Causes of SMT Chip Deformation and Warpage
The IPC standard stipulates that the maximum allowable deformation for SMT chip processing of circuit boards is 0.75%, and the maximum allowable deformation for circuit boards without SMT chip processing is 1.5%. The calculation method of circuit board warpage is (PCB diagonal length * 2) * 100%. The distortion and warpage of the circuit board will directly affect the welding quality, so SMT chip factory is very worried about this problem. In order to meet the quality requirements of high-precision SMT chip processing, many SMT chip manufacturers have strICt requirements on the deformation and warpage of circuit boards. What is the reason for the deformation and warping of the SMT chip of the circuit board?
PCB chip processing
1、 Analysis of the causes of SMT chip deformation and warpage
1. V-Cut on the circuit board is generally the main cause of deformation and warpage. Because V-Cut cuts grooves on the original large sheet to get a small sheet, V-Cut is prone to deformation;
2. Different circuit boards will have the maximum heat resistance value. When the reflow temperature is higher than the maximum value of the circuit board. It will cause the board to soften and cause deformation and warping.
3. Generally, after the SMT chip processing of the circuit board is completed, it will be directly transmitted through the reflow equipment track. If there are overweight parts on the board or the size of the board is too large, plus the high reflow temperature, the board will show a central depression due to its weight and heat, resulting in bending deformation.
4. Electronic products are developing towards small and lightweight, and the thickness of circuit boards is getting thinner and thinner. The thinner the circuit board, the easier it is to deform at high temperatures.
5. Generally, a large area of copper foil will be designed on the circuit board for grounding. When these large-area copper foils cannot be evenly distributed on the same circuit board, the problem of uneven heat absorption and heat dissipation speed will be caused, and warping deformation will also occur after cooling;
6. As many circuit boards are not supplied in the original packaging, due to the storage environment, there will be more or less water in the circuit boards. If no baking operation is carried out before the SMT chip processing of the circuit board, the moisture will evaporate when the reflow soldering appears high temperature, resulting in deformation and warping;
2、 Solution to SMT Chip Processing Deformation and Warpage
1. Most SMT chip factories use reflow soldering track transmission circuit boards. First of all, we try to use the long side of the PCB as the contact with the track to reduce the negative weight of the PCB itself. This prevents the circuit board from deforming and warping.
2. If the above point 1 is not improved, the tray can also be used to pass through the mesh belt of the reflux furnace to solve the problem of deformation and warpage;
3. If there is deformation during SMT chip processing and reflow soldering of the circuit board, the fixture shall be made according to the cost and production batch to assist in the completion.
4. When the circuit board is not in the original packaging, it needs to be baked at 120 ℃/4 hours before SMT chip processing to avoid deformation and warping caused by moisture during reflow soldering;
5. Since V-Cut will damage the structural strength of PCB boards during assembly, try not to use V-Cut sub boards or reduce the depth of V-Cut. Or give suggestions to relevant departments for improvement, and propose to use stamp holes to connect the plates.
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