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What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer PCB stack-up looks like a compromise. Clock is a high speed signal, and so is SPI dependi...
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#5: Post edited
What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer PCB stack-up looks like a compromise. Clock is a high speed signal, and so is SPI depending on the edge raise time. What works as reference layer for these signals?- A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient.
- As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups.
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- If not enough real estate for high speed signals on the top layer:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - GND plane
- 4 - high speed signals, sensitive signals
- If you find yourself hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- 5 - GND plane
- 6 – high speed signals, sensitive signals
- That's a common stack-up for a 6-layer PCB, although not the only good 6-layer stack-up.
- What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer PCB stack-up looks like a compromise. Clock is a high speed signal, and so is SPI depending on the edge raise time. Clock and SPI are on different layers: top and bottom. What acts as reference layers for these signals?
- A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient.
- As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups.
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- If not enough real estate for high speed signals on the top layer:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - GND plane
- 4 - high speed signals, sensitive signals
- If you find yourself hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- 5 - GND plane
- 6 – high speed signals, sensitive signals
- That's a common stack-up for a 6-layer PCB, although not the only good 6-layer stack-up.
#4: Post edited
What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer PCB stack-up looks like a compromise.- A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient.
- As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups.
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- If not enough real estate for high speed signals on the top layer:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - GND plane
- 4 - high speed signals, sensitive signals
- If you find yourself hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- 5 - GND plane
- 6 – high speed signals, sensitive signals
- That's a common stack-up for a 6-layer PCB, although not the only good 6-layer stack-up.
- What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer PCB stack-up looks like a compromise. Clock is a high speed signal, and so is SPI depending on the edge raise time. What works as reference layer for these signals?
- A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient.
- As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups.
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- If not enough real estate for high speed signals on the top layer:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - GND plane
- 4 - high speed signals, sensitive signals
- If you find yourself hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- 5 - GND plane
- 6 – high speed signals, sensitive signals
- That's a common stack-up for a 6-layer PCB, although not the only good 6-layer stack-up.
#3: Post edited
- What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer PCB stack-up looks like a compromise.
- A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient.
- As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups.
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- If not enough real estate for high speed signals on the top layer:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - GND plane
- 4 - high speed signals, sensitive signals
If you are hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB:- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- 5 - GND plane
6 – high speed signals, sensitive signals
- What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer PCB stack-up looks like a compromise.
- A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient.
- As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups.
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- If not enough real estate for high speed signals on the top layer:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - GND plane
- 4 - high speed signals, sensitive signals
- If you find yourself hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- 5 - GND plane
- 6 – high speed signals, sensitive signals
- That's a common stack-up for a 6-layer PCB, although not the only good 6-layer stack-up.
#2: Post edited
What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer stack-up looks like a compromise.- A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient.
- As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups.
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- If not enough real estate for high speed signals on the top layer:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - GND plane
- 4 - high speed signals, sensitive signals
- If you are hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- 5 - GND plane
- 6 – high speed signals, sensitive signals
- What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer PCB stack-up looks like a compromise.
- A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient.
- As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups.
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- If not enough real estate for high speed signals on the top layer:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - GND plane
- 4 - high speed signals, sensitive signals
- If you are hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB:
- 1 - high speed signals, sensitive signals
- 2 - GND plane
- 3 - VCC plane, other power distribution
- 4 - low speed and non-sensitive signals
- 5 - GND plane
- 6 – high speed signals, sensitive signals
#1: Initial revision
What you are proposing may be okay (depending on other specifics of the design), but your proposed 4-layer stack-up looks like a compromise. A high speed signal should have a reference plane layer next to it. A GND plane layer serves as good reference plane in theory and in practice. A VCC plane layer can serve as a reference plane in theory, but there are practical hindrances. If you want to route a signal through a via from the bottom layer which uses VCC plane as a reference to the top layer which uses GND plane as a reference, then you have to connect the reference planes near the signal via. How would you connect the reference planes if they are at different potentials? You would connect them through a coupling capacitor. But then you have to have a lot of these coupling capacitors, which isn't convenient. As a result of the above considerations, there are two non-compromised options for 4-layer PCB stack-ups. 1 - high speed signals, sensitive signals 2 - GND plane 3 - VCC plane, other power distribution 4 - low speed and non-sensitive signals If not enough real estate for high speed signals on the top layer: 1 - high speed signals, sensitive signals 2 - GND plane 3 - GND plane 4 - high speed signals, sensitive signals If you are hard pressed to do a 4-layer PCB with two GND planes, then consider a 6-layer PCB: 1 - high speed signals, sensitive signals 2 - GND plane 3 - VCC plane, other power distribution 4 - low speed and non-sensitive signals 5 - GND plane 6 – high speed signals, sensitive signals