Designer's Den - Glossary
Auto-insertion is the term used to describe the use of a computer automated machine to insert the part in the PCB. There are many different machines used to insert the different parts. These machines can cost hundreds of thousands of dollars, they are only used by assemblers who can produce enough assembled boards to justify this expense.
Board density is measured as the ratio of the area of the board used by parts to the total available area of the board. This calculation used to be done in "equivilent ICs." You took the total number of pins used by all parts on the board, divided this by 14 (the number of pins on a small DIP.) You then took this figure and divided by the available area in square inches. This was good for boards with little but ICs, but fell short for most designs. A better way is to calculate the actual area used by the parts, and divide this by the total available board area. This is more difficult, but yields more accurate results. A board with less than 50 to 60 percent of available area should be able to be done single sided, more than 75 to 80 percent may have to go to multi-layer.
A Dual Inline Package is an Integrated Circuit with two rows of pins.
Double Sideded is generally used in two ways in PCB design. The way it's used here is to note the board has signals on the top and bottom surfaces. The other way it is used is to note the board has parts on the top and the bottom of the board, which possibly may also be double sided. This shows just how confusing this industry can be sometimes.
A grid is an aid to placing components and traces. It can be considered as a matrix of lines in vertical and horizontal directions. The ECAD system will look at the location you have "picked" with your mouse and select the coordinate where the neerest lines intersect. This allows easier design, manufacturing, assembly, and test. Some ECAD systems can set patterns of grid lines for easier routing of dense designs.
Layer is the term used by many ECAD systems to identify a group of entities. It originated from the practice of drawing different parts of an assembly on separate sheets of vellum so they could be overlapped to show the complete assembly or viewed individually.
A Printed Circuit Board (PCB) is a mechanical assembly consisting of layers of fiberglass sheet laminated with etched copper patterns. It is used to mount electronic parts in a rigid manner suitable for packaging. Also known as a Printed Wiring Board (PWB).
Read The Fine Material (or something like that!).
The Silkscreen legend is text and lines representing the parts on the PCB. These are printed onto the board using the same process used to print t-shirts. The color of the ink used is usually white, although other colors are sometimes available on special order.
Soldering is the process of fastening a part lead to a PCB. It uses heat to melt a metallic compound around the lead and onto the copper pad of the board.
Most boards have a special coating, sometimes called "solder mask," added on top of the copper to keep out moisture and protect the traces. Solder mask must have clearance areas around
the pads to keep the material from touching the pad, making it difficult to solder. The material is usually green in color, although other colors may be available on special order.
A SMD or Surface Mount Device is an electronic component that mounts to the PCB by soldering the pins directly to the surface of the board. The main reason for not covering SMD here is that the size of the copper area the part is soldered to, sometimes called a "land pattern," is calculated from a lot of different factors and will change depending on the way the board is to be soldered, how the parts are to be placed on the board, and how accurate everything that goes into manufacturing and assembling the board is. The IPC has materials
available to help design these patterns.
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