Causes and Improvement of PCB Deformation
Circuit board reflow through the most likely to occur when the board bending plate Alice, serious, and even lead to component air welding, tombstoning, etc., how to overcome it?
1, PCB circuit board deformation of the hazards
In the automatic surface mount line, the circuit board if not flat, will cause the positioning is not allowed, components can not be inserted or installed to the board hole and surface mount pad, and even crashed automatic insertion machine. Installed components of the circuit board after welding bending, component feet difficult to trim neatly. The board can not be installed into the chassis or machine socket, so the assembly plant encountered plate Alice is also very troublesome. The current surface mount technology is moving towards high precision, high speed, intelligent direction, which is for the various components of the home PCB board made a higher flatness requirements.
In the IPC standard, the maximum allowable deformation of a PCB with a surface mount device is 0.75%, and the maximum amount of deformation allowed for surface mount PCBs is 1.5%. In fact, in order to meet the needs of high-precision and high-speed placement, part of the electronic assembly manufacturers on the deformation of the more stringent requirements, such as my company has a number of customer requirements to allow the maximum deformation of 0.5%, or even individual customer requirements 0.3%.
PCB board by the copper foil, resin, glass cloth and other materials, the physical and chemical properties of the material are not the same, after pressing together will inevitably produce thermal stress residue, leading to deformation. At the same time in the PCB processing process, will go through high temperature, mechanical cutting, wet treatment and other processes, will also have an important impact on the deformation of the plate, in short, can lead to PCB board deformation of the complex and diverse, how to reduce or eliminate due to material properties Different or processing caused by deformation, PCB manufacturers to become one of the most complex problems.
2, the deformation of the causes of analysis
The deformation of PCB board needs to be studied from the aspects of material, structure, pattern distribution, processing process and so on. This paper will analyze and explain the various causes and improvement methods that may be deformed.
Circuit board on the copper surface area is uneven, will deteriorate the board bending and board Alice.
The general circuit board will be designed with a large area of copper foil as a ground use, and sometimes Vcc layer will also have a large area of copper foil design, when these large areas of copper can not evenly distributed in the same piece of circuit board On the time, it will cause the endothermic and heat dissipation of the uneven problem, the circuit board will of course, thermal expansion and contraction, if the rise and fall can not cause different stress and deformation, this time the board if the temperature has reached The upper limit of the Tg value, the board will begin to soften, resulting in permanent deformation.
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