Surface mounth technology electronics circuits 04/02/2020
SMD - Insertion
The surface mount technology or surface , better known by its acronym SMT of the English surface-mount technology , it is the method of construction of electronic devices most used nowadays. It is used for both active and passive components, and is based on their assembly ( surface-mount component , SMC ) on the surface of the printed circuit . Both the equipment thus constructed and the surface mounting components can be called surface / surface mounting devices or SMD ( surface-mount device ). While components through hole technology ( through hole ) pass through the printed circuit board from one side to another, MDS analogs are often smaller, not cross: the connections are made via flat contacts, a matrix of spheres at the bottom of the package, or metal endings at the edges of the component. This type of technology has far exceeded and replaced the through hole in mass production applications (above thousands of units), low energy consumption (such as portable devices), low temperature and / or multi-application in size reduced (as computer equipment, measurement and instrumentation). However, due to its small size, the manual assembly of the parts is difficult, so more automation is needed in the production lines, and the implementation of more advanced design techniques is also required for the SMDs to function properly even in environments with high levels of electromagnetic interference (EMI).
Printed circuits have flat surfaces without holes, usually made of lead - tin (silver) or copper (gold), called solder terminals. The "solder paste", which consists of a mixture of flux and small tin particles, is applied to the terminals by a stenciling process , using steel or nickel die cut templates. Once the printed circuit board has been screen printed, it goes to a numerical control deposition machine, where a tool head places the components. These are usually packaged in rolls and tubes, so that a feeder allows the tool to suck each component. Next, the panels are transported to a refusion welding furnace .
In the first preheated zone, the temperature of the plate as well as the different components is gradually increased. In the next zone, at a higher temperature, is where the solder paste melts, thus joining the components to the plate terminals. The surface tension of the molten tin helps the components remain in position, even if they align with the circuit terminals themselves.