Steve Berry and Sandra Winkler Contributing Editors

"Some like it hot" is not a term applied to semiconductors. Excessive heat shortens the life of IC products and limits performance.

Elevated temperatures on a specific part can cause warpage, cracking, popcorning, lower reliability, semiconductor failure and early stages of reflow on adjacent parts.

Dissipating the heat from semiconductors has been an issue from the inception of the IC. With increasing speeds and densely packed PWBs, the challenge of getting the heat away from the chips has taken on a new significance.

Heat Traps

Issues of heat include not just the total volume of heat generated, but also the concentration in specific areas on the chip. Heat can also become trapped between die in 3D stacked packages.

Tools for dissipating heat include heat spreaders, heat sinks, heat slugs, heat pipes, thermal interface materials (TIMs), thermal greases, fans, cold plates and substrates designed for this purpose.

‘Some like it hot’ doesn’t apply to semiconductors.

Newer materials are being developed to control thermal issues and prevent future device failure, which will not only be more effective, but will also reduce the size and weight added to control the heat.

Substrates and PWBs that are designed to dissipate heat are somewhat new, and there are several products available.

The Bergquist Company has developed its Thermal Clad Insulated Metal Substrate intended for higher watt-density, surface-mount applications, where die size is reduced and heat issues are a major concern.

Thermagon Inc.’s T-lam System is a thermally conductive PWB. T-lam PWBs have a base layer of aluminum or copper metal and alternating, ceramic-filled epoxy (dielectric) and copper layers. Heat is drawn down through the thermally conductive layer to the metal base, which is spread and subsequently removed from the system.

The company’s T-preg 1KA is a thermally conductive, electrically insulating prepreg.

ThermalWorks has a thermal substrate product named Stablcor. This is a laminate material that can be used for both PWBs and substrates. It is a thermally and electrically conductive composite material which offers in-plane thermal conductivity and is used as a plane layer.

Stablcor increases reliability by acting as a heat sink or a heat spreader and reducing thermal stresses on components. It creates a matching CTE between the PWB and package substrate, resulting in more reliable solder connections. The increased stiffness prevents warpage, increasing yields.

New Materials

Other new materials, such as TIMs, are coming to light as well.

Enerdyne Solutions has invented the Indigo Thermal Interface System, which consists of an ultra-high-performing, low-melt alloy, TIM and advanced corrosion mitigation technology. Indigo provides an all-metal heat path and can perform regardless of CTE mismatch; Indigo is fully liquid at operating temperatures.

There is plenty of room for innovation in this area. Thermal issues will not go away and will only become more significant with the increasing power and densities of boards and chips.