PCB standards - Page 1
Forum section: electronics / beginners

author: XaeroDemon
author_rank: Contributor
timestamp: February 12, 2016, 07:06:23 pm
content: Hey Guys...First time hereThis is a total noob question but please bear with me..So I designed a PCB which only carries max current of 250mA I used a online calculator and the trace width came out 4.5 something mils for .25A in 1oz copper..But I went with 10 mils for all signals and power wires(signal wires conduct less current than 250mA).Heres the thing I have seen people use slightly larger traces for power wire on 250mA but the trace width calculator says 4.5 mils is enough I don't know if I can trust that online calculator(I used advance circuit one).I know that having larger traces is always better and reduce impedance but is it needed? and seeing power wires and signal wires at same width seem a little weird...Thanks in advance and thank you Dave for putting up all these content ..I learned lot from you.

author: AlxDroidDev
author_rank: Frequent Contributor
timestamp: February 12, 2016, 07:14:15 pm
content: Quote from: XaeroDemon on February 12, 2016, 07:06:23 pmHow are you going to manufacture the PCB? The answer for this will decide the minimum trace width of your PCB.

author: Wilksey
author_rank: Super Contributor
timestamp: February 12, 2016, 07:20:46 pm
content: Do you need to worry about impedance with what you are designing?4.5mil for internal traces, external are a lot smaller, your 4.5 will do 1/2 an amp (500mA), and it depends on factors such as how much you want to rise above ambient, so you are allowing a 10degC rise above ambient, so 4.5mil running half of what it is capable of will suffice I would have said.Some people have their own standards on what their "minimum" track width is, for example, I used to know a place that had 0.35mm for signal and 1.27mm for power minimum. I always make the power tracks fatter just because I think it looks more professional (personal opinion).I always double what I need unless it's say 10Amps, then I try and add a bit of overhead, so if you need 250mA, look for something that will take 500 or at least 350 I would have said.

author: XaeroDemon
author_rank: Contributor
timestamp: February 12, 2016, 07:33:15 pm
content: Thanks guys for replying @AlxDroidDev yes I am gonna use OSHpark for fab..so minimum is 6 mills and no this is not a impudence controlled design. @Wilksey trace width for 500mA seem 11 mils so I think I will settle down for 10 mils bcus its already over kill T rise will be below 10degC and its internal.but I agree fatter power traces look cooler ...But gosh...I hate unrouting traces...Thanks again

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 12, 2016, 07:39:57 pm
content: 10mil is fine.As a novice you don't want to go finer than 10mil trace / 10mil space anyways.

author: Wilksey
author_rank: Super Contributor
timestamp: February 13, 2016, 10:17:18 pm
content: 11mils for INTERNAL traces, not external "air" traces, internal are internal routing layers, on say a 4 layer board, the 2nd or 3rd, the external (open to the air) are about half of that, look at the advanced PCB calculator and you will see.