For a miniature product, I want the smallest possible product enclosure around the PCB. I figure I can get away with a 1mm thick metal sheet enclosure.
But I (probably) also need an insulator between the circuit board and the case, so nothing shorts out. What's the thinnest way I can make the inside of the metal case insulative? Paint? Powder coat? Paper?
(1 mm steel is thick!)
The isolation may not be required, since you're probably (S)ELV. Anyway, it's not going to cost you much space-wise. I wouldn't mess with paint sprays and such. Agreed, it's the thinnest, but I assume you can afford the thickness of a 0.1 mm PP (PolyPropylene, PP has very low water absorption) sheet?
Try to use only SMT parts, and mount them single-sided. PTH components will add at least 2 mm because of the pins sticking out at the other side. A single-sided PCB may be glued directly onto the PP sheet, which in turn you glue to the bottom of the enclosure. If you manage to do the wiring of the PCB single-sided as well you don't even need the PP insulation. It may be worth using a couple of 0 Ω jumpers to ease the layout.
You can save an extra couple tenths of mm by using a 0.8 mm PCB instead of the standard 1.6 mm. The thinner PCB is less stiff, but at the small size it's not a problem, and when glued against the enclosure it won't get any mechanical strain anyway.
Kapton tape as it's usually called, or generics found under "Polyimide Film Tape" is generally used for this sort of stuff - it's a good and thin insulator, but slightly expensive:
you could also just use normal (i.e. vinyl) electrical tape, which is a bit thinker, but also has the benefit of being "softer" and thus less prone to punctures/etc. which may result from a component leg or something sticking out, especially if it was "flush cut" which could result in a sharp edge
Single sided PCB, Plastic, Sheet rubber, Bubble wrap, Duct Tape, Wood veneer, a few drops of silicon.
