PCBA boards are prone to bending and warping when passing through the reflow furnace. As we all know, how to prevent PCBA boards from bending and warping when passing through the reflow furnace? Below, the editor will explain to everyone:
1. The effect of reducing temperature on PCB board stress
Since "temperature" is the main source of stress in the board, reducing the temperature of the reflow furnace or slowing down the heating and cooling rate of the board in the reflow furnace can greatly reduce the occurrence of bending and warping of the board. However, there may be other side effects, such as solder short circuits.
2. Using high Tg board
Tg is the glass transition temperature, which is the temperature at which a material transitions from a glass state to a rubber state. The lower the Tg value of a material, the faster its board begins to soften after entering the reflow furnace, and the longer the time it takes to become a soft rubber state, the more severe the deformation of the board. The use of plates with higher Tg can increase their ability to withstand stress and deformation, but the cost of materials is also relatively high.
3. Increase the thickness of the circuit board
Many electronic products, in order to achieve the goal of being lighter and thinner, have left a thickness of 1.0mm, 0.8mm, or even 0.6mm for the board. This thickness is a bit difficult to maintain when the board passes through the reflow furnace without deformation. It is recommended that if there is no requirement for lightness, the board can preferably use a thickness of 1.6mm, which can greatly reduce the risk of bending and deformation.
4. Reduce the size of circuit boards and the number of splices
Since most reflow furnaces use chains to drive the circuit board forward, the larger the size of the circuit board, the more concave it will deform in the reflow furnace due to its own weight. Therefore, try to place the long side of the circuit board as the board edge on the chain of the reflow furnace to reduce the concave deformation caused by the weight of the circuit board itself. The reduction in the number of assembled boards is also based on this reason, which is when it comes to the furnace, Try to use narrow edges perpendicular to the direction of the furnace to achieve the lowest amount of concave deformation.
5. Used furnace tray fixtures
If the above methods are difficult to achieve, the final step is to use a reflow carrier/template to reduce deformation. The reason why a reflow carrier can reduce bending and warping of the board is because whether it is thermal expansion or contraction, it is hoped that the tray can fix the circuit board until the temperature of the circuit board is lower than the Tg value and begins to harden again, and can still maintain the size of the circle.
If a single-layer tray cannot reduce the deformation of the circuit board, an additional layer of cover must be added to clamp the circuit board between the upper and lower layers of trays, which can greatly reduce the deformation of the circuit board through the reflow furnace. However, this furnace tray is quite expensive and requires manual placement and recycling of the tray.
6. Use Router instead of V-Cut for board splitting
Since V-Cut can damage the structural strength of circuit board splicing, it is recommended not to use V-Cut splitting or reduce the depth of V-Cut as much as possible.
