Description
Surface Mount and Through Hole
Pads are either though hole, where components with leads are pushed through from the top, soldered underneath, and then the excess lead snipped off, or surface mount, where the components are soldered to the top of the pad. Figure 1-2 shows a board that contains both surface-mount and through-hole components.
Surface-mount components are often referred to as surface-mount devices (SMDs) and are replacing through-hole components in most commercial products. This is so because SMD components are smaller and cheaper than their through-hole counterparts, and the boards that use them are also easier to make. You will also see the term surface-mount technology (SMT) used.
In commercial surface-mount PCB production, and increasingly for hobbyists, boards are soldered by creating a mask that allows solder paste to be deposited on the pads, then the components are placed precisely on the pads, and then the whole board is baked in an oven that melts the solder paste, soldering the components without the difficulty of soldering each component separately.
SMD ovens are still too expensive for most hobbyists, but many people have had success modifying toaster ovens to operate at the high and precisely controlled temperatures required. Such experiments usually require the safety features of the toaster oven to be disabled and are therefore often referred to as “fire starters” for good reason. However, like so many things in life, with care, common sense, and a watchful eye, such things can be made to work safely.
The choice of surface-mount versus through-hole design is less cut and dried for the hobbyist just wanting to make one or two boards for a specific project. For a single project that is never intended to be made as a commercial product, through-hole design is much simpler to solder by hand. Through-hole component leads are nearly always at least 0.1 in. apart, whereas surface-mount chips can have pins that are just 0.5 mm apart. Although many SMDs are easy enough to solder by hand, many others are just too small.
Figure 1-3 shows a selection of electronic components in both surface-mount and through-hole “flavors.” As you can see, the SMDs are very much smaller than their through-hole equivalents. This generally means that you can get a lot more of them on the same area of a PCB.
Prototyping
Ultimately, if you want to produce something of professional quality, then PCBs are the only way to go. However, while you are prototyping a design, it is a very good idea to test out your design before you start getting PCBs manufactured. Every time you find something wrong with your design and have to get a new batch of PCBs made, you will be increasing costs, both in time and in money. It is far better to get the design as perfect as possible before you commit to a board. This is a bit like writing a book—you wouldn’t print and bind the first draft; you need to be certain that the book is how you want it before you commit to paper.
This is a book about the EAGLE PCB and building PCBs. It is not an electronics primer, so if you need to learn more about electronics in general, then take a look at the books Hacking Electronics and Practical Electronics for Inventors, both from TAB Books.
Assuming that you have a schematic diagram for what you want to build, there are a number of useful construction techniques that you can use to build your prototypes quickly and easily.