Why make a PCB?
A very good reason to build a PCB is when a circuit has sensitive analog nodes or contains RF. On a printed circuit board, capacitance between traces can be made very low. Also, impedance to ground, which is crucial for high-speed analog and RF circuitry can be made very low.
For microwave circuitry that uses transmission line components, PCBs are a must. Well, we could use waveguide construction, but usually that's pretty bulky.Designing PCBs
If you're designing a circuit from scratch, computer programs that do schematic and PC board editing are very useful.
A computer can be used even if your circuit board layout comes from a magazine. By using a cheap flatbed scanner (mine was $39 from Office Max), you can get the circuit board layout into your computer. Then, you can use tools like Paintbrush, PhotoShop, or PaintShop Pro to edit the layout, adding your own logos or customizing the circuit to your likes.
To create a circuit board, you must do one of three things:
Where I work, we have something called a T-Tech mill that takes a file containing where traces are to go, and cuts (isolates) them from the surrounding copper. Optionally, the excess copper can be milled away (critical for microwave stuff). But, these machines are expensive to acquire (>$20,000) and run (mills are $220 per box, 5 in a box). They are mostly for engineering labs. But, if you are lucky to have the use of one...
That leaves etching. What we do there is put the traces we want on the board in the form of resist, a gummy chemical coating that makes the copper non-reactive. Then, we dunk the board in a solution that reacts with bare copper (it can be acidic or basic), until all the unwanted copper is removed. This is how 99% of commercial circuit board are produced.
Getting a pattern on the board
From least to most desirable:
NOTE: BEFORE PUTTING DOWN ANY RESIST, CLEAN THE BOARD WITH AN ABRASIVE CLEANER LIKE AJAX OR PUMICE, SOAP AND WATER! Finger oils are acidic, and will discolor the board and keep resist/tinplate from sticking. Try not to touch the copper after the board's cleaned and dried.
Masking tape, drafting patterns, and resist pens are all manual methods, prone to misalignment and fraught with error. Also, board made like this are usually one-of-a-kind and not reproducable. One advantage to using premade rub-on patterns such as those available from Datak is that the spacing of the IC pins will be correct.
Photographic methods used to be more popular before toner transfer came along. Used to be, you exposed a sensitized board to a negative of your pattern in the darkroom, then processed the board like a photograph. Nasty chemicals, horrible odors, and errors in alignment characterized this process.
Recently, positive-image pre-sensitized circuit boards are now available that can be exposed in direct contact to your pattern printed as a transparency (traces black, unwanted copper as clear). Only one step is required to develop them, and only a simple #2 photoflood bulb is needed for exposure. I have used these, with good results.
Toner transfer sheets (like from Techniks ) are available that print useable resist right from your laser printer. (And, if you don't have a laser printer at home, usually a school or office supply store can print your layouts for you. I have used Kinko's a number of times to do this.) The only catch here is that you have to print the pattern as a mirror image. Most printers and layout software can do this.
One you have printed your mirrored pattern onto the toner transfer sheet, you carefully iron the pattern onto the board, ink side down. Use a household iron on the lowest setting, with a sheet of printer paper in between the iron and toner transfer paper. Let the toner transfer cool (I've dunked the whole thing in water to "anneal" the plastic) before you carefully, SLOWLY peel it off, leaving your resist behind.Getting rid of excess copper
In etching, the most important thing is to have HOT, CLEAN etchant. I dump etchant that's been used more than twice (down the sink is okay, so long as you rinse it with plenty of water). You want the etchant hot to the touch, like scorching hot bath water. Around 110-120 degrees is great. The hotter it is, the faster it etches, and the quicker you get that acid away from your precious traces! The slower it etches, the more undercutting you have, running the risk of obliterating narrow traces. I've seen it happen.
Use a Pyrex or plastic tray to etch in. DON'T USE ANYTHING METAL, EVEN IF IT'S COATED! A microscopic crack in a ceramic-coated metal vessel could allow the etchant to eat right through the wall. Cover the board in about 1/2" deep of etchant.
While it's etching, gently slosh it around, bringing fresh etchant into contact with the bare copper. Or, use a little motor with a magnet mounted on it, and a magnetic stirrer from a lab store. I used to do that when I was etching a lot.
Also, use work clothes, tongs, gloves and be careful not to get it on your skin. Ferric Chloride STAINS! I call it "Green Vulcan Blood" :-)
A 3"x4" board, with about half the copper taken off, should take around 30 minutes to etch. If it takes much longer, it's too cold or you're not sloshing it around!
Did you clean the board before you etched it? Well, clean it again! This time, rub with steel wool and Ajax (or similar) abrasive cleaner. You must get off all the resist, all the fingerprint oils, and all etchant residue. AN OILY PATCH ON THE BOARD WILL NOT TINPLATE.
Like with etchant, use a Pyrex or plastic tray for tinplate (NOT the same one as the etchant--they are NOT chemically compatible!). Follow the directions on the tinplate package. Except for one point: I like to mix the tinplate crystals with HOT water, because they all dissolve that way. Be careful--there's an exothermic chemical reaction when those crystals hit that hot water! Use goggles.
Now, sit back, enjoy a beverage, and admire that nice-looking PCB for a bit before your put the components on it.
KEY words: single sided PCB, double sided board, PCB samples, PCB FABRICATION, FPC, Flex-rigid board, rigid flex PCB, HDI circuit board, blind via board, buried via PCB, aluminum board, HG-150 FR4, rogers PCB, laminate, PCB manufacturering, SOP PCB, power pcb, computer pcb, pcb mass production, pcb news, complex board, printed circuit board, pcb design, pcb forum discussion. CAM350, Altium Designer, Cadence Or CAD, PADS 2009, PowerPCB,DXP, Cadence,Altium Designer, protel, PCBA assembly, components assembly, though hole assembly, SMD, SMT assembly.