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How to prevent board bending and board warping when PCB board passes through reflow furnace?

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Update time : 2020-05-26 10:08:18
Everyone knows that board bending and board warpage are prone to occur when PCB board passes through reflow furnace, so how to prevent it? The following is for everyone:

1. Reduce the effect of temperature on the PCB board stress
Since temperature is the main source of board stress, as long as the temperature of the reflow furnace is lowered or the speed of heating and cooling of the board in the reflow furnace is slowed down, the occurrence of board 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 glass to rubber. The lower the Tg value, the faster the board begins to soften after entering the reflow furnace, and the time to become soft rubber will also become longer, and the amount of deformation of the board will of course become more serious. The use of higher Tg board 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 a thinner and lighter goal for many electronic products, the thickness of the board is already 1.0mm, 0.8mm, or even 0.6mm. It is really a bit difficult for the thickness to keep the board from deforming after reflow furnace. It is recommended that if there is no requirement for lightness and thinness, the board can preferably 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 circuit board and reduce the number of puzzles
Since most reflow furnaces use chains to drive the circuit board forward, the larger size of circuit board will be deformed in the reflow furnace due to its own weight, so try to put the long side of the circuit board as the edge of the board on the chain of the reflow oven, you can reduce the deformation caused by the weight of the circuit board itself. The reduction of the number of boards is also based on this reason, that is to say, when passing the furnace, try to use the narrow side perpendicular to the direction of the furnace to achieve the lowest amount of sag deformation.

5. Use the oven tray fixture
If the above methods are difficult to achieve, the last thing is to use a reflow carrier/template to reduce the amount of deformation. The reason why the reflow carrier/template can reduce the bending of the board is whether it is thermal expansion or contraction, it is hoped that the tray can hold the circuit board until the temperature of the circuit board is lower than the Tg value and begins to harden again, it can still maintain the original size.
If the single-layer tray still cannot reduce the deformation of the circuit board, you must add another layer of cover to clamp the circuit board with the upper and lower two-layer trays. This can greatly reduce the problem of deformation of the circuit board through the reflow oven. However, this kiln tray is quite expensive, and manual labor is required to place and recycle the tray.

6. Use Router instead of V-Cut board
Since V-Cut will destroy the structural strength of the puzzle between the circuit boards, try not to use the V-Cut sub-board, or reduce the depth of the V-Cut.