Saturday, November 17, 2012

Bubble etch tank complete

All the ebay ordered parts have arrived, and so I've assembled the etch tank. It all went together as planned in the last post - the only tricky detail was cutting some plastic strips to cover the hole where the semi-circular stand holder was removed from the inside of the frame.
Etch tank bubbles at 51 degrees
On the right is the aquarium air pump. This is connected to the air curtain, cut to length and sitting at the bottom of the tank. A right-angled connector for the air curtain was made from a scrap of polyethylene (aka, blue plastic chopping board) and the barb from a garden irrigation tube joiner. And a bit of hot-melt glue.

The multimeter is showing the temperature (Celsius) of the water in the tank, via the thermocouple in the tank top centre.

The water is heated by that white stick sitting vertically in the left of the tank - this is the heater - just two 30 ohm resistors in series, encased in heatshrink tubing.

The heater seems pretty effective. At 0.75A of current, I was able to raise the water temperature from 22 to 52 degrees in about 15 minutes, so it should be more than capable of maintaining the temperature of the etching solution, if it starts at the correct temperature. I'm driving the heater from an adjustable bench supply, so I'll adjust the current to find the equilibrium point is (or near enough).

Now, all I need is a project to etch...

Total cost

QuantityDescriptionCost
2"FORMAT" 6x8" photo frames$6.00
1Small tube of silicone sealant$8.50
1Aquarium air pump (incl delivery)$6.58
12 metre length of air tubing (incl delivery)$2.45
130cm air curtain (incl delivery)$1.96
230 ohm, 6 Watt wirewound resistors$3.68
1Length of heatshrink tubing-
1Length wire for heater-
Total:     $29.17

Friday, October 19, 2012

Heated Bubble Etch Tank...How Cheap?

Next up, I'm going to try and make a PCB etching tank, as cheaply as possible. The low-cost bar is set pretty low, as you can purchase a tank with heater and air pump for $72 from Kinsten, which is able to hold larger boards than mine - but that's not the point of the exercise, innit?

The basis for this will be an extruded plastic photo frame I found at the Reject Shop. Here's what it looks like:
Front - all glass except for the thin plastic edge

Back - the extruded plastic.
So the plan is to cut the short edge with the hanger off, cut webs out of the back, then silicone the front glass in from the back. Then, a second pane of glass will be siliconed onto the back. The thickness of the extrusion means there will be 11mm between the front glass and the back glass. Perfect. The internal dimensions will be 120mm x 170mm, but there will be that round hanger from the side poking out into that. I may cut and seal that off. That will complete the basic tank (some kind of "feet" will need to be siliconed on, I think). Total maximum volume will be about 230ml. I'm going to orient it "portrait" so that less etchant will be required to etch small boards - that is, you can half fill it.

Bubbles

I've ordered a small aquarium air pump, tubing and an "air-curtain" (aka, length of 10mm rubber hose with small perforations along it's length) from various Hong-Kong ebay retailers. This will be placed at the base of the tank.

Heater

Plan is to use a string of resistors encased in heatshrink tubing, placed at the bottom of the tank, above the air curtain. I haven't yet purchased these. It's suggested to keep the etchant solution at 55-60 degrees celsius, so I'll do a bit of calculation soon to see how much power is really required.

Total cost so far

QuantityDescriptionCost
2"FORMAT" 6x8" photo frames$6.00
1Small tube of silicone sealant$8.50
1Aquarium air pump (incl delivery)$6.58
12 metre length of air tubing (incl delivery)$2.45
130cm air curtain (incl delivery)$1.96
Total so far:     $25.49