modified: Sunday 5 January 2020
Prototyping using copper tape and PCB land pads
Previous prototypying technique articles on this site:
- Simpler PCB etching/making techniques for simpler boards
- Experimental homemade aluminium and silicone PCBs
In 2018 I read an article about creating circuits using copper adhesive tape and cardboard by Bunnie Huang. My interest was piqued -- using drilled protoboards has traditionally been successful at dissolving away hours of my life and making me go cross-eyed.
Copper tape is sold very cheaply on the usual greymarket platforms (eBay, Aliexpress, etc). A few dollars will get you a few meters. Buy wider than you will think you will need and cut it up with scissors as you go.
Caution: many sellers incorrectly call polyamide ("kapton") tape "copper tape", some even erroneously call it "conductive tape". Pay attention before purchasing.
It doesn't need to be on cardboard
Here's an audio amplifier I have working for some experiments in driving capacitive loads. It doesn't seem like much but it's still many hours of work to arrange and assemble the parts:
This device is made of several copper-tape and plywood modules. Whilst paper and cardboard are very convenient and cheap, they unfortunately curl up whilst soldering and wrinkle over time if left anywhere near water. I use a mixture of substrates depending on what is most convenient.
Plastic substrates also (surprisingly) work, but only if you are quick soldering. It's perfectly possible to make a substrate of (PVC) duct tape on other surfaces, but polyamide ("kapton") works better if you have it.
For those curious about the picture above: The main push/pull pair is a totem-pole style arrangement to allow it to be driven by lower voltage control circuity. A big thankyou to everyone on EEVblog forums who has given me advice on this topic , including TurboTom for this particular style of output. I plan to write up some of my experiences with this design some time soon, including adventures linearising it, dealing with crossover distortion and keeping it stable with capacitive loads.
You can layer infinitely
One of my first copper-tape circuits was a triangle wave generator:
Notice the yellow tape. This separates different layers of copper. You can use any old tape, even standard clear sticky tape seems to work fine as long as you are careful.
A layer limit is set by two things:
- Bulging. Taping over solder joints can make it hard for the tape to stay in contact.
- Fear. Having to dig up a layered mess to fix a mistake underneath.
So far the generally spread-out nature of this prototyping technique has prevented me from having any notable layering problems.
There is only one side. No board-flipping
Unlike soldering with protoboard and veroboard: you never, ever have to turn a copper-tape project over and solder from the other side. This is the biggest advantage of this prototyping method.
I go insane having to flip my prototyping boards over constantly whilst working on them, especially when trying to thread small wires from one side to the other and getting lost in mental mirror images of component footprints. Every time you count the shiny holes you end up at a different position, brrr.
Soldering is already a three-hand activity and I don't have the finances to afford nice, stable dedicated PCB flipover vice. One of those might help mitigate the problem, but it does not remove it entirely. Using copper tape does.
Working with SMD parts is easy
Small pin-count SMD parts can be handled by:
- Placing down a large piece of tape
- Cutting away this tape into a fan-out arrangment using a knife
- Peeling away the unwanted pieces of tape
Higher-count SMD parts are another story. Trying to cut 14 identical small parallel wires out from a part footprint is pure pain; as is trying to equivalently lay down thin pieces of copper tape. The adhesive doesn't work well at this scale and the thin pieces twist into spirals.
I initially reached for SMD breakout boards to try and work around this, sceptical that they would end up being more effort than they are worth. Here's a diode detector and audio amplifier I made a few months back to pickup AM that uses such a breakout board:
As it turns out: this method is absolute genius. It is vastly easier than using actual DIP parts (even though they have the same 2.54mm pin/pad spacing) because it provides female vias (instead of male pins) to solder to. You essentially:
- Stick a resistor/diode leg into one of the holes
- Solder it in
- Bend it over to where it needs to be & cut it to length
- Solder the other end
It's assembly heaven. These short wires can also very easily be bent to go above or around each other -- have a look at the photo above in detail.
If you are afraid of soldering SMD parts like this SOP/SOIC chip: don't be. General tips:
- Use a big-arse soldering tip. Never use a small tip unless it's an expensive tip and and expensive soldering station; otherwise it's complete non-thermally-conductive junk.
- Solder-tack one corner
- Solder-tack the other corner
- Over-solder the rest of the pins and clean up if need be.
Steps in visual form
(1) Don't throw yourself at the tape without pencilling up some plans first. It's just as complicated as laying out an actual PCB, despite not being as compact, so you often wire yourself into corners if you don't put some thought in.
A pencil and a rubber are indispensable.
(2) Rub the copper tape down with something hard and smooth (eg permanent markers or pencils with a curved rear end) after putting it down. This dramatically improves the tape adhesion, to the point it will now tear up your paper/wood when you try to remove it.
(3) Use larger tape pads if you plan to solder big/heavy parts. The adhesive will fail after enough heat & time.
(4) Spend as much time as possible laying tape with your soldering iron off. It's easier and simpler this way.
(5) Don't be afraid of going big. Going too small (eg PCB scale) is possible but simply not worth the 10x headache and effort. Enjoy building big, especially for your first projects using this technique until you improve.
PCB land pads
Manhattan-style prototyping is very common in the radio community. w3aew has a great video showing several methods.
No pictures here, sorry. I became very angry with my last PCB land pad construction and threw it out.
I have found the easiest way into this technique is to use an ordinary hole-punch (designed for paper) on a blank piece of copper-clad board. This gives you little round islands you can stick down and solder to. Plain FR2 copper clad board is cheaply available from the usual grey-market sources (eBay, Aliexpress, etc), but you will need to make sure you have a hole punch that accepts things as thick as these boards (typically 1.6mm).
Unfortunately my hole punch leaves the bottom of my pads a bit uneven, so I have to sand them flat for them to adhere down well.
Compared to copper tape
More effort and less flexibility. I still use this occasionally for certain parts, but generally I find that copper tape is superior.
If you need to construct on top of a ground plane: copper tape can still do this, provided you lay down some normal (insulating) tape across the entire board first. Cut small squares out of this to expose ground where it's needed.
At first I used superglue, but I don't recommend it. When you heat the pads to solder them: the superglue melts and evaporates. This:
- Leaves your pads completely un-glued.
- Provides a healthy source of inhalable cyanoacrylate (not part of normal dietary requirements)
Of all adhesives hot glue works really well. Yes I am being serious. It melts very easily, but once the pad cools back down it re-hardens and sticks the pad down. It doesn't disappear like superglue does, it's probably not anywhere as toxic to inhale the volatile products of and it's very useful to be able to intentionally reposition pads once you have put them down.
Go build something!