I'm looking for stack up recommendations (keeping in mind readily available materials) for a 6 layer board I'm working on.
Design requirements dictate the following:
- maximum 6 layers
- lots of high speed traces DDR3, SERDES, Gbit ETH, USB2.0 etc
- high speed signals due to BGA need to be 4mils wide
So for 50/100Ohm with 4mil traces, the two inner signal layers need to be close to the ground and VCC planes (about 6 mils), this results in a total stack up of only 35mils assuming 4.3mil outer cores and 8 mil center core. So either I have a "thin" PCB at 35 mils or increase the center core to 35 mils or so and that will hurt the inter-plane capacitance.
So is a less than nominal 63 mil board a bad idea (perhaps to much board flex?) or do the advantages of more inter-plane capacitance outweigh a thin board?
Any 50 Ohm, 4 mil trace, 6 layer stack up suggestions are welcome
Is this a PC based design with a south and north bridge chips?
How many positive supplies do you have?
BGA pin pitch, size, number of pins?
Board size, mounting hole positions?
End use and environmental factors?
Is this a PC based design with a south and north bridge chips?
How many positive supplies do you have? 4: +5V(pwr in), 3.3V, 1.5V(DDR), 1.0V (Core)
BGA pin pitch, size, number of pins? 689(1mm), 256(1mm), 96(0.8mm)
Board size, mounting hole positions? ~6" x 6", non standard holes
End use and environmental factors?
Is this a PC based design with a south and north bridge chips? No this is a processor board for an industrial related product using a dual core QorIQ (P1020)
How many positive supplies do you have? 4: +5V(pwr in), 3.3V, 1.5V(DDR), 1.0V (Core)
BGA pin pitch, size, number of pins? 689(1mm), 256(1mm), 4x96(0.8mm)
Board size, mounting hole positions? ~6" x 6", non standard holes
End use and environmental factors? Industrial -40 to +70
I agree on the 8 layer however one of the design criteria is "PCB to be 6 layers maximum". I'm 99% complete on the layout, will perform simulation in the next day or so with this stackup* and see how it looks.
*
1/2 oz -Top
2 x 106
1/2 oz - GND
6mil core
1/2 oz - signal
2 x 2116
1/2 oz - signal
6mil core
1/2 oz - VCC
2 x 106
1/2 oz - Bottom
In order to avoid possible cross-interference between neighbors signals, it is very important that routing in the adjacent layers are alternately mutually orthogonal one each to another, as follows:
In order to avoid possible cross-interference between neighbors signals, it is very important that routing in the adjacent layers are alternately mutually orthogonal one each to another, as follows: