high dielectric constant (>>10) laminate

[felinofico]

high dk laminates

hi,
i'm designing a coupled microstrip tx line, but my line needs to have 25ohm impedance and that's difficult to obtain with a standard laminate (i.e. FR4). so i'm searching a high dielectric constant (>>10) laminate: can anyone help me? do someone know a high dk laminates manufacturer? i've already searched in various catalogues (arlon, rogers, taconic) without results.
thanks,
fred

 

[senilicus]

Re: high dk laminates

trace impedance is controlled by the Dk , the distance to the reference plane and the trace width. If you need to control the impedance, the most easiest way to do is changing the trace width and/or the distance to the reference plane.
Also check with your pcb fabricator for other materials

The best way to handle is to contact your board manufacturer and explain the problem to them. They can help you out with materials and stackups.

 

[FvM]

Re: high dk laminates

DK 10 is achievable with fair RF properties with ceramic substrates. DK >> 10 is rubbish, because it would allow only very poor quality factors, if available at all as a standard substrate. As said, with an appropriate geometry 25 ohm is achievable with FR4 although it isn't a good RF substrate.

 

[felinofico]

Re: high dk laminates

the line that i'm designing it's a high voltage nanosecond pulse forming network: i need that the gap between the strips is at least 1.5mm. with this gap value with a standard RF substrate in order to obtain 25 ohm the subtrate height and the traces width takes very high values, that are not achievable. losses and low quality factors are not so important in my application.
do someone have a solution?
thanks

 

[FvM]

high dk laminates

The high DK substrate's dielectrical strength may be considerably lower than of standard material. I noticed, that Rogers even don't specify it in the datasheets.

Generally, I think there are many design options to build the intended circuit, you aren't restricted to simple microstrip. It's just engineering, I'm sure, others have solved similar problems before.

 

[felinofico]

Re: high dk laminates

i know that i have other solutions, but i must do things in this way, with microstrips.
i hope i will find a solution