I have not specificly looked at a P4 board for this. Different
manufactures may be slightly different.
In this level of technology, it is very common to have anywhere from 6
to 9 layers in these high technology boards. There are some industry
boards with many more layers. This is why it is really impossible to
start changing parts on these, unless it is a surface mount part that
is directly on the top or bottom surface. Naturaly, the proper surface
mount soldering tools would be required for reliability and minimal
possible damage.
If conventional parts are to be changed on these boards, when heating
and pulling out the leads for changing them, it is possible to do some
damage between the layers during the unsoldering operation. When
resoldering, there is also a chance of doing damage. Proper care must
be taken for this.
The idea of layers is to save space. Many manufactures are also using
embeded technology. This is where components can be etched in to the
surfaces in between the layers.
Jerry Greenberg