Pulsed current supply for reverse pulse electroplating - Page 1
Forum section: electronics / projects

author: BeePound
author_rank: Contributor
timestamp: August 14, 2021, 10:09:06 pm
content: Hi everyone,I'm looking for a hardware recommendation here. I am doing nickel-iron alloy plating, which needs to be current-controlled, not voltage-controlled, so a standard signal generator won't work "out of the box". Additionally, the power supply needs to be programmable; the "forward", or positive, current is followed by the "reverse", or negative, current, followed by an off time of zero current, all of which steps usually are only a few milliseconds, or maybe tens of milliseconds in length. You will normally see the currents as current densities; the actual value of the currents, for a RD lab, will probably be around an amp or less. A google search will turn up plenty of examples "pulse reverse plating" but here is one paper just to be clear, look on page 5, Figure 5:https://www.researchgate.net/publication/305037633_A_High-Q_In-Silicon_Power_Inductor_Designed_for_Wafer-Level_Integration_of_Compact_DC-DC_ConvertersAnyway, I have been trying to look through the literature and have found some power supplies that have been used previously, such as the Advantest R6145 or Keithley 6221, but documentation is sparse for the first and the second is very expensive (at least for our budget, which we're targeting $1-2k), even on ebay. Basically, I'm not expecting anyone to go on some grand quest to find the perfect power supply, I'm just wondering if anyone has any other power supply recommendations off the top of their heads.Thanks!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 14, 2021, 10:56:36 pm
content: A simple audio amp or power op-amp might do. Audio amp is a little tricky as the output is voltage-mode. If the cell's voltage is well defined, the current can be set with resistors. For example, use a variable square wave input signal, and a series resistor between output and cell. A DC coupled design is needed of course. If the cell voltage is more prone to fluctuation (during plating, as concentrations vary, or polarization (gas bubbles), temp rise, etc.), and your currents need to be more precise, an active (current regulating) circuit will be required. This can still be built using most audio amp chips, with some modification to get the current-feedback output.Or a polarity-switching bridge can be used. Pre-made examples are used for gate drivers, solenoid and motor drivers, etc. By controlling either the supply current to the bridge, or using a constant-voltage supply with current-limiting resistors at the output (use two diodes to set the current in each direction), you can get the desired characteristic.It seems like it would be desirable to have some automated control. The most drop-in solution would be an AWG (arbitrary waveform generator) or DAQ (data acquisition, i.e. typically including logic I/O, ADC and DAC functions on terminals), plus a current amplifier such as above. For a little work (and much less equipment cost), you can do the same thing with an Arduino or whatever, and program it for whatever kind of cycles, adjustments and interface you like.For the most custom design, I would probably do something like, an MCU (via Arduino or otherwise) controlling a switching regulator, which sets supply current into a polarity-switching bridge. High efficiency, good for pretty much whatever you might end up doing (say, resolution down to some ~mA, capacity up to say 10V 10A?), and that would take a few weeks to a month to design, build and program, for someone skilled in the arts.Tim

author: jonpaul
author_rank: Super Contributor
timestamp: August 15, 2021, 02:53:38 am
content: Bonjour, what is max I, V and duty cycle?Is load pure resistive?Solution: Programmable DC PS (off the shelf from HP, etc) followed by a polarity reversing H-Bridge.You can then pulse the H-bridge plus/minus/off as desired.Enjoy,Jon

author: BeePound
author_rank: Contributor
timestamp: August 15, 2021, 08:58:24 pm
content: Hi Jon, thanks for the reply. I would say the load is mostly resistive; there might be a very very small capacitative component. So I think what you described would possibly work. I do wonder though; sometimes with these plating waveforms it is useful to have the forward current be smaller than the reverse current. I guess I could just put some resistors in the "on" part of the H-bridge for that.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 18, 2021, 01:12:42 pm
content: How much current. How oftern does it need to be reversed? How may volts will it need to supply? Looking at the original paper it looks like you dont need a very high current density. So I think the question is how much area will you want to plate. If you follow their example you need a source that can output about 10A for 100cm2.

author: jonpaul
author_rank: Super Contributor
timestamp: August 18, 2021, 03:52:46 pm
content: Hello again: The H bridge can include adjustable current sources.Alternately just place power resistors in one leg of the bridge to reduce the current in a half cycleJon

author: BeePound
author_rank: Contributor
timestamp: August 24, 2021, 09:53:02 pm
content: Hi Terry,I'm working in a lab that works on 4" silicon wafers, so the max current we would be talking about is probably around 1 A. For 1 A, the voltage would be several, maybe up to 10, volts.As for how often does it need to be reversed, the nominal design would be to have a, say, 0.7 A forward current for 100 ms, followed by a 1 A reverse current for 30 ms, followed by no current for 70 ms. Then repeat the cycle a few million times (plating for ~5 days) to get the thickness that I need.

author: BeePound
author_rank: Contributor
timestamp: August 24, 2021, 10:13:22 pm
content: Thanks for your reply - I guess my reply will show you how uneducated I am on this topic! I agree with you that one could include two different current supplies, that makes sense.My concern is with the H-bridge is that when the bridge switches to the other polarity, or when it "switches legs", the power supply isn't "ready" for this change. What I mean is that the current-controlled power supply that the bridge just switched to isn't outputting any current, so it must ramp up the current very quickly, over say 1-5 ms. The pulses are potentially only 10s of milliseconds long, so that's why the power supply settling time must be so short. I was thinking there might be a way to put additional switches that lead to "dummy" loads in the H-bridge, such that the voltage and current that the current source needs to apply once that leg is turned on would be much closer to the nominal value, but I don't know if this is necessary or even a reasonable solution. I've attached a picture to show what I mean, where I have two current sources running with different currents, all switches S1 (S2) open or close at the same time, the electroplating bath has a resistance of R and so the dummy loads also have a resistance of approximately R. I would likely need some diodes too, but hopefully you get the idea.