It is a technology that is in charge of mounting or soldering SMD components / SMT devices to a PCB. It is known as surface mounting. Solder paste plays an important role here, because quality and efficiency depend on it. Paste printing is an apparatus that consists of a template, scraper, printing table and other parts, and it also plays a significant role in the SMT line.
Thanks to SMT, the production process is accelerated and the risk of failures is reduced. Defects can be the result of miniaturization of components and denser packaging of the board, but it is therefore crucial for the process to detect defects at the earliest stage. To get a lot more important information about this technology, keep reading and discover all about how SMT technology works.
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Factors affecting solder paste
The quality of the template has the greatest impact on the printed paste. Depending on the thickness and dimension of the opening, the print can be more or less high quality. For example, the consequence of excessive printing is bridging, while in the opposite situation there would be insufficient solder paste. There are also factors that affect the quality of the download. Some of them are the wall of the matrix and the shape of the opening of the template. Another factor that has a big impact is the quality of the solder paste. Note that shelf life at normal temperatures affects print quality. There is a limitation when it comes to scraper speed, stress, scraper angle and pattern, as well as bonding solder paste.
Print quality can significantly improve parameter control. In addition to establishing a good balance, precision devices also contribute to a better result. This achieves greater precision reprinting. External influences also contribute to quality or its reduction. These are temperature, humidity, hygiene and environmental conditions. For example, too high a temperature prevents the solder paste from setting while high humidity encourages the solvent to evaporate into the paste.
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Types of SMT templates
There is engraving as a popular choice at an early stage. It is a great option for an open hole that has more than 20mil. During the SMT process, laser is used as a very precise technique, and positioning with +/- 0.3mil is recommended. Electroform is best for printing below 5mil. Chemical copperplate is used when it is enough to shape it once and when you want to achieve faster work at a low price.
However, chemical copperplate has its drawbacks. This refers to insufficient etching, larger dimensions of the openings that are a consequence of excessive notching, but there are other factors that affect the final result. For example, these are experience, medicine, film, etc. Electroform also has its advantages and disadvantages. The advantages are smooth opening wall and ultra-fine pitch stencil, while the disadvantages are related to difficult control and contamination in the production process.
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AOI
It is an automated optical inspection that takes place after re-spilling. This is the final part of the surface mounting process to determine if an error has been made. For this purpose, AOI machines are used, which are intended to check the quality of solder joints. Thanks to 3D technology, the process is much more reliable. More accurate measurement and greater stability of the inspection process is achieved. Unlike older models, the new machines have advanced features that allow them to network together. This provides feedback to the previous machine. PCBASIC remind you that you should not check other quality control methods too.
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Advantages of the process
Unlike the older technique, SMT allows you to have smaller components, their higher density, as well as more connections. We must note that you can place the components on both sides of the board. When it comes to component connections, their biggest advantage is that they will not block routing space on the inner layers. This will also not affect the layers on the back. Less and less errors can be corrected immediately, and better mechanical performance during shocks and vibrations is noticed.
In addition, SMT requires drilling fewer holes, lower start-up costs as well as reduced set-up time for mass production. This is due to the use of automated equipment. Assembly is significantly faster than previous processes, which means that some machines can install over 130,000 components in one go.
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Disadvantages of the process
One of the biggest shortcomings of this process is reflected in the components that are subject to frequent mechanical stresses. Examples of such components are connectors. They are mainly used to connect external devices and are often attached and detached. In that case, this method is not the best choice. There is a risk of damaging the solder joints if they go through a thermal cycle. Manual prototyping can be another problem as well as repair. These are not simple processes, and are performed mostly by qualified operators.
Installation or repair requires expensive tools, and handling small components is very difficult. In that case, it is necessary to use tweezers and take care of the distance between the leads. It is necessary to have developed skills for this procedure, because SMT components move easily due to the slightest error. You can’t use SMD in combination with plug-in breadboards here, because the conditions are a custom printed circuit board for each prototype or mounting on a pin-leaded carrier. A smaller marking area is characteristic of smaller SMDs. They must have identification codes on certain parts. There is also a difference in the value of the components, because they are much smaller than the standard ones. In this case, magnification is used to read the codes while standard size SMDs can be read from a normal distance.
Conclusion
Obviously, SMT has many advantages over through-hole mounting methods. However, in order to know how to apply it in production, you need to know everything about this process. This applies not only to the stages of the process, but also to all the advantages and disadvantages you can expect when it comes to surface mounting. Only then will you fully understand its role in the electronics industry. This will make you more successful in optimizing PCB design.
