414
S. Shi et al.
prepared integrated foil and a resin layer are then made into a laminate. The integrated
foil is then imaged and etched per defined pattern to produce desired circuit pattern
and resistive components [9].
14.3.4 Dielectric Materials
The dielectric material, also called the layer build-up material, is mainly used to route
the electric power and signal as well as make the package meet application form factor
requirements. A successful dielectric material must have compatible chemistry with
core material, good adhesion to the core and copper, good dielectric properties to
meet electrical performance requirements, good thermal stability for lead-free solder
processing, good microvia manufacturability, and satisfactory reliability.
Theoretically, all the core laminates can be used as dielectric materials. However
glass cloth reinforced laminates are not suitable for build-up layers for high density
substrate applications as a result of via size and wiring density limitation of mechanical drilling. With the exception of very thin glass cloths, glass cloth reinforced
laminates are not practically compatible with other microvia-making methods such
as laser drilling, plasma etch, and photoimaging. The commonly used layer build-up
materials for high density substrate applications, such as 3D-packaging, are epoxy
and epoxy/BT resin, polyimide, aramid reinforced epoxy laminate, APPE, and liquid
crystal polymers (LCP) [3, 8–12].
Epoxy and epoxy/BT resin is one of the major dielectric materials employed in
high density substrates. The generic chemical structures and properties of epoxy and
epoxy/BT resins have been previously discussed. When these resins are used for
dielectric build-up layers, one of key considerations is the ability to fabricate via
holes, and their quality. Generally speaking, there are three ways to form via holes
for the epoxy and epoxy/BT resin dielectric materials: laser drilling, UV photodefining, and etching. Laser drilling and etching (both plasma dry etching and chemical wet etching) support more choices of resin systems. There are two types of
photo-definable epoxy resins [8]. The first type of photo-definable epoxy resin is
made by mixing the base epoxy resin with photosensitizing agents. The second type
is intrinsically photo-definable epoxy. There are more choices of the first type of
photo-definable epoxy than the second type. These resins can be used in either liquid
form or B-staged dry film form. Screen printing, curtain coating, and spin coating are
used to apply liquid epoxy/BT resin, while vacuum laminating is used for B-staged
dry film. Fillers are sometimes added to the resin system in order to gain desirable
properties such as lower CTE and easier copper plating. Since most of the epoxy
resins used for dielectric layers contains multifunctional epoxy groups with aromatic
backbone structures, they are rigid and brittle after curing.
S. Shi et al.
prepared integrated foil and a resin layer are then made into a laminate. The integrated
foil is then imaged and etched per defined pattern to produce desired circuit pattern
and resistive components [9].
14.3.4 Dielectric Materials
The dielectric material, also called the layer build-up material, is mainly used to route
the electric power and signal as well as make the package meet application form factor
requirements. A successful dielectric material must have compatible chemistry with
core material, good adhesion to the core and copper, good dielectric properties to
meet electrical performance requirements, good thermal stability for lead-free solder
processing, good microvia manufacturability, and satisfactory reliability.
Theoretically, all the core laminates can be used as dielectric materials. However
glass cloth reinforced laminates are not suitable for build-up layers for high density
substrate applications as a result of via size and wiring density limitation of mechanical drilling. With the exception of very thin glass cloths, glass cloth reinforced
laminates are not practically compatible with other microvia-making methods such
as laser drilling, plasma etch, and photoimaging. The commonly used layer build-up
materials for high density substrate applications, such as 3D-packaging, are epoxy
and epoxy/BT resin, polyimide, aramid reinforced epoxy laminate, APPE, and liquid
crystal polymers (LCP) [3, 8–12].
Epoxy and epoxy/BT resin is one of the major dielectric materials employed in
high density substrates. The generic chemical structures and properties of epoxy and
epoxy/BT resins have been previously discussed. When these resins are used for
dielectric build-up layers, one of key considerations is the ability to fabricate via
holes, and their quality. Generally speaking, there are three ways to form via holes
for the epoxy and epoxy/BT resin dielectric materials: laser drilling, UV photodefining, and etching. Laser drilling and etching (both plasma dry etching and chemical wet etching) support more choices of resin systems. There are two types of
photo-definable epoxy resins [8]. The first type of photo-definable epoxy resin is
made by mixing the base epoxy resin with photosensitizing agents. The second type
is intrinsically photo-definable epoxy. There are more choices of the first type of
photo-definable epoxy than the second type. These resins can be used in either liquid
form or B-staged dry film form. Screen printing, curtain coating, and spin coating are
used to apply liquid epoxy/BT resin, while vacuum laminating is used for B-staged
dry film. Fillers are sometimes added to the resin system in order to gain desirable
properties such as lower CTE and easier copper plating. Since most of the epoxy
resins used for dielectric layers contains multifunctional epoxy groups with aromatic
backbone structures, they are rigid and brittle after curing.