FR-4 and GF material

I think you will find they are the same material, Glass Fibre reinforced...

I've always referred to the pcb material as GFR-4 but there again I'm awkward!

John.

FR-4 = Fire Retardant class 4

If FR-4 means class 4 fire retardent and GF means glassfibre then GF is one of a class of FR-4 materials.

I get the impression that FR-4 is a subset of GF. If I had one of each in hand, I would go with FR-4. The stuff has been around since Christ was a corporal and it is well defined. At microwave frequencies you can design capacitors using the PC board as the dielectric between two pads on opposite sides of the circuit board. I concede of course that these are very low capacitance, but that is what you need at high frequencies. I am sure there are other more modern materials than FR-4, but I haven't looked at this in years.

Bill

Bill, back in the mid 70's at Marconi Instruments we ditched using GFR-4 for microwave work as the dielectric was too variable for microstrip calculations.

Instead we used ceramic substrates for the microstrip filters and transmission lines...

John.

John...

Makes sense to me... but I am kinda curious. Is the ceramic more succeptable to fracture? such as dropping it on the floor? I can remember an assembly worker dropping a whole tray of stuffed pc boards on the floor. Luckily they had already been wave soldered so we didn't have components all over the floor also... and boy am I glad it was not me that did it.

Sincerely

Bill

Ceramics which is often Alumina in thin white sheet is very hard material and it is neither easy to break or grid or drill into it. Lots of strength in it and is very high temperature material. Alumina which is basically Al2O3 is not affected by moisture. Alumina with impurities may be a bad material and hence to be specifically that is used for Hybrid Circuits. Glass may break so such PCBs to be used with care. Glass are also ceramics. Quartz or fused silica is highly fragile.

FR-4 is cheap compared to Alumina substrates. I will like to use it for charge amplifier designs and found a factory in Korea willing to do it for about US$3 per 2"x0.6" PCB in 10000 lots. I think FR-4 will be less than $1 for the same thing. If I ask for hole drilling then price will be higher.

FR-4 is epoxy filled Glass Fiber. Epoxy is organic filler and may differ considerably in its chemical contents. Glass type also may differ. Hence, FR-4 is something to be looked at manufacturer specific material with some similarities.

they often use thin teflon for stripline transformers and filters etc in the microwave region, in various thicknesses to make the right match. Being flexible it is immune to breakage.

I am not sure what the max frequency is? alumina and beryllium oxide also are good at extreme frequencies. The use of beryllium oxide will require a poison label on anything that uses it. 100 Mg is the LD50 for a 100 Kilo person

Teflon or FTFE materials are good for low current, high temperature and flexibility. However, I will like to add here that they are static prone and used as Electret Materials for radiation Sensing and if static charge stored inside is not removed then the circuit may work like an UFO material.

MEANWHILE... BACK AT THE RANCH...

We have been getting into the more exotic problems with PCB materials. We don't know the application so assuming that your product is not in the GHz range, and you are not trying to do microwave tricks, I would just go for FR-4. As John said earlier, they gave up using FR-4 back in the 1970's for microwave work. This shows how long it has been around. I would call it the standard of the industry if you are not getting too exotic.

FR-4 is very common material used for PCB. I am now worried about using it for GHz frequencies. Its capacitance is very unpredictable. I prefer to place components in air rather than on PCB.

Shyam... I would recommend that you ask John (Electroman) about that. He proposed PC substrates which ( I guess) have a more consistant value of epsilon than FR-4 over batch, and over frequency...

Bill