14 Fundamentals of Advanced Materials …
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applications thanks to its excellent combination of lower cost, electrical, mechanical,
and chemical properties. NE-glass found its use in some niche applications where
low CTE, low dielectric constant and low loss factor is preferred. S-glass has higher
mechanical strength but wore out drill bit much faster in making PTH or via holes.
D-glass and quartz have not gain much attention in substrate and PWB applications.
The fiberglass filament is first twisted into a yarn and the fiberglass yarn is then
woven into different cloth styles. The filament diameter usually ranges from 3.8 to
13.0 μm. The woven fiberglass cloth weight ranges from 0.019 to 0.234 kg/m
2 [3].
Considering the considerable numbers of glass compositions, filament diameters,
yarn types, and the number of different weave patterns, there are abundant number
of fiberglass cloth combinations that can be manufactured. However, plain woven
fiberglass cloth is most commonly used due to its good resistance to slippage and
fabric distortion during laminate core processing. Coupling agents such as epoxy
silane and amino silane are commonly applied to the surface of fiberglass to improve
the adhesion between the fiberglass and resin systems. Other types of surface finishes
may be applied to the surface of fiberglass for the filament production, abrasion and
ESD prevention, and aiding the holding of the filaments together.
Non-woven fiberglass can be sub-categorized into two types based on the orientation randomness of glass fibers: glass matte and linear continuous filament fiberglass.
Glass matte either consists of randomly oriented one to two inch long chopped fiberglass strand matte distributed evenly and bonded together or consists of continuous
strands of fiberglass in a random, spiral orientation. As a result of the fiberglass
loading, orientation randomness, and lack of the restriction from fiber to fiber, it
has poor slippage resistance and larger localized property variation. Therefore, glass
matte is only used for simple applications such as CEM-3 and G-10 cores. Linear
continuous filament fiberglass consists of three layers: bottom, middle, and top. The
fiberglass filaments in bottom and top layers are in parallel but perpendicular to the
filaments in the middle layer, and the number of linear filaments in the middle layer
is double of that for the top and bottom layers. This type of filament layout improves
the laminate core dimensional stability, but its usage is very limited [3].
The full name of aramid is aromatic polyamide, which is commonly used in
bullet-proof vests. One typical molecular structure of aramid material is presented
in Fig. 14.2. It contains amide functional group and rigid phenylene rings. The polar
amide group forms hydrogen bond among the molecular chains and form crystals,
and the phenylene rings limits the chain folding. The two effects provide aramid
fiber high strength, high thermal resistance, high dimensional stability, high chemical resistivity, and light weight (compared to fiberglass) [4]. Since the rigid polymer
chain is so tightly bonded to many other chains by the hydrogen bonding the chain
is stretched. When the material is heated, the free volume to each chain segment
increases and the chain segment curls back. Therefore, aramid fiber has negative CTE
along the axial direction. This negative CTE property is often leveraged to control the
substrate core CTE. Since aramid molecule heavily contains carbon atoms, a charcoal layer is formed at the surface during burning and prevents continuous burning.
Therefore, the aramid material has a self-retarding property. Aramids can easily
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applications thanks to its excellent combination of lower cost, electrical, mechanical,
and chemical properties. NE-glass found its use in some niche applications where
low CTE, low dielectric constant and low loss factor is preferred. S-glass has higher
mechanical strength but wore out drill bit much faster in making PTH or via holes.
D-glass and quartz have not gain much attention in substrate and PWB applications.
The fiberglass filament is first twisted into a yarn and the fiberglass yarn is then
woven into different cloth styles. The filament diameter usually ranges from 3.8 to
13.0 μm. The woven fiberglass cloth weight ranges from 0.019 to 0.234 kg/m
2 [3].
Considering the considerable numbers of glass compositions, filament diameters,
yarn types, and the number of different weave patterns, there are abundant number
of fiberglass cloth combinations that can be manufactured. However, plain woven
fiberglass cloth is most commonly used due to its good resistance to slippage and
fabric distortion during laminate core processing. Coupling agents such as epoxy
silane and amino silane are commonly applied to the surface of fiberglass to improve
the adhesion between the fiberglass and resin systems. Other types of surface finishes
may be applied to the surface of fiberglass for the filament production, abrasion and
ESD prevention, and aiding the holding of the filaments together.
Non-woven fiberglass can be sub-categorized into two types based on the orientation randomness of glass fibers: glass matte and linear continuous filament fiberglass.
Glass matte either consists of randomly oriented one to two inch long chopped fiberglass strand matte distributed evenly and bonded together or consists of continuous
strands of fiberglass in a random, spiral orientation. As a result of the fiberglass
loading, orientation randomness, and lack of the restriction from fiber to fiber, it
has poor slippage resistance and larger localized property variation. Therefore, glass
matte is only used for simple applications such as CEM-3 and G-10 cores. Linear
continuous filament fiberglass consists of three layers: bottom, middle, and top. The
fiberglass filaments in bottom and top layers are in parallel but perpendicular to the
filaments in the middle layer, and the number of linear filaments in the middle layer
is double of that for the top and bottom layers. This type of filament layout improves
the laminate core dimensional stability, but its usage is very limited [3].
The full name of aramid is aromatic polyamide, which is commonly used in
bullet-proof vests. One typical molecular structure of aramid material is presented
in Fig. 14.2. It contains amide functional group and rigid phenylene rings. The polar
amide group forms hydrogen bond among the molecular chains and form crystals,
and the phenylene rings limits the chain folding. The two effects provide aramid
fiber high strength, high thermal resistance, high dimensional stability, high chemical resistivity, and light weight (compared to fiberglass) [4]. Since the rigid polymer
chain is so tightly bonded to many other chains by the hydrogen bonding the chain
is stretched. When the material is heated, the free volume to each chain segment
increases and the chain segment curls back. Therefore, aramid fiber has negative CTE
along the axial direction. This negative CTE property is often leveraged to control the
substrate core CTE. Since aramid molecule heavily contains carbon atoms, a charcoal layer is formed at the surface during burning and prevents continuous burning.
Therefore, the aramid material has a self-retarding property. Aramids can easily