PCB Technical - Prevent PCB board bending and board warping when passing through the reflow furnace

Prevent PCB board bending and board warping when passing through the reflow furnace

Everyone knows how to prevent PCB bending and board warping from going through the reflow furnace. The following is an explanation for everyone:

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 in the reflow oven is slowed, the occurrence of plate 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 starts to soften after entering the reflow oven, and the time it takes to become soft rubber state 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, or even 0.6mm. Such a thickness must keep the board from deforming after the reflow furnace, which is really difficult. It is recommended that if there is no requirement for lightness and thinness, 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 circuit board and reduce the number of puzzles

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. Low dent deformation.

5. Used furnace tray fixture

If the above methods are difficult to achieve, *reflow carrier/template is used to reduce the amount of deformation. The reason why the reflow carrier/template can reduce the bending of the plate is because whether it is thermal expansion or cold contraction, it is hoped The tray can hold the circuit board and wait until the temperature of the circuit board is lower than the Tg value and start to harden again, and can also maintain the size of the garden.

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 oven tray is quite expensive, and it also has to be manually placed and recycled.

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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