How to determine the no. of PCB layers through visual inspection?

[Biggs]

Common sense would tell one that a 6-layer motherboard's PCB would be physically thicker than a 4-layer one. However, this just wasn't the case when I made the comparison between an Apacer 256MB PC133 and an Asus P3B-F. I placed them side by side and found out that both have the same physical thickness (give or take).

*Note that the Apacer uses 6-layer technology (as they state on their website) and that the P3B-F is a 4-layer motherboard.

Now, is this *really* the proper way of determining the number of PCB layers or am I missing out on something else.

Cheers.

 

[Mark R]

You can't tell how many layers from the thickness. The total thickness depends on the thickness of the copper layers and substrate layers, and how many there are.

I've seen PCB materials for a 0.05 mm insulation layer. Copper layers are typically 0.035 mm, but may be much, much thicker if needed (e.g. layers for carrying power to a CPU may be 10 times thicker). Some high-end server motherboards use 16 (or more) layers, but are still usually only 1.6 mm thick.

If you look carefully at the edge of the board, you may be able to see the individual layers of copper. But unless you actually cut into it, you can't really tell just by looking.

You could ask the manufacturer - alternatively, you could burn a board - this will burn the epoxy bonding, and leave the individual copper foil layers and fibreglass substrate Not recommended, they produce loads of thick black toxic smoke.