etching Alu boxes-Tom?

[Mike Burgundy]

Okay, one drawback of this forumstyle is that replies with new questions get buried and missed easily. So, in a new topic then:
I had a go at this a couple of days ago (befor the blaster worm took hold of my computer, blast!) but the resist I used wasn't strong enough. It apparently thakes a LONG time to etch a significant dent in there - even though it fizzes and gets hot all on it's own.
Any tips?
How deep can one etch the metal away?
What I'd like to have is about half a mil deep, rub some black paint in, and then polish the rest.

[troubledtom]

i use nail polish and old rat shack pcd etchant [ sp? ] its easy to keep an eye on the progress and the results you want.
                        peace,
                            - tom

[Mike Burgundy]

What depth is realistic?

[Mark Hammer]

The depth would depend on how much heat your bath container can tolerate.  The etchant reacts with aluminum a little more "enthusiastically" than it does with copper if I remember correctly, so it generates more heat.  Were not talking bubbling cauldron here, but it does get warmer than you're used to.

The other thing to consider is the relationship between horizontal and vertical etching.  Remember that the resist pattern you lay down only covers the top but the etching works in all 3 dimensions.  Once you've etched below the surface of the box, and below the level of the resist pattern, there IS no resist to prevent lateral etching eating away the sides of the furrows and making them irregular.  This is, of course, a perennial problem for folks who don't keep their boards clean or use older etchant or find air bubbles trapped under their boards - while one corner/segment of the board still has to etch away the copper surface material, over on another section of the board the etchant is happily eating away at the sides of the traces providing those disgusting corroded lines that NEVER buff up smooth and often have tiny cracks.

It doesn't really take all that much depth, though, to "hang onto" paint, so I don't think you'd need to keep the boxes in there for a dangerously long time.  The other nice thing about the negative etching is that should the box ever get grungey, you can always just buff it with steel wool or emery cloth, fill the etched areas with paint as needs be and wipe off the excess.

[mattburnside]

FP did some box etching several months back and sent me pics. Looked really good. I'll try to contact him telepathically so he can tell us how he did it.

Or maybe I'll e-mail him.