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Chip Scale Review November • December • 2018

[ChipScaleReview.com]

To improve the performance of heat

sinks, fans or blowers can be added to a

system. Through the years, fan designs

have improved. Fan blades have been

streamlined to produce great flow rate

with less noise and fans have become

more power efficient to meet the desires of

customers trying to use less resources and

save costs.

New materials are constantly being

developed to improve the effect of air

cooling. Graphene/graphite and diamond

are two options that increase the heat

transfer capabilities of a heat sink but are

limited by issues of manufacturability and

cost. In addition, engineers are exploring

new thermal interface materials to improve

the connection between the heat sink and

the chip, which will increase heat transfer.

Not only are the components themselves

getting higher powered, but increased

demand for functionality in ever-smaller

packages has meant that these components

are increasingly being squeezed into

tighter areas. Engineers have turned to

heat pipes or vapor chambers as tools to

transfer heat away from components. Heat

pipes alone will not remove the heat, but

rather simply move it from one place to another, they can, however, be attached to a heat

sink assembly that will remove the heat to the ambient. The small form factor of heat pipes

make them increasingly popular in telecommunications, mobile, and Internet of Things

(IoT) applications where space is at a premium and a heat sink may not fit on top of a chip.

Liquid cooling

There has been talk for years about how liquid cooling is the f ut ure of

electronics thermal management. While air cooling retains its supremacy, the

future is now moving to liquid cooling. Many engineers have designed liquid

solutions for removing excess heat from ICs and other components. Typically, a

liquid loop contains a cold plate (usually aluminum or copper) located on top of

the component to pull heat away from the chip and transfer it to a fluid and a heat

exchanger that transfers the heat from one f luid to another (either air or liquid)

before the fluid flows back across the chip.

Water transfers heat much better than air, so liquid cooling provides higher

thermal performance than a heat sink, but it also requires a pump to keep the fluid

circulating, which increases the energy costs of the system, and can be bulky and

difficult to implement at the chip level. There are challenges to liquid cooling,

but cold plates can keep junction temperatures within the operating range while

dissipating several hundred W/cm

2

.

Liquid is increasingly common in electronics as new materials are used in chip

packaging, such as silicon carbide (SiC) and gallium nitride (GaN), which can

withstand higher power densities and higher temperatures. But the higher heat

loads and the desire for smaller packaging mean passive, air cooling techniques

are unlikely to accommodate the thermal management needs of the system.

Researchers have also designed on-chip cooling solutions, immersion cooling

solutions, and liquid cooling of three-dimensional chip stacks that can remove

even greater heat f luxes. Boiling and jet impingement (spray) cooling solutions

that were originally designed for larger systems are also

being integrated for thermal management at the chip level.

Nanof luids (or engineered f luids) are another important

development in IC liquid cooling. The nanoparticles dispersed

in a base f luid are typically metal or metal oxide particles

with a size range of 1-100nm. Researchers were able to

demonstrate as much as a 20% enhancement in heat transfer

performance of the single-phase, liquid-cooled system

when nanoparticles were introduced.

Summary

At the chip level, designers need to factor in the package type

and materials, power dissipation fluctuations, power dissipation

from adjacent components, spacing between components,

and the thermal resistance of critical components to design an

optimal thermal management solution. Engineers continue to

use air cooling solutions as a cost-effective means for dissipating

enough heat to keep IC junction temperatures at proper operating

levels. Heat sinks (along with fans or blowers) provide the

necessary cooling for the majority of chips, but as semiconductor

technology continues to develop and chips become denser and

more powerful, then liquid solutions will be required.

Advanced materials are creating new packaging techniques

to mitigate the effects of heat at the packaging level and there

are techniques, such as microfluidics, that hold promise for the

future of IC cooling.

Biography

J o s h P e r r y i s a M a r k e t i n g C o m m u n i c a t i o n s

Specialist at Advanced Thermal Solutions, I nc.; email

jperry@qats.com.