DJ,
I just realized via your last name and the Spiral Challenge URL, that you
are the owner/keeper of the Challenge. And, we may have chatted/email before
on other issues.
Thanks for the Challenge, and insight.
Yes, the resistance between traces is greater the several Meg ohms. I
updated the blog page a little.
I think with more attention to details, I could successfully produce a
flawless 10/10 Challenge board, using the Toner Transfer Method. Or maybe
even a higher resolution version with smaller traces.
Perhaps a PCB Software Vendor, Transfer Paper Vendor, or an Industry Leader
would like to sponsor a Homebrew PCB Contest or a Formal Challenge.
It would be fun.
Thanks for your Homebrew PCB support and efforts.
Regards,
Eldon Brown
72 - Eldon - WA0UWH - CN88xc -
http://WA0UWH.blogspot.com/ On Thu, Aug 4, 2011 at 10:08 AM, DJ Delorie <dj@...> wrote:
> ∗∗
>
>
>
> Sweet!
>
> Here's a tip: you know the track-to-track spacing is 20 mil (you did say
> 10/10 pattern, yes?). Given that, you can calculate the actual DPI of
> the photo (about 4300 dpi for the spot I was measuring). Also measure a
> track, and you can compute the actual track width (about 9.2 mil in some
> spots, 7.1 in others).
>
> But simply measuring pixels-of-copper vs pixels-of-space should
> tell you how close to "perfect" you are.
>
> Your ohms are a little high, some things that might cause that:
>
> ∗ pinholes cause "necks" in the copper which add resistance
>
> ∗ cleaning/scraping/sanding the copper might thin it somewhat
>
> ∗ thinner traces on average would increase it
>
> If you just go by the ohms ratio, it says your average trace width is
> 18/23 ∗ 10 = 7.8 mil, which sounds close enough.
>
> Did you measure the high ohms between the two tracks?
>
> Also, if you have a flatbed scanner, they're often useful for
> high-accuracy PCB scans.
> ,___
>
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