Rigid-flex PCB board design case

[plate type]:

Rigid-flex board

[Contacts]:

1500+

[Floor]:

8th floor

[difficult]:

1. Rigid-flex board, DDR \ LVDS signal on the board, need impedance control;

2. The customer first designed the cascade, did not consider the particularity of the soft board, resulting in the actual processing can not meet the impedance requirements;

[Our countermeasures]:

Analyze the customer's original cascading and find the following issues:

1.1.6mm, 6-layer design, 3/4 layers are soft boards, the layout of 3/4 layers is 28 mils when laminated, and the thickness of PI board is the largest between 3/4 layers on the hard board. Can be 6mil, this stack is not possible;

2.According to the factory's process requirements, adjust the achievable stack, reduce the spacing of 3 / 4 layers, and increase the spacing of 2-3 layers, 4-5 layers (because the bottom layer also has impedance design); but the adjusted stack The 3/4 layer traces cannot meet the impedance requirements; if the impedance is to be met, the board thickness needs to be adjusted to 1.2 mm;

Our countermeasures:

1. After confirming with the customer, the thickness of the board cannot be changed due to the heavy components on the board to ensure its reliability;

2. By redesigning the cascading of engineers and our processes, and considering the ability to meet both thickness, impedance and processing capabilities, we recommend changing the cascading to 8 layers between 2/3 and 4/5. Add a planar layer to ensure that the 4/5 traces on the hard board have a complete reference plane and meet impedance requirements;

3. The flex board PI changed from 6mil to 5mil, reducing the thickness of the soft board to ensure its softness;