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What is the best way to control the impedance of a PCB substrate?

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garypang

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Hi,

I am designing a PCB substrate (FR4 with 1mm thickness) to place 4 pads chip on top, and then it has a thru hole connect to the bottom layer of the PCB, and the PCB will be mounted on a flex circuit.

What is the best way in controlling the impedance of the PCB substrate since it do not have traces (only pads with via holes) while ensuring its signal integrity on high speed?

Thank you and hope that someone can help in this matter.
 

marce

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Re: PCB Substrate Design

Could you provide a bit more detail please.
 

garypang

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Re: PCB Substrate Design

Hi,

I have a chip with 4 150um x 150um pads and I would like to attach it on a FR4 substrate and mount on a PCB (see attached figure).
Basically the FR4 will have a dielectric of 4.6 and the flex will have dielectric of 3.5.

How can I ensure the impedance control throughout the design from the chip to the flex?

Thank you and hope someone can help in this matter.

Flex Rigid.PNG
 

marce

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Basicly use an impedance calculator such as:
Microstrip Impedance | Electrical Engineering Tools | EEWeb
and work out the required width of track for the ridgid part and the flex part to keep the same impedance, or better still, if you have a manufacturer in mind as them for information as they probably have the Polar tools and will give you a more definitive answer based on thier fabrication requirements and preffered materials.
 

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