Introduction: Coke Bottle Vertical Etching Tank
Not sure if vertical etching is for you? Try it out! Make a small scale, pint-sized, leak-proof etch tank in about 10 minutes, with 2 things you already have lying around: a DVD case and a 2L bottle.
Step 1: Parts List
What you'll need:
Now go buy:
an aquarium bubbler - $15.00
aquarium tubing - $3.00
a 2L bottle of soda - $2.00
Step 2: Step 1
Cut the top off your 2L bottle.
Step 3: Step 2
Stuff a standard sized DVD case into the top of the bottle.
Step 4: Step 3
Blast it with your heat gun until the bottle becomes DVD-case-shaped.
Step 5: Optional
Instead of hanging your board from a string, you might want to make a pcb holder like the one that I came up with. It's made from styrene.
Step 6: End
Using your heat gun, bend the aquarium tubing into an L shape. Weigh down with something to keep it on the bottom of the tank.
Fill it up and try it out.
The 1/2 oz test board (picture on the title page) took about 10 min to (over) etch at room temp.... and another 5 minutes to photoshop :). The part where my gimpy bubbler was directed over-etched pretty badly. Bubbling really does speed up the process quite a bit!
Step 7: So the Verdict Is In
It's been more than a few years since I wrote this Instructable, and I thought I would give an update on how things have worked out. There are some drawbacks to a vertical etch tank, but these can be overcome with some work. Here's a look at how my etching method has evolved over the years.
Step 8: Space Savings
The first issue with a vertical etch tank is space. It's supposed to save a lot of space. My current etch tank is 11" tall x 11" wide x only 1" thick. That's an 11 square inch footprint. But in reality, you need a stable base for the tank. So instead of taking up 20% of the space of a comparable tank, it ends up taking, say, 40% of the space. That's still great, right? Well, on top of that, you need WATER. When the board comes out, you need to catch the drips and rinse the board. I was using a glass baking dish for this. So now I'm up to 75-80% of the space that a regular setup would take. Clearly, in addition to a vertical etch tank, you need a vertical rinse tank, too. And if you have a good outdoor bench where you can put your tanks, you don't even need a base!
Step 9: PCB Holder
One of the other drawbacks to vertical etching is the question of how do you hold the board in the right position? With a tray + mechanical agitation, you just drop it in. In a horizontal etch tank with sufficiently fine bubblers, you can just lay the board on top of the etchant, and it will float. With a vertical tank, you need a holder of some kind. For single sided boards, you can just tape or hotglue them to a plate, and slide that into the tank. Or you can tie things up with strings. But I have come up with a pretty good PCB holder. This holds the board, firmly, and it allows easy adjustments to the board depth. The nylon hardware on it also keeps the board from tilting against the tank wall.
Step 10: Messy!
Another issue with a thin vertical tank is tank maintenance. The thin lip of the tank makes it difficult to extract the copper-rich etchant that builds up, and to pour in more acid solution. To eliminate the mess, I have finally found the right tools for the job. A turkey baster easily reaches into the tank to extract solution. And to eliminate the drips, I found I could stuff a piece of silicone aquarium tubing into the tip. The tube is melt-sealed on the inside end, and several small holes are drilled in it. And to add the acid solution, I keep a squirt bottle of acid and one of water (actually 97% water, 3% peroxide) in spray bottles. The spray bottles are convenient for adding solution directly to the tank. Also, you can spray the board, directly, if your etchant dies before a board is done. A third good reason to have these solutions in spray bottles is they're what you need to remove etchant stains! If you spill any etchant on concrete, for instance, hose it down with water. Then spray the spot with H202. Finally squirt a little acid on it, then wash away after only a couple seconds. Stain gone! (Always wear eye protection when handling strong acids. And be sure to squeeze some of the air out of the acid bottle before closing it, or some will dribble out when the ambient temp rises!)
Step 11: Etching Capacity
One of the attractions of a vertical tank is that you can use less etchant for a given board size. But less etchant means less etching capacity. My tank hold approximately 1.3L of etchant when properly filled. It will barely eek one double-sided 6"x9" board with a 2oz copper pour if I'm only doing one side (meaning the entire bottom needs to be etched away!) Afterward, it will need several hours to recharge! Vertical tanks can theoretically utilize air bubble regeneration more efficiently than horizontal tanks, because the air bubbles travel a longer distance. But you can't put as many bubblers in a vertical tank, and cupric air-regeneration is slow, regardless! To maximize aeration, I use a bubble wand run from compressed air. The bubbles are extremely fine, versus poking holes in a tube. Running it this way, when my solution is too rich it will precipitate out large amounts of white precipitate (I presume some form of copper oxides) that I have never seen before! But it works good! I haven't done any scientific testing, but it seems to me that my tank recharges in about 4-6 hours. With a regular fish tank pump, it took at least overnight. This fine and copious amount of bubbles also alleviates another con to vertical etching. Some people have a hard time getting a vertical tank to etch, evenly. The bubbles can tend to focus on certain spots on the board. By flooding the entire tank with fine bubbles, etching occurs more evenly. Word of warning, here, if you try this! Do not let your compressor run all the way down! The tank only takes a couple psi before it will froth over, and regulators need a certain amount of positive pressure differential. If your tank pressure drops too low, the regulator will leak higher pressure air.... and when you come back to check on the board, it'll look like a leprechaun got sick on your patio after a weekend of partying. BTDT, so hopefully you don't have to! So make sure your compressor is on! It doesn't take much air, though. While running my tank, my small pancake compressor only turns on once every 1-2 hours.
In the end, a small vertical etch tank fits my needs fairly well. I rarely need more production capacity, and thus, I almost never actually drain the tank. Some minor maintenance is most all that's needed, and my hands and workplace stay clean!
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