Copper finishing for printed antenna

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alftel

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I designed printed PCB antenna for dual-band WiFi application, and while initial FR4 and ENIG based design produced decent results I decided to take to the next level and try RO4003C material. Results are excellent, but since I choose (after a small research) silver immersion finishing I do face another issue - oxidation. What is a general community experience with copper finishing for PCB antenna that produces the best results? Or, is there any way to prevent silver immersion from oxidation? My PCB manufacturer can do bare copper which will be covered by solder mask - will solder mask affect antennas performance and to which extent? What are general community experience regarding PCB antenna copper finish?
 

Hi,

With time the silver exposed to air is going to tarnish. But if your antenna is protected by something (like a box) even if the silver is tarnished, this will not be a problem for your application. But you need to take into account the effect of the box too !

You can try an immersion gold to avoid oxydation. The gold doesn't oxidize. You can also put some solder mask (varnish) to avoid any oxydation but of course you need to take it into account in your simulation.


You need to ask :
  • What is the permittivity of the solder mask ?
  • What are the tolerance of the solder mask thickness ?
With these information, you can take an average of the tickness of the solder mask and make the EM simulation. This is going to give you good results.

Cheers,
 
Agree to Pierre_B, but even known PCB manufacturer sometime may change manufacturing process and used chemicals.
For humid application I would use solder mask and perform regular performance measurements between batches. And it will be not that hard and expensive for frequencies below 5GHz to prepare a good measurement setup with some 3d printed fixtures to perform repeatability testing.
 

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    Pierre_B

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