1. The effect of temperature drop on PCB board stress

Temperature is already the primary source of stress on the board, so 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 down, the phenomenon of board bending and warping can be greatly reduced. However, there may be other side effects, such as solder shorts.

2. Choose high Tg sheet materials

Tg is the glass transition temperature, which is the temperature at which the material changes from a glassy state to a rubbery state. The lower the Tg value, the faster the board begins to soften after entering the reflow furnace, and the longer the time it takes to become a soft rubbery state, resulting in more severe deformation of the board. Choosing a board with a higher Tg can enhance its ability to withstand stress and deformation, but the cost of the materials is also relatively high.

3. Add the thickness of the circuit board

Many electronic products have reduced the thickness of the board to 1.0mm, 0.8mm, and even 0.6mm in order to achieve a more lightweight purpose. It is a bit difficult to ensure that the board does not deform after passing through the reflow oven. It is recommended that if there is no lightweight requirement, the board should preferably use a thickness of 1.6mm, which can greatly reduce the risk of board bending and deformation.

4. Reduce the size of circuit boards and the number of spliced boards

Most reflow furnaces already use chains to drive circuit boards forward. The larger the size of the circuit board, the more it will sink and deform in the reflow furnace due to its own weight. Therefore, try to place the long side of the circuit board as the board edge on the chain of the reflow furnace to reduce the sink deformation caused by the board's own weight. The reason for reducing the number of spliced boards is also based on this, that is, when passing through the furnace, try to use the narrow side perpendicular to the furnace direction as much as possible to achieve the lowest sink deformation.

5. Use furnace tray fixtures

If the above methods are difficult to achieve, the ultimate solution is to use a reflow carrier/template to reduce deformation. The reason why the reflow carrier can lower the bending and warping of the board is because whether it is thermal expansion or contraction, it is hoped that the tray can fix the circuit board ratio and the temperature of the circuit board below the Tg value. After re hardening, it can also maintain the original size.

If a single-layer tray is still unable to reduce the deformation of the circuit board, an additional layer of cover must be added to clamp the circuit board between the upper and lower trays, which can greatly reduce the problem of circuit board deformation during reflow soldering. However, this furnace tray is quite expensive and requires additional manual labor to place and recycle the tray.

6. Use Router instead of V-Cut for board partitioning

If V-Cut can already damage the structural strength of the circuit board splicing, then try not to use V-Cut splitting or reduce the depth of V-Cut as much as possible.

Article source: Jiangmen PCB Customizationhttp://www.yonghongpcb.com/