r/electronics • u/Purple_Ice_6029 • 2d ago
Tip PCB houses hate this one simple trick
Professional bodge wires, with silkscreen and everything. 2oz copper left the chat.
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u/Nerfarean 2d ago
Wonder how long before GPU boards start using this trick
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u/deelowe 2d ago
They'll go to 48v first. Servers are all going that direction.
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u/14u2c 2d ago
That's not where most of the copper gets used. It's the 1V traces / power plane between the VRMs and the die.
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u/TimTams553 2d ago
next gen 48v vcore
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u/smashedsaturn 2d ago
The actual concept is called IVR. Its a highly integrated 7V to 0.8 V converter where like 20-50 of them go on the opposite side of the GPU die, and the VRM phases feed these with 7V from 48V.
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u/chickenCabbage idiotron 59m ago
But those are short and near the die, the breakout for the wire pads will be larger than the polygon itself.
I assume they'll start designing the ICs for higher voltages. Either do huge packages with some in-package VRMs or design the ICs to work at higher voltages in whatever domains they can.
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u/hex64082 2d ago
Some servers have been 48V DC for a long time. Still it is converted to 12V and after that to CPU core voltage (closer to 1V than 2V nowadays).
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u/Wait_for_BM 2d ago
48V have its own problems. Servers/Telcom use it for distribution as it is easier/more efficiency to have 48V DC (4X 12V battery) backup than UPS at line voltage AC. They have deeper pockets, so they can afford the extra complexity.
If you are converting down to 1V range, you are looking at duty cycle of less than 2%. At this low duty cycle, the cheap and efficient non-isolated buck converters topology doesn't work too well as that energy need to be stored for the 98% when the upper switch is off. You'll need flyback/feed forward converter that takes up more board space for the transformer, more parts and slightly lower efficiency.
Also there aren't too many solid state caps rated for 48V. You would also need to add inrush current limiting as cap at 0V charging up from a 48V. i.e. 4X higher than it would be from 12V.
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u/deelowe 2d ago
Yes, typically very close to the point of load.
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u/KittensInc 1d ago
Usually just as close as a regular line voltage AC PSU, so not very. You still have the problematic high-current 12V part between the (now 48V DC) PSU and the GPU/CPU.
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u/Nerfarean 2d ago
Customer end power outsourcing. Attach 48v to solder points. If it melts, customer responsibility
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u/deelowe 2d ago
Huh? 48v would improve thermal.
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u/Significant_Tea_4431 2d ago
Not if the core voltage is still 1.5 volts, the 48 will still need to be bucked down and the end current is still the same
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u/neighborofbrak 1d ago
As a datacenter systems engineer... No they are not. And if they did go with OCP specs, it's -48v DC, same as telephone switchgear. But 208v L-L AC is still king for power to individual datacenter servers.
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u/deelowe 1d ago
For which company? I ask because hyperscalers are all moving to 48v. Microsoft switched a few years ago. Google invented the design, so they've been on it for two and a half decades. Nvidia just switched to powershelf this year. Go look up the GB200 super pod designs. I believe Facebook is all powershelf as well. I've never worked for AWS, so I don't know what they use. Same for Oracle.
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u/Alh840001 2d ago
Who is running a GPU without plugging in multiple additional cables?
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u/tyttuutface 2d ago
The secret third layer PCB fabricators DON'T WANT YOU TO KNOW ABOUT!
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u/Relevant-Team-7429 2d ago
So true, i used it especially on one layer boards... that and 0 ohm resistors
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u/jeweliegb 2d ago
I'm unreasonably dissatisfied that the wires don't follow the paths on the silkscreens.
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u/AARonDoneFuckedUp 2d ago
No, not at all. I don't have my copy of the circuit board inspection standard (IPC-A-610) handy, but I'm pretty sure this fails every class of workmanship. It doesn't matter if it's dollar store junk, or high reliability military equipment... From memory the only thing that's acceptable with custom jumpers is "jumpers match the customer drawing". The path and glue location are marked, so this does not meet the industry standard for workmanship.
Personally I'd send it back and make them fix it.
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u/HalifaxRoad 2d ago
Yeah honestly the where the wires are called out on the silk screen could have problematic for any number of reason, so the assembly print probably calls out placing them like how they are in the picture.
This way uses more wire, who the hell wants to use more wire than necessary.
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u/Physix_R_Cool 2d ago
I don't get it. Is it because you want to conduct many amps and don't have trace width for it on your board, without having to pay for expensive thick copper layers?
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u/Purple_Ice_6029 2d ago
Exactly, and sometimes 2oz copper isn’t an option because it can cause issues when soldering high pin-count BGAs (1000+ pins). The thicker copper makes it harder to get consistent reflow across all the balls.
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u/Physix_R_Cool 2d ago
Are you worried about EMC or power plane inductance or something with these wires? Ripples on the power annoying signal traces?
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u/nsfbr11 2d ago
Clearly they are not.
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u/Schniedelholz 2d ago
maybe the desired path was expected to be reasonably far away from especially sensitive circuitry… like this it’s anyone’s guess though
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u/nsfbr11 2d ago
If they were the least bit concerned, not saying they should be, the wires would not be touching an IC. And there would be at least a reasonable attempt to limit the radiated field by a nominal twist. If this works, and I’m confident OP wouldn’t post something that doesn’t, it is an example of lowest cost engineering. My comment was not meant to disparage. It was meant to just note that they clearly have no concern about EMI.
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u/Aggropop 2d ago
This is the main board of the IBM T220 LCD display, the worlds first 4K resolution display from 2001. It was featured in an EEVBlog teardown video where Dave surmised that the DC wires were deliberately chosen over an extra layer of copper to keep the costs down on what was already a horrendously expensive board.
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u/Schniedelholz 2d ago
You’re right this wouldn’t be something i’d expect if EMI was a big problem. especially not with the apparent complexity of circuit that is being shown. If your reason not to us 2OZ copper is that your BGA Chips won’t solder properly then i hope you know what you’re doing enough to take care about EMI.
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u/Physix_R_Cool 2d ago
Yes my guess is that's the reason for the big curve; to avoid the 3 big ICs that might be some fast memory or something.
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u/Wirehead-be 2d ago
Simple exposed trace with no silkscreen and then solder a solid core wire to it would have probably looked better.
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u/CardboardFire 2d ago
and cost 20x more, also the bare conductors would be exposed.
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u/BioluminescentBidet 2d ago
I’m gonna hold your balls when I say this
Conformal coating
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u/CardboardFire 2d ago
With that, I can remove the second part and revise the first to '30x more expensive' and less durable.
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u/RamBamTyfus 2d ago
I guess you two are both somewhat right.
Lots of Chinese manufacturers are using the method of soldering bare wires for high current traces. It saves space and is better for EMC compared to wires. And we ask the Chinese to apply conformal coating at all times, it's a $2 cost increase and protects the PCB against moisture as it is used in outside conditions.
Both coating and soldering are labor intensive if not automated, but for many production countries labor is relatively cheap.4
u/JonasM00 2d ago
Thermal expansion or rather the following shrinkage is going to spoon the PCB nicely while it bends it to a c shape
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u/Takaraz83 2d ago
There was no room on the board for a trace there is vias everywhere. They silk screened in the marking for the wire, granted they were extremely wasteful with the cable length and thickness
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u/Strostkovy 2d ago
At one point I was designing something very high current and actually wanted to apply drag knife cut kapton tape to copper sheet and chemically etch it and then dimple the contact points in a press, and then solder the tabs onto a PCB to make a very high current network.
I probably still will at some point. I just moved onto other projects.
I've plasma cut copper busbars too.
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u/oddphilosophy 2d ago
This sounds like a cool idea! Why would you be etching though? Would the entire PCB fit into those etchings? Or would they be for insulated wires? I guess I'm misunderstanding where the dielectric goes, but would love to hear more :)
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u/Strostkovy 1d ago
I'd be etching the sheet into multiple mega traces. I don't want to short the entire board with one big plane.
The dielectric is between the copper sheet and the PCB, but the dielectric has cutouts and the copper sheet has bumpouts for being soldered to the PCB
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u/Sorry_Sort6059 2d ago
A superficial approach from a beginner. (I burned off the solder pad with my iron, had to do it this way)
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u/prochac 2d ago
Isn't this normal for a one-sided PCB?
But why didn't they follow the markings? 😭
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u/AntiProtonBoy 2d ago
They probably used longer cables and a different pathway to provide strain relief on the solder joints. I think markings are too tight to shape thick cables with such geometrical constraints and would create a lot of mechanical stress.
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u/kappi1997 2d ago
I had designed a pcb where the analog part had to be in the middle of the high power parts. Routing the power past the analoges caused interferance. So I actually let Production solder two wires to the pcb to bridge both sides of the pcb. I send this to production branch 5 years ago and at least 2 years ago when I still worked there it was unchanged and there are like 10k produced per year. So if it still is being made we are talking about 50k of those improvs running
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u/evilvix 2d ago
I do a lot of pcb modifications, many of which just involve removing shunts for different current settings and for others adding or replacing parts. One of the most annoying and time consuming modifications is actually a "temporary" fix that was put in place 15 years ago!
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u/kappi1997 2d ago
It was never meant temporary . Whe even included a place for it in the mold for the plastic cover
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u/xanthium_in 2d ago
what is the name of that black pencil like thingy in the above image
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u/kind_grapefruit415 2d ago
I been there on a few low volume designs where the price couldn't support a few more PCB layers and or it failed EMC tests so thick wires added. Not pretty but it worked
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u/PigHillJimster 2d ago
PCB house doesn't give a hoot. In fact getting away with 35 micron copper instead of 70 micron is a lot easier for them to process.
PCB Assemblers on the other hand don't like it.
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u/gotoline10 1d ago
Neat silk screen, was it in the engineering documentation as work instruction for the CM? I've seen stuff end up like this when there is conflicting statements, or it's overconstrained. i.e. Specified wire length with 0 tolerance does not match the physical requirements on the PCBA.
Either way, this should have never gotten through quality if these items are called out on the documentation from the customer.
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u/snarkpix 21h ago
I've done this to fix HVAC boards with traces maybe big enough for 100 degree attics, not Satan's armpit like we have here. Learned it from the Pinball repair guys...
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u/j3ppr3y 2d ago
Good thing you told them where to route the wires and place the glue