Thickness has very little to do with the number of layers. One specifies the thickness of the fabricated board, and usually the thickness and composition of each layer. So for me all my boards are 65mils (0.065") thick regardless of the layers, which range from 2 layer to 8 layer. The difference between a two layer and four layer is obvious - on a four layer some vias have no traces, or a trace on only one side. If you can see through the board in a bright light you can generally say it's two layer since four layer usually means power planes. The difference between 4 and 6 layers is still pretty obvious, because nearly every 4 and 6 layer board has two layers dedicated to power. Thus if the board has any vias with no connections on the outside layers then it is very likely a 6 layer board - a via going from one inner signal layer to the other inner signal layer. Typically the power and ground are the two innermost layers to get the board to act as a capacitor with as high a capacitance as possible - as well as a few other benefits. Alternately you can look at the board in a strong light (not through the board) and view the layers - once you get past 4 layers each layer is so thin you can usually see traces under the top layer. Boards with more than 6 layers are hard to differentiate without board markings to indicate the layer count and orientation. But I'm sure it can be done by those with experience. -Adam On 6/10/06, 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? > > Jim > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist