If the prototype can tolerate these limitations, the design can be accelerated and completed in a matter of days and the feeling of having something that looks so professional made at home is highly satisfactory!<\/p>\n
I have made many prototyping using home made PCBs and was always frustrated by doing the process manually using very cumbersome techniques to heat and stir the etchant. For this reason I have designed and built an etching station that makes the process very fast and automatic! You can read about the full fabrication process in another post in the blog<\/a>, in this post I will concentrate on the etching station design.<\/p>\n In this section I will describe in detail every part of the etching station, in the hope that it will inspire others to pursue making one of their own, taking my design as a whole or just a part of it. I will begin with describing the chemistry, and continue with the mechanical design. The source files for the mechanical design, electrical design and code can all be downloaded here<\/a>.<\/p>\n Note, that the 3D printed parts are all made of PETG. The plastic has shown good resilience to the etchant, though, if you own Polypropylene filament, it may be a better choice for this application.<\/p>\n The etchant I use is copper-chloride (Cu2Cl), it produces very little waste and can be renewed by solely adding Hydrochloric (HCl) acid to the solution. You can read more on the subject on this website<\/a>.<\/p>\n The reaction of the etchant is the following: At some point white\u00a0CuCl crystals should appear in the solution and will not disappear even when the solution is added with oxygen. This is an indication that the solution HCl. This occurs as\u00a0chlorine (Cl2<\/sub>) evaporates from the solution and as regenerating the solution after each etching consumes more of the acid.<\/p>\n To create the copper-chloride etchant I used 30% HCl mixed with 3% hydrogen peroxide (H2O2) and copper wire.\u00a0 When the solution became dark green, I removed the leftover copper filtered out solid contaminant.<\/p>\n Keep in mind that the solution fumes out chlorine gas (it’s toxic!), especially when it is heated. Moreover, chlorine gas is heavier than air, and may stay below the window level if the room is not ventilated with wind or a fan.<\/p>\n The etching station is made of the following components:<\/p>\n The bath itself is an airtight food container, it has a glass bottom and a plastic top. The glass is ideal for its high resistance to chemicals and heat, and the plastic cover is ideal for easy drilling to add feed-throughs for the different components of the etching bath.<\/p>\n The heating element is a PCB with traces zigzagging across the plate. It is has a resistance of 7\u03a9, designed to deliver 50W at 19V of a laptop power adapter. The heating element is coupled to the glass bottom via thermal paste, and is glued with RTV around its perimiter. Similar heating elements can easily be sourced in online stores, they are very popular in desktop 3D printers, the resistance may vary from board to board, but the power delivery can be adjusted using an additional step up\/down module.<\/p>\n The temperature sensor is a ds18b20 soldered to a band of three wires. It is protected from the etching solution with a silicon tube (aquarium airline tube) which was sealed with RTV glue on one end . The control loop is operated by a micro-controller (uC) that turns on and off according to aset-point defined by the user.<\/p>\n The stirrer is a PTFE (Teflon) coated magnet, magnetically couple to a motor mounted Neodymium magnet (with the help of a 3D printed mount) below the bath. The motor is a DC type and is speed controlled via PWM, as speed should be adjusted so the motor does not move too fast that the stirring magnet fails to follow.<\/p>\n To revert the solution to it’s oxidative state the etchant is pumped with air in the form of small bubbles generated by the air stone. The air stone is pressured by a small diaphragm pump, and PWM controlled by the uC. It may be worth noting that once in a while the air-stone becomes clogged (I’m unsure why), but it can be undone simply by soaking it in hydrogen peroxide (or laundry bleach).<\/p>\n As we boost the etching rate using temperatures of ~50\u00b0C the evaporation rate of chlorine gas\u00a0increases greatly. To remove the fumes, a pump sucks the air inside the enclosed bath, and evacuates it out of the room. The pump I use is a Venturi pump I designed and reported on in another blog post<\/a> I published. The Venturi pump is powered by the air flow generated by a diaphragm pump and the air from inside the bath is sucked out and continues out through the remaining port of the pump.<\/p>\n As the fumes are sucked out, fresh air enters through a venting port (via the small holes). When the bath is non-operational, the venting port should be shut by screwing in the cap.<\/p>\n In case your are wondering, the diaphragm pump is cooled by a small fan as it heats up quite a lot. cooling it will surely increase its service.<\/p>\n The device is operated using an ATMEGA328au \u03bcC. It measures the temperature inside the etching solution and controls the stirrer motor, heater and pumps using power MOSFET. The device is controlled via a simple user interface implemented with a small TFT screen (128 x 64) and a rotary encoder (EC11).<\/p>\n Two step down converters are installed to produce 5V and 12V rails. The first is used to power the \u03bcC and stirrer motor, the second operates the pumps and cooling fans. The two step down converters are powered by a 18\/19V generic laptop power adapter (>60 watt). The heating bed is powered directly by the power adapter, though it could be nice to make a third rail in the future to adjust the voltage for different heating elements with different resistances.<\/p>\n The enclosure of the control board is cooled by a fan together with venting holes on the other side, forcing air to flow through.<\/p>\n The device can be programmed with a USB-to-Serial using the four male headers (GND,RST,RX,TX). Also, the device has a serial port for communication over Bluetooth, but no interface has been implemented up until now.<\/p>\n The software inside the \u03bcC is quite simple, it applies a bang-bang temperature control over the etching solution, a count-down timer for setting the etching time, and a UI for the user to interact with the configurations.<\/p>\n The device has 4 different operations modes:<\/p>\nEtching station<\/h1>\n
![\"\"](\"http:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/etching-station.png\")
<\/p>\nChemistry<\/h2>\n
\nCuCl2 {aq}<\/sub> + Cu {s}<\/sub> \u2192\u00a0 2CuCl {aq}
\n<\/sub>As copper is being etched into the solution, the CuCl2 concentration lowers and the CuCl concentration is rises, slowing down the reaction, and eventually stops it completely. Luckily, the etchant can be regenerated by adding oxygen to the solution:
\n2HCl {aq}<\/sub> + 2CuCl {aq}<\/sub> + O {aq}<\/sub> \u2192\u00a0 2CuCl2<\/sub> {aq}<\/sub>\u00a0 + H2<\/sub>O{aq}<\/sub>
\nThis can be done by either adding hydrogen per-oxide, or, by bubbling air into the solution.<\/p>\nMechanical Design<\/h2>\n
\n
Bath<\/h3>\n
<\/p>\n
Temperature control<\/h3>\n
\n
![\"\"](\"https:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/heating-overview.jpg\" "\\"heating")
<\/li>\n ![\"\"](\"https:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/heater-plate-exploded-e1561766627160.jpg\" "\\"heater")
<\/li>\n ![\"\"](\"https:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/Untitled.jpg\" "\\"Untitled\\"")
<\/li>\n <\/ul>\n <\/div>\n \n <\/div>\n<\/div>\nStirrer<\/h3>\n
![\"\"](\"http:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/stirrer.png\")
<\/p>\nEtchant oxidation<\/h3>\n
![\"\"](\"http:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/oxidation.png\")
<\/p>\nExhaust<\/h3>\n
![\"\"](\"http:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/exhaust-2.png\")
<\/p>\nElectrical design<\/h2>\n
\n
![\"\"](\"https:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/enclosure-1-e1560715409438.jpg\" "\\"enclosure")
<\/li>\n ![\"\"](\"https:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/controller-e1560715384119.jpg\" "\\"controller\\"")
<\/li>\n ![\"\"](\"https:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/supply-e1560715366198.jpg\" "\\"supply\\"")
<\/li>\n ![\"\"](\"https:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/shcematic.png\" "\\"shcematic\\"")
<\/li>\n ![\"\"](\"https:\/\/fenneclabs.net\/wordpress\/wp-content\/uploads\/2019\/06\/board.png\" "\\"board\\"")
<\/li>\n <\/ul>\n <\/div>\n \n <\/div>\n<\/div>\nOperation<\/h2>\n
Operation modes<\/h3>\n
\n