As we all know, PCB is prone to bending and warping when passing through the reflow oven. How to prevent PCB from bending and warping when passing through the reflow oven is described below
1. Reduce the influence of temperature on PCB stress
Since “temperature” is the main source of plate stress, as long as the temperature of reflow furnace is reduced or the heating and cooling rate of plate in reflow furnace is slowed down, the occurrence of plate bending and warping can be greatly reduced. However, there may be other side effects, such as solder short circuit.
2. Adopt high TG plate
TG is the glass transition temperature, that is, the temperature at which the material changes from the glassy state to the rubberized state. The lower TG value of the material, the faster the plate begins to soften after entering the reflow furnace, and the longer the time to become the soft rubberized state, the more serious the deformation of the plate. The ability of bearing stress and deformation can be increased by using the plate with higher TG, but the price of the material is relatively high.
3. Increase the thickness of the circuit board
Many electronic products in order to achieve the purpose of thinner, the thickness of the board has been left 1.0 mm, 0.8 mm, or even 0.6 mm, such a thickness to keep the board after reflow furnace does not deform, it is really a bit difficult, it is suggested that if there is no thin requirements, the board can use 1.6 mm thickness, which can greatly reduce the risk of bending and deformation.
4. Reduce the size of the circuit board and the number of panels
Since most reflow ovens use chains to drive the circuit boards forward, the larger the size of the circuit board, the more concave it will be in the reflow oven due to its own weight. Therefore, if the long side of the circuit board is placed on the chain of the reflow oven as the edge of the board, the concave deformation caused by the weight of the circuit board can be reduced, and the number of boards can be reduced for this reason, That is to say, when the furnace, try to use the narrow side perpendicular to the direction of the furnace, can achieve to low sag deformation.
5. Used the pallet fixture
If all the above methods are difficult to achieve, It is to use reflow carrier / template to reduce the deformation. The reason that reflow carrier / template can reduce the bending and warping of the board is that no matter whether it is thermal expansion or cold contraction, the tray is expected to hold the circuit board. When the temperature of the circuit board is lower than TG value and begins to harden again, it can maintain the round size.
If the single-layer tray can not reduce the deformation of the circuit board, we must add a layer of cover to clamp the circuit board with two layers of trays, which can greatly reduce the deformation of the circuit board through the reflow oven. However, this furnace tray is very expensive, and also need to add manual to place and recycle the tray.
6. Use router instead of V-CUT
Since the V-CUT will damage the structural strength of the circuit boards, try not to use the V-CUT split or reduce the depth of the V-CUT.
Post time: Jun-24-2021