404
S. Shi et al.
Dissipation factor or loss tangent is another important material property of an
insulating material. It is expressed as the ratio of the total power loss in a material
to the product of the voltage and current in a capacitor being made of the material
between two electrode plates at a given frequency. Dissipation factor measures the
efficiency of a material interacting with electrical signals. When a material is placed
in an oscillating electrical field, the molecules inside the material oscillate as well.
This dielectric polarization oscillation is accompanied by the motion of the atoms
with partially electrical charges which result in energy loss. Since high dissipation
factor means higher energy loss, and results in larger signal or voltage attenuation, and
undesired heating, materials with lower dissipation factor are desired for substrate
applications. Materials with less electrical field induced atom and molecule motion
usually have lower dissipation factor.
Volume resistivity is the ratio of potential drop over a unit length of material to
the current flowing through a unit cross-sectional area. It is an intrinsic property that
quantifies how strongly a given material opposes the flow of electric current. Since
the volume resistivity of organic base materials is usually higher than 10
7
cm [3].
The leakage current is not a concern even for very current-sensitive medical device
applications including pacemakers and defibrillators. However, volume resistivity is
usually a good measurement to detect process or reliability issues.
Electrical strength refers to the maximum electric field that a dielectric material
can withstand without breaking down in the direction perpendicular to the plane
of the material. It is an intrinsic property of the bulk material. When a dielectric
material is placed in a sufficiently high electrical field, free electrons from ambient
radiation may become accelerated to velocities that can liberate bound electrons in
the material during collisions with neutral atoms or molecules. This process is termed
avalanche breakdown and can happen abruptly. Once avalanche breakdown happens,
an electrically conductive path was formed and the material loses its insulation ability.
Since common fiberglass-reinforced materials usually have electric strength above
1200 V/mil at ambient condition, electrical strength is not a main concern for most
applications [3]. However, some medical devices such as defibrillators can have
voltage being pumped to more than 1000 V and the electrical strength of the selected
material becomes important. The experimentally measured electrical strength often
impacted by the moisture content and pre-conditioning conditions.
Dielectric breakdown is similar to the electrical strength but the electrical breakdown happens in the direction parallel to the plane of material. Its measured value
is impacted by moisture content and pre-conditioning conditions. With the increase
of substrate wiring density, the pitch between two adjacent traces in the same build
up layer is shrinking. Dielectric breakdown consideration is needed for high voltage
applications and implementation of electrical static discharge (ESD) controls.
Material surface properties mainly impact the interfacial property of the multiple
interfaces in substrate, and the interfacial properties impacts both substrate quality
and reliability. Surface roughness, surface free energy, surface resistivity, and arc
resistance are the following four properties introduced.
Surface roughness refers to the deviations in the direction of normal vector of a
real surface from its imaginary ideal surface (i.e. perfectly flat and smooth) and is
S. Shi et al.
Dissipation factor or loss tangent is another important material property of an
insulating material. It is expressed as the ratio of the total power loss in a material
to the product of the voltage and current in a capacitor being made of the material
between two electrode plates at a given frequency. Dissipation factor measures the
efficiency of a material interacting with electrical signals. When a material is placed
in an oscillating electrical field, the molecules inside the material oscillate as well.
This dielectric polarization oscillation is accompanied by the motion of the atoms
with partially electrical charges which result in energy loss. Since high dissipation
factor means higher energy loss, and results in larger signal or voltage attenuation, and
undesired heating, materials with lower dissipation factor are desired for substrate
applications. Materials with less electrical field induced atom and molecule motion
usually have lower dissipation factor.
Volume resistivity is the ratio of potential drop over a unit length of material to
the current flowing through a unit cross-sectional area. It is an intrinsic property that
quantifies how strongly a given material opposes the flow of electric current. Since
the volume resistivity of organic base materials is usually higher than 10
7
cm [3].
The leakage current is not a concern even for very current-sensitive medical device
applications including pacemakers and defibrillators. However, volume resistivity is
usually a good measurement to detect process or reliability issues.
Electrical strength refers to the maximum electric field that a dielectric material
can withstand without breaking down in the direction perpendicular to the plane
of the material. It is an intrinsic property of the bulk material. When a dielectric
material is placed in a sufficiently high electrical field, free electrons from ambient
radiation may become accelerated to velocities that can liberate bound electrons in
the material during collisions with neutral atoms or molecules. This process is termed
avalanche breakdown and can happen abruptly. Once avalanche breakdown happens,
an electrically conductive path was formed and the material loses its insulation ability.
Since common fiberglass-reinforced materials usually have electric strength above
1200 V/mil at ambient condition, electrical strength is not a main concern for most
applications [3]. However, some medical devices such as defibrillators can have
voltage being pumped to more than 1000 V and the electrical strength of the selected
material becomes important. The experimentally measured electrical strength often
impacted by the moisture content and pre-conditioning conditions.
Dielectric breakdown is similar to the electrical strength but the electrical breakdown happens in the direction parallel to the plane of material. Its measured value
is impacted by moisture content and pre-conditioning conditions. With the increase
of substrate wiring density, the pitch between two adjacent traces in the same build
up layer is shrinking. Dielectric breakdown consideration is needed for high voltage
applications and implementation of electrical static discharge (ESD) controls.
Material surface properties mainly impact the interfacial property of the multiple
interfaces in substrate, and the interfacial properties impacts both substrate quality
and reliability. Surface roughness, surface free energy, surface resistivity, and arc
resistance are the following four properties introduced.
Surface roughness refers to the deviations in the direction of normal vector of a
real surface from its imaginary ideal surface (i.e. perfectly flat and smooth) and is