FR4 laminate [help me]

hi
about FR4 laminate: what's the highest frequency of using it? is it responsing in 1200MHz-1400Mhz?

the main there are some problems in FR4
1) high loss tangent
2) the εr of it is changing with frequency "nonlinearly"

so u can use it with some precautions check use trances as short as possible ,
and u need to charctrize the FR4 using some TLs to check the attenuation and so it

i have used FR4 to design 3 GHz oscillator , it worked very good but i needed to tune the design 2 or three time , to adjust the resonator

khouly

There is no reason not to use FR-4 at very high frequencies. We have used it many times at 10GHz or even higher. Also for digital 10Gbps prototype designs...

elec350 said:

hi
about FR4 laminate: what's the highest frequency of using it? is it responsing in 1200MHz-1400Mhz?

Click to expand...

There are some problems created by your incomplete questions.
Depending how many layers you have on your design, and how the stack is configured you must take in account about 10% error of the FR4 epsilon. Based on the resin content on laminations, the epsilon is increasing between 3.6 to 4.5.
That's why if you're designing an oscillator based on distributed PCB components you need to tune it. But for microstrip short lines, there is no problem of using FR4 up to 10Ghz. As small the layer numbers and limited lamination per layer, as better.

There is a common error when discussing PCB laminates. FR4 is NOT one material with one set of specifications. It is a CLASS of materials based on its flamibility. FR4 is an abbreviation for FLAME RETARDANT (FR) class 4 material.

There are FR4 laminates with properties that are entirely suitable for use in the frequency range that you are planning to use. At our company, we normally use a high Tg FR4 with Er=3.5 for boards with fast risetime digital, and RF into the 8GHz range.

I suggest you talk with your board fab, and possilby some of the laminate manufacturers to see what FR4 materials are available to you.

Remember, FR4 is not one material - it is an entire class of materials with different properties depending on the type and amount of glass and resin.

FR4 properties vary with manufacturer to manufacturer too !

Before using it make a test run with one manufacturer's FR4 and make some preliminary basic tests.
Also some preliminary simulations are also proposed.

But worth trying, if cost is an important factor.
It can be used up to 8 - 10 GHz without problems, in low Q applications.

At your frequencies FR4 should work fine. Material cost drives the use of this PCB laminate over the wide range of other choices.

I start looking at other alternatives above 2 GHz but as you can see there is not universal agreement about how high in frequency one can reasonably push the material. That choice depends upon your particular parameters.

I have used it up to 5 GHz. You will not be able to do any filters or any low loss lines in it.

Another consideration is the mechanical strength of FR4. It can be a fairly good structural support and epoxy adhesives stick well. I have used it in antenna structures more for the strength particularly when it can be a real trick to stick things to a teflon based PCB material.