John Davis contributed: > >This is real cookery! As an alternative to etching face down in a flat >dish, it is simple to use a vertical tank as supplied for etching PC boards. >These are tall and very thin - about 1.5 cm wide, and big enough to take the >plate that is being etched.
>Easy to make with two sheets of perspex spaced >apart and sealed with silicone. Agitation is provided by a steady stream of >air supplied to a perforated tube in the bottom of the tank by an aquarium >pump. A heater, again of the sort to stop your tropical fish freezing, gets >the ferric chloride to a usable 40C. > >The key is to get a good quality photoresist that doesn't fail - the aerosol >type has a very limited shelf-life, I've found. > I'm ever ready to yield to the voice of experience as my own is limited to several hundred printed circuits and a few dozen deep etched sundials over the years. For the benefit of the List members who might consider trying the process, I have a few observations which beg a number of questions, There is a world of difference between cloisonne-depth etching - typically 0.3 - 0.5mm - and printed circuit making where something like .05mm has to be etched away and the process stops on reaching the substrate. The metallic layer is so thin that 'undercutting' is hardly a consideration and etch time is in minutes rather than hours. I'm sure John is quite right in championing the efficiency of the 'on edge' type of bubble etch tank for printed circuits with a stream of bubbles to provide not just mechanical agitation but aeration which speeds the process. Commercial processes go further (or did) in directing jets of hot ferric chloride carrying entrapped air against vertical circuit boards. They probably cut them out with lasers these days for all I know! In any event, the process is quick and the etching is shallow. I've not tried deep etching 'one edge' so I can't quote from experience but I suspect that there might be problems with undercutting on the upper edge of horizontal features unless the plate is turned regularly. When etching is prolonged and agitation vigorous there is a real chance of the resist breaking down and peeling away. Surface preparation is important here. The grade of abrasive must be coarse enough to provide a 'key' for the coating to grip but not so coarse as to make finishing problems. Mirror finished metal is a disaster! As the resist is removed by an alkaline 'developer' - very similar, if not identical to, dishwashing machine powder (MUCH cheaper!) - I employ an acidic pre-coating wash by using ordinary kitchen vinegar as the 'lubricant' for my 'wet & dry' abrasive paper followed by a thorough wash in warm water and drying with clean paper towel to remove any possibility of alkaline contamination. Then there is the consideration of volume of etching fluid. With 'on edge' tank you must fill it each time if you want to use fresh etchant for consistent results and that will increase your costs. Horizontal dish etching requires just enough to immerse the lower face of the plate. I have my dish rocking machine set to give a shallow tilt to the dish every six seconds. Plastic 'cat litter' trays cost buttons and are ideal for this. The shallow tilt gently changes the solution in contact with the metal carrying away slurry but not attacking the delicate resist by any mechanical action - quite the reverse of printed circuit making. As a result undercutting is kept to a minimum until full depth has been achieved. JPEG of a closeup of a sample of deep etching in due course. I remain to be convinced but even then I'll probably stick with what works for me out of laziness if nothing else.. The dinosaur saddles I make are the finest available and I only charge one handful of tyrranosaur teeth for them. :-) Best Wishes Tony (Flintstone) Moss P.S. This must be deadly boring for 'mainstream' sundiallers so I think it's time to hibernate for a while.
