High Speed Flex Circuit Design

Hi,

I have recently designed a 2 layers high speed flex circuits where top layer is the high speed trace and bottom layer is the ground plane.

I have designed the flex using microstrip method.

There are 2 variations of the design. One of them the soldering pad (for high speed trace >10GHz) is designed with via hole (see the attached image) and another one without.



From the measurement data for the transmission loss (S21) of the high speed trace, the design with via hole on soldering pad has much higher losses as compared to the one without.
Are there any way to compensate the losses caused by the via hole on the high speed trace? The via hole is used for simpler assembly during soldering process.

Thank you and hope that someone can provide your comment on this matter.

There are a few FCC connectors that allow double sided contacts, so you can avoid vias.
Have a look at:
http://www.molex.com/molex/products...tle=Introduction&parentKey=ffc_fpc_connectors

marce said:

There are a few FCC connectors that allow double sided contacts, so you can avoid vias.
Have a look at:
http://www.molex.com/molex/products...tle=Introduction&parentKey=ffc_fpc_connectors

Click to expand...

But the flex is for high speed (>10GHz) transmission. Can those connector transmit with low losses at high frequency?

Thank you.

It is a pointer to what is available. I had a similar problem and had to look for connectors that would allow me to do double sided flexis. You can also look at Samtec and Hirose products to name a couple more manufacturers.
In this instance you will have to do the research, what I did is covered by NDA's and such like. Sorry.