[SOLVED] What are the PCB manufacturing challenges in making spiral traces for planar magnetic

[kended]

Hi,

I am currently designing a planar magnetic using spiral traces acting as primary/secondary coils. Although I was able to get a few prototypes done, most of the PCB fab say they do not do spiral traces PCBs (apparently they don't have the capability!) but it is unclear why.

This is somewhat of a surprise to me as I don't see the difference between straight and spiral traces as far as PCB etching is concerned. What would be the issue here? For you information my traces are 10 mils wide / 7 mils spacing, 31mils PCB width, 2 oz copper, 1 oz plating.

Could this be related to the difficulties for testing them (for example an normal electrical test here would not work)? But then again using AOI that could be easily done.

Any thoughts?

Thank you.

 

[marce]

Done loads never had a problem, got a picture to look at?

 

[volker@muehlhaus]

most of the PCB fab say they do not do spiral traces PCBs

Did they refer to square or octagon or circular spirals?

Or their concerns might be related to the combination of thick copper and narrow gap and the local chemical effects during etching ar large metal density (many closely spaced inductor turns).

 

[kended]

Here you go..

 

[kended]

Did they refer to square or octagon or circular spirals?

Circular

Or their concerns might be related to the combination of thick copper and narrow gap and the local chemical effects during etching ar large metal density (many closely spaced inductor turns).

But then, what if we were straight lines? Wouldn't it be the same (same metal density, closely spaced, copper thickness)? Btw, these were mostly answers I got from Chinese manufacturers who couldn't clearly explain the issues except to say "we don't do spiral traces" ! I am still puzzled. Luckily two of them did not see this as a problem, but I'm trying to understand why others won't simply quote.

Thx for your time.

 

[marce]

Strange, they should be able to make those boards. though they may prefer to start with 1oz copper due to the 7 thou gap and plate up to 2oz (you have 2oz start 1oz plate) if you can live with that.

 

[kended]

Thanks for your inputs. For now I guess I'll work with those who don't see an issue!