1. The hazards of PCB board deformation

On the automated surface mounting line, if the circuit board is not flat, it can cause positioning blockage, prevent the insertion or mounting of components into the holes and surface mounting pads of the board, and even damage the automatic insertion machine. After soldering the circuit board with the original equipment, it becomes twisted and the component pins are difficult to cut flat and neat. The board cannot be installed on the chassis or socket inside the machine, so it is also very troublesome for the assembly plant to encounter board warping. The current surface mount technology is moving towards high precision, high speed, and intelligence, which puts higher demands on the flatness of PCB boards as the home of various elemental equipment.

In the IPC specification, it is specifically stated that the maximum allowable deformation for PCB boards with surface mount equipment is 0.75%, while the maximum allowable deformation for PCB boards without surface mount equipment is 1.5%. In fact, in order to meet the requirements of high-precision and high-speed mounting, some electronic assembly manufacturers have stricter requirements for deformation, with a maximum allowable deformation of 0.5% for a single customer, and even 0.3% for a single customer.

PCB board is composed of materials such as copper foil, resin, glass cloth, etc., and the physical and chemical properties of each material are different. After being pressed together, thermal stress residue will inevitably occur, leading to deformation. During the PCB processing, various processes such as high temperature, mechanical cutting, and wet treatment are involved, which can have a significant impact on the deformation of the board. In short, there are various reasons that can cause PCB board deformation. How to reduce or eliminate the deformation caused by different material properties or processing has become one of the chaotic problems faced by PCB manufacturers.

2. Analysis of the causes of PCB board deformation

The deformation of PCB board needs to be studied from several aspects such as material, structure, graphic distribution, and processing technology. This article will analyze and discuss various reasons and improvement methods that may cause deformation.

Uneven copper surface area on the circuit board can worsen board bending and warping.

Generally, large areas of copper foil are planned on circuit boards for grounding purposes. Sometimes, the VCC layer also has large areas of copper foil planned. When these large copper foils cannot be evenly distributed on the same circuit board, it will cause uneven heat absorption and dissipation rates. The circuit board will also experience thermal expansion and contraction. If the expansion and contraction cannot be combined, different stresses will be formed and deformation will occur. At this time, if the temperature of the board has reached the upper limit of Tg value, the board will begin to soften, forming permanent deformation.

The connection points (vias) on each layer of the circuit board will limit the board's expansion and contraction.

Nowadays, most circuit boards are multi-layer boards, and there are rivet like connection points (vias) between layers. The connection points are divided into through holes, blind holes, and buried holes. The areas with connection points will limit the expansion and contraction of the board, and indirectly form board bends and warping.

Reasons for PCB board deformation:

(1) The component of the circuit board itself will cause the board to sink and deform

Generally, reflow ovens use chains to drive the circuit board to move in the reflow oven, that is, using the two sides of the board as support points to support the entire board. If there are heavy parts on the board or the size of the board is too large, it will show a concave phenomenon in the middle due to its own size, forming a board bend.

(2) The depth and connecting strip of V-Cut will affect the deformation of the splicing board

Basically, V-Cut is the culprit that damages the structure of the board. As V-Cut cuts grooves into a large sheet of board, the local area of V-Cut is prone to deformation.

Article source: PCB manufacturerhttp://www.yonghongpcb.com/