Why Symmetrical Layer stack is requried ?

The answer to your question depends on who is telling you a symetrical stack is a requirement.

Although a PCB can be designed, and built with an asymetrical layer stack, this is not recommended. Asymetric boards are more likely to warp when subjected to the assembly processes.

For a more complete answer, consult with the fabrication facility that will be making the board to discuss your specific design.

Regards,

Harold Pattie CID+

harold.pattie@ericsson.com

Thank you Very much for response...

 Is there any relation with high speed signals and symmetrical layer stackup. How symmetrical layer stackup is helpful.

I have designed a board already with Asymmetrical Layer Stack up which has most of High speed signals, wil Asymmetrical Layer Stack up  will have any major issue on performance of board.

 Counting on your valueable inputs.

 Thans in Advance.

:-)

Without knowing the specifics of your design, this is a difficult question to answer. The first question would be how do you define board performance? Also, what is your high speed, and what is the edge rate of your signals?

The quality of your signaling is more dependent on issues like return path, cross talk, and impedance.

I would refer you to Eric Bogatin's "Be The Signal" lecture series.

Symetric or Asymetric board stack ups have more to do with the mechanical aspects of form, fit, and reliability.

Regards,

Harold Pattie CID+

harold.pattie@ericsson.com

 As I understand it a symetrical stackup is a requirement of the solder process. A non symetrical card will have different co-efficients of thermal expansion either side of the centre of the card stack - therefore it will curve when heated.

My approach is  to know is there any Asymmetrical Layer Stack will effect on board performance with respect to life time, EMI and EMC etc...

expecting some genral gudliness.

 Thans in Advance.