HI AllI am working on a board in which I have 7 different power supplies ranging from -4V to +5V. I would really appreciate I someone could tell me how many layers I have to add and more importantly what are the important criteria or assumption one make in deciding the the total number of layers for a board.I have one more questions how can we assign nets to different layers.ThanksGaurav
Hi. The last one could be done in the electrical constaint spreadsheet (think it is called Constraint manager in A16.'). The number of power nets does NOT demands a specific numbers of layers. difficulties, complexity, "compactness" does. The current board i'm at right now have 2 power layers and 16 power supplies. But what's making it easy is, that i do only use one or 2 in common the rest is "local created" supplies.Rgds Klavs.
ThanksCan you please explain more regarding the local created supplies. Input to the board is 12V dc and then all the remaining power supplies are generated on the board. can you also please suggest a possible layer stack upThanksGaurav
Hi. Out of that info alone. Sorry but no. Imagine You have a PC motherboard. Here You have the huge Power connetor with 3V3, 5V and 12V. The 1V8 i created near the cpu by a dc-dc converter (or as i call it a local PS ). But this board can be everything from 4 to N layers. The board i'm at right now also is supplied by 12V and have 12 layers. But that is due to some DDR2 and some high pinnumbered BGA's with several diff pairs. If Yours is a power supply "only" 4 layers could be enought (read could, not is). A thumbrule is having a bga where only 2 cline can go between pads or via's, You need a routing layer for each second ring of pad minus 2. EG having a bga of 10 * 10 pin gives 3 inner rings and thats demands 2 routing layers, and top + bottom + power/ground layers. Sorry my explanation, but i could not find an easier way :-).Rgds Klavs.