# What design limitations does a higher-than-average resistance trace impose?

There's a Kickstarter running right now for a machine that prints circuit boards. Rather than a traditional etching process, they use conductive (silver-based) ink to print traces and pads. It has a resistance of 12 m$\Omega$/in^2. What design limitations does this impose? More specifically, what kinds of circuits would I not be able to produce with these parameters?

I assume high frequency things like high speed busses (LVDS?) and printed antennas? Other things?

Note: I am specifically not placing a link to the project here as this question isn't meant as an advertisement for it.

• +1 for thinking to look at this parameter I was thinking of buying one this morning just to play with :) Commented Feb 10, 2015 at 22:42
• Should your title say resistance (or maybe resistivity) instead of reactance? If you really mean reactance, could you edit the question to be more clear about how the machine makes traces with higher reactance? Commented Feb 11, 2015 at 5:28
• @ThePhoton you're right. I meant to encompass both resistance and inductance, but worded wrong. Commented Feb 11, 2015 at 5:51
• The inductance shouldn't be any worse than for an etched PCB. It comes from trace geometry and the separation from the return path. Commented Feb 11, 2015 at 5:53
• Just get a voxel8 one, they support 3d printing of traces ;) Commented Feb 11, 2015 at 12:25

## 1 Answer

1/2 oz copper (about the lightest typically used) has a resistance of approximately 1m$\Omega$/$\square$, so it's more than an order of magnitude worse, and about 50x worse than the 2-oz copper typically used for power circuits.

You'd have to take that into account for power circuits, for analog circuits and for digital circuits that draw a lot of power. If you're just flashing LEDs with a microcontroller.. maybe okay. A 10 mil trace 3" long would have a resistance of 3.6 ohms, so at 50mA it would drop almost 0.2V.

• On all browsers I can currently access this shows "1mΩ/[]" (some square box). I guess you used some rather new utf8 char there, maybe you can replace it by some inline latex? Commented Feb 11, 2015 at 12:22
• @PlasmaHH The units of sheet resistance are ohms per square so I used the empty square box.. \square in LaTex. The Wiki page I linked uses \Box which is very similar. Commented Feb 11, 2015 at 12:44