Pad shape influence on the strength and reliability of the soldering joints
The welding of chip components is the key technology of SMT chip processing, and it is the guarantee of product quality and reliability. Surface assembly technology is to align the solder terminals of the chip components with the pads on the printed board, use the viscosity of the adhesive or solder paste to stick the chip components to the printed board, and then pass the wave soldering or reflow soldering and realize welding. The typical process flow of SMT is as follows: printed circuit board SMT program design-printing adhesive or solder paste-mounting chip components-wave soldering or reflow soldering-cleaning-testing. Corresponding SMT equipment is a glue machine or printing machine, placement machine, wave soldering machine or reflow soldering machine, rework workstation, cleaning machine and test equipment.
There are generally four types of surface mounting: single-sided pure chip component mounting, double-sided pure chip component mounting, single-sided chip components and through hole components mixed, double-sided chip components and through hole components mixed. The shape of the pad on PCB has an important influence on the strength and reliability of the soldering joints. The basic requirements are:
1. The center distance between adjacent pads of the same component should be equal to the center distance between the corresponding pins;
2. The width of the pad is equal to the width of the lead or welding head plus a constant, and the value can be adjusted in practice;
3. The length of the pad depends on the height and depth of the welding head or pin.
Generally speaking, the length of pad is more important than the width of pad.