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Anyone have any recommendations for PCB fab that can do 10oz copper for a fair price. (with PCBA service too).
(Size around 140x140mm and volume 200pcs)
I had a quick look at pcbway as they have an option for 10oz but I doubt those online prices are competitive, since it's not exactly an area that PCBway specialize in, or do often.
On a similar subject, can you get anything like pic-n-place-able copper bus bars that I could get placed onto a PCB as a standard SMT part to increase current consumption at various locations as a cheaper alternative to thicker pcb copper? -
On a similar subject, can you get anything like pic-n-place-able copper bus bars that I could get placed onto a PCB as a standard SMT part to increase current consumption at various locations as a cheaper alternative to thicker pcb copper?
I've not seen SMT busbars as a "standard part" but there are a few metal etching and precision sheet metal fabricators I've seen who offer design and fab services for them, its not a hugely complex manufacturing process so pricing should be reasonable. THT board stiffeners can be used as busbars if that add a few search criteria terms. A THT version can be quite readily laser cut if you go custom but an SMT version would require a bit of thought and forming so that it keeps stable and upright during reflow. -
You should think if increasing layer count is more cost effective than using a very thick copper. With more layers, you can also make wider traces since on internal layers you have no parts to wiggle around. Say 6 layer board with outer 2 Oz and internal 1.5 Oz copper is much cheaper than 2 layer board with 10 Oz cu. Not to say thick copper will cause problems with SMT components.
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On a similar subject, can you get anything like pic-n-place-able copper bus bars that I could get placed onto a PCB as a standard SMT part to increase current consumption at various locations as a cheaper alternative to thicker pcb copper?
I've not seen SMT busbars as a "standard part" but there are a few metal etching and precision sheet metal fabricators I've seen who offer design and fab services for them, its not a hugely complex manufacturing process so pricing should be reasonable. THT board stiffeners can be used as busbars if that add a few search criteria terms. A THT version can be quite readily laser cut if you go custom but an SMT version would require a bit of thought and forming so that it keeps stable and upright during reflow.
why put smd up right?
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How thick can you go with copper oz before you start to get component placement/soldering issues?
Maybe 6 layer 4oz would be better. -
How thick can you go with copper oz before you start to get component placement/soldering issues?
The minimum track/spacing will increase with copper weight - you won't be putting a 0.5mm QFP on a 10Oz boards!
10Oz is so far away from a normal process that busbars or even wires would be worth a serious look. -
in terms of bus bars i dont know of any 'smd' components ones but for soldering you would probably have to source your own solder them with super low temp solder and solder them before anything else because of the amount of thermal stress required.
So instead you shouldnt solder it you should have screw terminals with nuts and washers to hold it to the board a bus bar will swallow heat like nothing else on that pcb so thats why i dont recommend soldering it -
FYI,
I ordered 3oz PCB from PCBWAY once, and after some correspondence from them, I think the conclusion was that 3oz and above they outsourced to another PCB manufacturer. Not that it really matters. Also, the advertised minimum track/clearance spacing was not really accurate. I think for 3oz they wanted 10mil/10mil, even though the website said 8mil/8mil. So...10oz copper, I imagine the spacing needs to be quite large.. 20mil(??) for your "average" factory.
Just a heads up if you haven't worked with this type of copper thickness before. -
2 oz is OK, 3 oz marginal and 10 oz very bad for soldering, production, etc.
A copper heat sink and wider traces or lay on bus wire jumpers is preffered.
Jon -
And for those that don't know --
https://www.digikey.com/en/products/detail/harwin-inc/S1621-46R/2264455
Besides 0-ohm resistors, there are parts like this.
You can also find 0-ohm resistors in "solid metal" types, so they have the same enameled chip body you're used to, but they actually handle more than a few amperes.
Tim -
That's actually pretty cool especially if you only need higher current capacity on some subsystems and not the whole board.
My concern, from a few bad experiences, is that that part will not reflow properly. I can imagine cold joints everywhere -
Yeah, you need good soldering to get good soldering, of course.
Also an option, use a riser board to handle the control circuits, etc. This can be whatever, and a big bulky header carries signals into the heavy board -- this solves problems like SMT trace/space limitations, and saves precious board area.
Also good practice to simply not need traces at all, as much as possible. An inverter bridge for example, can be laid out with the transistors and connectors stacked all right next to each other, so that the current paths are as wide as the components, and less than a mm long, say. The current density might be off the charts, but it's so short that it's really pretty irrelevant. You're relying on lateral heat spreading here, not surface dissipation.
Ampacity can also be improved with thermal transfer (clamp the board between thermal pads and heatsinks?), minding that, while that saves trace temperature, you still have all those losses, which need to be dissipated for one, and also amount to whatever mV of wasted voltage.
The same is true of the previous paragraph, i.e. all those transistors, and what little connecting copper lies between them, all needs to be heatsinked.
This is getting into the regime where rules of thumb (like trace ampacity) are irrelevant, and even hand-waving calculations are questionable (estimating the voltage drop of some trace by an equivalent rectangular bounding box). You really might want to just build a 3D model and simulate it in a thermal physics sim, or budget the time and money for several protos to measure it directly, and iterate upon.
Tim -
Ah sure you can make room-temperature superconductors out of 0 ohm resistors if you manage to keep them all pushed together without using solder between them
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And for those that don't know --
Yes, these are great, 10A+ through this and a regular PCB in parallel, easily works.
https://www.digikey.com/en/products/detail/harwin-inc/S1621-46R/2264455
Besides 0-ohm resistors, there are parts like this.
You can also find 0-ohm resistors in "solid metal" types, so they have the same enameled chip body you're used to, but they actually handle more than a few amperes.
Tim
If I could drop my own question:
Does anyone know cheap SMD spacers that can be used to bolt a busbar to?
Parts like these, but without heart attack after getting a qoute for them:
https://www.we-online.com/katalog/en/WP-SMBU_THROUGH-HOLE
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And for those that don't know --
Yes, these are great, 10A+ through this and a regular PCB in parallel, easily works.
https://www.digikey.com/en/products/detail/harwin-inc/S1621-46R/2264455
Besides 0-ohm resistors, there are parts like this.
You can also find 0-ohm resistors in "solid metal" types, so they have the same enameled chip body you're used to, but they actually handle more than a few amperes.
Tim
If I could drop my own question:
Does anyone know cheap SMD spacers that can be used to bolt a busbar to?
Parts like these, but without heart attack after getting a qoute for them:
https://www.we-online.com/katalog/en/WP-SMBU_THROUGH-HOLE
Not really what you’re looking for but at work we use this company for a lot of hardware: http://www.kangyang.com/products_list_detail.php?id=8605&main=11&cid=0
Could accomplish similar result. Price is low in quantity. -
PEM is the standard US source for all things press-in (and some solder and weld types).
Leaded connectors are generally better, as they don't rely on the PCB's structure, which cold-flows under compression making direct screwing unreliable, and surface mount nuts don't have much meat to hold on with (the kind with a thru barrel -- often swaged in place -- can be alright).
https://www.digikey.com/en/products/detail/keystone-electronics/8197/316833
Like the above, or this one which is only rated 30A but I'm sure you can get more out of it, it's quite beefy. Maybe a larger screw (or a more conductive one?) would be preferable, or simply enough meat to sink the heat out of the way (i.e. a bus bar).
Speaking of bus, if you're getting into the special-order range of things, don't be afraid to draw up something from waterjet or punched* copper that solders or screws in place. Parallel plates for low inductance, stand 'em up on edge to take less area, fab your own heatsinks (well, if you don't need too many fins on them), etc.
*Not as bad as it sounds: there are CNC punches that can do a very nice job indeed, on similar budgets as other fab items (waterjet/laser cut). Embossing is also a possible feature! CNC brakes too, they can do some pretty sharp stuff at proto prices.
Tim -
https://www.digikey.com/en/products/detail/keystone-electronics/8197/316833
Like the above, or this one which is only rated 30A but I'm sure you can get more out of it, it's quite beefy.
Yeah, I’ve used the kind I linked above at close to 40A and thermal testing didn’t reveal any issues with the metal piece itself. I have a feeling the rating is set conservatively to account for varying quality of screw connection. -
PEM is the standard US source for all things press-in (and some solder and weld types).
Leaded connectors are generally better, as they don't rely on the PCB's structure, which cold-flows under compression making direct screwing unreliable, and surface mount nuts don't have much meat to hold on with (the kind with a thru barrel -- often swaged in place -- can be alright).
https://www.digikey.com/en/products/detail/keystone-electronics/8197/316833
Like the above, or this one which is only rated 30A but I'm sure you can get more out of it, it's quite beefy. Maybe a larger screw (or a more conductive one?) would be preferable, or simply enough meat to sink the heat out of the way (i.e. a bus bar).
Speaking of bus, if you're getting into the special-order range of things, don't be afraid to draw up something from waterjet or punched* copper that solders or screws in place. Parallel plates for low inductance, stand 'em up on edge to take less area, fab your own heatsinks (well, if you don't need too many fins on them), etc.
*Not as bad as it sounds: there are CNC punches that can do a very nice job indeed, on similar budgets as other fab items (waterjet/laser cut). Embossing is also a possible feature! CNC brakes too, they can do some pretty sharp stuff at proto prices.
Tim
when we have have custom shield cans made they were etched much like PCBs
here's an example of something that looks laser or waterjet cut copper
http://wiki.lofarolabs.com/index.php/File:Mosfet-soldering-part1.jpg
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Ah yeah, that's a thing too, etching for precise lines. Partial depth for bend lines or scoring, full depth for, well, cutting.
Mass produced ones can be die drawn, but obviously you aren't going to get those in less than millions quantity; folded corners and edges, and rivets or hooks or solder, are fine retention methods for the most part, and easily made this way.
Easy to do at home, too! Not that you'll necessarily want to sit there etching and bending like a hundred of 'em, but...
Tim -
https://www.we-online.com/web/en/leiterplatten/produkte_/wirelaid_/wirelaid_2.php
Doubt it will be cheap though!