Reduce the effect of temperature on board stress

Since temperature is the main source of board stress, as long as the temperature of the reflow oven is lowered or the speed of the board heating and cooling in the reflow oven is slowed down, the warpage of the PCB can be greatly reduced. However, other side effects may occur, such as solder shorts. Tg is the glass transition temperature, that is, the temperature at which the material changes from a glass state to a rubber state. The lower the Tg value of the material, the faster the board starts to soften after entering the reflow oven, and the time it takes to become a soft rubber state. It will also become longer, and the deformation of the board will of course be more serious. convert ethernet to wifi The use of a higher Tg sheet can increase its ability to withstand stress and deformation, but the price of the corresponding material is also relatively high. In order to achieve lighter and thinner thickness of many electronic products, the thickness of the board has been left at 1.0mm, 0.8mm, and even 0.6mm. Such a thickness should keep the board from deformation after passing through the reflow furnace, which is really a bit difficult. It is recommended that if there is no requirement for thinness and lightness, the thickness of the board should preferably be 1.6mm, which can greatly reduce the risk of warping and deformation of the PCB board.Since most reflow ovens use chains to drive the circuit board forward, the larger size of the circuit board will be dented and deformed in the reflow oven due to its own weight, so try to put the long side of the circuit board as the board edge. On the chain of the reflow oven, the concave deformation caused by the weight of the circuit board itself can be reduced. rs232 to ethernet adapter This is also the reason for reducing the number of panels. That is to say, when passing through the furnace, try to use the narrow side to be perpendicular to the furnace direction, which can achieve the lowest The amount of concave deformation. If the single-layer tray fixture 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 oven. . However, this oven tray is quite expensive, and you have to add labor to place and recycle the tray.