PCB pad design has a great impact on the SMT product manufacturability, reliability , PCB design is a very important part. Good PCB pad design can avoid Weld, short circuit, tombstone , shadow effects and other issues. IPC provides a surface mount pad structure design standards - IPC-SM-782A, 2005 the IPC released IPC-SM-782A alternative to standard IPC-7351. Because many factors affect the size of the pad must be fully considered in order to do , should make their own products, PCB pad design specifications of the actual situation , and can not rely entirely on IPC standards.
General considerations for the order of PCB pad design : to ensure good electrical properties ; reliability ; manufacturability ; serviceability . PCB pad design elements to be determined , including the size of the pad itself , green oil or solder window size , covering the range of components , wiring or glue components used under the dummy pad and so on.
The main factors that determine the size of the pad has five aspects : the shape and size of components, substrate type and quality , assembly equipment capacity , the process used by the type and capacity , quality standards or standards. In considering the pad must be designed with the above five factors considered as a whole . When calculating the dimensional tolerances , the industry is more commonly used statistical methods in the rms value or accepted , this approach can achieve a better balance in all aspects.
A good PCB pad design , it should be provided in the process is easy to assemble , easy inspection and testing, and the assembled condition of joints and long life . PCB pads to ensure good conditions for the design :
( 1 ) Create the component package data files ;
( 2 ) to establish the device libraries for each package size SMD;
( 3 ) determine the size of the error from different vendors ;
( 4 ) the establishment of a substrate specification ;
( 5 ) the ability to develop plant processes and equipment specifications ;
( 6 ) knowledge of the problem and the various manufacturing processes have sufficient understanding ;
( 7 ) the development of quality standards for the plant or on a product .
L- pin IC pad design
( 1 ) Adaptation: Lead in SOT, SOIC, (S / T) SOP, (P / S /-C) QFP and other package.
( 2 ) Parameter Description :
t: Lead Thickness (lead thickness) is typically 0.1 ~ 0.15mm
