On Sat, 2006-06-10 at 18:32 +0800, james tornes wrote:
> A guy giving a presentation to us was looking at various motherboards
> and making assesments like "this is a 4 layer board", "that one is 6
> layers". Can someone actually differentiate with an average eye,
> between boards with 4 layers and 6 layers? Thickness of boards can
> vary a bit even in-between runs so what's the technique here?

Someone experienced enough could probably pick out whether a board was 4
or 6 layers. The most obvious way to be to look through the board and
find a spot where you can see the routing of the internal layers.
Usually there are only a few spots on the board where this would be
possible.

Another possibility is if this person has alot of layout experience they
can likely tell by the DDR/DDR2 routing whether the board has 4 layer or
6 layer routing (it's usually the big parallel busses that require the
extra layers of routing, DDR is bad, PCI and AGP were also bad, with
PCIE things are getting better, meaning 4 layer boards will probably
become more common).

There was a time when most multilayer boards had a specific area set
aside so you could figure out how many layers it was very easily.
Usually it was a small area where each layer had it's number etched,
side by side, with none of the other layers having anything at that
specific spot. That's getting pretty rare these days.

Of course, with motherboards the person is cheating, since almost all
production mother boards are either 4 or 6 layer. Now, if this person
could differentiate between the 18 layer and 24 layer boards I work with
by eye alone, I'd be impressed. The 32 layer boards I've worked on are
OTOH so think it's pretty obvious they are a huge number of layers... :)

TTYL

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