--- In
Homebrew_PCBs@yahoogroups.com, Philip Pemberton <ygroups@...> wrote:
>
I have used only photo-etch so hopefully I can answer some of your questions.
> I managed to find a used UV exposure unit
I have always made my own. My first and second were wooden boxes, but my last two have been somewhat different.
One of them was in an old flatbed scanner housing, one of the old deep ones. Got four tubes, starters and ballasts from Mega directly (they take phone orders with credit cards). It worked fine but was not perfect.
My most recent one is a dozen UV leds (mounted on veroboard to start with, its first board was what is now its main circuit board; talk about bootstrapping! ) driven by a spare 12V PSU (modified PC PSU, cost three quid from ebuyer.co.uk).
> - Photoresist PCBs
I get mine direct from Mega. I use the economy board (stock code 400-040-1 for SS, 400-054-1 for DS). Yes the microtrak stuff is better for fine work, but to be honest unless I am doing something with MBGAs or TQFPs on a 2mil pitch, the economy is stuff is good enough.
> - Developer chemistry
Best VFM I have found is 4007V00 Seno, again from Mega. Keeps forever in power form and last weeks when made up. Needs to be heated to about 30 deg C for best results. I make 1 litre from each plastic package, and when warm works in seconds.
> - Another developer tray or two (not hard to find)
Maplin, Farnell, gardening centre (yes really) and almost any photographic supply shop.
> - Some OHP transfers (I have some Stabilo inkjet ones, but they've been on
Now here is the bit that is my big secret; I use a different type of printer, specifically a Xerox Phaser 8400 (now the 8550). It uses four solid wax blocks (one each black, cyan, yellow and magenta) to lay down colour output, but I use it in B&W mode. I get 1200 DPI output that is so solid I have had pros ask me what photoplotter I used!
Yes the ink costs a lot, and the basic printer is not cheap (about 500 quid now, but comes with network interface and postscript as standard) but the output beats inkjet,laser and the various dye sub printers I have tried. As a bonus I get great high colour magazine quality gloss photos at the rate of 12 pages per minute!
The film I use is a cheap knock off we had at work. When OHPs went the way of the dodo they threw it all out, so I scooped it up and have been using it for the last ten years with no problems. I think it might be made by HP (the part number is an HP one) but the box in basically unmarked.
> Lastly, I'd like to know if anyone has any hints on aligning the
> transfers for double-sided work.
I have a special jig. A friend spotted an article in Elektor about ten years ago and we developed the jig from that.
Basically it is two panes of glass, each held in an MDF frame. The frame is about four inches around each side of the glass sheets. I got some toughened, non-coated glass from a local glazing firm, he cut the MDE and we glued and bolted the whole things together.
Each of the top corners, and in one place along the bottom edge has a bolt protruding from the bottom frame. On the top frame there are slots cut, and by carefully moving the top frame with respect to the bottom one film attached to the glass can be aligned very accurately. I have done stuff with tracks down to 6mil with no problem.
Is it OK to post photos here?
If so I will post up a few pictures of the frame
> (And yes, I'm planning to get a metal shear of some description to
> cut the PCBs.
A wise investment, and one I made many years ago.
Of course if you can get an old paper guillotine, one with a long blade on one side that will work just as well. I know this as the same friend who made the jigs with me found one for a quid in a second hand shop, sharpened the blade and has been using it ever since!
I hope the above helps.
Please feel free to ask for more details on anything I have might have been vague over.
Now comes my request for info.
I have a number of ideas I want to try and would like to know if others have had any success.
First I want to try the heat transfer to do silk screens. This site says they work (
http://www.pcbfx.com/) but has anybody here tried them? I do happen to have the laminator they talk about so I was thinking of investing a set of the green ones (the top of the board I use is white) as they do not do black despite the photos on the site showing black results!
Second I am interested in through hole plating. I know there are various mechanical work arounds (panel pins, favorits, etc) but I would like to try and make a real through hole plating machine.
I have some heated pressure rollers (they goto about 200 C) and have got a working control board for them. What I need to do is figure out how to melt solder and flow it over the board. My best idea is to get some of those ceramic heating elements (from hair tongs) and line a hopper with them, then use gravity to get the molten solder to flow onto the joint between the rollers, feed the board into that and catch the drip (and the board) on the other side. Has anybody tried this before?
Lastly (for now) I want to build an SMT oven. Again inspired by a design in Elektor I think one would be possible, but I intent to cheat a bit as I will be using an very different oven, one made for pizza!
It is thin and flat with massive heating elements both top and bottom. Do you think it will be better than the usual toaster oven?
Sorry for the long post, but I know I have a lot to learn, so all pointers most welcome.