3D-Printed "Metamaterial" Could Enable Heat-Resistant Circuit Boards

Almost all solid materials expand when heated - only in rare instances do certain materials buck this trend and shrink with heat. An interdisciplinary research team led by MIT mechanical engineers has now manufactured tiny, star-shaped structures out of interconnected beams, or trusses, that quickly shrink when heated to about 540 degrees Fahrenheit. Each structure's trusses are made from typical materials that expand with heat. The researchers realized that these trusses, when arranged in certain architectures, can pull the structure inward. The researchers consider the structures to be 'metamaterials' - composite materials whose configurations exhibit counterintuitive properties not normally found in nature. Such materials could have applications in computer chips, which can deform when heated for long periods of time. The research team had pioneered a 3D printing technique called microstereolithography, in which light from a projector is used to print very small structures in liquid resin, layer by layer. "We can now use the microstereolithography system to create a thermomechanical metamaterial that may enable applications not possible before," says Christopher Spadaccini of Lawrence Livermore National Laboratory.

Transcript

00:00:00 [MUSIC PLAYING] Heat is a powerful force that can affect a material in many ways. For example, almost all solid materials when heated, inevitably expand. It is only in very rare instances certain materials do the opposite and actually shrink when heated. It is this curious class of heat-shrinking materials, known

00:00:24 as metamaterials, that a team of engineers from MIT, the University of Southern California, and elsewhere are interested in learning more about. To learn more about how these metamaterials behave, the team manufactured small three-dimensional star-shaped structures using a 3D printing technique called Micro-StereoLithography, in which the researchers use light from a projector to print very small structures in liquid resin, layer by layer. The structures are comprised of interconnecting

00:00:53 beams of two different ingredients-- a stiff, slow-to-expand copper-containing material and a more elastic, fast-expanding polymer substance. The internal beams were made from the elastic material while the outer trusses were composed of stiff copper. They then put their composite structures to the test by placing them within a small glass chamber and slowly increasing the chamber's temperature to up to about 540 degrees Fahrenheit.

00:01:17 What they observed was that the structure at first maintained its initial shape but then gradually bent inwards, shrinking in size. Although the composites only shrink about 0.6%, the researchers say it is more significant that they do not expand as for most heat-resistant applications, designers may simply want their products to not expand with heat. In addition to their experiments, the researchers developed a computational model

00:01:41 to characterize the relationships between the interconnecting beams, the spaces between the beams, and the direction and degree to which they expand with heat. Having the ability to digitally tune individual components of stiffness and thermal expansion within a structure allows researchers to design structures with specific configurations that shrink or resist expanding with heat. The researchers say metamaterials such as these

00:02:04 may be useful in situations requiring structures that are impervious to dramatic temperature changes-- such as computer chips where parts must be able to resist expanding when heated from, say, the running central processing unit. [MUSIC PLAYING]