LAND PATTERN OR FOOTPRINT
*A footprint or land pattern is the arrangement of pads used to physically attach and electrically connect a component to a printed circuit board. The land pattern on a circuit board matches the arrangement of leads on a component.
*SMD PAD Design:A good pad stack promotes the best solder joints between a components terminal[pins] and the PCB. Pad stack must allow for component dimension variations,PCB Fabrication tolerance,and solder fillet specifications.
*An example of Land Pattern is given below.
1-Inner Distance of row and column pad [G]
2-PAD size:Pad Size is shown as X and Y
3-Pitch:Pin to Pin Pitch is distance between two Leads that is mentioned in figure as E.
4-Row Pitch:The Pitch between row terminals shown as C.
* The three dimensions [X , Y, G and C] given above are depends on five dimension of SMD components. These are mentioned below.
1-Toe Fillet 2-Side Fillet 3-Heel Fillet.
The image of fillets given below.
4-PCB Fabrication tolerance:
5-Component dimensions variation:
