Equipment/PCB etch station

Etch station

Important Warnings

• CLEAN UP AFTERWARDS
• Do not run any heater unless the tank is full of liquid. It should blow a thermal fuse before melting the tank, but that may involve replacing the heater. Keep unused heated tanks full of plain water or disable the heaters by unplugging the associated connector inside the cupboard door.
• Do not etch anything except copper (other metals will pollute the etchant).
• Do not drink the contents, even when there's no beer.
• Do not allow children or drunken hackers to play with the tanks.
• Check the power has been turned off after use.
• Do not dip a basket soaked in one chemical into the tank of another chemical.
• Read the instructions (pdf)
• CLEAN UP AFTERWARDS

Less important warnings

• You normally place boards to be etched in the plastic basket under a tank lid, then dip it into the tank. If the PCB is too close to the open end, it will fall out. You may have to drain the tank to retrieve it. You don't want to do this, so put the pcb well into the opening and don't tip it forwards as you remove the basket from the tank.
• Very small PCBs may fall through the holes. A possible solution is to put them in fine-mesh envelopes before putting them in the basket. Finding a suitable envelope is left as an exercise for the user (hint - look on the Mega website).

Status

Developer, FeCl3 etch and stripper tanks working. Tinning tank now contains CuCl2 etchant.

I have done a brief test with the CuCl2 etch - it seemed slower than the FeCL3 but I was only agitating it occasionally. It sped up hugely at the end when I agitated it continously - but this might have been because the last bits of copper are thin and suddenly go. If you use it, don't rely on the small bubbler to provide agitation - keep it moving the whole time (and be careful your board doesn't walk out the end of the basket when you do that). The small bubbler is really only there to re-aerate the solution after use, as it's quiet enough to leave on.

CuCl2 Etchant

The bath for Cupric Chloride etch is being prepared in the tinning tank using the slow method : leave some copper in acid, allow corrosion to occur generating some oxides, add further copper and acid as required. Water, acid, copper and hydrogen peroxide (if used) should be noted as it's easy to over-dilute if you just add stuff randomly.

The preparation so far contains 540g copper, 2900ml 38% HCl, 1750ml water. SG is 1260. This is close to completion - air has been bubbled through it and it has reached the bright green colour indicating it has converted copper to cupric chloride. The acid concentration appears to be correct and I have reconnected the heater. It may be used for etching, but there is no large air bubbler in the tank so may need to be agitated by hand (jiggle the basket containing your PCB). If the etchant is not bright green, please leave the small fishtank bubbler running. The bubbles will regenerate the etchant.

DO NOT ETCH ANYTHING EXCEPT COPPER IN THIS TANK

See File:CuCl.pdf for maintenance instructions. These are basically : Check colour. Bubble if dark. Titrate against 0.1 molar NaOH to check acid concentration (this only requires a check for precipitate, no need for acid indicator). Add HCl if necessary.

Usage configuration

• Since it's already stained there's no problem in putting ferric chloride in it if we have some available (it needs 5 litres but 3 or 4 would do).
• We can use a spare tank to start brewing the cupric chloride if we want to do that

Placement

• It would be nice to have power without using the extension lead. The existing ring main might be extended fairly easily to put sockets on the wall near the sink.
  • Again, depending on when electrical stuff is needed, I could go out and get conduit/socket/back box/etc. on Fri/Sat. -- Elliot
  • I see there's a bit of conduit near #23 back door. Needs a socket plate and probably some more 2.5mm wire to link into the ring. Could be patched up but a better plan might be to look at fixing a couple of electrical jobs and buy the bits at the best price rather than in small pieces.

Model

• Make: Mega Electronics
• Model: PB710S - PCB 7 tank production line with sink

Controls

The leftmost button on the control panel is mains power. If you see it lit up when no-one is using the tank, please turn it off (but if someone _might_ be waiting for it to warm up, please check first!). Probably a good idea to switch off at the mains as well.

Each tank and rinser then has a control section. Working from left to right, these are:

• Developer - Heat button and 'heater active' light. Set to about 28°C. Heating not normally required.
• Developer rinse - Spray button activates spray bar.
• Etch - Heat button and 'heater active' light. Set to about 48°C. Takes about 15-20 minutes to get hot.
  • Air bubbler button - only active when heating is also on.
• Etch rinse - Spray button activates spray bar.
• Photoresist stripper - Heat button and 'heater active' light. Set to about 50°C. Optional.
• Stripper rinse - Spray button activates spray bar.
• Tinning - Heat button and 'heater active' light. Set to about 50°C. Optional.

The spray bars work best if only one is on at a time (and unless you're making a lot of boards at once, you probably only need one).

Notes

The pump was replaced with a heavier duty medical unit mostly because it was cheap & available. The original was a fishtank pump and is still mounted on the front of the tank. It worked, but seemed not to have enough pressure available to overcome backpressure if the aeration tube had partly filled with etchant. Fitting it involved a few peculiarities, though.

• There is a clamp on the tube near the pump, which can be used to restrict the airflow and hence the vigor of the bubbles.
• The pump is no longer fitted to the tank, but instead rests in the cabinet
• It is still possible to remove the tank for maintenance: the cable and pipe connecting to the pump are very long but if they need to be detached the cable can be unplugged from the back of the pump and the pipe unplugged from the silicon/pvc tubing joint.
• There is now a one-way valve between the pump and the antisyphon trap to reduce the possibility of etchant flowing into the pump.
• The power connection to the pump has no earth wire connected and apparently swaps black/white colour coding. This is not just carelessness : the original black/white wiring apparently had black as neutral, white as live to the fish tank pump. The IEC lead to the new pump uses conventional euro colours : black is live. So black and white swap at the join.
• The earth pin in the cable to the pump is not connected at the pump end (it's a 2-pin connector) so there was no point connecting it at the tank end.

Instructions

The tank was previously in a school and there is a laminated sheet with usage instructions. It may not be applicable to our use but is worth looking at.

• pcb etching instructions
• Manufacturer's instructions (local copy)
• Heater and bubble bar Maintenance - also see Mike's posting on mailing list.
• Ferric Chloride
• Stain remover
• Fine etch crystals - we don't use this at present but it's been suggested.
• Photoresist stripper
• Tin plating - We have a small tub of this, possibly unusably old.
• All Mega MSDS and data sheets
• Maintaining ferric chloride etchant