The reasons for the deformation of the PCB board are:
1. When the circuit board is designed, the copper is unevenly distributed and warped after compressing.
2. The circuit board is impacted by the external heat and cold, causing sudden cooling and heating.
3. The quality of the circuit board raw material is poor.
4. The size of the panel is too large.
5. The circuit board profile is irregular.
The solutions given for the causes of PCB board deformation are:
1. Lower the reflow soldering temperature
Temperature is the main source of PCB board internal stress. As long as you lower the temperature of the reflow oven or slow down the heating and cooling speed of the circuit board in the reflow oven, the occurrence of board bending and board warping can be greatly reduced.
2. Use high TG CCL
TG value is the temperature at which the material changes from the glass state to the rubber state. The lower the TG value, the faster the circuit board starts to soften after entering the reflow oven, and the time it takes to become soft rubber state will be shorter. Of course, the deformation of the circuit board will be more serious, and the use of a higher TG CCL can increase its ability to withstand stress and deformation.
3. Increase the thickness of the PCB board
If there is no requirement for lightness and thinness, it is best to use a thickness of 1.6mm for the PCB board, which can greatly reduce the risk of bending and deformation of the board.
4. Reduce the size of the PCB board and the number of PCB in each panel
Most of the reflow ovens use chains to drive the PCB board forward. Try to put the long side of the PCB board as the board edge on the chain of the reflow oven, which can reduce the depression and deformation caused by the weight of the PCB board itself. The decrease in panelization number is also based on this reason. That is to say, when passing the oven, try to use the narrow side perpendicular to the direction of the oven to achieve the lowest depression deformation.
5. Use tray fixture during reflow soldering
Whether it is thermal expansion or cold contraction, the tray can hold the PCB board and wait until the temperature of the board is lower than the TG value and start to harden again, and it can still maintain the original size.
If a single-layer tray cannot reduce the deformation of the PCB board, add a tray as lid to hold the PCB board with the upper and lower two layers trays, so that the problem of PCB board deformation through the reflow oven can be greatly reduced.
6. Use real connections and stamp holes instead of V-Cut to connect boards
Since V-Cut will destroy the structural strength between the PCB boards, try not to use the V-Cut in panel arrangement, or reduce the depth of the V-Cut.
In the automated surface mounted line, if the PCB board as the basement of various components is not flat, it will cause inaccurate positioning, the components cannot be inserted or mounted precisely on the holes or surface mounted pads of the circuit board. In severe cases, the automatic insertion machine may be damaged.