The Secrets of Circuits Assembly--surface mount

We had talked about soldering paste, and next let's take a close view of SMT (surface mount technology).


By its name says, the SMT means to "mount" components on the surface of circuit boards. The soldering paste layer on the pads can "catch" and "hold" the components even without melting, to prepare for the next procedure of circuits assembly.


The SMT process is the most important step of circuits assembly, so as people get use to do, the circuits assembly factory also known as "SMT factory".


It looks so simple, isn't it? Hand soldering means to use tweezers pick up the components and place it to circuit boards, while SMT machine just replace human hands with mechanical arm.



How does the SMT machine really work?

First of all, we should know how the components are prepared. Those in smaller size, including chips, are stored in a round tape in queue. There are a series of standard size holes on the tapes that can stuck into the gears of SMT machines, so to move ahead little by little to realize components feeding. Well, now you get the official name of this part "Feeder"!


Components on the feeder are placed like solders, the mechanical arms of machines come and pick up the front "solder" and place it to PCB, with pre -programmed orders.


How does the mechanical arm to pick up such an small item?

No they do not work on fingers, actually they do not have fingers. The arm work by using suction nozzle. With each nozzle it can suck one components, so with more nozzles it can pickup and move several ones in the same time, and place to soldering pads.


Different packaged components goes to its matching suction nozzle, and for those components heavier, the inertia goes bigger while moving arms, so usually there are serveral diversified area in SMT machine, the bigger components area with slower arms, the smaller components area with quicker arms.



How does the mechanical arm know where to put the components?

There should be a file called "pick and place", it has marked the relevant coordinants of all the components. Before the SMT machines starts, engineers will input all the coordinants information in the machines software and then, machine will work as it tells. This process in circuits assembly factory called programme, there is a person whose job is to do this and for a board with hundreds of components, the programing will take almost a day.


How to align the position of soldering pads and components?

There has some tiny cameras on the mechanical arms, it will collect pictures and data in real time. Every components has been picked up will be photoed at once and then scan if the position is just right or with some deviation. If deviation happens, the system will make compensation whiling in place, just to ensure they are placed 100% in line.


Next page, we will review some information of reflow soldering and wave soldering.



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