1. Effect of temperature reduction on PCB stress
Since "temperature" is the main source of plate stress, so as long as the temperature of the reflow furnace is reduced or the speed of temperature rise and cooling of the plate in the reflow furnace is slowed down, the situation of plate bending and plate warping can be greatly reduced However, there may be other side effects, such as solder short circuit.
2. High Tg plate
TG is the glass transition temperature, that is, the temperature at which the material changes from glass state to rubber and glue state. The lower the TG value is, the faster the board will start to soften after entering the reflow furnace, and the longer the time to become soft rubber and glue state will be, of course, the more serious the deformation of the board will be. The use of high Tg plate can increase its ability to withstand stress and deformation, but the price of relative materials is also relatively high.
3. Increase the thickness of circuit board
In order to achieve the purpose of being lighter and thinner, many electronic products have left 1.0mm, 0.8mm, or even 0.6mm thickness of the board. It's really hard to keep the board from deforming after the reflow furnace. It's suggested that if there is no requirement of being lighter and thinner, the board can use 1.6mm thickness, which can greatly reduce the risk of bending and deformation.
4. Reduce the size of circuit board and the number of panels
Since most of the reflow soldering furnaces use chains to drive the circuit board forward, the larger the size of the circuit board, because of its own weight, the concave deformation in the reflow soldering furnace, so try to put the long side of the circuit board as the plate side on the chain of the reflow soldering furnace, it can reduce the concave deformation caused by the weight of the circuit board itself, and the reduction of the number of panels is also based on this reason, that is to say Said when the furnace, try to use the narrow side perpendicular to the furnace direction, can achieve a low sag deformation.
5. Use the furnace tray fixture
If the above methods are difficult to achieve, * is to use the reflow carrier / template to reduce the deformation. The reason why the reflow carrier / template can reduce the bending warpage of the plate is that the tray is expected to hold the circuit board until the temperature of the circuit board is lower than the TG value and start to harden again, and then maintain the size of the circle.
If the single-layer tray can not reduce the deformation of the circuit board, it is necessary to add another layer of cover to clamp the circuit board with two layers of trays, so that the deformation of the circuit board through the reflow furnace can be greatly reduced. However, the trays are very expensive and need to be placed and recycled manually.
6. Use router instead of V-CUT
Since V-CUT will destroy the structural strength of the boards, try not to use V-CUT board splitting or reduce the depth of V-CUT.
Oct 29, 2019
