how to impedance control pcb build

Dear all,

Could anyone teach me that how do you do the impedance control (RF trace width) on the mass PCB production? It is because I have not much experience on the RF trace impedance control on the mass PCB production.

As I am doing in research, I just calcuated the width on the RF trace (50ohms trace) and then make it on the PCB directly. However, how could I do the impedance control on the mas PCB in order to make sure that the board variation is not so large? Morevoer, what is the acceptable error percentage? +/-10% or less?

Thanks

wccheng

Again you need a CAD tool. You can do the "Yield test" by varying the trace width and see how much it deviates from your desired values.

Generally speaking, +/-8% is the highest accuracy you could get from PCB manufacture. So most important is to ensure your circuit could survive under the worst condition.

My experience is that there are two main problems, lot to lot variation in board dielectric constant, and variations in thickness of solder mask. Mostdesigns I do over a few GHz do not have any solder mask, except for thin whisps here or there to control solder flow around leadless chip carriers.

Could anyone answer this question, because i too have the same question