PCB stackup for an 8-layer PCB
$begingroup$
We are considering to have the following stackup for an 8-layer PCB we are designing.
What we want with this stackup is to route the signals with approx. rise time of 3ns on layer 6 using a separation between traces of 8mils between them to get a crosstalk coefficient around -26dB.
Questions:
- Is the 3mil spacing between Lyr5&Lyr6 and between Lyr6&Lyr7 common?
- Do you guys see any possible electrical or manufacturing problem with this stackup?
stack-up
edited Feb 15 at 16:00
JYelton
16.2k2891191
asked Feb 15 at 13:42
AldanajaramilloAldanajaramillo
1265
$endgroup$
add a comment |
$begingroup$
We are considering to have the following stackup for an 8-layer PCB we are designing.
What we want with this stackup is to route the signals with approx. rise time of 3ns on layer 6 using a separation between traces of 8mils between them to get a crosstalk coefficient around -26dB.
Questions:
- Is the 3mil spacing between Lyr5&Lyr6 and between Lyr6&Lyr7 common?
- Do you guys see any possible electrical or manufacturing problem with this stackup?
stack-up
edited Feb 15 at 16:00
JYelton
16.2k2891191
asked Feb 15 at 13:42
AldanajaramilloAldanajaramillo
1265
$endgroup$
3
$begingroup$
Following @Elmesito good answer, you need to work with your chosen PCB fabricator. This isn't a simple 2 or 4 layer job that can be thrown at any PCB fab; the materials & foils available vary from fab to fab, but you have very specific parameters - so you need to choose your fab first, then get their specific stackup advice for their fab service, then proceed with your design.
$endgroup$
– Techydude
Feb 15 at 17:12
1
$begingroup$
-26dB is poor for crosstalk, how about -60dB? what is your ripple spec? Do you care about cumulative crosstalk and glitches? Are you going with 5/5 or 3/3 mil track/gap? This layout is far from ideal for size and cost for this performance
$endgroup$
– Sunnyskyguy EE75
Feb 15 at 17:19
add a comment |
$begingroup$
We are considering to have the following stackup for an 8-layer PCB we are designing.
What we want with this stackup is to route the signals with approx. rise time of 3ns on layer 6 using a separation between traces of 8mils between them to get a crosstalk coefficient around -26dB.
Questions:
- Is the 3mil spacing between Lyr5&Lyr6 and between Lyr6&Lyr7 common?
- Do you guys see any possible electrical or manufacturing problem with this stackup?
stack-up
edited Feb 15 at 16:00
JYelton
16.2k2891191
asked Feb 15 at 13:42
AldanajaramilloAldanajaramillo
1265
$endgroup$
We are considering to have the following stackup for an 8-layer PCB we are designing.
What we want with this stackup is to route the signals with approx. rise time of 3ns on layer 6 using a separation between traces of 8mils between them to get a crosstalk coefficient around -26dB.
Questions:
- Is the 3mil spacing between Lyr5&Lyr6 and between Lyr6&Lyr7 common?
- Do you guys see any possible electrical or manufacturing problem with this stackup?
stack-up
stack-up
edited Feb 15 at 16:00
JYelton
16.2k2891191
asked Feb 15 at 13:42
AldanajaramilloAldanajaramillo
1265
edited Feb 15 at 16:00
JYelton
16.2k2891191
asked Feb 15 at 13:42
AldanajaramilloAldanajaramillo
1265
edited Feb 15 at 16:00
JYelton
16.2k2891191
edited Feb 15 at 16:00
JYelton
16.2k2891191
edited Feb 15 at 16:00
JYelton
16.2k2891191
16.2k2891191
asked Feb 15 at 13:42
AldanajaramilloAldanajaramillo
1265
asked Feb 15 at 13:42
AldanajaramilloAldanajaramillo
1265
asked Feb 15 at 13:42
AldanajaramilloAldanajaramillo
1265
1265
3
$begingroup$
Following @Elmesito good answer, you need to work with your chosen PCB fabricator. This isn't a simple 2 or 4 layer job that can be thrown at any PCB fab; the materials & foils available vary from fab to fab, but you have very specific parameters - so you need to choose your fab first, then get their specific stackup advice for their fab service, then proceed with your design.
$endgroup$
– Techydude
Feb 15 at 17:12
1
$begingroup$
-26dB is poor for crosstalk, how about -60dB? what is your ripple spec? Do you care about cumulative crosstalk and glitches? Are you going with 5/5 or 3/3 mil track/gap? This layout is far from ideal for size and cost for this performance
$endgroup$
– Sunnyskyguy EE75
Feb 15 at 17:19
add a comment |
3
$begingroup$
Following @Elmesito good answer, you need to work with your chosen PCB fabricator. This isn't a simple 2 or 4 layer job that can be thrown at any PCB fab; the materials & foils available vary from fab to fab, but you have very specific parameters - so you need to choose your fab first, then get their specific stackup advice for their fab service, then proceed with your design.
$endgroup$
– Techydude
Feb 15 at 17:12
1
$begingroup$
-26dB is poor for crosstalk, how about -60dB? what is your ripple spec? Do you care about cumulative crosstalk and glitches? Are you going with 5/5 or 3/3 mil track/gap? This layout is far from ideal for size and cost for this performance
$endgroup$
– Sunnyskyguy EE75
Feb 15 at 17:19
3
3
$begingroup$
Following @Elmesito good answer, you need to work with your chosen PCB fabricator. This isn't a simple 2 or 4 layer job that can be thrown at any PCB fab; the materials & foils available vary from fab to fab, but you have very specific parameters - so you need to choose your fab first, then get their specific stackup advice for their fab service, then proceed with your design.
$endgroup$
– Techydude
Feb 15 at 17:12
$begingroup$
Following @Elmesito good answer, you need to work with your chosen PCB fabricator. This isn't a simple 2 or 4 layer job that can be thrown at any PCB fab; the materials & foils available vary from fab to fab, but you have very specific parameters - so you need to choose your fab first, then get their specific stackup advice for their fab service, then proceed with your design.
$endgroup$
– Techydude
Feb 15 at 17:12
1
1
$begingroup$
-26dB is poor for crosstalk, how about -60dB? what is your ripple spec? Do you care about cumulative crosstalk and glitches? Are you going with 5/5 or 3/3 mil track/gap? This layout is far from ideal for size and cost for this performance
$endgroup$
– Sunnyskyguy EE75
Feb 15 at 17:19
$begingroup$
-26dB is poor for crosstalk, how about -60dB? what is your ripple spec? Do you care about cumulative crosstalk and glitches? Are you going with 5/5 or 3/3 mil track/gap? This layout is far from ideal for size and cost for this performance
$endgroup$
– Sunnyskyguy EE75
Feb 15 at 17:19
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
To answer your questions:
Using thin prepregs is not uncommon, and in your case for example the standard 1080 prepreg is close to your 3mils thickness. ( a list of the most common thicknesses can be found here)
The issue I see is that you are using a buildup construction, which non all manufacturers are comfortable with using. Another thing that is worth pointing out is that you have an asymmetric layer distribution, which means that you have the risk of having issues with the board flatness, after the assembly process. You might end up with a board that is shaped like a banana.
What I suggest is that you contact your manufacturer of choice, and get them to approve your stacking, making sure you specify what are the limitations that you require.
That is the only way you will get the answer you need.
edited Feb 15 at 16:01
JYelton
16.2k2891191
answered Feb 15 at 14:38
ElmesitoElmesito
1,644210
$endgroup$
add a comment |
$begingroup$
AFAIK the "stackup" will be called a "layup" at the PWB shop.
your problem for the calculation you're making is it doesn't have tolerances. you need to find the worst case because it will be the first production lot. everything is variable including Er as the glass/epoxy ratio varies. You need to nail down the corner cases.
You also have a lot of unexplored questions because you don't really need a coefficient, you need a noise margin and the devil is in the details of the split plane and any issues with ground plane inductance running through zones with too many PTHs and how much if any copper remains on the planes at min hole spacing.
answered Feb 15 at 20:38
Noah TsayingNoah Tsaying
112
$endgroup$
add a comment |
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2 Answers
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active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
To answer your questions:
Using thin prepregs is not uncommon, and in your case for example the standard 1080 prepreg is close to your 3mils thickness. ( a list of the most common thicknesses can be found here)
The issue I see is that you are using a buildup construction, which non all manufacturers are comfortable with using. Another thing that is worth pointing out is that you have an asymmetric layer distribution, which means that you have the risk of having issues with the board flatness, after the assembly process. You might end up with a board that is shaped like a banana.
What I suggest is that you contact your manufacturer of choice, and get them to approve your stacking, making sure you specify what are the limitations that you require.
That is the only way you will get the answer you need.
edited Feb 15 at 16:01
JYelton
16.2k2891191
answered Feb 15 at 14:38
ElmesitoElmesito
1,644210
$endgroup$
add a comment |
$begingroup$
To answer your questions:
Using thin prepregs is not uncommon, and in your case for example the standard 1080 prepreg is close to your 3mils thickness. ( a list of the most common thicknesses can be found here)
The issue I see is that you are using a buildup construction, which non all manufacturers are comfortable with using. Another thing that is worth pointing out is that you have an asymmetric layer distribution, which means that you have the risk of having issues with the board flatness, after the assembly process. You might end up with a board that is shaped like a banana.
What I suggest is that you contact your manufacturer of choice, and get them to approve your stacking, making sure you specify what are the limitations that you require.
That is the only way you will get the answer you need.
edited Feb 15 at 16:01
JYelton
16.2k2891191
answered Feb 15 at 14:38
ElmesitoElmesito
1,644210
$endgroup$
add a comment |
$begingroup$
To answer your questions:
Using thin prepregs is not uncommon, and in your case for example the standard 1080 prepreg is close to your 3mils thickness. ( a list of the most common thicknesses can be found here)
The issue I see is that you are using a buildup construction, which non all manufacturers are comfortable with using. Another thing that is worth pointing out is that you have an asymmetric layer distribution, which means that you have the risk of having issues with the board flatness, after the assembly process. You might end up with a board that is shaped like a banana.
What I suggest is that you contact your manufacturer of choice, and get them to approve your stacking, making sure you specify what are the limitations that you require.
That is the only way you will get the answer you need.
edited Feb 15 at 16:01
JYelton
16.2k2891191
answered Feb 15 at 14:38
ElmesitoElmesito
1,644210
$endgroup$
To answer your questions:
Using thin prepregs is not uncommon, and in your case for example the standard 1080 prepreg is close to your 3mils thickness. ( a list of the most common thicknesses can be found here)
The issue I see is that you are using a buildup construction, which non all manufacturers are comfortable with using. Another thing that is worth pointing out is that you have an asymmetric layer distribution, which means that you have the risk of having issues with the board flatness, after the assembly process. You might end up with a board that is shaped like a banana.
What I suggest is that you contact your manufacturer of choice, and get them to approve your stacking, making sure you specify what are the limitations that you require.
That is the only way you will get the answer you need.
edited Feb 15 at 16:01
JYelton
16.2k2891191
answered Feb 15 at 14:38
ElmesitoElmesito
1,644210
edited Feb 15 at 16:01
JYelton
16.2k2891191
edited Feb 15 at 16:01
JYelton
16.2k2891191
edited Feb 15 at 16:01
JYelton
16.2k2891191
16.2k2891191
answered Feb 15 at 14:38
ElmesitoElmesito
1,644210
answered Feb 15 at 14:38
ElmesitoElmesito
1,644210
answered Feb 15 at 14:38
ElmesitoElmesito
1,644210
1,644210
add a comment |
add a comment |
$begingroup$
AFAIK the "stackup" will be called a "layup" at the PWB shop.
your problem for the calculation you're making is it doesn't have tolerances. you need to find the worst case because it will be the first production lot. everything is variable including Er as the glass/epoxy ratio varies. You need to nail down the corner cases.
You also have a lot of unexplored questions because you don't really need a coefficient, you need a noise margin and the devil is in the details of the split plane and any issues with ground plane inductance running through zones with too many PTHs and how much if any copper remains on the planes at min hole spacing.
answered Feb 15 at 20:38
Noah TsayingNoah Tsaying
112
$endgroup$
add a comment |
$begingroup$
AFAIK the "stackup" will be called a "layup" at the PWB shop.
your problem for the calculation you're making is it doesn't have tolerances. you need to find the worst case because it will be the first production lot. everything is variable including Er as the glass/epoxy ratio varies. You need to nail down the corner cases.
You also have a lot of unexplored questions because you don't really need a coefficient, you need a noise margin and the devil is in the details of the split plane and any issues with ground plane inductance running through zones with too many PTHs and how much if any copper remains on the planes at min hole spacing.
answered Feb 15 at 20:38
Noah TsayingNoah Tsaying
112
$endgroup$
add a comment |
$begingroup$
AFAIK the "stackup" will be called a "layup" at the PWB shop.
your problem for the calculation you're making is it doesn't have tolerances. you need to find the worst case because it will be the first production lot. everything is variable including Er as the glass/epoxy ratio varies. You need to nail down the corner cases.
You also have a lot of unexplored questions because you don't really need a coefficient, you need a noise margin and the devil is in the details of the split plane and any issues with ground plane inductance running through zones with too many PTHs and how much if any copper remains on the planes at min hole spacing.
answered Feb 15 at 20:38
Noah TsayingNoah Tsaying
112
$endgroup$
AFAIK the "stackup" will be called a "layup" at the PWB shop.
your problem for the calculation you're making is it doesn't have tolerances. you need to find the worst case because it will be the first production lot. everything is variable including Er as the glass/epoxy ratio varies. You need to nail down the corner cases.
You also have a lot of unexplored questions because you don't really need a coefficient, you need a noise margin and the devil is in the details of the split plane and any issues with ground plane inductance running through zones with too many PTHs and how much if any copper remains on the planes at min hole spacing.
answered Feb 15 at 20:38
Noah TsayingNoah Tsaying
112
edited Feb 15 at 20:43
answered Feb 15 at 20:38
Noah TsayingNoah Tsaying
112
answered Feb 15 at 20:38
Noah TsayingNoah Tsaying
112
answered Feb 15 at 20:38
Noah TsayingNoah Tsaying
112
112
add a comment |
add a comment |
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3
$begingroup$
Following @Elmesito good answer, you need to work with your chosen PCB fabricator. This isn't a simple 2 or 4 layer job that can be thrown at any PCB fab; the materials & foils available vary from fab to fab, but you have very specific parameters - so you need to choose your fab first, then get their specific stackup advice for their fab service, then proceed with your design.
$endgroup$
– Techydude
Feb 15 at 17:12
1
$begingroup$
-26dB is poor for crosstalk, how about -60dB? what is your ripple spec? Do you care about cumulative crosstalk and glitches? Are you going with 5/5 or 3/3 mil track/gap? This layout is far from ideal for size and cost for this performance
$endgroup$
– Sunnyskyguy EE75
Feb 15 at 17:19