PDA

View Full Version : Layers in the board



electronics
06-07-2012, 04:27 PM
Can you tell how many layers are in a PCB just by looking at the fabricated PCB? For example, the PCB has 20x20 BGA pads. I would guess, the PCB contains 6 layers as my understanding is only 4 pads in one column could be allowed in one layer. That is how I got 6 layers. I may be wrong. Suggestions are very very welcomed.

jwatte
06-07-2012, 07:14 PM
Yes, you can tell how many layers by looking at it. Specifically, you have to look at the side of it (and you may have to scrape off some of the soldermask/conformal coating/protection.)
No, there is no particular relation between the number of pads for a BGA and the number of layers. As long as you can run the traces out, using vias, or zig-zagging beween pads, you can use a BGA package in general. More layers means you have more dimensions to play with to get really tight spacings out, and very high pin counts often go with very high frequencies, so you'll often expect the board to be more advanced in these cases, but there's no hard and fast rule that says that it *has* to be so.