1. Pad spacing requirements:
Should be avoided as far as possible in the fine pitch components between the pads through the connection, indeed need to cross the connection between the pads, the use of solder mask to be a reliable cover.
2. Pad Length:
The length of the pad plays a more important role than the pad width. The reliability of the pad depends mainly on the length of the pad, not the width, depending on the reliability of the pad.
3. Pad width:
For more than 0805 resistance, capacitance components, or pin spacing in more than 1.27mm so, soj package IC chip, the width of the general component of the pin on the basis of an additional amount of value, the data Range: 0.1 ~ 0.25mm;
For chips below 0.64 (including 0.64mm), the pad width is equal to the pin width;
For fine-pitch QFP package devices, sometimes the width of the pad is reduced relative to the pin (if a lead is required between the two pins).
4. Pad symmetry requirements more stringent:
For the same components, any symmetrical use of the pads, such as QFP, SOIC package, the design should be strictly guaranteed full symmetry.
Namely, the shape and size of the pad and the pattern are exactly the same so as to ensure that the surface tension of all the solder joints on the device is balanced when the solder melts, so as to form an ideal high-quality solder joint without displacement.