On automated surface mount lines, if the board is not flat, it will cause misalignment, components can not be inserted or attached to the board's holes and surface mount pads, and even the automatic inserter will be damaged. The board on which the components are mounted is bent after soldering, and the component legs are difficult to trim. The board can't be installed in the chassis or the socket inside the machine, so it is very troublesome for the assembly factory to encounter the board. The current surface mount technology is moving toward high precision, high speed, and intelligent direction, which puts higher flatness requirements on PCB boards as homes for various components.
In the IPC standard, it is specifically pointed out that the maximum allowable deformation of a PCB board with a surface mount device is 0.75%, and the maximum allowable deformation of a PCB without a surface mount is 1.5%. In fact, in order to meet the needs of high-precision and high-speed placement, some electronic assembly manufacturers have stricter requirements on the amount of deformation.
The PCB board is composed of copper foil, resin, glass cloth and other materials. The physical and chemical properties of each material are different. When pressed together, thermal stress remains inevitably, resulting in deformation. At the same time, in the processing of PCB, it will undergo various processes such as high temperature, mechanical cutting and wet processing, which will also have an important impact on the deformation of the board. In short, the causes of PCB board deformation are complicated and diverse, how to reduce or eliminate the material characteristics. Different or processing-induced deformations have become one of the most complex problems faced by PCB manufacturers.