Infineon Technologies has found a "solid" way out of the
impending wiring crisis of the semiconductor industry. Researchers of
the Munich-based company have developed a technique to solder different
types of integrated circuit chips together to form a "sandwich"
chip system, packing more capability into the same area as a single
chip and creating high-speed connections that allow an increase in complexity
while reducing costs.
For a first sample, Infineon produced the upper and lower modules of
these new sandwich chips in Dresden, Germany, demonstrating the feasibility
of the new approach to a problem the industry has tried to solve for
ten years. The technique uses standard chip making and packaging machinery
to take a giant step forward in chip integration. The soldering technique,
called SOLID, combines the multiple chips in a single package to create
a single product. The technology promises both to speed up chip performance,
and to help reduce the price of current chip solutions by up to 30 percent.
Hundred times the number of connections
In all semiconductor-based applications, such as mobile phones, multiple
chips exchange electronic signals using fine wires laid out precisely
on printed circuit boards. The longer the lines between the adjacent
(planar) chips are, the more time an electrical signal needs to travel.
This makes design more complex and can slow down the performance. Additionally,
the number of possible circuit wires is strongly limited in a tiny space.
As chips become more complex, a "wiring crisis" is making
it very difficult and therefore expensive to implement applications
that require high frequencies - such as communication technology - at
the speeds required to satisfy design requirements.
With the SOLID technology, the tracks between the contacts are much
shorter. Interior contacts within a single chip package conduct signals
directly between the individual segments of a chip. A SOLID product
can achieve clock rates of up to 200 GHz (100 times faster than today's
fastest desktop PC processors) and support more communications lines
between the chips in the package. Compared to existing chip systems,
it is possible to pack hundred times the number of connections into
the same space. This enables manufacturers of electronic equipment to
use smaller printed circuit boards and thus to develop new and more
cost-effective products. Soon systems will be created that handle complex
tasks much faster in less space.
The SOLID process
The name SOLID is derived from the soldering process used, which is
diffusion soldering (the exact term is solid-liquid inter-diffusion).
Prior to soldering, the upper and lower sides of the "sandwich"
chip are coated with a very thin layer of copper. The solder is applied
with a thickness of only 3 micrometers (1 micrometer is one thousandth
of a millimeter). Both chips are then soldered together at a temperature
of 270 degrees C and 3 bars of pressure to create a permanent bond.
The combined chips will not be higher than "normal" chips
because flat ("thinned") silicon wafers are used as a basis.
These silicon wafers usually have a thickness of 120 micrometers. For
SOLID products, Infineon will reduce them to only 60 micrometers in
a cost-effective standard process. This corresponds approximately to
the diameter of a human hair. The "chip sandwich" is provided
with the same outer layer for semiconductor components made of compound
material and plastic as normal chip systems - this allows a savings
of up to fifty percent of the material and the cost for packaging.
Mastering the challenges of the future
The new technology is suitable for almost any semiconductor application,
from chips for mobile communications to industrial and automotive systems.
Existing products can be made with up to 30% less cost through the more
effective utilization of production facilities - for example by producing
the highly complex upper sides and the less complex bottom sides of
the 'sandwich' chip separately. A chip that is manufactured with the
SOLID process also requires up to 50 percent less space than conventional
products with the same functionality that are arranged side by side.
The shorter tracks reduce the power consumption, which results in a
lower operating temperature. With these features, the SOLID technology
provides more convenience for the use of mobile phones and notebooks
because the batteries last longer and the mobile devices become less
hot than today's products.
The first prototype being produced in the new technology is a smart
card controller. Current
smart card controller products combine both a logic chip and memory
chip on a single planar surface. Therefore the controller has only a
limited memory capacity, typically 32 Kbytes of memory. A first prototype
of a smart card controller manufactured by Infineon using the SOLID
process has 160 KBytes of non-volatile memory. This means that it is
not only possible to store more data on the chip but also that the working
smart card can use a more complex, operating system and execute more
software applications.