14 Fundamentals of Advanced Materials …
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many cases, some of these properties are correlated each other. Substrate manufacturers must study and understand all these properties and their interactions in an
integrated way. The most common bulk material properties relevant to microelectronic packaging substrates and PWB applications include glass transition temperature (T g ), coefficient of thermal expansion (CTE), modulus, toughness, flexural
strength, density, decomposition temperature (T d ), flammability, moisture absorption, chemical resistance, dielectric constant or permittivity, dissipation factor or
loss tangent, volume resistivity, electrical strength, and dielectric breakdown. The
common surface properties of the base materials include surface roughness, surface
energy or surface tension, surface resistivity, and arc resistance. The measurement
of these properties is beyond the scope of this chapter. However, readers can refer
to IPC-TM-650, ASTM, and JEDEC standards for testing procedures of most of the
mentioned properties.
Glass transition temperature (T g ) is used to describe the response of a molecular structure movement as a whole to the temperature change for solid amorphous
materials. For polymeric materials used in microelectronic substrates, glass transition refers to the material change from rigid glassy state to soft rubbery state. T g
is a temperature above which the free volume becomes large enough for macromolecular chain segments to move and change their conformation. Below T g , the
chain segments does not have sufficient free volume and they are locked in place.
Although T g can be measured by multiple methods and often expressed by a single
temperature point, the glass transition occurs across a temperature range. T g is a
critical polymeric material property as most of the material properties mentioned
above change greatly during the glass transition region. Among them, the CTE and
modulus changes during the glass transition region often catch most attention in base
material selection for microelectronic substrate applications.
The coefficient of thermal expansion (CTE) is an intrinsic physical property of a
material. Like most of materials, the base materials used in substrates expand when
they are heated and contract when they are cooled. The CTE can be calculated by
l/(l · T ), where l is the linear dimensional change in a given direction, l is the
original dimension in the direction, and ΔT is the change of temperature. Starting
with the same dimensional length, materials with larger CTE expand or contract
more over same range of temperature change. CTE is one of key physical parameters
in the selection of base materials because the large CTE differences among the
substrate base materials generate large internal stresses and can result in interface
layer delamination and substrate warpage.
Modulus is a mechanical property of a solid material, measuring a material’s
resistance to being deformed to an applied force, often expressed by Young’s modulus
and dynamic modulus. The Young’s modulus is also called tensile modulus, or elastic
modulus. It is the slope of stress-strain curve in the elastic deformation region of
a material. The Young’s modulus is commonly used for elastic materials such as
glasses, ceramics, and metals. The dynamic modulus is the ratio of stress to strain
under vibratory conditions. It is more commonly used for viscoelastic materials
such as polymeric materials. The dynamic modulus consists of two components:
storage modulus and loss modulus. The storage modulus measures the stored energy
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many cases, some of these properties are correlated each other. Substrate manufacturers must study and understand all these properties and their interactions in an
integrated way. The most common bulk material properties relevant to microelectronic packaging substrates and PWB applications include glass transition temperature (T g ), coefficient of thermal expansion (CTE), modulus, toughness, flexural
strength, density, decomposition temperature (T d ), flammability, moisture absorption, chemical resistance, dielectric constant or permittivity, dissipation factor or
loss tangent, volume resistivity, electrical strength, and dielectric breakdown. The
common surface properties of the base materials include surface roughness, surface
energy or surface tension, surface resistivity, and arc resistance. The measurement
of these properties is beyond the scope of this chapter. However, readers can refer
to IPC-TM-650, ASTM, and JEDEC standards for testing procedures of most of the
mentioned properties.
Glass transition temperature (T g ) is used to describe the response of a molecular structure movement as a whole to the temperature change for solid amorphous
materials. For polymeric materials used in microelectronic substrates, glass transition refers to the material change from rigid glassy state to soft rubbery state. T g
is a temperature above which the free volume becomes large enough for macromolecular chain segments to move and change their conformation. Below T g , the
chain segments does not have sufficient free volume and they are locked in place.
Although T g can be measured by multiple methods and often expressed by a single
temperature point, the glass transition occurs across a temperature range. T g is a
critical polymeric material property as most of the material properties mentioned
above change greatly during the glass transition region. Among them, the CTE and
modulus changes during the glass transition region often catch most attention in base
material selection for microelectronic substrate applications.
The coefficient of thermal expansion (CTE) is an intrinsic physical property of a
material. Like most of materials, the base materials used in substrates expand when
they are heated and contract when they are cooled. The CTE can be calculated by
l/(l · T ), where l is the linear dimensional change in a given direction, l is the
original dimension in the direction, and ΔT is the change of temperature. Starting
with the same dimensional length, materials with larger CTE expand or contract
more over same range of temperature change. CTE is one of key physical parameters
in the selection of base materials because the large CTE differences among the
substrate base materials generate large internal stresses and can result in interface
layer delamination and substrate warpage.
Modulus is a mechanical property of a solid material, measuring a material’s
resistance to being deformed to an applied force, often expressed by Young’s modulus
and dynamic modulus. The Young’s modulus is also called tensile modulus, or elastic
modulus. It is the slope of stress-strain curve in the elastic deformation region of
a material. The Young’s modulus is commonly used for elastic materials such as
glasses, ceramics, and metals. The dynamic modulus is the ratio of stress to strain
under vibratory conditions. It is more commonly used for viscoelastic materials
such as polymeric materials. The dynamic modulus consists of two components:
storage modulus and loss modulus. The storage modulus measures the stored energy