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Pencil Use writing onto IC

iman

#22651

Pencil Use writing onto IC | 11 December, 2002

Was visting a production floor, of an SMT assembly line, and saw operators using mechanical pencils to write "process stage identification markings" onto the SOIC packages, after the post-reflow inspection.

was wondering if such pencil markings is common for SMT lines? and if it is permissible from a ESD or cleaniness point of consideration?

from my further investigation, the pencil markings do not get rub off nor does the pencil marking get washed off by subsequent DI water rinse, so is it just me being curious and worried over nothing? Does long term use of such pencil, generate any contamination for the close-loop Aqueous Cleaning system*machine*?

appreciate if anyone could share their experiences and scientific opinions, on this issue of using pencils to write identification markings on IC packages?

Thanks.

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#22655

Pencil Use writing onto IC | 11 December, 2002

The lead in pencils is banned by the Euroland No-Lead Imperative

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Randy Villeneuve

#22656

Pencil Use writing onto IC | 11 December, 2002

Lead in pencils is conductive, so if dust or lead particals were to break off (which they could easily do) this could cause shorts on the board, etc. Its common practice not to use lead pencils in electronics manufacturing.

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Stephen

#22663

Pencil Use writing onto IC | 11 December, 2002

The "lead" in pencils is no longer lead. (not for several decades) It's graphite. And it is very conductive. I found out the hard way in high school science class.

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#22665

Pencil Use writing onto IC | 11 December, 2002

Funny how people keep refering to the material in pencil as "lead" when actually it is graphite. As such, it is not soluble in water or alcool, so should not interfere with contamination testing. As for the dust causing shorts, very unlikely. Plus, you can erase it easily.

For the historical origin of the use of the word "lead" in pencil see: http://www.pencils.com/unlead.html

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Randy Villeneuve

#22675

Pencil Use writing onto IC | 12 December, 2002

Now the big question is how do they get the lead in the pencil? Don't answer that. Anyway now that we all know that there is no lead in the lead pencil (which we already knew) I still feel it is not good practice to use a lead (Graphite-clay) pencil in electronics manufacturing. For many years I worked in microelectronics manufacturing and lead pencils were absolutely banned. I carried that practice over to PCB assembly and feel its a good practice even though the risks are lower..

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MA/NY DDave

#22681

Pencil Use writing onto IC | 12 December, 2002

Hi

Fun Posts,

Everyone beat me to the graphite solution, SHUCKS!! A dollar late again

You know I didn't know that for years, and never gave it any thought. I felt dumb when I realized it since I was in soldering, knew about lead poisoning, and at an early age actually did use real lead as a marker. Hard to write with. Now that wasn't the first time I was dumb.

While I agree that the amount of dust (carbon) would be small and probably burn up fast if ever really shorted, a common problem is the breaking off of the point which could then get lodged someplace. So I don't think it is a good idea. I go for a marker with an appropriate tip.

YiE, MA/NY DDave

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