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'PCB power plane question'
2008\11\24@130554 by Alan B. Pearce

face picon face
Personally I would do it as follows: -

Layer1: signal
Layer2: 5v plane & 12V track as required.
Layer3: ground
Layer4: signal

The area supplied by 12V will probably be only a small portion of the PCB,
and I would have 12V to just that area, with the rest of that layer as a 5V
plane.

However without knowing precisely what you are setting out to do, it is
difficult to advise you properly.

2008\11\24@134347 by Andre Abelian

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face

Alan,

In this case I can use 5 and 12 split mixed plane.

One of my main reason I do signals in middle layers
is to protect circuit agents reverse engineering. Most engineers give up
when they see no traces on top or bottom of the board.


Andre



{Original Message removed}

2008\11\24@170645 by olin piclist

face picon face
Andre Abelian wrote:
> I am doing PCB layout that has 12v and 5v. 12v has 2A load
> and it is used to power leds and 5v is to supply logic.
> The board is only 4 layers and I am not sure about power plane
> Should I use 12v as part of power plane or 5v.

If they all have a common ground, make layer 3 the ground plane and route
everything else as needed.  It's rarely necessary to use planes for power.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\11\25@095034 by Bob Barr

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face
On Mon, 24 Nov 2008 10:44:43 -0800, "Andre Abelian" wrote:

>
>Alan,
>
>In this case I can use 5 and 12 split mixed plane.
>
>One of my main reason I do signals in middle layers
>is to protect circuit agents reverse engineering. Most engineers give up
>when they see no traces on top or bottom of the board.
>

I think that method would only deter the most casual of
reverse-engineering efforts.

If it's really worth it to someone for them to reverse-engineer your
PCB, it would be very little trouble to depopulate a board, slap it on
a bed-of-nails tester, and extract a netlist directly from the
interconnects. In fact, for someone with sufficient time (or enough
cheap labor available), they could probably do the same thing with an
ohmmeter.

Another possibility would be to delaminate a board into its separate
layers and view the tracks directly.

Heck, it may even be possible to use Xray methods to recover the inner
layer layouts. (Given the distances involved, though, doing that may
not be feasible.)


Regards, Bob

2008\11\25@105211 by Alan B. Pearce
face picon face
>Heck, it may even be possible to use Xray methods to recover
>the inner layer layouts. (Given the distances involved, though,
>doing that may not be feasible.)

It has been done with other items.

How to read a document without physically opening it ...

http://www.diamond.ac.uk/News/LatestNews/press_release_13Sept.htm

The instrument that did it does cost a pretty penny though ... ;)))

2008\11\25@122240 by John Day

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face
At 09:50 AM 11/25/2008, you wrote:
{Quote hidden}

Indeed, if you really want to reverse engineer something reasonably
simple, their are firms in Eastern Europe who will completely reverse
engineer a PCB for you. For about $1000 US they will do a  6 layer
100x160mm PCB back to schematics unless it has any BGA packages, then
it is between $1400 and $1600.

For about $5000 they will completely recover the code in most micros too.

I have put signal layers between planes, but not for security -
mainly for noise reduction. But you still need to bear in mind the
issues of thickness balancing.

John


>Another possibility would be to delaminate a board into its separate
>layers and view the tracks directly.
>
>Heck, it may even be possible to use Xray methods to recover the inner
>layer layouts. (Given the distances involved, though, doing that may
>not be feasible.)
>
>
>Regards, Bob
>
>

2008\11\25@133205 by Andre Abelian

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face

John,

If I erase IC numbers, conformal quote the board and put the board in
epoxy Can they still reverse engineer the board?

Andre



{Original Message removed}

2008\11\25@133550 by PAUL James

picon face
yes

-----Original Message-----
From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu] On Behalf
Of Andre Abelian
Sent: Tuesday, November 25, 2008 12:33 PM
To: Microcontroller discussion list - Public.
Subject: RE: PCB power plane question


John,

If I erase IC numbers, conformal quote the board and put the board in
epoxy Can they still reverse engineer the board?

Andre



-----Original Message-----
From: piclist-bouncesspamKILLspammit.edu [.....piclist-bouncesKILLspamspam.....mit.edu] On Behalf
Of John Day
Sent: Tuesday, November 25, 2008 9:20 AM
To: Microcontroller discussion list - Public.
Subject: Re: PCB power plane question

At 09:50 AM 11/25/2008, you wrote:
>On Mon, 24 Nov 2008 10:44:43 -0800, "Andre Abelian" wrote:
>
> >
> >Alan,
> >
> >In this case I can use 5 and 12 split mixed plane.
> >
> >One of my main reason I do signals in middle layers is to protect
> >circuit agents reverse engineering. Most engineers give
up
{Quote hidden}

Indeed, if you really want to reverse engineer something reasonably
simple, their are firms in Eastern Europe who will completely reverse
engineer a PCB for you. For about $1000 US they will do a  6 layer
100x160mm PCB back to schematics unless it has any BGA packages, then it
is between $1400 and $1600.

For about $5000 they will completely recover the code in most micros
too.

I have put signal layers between planes, but not for security - mainly
for noise reduction. But you still need to bear in mind the issues of
thickness balancing.

John


>Another possibility would be to delaminate a board into its separate
>layers and view the tracks directly.
>
>Heck, it may even be possible to use Xray methods to recover the inner
>layer layouts. (Given the distances involved, though, doing that may
>not be feasible.)
>
>
>Regards, Bob
>
>

2008\11\25@141422 by Wouter van Ooijen

face picon face
> If I erase IC numbers, conformal quote the board and put the board in
> epoxy Can they still reverse engineer the board?

For some value of THEY they will even reverse-engineer the ICs.

--

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu

2008\11\25@160139 by John Day

flavicon
face
At 01:33 PM 11/25/2008, you wrote:

>John,
>
>If I erase IC numbers, conformal quote the board and put the board in
>epoxy Can they still reverse engineer the board?
>
>Andre

Pretty much, yes. The first thing they do is x-ray everything and
then they know what the chips are. Then they remove the epoxy. The
formula I have seen is Methyl Ethyl Ketone (MEK), Aceton and Toluene
- most people say in equal parts. Working in a fume hood coat the
epoxy and slowly work it off. Be careful or you can dissolve the
resin in the PCB laminate.

Hard conformal coatings are usually epoxy, so off they come too.

If the x-ray technician is good then the shading in the image will
show the copper areas.

Once upon a time it was common to see people do all of those things
to protect their design. But the reality is that if someone wants
your design they will get it. One fellow I worked for many years ago
used to remove the IC part numbers and then coat the boards in a
rubber gunk that was truly disgusting to try and remove. Far worse
than conformal coating. He went to a lot of trouble, but I told him,
you aren't really protecting yourself.

He didn't believe me, but I gave a board to a friend who had access
to a low poewr inspection type x-ray. He set up and x-rayed very TTL
and linear IC he had - so now he had a set of master patterns. The he
x-rayed the board and the next day rang my boss and told him what the
IC's were. He was incredulous. Then about two days later he came back
with the complete schematic, and he had even hand built a prototype
of the circuit just to check he had gotten things like resistor values right.

The truth is there is really no easy way to protect your design. You
can keep it away from the prying eyes of the curious, but are they a
real threat to you? If your product is that important or profitable
or desirable then whatever you do will only delay the reverse
engineering experts by a few days.

Here is another example. this time about chips. I had been supplied
some supposedly Intel CPU chips recently. I was suspicious, because
the top surface didn't look right, it had a different texture to what
I would have expected. We tried two on boards - no go. So I had them
x-rayed. Within hours I knew they were fakes - they would never work
because the chip inside was something totally different. I could
actually read the manufacturers markings on the dice.

John






>{Original Message removed}

2008\11\25@235249 by Vasile Surducan

face picon face
On a 4 layer there isn't too many layer stack combinations.
However (just for the persons who didn't know, not Alan) layer stacks
are standardised.
You can see this here:
www.pcbmatrix.com/Downloads/GeneralDocuments.asp
the document is named "layer configurations"

Protecting a PCB for reverse engineering is a lost of time. The real
reason why midlle layers is good to become signal layers is to avoid
interferences and EMI radiations.
There are plenty articles about this issue on the web.
The best choice is that signal layers to be defined as mixed
signal/ground planes.

Vasile

BTW Russell, for you sanity check, this email should have TECH or EE tag ?
Please put yourself the (in)appropiate tag...if you can decide which
is the "correct" one.
:)


On 11/24/08, Alan B. Pearce <EraseMEAlan.B.Pearcespam_OUTspamTakeThisOuTstfc.ac.uk> wrote:
{Quote hidden}

> -

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