The process of joining electronic components to a printed circuit board is called “board mounting,” and “soldering” is used for board mounting. This section describes the visual inspection of board mounting and soldering We are going to introduce basic knowledge of board mounting and soldering, types and causes of common defects, and inspection examples using conventional inspection methods and the latest image processing systems.
About board mounting
Board mounting (printed circuit board mounting) is the process of joining electronic components to a printed circuit board so that it functions as an electronic circuit. “Soldering” is used as a method of joining electronic components. In addition, there are two methods for joining electronic components: “Insertion Mount Technology (IMT)” and “Surface Mount Technology (SMT)”. In addition, there is also “bare chip mounting” in which electrodes are provided on bare semiconductors and mounted on a printed circuit board, but this time, basic “Insertion Mount Technology (IMT)” and “Surface Mount Technology (SMT)” This section explains.
Through-hole technology (IMT)
Insertion mounting technology (IMT) is a mounting method in which leads (electrodes) are inserted into through holes (holes) in a printed circuit board and soldered together. Since the parts are placed on the board, the board becomes large and it is difficult to reduce the size.
Surface Mount (SMT: Surface Mount Technology)
The current mainstream of board mounting is “Surface Mount Technology (SMT)”. In surface mount technology (SMT), the electrodes of electronic components are soldered to the pads (lands) on the surface of the board without using through holes (holes). Unlike insertion mounting technology (IMT), leads (electrodes) do not penetrate, so many electronic components can be placed on both sides of the board, and the advantage is that they can be miniaturized. In addition, small, high-density electronic components that do not have leads for surface mounting are called “Surface Mount Devices (SMDs)”.
About surface mounting method
The surface mounting process can be roughly divided into two processes: “hand soldering process” and “reflow process”. As the name implies, the manual soldering process is manual soldering performed by humans. On the other hand, in the reflow process, solder paste inspection is applied (printed) to the pad (land) of the substrate, and a surface mount device (SMD) is mounted on it, which is a device called a reflow furnace. Heat the entire board with to melt the solder and join.
General flow of surface mounting
Currently, “surface mounting + reflow process” is the mainstream in the manufacture of mass-produced products, so we will introduce general work processes.1. Printing Engineering
The printing process in surface mount technology (SMT) refers to the transfer of solder paste inspection to a pad on a substrate. When you think of printing, you might think of printing on a printed circuit board, but be careful not to confuse it. Printing uses a printing plate with holes in a thin stainless steel plate, commonly called a metal mask.2. Mounting process
Mounting is the process of mounting a surface mount device (SMD) on a board printed with solder paste inspection. Please note that in the mounting process, the electronic components are only mounted on the printed circuit board and are not fixed, so the position can easily be displaced by impact.3. Reflow process
Reflow is the process of putting a printed circuit board on which solder paste inspection and surface mount devices are placed in a furnace and heating it. By heating in a facility called a reflow furnace, solder paste inspection is melted and surface mount devices (SMD) are joined. When it is finally cooled, the board mounting is completed.