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Epoxying over chip numbers?

Discussion in 'General Electronics' started by John Muchow, Jul 2, 2004.

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  1. Rich Grise

    Rich Grise Guest

    Was it really the girl's head in the box?
  2. Al

    Al Guest

    A couple of years ago I found a nice computer interface box in our
    recycling center. It contains a PCB, back-up battery, LCD display and 10
    pushbuttons. The circuitry consists of the Z80 family of components.

    When I powered it up, the cursor on the display blinked, but nothing
    else happened. I suppose it needed to connect to a computer via the
    RS232 line and needed a complementary software interface.

    I tracked down the design engineer as he had put his name in the PCB in
    copper! He was quite pleased that something that he had designed so long
    ago was around. He was shocked at how easily I had found him using the

    At any rate, he said that it would be very, very difficult for me to
    reverse enginner the product. Why, you ask? He had scrambled the data
    and address lines. The software, burned into an EPROM, was also
    scrambled so that it negated the scrambling in the hardware. Even if you
    used a disassembler to get the code, it would not make sense to you as
    the physical addresses were different from that of the code. He used
    some sort of lookup table to descramble the addresses.

    Looks like he and his group were sorta paranoid. Maybe this interface
    box was state-of-the-art at the time, but it could be easily duplicated
    in function, at any rate, today.

    I remember that ATARI and other game companies also spoofed the
    competition by adding extras ICs to their designs and remarking the ICs.
    So, they might remark a 7474 as a 7414 or the like. And if you remember,
    the board were large and densely packed for games line PONG.

    Using microcontrollers with protected software is the best way to
    disquise your design. Maybe the gov't could reverse engineer it, but at
    a cost that any commercial output could not afford.

  3. At any rate, he said that it would be very, very difficult for me to
    Foolish hope. A simple quick-n-dirty program on your PC and a couple
    of hours (if that) groveling over the board to determine the mapping,
    and that protection is gone.
  4. John Muchow

    John Muchow Guest

    I think that removing the legends off ICs will only pique someone's
    Good tips, thanks.
    And you bring up a very good point about piquing someone's interest!

    But, for the prototypes we're hoping that the short time each user has
    them makes it improbable (famous last words) that they'll reverse
    engineer everything.

    John Muchow
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  5. John Muchow

    John Muchow Guest

    If they're though-hole chips, fold the legs over and mount the chip on
    Two great ideas I would have never thought of. We tried manual
    sanding with the paper wrapped around various objects and the chips in
    conductive foam...but it didn't work well at all.

    John Muchow
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  6. John Muchow

    John Muchow Guest

    To use epoxy and make it stick, you'd have to sand the chips anyway.

    That's what I was afraid of. And I didn't realize until I sent the
    first post that no epoxy was going to stick well enough (probably) to
    a CERDIP.
    Angle-grinder? Ouch. :)
    We're currently using an abrasive-filled rubber wheel in the Dremel.
    I've forgotten what the wheel is called. We have a drawer full of
    them and nothing is marked, of course.

    But they work great. We're just lazy though and wanted an easier way
    to do this. A method that had a lower chance of damaging the chip
    would be nice too. :)

    John Muchow
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  7. John Muchow

    John Muchow Guest

    How many protos are you talking about? 10s, 100s, more?

    Several lots of 5-10pcs. This will be a regular thing as new products
    are developed so we're looking for good ideas for use now and in the
    Good idea but we need access to right-angle DIP switches from the
    sides of the boards.
    Ummm....not just yet. :)
    Interesting idea and definitely worth considering if we were going to
    remove numbers from the chips in the production runs.

    Hmm, wait a sec.....we do have a couple of chips that are used in
    every product. Might be worth lasering a couple hundred of each for
    future prototypes.

    Good idea, thanks!

    John Muchow
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  8. Rich Grise

    Rich Grise Guest

    Don't exactly pot the board, but conformal coat it really thick with
    something tough and opaque. In either case, just mask off the switch.

    I was gonna respond to another comment, about a safer method, by saying
    "operator training." ;-)

    Find out from your chip vendor what it costs to get house numbers
    on, say, 1000 parts. You might save money, not to have to pay somebody
    to sand chips. Just make up some random part numbering system, and
    keep it a secret.
    BZQX == 7400
    #q87S == CD4060

    (of scourse, you could make up house numbers that sound like
    actual house numbers, like 04-101, 03-227, and so on. be careful
    not to lose the cross-reference!)

    Like when Peggy Hill said to the shoe guy, I'd like a pair of
    women's size 16 bowling shoes, marked 8 1/2. He measures her foot,
    and says, "No, you want a pair of women't size 16 _and a half_
    bowling shoes, marked 8 1/2." I think she cried. ;-)
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