Impedance control in PCB Manufactures

[barakg]

Hi,

First of all I'll apologize for my newbish question

I've always wondered why do we have the option "Impedance control" in some PCBs manufactures when quote a PCB.
If I have the specific PCB stack-up from the manufacture and according to these data I calculate and gets the width of the signal to achieve the required impedance, considered the manufacture capabilities. so if I get it right, the manufacture will manufacture the PCB with the width that I did in the design according to the DFM files that I supplied in my order.

So, Why do I need this option "Impedance control"? What else the manufacture do?

Thanks.

[robertferanec]

It is much more complicated. I am preparing a video about that.

For example, during PCB manufacturing they have to heat up the materials and press them (they call it lamination) - and during the process some properties of materials will change e.g. thickness of prepreg. So, theoretical calculations are only approximate, they have to adjust the parameters based on their experience.

[barakg]

So the calculations that I did in, lets say, PCB Toolkit, are not correct?

[robertferanec]

They are approximate.

[MadhuWesly]

Hi Robert,
I have a query reg. RF PCB design, hope you answer. Thanks in advance.
Image(PFA) explanation:
The attached image is the "output end of a power amplifier(PA)", which gives 1.5-j1.7Ohm impedance at output pads(12th & 10th) of the PA. And then it is being matched to 50 Ohm single ended impedance using matching circuitry.
From the following link I have understood that "we no need to worry about controlled impedance when trace length is less than 1.6 cm in my RF PCB design."

https://electronics.stackexchange.com/questions/322750/should-we-maintain-the-same-impedance-for-the-traces-carrying-rf-signal-line

Note: we have replaced strip-lines in the schematic with inductors.

Questions:
1. Do I need to worry about impedance matching in this design since there is already matching circuitry for achieving 50 Ohm at the end?

2. Is it OK if I start drawing the trace of 50 Ohm impedance from the output pads of the PA though at that points the actual impedance is 1.5-j1.7 Ohms?
3. From where to where I have to consider as total trace length whether from output pads(12th & 10th) of the power amplifier to open end(RF OUT - the end point where the antenna is connected) or length of each Trace segment between the pad to pad(or component to component)?
Awaiting your reply.

Best regards,
Madhuwesly.