PCB Reflections when trace move from one trace to other

[hioyo]

What are the things needs to be taken to avoid reflections

1) When trace is routed in multiple layers.

 

[barry]

1) Match impedance.

 

[crutschow]

What type and frequency of signal are you referring to?

 

[hioyo]

Lets us say DDR4 address and CLOCK lines as an example

--- Updated Dec 5, 2022 ---

1) Match impedance.

May I know how to do that when the signal is moving via multiple layers

 

[barry]

Lets us say DDR4 address and CLOCK lines as an example

--- Updated Dec 5, 2022 ---

May I know how to do that when the signal is moving via multiple layers

With vias?

I don’t understand your question.

 

[FvM]

Apparently the question is referring to discontinuities caused by vias.
Additional options:
- use a signal integrity design tool to check the signal quality with actual PCB layout
- design the via padstack (e.g. by adjusting the antipad size) to match the trace impedance
- minimize number of vias used along a trace
- use backdrilling if necessary

 

[hioyo]

Apparently the question is referring to discontinuities caused by vias.
Additional options:
- use a signal integrity design tool to check the signal quality with actual PCB layout
- design the via padstack (e.g. by adjusting the antipad size) to match the trace impedance
- minimize number of vias used along a trace
- use backdrilling if necessary

This question was asked to me in an interview.The Question was "What are the precautions needs to be taken when a high speed signal is routed in multiple layers,to avoid SI problems and impedance dicontonuity issues"

My answer was put vias near to the trace where it is crossing,so that return current can take that path.

May I know the correct answer.

 

[sapphire_2010]

This question was asked to me in an interview.The Question was "What are the precautions needs to be taken when a high speed signal is routed in multiple layers,to avoid SI problems and impedance dicontonuity issues"

My answer was put vias near to the trace where it is crossing,so that return current can take that path.

May I know the correct answer.

your answer seems correct. A ground stitched VIA or a stitched capacitor is required when changing reference layer or if a signal is routing in multiple layer. This is to avoid EMI issues. You also need to make sure to re-calculate trace impedance for those layers where transition is happening.

 

[kingcrediepcba]

What are the things needs to be taken to avoid reflections

1) When trace is routed in multiple layers

The below methods can mitigate the reflections in PCB.

Impedance Matching
Design control impedance Lines
Use signal routing and layer stack-up
Differential Signaling

regards
Linda