Dougal Stewart,
> On another issue, I always get confused when people talk about FR3,
> G10, G200, CEM 1, CEM3 etc. I know what FR4 is - glass fibre
> reinforced epoxy laminate - but could someone put the other
> materials into similar English for me?
Robert,
Hopefully I can give a bit of information to you that may help, I was
in the same boat too...I had to dig around in some old NEPCON proceedings
to freshen-up a bit, so here goes:
First off, FR-4 is a widely used generic term to describe the standard
epoxy/fiberglass/copper laminate...but it doesn't fully or accurately
describe the material.
"FR" really stands for "Fire-retardant", and the "4" designates an
electronic grade glass fiber that has been woven into cloth. Prior to
that, back in the early days, UL began to require laminate materials to
be fire retardant in which chemicals such as bromine were added to a
kraft or alpha-cellulose paperbase material impregnated with a phenolic
resin and designated FR-2. Epoxy was then used with the paperbased
material and designated FR-3.
There are several grades of fiberglass reinforced laminates in which
the designations change depending on the bonding resins used.
Here are several:
* G-5 - Uses a melamine resin and has great mechanical properties, but is
difficult to machine or drill. The military calls it GMG and GME
styles.
* G-7 - Uses a silicone resin.
* G-10 - Uses an epoxy resin as FR-4 does, but it is not fire retardant.
* G-11 - Also uses and epoxy resin but has better mechanical properties
than does G-10, it is also harder to machine.
* FR-5 - Is the Fire retardant version of G-11.
* GPO-1 - Uses a polyester resin and a fiberglass "mat" material and is
less expensive than woven cloth. The mat material is chopped
into bits and randomly layered.
* Expanded Teflon - With a Polytetrafluoroethylene resin (PTFE resin) is
one of the highest costing materials and has excellent
low dielectric constant properties for high frequency
microwave circuits, but suffers from poor dimensional
stability...it can shrink 1-2% after copper etching.
A bit about the reinforcing materials.....
Fiberglass accounts for around 95% of the reinforcing material used in
PC board laminates. The fiberglass is designated into two types; E-glass
and S-glass, both are made of soda lime fibers bundled into yarn and
woven into cloth.
The E designates it as electrical class, and the S designates it as
high strength class. There is another type glass that is designated D
class which offers a lower dielectric constant, but it is not as strong
as either the E or S class glass....(say that 10-times real fast!!)
Of course there are different grades of weave density which determines
how smooth the surface of the laminate is, how many layers are
laminatable, and the CTE in the Z-axis.
Other reinforcing materials used in special applications include:
quartz, aramid (kevlar 29 & 49) fiber, ceramic, insulated steel, anodized
aluminum, and copper bonded to flexible substrates such as mylar or
polyimide.
A bit about the bonding resins.....
Difunctional epoxy has been the most widely used type of epoxy for
board laminates. The type of epoxy chosen is based on the requirements
needed for the assembly. Two other types of epoxy's are used which are
known as multifunctional, and tetrafunctional epoxy, each type having a
progressively higher Tg than the previous one.
There are five areas that are analyzed when deciding the type of resin to
be used in the laminate:
Glass transition temperature
Relative dielectric constant
Loss tangent
Thermal conductivity
coefficient of thermal expansion
A few other types of resin used in special applications are:
* Bismaleimide Triazine (BT) resin also known as cyanate ester resin.
* Polyimide resin (also used in Kapton tape and TAB)
* Polysulfone (a thermoplastic polymer resin)
* Polyetherimide (also a thermoplastic polymer resin)
Well, I'm about tapped-out as far as anymore knowledge on laminates...
Most of the time, the only thing I'm concerned with about PC boards is
whether or not the darn things solder good!!
I hope this was of some help,
////
| @@ / Steve Gregory
C ) Process Training Engineer
////
\_o Pragmatech Incorporated
| @@ / 101 Nicholson Lane
C ) San Jose, California 95134
\_o ////
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| @@ / Phone:(408) 943-1151
C ) Fax:(408)943-1461
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