PC Board Etching Tank

This homemade circuit board etching tank is made from HDPE and acrylic sheet, and allows fabrication of circuit boards up to 10 x 9 inches. The parts were picked up at Walmart and Home Depot.

This is not my first vertical tank. It was designed after the large etching tank elsewhere on the site. There was one thing I hadn't considered. Well, one that comes to mind. The problem is in the size. Not that it can hold 2-1/2 gallons, but that 2-1/2 gallons doesn't fit in one container when it is put away. It becomes a real task to empty the thing, so it doesn't really lend itself to the "I think I'll do a printed circuit board today" mindset. It needs to be easier.

The solution to that particular problem is to find a 2-1/2 gallon container to store the etchant in, and I will do that, but a possibly more practical solution is to build a tank that holds less than one gallon of etchant, but can etch the same sized printed circuit board. This page is about that solution.

The small printed circuit board etching tank
It can hold a 10 inch by 9 inch circuit board

The printed circuit board capacity for this tank is about 10" x 9" maximum. It has built in aeration, with a valve to adjust the air flow. There is another valve for filling and draining the etchant.

  • 2 ea. Sheet acrylic, 11" x 14" x 0.92", although about any thickness will work.
  • 1 ea. Sheet HDPE 1" x 11" x 3/8" (bottom).
  • 2 ea. Sheet HDPE 1" x 13.75" x 3/8" (sides).
  • 1 ea. Sheet HDPE 0.875" x 10.25" x 3/8" (lid-bottom).
  • 1 ea. Sheet HDPE 1.25" x 11" x 3/8" (lid-top).
  • One tube of silicone sealer. Clear or white (no latex!)
  • 22 ea. #6 x 1/2 in. Stainless-Steel Pan-Head Phillips Sheet Metal Screws.
  • 2 part epoxy to coat the screw heads for protection.
  • 2 ea plastic valves.
  • 11" 1/4" pvc pipe.
  • 10-5/8" 1/4" pvc pipe.
  • 1 ea. 1/4" PVC 90° Elbow.
  • 1 ea. 1/4" PVC Tee.
  • 2 ea. 1/4" PVC Caps.
Hole placement on the bottom ends of the sides.

Preparation

The cutting board needs to be sawn to make the pieces. Rip one edge clean, then rip five 1" wide strips lengthwise from the cutting board. Rip one piece 1.25" wide. Rip one piece 0.875" wide. Cut to the lengths listed above. The HDPE pieces need to have a simple joint cut on them, since there won't be room for screws. The joint prevents the HDPE from moving sideways. The acrylic keeps the HDPE from moving forward or backward, and the screws keep it from moving up and down. The following drawings assume you have a 1/8" blade in your table saw or router table.

Saw the groove in the bottom piece of HDPE

The inside of the HDPE bottom piece is facing down in this drawing. Do this to both ends of the bottom piece.

Saw the tongue in the side pieces of HDPE

The outside of the HDPE side piece is facing down in this drawing. Do this to only one end of each side piece.

Drill the two 9/16" holes for the aerator pipe 1" from each end of the left side.

Drill a 7/64" hole for the aerator pipe cap 1" from the bottom end of the right side piece.

HDPE and acrylic pieces laid out

Drill the holes in the acrylic using a drill bit made for acrylic. A metal or wood bit will only crack and split the acrylic. I used a 1/8" bit. The holes must be oversized because acrylic has a high coefficient of thermal expansion. It is going to move around as the temperature changes, but silicone sealer acts as a flexible gasket to allow for expansion.

Assembly Summary

Follow these steps to assemble the HDPE tank parts you prepared above:

  • Apply a 1/8" bead of silicone sealer to the bottom edge of one side piece.
  • Join the side to the bottom.
  • Repeat for the other side piece.
  • You should now have a U-shaped HDPE assembly on your bench.

Follow these steps to add one of the acrylic sides to the HDPE parts:

  • Lay a pre-drilled acrylic side panel on the HDPE assembly and mark the holes.
  • Put a piece of tape on the HDPE side pieces to mark the top of the acrylic.
  • Remove the acrylic panel and drill the holes all the way through the HDPE using a 7/64" drill bit.
  • Run a 1/8" bead of silicone over the edge of the HDPE, starting and stopping at the tape.
  • Carefully set the acrylic on the HDPE assembly.
  • Screw it on, stopping just when the bead of silicone squeezes out of both sides of the joint.
  • Wipe or scrape the squeeze-out from the outside edge. Leave the squeze-out on the inside edge.
  • Leave it to cure for an hour or more.

Layout of the aerator assemly

Cut and dry fit the aerator piping as shown in the drawing below. The aerator pipe on the bottom of the tank must have holes drilled for air to escape. Either draw a line down the length of it, or chuck it in a vise, but either way, use a drill press to drill 1/32" holes every 1/2" down the center line of the pipe, starting 1" from one end, and ending 1" from the other end. Do not drill through both sides of the pipe, except the hole closest to one end. Drill it all of the way through, then enlarge it with a 1/8" drill. This is to allow you to adjust the position using a 1/8" drill bit to get the holes at the exact bottom of the aerator pipe when it is assembled.

Glue the horizontal connections together first

To begin, glue the short pipe to the tee and the aerator pipe to the elbow as shown below. The 1/8" hole goes nearest the elbow. Be sure to get the holes in the aerator at the bottom. You can use the 11" pipe in the other outlet of the elbow, and a 1/8" drill bit to help align it. Fill the 1/8" holes with silicone when you are done.

Then glue the vertical connections

Next, glue the 11" riser pipe into the tee and the elbow, making sure that when you finish, the distance between the pipes is the same as the distance between holes on the side panel (12").

Apply silicone sealer to the cap that holds the aerator pipe

Put a ring of silicone around the screw hole in the right side. Put the drilled cap on and drive a screw in. Stop just before all of the silicone squeezes out. Add some silicone in the screw hole on the outside, and wipe off the excess.

Seal the screw in the cap, too

Cover the screw in the cap with silicone. Don't fill the cap - we still have a pipe to insert. Also, don't wait for the silicone to cure.

Seal around the places where pipes penetrate the HDPE

Insert the aerator assembly into the side panel, stopping 1/2" from seating it. Put a ring of silicone where shown in red below. Put some PVC glue on the end of the aerator pipe. Insert the aerator pipe into the cap and push until the elbow is against the left side panel.Add PVC glue to the remaining cap and push it onto the top short pipe. Push it up against the side so the side is pinned between the tee and the cap.

Put a fillet of silicone around the aerator pipe where it meets the left side, and around the cap at the top, as shown in blue.

Finish with these steps:

  • Apply a uniform 1/8" bead of silicone sealer to the HDPE. Stop at the tape.
  • Leave it to cure for 15 minutes.
  • Strip the protective cover off of both sides of the acrylic panel.
  • Carefully place the acrylic side panel back on the HDPE assembly, lining up the screw holes.
  • Drive the #6 x 1/2" screws through the acrylic into the HDPE, but stop when the silicone oozes out - do not sqeeze it all out..
  • Scrape excess silicone sealer flush with the outside edge, but leave any squeeze-out on the inside.
  • Leave the assembly to cure 24 hours.

Testing

Test it on water with Koolaid or food coloring in it. Look at all of the seams to verify there are no leaks. This is a good reason to use clear silicone sealer. If there are no leaks, rinse it out and coat the screw heads with epoxy to keep them from being eaten by the fumes from the etchant. If there are leaks, rinse out the tank and tighten all of the screws on the leaky side one quarter turn and test it again.

Use

The tank should be rinsed out before and after each use, and stored in a bag or box to keep dust and other contaiminates from settling inside. Set the tank on a level surface, pour in one gallon of etchant. Using insulated wire long enough to reach from the edge of the acrylic sides to the top of the printed circuit board when it is in place in the etchant, and back to the plastic pipe. Drill two holes in the printed circuit board, one in each upper corner, and run the wire through each of them. The lid is put on to keep the wires in place.