marking pcb's

[zapp]

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

 

[DarkMatter]

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?

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".

 

[CWatters]

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.

 

[Ross Mac]

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.


PCB.

That's it CW....put it on the artwork....that way its etched in!......Ross

 

[DarkMatter]

That's it CW....put it on the artwork....that way its etched in!......Ross

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.

 

[JustMe]

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

 

[CWatters]

The guy wants serializations. Who is going to pay the tooling
charge for each new gerber setup? Certainly not the PCB house.

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

 

[Ross Mac]

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

PCB.

That's the most common way!

 

[Ross Mac]

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.

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....

 

[DaveC]

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?

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,

 

[DarkMatter]

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

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.

 

[DarkMatter]

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....

Wrong. Odds are.. each board is the same, and each student is being
tested on assembly process ability.

 

[DarkMatter]

A solution has not yet been suggested that meets these requirements.

Bullshit. My edge notch encoding scheme makes unique, all but
un-decodable (except by the instructor) PCB coding/serializations.

 

[DarkMatter]

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.

I'll bet that the PCBs are all the same, and the test is for
assembly skill as well as finished assy function.

 

[DarkMatter]

My impression was that these are identical "project boards" etc.
Else it wouldn't really be an issue, would it?

Some of these readers' interpretive powers wane when they arrive
home from work. Some waned long ago.

I agree with you.

 

[DarkMatter]

Or a very subtle (and secret) code of small notches on one edge?

That's what *I* suggested.

 

[zapp]

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

 

[Terry]

zapp threw some tea leaves on the floor

I need to mark around 50 student PCB's for a microprocessor design lab.

How are the pcbs designed and made ?

This is to make sure that no one is cheating by using someone else's PCB.

Do you mean someone elses pcb *design* ?

I
would like to engrave a number or initials. Anyone have any suggestions?

A hand engraver ?

 

[CWatters]

Dallas Semiconductors (now owned by Maxim) used to make a part in small two
pin package that contained a unique 64 bit serial number (eg every one is
different). I think it was the DS2400 and they were intended for
applications like MAC addresses on NIC's.

One of these epoxied into a hole in the PCB would be impossible to remove
and replace without damage.

The nearest I could find on the Maxim web site now are these ibuttons which
are a bit too big I think but perhaps I didn't look hard enough.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3711

 

[Philip Pemberton]

In message <[email protected]>

Dallas Semiconductors (now owned by Maxim) used to make a part in small two
pin package that contained a unique 64 bit serial number (eg every one is
different). I think it was the DS2400 and they were intended for
applications like MAC addresses on NIC's.

The original was the DS2400. The silicon designs have been tweaked by DalSemi
to fix a few glitches in the 1-Wire driver. The new part number (when I say
"new" I mean "since 1996-ish") is DS2401. ISTR there's even a Chipscale
version - solder some really tiny wire to it and embed it in hole on the
board. Add some Araldite and you've got a usable anti-tamper method. You'd
need a 1-Wire reader (a DS9097U and a Blue Dot Receptor) to read the codes,
though. Keep a database using Access or Excel (or whatever) - use the 1-Wire
Viewer to read the code off the chip, then look it up in your database.

Later.