Big Old Fat Traces (High Current PCB) - Page 1
Forum section: electronics / general

author: the_enginerd
author_rank: Newbie
timestamp: February 13, 2019, 10:16:26 pm
content: I'm designing a PCB for an audio amplifier that has the potential to put out 40A (instantaneous), and honestly, I'm out of my comfort zone. The connectors are rated to a min 35A and I'm basically going for big fat traces to take the current load.All components in the assembly are pass-thru connectors, nothing to overheat besides the board itself.The narrowest neck is 5.5mm thick (besides certain spots where I have to taper down by the molex)I plan on using 4oz copperI read about doing a waves solder to help as well, same goes for buss barsTrace/Pad clearances are 50mil (plz don't harass me for using mm and mil)What I'm looking for answers to1) Is this just dumb? Am I crazy?2) Any suggestions3) General high current PCB design suggestionsProto-types for testing will be done, but I'd rather not spend the money if this won't work out of the box.Thanks for the feedback

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 13, 2019, 11:57:42 pm
content: Audio? The RMS level over thermal time scales (seconds) is a tiny fraction of the peak. 10A would be overkill, I would think. Don't worry about it!Tim

author: DerekG
author_rank: Frequent Contributor
timestamp: February 13, 2019, 11:58:36 pm
content: Quote from: the_enginerd on February 13, 2019, 10:16:26 pmSo you need to ask yourself - Under a fault condition, can the 40A be continuous? If so, perhaps add in a slow blow fuse/circuit breaker rated at 35A to prevent connector/pcb track failure.You will need to choose the "slow blow" fuse/circuit breaker with care.Open up the solder mask as you have suggested to coat the current tracks with a bit more tin (tin/Pb) during wave soldering. Perhaps look at which way the board should travel through the wave solderer, remembering the leading edges of the thick tracks will receive a "normal" amount of solder & the trailing edges of the thick tracks will often receive a "thicker" amount of solder due to the meniscus effect.Also look at the maximum temperature the board will rise to when being pushed hard.

author: the_enginerd
author_rank: Newbie
timestamp: February 14, 2019, 02:59:53 am
content: Quote from: T3sl4co1l on February 13, 2019, 11:57:42 pmThis is what been pondering in my mind. We are setting up a test to nail this down tomorrow but this is what we are hoping for. This also makes sense as to why when I look at the same manufacturer's speakers and components in the amplifier that I see parts rated to a more reasonable 15A.Would you think if we find that it's at a much more reasonable level that I could employ my fat traces but go down to 2 oz CU?

author: LapTop006
author_rank: Unknown
timestamp: February 14, 2019, 04:01:41 am
content: Quote from: the_enginerd on February 14, 2019, 02:59:53 amYou could also get a test board with standard 1oz copper and measure what the actual trace resistance is to see if you really need to care.

author: free_electron
author_rank: Super Contributor
timestamp: February 14, 2019, 01:27:28 pm
content: even though your board may be 4 oz copper : the plating in the holes won't be ! So whenever you experience a layer-hop : shoot a ring of via's around the holes.For example : your power arrives on bottom layer to a capacitor pin , then leaves on top layer. Don't bank on the solder and the pin ! it may not flow up far enough in the hole to guarantee a nice solder fillet under the component. It wouldn't be the first board where the plating burns out...