High power, 5mm thick PCB - Page 1
Forum section: electronics / general

author: mjt
author_rank: Unknown
timestamp: June 30, 2019, 11:13:17 am
content: I have in my possession a "SunFire X4600 M2Power Distribution Board" which was used as a backplane for 4 xArtesyn DS850-3supplies, each of which supplies 12v @ 70A in a'3+1' redundant configuration. So presumably it can safely carry at least 140A, and maybe as much as 280A.Click images for larger versions:My rough measurements are that the board weighs 147g sans connectors, and after subtracting the cutouts has an area of about 97cm². It's about 5mm thick, and the two outer copper layers are each about 0.09mm thick, if my cheap vernier calipers are to be believed. If one assumes the PCB is 50% copper by weight, that's 24 ounces/ft². Of course, it carries both power and ground. The cutouts are to allow airflow from the power supplies' forced air cooling, which presumably would have provided some cooling to this PCB too.I've got a project carrying similar currents - currently we use laser-cut copper bus bars, and I was wondering if there was wisdom in the Sun design I could learn from. It certainly feels lighter than the bus bars we use at the moment!None of the PCB price calculators I've tried offer 5mm thickness, and none of the trace current calculators will go beyond the 35A performance figures offered by IPC 2221. Is an extra-thick PCB a good and cost-effective design, or is the fact other designs work better the reason it's rare to see such PCBs?If you've designed such a high power PCB, how well did it work, and what guidance did you follow while designing it?Thanks for taking the time to read my message!

author: Rerouter
author_rank: Super Contributor
timestamp: June 30, 2019, 11:28:30 am
content: Copper by weight is pretty cheap, however the time and knowledge to get an even plating of copper that thick, and the dedicated machine time while they are plating those boards is what drives up the cost.In reality you can cheat a lot with PCB's like this, its all a game of managing your resistances. and similarly managing heat flow, E.g. if your carrying 100A to a PCB, well that means you likely have thick wires connecting that 100A to the PCB, those wires are a beautiful heat sink. If your screwed to a metal enclosure, that is more free heatsinking, If your willing to let things get say 50C above ambient, you can flow a suprising amount of current through 2oz copper, e.g. a 65mm wide 2 Oz trace that is running top and bottom of the board would be good for 110A ignoring the heatsinking of the wiresAdd them and things get much narrower,Quadcopter power distribution boards are a good example of this, most are 2oz, but may be pushing 140A on a tiny PCB

author: IconicPCB
author_rank: Super Contributor
timestamp: June 30, 2019, 11:15:34 pm
content: In an experimental EV board we pushed 2 ounce board up to 190Amps.The designer wanted to see the temperature rise of the power fets under such conditions. The board survived however the solder did not . The Fets were floating on pools of molten solder.The only heat sinking on the board was due to the copper plating no additional forced cooling.Thermistors were part of components complement and were used to log temperature around the board.

author: DerekG
author_rank: Frequent Contributor
timestamp: July 01, 2019, 01:48:49 am
content: Quote from: IconicPCB on June 30, 2019, 11:15:34 pmYes, we have had much the same, forcing a move from SMD to through hole mosfets (still bolted directly to the PCB for heatsinking).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 01, 2019, 05:37:30 am
content: Right, you won't get automatic quotes for a board that ornate. Do a full custom quote.I'm guessing it'll be a few $1000 from most sources.Advantages compared to bus bar: precision dimensions, allowing press-in connectors; routing of signals as well as power; placement of components; etc.Tim

author: IconicPCB
author_rank: Super Contributor
timestamp: July 01, 2019, 08:34:13 am
content: Typical plating time for our process ( non pulse plating ) is 86 minutes per half ounce of copper.Pulse plating is somewhat quicker.So 24 ounce copper would take us ( assuming we start with 0.5 ounce laminate ) 67 hours of non stop plating....An expensive proposition...We have in the past used copper sheet metal, cleaned etched the surface and laminated it in the multi layer press.This was used to fabricate some high power LED gear.A major issue with such heavy copper is ensuring the etching of layers does not result in undercut copper.The thinnest copper we could source was 1.2mm thick material. This is approximately 34 ounces of copper.

author: alanambrose
author_rank: Frequent Contributor
timestamp: July 01, 2019, 10:03:49 am
content: Hi,>>> I've got a project carrying similar currents - currently we use laser-cut copper bus barsI've an interest in this area too - is it possible to say a little more about your current set-up (ha!) and /or an image. Are these wave soldered to the pcb? What wire-to-board connectors do you use? How do you handle the transition from the connectors to the busbar?Thanks, Alan

author: mjt
author_rank: Unknown
timestamp: July 01, 2019, 12:47:53 pm
content: Quote from: alanambrose on July 01, 2019, 10:03:49 amThe high-current parts being connected in my case are power coming in from a battery, an isolator switch, a large fuse, some power contactors, some smaller fuses, and wires going off to other devices.The current arrangement is thick copper bars that looksomething like thisconnected with copper bolts, and cables the size of your finger with eye crimps. It's not a bad design - but it does transfer the design work away from the electronics design team and onto the mechanical design team.We don't put anything above ~30A across a PCB; needless to say, PCB connectors are much easier to find for these lower current levels!The PCB pictured above uses "Amphenol PWRBLADE" connectors which, as you might be able to see, are blind mating with power and data, and they're reasonably cheap. Don't know how you'd get that much current away from them though, hence my post! Anderson Power Products have some quite keen pricing for high-current connectors too. And you might look at "Amphenol SurLok Plus" if you want more of a deluxe connector.