Testing The Efficiency Of PCB Etchants

etchIn the interest of the scientific method [Feynmaniac] (great name, btw) over on Instructables has posted a little experiment on something we all, no doubt, care about: putting PCB traces in copper clad boards with the most common etchants out there.

The experiment used the ‘ol standard, ferric chloride, and the safe, inexpensive newcomer, vinegar, hydrogen peroxide, and table salt. Finding the most efficient mixture of ferric chloride is easy: just use what’s in the bottle. The vinegar and H2O2 requires some stoichiometry, though, and [Feynmaniac] calculated that with an 8% acetic acid solution and the most commonly available 3% peroxide solution, a 2:3 ratio of peroxide to vinegar is the best. Salt to taste, or until everything turns green.

Four copper clad boards were used for the test, masked off in a ‘barcode’ pattern. Two methods of applying the etchant were used: either rubbing the etchant on with a sponge, or immersing the boards in a bath of the etchant being tested.

In terms of speed, ferric chloride was by far the fastest, with 3 minutes until the board was etched using the rubbing method, or 10 minutes when simply immersed. Vinegar/peroxide took longer with 11 minutes rubbed, and 20 minutes immersed. No differences in the quality of the etch were noticed.

While ferric chloride was by far the fastest etchant, it does have the downside of being environmentally unfriendly and fairly expensive. The vinegar and peroxide etchant is safe, cheap, and can be found in any grocery store on the planet.

This experiment didn’t test other common etchants like HCl and H202, or cupric chloride (which is is the byproduct of HCl and H202). Still, it’s a good confirmation that the vinegar and peroxide method actually works, in case you were wondering.

PCB agitator from a broken CD-ROM drive

pcb-agitator

Etching PCBs goes a lot better if you agitate the solution in order to carry away the dissolved copper and get fresh etchant to the area. With that in mind [Rohit Gupta] designed a mechanism in Sketch Up before realizing he was going about it the hard way. He ended up basing his agitator on a broken CD-ROM drive instead of starting from scratch.

He uses the CD sled from the drive, ditching the lens and its support structure. To get direct access to the motor that drives the tray he uses an L293D H-bridge chip. This is controlled by an MSP430G2231 microcontroller. The driver board seen in the upper right includes a voltage regulator, three status LEDs, and one user input switch. Once triggered, the sled will move back and forth, contacting an old mouse microswitch which acts as the limiting switch. We find it entertaining that [Rohit] prototyped the circuit on a breadboard, then used that success to etch the final circuit board (shown in the video below).

If you’ve been following the hacker creed and never getting rid of any junk you’ll have no problem finding a donor drive to make one of your own. But just in case you can’t get a hold of this hardware a similar agitator can be built using a hobby servo.

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Comprehensive home PCB fabrication tutorial

home-pcb-fabrication

From what we’ve seen we’d say [Jianyi Liu] is really good at etching PCBs at home. Now you can learn from his experience. He just published a mammoth guide to fabricating your own PCBs at home. That link goes to his index page which leads to all eight parts of the guide.

He starts off by mentioning that fab house boards are rather inexpensive these days. This will save you a lot of trouble (like acquiring the equipment and raw materials needed to get up and running) but you can’t beat the turnaround time of doing it yourself.

After discussing the particulars about trace width, copper thickness, and a few design considerations he lays out his board and prints the artwork to a sheet of transparency film. A pre-sensitized board is cut to size before a trip through an exposure rig with the film taped onto it. The image above shows him rinsing the board after applying the developer chemical. From here he uses cupric chloride he mixed himself to etch the board. [Jianyi] recommends populating the components before cutting the panel apart — a task which he accomplishes with a hack saw.

“Machining” copper parts using Cupric Chloride

[Ben Ardwin] was asked by a friend to help fix an old motor. It needed a new set of brushes. They’re just thin pieces of copper that mount on the motor housing and contact the commutator. The metal is so thin he thought he’d try fabricating replacements by dissolving copper stock.

This is not copper clad board; the raw material used in PCBs that has a copper-covered fiberglass substrate. It’s just thin sheets of copper stock. [Ben] started by covering top and bottom with painter’s tape. This will act as a resist for the chemical etchant. He headed over to the laser cutter to remove the tape mask around the outline of the parts. From there it’s into the Cupric Chloride for about two hours.

The etched parts are a bit rough around the edges so he cleaned them up by hand using a file. When writing to us about the process he suggests a few improvements. The tape used for masking wasn’t ideal and he would try a different method. He would also remove less area around the parts to help speed up the process.

This technique is a really becoming popular as a home-fabrication tool. Recently we’ve seen etched copper used to make a faceplate for an enclosure, and a translucent template for a clock.

Etching PCBs with vinegar

When we hear about etching PCBs at home we assume that either Ferric Chloride or Cupric Chloride were used to eat away unmasked copper from the boards. But [Quinn Dunki] just wrote up her PCB etching guide and she doesn’t use either of those. Instead, she combines vinegar, hydrogen peroxide, and salt. It’s easier to find vinegar than muriatic acid (Cupric Chloride is made using this, peroxide, and adding the copper) so this is something to keep in mind if you’re in a pinch (or a Macgyver situation).

The rest of the process is what we’re used to. She’s using photoresistant boards which can be masked with a sheet of transparency instead of using the toner-transfer method. Once they take a bath in the developer solution she puts them in a shallow dish of vinegar and hydrogen peroxide along with a teaspoon of salt. She wipes the surface with a foam brush every minute or so, and inspects them every ten minutes to see if they’re done.

She does discuss disposal. Seems that she throws the solution in the garbage after each use. The liquid will contain copper salts which are bad for wildlife. We’ve heard that you should neutralize the acid and make a block of concrete using the liquid, then throw it in the garbage. Does anyone have a well-researched, ethical, and environmentally friendly way of getting rid of this stuff?

Create PCBs in just minutes with this awesome spray etching machine

pcb-sprayer

If you have ever produced your own PCBs at home, you know that it can be somewhat of a time consuming process. Spending 20 or so minutes manually agitating a board is a drag, and while aquarium bubbler setups improve the process, they are far from ideal. [Christian Reed] knew that if he really wanted to streamline his PCB production he had to emulate the big boys and build a PCB sprayer of his own.

His spray etcher is contained in a custom acrylic case built mostly of scraps from previous projects. It contains two compartments – one for spraying etchant on the PCBs, and another for rinsing the finished work. The system is impressive to say the least, featuring a maze of tubes and piping which allow him to etch boards and manage his chemicals with ease.

[Christian] says that although the parts list might seem daunting at first, it really is pretty easy to assemble the device. Seeing as he can etch and wash a board in about two minutes flat, we think that any amount of effort would be worth the results.

[Christian] points out that he was unable to find a guide for building this type of PCB sprayer anywhere online, so he documented the process in painstaking detail in order to make it as easy as possible to replicate his work. Be sure to check out the video below to see his etch tank in action – we’re pretty sure it will have you itching to build one this weekend.

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Ferric chloride etching chemistry

etch

[ladyada] has republished an interesting snippet from the synthDIY mailing list. [David Dixon] discusses the actual chemistry behind ferric chloride based home circuit board etching. He concludes that ferric chloride is essentially a ‘one-shot’ oxidant. It can’t be regenerated and can be difficult to dispose of properly. The use of acidified copper chloride is a much better path and becomes more effective with each use, as long as you keep it aerated and top up the acidity from time to time. This etchant solution is actually the result of initially using hydrogen peroxide as an oxidant along with muriatic acid. You can see us using this solution in our etching how-to and while creating the board for our RGB lock. For more information on using hydrogen peroxide, check out [Adam Seychell]‘s guide and this Instructable.

Aside: [ladyada] has added the receiver code to the Wattcher project page.