PIC SMD Tutorial: Definitions
This is part one of a six-part tutorial. The six parts will cover terminology, circuit design, component selection, board layout, board manufacturing, through-hole and surface-mount soldering, and embedded programming. This tutorial is designed to teach surface-mount soldering using relatively simple components with relatively large terminals and pins.
The first part focuses entirely on terminology. Keep this open in a new tab as you work.
- Microcontroller: programmable chip that controls the rest of the hardware.
- MCU: Microcontroller unit (used interchangeably).
- Soldering iron: The very hot piece of metal, terminated in a tip, that you use to melt solder.
- Solder: Malleable, easily meltable metal. Usually a mixture of lead, tin, and/or silver. Often has flux in the middle. Melts and electromechanically connects contacts to circuit boards.
- Flux: Yellow-orange sticky liquid. While solder is molten, it removes all sorts of impurities from the solder and the surfaces, allowing the solder to easily flow and bind to contacts. Often inside solder (rosin core). Can also be applied from a tube or a bottle, usually with a marker or a syringe.
- Wick / Braid: Desoldering wick or braid is a copper ribbon used to desolder components. Uses surface tension and capillary action to suck up solder. To use, place on top of solder, then place soldering iron on top of braid; wait until solder seeps in, then remove braid.
- Pinout: Definition of where each pin is, and reference to its function.
- Lead: Metal contact coming out of the device. Same as a pin, but usually means a longer contact.
- Terminal: Metal contact surface exposed on the device. Same as a pin, but usually there's no piece of metal that sticks out, just a flat or curved exposed surface.
- Through-hole: Devices with leads that are inserted through holes in the circuit board, then soldered. Leads are often bent during soldering and snipped after soldering.
- Surface-mount: Devices with pins and terminals that are placed on flat pads on the circuit board, then soldered.
- Footprint: Specifications of how the device fits on the circuit board; this defines all of the connections, the size of the pads or holes needed to ensure solid electrical and mechanical connections, as well as the size on the board given to the component. May include more complex specifications.
- Package: The same device may be sold in different shapes; the shape is the package. A package has defined pinout, footprint, shape (widths/heights/lengths), weight, and so on.
- Signals broken out: Signals made accessible. Generally means that the signals are brought out to the edges of the board, and are easily accessible for interfacing with breadboards or wires, without any special tools.
- IC: Integrated Circuit. Any chip is an IC. ICs usually refer to large monolithic blocks with several inputs and outputs, though they may refer to simpler devices such as chip LEDs that we will be using.
- Discrete component: The opposite of an IC. If an IC that we will use might be several thousand transistors, one might theoretically recreate the entire logic using separate transistors, each with a drain/source/gate lead.
- mil: Thousandths of an inch. In mechanical engineering, mils are different. Common grids will be 100mil (0.1inch), 50mil, 25mil, etc.
- SIP: Single inline package. A set of holes in a straight line. Spacing between holes (pitch) is often 100mil.
- DIP: Dual inline package. A set of holes in two parallel lines. Pitch is often 100mil.
- PDIP: Common IC package. Plastic dual inline package. This is for common through-hole ICs. Usually a 100mil pitch, and either 300mil or 600mil width.
- SOIC: Small-outline integrated circuit. Common width is 150 or 300mil. Common pitch (distance between the midpoints of leads) is 0.65mm.
- 1206, 0805: Two-terminal components such as resistors have standard sizes in surface mount packages. 1206 is a fairly large, hand-solderable size. 0805 is also fairly straightforward. 0603 and 0402 are better for machine placement, and going smaller than that will usually cost extra to assemble automatically. There are sizes larger than 1206, of course.
After your eyes have properly glazed over, open the next part in a new tab: You're done with this section! Up next: Circuit Design!
January 10, 2014