Of course low DK isn't just applicable to high speed design. Dave Jones has done teardowns of some vintage precision test equipment that had components in the most sensitive ranges mounted on PTFE standoffs because the fiberglass board would be hopelessly lossy at those ranges. I specifically remember the Keithley 617 Electrometer and the Fluke 5450A Resistance Calibrator.
Yeah there is also the temperature cycling/reliability argument to be made with PTFE. Unreinforced PTFE is also really nice with precision measurement at high frequencies because the phase response is much more predictable compared to anything with a glass weave, even with spread glass. I recently had a fab house try to push glass reinforced PTFE on me for a radar module. I ended up going to a different fabricator.
That's a good question and there isn't a cheat sheet unfortunately. Not all material options will have all possible thickness values available. I think once you start using various materials you will start to see what thickness options are available. Some of the thickness values are specified in the datasheet, or you can always email the company and ask what thicknesses are available if this is not clearly specified.
Yes. I have built many boards that use wifi at 5-6 GHz on FR4 and they work fine. I have explained this many different times, up to about 3-5 GHz you can use many different materials that are FR4 grade. If you find that you want to reduce loss, you can go to a more advanced FR4 laminate, which may have loss tangent from 0.007 to 0.01, this is a good improvement on low cost FR4 but without large additional costs.
Yes these are fine for high speed designs but you should only consider this if you're operating with signal bandwidths exceeding a few GHz. Regular moderate-loss or low-loss FR4 will be fine up to WiFi frequencies (up to 6 GHz). If you're working with something at much higher bandwidths (like fast SerDes channels) then you should use a lower loss laminate that can be processed with smoother copper and with lower loss. The other thing about Duroid is the thickness, some duroid laminates will be thicker (like 7.5 or 10 mils) and these might not work if you need higher layer counts.
The meaning of "high speed" does not relate to the clock frequency. The edge rate of a signal is what determines whether we consider it a "high speed" signal. The edge rate is the rate at which a signal transitions between two levels, usually taken as the 10% to 90% rise time or the equivalent fall time. You can have very slow clocks and still have the signals running at high speed. For example, I have one design now where we are using a clock buffer that only operates at 40 MHz, but the edge rates are very fast (2-3 ns) and the device would be considered high speed digital.
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Of course low DK isn't just applicable to high speed design. Dave Jones has done teardowns of some vintage precision test equipment that had components in the most sensitive ranges mounted on PTFE standoffs because the fiberglass board would be hopelessly lossy at those ranges. I specifically remember the Keithley 617 Electrometer and the Fluke 5450A Resistance Calibrator.
Yeah there is also the temperature cycling/reliability argument to be made with PTFE. Unreinforced PTFE is also really nice with precision measurement at high frequencies because the phase response is much more predictable compared to anything with a glass weave, even with spread glass. I recently had a fab house try to push glass reinforced PTFE on me for a radar module. I ended up going to a different fabricator.
thank you very much!
You're welcome!
We used Rogers for 77GHz RADAR.
Very useful thanks. Do you know of a good cheat sheet that would help decide laminate material and thickness?
That's a good question and there isn't a cheat sheet unfortunately. Not all material options will have all possible thickness values available. I think once you start using various materials you will start to see what thickness options are available. Some of the thickness values are specified in the datasheet, or you can always email the company and ask what thicknesses are available if this is not clearly specified.
can we use FR4 material for WIFI6E? Chandravel, Librewireless
Yes. I have built many boards that use wifi at 5-6 GHz on FR4 and they work fine. I have explained this many different times, up to about 3-5 GHz you can use many different materials that are FR4 grade. If you find that you want to reduce loss, you can go to a more advanced FR4 laminate, which may have loss tangent from 0.007 to 0.01, this is a good improvement on low cost FR4 but without large additional costs.
@Altium Academy, Is RT/duroid laminate is a very good low Dk material especially for high speed designs?
Yes these are fine for high speed designs but you should only consider this if you're operating with signal bandwidths exceeding a few GHz. Regular moderate-loss or low-loss FR4 will be fine up to WiFi frequencies (up to 6 GHz). If you're working with something at much higher bandwidths (like fast SerDes channels) then you should use a lower loss laminate that can be processed with smoother copper and with lower loss. The other thing about Duroid is the thickness, some duroid laminates will be thicker (like 7.5 or 10 mils) and these might not work if you need higher layer counts.
hi, by high speed, how many MHz do you mean above?
The meaning of "high speed" does not relate to the clock frequency. The edge rate of a signal is what determines whether we consider it a "high speed" signal. The edge rate is the rate at which a signal transitions between two levels, usually taken as the 10% to 90% rise time or the equivalent fall time. You can have very slow clocks and still have the signals running at high speed. For example, I have one design now where we are using a clock buffer that only operates at 40 MHz, but the edge rates are very fast (2-3 ns) and the device would be considered high speed digital.