Keeping electronics cool has become a increasing problem with the
advent of high density interconnects. Back in the days of 0.012-inch
lines and spaces on 2-ounce copper signal layers, it was easy to keep
designs cool. There was always lots of copper. As density increased
however, line widths have gotten smaller, spacing is tighter and the
cross-sectional copper area has been reduced exponentially. The net
result is that cooling has now become a big problem for system
designers.
The use of thermal simulation software helps
engineers and designers create a system that maximizes heat dissipation
within the confines of the construction materials, product performance
requirements, the resulting circuit and component densities, power
requirements and overall system size and weight factors. Adding thermal
simulation early in the design equation will only become more critical
as electronics systems increase in functional density. The
International Technology Roadmap for Semiconductors has forecast that
logic ICs will drop from 25 nm to 6 nm by 2013. At the same time,
functional densities will increase from 1.11 billion transistors to
4.42 billion. As performance increases, so does heat throughout the
system.
As Robin Bornoff of Mentor Graphics points out in our
cover article, “Fluid Dynamic Simulation for Cool Designs,” the thermal
resistivity of FR-4 contributes to thermal dissipation problems. While
the epoxy and glass matrix of FR-4 makes for an excellent electrical
insulator, these materials are very poor thermal insulators. Heat
generated in the copper circuits spreads through FR-4, which traps it
in and around the heat flow path, making it more difficult to dissipate
from the source.
New heatsink materials promise to help keep
next-generation electronics cool. Scientists at the Fraunhofer
Institute for Manufacturing Engineering and Applied Materials Research
(IFAM) recently announced a new material that combines copper and
diamond powder. Diamonds conduct heat five times better than copper.
Copper and diamonds together produce a material that has better heat
dissipation characteristics and a closer CTE match to ceramic
materials.
But the real answer to beating the heat is not
likely to come from a material's improvement, but from a new way of
transferring information. The Department of Energy and Stanford
University have demonstrated that bismuth telluride can be used as a
topological insulator. According to the researchers, this new material
functions at room temperature and allows electrons to travel on its
surface without any loss of energy. The problem of heat generation in
electronics is more troublesome than merely thermal dissipation
considerations. Up to 40 percent of the power in a circuit is lost due
to heat leakage. This makes it increasingly difficult to miniaturize
without increasing heat. Enter spintronics.
Spintronics uses
the intrinsic spin of electrons to transport and store information.
Unlike the voltage-based system used in today’s electronics,
spintronics uses topological insulators to carry electrons. Topological
insulators offer no resistance and therefore no heat is generated in
the process. Unlike previously studied superconducting materials,
bismuth telluride has demonstrated the ability to act as a topological
insulator at room temperature.
The lack of resistance
associated with topological insulators will result in lower energy
requirements in part due to the elimination of heat generation. This is
likely to lead to increased computing speeds. The system is, however,
limited to low power applications, and will be particularly useful in
memory applications.
The cooling effects of spintronics and
topological insulators like bismuth telluride still have a long way to
go before they become a mainstream solution. In the meantime, proactive
engineering design and the use of advanced materials to improve heat
dissipation are going to become increasingly important.
These
challenges cut across the supply chain, from the systems engineer; to
IC, package and PCB designers; and on to the PCB fabricator and
assembler. If the industry is going to adequately address the problem
of hot computers, sizzling cell phones and a host of other overheated
high-performance, small form-factor devices, communication and
cooperation need to improve. Working together, supply-chain members
will be able to meet the short-term demands for cooler electronics as
we wait for advancements that will bring a cooler spin on things.
