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A Homemade PCB Spray Etching Machine



This page gives a quick illustration of the spray etching machine I built for etching PCBs. This project started out from a simple idea of using a low cost pump and spray nozzles to build a spray etcher. The idea turned into very long and challenging project, which ended up taking lot more of time and money than originally anticipated. Even so, I found this a interesting hobby project which learned a lot from. Please email me i your interested in drawings or other detailed construction information.


Spray Machine Data

Pumps

Manufacture: Shurflow
Part number:  2088-422-144
Type: diaphragm.
Configuration:  two pumps in parallel.
Power consumption: 13.2V (at pump wires) at 13A

Tank

Capacity: 12 liters
Designated etching area: 310 x 205 mm
Maximum panel size:  225 x 340 mm
External dimensions:  500(W) x 370(D) x 300(H) mm
Material: rigid PVC

Nozzles

Manufacture: Spraying systems Co.
Part number: H1/4VV-KY6508
Type: 65° tapered edge flat pattern
Configuration: 4 nozzles total. 2 nozzles positioned on either side of PCB.
Nozzle pitch: 115 mm
Panel surface to nozzle tip
spacing:  88 mm
Angle offset: 4~6°

Etchant transfer

Total flow rate: 9~10 liters /minute
Pressure:  280 kPa



Images


A picture of entire spray machine during development. The wooden frame supports the spray tank and all associated hardware. There is a hinged lid on the frame to convert it into a table top when not in use. The whole machine has been designed to be stored and operated permanently outdoors.

A picture when I was in the middle of developing the control box firmware. The stepper motor drive, had taken quite some programming effort from me.
Early in construction. Here I was gluing PVC strips to the tank wall. This is a ledge to support the glass lids.

Top view of whole machine. Next to the spray tank is a 3 stage counterflow rinsing tank. This was added because of the need to quickly rinse PCBs after etching. For the alkaline ammonia copper chloride type etchant I am using, any residue etchant will dry and cause thick film of copper hydroxide that is difficult to rinse. The gray strip in the center is a cover for the PCB opening slot.

The tank top shown with the slot cover laid up side down. The PCB is inserted in the slot between the two glass lids. At one side of the PCB slot there is a stationary rubber lip, while other other side has an opposing PVC hinged door than can open and close. This shutter arrangement is located just below the two glass lids and will prevent etchant mist or spray from escaping out. This idea was based on about 4 previous design attempts I had at trying to stop spray mist while also allowing PCBs to be inserted.

The spray tank with both glass lids removed. The hinged shutter is still installed. You can see a titanium pin at each end, which is feed through into the tank side walls. A piece of 1.5mm thick rubber is glued to the shutter and makes contact under the glass lid to seal against spray mist. This piece of  rubber also acts as a spring to force the door shut. Two small leavers located at each end of the shutter are to open the door by pressing down on them with your finger.

Front view of tank. You can see the stepper motor housing and external pulleys for driving the spray arm. The front cover of the machine is resting beside the tank, with a bundle of wires poking through a hole and into the control box on the other side.

View of the sealed shaft and bushing for driving the spray arm. This is a packing type seal, where PTFE tape is wrapped around a 3 mm titanium shaft and packed down by a plunger. Two M3 screws force down the plunger and compress the PTFE tightly around the shaft forming a liquid tight corrosion resistant seal.

The spray arm assembly. This is the traveling spray arm which directs etchant onto either side of the PCB. It moves at constant velocity back and forth over the etching area. Three white polyethylene wheels are responsible for guiding the spray arm. A 8 mm diameter plastic coated steel shaft (not shown) feeds in between the three wheels with neat fit into grooves machined in each wheel. The 8 mm shaft spans the length of the tank and is fastened to the tank wall at a fixed height. The opposite side to these wheels is a free running wheel that simply runs on the tank bottom. All wheel shafts are of polished 3 mm titanium rod. The flat EPDM rubber belt is clamped down to the spray arm is for driving back and forth by two opposing pulleys fixed to the tank wall.

Nozzle close up view with flow restrictor. The two lower nozzles required a slightly reduced flow rate to match etching rate of the upper nozzles. I suspect the added etchant contributed by solution run off from the upper nozzles causes increased etching on the lower side. The upper 2 nozzles do not haveadded flow restriction.

The hall effect sensor. This sensors the mid point position of the spray arm. A magnet is embedded in the spray arm to trip this hall effect sensor external to the tank.

The control box close up view. A simple interface. The knob is rotated to desired number of spray sweeps and start button is pressed. The temperature is also continuously displayed.

Stepper motor and housing for driving the spray arm. The stepper motor is a 55mm tin can type with 7.5°/step and was salvaged from an old printer. It is mounted in a end cap of 100mm PVC sewage pipe.

Closeup view of pumps. The mounting plate has four folded down sides to prevent falling liquid from running onto the motor and electrics. 

Machine bottom front view. This shows the two pumps, the pump mounting plate, the drain valve, filter housing, and associated plumbing and wiring.

Machine bottom view of  from a side angle. Shown are the three hoses connected to the tank bottom. The left two (clear hose) go to pump inlets, the right hose (black) goes to the filter outlet.

The pressure gauge and diaphragm seal. The pressure shown is during normal etching. Pressure is sensed at the pump outlets and  prior to the the filter.



Etchant Tests


etching uniformity tests
Etching uniformity test # 1