Thermal paste: a guide to dissipation in electronics

When an electronic component operates, it generates heat. The problem arises when that heat cannot dissipate quickly enough.

This is a common scenario in power electronic circuits, inverters, control units, microprocessors, and many other devices where temperature can directly affect the correct operation and lifespan of the components.

The difficulty does not only concern the presence of a heat sink. In fact, small gaps occupied by air can remain between the heat-generating component and the heat sink. And air is not a good heat conductor.

It is precisely at this interface that thermal paste, also called thermally conductive paste, thermally conductive grease, or heat-dissipating paste, comes into play. Its function is to create a more effective thermal contact between the surfaces and promote heat transfer to the heat sink.

Conductive pastes: the difference between thermally conductive and electrically conductive

The term conductive paste generally refers to a material in paste form formulated to promote a conduction phenomenon.

In electronics, however, this expression can refer to very different properties: a formulation can be designed to transfer heat or to allow the passage of electric current. For this reason, speaking simply of “conductive paste” without specifying its function can create ambiguity.

When referring generically to conductive paste, one can therefore indicate two very different families of materials, and it is precisely in this distinction that the fundamental difference between thermally conductive and electrically conductive pastes lies:

A thermally conductive paste promotes heat transfer between the component and the surface responsible for dissipating it. In this case, the paste is electrically insulating.

An electrically conductive paste is designed to create electrical conduction between the relevant parts. Therefore, it improves electrical transfer between 2 surfaces and, being normally loaded with noble metals, it is simultaneously thermally conductive.

In applications dedicated to thermal dissipation, the goal is normally to transfer heat without simultaneously creating an electrically conductive path between components.

This does not mean, however, that any thermal paste can automatically be considered electrically insulating. Electrical properties depend on the individual formulation and must be verified on the selected product.

What thermal paste is and what it is used for

Thermal paste is a material used between a heat-generating component and a surface responsible for dissipating the heat.

The principle can be represented simply:

The two surfaces that must be coupled are not perfectly uniform. Even when they seem to adhere correctly, small voids and irregularities can remain. Without an interface material, these spaces are occupied by air, which is a poor heat conductor.

The thermally conductive paste instead distributes itself between the surfaces, fills the irregularities, and allows the heat to reach the heat sink more easily.

This principle is particularly evident in power electronics. Small areas occupied by air can remain between an electronic board and an aluminum heat sink. By inserting a thermal paste, the heat produced by the component can be transferred to the heat sink more effectively, helping to limit overheating.

Why thermal pastes are used

Thermally conductive pastes are particularly interesting when the interface to be filled is thin.

Among the main application advantages, we find the possibility of creating very thin layers, adapting to non-uniform surfaces and, in the case of non-curing formulations, being used without a mixing or curing phase.

This simplicity does not mean, however, that a thermally conductive paste is suitable for any application without distinction. Depending on the formulation and operating conditions, it is also necessary to evaluate aspects such as:

• material migration;
• pump-out during operation;
• separation or sedimentation;
• behavior over time at high temperatures.

The choice must therefore start from the electronic system as a whole, not just from a single thermal conductivity value.

Types of thermal paste: silicone and non-silicone

One of the main distinctions between thermal pastes concerns the material matrix.

The two main families are:

• silicone thermal pastes;
• non-silicone thermal pastes.

These are not simply two variants of the same product. The matrix can influence the paste’s behavior, the operating temperature, and compatibility with the application.

DOWSIL™ silicone thermal pastes

Silicone thermally conductive pastes use a silicone-based matrix and are particularly used when the application must operate at high temperatures.

In general, silicone thermal pastes tend to maintain their performance over higher temperature ranges compared to non-silicone formulations. As a guide, many silicone pastes can reach temperatures of around 200 °C, while many non-silicone formulations are more often around 120-130 °C.

The operating temperature remains a specific characteristic of the individual formulation and must always be verified on the relative technical data sheet.

The silicone solutions in the Mascherpa range include several DOWSIL™ pastes.

Electrolube and E-MAX silicone thermally conductive pastes

In addition to DOWSIL™ solutions, Mascherpa also offers Electrolube and EMAX silicone thermally conductive pastes, suitable for different thermal management needs in electronics.

DOWSIL™ TC-5026 in the IGBTs of an inverter

A particularly representative example concerns the thermal dissipation of IGBTs, power components used in inverters.

During operation, these components generate heat. If the temperature becomes too high, they can operate outside the intended conditions and suffer damage.

In this application, DOWSIL™ TC-5026 is deposited on the back of the IGBTs. The thermally conductive paste is transferred through a stencil that allows for a precise pattern and a controlled thickness. The module is then coupled to the electronic board and its dissipation system.

The point is not simply to add material between the two surfaces. The goal is to create an interface through which the heat generated by the IGBTs can more effectively reach the aluminum heat sink.

Questa soluzione trova applicazione, ad esempio, negli inverter utilizzati nelle stazioni di ricarica dei veicoli elettrici, dove l’elettronica di potenza deve gestire elevate quantità di energia e, di conseguenza, una produzione significativa di calore.

Thermal paste in the management of a control unit on an industrial vehicle

Another Mascherpa application involved an electric industrial vehicle.

In this case, the system included a battery pack and a plate responsible for carrying away the heat generated during operation.

A silicone thermally conductive compound was used between the electronic system and the surface intended for dissipation. The principle is the same as seen in the case of the IGBTs: improving thermal contact between surfaces so that heat can be transferred to the element responsible for dissipating it.

This application clearly demonstrated how thermal pastes do not only belong to the world of computers, but also find use in E-Mobility, battery-powered systems, and industrial electronics.

Non-silicone thermal pastes

Not all applications require a silicone matrix.

Non-silicone formulations represent a second family of thermally conductive pastes and can be used when the project requires avoiding the presence of silicone or when operating conditions make a different matrix more suitable.

Mascherpa solutions include products from the Electrolube and MG Chemicals ranges.

The distinction should not be interpreted as a comparison between a better and a worse solution. The correct question is:

Which matrix best responds to the conditions of the specific application?

How to choose a thermal paste for electronics

Looking only at thermal conductivity risks oversimplifying the problem. A thermal paste for electronics works within a system and must be chosen considering how it will actually be used.

Operating temperature

Temperature is one of the first discriminants. If the application develops high temperatures, the product’s matrix and its relative operating range become particularly important.

The distinction between silicone and non-silicone thermal pastes also stems from this: in the ranges considered, the former generally allow for operation at higher temperatures than many non-silicone formulations.

Type of component and application

It is not the same thing to dissipate the heat produced by:

• an IGBT;
• a CPU;
• a power module;
• a control unit;
• an electronic board;
• a system connected to a battery pack.

Geometries, surfaces, operating conditions, and the amount of heat to be transferred change. For this reason, the question should not simply be: “Which is the best thermal paste?” but: “Which is the most suitable thermal paste for this application?”

This is an important difference, especially in the industrial world, where the choice must be linked to the project and not to a generic ranking of products.

Interface thickness

Thermally conductive pastes are particularly effective when they must create thin layers between the component and the heat sink. In some applications, the thickness is controlled through stencils or other deposition systems.

The amount of material should not be chosen randomly. The goal is to create the interface necessary to thermally connect the two surfaces. When, instead, the gap to be filled becomes wider or presents very different geometries, it may be necessary to evaluate other thermal interface technologies.

Electrical requirements

Thermally conductive does not automatically mean electrically conductive. In many electronic applications, it is necessary to transfer heat while simultaneously maintaining adequate electrical insulation.

Electrical properties must therefore be verified on the individual product and considered together with the thermal characteristics. It is not correct to assume that any thermal paste automatically guarantees the same level of insulation.

Application process

The production process also affects the choice.

Depending on the formulation, a paste can be applied through:

• dispensing;
• stencil;
• screen printing;
• serigraphy;
• manual application.

The most suitable solution therefore also depends on how the material must be integrated into the production process and the level of control required over geometry and deposited thickness.

Stability over time and rework

In the case of non-curing pastes, the material’s behavior during use must also be considered.

Depending on the formulation and operating conditions, phenomena such as the following can become relevant:

• migration;
• pump-out;
• separation;
• sedimentation;
• aging at high temperatures.

At the same time, the fact that the material remains uncured can facilitate rework or component replacement. This aspect must also be evaluated according to the project’s needs.

Applications of thermally conductive pastes in electronics

Thermal pastes are used in numerous industries, from electronics to E-Mobility, until the applications for the production and conversion of energy.

Il denominatore comune è sempre lo stesso: un componente genera calore e questo calore deve essere trasferito verso una superficie in grado di dissiparlo.

Thermal paste for IGBTs and inverters

IGBTs represent one of the clearest examples. These are power components commonly used in inverters and capable of generating significant amounts of heat during operation.

Thermal paste is applied in the interface to the heat sink so that the heat produced can be transferred more effectively. This is precisely the principle applied in the case of DOWSIL™ TC-5026.

Thermal paste in charging stations

Electric vehicle charging stations represent one of the possible applications for inverters. During energy transfer to the vehicle, power electronics must manage high loads and can develop significant amounts of heat.

By inserting a thermally conductive paste into the interface between the electronic module and the aluminum heat sink, heat can be transferred more effectively to the surface responsible for dispersing it.

Thermal paste for photovoltaic and wind inverters

The same principle also applies to inverters used in energy production plants.

Possible applications include:

• photovoltaic systems;
• wind power plants;
• systems in which energy must be transformed between direct and alternating current.

In these cases, too, power electronics generate heat and require correct thermal management.

Thermal paste for batteries and industrial vehicles

Another application area concerns electric industrial vehicles and battery-powered systems.

The heat generated by the system must be transferred to plates or other surfaces responsible for dissipating it. Thermally conductive paste can be used to improve thermal contact between the components and the dissipation system.

Thermal paste for CPUs and industrial microprocessors

CPUs and microprocessors generate heat during operation and must therefore be coupled to a system capable of dissipating it effectively.

Between the component and the heat sink, thermal paste is applied, which distributes itself on the interface between the two surfaces and promotes heat transfer to the heat sink.

The same principle is also applied to microprocessors used in industrial electronics, for example inside machines, control systems, and other professional equipment.

In all these cases, the function of the paste remains the same: to improve thermal contact between the heat-generating component and the surface responsible for dissipating it.

How a thermally conductive paste is applied

There is no single application method valid for every component. In the case of the IGBTs seen previously, for example, a stencil is used.

The material is distributed on the surface and transferred through the stencil to obtain:

• a defined geometry;
• a controlled thickness;
• a repeatable distribution.

In other cases, dispensing, screen printing, or serigraphy may be used, depending on the formulation and the production process.

The goal is not to apply as much material as possible. A thermal paste must create the interface necessary to thermally connect the surfaces according to the requirements defined by the project.

Frequently asked questions about thermal paste

Find the right thermal paste for your application

The choice of thermal paste depends on the characteristics of the component, the operating temperature, the interface to be managed, and the application process.

Mascherpa offers various DOWSIL™, Electrolube, MG Chemicals, and E-MAX solutions for thermal management in electronics and supports designers and companies in identifying the most suitable product.

For more information on thermally conductive pastes, contact our Mascherpa experts or visit the dedicated page on the website.