On the automated surface mount line, if the circuit board is not flat, it will cause inaccurate positioning, and the components cannot be inserted or mounted on the holes and surface mount pads of the board, and may even damage the automatic insertion machine.
After the circuit board with components is welded, it is difficult to cut the component legs neatly. The board cannot be installed on the chassis or the socket inside the machine, so it is also very annoying for the assembly plant to encounter board warping.
The current surface mount technology is developing in the direction of high precision, high speed and intelligence, which puts forward higher flatness requirements for PCB boards as the home of various components.
The IPC standard specifically points out that the allowable deformation of PCB boards with surface mount devices is 0.75%, and the allowable deformation of PCB boards without surface mount is 1.5%.
In fact, in order to meet the needs of high-precision and high-speed mounting, some electronic assembly manufacturers have stricter requirements on deformation, such as requiring the allowable deformation to be 0.5%, and even some require 0.3%.
PCB boards are made of copper foil, resin, glass cloth and other materials. The physical and chemical properties of each material are different. After being pressed together, thermal stress will inevitably remain, causing deformation.
At the same time, during the processing of PCB, it will go through various processes such as high temperature, mechanical cutting, and wet treatment, which will also have an important impact on the deformation of the board. In short, the reasons that can cause PCB board deformation are complex and diverse. How to reduce or eliminate deformation caused by different material properties or processing has become one of the complex problems faced by PCB manufacturers.
