If you are new to electronics or want a refresher, I suggest reading "Basics of Through-Hole Electronics" first.
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Common SMD Components and Packages
SMD components are usually much more standardized than their through-hole counterparts, and easier to identify.
ResistorsTired of having to decode colored bands on your resistor? No more need with SMD! Most SMD resistors will have the resistance written directly on them, in either a 3 or 4 digit code, as seen to the left. The code is scientific notation for the resistance. Simply put, you'd multiple the first 2 or 3 numbers (depending on if there are 3 or 4 numbers total, respectively) by 10 raised to the power of the last number.
The two resistors to the side area (10*10^1) = 100 ohms and (430*10^0) = 430 ohms.
Resistors, capacitors, LEDs, fuses, and many other passive electrical components are commonly found in a rectangular form factor, named for the width and length of the part. For example, "1206" is a common package, which means the part measures .12 inches by .06 inches. Other common sizes are 0805, 0603, 0402, and 0201.
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Light Emitting DiodesLight emitting diodes come in the same standard package size as resistors and capacitors, but just like through-hole ones, have a polarity you need to keep in mind. While the exact method used varies from manufacturer to manufacturer, some of the more common ways to identify the cathode (negative side) of an LED are an arrow on the underside, a line on the underside, or a colored dot on the top surface ( as seen to the left).
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InductorsInductors will commonly come in either black standard rectangular packages, similar to resistors but without markings, or in an "open coil winding" package, like seen to the left. The open winded parts are more tolerant to high current and temperature, not to mention less expensive, so are more commonly used. They are usually labeled on the top with the inductance, as measured in uH. The one to left reads "3R3" which is code for 3.3 uH.
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PolyfusesPolyfuses are a cool and inexpensive way to protect your circuit from over-current and short-circuits. A polyfuse is multiple layers of polymer full of tiny metal beads, commonly titanium. At room temperature, the polymer is contracted enough that the beads touch and electricity can flow through. As the amount of current through the beads increases, they begin to warm up and the polymer expands, slowly moving the beads away from each other, further increasing how fast they heat up. Eventually, the beads are too far apart and electricity can no longer flow through. Polyfuses are also referred to as "self healing" fuses, since once the electricity is removed, they will cool down and go back to conducting like normal.
Polyfuses have a standard labeling scheme that can be decoded using the part's datasheet.
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Diodes
Diodes often come in "SOD" packages, which are distinct from similarly-sized 1206 packages in that there are pronounced leads on either side of the part, rather than just metal sides to solder to.
The cathode of a diode is most commonly identified by a line or dot in the top of the plastic of the package. Many diodes will also have an identifier on the top, but these do not provide any meaningful information about the diode without the associated datasheet.
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Momentary SwitchesMomentary switches, more commonly referred to as buttons, are usually not surface-mount. Through-hole buttons hold up to use better and tend to be cheaper, but SMD buttons are commonly used in space-constrained applications, since parts can be mounted on the opposite side of the board from the button.
SMD buttons follow the same packaging identification standards as through-hole buttons, being identified by their length and width. For instance, the button to the left is a 6mm button.
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Integrated CircuitsIntegrated circuits are a way of compressing a lot of small electrical components into a single, easy-to-use package. Integrated circuits, or ICs for short, can be as simple as dozens of resistors to millions of transistors creating complex logic gates and microcontrollers.
While ICs can be found in hundreds of packages, the most common for SMD is the SOIC (small outline integrated circuit). SOICs are a plastic body with the 2 long sides covered in pins. SOICs are defined by the width of the body (most common being .15 inches) and the number of pins. Some ICs made for more compact situations may also define a non-standard pitch, or the distance between pins.
ICs have directionality to them, and it is important to mount them properly. While different manufacturers use different methods of orienting their chips, the 2 most common are to put a dot in the corner of part next to pin 1 (either engraved on like the writing or molded into the plastic), or a chamfer on the side of the IC where pin 1 is. The IC to the left exhibits both of these identifiers. You should always double-check the datasheet to make sure you have the right alignment process, as some manufacturers will use the opposite of these standards (i.e. the chamfer is on the side that is not pin 1, or the mark will be next to a different number pin).
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