life. You can find them at http://www.pmrsystems.com

3. Do you implement paste inspection? This can be done offline for random checks or on-line. CyberOptics provides these systems (LSM 300 for offline & SE 200 & 300 for on line paste inspection) you can find more data at http://www.cyberoptics.com CyberOptics also provides Automated On-line Inspection (AOI) systems for component placement inspection. Component placement may not be the most likely issue, but log your tombstones and you may find consistencies with component failures based on the pick or the place. An AOI will help you if this is the real issue.

Hope this helps......good luck

Please feel free to contact me if you have any questions or concerns.

Thank you, Sean 480-829-8170 ext.14

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