Views:4 Author:Site Editor Publish Time: 2016-12-08 Origin:Site
Surface-mount technology (SMT) is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). An electronic device so made is called a surface-mount device (SMD). In the industry it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. Both technologies can be used on the same board, with the through-hole technology used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.
An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of solder balls ( BGAs ), or terminations on the body of the component.
The main advantages of SMT over the older through-hole technique are:
· Smaller components. As of 2012 smallest was 0.4 × 0.2 mm (0.016 × 0.008 in: 01005). Expected to sample in 2013 are 0.25 × 0.125 mm (0.010 × 0.005 in, size not yet standardized)
· Much higher component density (components per unit area) and many more connections per component.
· Higher density of connections because holes do not block routing space on inner or back-side layers.
· Components can be placed on both sides of the circuit board.
· Small errors in component placement are corrected automatically as the surface tension of molten solder pulls components into alignment with solder pads.
· Better mechanical performance under shake and vibration conditions.
· Lower resistance and inductance at the connection; consequently, fewer unwanted RF signal effects and better and more predictable high-frequency performance.
· Fewer holes need to be drilled.
· Lower initial cost and time of setting up for production.
· Simpler and faster automated assembly. Some placement machines are capable of placing more than 136,000 components per hour.
· Many SMT parts cost less than equivalent through-hole parts.
· Better EMC performance (lower radiated emissions) due to the smaller radiation loop area (because of the smaller package) and the smaller lead inductance.