How to prevent PCB board from bending and warping in back welding furnace

In PCB board backwelding furnace prone to plate bending and plate warping, we all know, so how to prevent PCB board backwelding furnace plate bending and plate warping, the following for you to elaborate:

1. Reduce the influence of temperature on the stress of PCB board

Since "temperature" is the main source of plate stress, so as long as reducing the temperature of the backwelding furnace or slow down the heating and cooling speed of the plate in the backwelding furnace, the bending and warping of the plate can be greatly reduced. But there may be other side effects, such as a short circuit in the solder.

2. High Tg plate is used

Tg is the glass conversion temperature, that is, the temperature at which the material changes from glass state to rubber state. The lower the Tg value is, the faster the board will become soft after entering the backwelding furnace, and the longer it will take to become soft rubber state, the more serious the deformation of the board will be. The plate with higher Tg 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

Many electronic products in order to achieve the purpose of thinner, the thickness of the board has been left 1.0mm, 0.8mm, and even 0.6mm thickness, such a thickness to keep the board after the welding furnace without deformation, really a bit of a force, it is suggested that if there is no light and thin requirements, the board can use the thickness of 1.6mm, Can greatly reduce the risk of bending and deformation of the plate.

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

Since most backwelding furnaces use chains to drive the circuit board forward, the larger the size of the circuit board will sag and deform in the backwelding furnace because of its own weight, so try to put the long side of the circuit board as the board side on the chain of the backwelding furnace, you can reduce the weight of the circuit board caused by the sag deformation, reduce the number of plates is also based on this reason, That is to say, when the furnace, try to use the narrow side of the vertical direction of the furnace, can reach the lowest depression deformation.

5. The tray fixture has been used

If the above methods are difficult to achieve, * is to use the reflow carrier/template to reduce the deformation. The reason why the Reflow carrier/template can reduce the bending and warping of the plate is that whether it is hot expansion or cold contraction, It is hoped that the tray can hold the circuit board and maintain the size of the garden when the temperature of the circuit board is below the Tg value and begins to harden again.

If a single layer of tray can not reduce the deformation of the circuit board, it is necessary to add a layer of cover, the circuit board with two layers of tray clip up, so that you can greatly reduce the circuit board over the welding furnace deformation problem. But the trays are expensive, and you have to add labor to place and retrieve them.

6. Use the Router instead of the V-Cut

Since V-cuts can damage the structural strength of the board, try not to use V-Cut subboards, or reduce the depth of the V-Cut.

Welding resistance film design skills

In fact, no matter what type of PCB design software you prefer to use, soldering masks are optional. The welding mask can be easily designed by completing the filling of a few parameters. Some software even offers automatic welding of masks. 

Prior to the actual design, it is essential to contact a contracted PCB manufacturer to properly understand their capabilities in terms of the thickness of the welded mask and the minimum spacing between the brazing pads, which are not cured per plate. 

Boards will fail due to silly problems with welding masks (such as not enough openings, too many openings, and a mismatched number of openings to the brazing pads in the circuit plane). These problems can result from negligence or design document changes, but they do take a long time. Some even cause disasters. Therefore, your design document is well worth a close look.