Surface mounted technology (SMT) PCB involves mounting components on the surface of the board by soldering the SMD (surface mounted device) components to the contact pad.
This type of mounting allows you to place components on both sides. The development of SMD technology dates back to the 1960s.
Nevertheless, SMD mounting on layered boards has appeared not so long ago.
The strengths of SMD are small components and high density. The larger holes were replaced by smaller ones for conducting signals between the sides of the board and the inner layer.
The main focus used in SMD technology is the use of smaller passive components such as capacitors, resistors, inductors, and chokes. Resistors and capacitors were also used inside the PCB layers.
The use of passive components provides additional space for larger components.
In the application of active components that are used in surface mounting (SMD), 2 opposing directions can be observed.
On the one hand, the size of memory components (RAM, SDRAM, etc.) is reduced.
At the same time, the size of microprocessors and application-specific integrated circuits (ASICs) is increasing due to the increased functionality of large crystals.
The housings for these devices were transferred from the remote location of the terminals to the matrix ones.
Matrix pin packages include GA packages and smaller components (CSP and DCA / FC).
Among the advantages of matrix SMD mounting technology is the reduction of the area set aside for the component, due to the elimination of leads that protrude from the case.
At the beginning of development, the size and pitch of the matrix package pins in surface-mount PCB technology were larger than those used at the time.
However, as the number of leads increased along with the increase in the functionality of the components in matrix packages, the size of the solder balls and the pitch decreased quite significantly.
A particular advantage of surface mount technology is the reduction in production costs through an automated assembly process.
Solder paste, which is a mixture of flux, solder metal powder, and thixotropic agents, is applied in controlled quantities by screen printing and using a dispenser.
The components are held in place by the increased tackiness of the flux in the paste.
The machines, which perform operations at each stage of installation – at the stage of screen printing of paste, installation of components, and reflow soldering, are connected by conveyor belts to form technological production lines.
Thus, cleaning the boards, which is the last step, can also be included in the assembly sequence.
You can apply different levels of SMD installation automation based on production volumes and costs. However, the constant miniaturization of surface-mount products, as well as the stringent requirements for high-precision reproducibility of solder paste volumes and component placement, requires premature SMD design based on full automation.
Surface Mounting of Printed Circuit Boards
In the modern world, everyone uses a variety of electronic devices from a TV or computer to a smartphone. The basis of any electronic device is the board.
Surface mount technology (SMT) has been developed to reduce the price of electronic devices, as well as to be able to produce these devices in large volumes.
Thanks to this technology, mass production of high-quality soldered joints became possible. In addition, this technology allows you to change the type of manufactured products in a short time.
Surface Mount Equipments
1. Printer Applying Solder Paste
The board is launched into the printer from automatic cassettes with printed circuit boards, then the fiducial mark recognition system matches the fiducial marks on the board and on the stencil. solder paste is applied on the printed circuit board through the holes in the stencil.
Then, passing along the conveyor table, the board undergoes quality control of the application of solder paste to the pads on the printed circuit board.
2. Automatic Installer of Chip Elements
After the solder paste is applied, the board goes into the machine for installing the chip components.
All SMD items will arrive in ribbon or tray. For all products, programs of coordinates for mounting a component on a board, a rotation angle are created.
Next, a visual image of each element is created, and the machine’s system on the visual control camera checks against the images of each element.
If the element is defective, then it will not rise, and in the case of taking an element with an offset, the machine will automatically adjust the setting of this element to exclude the offset. After installing the elements, a conveyor table is also optionally installed for visual inspection of the product.
3. Convection Brazing Oven
After that, the board will enter the convection brazing oven. There are 2 types of soldering: in an oxygen environment and nitrogen. The most common is oxygen brazing.
The oven is also a conveyor, optionally from 3 to 6 zones. A uniform increase in t up to 285C and a zone for cooling, to exclude thermal shock.
The goal of PCBMAY is to offer services for PCB assembly of electronics at a consistently high quality.