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How to prevent PCB Board From Bending In The Reflow Oven Process

As we know, it is easy to cause circuit board bending and warping in the PCB board over-reflow oven process, so how to prevent it happens? 

1. Reduce the effect of temperature on PCB board stress

Since "temperature" is the main source of stress in the board, as long as the temperature of the reflow furnace is lowered or the temperature of the board is raised and cooled in the reflow furnace, the plate bending and the board warping can be greatly reduced. However, there may be other side effects, such as solder short circuit.

2. Use high TG plate

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, the faster the board starts to soften after entering the reflow oven, and the time to become soft rubbery state. It will also become longer, and the deformation of the board will of course become more serious. The use of a higher Tg sheet can increase its ability to withstand stress and deformation, but the price of the material is relatively high.

3. Increase the thickness of the PCB board

In order to achieve a lighter and thinner purpose, many electronic products have a thickness of 1.0mm, 0.8mm, and even a thickness of 0.6mm. This thickness is such that it is difficult to keep the PCB board from deforming after passing through the reflow oven. It is recommended that if there is no thin and light requirement, the board can use a thickness of 1.6mm, which can greatly reduce the risk of bending and deformation of the printed circuit board.

4. Reduce the size of the PCB board and reduce the number of PCB boards

Since most reflow ovens use chains to drive the board forward, the larger the size of the board will be deformed in the reflow oven due to its own weight, so try to place the long side of the board as a board edge. On the chain of the reflow furnace, the deformation of the recess caused by the weight of the circuit board itself can be reduced, and the number of the plates is also reduced. That is to say, when go to the oven, try to use the narrow side perpendicular to the direction of the furnace to achieve a low amount of depression.

5. Use the oven tray fixture

If the above method is difficult to achieve, it is to use a reflow carrier/template to reduce the amount of deformation. The reason why the furnace tray can reduce the bending of the plate is because the tray is desired regardless of thermal expansion or contraction. It is possible to hold the board and the like until the temperature of the board is lower than the Tg value and then harden again.

If the single-layer tray can not 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 two-layer trays, so that the problem of deformation of the circuit board over the reflow furnace can be greatly reduced. However, this oven tray is quite expensive, and it has to be manually placed to place and recycle the tray.

6. Use Router instead of V-Cut

Since V-Cut will destroy the structural strength of the board between boards, try not to use the V-Cut board or reduce the depth of the V-Cut.

 

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