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10-02-2018, 12:18 AM
Library Parts: Packages (Part-1)
Electronic components are manufactured in different shapes and sizes of casings with terminations or leads for the connections, all of which is called a PACKAGE. Some components have only one package where others might come in a range of sizes. The Eagle library has many standard parts of different kinds, like transistors, resistors, diodes, capacitors, and ICs, to list a few. We all know that resistors come in a range of power ratings and each has its own size and shape - a 1W resistor is larger than a 1/2W, but smaller than a 5W part. The Eagle library contains a range of these packages, but there will be times when we must create our own.
We begin either with a mechanical drawing of the component supplied by the manufacturer of the part, or we have the physical part already and make our own measurements. If we are doing the latter, it is important to make as accurate measurements as possible. Ideally, we use an inch-scale marked in tenths, or a metric scale in millimetres, or we use a caliper.
In Eagle, we are always looking at the top of the board and see through the board to the bottom traces. The footprint for the component must be as viewed from the top, as well, which means we have to "see through it" to where the pins are. We can get to that end in many ways.
Some mechanical drawings already show the footprint as it should be for the PCB layout, since any component designed for PC-mounting is likely to end up an a PCB. Other drawings show you exactly what you see when you look at the bottom of the part at the pins. Hopefully in both cases there is a note stating explicitly what the view is: "Bottom view" or "Top view". When you have the part in hand it is clear what view you have.
Make your drawing by hand on paper at first and make it large. Draw the pin locations but do not be super critical about aligning them. Instead, draw a line through rows of pins that are in a line even if it is a crooked line on your doodle. measure the distance between the pins and note this beside one of the gaps between the pins. Measure the distance between the rows of pins (if this applies) and note the dimension. Measure the overall width and length of the part. measure the distance between the pins and the edge of the part. You could end up with some redundant measurements here, so it is often good to pick either a pin or a corner of the package as a reference, then measure everything from there. However this evolves should be obvious from the nature of the component shape. The reference point is called the ORIGIN for the part.
A circular component has fewer dimensions to note: the diameter and the pin spacing. If it is a two-pin capacitor, the pins will be on a centre-line through the circle and equally spaced from the centre of the circle. The centre of the circle will be used as the ORIGIN for the part.
Electronic components are manufactured in different shapes and sizes of casings with terminations or leads for the connections, all of which is called a PACKAGE. Some components have only one package where others might come in a range of sizes. The Eagle library has many standard parts of different kinds, like transistors, resistors, diodes, capacitors, and ICs, to list a few. We all know that resistors come in a range of power ratings and each has its own size and shape - a 1W resistor is larger than a 1/2W, but smaller than a 5W part. The Eagle library contains a range of these packages, but there will be times when we must create our own.
We begin either with a mechanical drawing of the component supplied by the manufacturer of the part, or we have the physical part already and make our own measurements. If we are doing the latter, it is important to make as accurate measurements as possible. Ideally, we use an inch-scale marked in tenths, or a metric scale in millimetres, or we use a caliper.
In Eagle, we are always looking at the top of the board and see through the board to the bottom traces. The footprint for the component must be as viewed from the top, as well, which means we have to "see through it" to where the pins are. We can get to that end in many ways.
Some mechanical drawings already show the footprint as it should be for the PCB layout, since any component designed for PC-mounting is likely to end up an a PCB. Other drawings show you exactly what you see when you look at the bottom of the part at the pins. Hopefully in both cases there is a note stating explicitly what the view is: "Bottom view" or "Top view". When you have the part in hand it is clear what view you have.
Make your drawing by hand on paper at first and make it large. Draw the pin locations but do not be super critical about aligning them. Instead, draw a line through rows of pins that are in a line even if it is a crooked line on your doodle. measure the distance between the pins and note this beside one of the gaps between the pins. Measure the distance between the rows of pins (if this applies) and note the dimension. Measure the overall width and length of the part. measure the distance between the pins and the edge of the part. You could end up with some redundant measurements here, so it is often good to pick either a pin or a corner of the package as a reference, then measure everything from there. However this evolves should be obvious from the nature of the component shape. The reference point is called the ORIGIN for the part.
A circular component has fewer dimensions to note: the diameter and the pin spacing. If it is a two-pin capacitor, the pins will be on a centre-line through the circle and equally spaced from the centre of the circle. The centre of the circle will be used as the ORIGIN for the part.
