Build-up substrates: an idea born
from semiconductor concepts
While there are many types of multilayer substrates,
the type that appeared before the build-up substrate
and is now widely used is the through-hole substrate
(plated through-hole method). (See the figure at
the right.) However, this method, in which through
holes that pass through all layers are drilled, and
connections between the conductor patterns on each
layer are made by plating internally, has the following
disadvantages.
1. Since the through holes are formed by drilling,
there are limits to the degree of miniaturization.
2. Since the wiring associated with a through hole
has a direct linear form, the wiring geometry is
constrained and inflexible.
Given those problems, a new method, the build-up
method, was developed in Japan at the start of the
1990s.
The build-up method can be said to have been born
as an application of the layering technology used in
semiconductor fabrication to substrates. On a core
layer created with the normal plating through-hole
method, insulating and conducting layers are stacked
alternately to form the build-up layers.
In most cases holes are drilled with a laser (laser
vias) and electrical connections are made to create
the connections between the build-up layers and the
core layer. Laser vias have smaller diameters than
mechanically drilled holes and since the holes can
be positioned at each layer, laser vias provide much
greater flexibility than mechanically drilled vias.
Difficult Technical Issues Resolved by
Sony's Overall Technical Prowess and
the Latest Processing Methods
Build-up substrates resolve the deficiencies of through-hole
substrates and, due to their even higher wiring
density and high-density mounting, make further
miniaturization and thinner form factors possible. As
a result the range of applications for this technology
has grown and now they are widely used for interposer
substrates in applications such as cellular phones and
game equipment.
There are, however, only a very small number of
companies that supply LAMINATE multilayer build-up
interposer substrates. This is because of the high
technical levels required for circuit formation, interlayer
connection, leveling of the build-up layers, and
other aspects, and thus assuring reliability is difficult.
Sony has now achieved in-house production of
LAMINATE substrates using the latest processes by
applying the Sony Group's semiconductor technology
and know-how while at the same time taking full
advantage of the fine fabrication technology fostered
at the Neagari Plant of Sony Chemical & Information
Device Corporation.
The figure above shows representative technologies in
these new processes.
As opposed to existing processes for forming patterns
by removing plating (etching process), the new process
(pattern plating process) in which, inversely, the plating
is grown, can create even more precise patterns.
Also,
the LDI (Laser Direct Imaging) method, unlike the
existing mask exposure method, does not require a
photo mask. As a result, factors that lead to instability
in the quality, such as the mask itself and variations
in positioning precision, are excluded, and reliability
can be radically improved.
Sony has introduced the
most advanced technologies from the technologies
and processing methods that have been actually
applied worldwide, and has further added Sony's own
arrangements to these technologies. Despite being a
late entry to the field, Sony has acquired, in a short
period, strengths that can compete with the leading
suppliers of LAMINATE substrates in all aspects,
including quality, price, and delivery time.
■ Types of interposer substrates
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Semiconductor and Substrate Technologies are Combined and New Process Methods Adopted
Vol.57