Semiconductor devices such as smartphones, LEDs, and high-power semiconductor lasers that process AI technology are becoming smaller and more powerful. This results in large amounts of electrical energy being injected into a small area (component), which generates rapid heat and prevents semiconductor chips from reaching their full potential and shortens their lifespan.
In addition, devices such as BEVs generate large amounts of heat due to the large amount of current applied to the power semiconductors and LIBs. Controlling that heat has a significant impact on improving electricity costs. For this reason, heat dissipation measures are becoming significantly important.
Therefore, demands for TIM (Thermal Interface Material) as a heat dissipation measure are increasing, but there are various issues in TIM evaluation methods. This article provides a detailed explanation of TIM and introduces TIMA5, a device that enables evaluation of TIM heat dissipation performance under conditions close to those of actual products.
This article describes TIM in detail and introduces TIMA5, a device that enables evaluation of TIM’s heat dissipation performance in-situ situation.
Thermal Interface Material (TIM) is a term used to refer to thermally conductive materials put between components to efficiently dissipate unwanted heat generated inside electronic devices. It is generally used in the form of an insert between a heat-generating element such as an IC (integrated circuit) and a heat-dissipating component such as a heat spreader or a heat sink. Even though the surfaces of heat-dissipating devices such as ICs and heat sinks may appear flat to the naked eye, slight surface roughness exists. Therefore, even if the two are directly adhered to each other, there is still a small amount of air space between the IC and the heat sink. Since air is a very good insulator (low thermal conductivity and high thermal resistance), heat from the IC is transferred by avoiding the air gap, and as a result, heat cannot be efficiently dissipated to the outside. TIM is the best solution to this problem.
By putting a TIM, which is a thermal conductive sheet, between the IC and the heat sink, the TIM is inserted between the fine irregularities on the surfaces of the two devices. The TIM with good thermal conductivity adheres to both surfaces without gaps between them, creating a heat propagation path using the entire adhered surface and allowing the IC to efficiently dissipate heat to the outside. This material works to help transfer heat between objects.
TIM types include heat-dissipating grease, heat-dissipating sheets, and heat-dissipating putty.
Thermally conductive grease
This is a paste-like heat-conductive material made by mixing fillers with viscous resin. It generally has high thermal conductivity and low contact resistance (interfacial thermal resistivity), and can be easily set using a dispenser. However, over time, due to the difference in thermal expansion coefficient between the heating element and the heat sink, pump-out phenomenon, etc. may occur.
Heat Dissipation Sheet
Thermal conductive material molded in sheet form. It is highly stable and does not cause pump-out. However, it generally has lower thermal conductivity and higher contact resistance (interfacial thermal resistivity) than heat-dissipating grease.
Heat-dissipating putty
A highly viscous clay-like (putty-like) heat-conductive material. Although it has low fluidity, it can follow various shapes.
TIM has many roles and is used in various places, but R&D departments that are developing or considering the adoption of these TIM materials face a variety of challenges in their material evaluation methods.
ASTM D5470-17 is the most practical measurement method specified as a standard exclusively for TIM. However, it is difficult to compare the thermal conductivity (W/m-K) published by different companies, because each company uses different methods, equipment, and conditions to measure thermal conductivity.
ASTM D5470-17 specifies the steady-state method, and the most important items to measure are the sample thickness control (measurement) and the measurement of the amount of heat transferred at that time. With some measurement devices, the sample thickness is set by the operator using shims, etc., and is replaced by an alternative measurement method, which is a very complicated process.
If TIM is evaluated only by thermal conductivity values, it often does not reflect the truly required characteristics of TIM, such as flexibility and filling gaps between heating elements and heat sinks. Also, thermal conductivity is a constant parameter regardless of thickness, and does not include the actual thickness of the TIM used, or contact resistance or interface thermal resistance.
Thermal conductivity is not the only role of TIM.
The performance required of TIM is not only thermal conductivity, but also the ability to become as thin as possible (to shorten the thermal conduction distance), to have lowered thermal resistance, and to bring the interface thermal resistance (contact resistance) close to 0 (zero), that is, to eliminate the gap between the heating element and the heat sink and the air.
Which TIM has higher performance, one that can be used only at 100 W/m-K and 10 mm or one that can be used at 1 W/m-K and 10 μm, with the same interface thermal resistivity?
At first glance, the 100W/m-K TIM appears to have higher performance, but since it can only be used with a thickness of 10mm, its thermal resistance increases. Conversely, 1 W/m-K TIM, which can be used as thin as 10 µm, is considered to have higher heat dissipation performance due to its lower thermal resistivity.
As an example, silicone resin, a soft material, has low thermal conductivity, rarely 100 W/m-K. However, its flexibility allows it to tightly fill the gap between the heating element and the heat sink. Furthermore, the thermal conductivity can be improved by mixing silicone resin with a filler with high thermal conductivity (insulating materials are generally preferred).
Since the transient method cannot directly derive thermal resistance and thermal conductivity, specific gravity and specific heat must be measured separately.
Also, there was no way to evaluate the problem of pump-out phenomenon, which is a drawback of heat-dissipating grease in terms of measurement under load and long-term reliability at the thickness of the material actually used.
What is pump-out phenomenon?
Pump-out phenomenon is a phenomenon that mainly occurs when thermal conduction grease is used, and is a phenomenon in which the thermal conduction grease is deformed by thermal cycling, causing gaps and grease to be pushed out.
When pump-out occurs, the amount of thermal conduction grease decreases and the thermal conductivity drops. As a result, the temperature of heat-generating parts rises, which may cause failure.
The Thermal Interface Material Analyzer TIMA5 solves these TIM evaluation method issues.
TIMA5 is an instrument that can measure the interface thermal resistivity (mm²-K/W), thermal resistivity (mm²-K/W), and thermal conductivity (W/m-K) of thermally conductive materials such as TIM.
TIMA5 fully complies with ASTM D5470-17.
It solves the issues of heat dissipation performance evaluation required for TIM, such as reliability that can cope with pump-out phenomenon, cycling control function that can perform lifetime tests, etc., and a system that uses TTV (Thermal Test Vehicles) to make the heating element an actual chip.
Features of TIMA®5
・Fully compliant with ASTM D5470
・More accurate calculation of interfacial thermal resistivity
・Sample thickness from 1 µm and load from ±1 N can be freely controlled and monitored.
・Cycling control function for reliability and lifetime testing to cope with pump-out phenomenon, etc.
・The system can reproduce and measure phenomena such as pump-out caused by the gap change in thermal contraction of electronic components by controlling the thickness and pressure of TIM such as gels and sheets, and performing cycling tests.
・Abundant test heads
・10 to 25.4 mm dia., 13 to 25.4 mm dia., both copper and aluminum test heads are available.
・TTV (Thermal Test Vehicles) system that enables evaluation of heat dissipation characteristics using a TTV chip that realizes heat generation and temperature measurement using a chip with the same shape as the actual IC circuit.
・We began selling TIMA5 manufactured by Nanotest of Germany in Japan in the summer of 2023.
For inquiries about our products or to request a demo, please click here
Matsuo Sangyo Co., Ltd.
Advanced Technology Division
E-mail: advanced-t@matsuo-sangyo.co.jp
TEL:＋81-6-6261-1212
Opening hours are from 9:00 to 17:30 every weekday.
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