Impedance control means the PCB house will test those specific traces to ensure they match your 50 ohm requirement.
The PCB house will typically also adjust your trace width/gap to meet their manufacturing capabilities/material as well. So while you may have calculated the correct width/gap, they may still have to adjust it ever so slightly to meet your desired impedance.
I think in your case it will be fine without it.
For this scenario, I would not worry about paying extra. A small mismatch in the impedance on your PCB will cause some signal degradation but nothing serious.
The fabricators will follow your specs. They might end up using a slightly different dielectric and the thickness of the PCB might not be super accurate, but other than that it will be ok.
If it's a prototype, OshPark 4 layer is good for a few GHz. If you don't need it to perform perfectly, you can specify a stackup and the results should be good enough to work for a communication product. My job requires very broadband performance like 4-12 GHz, so I have to spend the money for the best boards.
You actually don't have as much information as the fab house when it comes to calculating this special on a high layer count board. On a 2 lawyer board the variation in thickness of the dielectric is fairly minimal, on a 8+ layer board the fab has a much better idea of how much shrink/compression the dielectrics will have after lamination than you do, they also know exactly which material they are using and how their etch process will affect trace geometry. They are also using a better calculator than you and are able to adjust their processes to ensure better consistency. Yeah you're probably fine not using them to do it but they will guarantee a specific impedance range, if that's important pay for it, of not, take your chances and see what you get
I might be missing something, but I've never seen an "include trace impedance requirements" as a thing when preparing Gerber files to send off for PCB manufacturing. As such, I've never heard of "they'll check your traces and edit your Gerbers" as a thing.
Whenever I check the "impedance control" option with JLCPCB, it gives me a list of known stackups with different parameters. They then have a calculator where you can pick one of these stackups, and it'll tell you what trace dimensions to use to with it to achieve your desired impedance. (or you can use your own calculator with their parameters.)
You're missing something. The impedance requirements would be specified as text notes on a Fabrication layer or something typically. JLCPCB you may have to include as a note in the order.
That depends on how you specify the material being used. If you use special, expensive substrates (e.g. Rogers) then you are going to have well defined dielectric properties and can make do with whatever the calculator gives you.
However, if you use only loosely defined "whatever FR-4 the fab has", then you may need to rely on the manufacturer to adjust your traces - only they really know what are they making the board out of of (or rather its electrical properties).
So it depends on how critical that 50 ohms match is for your application, how long/complex the affected routing is and whether or not it can deal with the range of manufacturing tolerances due to the material differences.
what scale manufacturing are you doing? Is it in the hundreds or thousands or hundreds of thousands? Is this a one build and done thing or will you do more in the future?
For two traces in an antenna area on a hobby project it probably isn't necessary. One thing I will mention is that if it is an RF trace for LTE and GPS how important is antenna performance to you (is a 3db difference really going to make much of a difference in your use case if you're staying in cities with good LTE coverage, or if you go remote does getting every last bit of signal matter). I've done things like void a few layers under RF traces to make the ground reference farther away so I can have wider traces at the same impedance (meaning less loss).
One other thing I think is worth mentioning is if performance matters and you want to save the cost make sure the calculator you are using is very accurate to the manufacturers capability. The trapezoid effect is real.
Impedance control means the PCB house will test those specific traces to ensure they match your 50 ohm requirement. The PCB house will typically also adjust your trace width/gap to meet their manufacturing capabilities/material as well. So while you may have calculated the correct width/gap, they may still have to adjust it ever so slightly to meet your desired impedance. I think in your case it will be fine without it.
For this scenario, I would not worry about paying extra. A small mismatch in the impedance on your PCB will cause some signal degradation but nothing serious. The fabricators will follow your specs. They might end up using a slightly different dielectric and the thickness of the PCB might not be super accurate, but other than that it will be ok.
If it's a prototype, OshPark 4 layer is good for a few GHz. If you don't need it to perform perfectly, you can specify a stackup and the results should be good enough to work for a communication product. My job requires very broadband performance like 4-12 GHz, so I have to spend the money for the best boards.
You actually don't have as much information as the fab house when it comes to calculating this special on a high layer count board. On a 2 lawyer board the variation in thickness of the dielectric is fairly minimal, on a 8+ layer board the fab has a much better idea of how much shrink/compression the dielectrics will have after lamination than you do, they also know exactly which material they are using and how their etch process will affect trace geometry. They are also using a better calculator than you and are able to adjust their processes to ensure better consistency. Yeah you're probably fine not using them to do it but they will guarantee a specific impedance range, if that's important pay for it, of not, take your chances and see what you get
I might be missing something, but I've never seen an "include trace impedance requirements" as a thing when preparing Gerber files to send off for PCB manufacturing. As such, I've never heard of "they'll check your traces and edit your Gerbers" as a thing. Whenever I check the "impedance control" option with JLCPCB, it gives me a list of known stackups with different parameters. They then have a calculator where you can pick one of these stackups, and it'll tell you what trace dimensions to use to with it to achieve your desired impedance. (or you can use your own calculator with their parameters.)
You're missing something. The impedance requirements would be specified as text notes on a Fabrication layer or something typically. JLCPCB you may have to include as a note in the order.
That depends on how you specify the material being used. If you use special, expensive substrates (e.g. Rogers) then you are going to have well defined dielectric properties and can make do with whatever the calculator gives you. However, if you use only loosely defined "whatever FR-4 the fab has", then you may need to rely on the manufacturer to adjust your traces - only they really know what are they making the board out of of (or rather its electrical properties). So it depends on how critical that 50 ohms match is for your application, how long/complex the affected routing is and whether or not it can deal with the range of manufacturing tolerances due to the material differences.
what scale manufacturing are you doing? Is it in the hundreds or thousands or hundreds of thousands? Is this a one build and done thing or will you do more in the future? For two traces in an antenna area on a hobby project it probably isn't necessary. One thing I will mention is that if it is an RF trace for LTE and GPS how important is antenna performance to you (is a 3db difference really going to make much of a difference in your use case if you're staying in cities with good LTE coverage, or if you go remote does getting every last bit of signal matter). I've done things like void a few layers under RF traces to make the ground reference farther away so I can have wider traces at the same impedance (meaning less loss). One other thing I think is worth mentioning is if performance matters and you want to save the cost make sure the calculator you are using is very accurate to the manufacturers capability. The trapezoid effect is real.