thermal paste vs. thermal pads

Thermal paste vs. thermal pad

Differences of thermal pads vs. thermal paste

Thermal interface materials are undoubtedly a very critical aspect of electronic component design.  They can very well make the difference between a working product and a faulty product.

The purpose of thermal pads and thermal paste is to provide a preferential heat transfer path between heat-generating components such as integrated circuits (CPUs) and heat dissipaters such as a heat sink.

The surface of a CPU or heatsink is never going to be completely flat or level. There will be tiny bumps, gaps and voids that allow air to pass through the components.

Since air is not a good conductor of heat, these gaps have a very negative effect on heat transfer.

Therefore, a thermal material with high thermal conductivity is needed to fill these gaps and improve thermal conductivity between the CPU and the heatsink. In our post 8 ready-made thermal management solutions, we described various materials that can be used for heat dissipation. We supply thermal pads with thermal conductivities up to 15 W/mK and thermal pastes with thermal conductivities up to 10 W/mK.

Thermally conductive paste

Heat conductive paste or cooling paste is a sticky mass that is applied between the heat sink and the CPU as the most common thermally conductive material. High quality pastes achieve the best performance in this regard when it comes to dissipating and transferring heat.

Thermal paste adheres for a very long time and is a very good option when it comes to heat dissipation to the heatsink: one layer of thermal paste ensures complete wetting of the component surface.

Since thermal paste is a viscous liquid, it fills all micro-depressions on the component or on the underside of the heat sink. This results in much better heat dissipation to the heat sink.

Unfortunately, application is often not easy, especially for beginners, and can lead to difficulties. Also, unlike some types of thermal pads, thermal paste is not designed to bridge larger gaps.

Thermal pads

Thermal pads are much easier to install than thermal paste. Some heatsinks already come with the pads, because they can be applied cleanly and easily and even newcomers have no difficulties here. Heat conduction pads are also preferred in industry. Unfortunately, the heat conduction is not always as good as that of the thermal paste.  However, there will still be very small gaps between the processor and the heat conduction pad. These small air gaps make for slightly lower thermal conductivity, as air is less thermally conductive.

It is important to remember that thermal pads are a one-time solution. They must be completely replaced if the heatsink is to be relocated or exchanged. In this case, all adhesive residue must also be removed, otherwise new bumps and gaps will appear. But thermal paste must also be completely removed and replaced.

Thermal pads vs. thermal paste: Durability

From a durability standpoint, some designs are expected to last for decades under harsh operating conditions. Using thermal paste to dissipate heat from the heatsink will outperform any pad in this regard, and is the more robust option in terms of wear resistance.  In contrast, a thermal pad will become brittle over time under repeated thermal cycling, which can interrupt the thermal path between the heat sink and the component

This is simply due to the material used in these products. Thermal paste or thermal grease adheres and solidifies after application. Thermal pads, on the other hand, are made of a sponge-like material or soft, rubbery material. Thermal paste is more durable and less expensive. This is especially true for recurring temperature cycles.

Advantages of thermally conductive pads compared to thermal paste

1. No mess – Applying thermal paste can be a messy process. Using thermal pads is a simple peel and stick process.
2. Fills larger gaps – Thermal pads are available up to 20mm as opposed to a thin layer of thermal paste.
3. Easier Installation – Thermal pads can be die-cut to the exact specifications of the component to ensure a perfect fit – every time.
4. Conformance – Thermal pads conform precisely, regardless of surface, to ensure no air is allowed to pass through. However, small pockets of air may remain.

Common mistakes and how to avoid them

Problems often occur when installing thermal paste and thermal pads. Therefore, here are some tips to avoid them:

Never use paste and pads together. Just because both are used together does not mean better thermal conduction is achieved. In fact, the opposite is true. Applying thermal paste additionally to the pads reduces the desired effect.

In addition, several pads should never be applied on top of each other. If two or more pads are placed on top of each other between the heatsink and the CPU, this can cause damage to the processor as the heat builds up.

 

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NBR vs. EPDM

NBR vs. EPDM: What is the difference?

 

Synthetic rubber comes in nearly a dozen major types with different properties for different applications. Two common synthetic rubber compounds are known as EPDM and nitrile rubber. The major differences between these two rubber products are their resistance to petroleum-based fuels and lubricants and their resistance to weathering.

The main difference between NBR and EPDM is that NBR is a non-aromatic polymer compound, while EPDM is an aromatic polymer.

NBR and EPDM are two types of rubber materials. Rubber is a material that can stretch when an external force is applied and sink back to its original shape after the applied force is removed. Natural rubber, which is derived from the milky sap of the rubber tree, is the most common way to make rubber-like materials; however, there are also synthetic ways.

What is NBR?

The term NBR stands for nitrile butadiene rubber. It is also known as nitrile rubber, Buna-N, and acrylonitrile butadiene rubber. It is a synthetic form of rubber made from the monomers acrylonitrile and butadiene. The most common trade names for this rubber are Perbunan, Nipol, Krynac and Europrene.

NBR material is unusually resistant to oil, fuel and most chemicals. Therefore, it is used in the automotive and aerospace industries to make hoses, seals, grommets, and fuel tanks for fuel and oil.

Also, NBR is used in the nuclear industry to make protective gloves. This material has very high stability in the temperature range from minus 40 degrees Celsius to 108 degrees Celsius. This makes it an ideal material for aerospace applications. In addition, NBR is important for the production of molded articles, shoes, adhesives, sealants, sponges, foams and floor mats.

The exceptional elasticity of NBR also makes it important for the production of disposable laboratory items, cleaning purposes and examination gloves. Compared to natural rubber (NR), NBR is more resistant to oils and acids. NBR also has higher strength and does not cause allergic reactions (natural rubber can cause allergic reactions on the skin).

Advantages of NBR

• excellent compression set
• good tear resistance
• good abrasion resistance
• good resistance to mineral oil based oils
• good resistance to mineral oil based hydraulic fluids
• good resistance to solvents, water and alcohols

Disadvantages of NBR

• poor resistance to weathering
• moderate heat resistance
• not suitable for use in brake fluids
• not suitable for use in highly polar solvents

What is EPDM?

The term EPDM stands for ethylene propylene diene monomer rubber. It is a type of synthetic material that belongs to the group of elastomers and consists of saturated polyethylene chains. EPDM is an aromatic compound. The monomers used to produce this polymer material are ethylene, propylene and a diene comonomer. Its structure allows crosslinking by sulfur vulcanization.

The presence of a saturated component makes EPDM much more resistant to heat, light and ozone compared to the other unsaturated rubber materials such as natural rubber, SBR and neoprene. In addition, EPDM can be formulated into a temperature-resistant form of the polymer that can withstand temperatures up to about 150 degrees Celsius. It can be used outdoors for many years without deteriorating. In addition, this material has good low-temperature properties such as elasticity.

Advantages of EPDM

• excellent resistance to weathering and ozone
• excellent resistance to water and chemicals
• excellent resistance to gas permeability and aging due to steam action
• good in ketones and alcohols
• good heat resistance
• good low-temperature flexibility

Disadvantages of EPDM

• poor resistance to fuels and solvents
• not recommended for food applications
• not recommended for contact with aromatic hydrocarbons

What is the difference between NBR and EPDM?

NBR and EPDM are two types of rubber materials. NBR stands for nitrile butadiene rubber, while EPDM stands for ethylene propylene diene monomer rubber. The main difference between NBR and EPDM is that NBR is a non-aromatic polymer compound, while EPDM is an aromatic polymer. Also, NBR is made from the monomers acrylonitrile and butadiene, while EPDM is made from ethylene, propylene and a diene comonomer.

Summary – NBR vs. EPDM

EPDM, or ethylene-propylene-diene monomer, is widely used to make O-rings, washers and other seals in water and steam pipes, as well as in cooling and braking systems in cars and trucks. EPDM seals are resistant to mild acids, detergents, silicones, glycols, ketones and alcohols, and can withstand temperatures from -30C to +150 C. They are resistant to ozone. The major weakness of EPDM rubber gaskets and other seals is that they fail and exhibit poor sealing performance in systems that use petroleum-based fuels, oils and solvents.

Nitrile rubber, also known as Buna-N, Perbunan, Nipol, Krynac and Europrene is made by combining the polymers butadiene and acrylonitrile. It offers excellent resistance to gasoline, diesel fuel, motor oil and other petroleum-based products.

For this reason, it is widely used for washers and O-rings that seal fuel systems of automobiles, boats, aircraft and stationary engines.

It can be formulated to withstand temperatures from -55 C to 135 C. The main disadvantage of nitrile rubber is that it can be affected by sunlight, general weathering or ozone from electrical equipment, unless it has been specifically manufactured for these purposes.

Stamped parts made of EPDM and NBR

Dr. Dietrich Mueller GmbH manufactures stamped parts, strips and blanks from both materials. The processes used are water jet cutting, punching and roll cutting.

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Thermal management for rechargeable li-ion batteries

Thermal management for rechargeable Li-ion batteries

The rapid growth of the electric vehicle market (such as electric cars, electric buses and electric trucks) has led to ever-increasing demands on the efficiency and lifetime of lithium-ion battery systems.

Only when vehicle ranges increase significantly will acceptance increase significantly.

The performance of lithium-ion batteries is highly dependent on the proper maintenance of cell temperature. Therefore, an effective thermal management system is critical to achieve maximum performance when operating under various environmental conditions.

Primary influencing factors for battery thermal management systems

There are four primary influencing factors that should be the focus of an appropriate battery thermal management system:

1. Cooling
2. Heating
3. Insulation
4. Ventilation

These four primary factors, when properly combined, maximize safety, life expectancy, available power and battery capacity.

Cooling rechargeable Li-ion Batteries

Due to the inherent inefficiencies of lithium-ion battery systems, the cells of the batteries generate heat when they release energy. For safety and performance reasons, this heat must be conducted away from the system to prevent overheating, which can damage the cells.

Dr. Dietrich Müller GmbH supplies various ready-made solutions here, which are explained in the article 8 ready-made thermal management solutions

Heating of rechargeable Li-ion batteries

Conversely, if the cell temperature falls below the desired temperature limit, performance is also compromised and the cells require an additional heat source.

Dr. Dietrich Müller GmbH supplies 4 different heating systems that can be used to achieve the desired and required heat output.

The four heating systems for the rechargeable Li-ion batteries are as follows:

1. wire heaters – wire heating
2. PTC Heaters – PTC heater
3. polyimide film based heaters – polyimide film heaters
4. high-performance paper based heaters – high temperature paper heaters

Insulation of rechargeable Li-ion batteries

The use of appropriate insulation materials helps to reduce temperature fluctuations within the battery pack when it is exposed to extreme weather conditions.

It also reduces the power required to maintain a constant and desirable internal temperature, which is necessary for optimum battery performance.

Battery thermal insulation materials are capable of performing the following functions:

1. Thermal insulation of rechargeable Li-ion batteries.
2. UL94 V0 – fire protection
3. electrical insulation
4. compressibility
5. technical cleanliness
6. burst protection

Ventilation of rechargeable Li-ion batteries

A well-designed ventilation system serves two functions, to exhaust hazardous gases within the battery system and to support the cooling system. However, a venting system can also undermine the heating and insulation of the battery if it is not properly designed.

Dr. Dietrich Mueller GmbH’s materials for venting rechargeable Li-ion batteries are permeable membrane materials that are formed into various contours.

We also manufacture membranes that include an installable frame.

 

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Punched parts made ​​of 3M VHB Tapes

As well as a range of punched and moulded parts made from non-adhesive materials, such as Nomex®, Mylar®, Hostaphan® and Pertinax®, Dr. Dietrich Müller GmbH (Ahlhorn) also manufactures punched parts with adhesive materials. They consist of a converter 3M VHB adhesive tape.

The 3M VHB tapes are high-performance adhesive tapes, which can replace many applications of mechanical fixtures such as screws, rivets, clips and spot welding. Good immediate adhesion, further processing possibilities, stress-free adhesion of different materials, high temperature resistance and application-optimized die-cut parts, allow a more secure, reliable and efficient connection.

The VHB core products offer a perfect adaptability to adhesive surfaces, a feature that is characteristic of this patented 3M technology. This product group is the starting point for choosing the right VHB producing high performance connection systems.

The VHB material is suitable for the widest range of surfaces (glass, metal, powder coatings and many plastics). It is used in a variety of applications in the automotive industry: attaching trim, emblems and antennas etc.

Because powder coating is growing into more and more industries, it is necessary to produce self-adhesive parts for this area, also. Up to now however, the joining of powder-coated materials has been difficult and time consuming. But, with the new, special developed powder-coated surfaces for 3M VHB adhesive tapes, materials can be connected quickly and securely.

Moreover, it makes for complex surface pretreatments, such as the primers or the roughening of the surface to be bonded. Additional benefits of this new 3M adhesive tapes are the high instantaneous bond and the optimal adaptability of the powder-coated surface to be bonded.

An overview of the most important product variants in VHB from 3M

3M VHB for joining low energy materials

for powder coated surfaces
Plastics: PE, PET or PP, among others.
Example:

• 3M VHB high-performance bonding systems 5952
• 3M VHB High Performance Joining System 5958FR

3M VHB for joining high energy materials

Joining metals
Plastics: Rigid PVC, ABS, AcrylicGlass [PMMA], Soft PVC.
Example:

• 3M VHB 5952F – double-sided adhesive tape
• 3M VHB 5906 – Double-sided high-performance adhesive tape

3M VHB Bonding of transparent materials

especially bonding of glass, acrylic glass, polycarbonate
And numerous other transparent plastics
Examples:

• 3M VHB 4910 – Double-sided high-performance adhesive tape.
• 3M VHB 4915 – Double-sided high-performance adhesive tape

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8 ready-made thermal management solutions

In the automotive industry and medical technology, there are ever greater challenges in the field of electronics. The heat to be dissipated poses ever-increasing tasks.

In this article we present 8 ready-made thermal management solutions:

1. Standard thermal conductive foils
2. Thermally conductive pads
3. Thermally conductive pastes
4. Phase change materials
5. thermally conductive adhesive
6. double-sided thermal conductive tape
7. silicone-free graphite foils
8. liquid gap fillers

Standard thermally conductive foils

Standard thermal conductive foils are manufactured for smooth and parallel surfaces that do not show any gap to the naked eye. The material smooths out microscopic irregularities in the contact surfaces, which improves the thermal interface and thus increases heat dissipation. They are electrically insulating and typically come in thicknesses between 0.1 mm and 0.3 mm to optimize thermal impedance.

Some films come with an optional adhesive and some use fiberglass reinforcement to improve handling characteristics.
Some silicone-free versions are also available.

Thermally conductive pads/Gap pads

Thermal contact between non-optimal surfaces requires a softer, thicker material to bridge the gaps between the active component and heat sink. They are softer than standard films and, thanks to their excellent compressibility, create optimal thermal contact while providing electrical insulation.
The thicknesses supplied range from 0.5-12.0 mm. Other thicknesses or shapes are available upon request. Some materials have fiberglass reinforcement or are dual-layered for improved handling. Silicone-free versions are also available.

Thermally conductive pastes

Thermal conductive pastes are thixotropic compounds that have good plasticity and very low thermal resistance. Due to the non-crosslinked silicones, there is no drying or leakage of the silicone components. Silicone-free versions are also available.

Phase Change Materials (PCM)

Phase Change Material consists of a combination of hot melt waxes. These films compensate for even the smallest unevenness between the power module and the heat sink, improving contact between the surfaces and increasing heat transfer. There are versions with electrical insulation based on polyimide foils or PEEK foils, as well as electrically non-insulating versions based on copper or aluminum foils.

Thermally conductive adhesive

Thermal conductive adhesives are available as two-component epoxy-based adhesives for permanent mounting of components such as CPU, GPU, BGA, heat sinks, etc., as one- or two-component versions as silicone adhesives, or as adhesive films that are applied to standard foils or gap fillers to help mount components.

Double-sided thermally conductive adhesive tape

Thermal conductive tape is a ceramic-filled, double-sided adhesive tape with excellent, permanent adhesive strength. When properly applied, no mechanical fastening is required. They also provide good thermal performance and excellent electrical insulation.

Silicone-free graphite foils

Graphite foils are based on 100% pure graphite or natural graphite. They have anisotropic thermal conductivity, with very high thermal conductivity in the XY plane and still very good thermal conductivity in the Z axis. Because of their thermal behavior, they are often used as heat spreaders, but also provide a cost-effective solution when electrical insulation is not required.

Liquid Gap Fillers

These gap fillers are two-component silicone materials that are applied through a mixing tube or poured into complex molds. Gap Filler liquids cure at room temperature within 1-24 hours, allowing wet-on-wet assembly of any component without the need for an additional heating step. Automatic dispensing systems enable cost-effective high-volume production.

 

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PTFE vs. PEEK

High-performance plastics are characterized primarily by their temperature resistance, but also by their mechanical properties.

They are often chosen for applications that require good chemical resistance, performance at high temperatures, low coefficient of friction and high strength.

They are found in many demanding applications in a variety of industries including oil and gas, aerospace, nuclear and chemical, but how do you decide which material has the properties needed for your specific application?

Although both PTFE and PEEK are well established in their respective fields, the question often arises as to which material is better suited for a particular application. OEMs typically need to make a selection based on technical suitability and therefore need to be better informed on how these materials compare.

What’s in PTFE’s favor?

PTFE is a versatile and cost-effective material with medium tensile strength. It has very good thermal properties and excellent chemical inertness, especially to strong acids. The coefficient of friction is unusually low and is said to be lower than any other solid material. PTFE is an excellent electrical insulator over a wide range of temperatures and frequencies.

PTFE is a thermoplastic. However, due to its high viscosity, PTFE cannot be processed using conventional polymer processing techniques. Therefore, PTFE is processed by cold forming followed by heat treatment (sintering), which fuses the polymer particles into a solid molded part.

PTFE films are peeled from such blocks.

Applications of PTFE:

• Pharmaceutical and medical technology
• Chemical industry

Delivery forms of PTFE:

Sheets, tubes, rods, films, finished parts.

Properties of PTFE:

• High chemical resistance
• Minimal surface tension
• Difficult to bond or weld

What are the advantages of PEEK?

PEEK is a semi-crystalline thermoplastic with excellent mechanical and chemical resistance properties that are maintained even at high temperatures. It is highly resistant to thermal degradation and to attack by organic and aqueous environments.

PEEK is attacked by halogens and strong acids, as well as by some halogenated compounds and aliphatic hydrocarbons at high temperatures. It dissolves completely in concentrated sulfuric acid at room temperature.

PEEK can be processed by conventional methods such as injection molding, extrusion and compression molding. PEEK is a much more expensive polymer, but adds value by allowing parts to be made with properties such as light weight, strength or toughness, and the ability to survive longer in harsh environments.

Applications for PEEK:

• Automotive
• Food industry
• Medical technology

Delivery forms of PEEK:

Sheets, tubes, rods, foils, finished parts

Properties of PEEK:

• High chemical resistance
• Excellent sliding function
• Very high temperature resistance

PEEK vs. PTFE

PEEK and PTFE are compared in 4 areas:

• Tensile strength
• Temperature resistance
• Wear resistance
• chemical resistance

PEEK vs. PTFE: High tensile strength

In the polymer field, it’s hard to find anything tougher than PEEK. In fact, it’s so strong that PEEK is subject to the same machining guidelines as metals.
This strength allows PEEK to be used in applications such as seals and automotive components – especially where metals cannot be used but metal-like resistance is required.

PEEK vs. PTFE: High temperature resistance

PEEK melts at about 400 degrees Fahrenheit and is capable of operating in environments of 300-325 degrees without deforming. While PTFE can withstand up to 250 degrees, any pressure/stress on PTFE at this temperature will inevitably cause deformation. In the case of PEEK, its hardness allows it to be used in a high-stress, high-temperature environment without losing its molding properties.

PEEK vs. PTFE: High wear resistance

Again, while both PTFE and UHMWPE can withstand significant wear, PEEK has a high PV value and can withstand wear in harsh physical and chemical conditions.

PEEK vs. PTFE: Chemical Resistance.

While PEEK is not on the same level as PTFE in terms of pure chemical inertness, it does exhibit resistance to many aggressive chemicals, allowing it to be used in corrosive environments and under heavy loads.
In short, PEEK’s ability to remain dimensionally stable under harsh conditions makes it a highly sought-after polymer. OEMs that use PEEK do so knowing full well that PEEK is unique for the properties it offers and therefore expensive.

In summary, PEEK has remained a niche polymer primarily because of its high price. If it were cheaper – at about the price of PTFE – it could capture a significant portion of the PTFE market. PTFE is still much better than PEEK in properties such as coefficient of friction and dielectric strength, but when it comes to pure strength, PEEK is unsurpassed among polymers.

 

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Silicon adhesives vs. acrylic adhesives

Silicone and acrylic adhesives are those adhesives most commonly used in polyimide tapes. Polyimide adhesive tapes consist of two layers:

• the polyimide film and
• the adhesive that is applied to this film.

Although silicone adhesives are most commonly used for the adhesive layer, many applications require the tape to have an acrylic adhesive. The only way to understand why this is so is to compare the two types of adhesives – silicone and acrylic.

Silicone adhesives – the properties

Silicone offers better elongation at break. It is used for electrical insulation of electrical equipment. Since it offers the highest heat resistance among adhesives, it is also widely used for high-temperature insulation. Some of the properties of silicone adhesive tapes are listed below for better understanding:

• Silicone is highly flexible at temperatures below ambient.
• It can provide consistent performance over wide temperature ranges.
• It has very good aging and UV resistance.
• It can withstand high temperatures.
• Silicone also shows good resistance to polar solvents.

Acrylic adhesives – the properties

There are two types of acrylic adhesives:

• water-based and
• solvent-based.

Water-based acrylic adhesives dry more slowly compared to solvent-based adhesives. However, solvent-based acrylic adhesives usually have better resistance to other solvents, chemicals and water. Some of the properties of acrylic adhesives are as follows:

• Acrylic adhesives have adequate adhesion to a wide range of substrates.
• It has good aging, transmission and UV resistance, which are suitable for fiber optic applications.
• It also has reasonable temperature resistance, but is not as good as silicone adhesives.
• It has lower tack, which means it will stick less after drying.

Silicone vs. acrylic adhesives

Now that we know the properties of silicone and acrylic adhesives, we can move on to comparing the two types of adhesives.

Silicone adhesives can withstand a higher temperature range compared to acrylic adhesives. Acrylic adhesives have the property of being more brittle and therefore can break even at extremely low temperatures. Generally speaking, acrylic adhesives adhere better at medium temperatures, i.e., in a temperature range between 0°C and 100°C. On the other hand, silicone adhesives have higher adhesion at lower temperatures, i.e., below 0°C, as well as at higher temperatures, i.e., above 100°C.

So it seems that silicone adhesives are rather standard and preferred for most applications. However, in some situations where silicone cannot be used, acrylic adhesives must be used. As for the point of lower tack with pure acrylics, again, there is an alternative for better performance. Modified acrylic or rubber adhesives can be used for better tack. Pure acrylic adhesives are commonly used for tapes used for bonding, sealing or surface protection.

 

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