Jul 26 , 2019

Publisher: SanDeYing

How to prevent the board from bowing and twisting issue ?

How to prevent the board from bowing and twisting issue ?

When the PCB board passes through the reflow oven, it is easy to cause problems such as plate bending and plate warping. As we all know, how to prevent the PCB board from going through the reflow oven and causing plate bending and plate warping, the following is explained for everyone:

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. Using high TG materials

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 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 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 board.

4. Reduce the size of the board and reduce the number of 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 for this reason, that is to say, when the furnace is over, the narrow side is used to cross the furnace direction as much as possible. Low amount of depression.

5. Use the oven tray fixture

If the above methods are difficult to do, * is to use a reflow carrier / template to reduce the amount of deformation, the reason that the furnace tray can reduce the bending of the plate is because whether it is thermal expansion or contraction, it is hoped The tray can hold the board until the temperature of the board is lower than the Tg value and then harden again, and the size of the garden can be maintained.

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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