How to prevent PCB board bending and board warping from going through the reflow furnace
PCB factories are prone to board bending and board warping when the PCB board passes through the reflow furnace. Everyone knows how to prevent the PCB board from going through the reflow furnace.
1. Reduce the influence of temperature on PCB board stress
Since temperature is the main source of board stress, PCB manufacturers only need to lower the temperature of the reflow furnace or slow down the heating and cooling rate of the board in the reflow furnace, which can greatly reduce the occurrence of board bending and warping. However, other side effects may occur, such as solder short circuit.
2. Using high Tg sheet
Tg is the glass transition temperature, that is, the temperature at which the material changes from the glass state to the rubber state. The lower the Tg value of the material, the faster the board starts to soften after entering the reflow furnace, and the time it takes to become soft rubber state It will also become longer, and the deformation of the board of the circuit board factory will of course be more serious. The use of a higher Tg sheet can increase its ability to withstand stress and deformation, but the price of the material is relatively high.
3. Increase the thickness of the PCB
In order to achieve the purpose of lighter and thinner for many electronic products, the thickness of the board of the PCB factory has left 1.0mm, 0.8mm, or even 0.6mm. Such a thickness must keep the board from deforming after the reflow furnace, which is really a bit It is difficult. It is recommended that if there is no requirement for lightness and thinness, the thickness of the board should be 1.6mm, which can greatly reduce the risk of bending and deformation of the board.
4. Reduce the size of the PCB and reduce the number of puzzles
Since most of the reflow furnaces of the circuit board factory use chains to drive the circuit board forward, the larger the size of the circuit board will be due to its own weight, dent and deformation in the reflow furnace, so try to treat the long side of the circuit board as a board. Putting it on the chain of the reflow furnace can reduce the depression and deformation caused by the weight of the circuit board itself. This is also the reason for reducing the number of panels. That is to say, when passing the furnace, try to use the narrow side to pass the furnace direction as far as possible. Can reach the lowest amount of depression deformation.
5. Used furnace tray fixture
If the above methods are difficult to achieve, the last is to use the furnace tray to reduce the amount of deformation. The reason why the circuit board factory furnace tray can reduce the bending of the board is because whether it is thermal expansion or cold contraction, it is hoped that the tray can be fixed. Hold the circuit board and wait until the temperature of the circuit board is lower than the Tg value and start to harden again, and the original size can be maintained.
If the single-layer pallet cannot reduce the deformation of the circuit board, you must add a layer of cover to clamp the circuit board with the upper and lower pallets, which can greatly reduce the problem of circuit board deformation through the reflow furnace. However, this furnace tray is quite expensive, and manual labor is required to place and recycle the trays.
6. Use Router instead of V-Cut to use the sub-board
Since V-Cut will destroy the structural strength of the board between the circuit boards, the china PCB manufacturer should try not to use the V-Cut sub-board or reduce the depth of the V-Cut.