I need to mark around 50 student PCB's for a microprocessor design lab. This is to make sure that no one is cheating by using someone else's PCB. I would like to engrave a number or initials. Anyone have any suggestions?
Zapp
On Sun, 14 Dec 2003 20:21:31 -0500, "zapp" Gave us:
Locktite Black, Gap filling super glue.
Use a serialized stamping tool (rubber stamp), and use the super glue as the ink. The only way to remove it is by scrapping it.
You could also use a simple scribe to scrawl serializations on therm. n Put drop os varnish over it, and tell them that damaged varnish or serial numbers results in a Grade "F".
>I
Numeric "punches" from the hardware store? Like these...
Professional PCB layout engineers usually put part numbers, version numbers, and layer ident marls (L1, l2 etc) on the artwork itself so that it appears "in copper". I guess it's too late to do that.
I
numbers,
appears
PCB.
suggestions?
That's it CW....put it on the artwork....that way its etched in!......Ross
On Tue, 16 Dec 2003 03:19:45 GMT, "Ross Mac" Gave us:
The guy wants serializations. Who is going to pay the tooling charge for each new gerber setup? Certainly not the PCB house.
One can place a "pad" on the board. A rectangular area of reference designator silk screen area that marks the location for placement of a high temperature serial number label.
Put conformal coat over that (the varnish types) to set up the ID.
Hell, any label under varnish will do, if it isn't going back into the reflow oven. That is... if it is an SMT design. The high temp labels are cool though, and quite resilient. The conformal coating guarantees non tampering if put down with a high gloss look.
(Dolph's AC-41) Don't allow access to the varnish can, of course. Don't mention anything about solvents.
One can also encode the edge of the PCB with a file for quite a large number count. Four edges allows for a nice matrix, depending on the size of the board. One could encode thousands of serializations in that manner. Triangle file... small notches, no intrusion into any conductors or power planes, of course. The same varnish will seal the edges of the PCB to prevent tampering with that form of coding.
If he is the only one that knows the coding scheme, he could keep them honest.
Just use a hand operated pencil engraver for metal, wood, glass, etc.- these are cheap ($10-$20) and they can be used to etch a permanent serial number into the board. Make sure that you don't etch over traces so you don't accidentally cut any traces in half.
justme
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I assumed each student had designed their own PCB so they were all different anyway. Perhaps that's not what he meant.
If the yare all the same just engrave them with a cheap engraving nmachine.
Colin
these
PCB.
suggestions?
That's the most common way!
lab.
in!......Ross
Odds are each board is different...so artwork would not be a problem....otherwise, break out the old engraver...that's the most common way to track boards through a shop, other than cropping the corners I suppose....
On Sun, 14 Dec 2003 17:21:31 -0800, zapp wrote (in message ):
Do you also mean such that no one will be able to duplicate the s/n on another PCB? Is this a requirement? One can easily duplicate a fellow student's PCB *design* and put their own s/n (assigned to their original PCB by you) on it.
You need a method that is unique for each PCB, and not easily forged. Many of the methods mentioned in response can be easily done by the "wayward" student, ie, to a pinched PCB *design*.
A solution has not yet been suggested that meets these requirements.
I suggest a digital photo of the PCBs, both sides. No s/n required. Simply compare the handed-in project to the photos you keep on file. 50 projects is a bit much, I realize, but I don't know any other way to be sure the handed-in *design* is the student's own.
Good luck,
-- DaveC me@privacy.net This is an invalid return address Please reply in the news group
PCB
My impression was that these are identical "project boards" etc. Else it wouldn't really be an issue, would it?
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Using a conventional "vibrator" engraving tool is easily "forged" OTOH, using the punches as I suggested makes it significantly more difficult to cheat.
Or a very subtle (and secret) code of small notches on one edge?
On Tue, 16 Dec 2003 10:31:36 GMT, "CWatters" Gave us:
The PCBs are the same. The folks building (read assembling) them differ. It seems to be a hand assembly skills exercise.
Any engraving should include being sealed with a varnish afterward.
On Tue, 16 Dec 2003 10:36:47 GMT, "Ross Mac" Gave us:
Wrong. Odds are.. each board is the same, and each student is being tested on assembly process ability.
On Tue, 16 Dec 2003 7:01:17 -0800, DaveC Gave us:
Bullshit. My edge notch encoding scheme makes unique, all but un-decodable (except by the instructor) PCB coding/serializations.
On Tue, 16 Dec 2003 7:01:17 -0800, DaveC Gave us:
I'll bet that the PCBs are all the same, and the test is for assembly skill as well as finished assy function.
On Tue, 16 Dec 2003 07:09:51 -0800, "Richard Crowley" Gave us:
Some of these readers' interpretive powers wane when they arrive home from work. Some waned long ago.
I agree with you.
On Tue, 16 Dec 2003 07:09:51 -0800, "Richard Crowley" Gave us:
That's what *I* suggested.
Thanks for all the replies! Elaborating, these are identical microcontroller boards with a perfboard wirewrap area. After some time into the semester, there will be many of hours of wirewrap work put into each board. Hopefully, the identifying mark will prevent a student from casually using another's work.
Varnish can be dissolved, someone seemed to mention. Is epoxy insoluble? Also, does it come in clear forms? Perhaps epoxy over a paper label or engraving.
The digital camera may work, but there are several lab instructors.
Zapp
Simply
is
How are the pcbs designed and made ?
Do you mean someone elses pcb *design* ?
A hand engraver ?
--
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