As we all know, how to prevent the PCB board from bending and warping after passing through the reflow furnace is as follows:

1) The effect of reducing temperature on PCB stress

Since "temperature" is the main source of plate stress, the bending and warping can be greatly reduced by lowering the temperature of the reflow furnace or slowing down the heating and cooling speed of the plate in the reflow furnace. However, there may be other side effects, such as solder short circuit.

2) Use high Tg plate

TG is the glass transition temperature, that is, the temperature at which the material changes from glassy state to rubberized state. The lower the TG value, the faster the plate begins to soften after entering the reflow furnace, and the longer the time to become soft rubber state. Of course, the deformation of the board will be more serious. However, the price of the material is relatively high.

3) Increase the thickness of circuit board

For many electronic products, in order to achieve the purpose of being thinner, the thickness of the board has been left 1.0 mm, 0.8 mm, or even 0.6 mm. It is really difficult to keep the plate from deformation after the reflow furnace. It is suggested that if there is no requirement for lightness, the thickness of 1.6 mm can be used for the board, which can greatly reduce the risk of bending and deformation.

4) Reduce the size of circuit board and the number of assembly board

Since most of the soldering furnaces use chains to drive the circuit board forward, the larger the size of the circuit board will sag and deform in the soldering furnace because of its own weight, so try to put the long side of the circuit board as the board edge on the chain of the reflow furnace, which can reduce the concave deformation caused by the weight of the circuit board. This is also the reason for reducing the number of panels When talking about the furnace, try to use the narrow side perpendicular to the furnace direction, so as to achieve low sag deformation.

5) Using furnace tray fixture

If the above methods are difficult to achieve, it is to use the reflow carrier / template to reduce the deformation. The reason why the furnace tray can reduce the bending and warping of the board is that it is hoped that the tray can hold the circuit board whether it is hot expansion or cold contraction. When the temperature of the circuit board is lower than the TG value and starts to harden again, it can still maintain the round size. If the single-layer tray cannot reduce the deformation of the circuit board, it is necessary to add a layer of cover to clamp the circuit board with the upper and lower trays, which can greatly reduce the deformation of the circuit board through the reflow furnace. But the tray is very expensive, and you have to put and recycle the tray manually.

6) Use router instead of V-CUT

Since the V-CUT will destroy the structural strength of the panel between circuit boards, try not to use the V-CUT sub board or reduce the depth of the V-CUT.