I am going to use aluminum bus bars in a high-current PCB. What is the best technique to establish contact between the PCB and the bars?
I plan to make my own bars. The current is generally going to be around 100-150 A per single connection (a bar will be connected in several places).
If you want the bar to be flush against the PCB, consider broaching PCB PEM nuts.
If you want to raise the bus bar, consider pressfit threaded terminals.
https://www.digikey.com/short/2hm8p02f
If you want the bus bar to slip onto the PCB, consider busbar clips.
{Molex}
Beware of creep and oxidation: high conductivity aluminum alloys are soft and may creep under clamping force. Regardless of alloy, beware of differential thermal expansion, which will cause the mating surfaces to shift as they heat up and cool down, causing wear and oxidation.
Once the aluminum surface oxidizes, that's it, you have an insulator in the affected spot. Over time, connection resistance increases, until eventually it overheats, and damages surrounding circuitry, or melts, or starts a fire.
Joints must be clamped tightly, gas tight or greased (with a suitable anti-ox formulation), stuff like that.
Don't take my word for it, or anyone else's un-cited words; I strongly recommend looking up proper industry-recommended practices, or code standards, for aluminum wiring. Afraid I don't have experience in this field [power transmission and use of aluminum conductors] so I don't have any to recommend (anyone chime in in comments?), but this may also vary by region (permitted equipment wiring practices) so you are best looking up regulations in the place(s) being marketed to / installed in.
Regarding creep, consider: Copper wires resist mechanical creeping - Leonardo Energy They give several academic references that may be of interest.
Also keep in mind, PCB material is subject to creep, or cold-flow. Preferably, use soldered or press-fit terminal blocks; if clamping board material directly, use a bolting solution with lots of compliance, such as using Belleville washers.
I have done this to mount a 500A copper bus bar to a PCB, but the techniques should also be valid for aluminum.
First of all, the bus bar should be plated. Aluminum especially, is going to develop an insulating film if you don't plate it.
The pad on the PCB side should also have a plating that will not corrode if left exposed for extended periods of time (so not bare copper).
To make electrical contact with the PCB, we included a large, exposed, plated metal area under the entire bus bar (with a bit of clearance on either side to account for tolerances).
We used several screw holes in the bus bar that would clamp the bus bar to the PCB. In our particular case, it was four holes down the center of the bar, and the PCB used PEM nuts to receive the screws on the board side.
Could you use something similar to the below picture. Providing that the screw Terminal is within the current limits & the PCB is designed correctly.
I haven't personally used them in my designs, but have seen them in a number of high current products.
The pictured screw terminal is manufactured by Wurth Elektronik, but multiple manufacturers have similar products & the likes of Mouser/Digikey stock them.
(Image source: RS Components)
