ROOT CAUSES AND SOLUTIONS FOR WARPING PCB

The cause of board warping is a combination of different factors, the root causes and solutions might include -

[DESIGN]

1. Long and narrow shapes, or other irregular shapes

2. Boards with blind and buried holes; boards require via plugging

boards with blind and buried holes require multiple times of lamination. High temperature will be applied during lamination and via plugging.

3. Asymmetrical stack-up structure

4. Imbalanced copper pour on different layers

imbalanced copper pour might result in unmatched thermal expansion.

5. More and larger tabs on panel structure

Copper pattern on panel handling edges helps reinforce the boards

[MANUFACTURING]

6. Lead-free soldering manufacturing

Compare with lead soldering, higher temperatures required for lead-free solder, and temperature is one of major source of impacting PCB stress and board warpage.

7. High-TG material (High-TG FR4)

High-TG FR4 has better performance of PCB heat resistance, thermal expansion and other characteristics.

8. FR4 Core orientation on each layer

The CTE(coefficient of thermal expansion) of FR4 Core material are slightly different by portrait and landscape orientation.

9. Running boards through reflow with carrier pallet helps warpage control