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After you clean the board, follow these steps to prepare and drill it:
1. Remove the resist with lacquer thinner or thoroughly scrub the board with a non-metallic scouring pad and cleaner.
We regularly use Ajax® cleanser and green Scotchbrite™ scouring pads. When you’ve completely removed the resist, the copper should be bright and shiny, with no evidence of undercutting.
2. If you find that the board was over-etched and it’s missing some of the traces, you can repair the board by soldering short lengths of wire to bridge the gaps or by applying copper tape to the missing portions.
You can find a variety of copper tape and pads to make or repair PCBs. Check out the Appendix for a list of several online sites that carry printed circuit board-making products. The copper pieces have adhesive backing that you use to fix them to the board.
3. Drill the board using a small 0.040” or 0.070” drill; we recommend the smaller drill for IC sockets and small resistors and capacitors.
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Use a small drill press to drill the holes in your PCB.
We also recommend a small drill press, like the one you see in Figure 12-7, or a drilling stand. For best results, keep most of the bit tucked inside the drill motor chuck. With only X to X inch protruding from the chuck, you have less chance of breaking or bending the bit. If you’re in doubt about how to use your drill or drill press, check the instructions that came with it!
4. Position the drill exactly within the hole on each pad. If a component pad doesn’t have a hole, drill in the approximate center of the pad.
Most components don’t require precision drilling, but with some — most notably, ICs — you must drill the hole within about 35o of an inch of the proper spot. If the drill bit dances around the copper foil before it digs in, use a center punch to make a small dimple in the board. The dimple helps you aim the bit at the exact spot that you want for the hole.
5. After drilling, inspect the copper for burrs and remove them with an emery board or fine steel wool.
6. Examine the back of the board for chips and cracks; remove broken pieces of epoxy and file away the rough spots.
Drill from the foil (copper) side of the board to the back. You can prevent splitting and chipping the back of the board by placing a sheet of scrap wood underneath it, but don’t use particle board because it quickly dulls the drill bit.
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272 Part V: A Plethora of Projects
One more cleaning duty: Thoroughly wash the board to remove pieces of copper, epoxy, wood, steel wool, and other contaminants. Use a non-metal scouring pad (such as 3M Scotchbrite™) and cleanser to thoroughly clean the copper foil.
You’re now ready to solder the components to your custom-made printed circuit board. (You can get into the soldering groove by checking out Chapter 8.)
If you don’t plan to use the board for a while, place it in a plastic baggie and store it in a safe place where it can’t get dirty.
PCBs R Us: Using a PCB Service
What if you don’t want to get your hands dirty making a PCB with the methods that we describe in the earlier sections of this chapter, but you still want to permanently mount that circuit? Just have a company that makes PCBs for a living make one or two (or a hundred) for you.
Now you're a board designer
To get a PCB board made by a PCB manufacturer, you first need to generate the PCB layout. You can generate the layout with Computer Aided Design (or CAD) software (which we discuss in more detail in the section “Using CAD to Make Artwork,” later in this chapter). Using CAD software, you generate data files (called Gerber files), which you then send to the PCB manufacturer. The manufacturer uses these files to give you a quote, and if you’re okay with the price, they go ahead and make the board for you.
PCB design is full of rules, just like so many other things in life. Before you generate Gerber files, check out the manufacturer’s design rules. Design rules insure that the PCB you want doesn’t require features that the manufacturer’s equipment and processes can’t handle. The manufacturer checks your files to see that they meet the design rules (this once-over is called a design rule check, or DRC). Most manufacturers probably won’t do the job until you correct any design rule errors.
Common design rules require that you maintain a certain minimum
^ Trace width ^ Space between traces
^ Space between a trace and the outside of a board ^ Pad size
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The list above doesn’t cover everything, so be sure to check the manufacturer’s Web site for their complete design rules.
A word to the wise: Some PCB vendors offer the option of getting boards at a lower price by skipping the silk screen and solder mask steps. Silk screening puts ink letters and numbers on the board for specific purposes, such as marking the hole into which you should solder resistor R3. Solder mask is a green film that protects the traces on the board if you get a little sloppy and spill solder where you shouldn’t. Generally, we recommend getting your board made with silk screening and the solder mask: These features are worth the few extra dollars that you spend because they help you keep track of components and protect your board.