PCB Technical - How to avoid the PCB board becaome warped?

After reflow the PCB board easy become warped,,How to avoid it? Let's discuss it.:

Prevention:

- Drying board before cutting. Usually 150 degrees 6 – 10 hours, remove the water vapor inside the board, to further cure the resin completely to eliminate the stress within the board; preheating bake board, both inner or double need!
- Attention should be paid to the latitude and longitude of the multi-layer laminated plate before curing.

- Laminated thickness to eliminate stress plate cold, trim egde
- Bake board: 150 degrees 4 hours

- the best sheet without mechanical brushing, it is recommended to use chemical cleaning; plating when the use of special fixtures to prevent bending the board folded.

- After the surface treatment on the flat marble or steel cooling to room temperature or air bed cooling and cleaning;