How to prevent the occurrence of rocker when the PCB board goes through the reflow furnace
Everyone knows that PCB boards are prone to bending and board warping after going through the reflow process. So how to prevent it?
1. Reduce the influence of temperature on PCB board stress
Since temperature is the main source of board stress, as long as the temperature of the reflow oven is lowered or the rate of heating and cooling of the board is slowed, the occurrence of bending and warpage can be greatly reduced. However, other side effects may occur, such as solder short circuit.
2. Using high Tg sheet
Tg is the glass transition temperature, that is, the temperature at which the material changes from the glass state to the rubber state. The lower the Tg value of the material, the faster the board begins to soften after entering the reflow furnace, and the time it takes to become soft rubber It will also become longer, and the deformation of the board will of course be more serious. Using a higher Tg plate can increase its ability to withstand stress and deformation, but the price of the material is relatively high.
3. Increase the thickness of the circuit board
In order to achieve the purpose of lighter and thinner for many electronic products, the thickness of the board has left 1.0mm, 0.8mm, and even a thickness of 0.6mm. It is really difficult for such a thickness to keep the board from deforming after the reflow furnace. It is recommended that if there is no requirement for lightness and thinness, the board should be 1.6mm thick, which can greatly reduce the risk of bending and deformation of the board.
4. Reduce the size of the circuit board and reduce the number of panels
Since most of the reflow furnaces use chains to drive the circuit board forward, the larger the size of the circuit board will be due to its own weight, dent and deformation in the reflow furnace, so try to put the long side of the circuit board as the edge of the board. On the chain of the reflow furnace, the depression and deformation caused by the weight of the circuit board can be reduced. The reduction in the number of panels is also based on this reason. That is to say, when passing the furnace, try to use the narrow edge to pass the furnace direction as far as possible. The amount of depression deformation.
5. Used tray fixture
If the above methods are difficult to achieve, the last is to use the tray to reduce the amount of deformation. The tray can reduce the bending of the board because the tray can be used to fix the circuit board regardless of thermal expansion or cold contraction. After the temperature of the circuit board is lower than the Tg value and starts to harden again, the original size can be maintained.
If the single-layer pallet cannot reduce the deformation of the circuit board, a cover must be added to clamp the circuit board with the upper and lower pallets, which can greatly reduce the problem of the deformation of the circuit board through the reflow furnace. However, this furnace tray is quite expensive, and manual labor is required to place and recycle the trays.
6. Use Router instead of V-Cut to use the sub-board
Since V-Cut will destroy the structural strength of the panel between the circuit boards, try not to use the V-Cut sub-board or reduce the depth of the V-Cut.
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