Winning the lottery… eating at a Michelin-star restaurant… choosing a thermally conductive adhesive… one of these things is not like the others.
Choosing a thermally conductive adhesive isn’t the most exciting way to spend an afternoon, but it IS a critical step to developing safe and effective electrical products.
Although Strouse is a flexible material converter, we can confidently say we’ve built various thermally conductive parts over the past few decades. Rather than push you towards a specific method, we’d prefer to show you your options so you can find the best possible solution for your project.
Before we explain the factors determining how to choose a thermally conductive adhesive for your project, we'll compare the different types of adhesive you might encounter to help you understand your options throughout the discussion.
You’ll understand the pros and cons of using each type of thermally conductive adhesive, enabling you to make the right choice or have the knowledge available to discuss your project details with a converter.
Types of Thermally Conductive Adhesives
Thermally conductive adhesives are commonly used in electronic devices to control heat flow. Because electronic devices can overheat, thermally conductive adhesives help redistribute heat to the correct areas of the device for dissipation.
Many types of thermally conductive adhesives exist, including but not limited to thermal glue, epoxy, grease, paste, pads, and film. We’ll review the benefits of each adhesive before examining factors that affect your application selection and offer advice on preparing for production.
THERMAL GLUE OR EPOXY
Thermal glue and epoxy are liquids that share conductive properties thanks to their filler materials. They are often sold in application tubes and can be applied by hand or fitted into an automated process.
Pros:
- Thermal glue and epoxy are applied in a liquid state, allowing them to seep deeper into surface textures
- Epoxy and glue applications can be machine-automated
- You can adjust the level of conductive particles to alter their conductivity
Cons:
- The application can be messy and imprecise
- Epoxy has a two-part application process (requires curing/hardening)
- Can become brittle over time due to repeated thermal cycling
- Epoxies are a harder material, which makes it challenging to rework parts once cured
- Overflow could damage circuits
THERMAL GREASE OR PASTE
You might’ve heard the terms “thermal grease” and “thermal paste,” but they’re essentially the same material. Thermal grease and paste are liquids with less adhesive qualities than glue and epoxy.
Pros:
- Gets into textured surfaces and eliminates air gaps/areas of low conductivity
- Doesn’t necessarily contain adhesive, so the components can be disassembled with minimal damage
Cons:
- The material could eventually dry out and need replenishment, which could range from every couple of months to every few years (depending on how hard the system is running)
- A potentially messy and imprecise application requiring multiple rounds of thin layers
- Overflow could damage circuits
THERMAL PADS
Thermal pads, or thermal conductive pads, are placed between a device’s Printed Circuit Board (PCB) and heat sink. When an electrical current passes through the board, it transfers heat into the thermal pad, redistributing it evenly throughout the heat sink.
Pros:
- Easy to peel and attach for quick application
- Can be electrically conductive OR non-electrically conductive
- Attaches via adhesive bond OR lacks adhesive
Cons:
- Won’t eliminate all microscopic air gaps
- There could be natural degradation over time
THERMALLY CONDUCTIVE ADHESIVE FILM
Thermally conductive adhesive films are die cut into more complex shapes to bond a specific part or area. They can hold device components in place while retaining conductive properties.
Pros:
- Consistent application and performance due to an even distribution of conductive material
- Options for machine-automated applications
- No risk of overflow
- Adjustable thickness
Cons:
- Doesn’t fill certain roles like heat sinks or potting
- There could be microscopic air gaps
5 Factors to Consider When Choosing a Thermally Conductive Adhesive
Each type of adhesive can be valuable if used in the right situation, meaning that while different types of thermally conductive adhesive might suit your product, it’s up to you to choose a material by evaluating the importance of different traits for a specific product.
Here are the different factors you’ll encounter when choosing a thermally conductive adhesive for your design to help you decide upon your final selection:
FACTOR #1: THERMAL RESISTANCE
For many engineers, the first step in choosing a thermally conductive adhesive is determining the thermal resistance level it needs to withstand.
The thermal resistance of your adhesive depends on your material and the type of adhesive you use.
For instance, thermal pads are designed to withstand high temperatures in order to conduct the flow of heat from the printed circuit board into its heat sink. To prevent failure in the PCB setup, selecting adhesive requires you to consider a thermal pad’s conductive strength, size, thickness, and thermal resistance.
If an application were in constant motion, converters might not recommend something like thermal grease or paste due to their lack of adhesive ability, which might cause the internal components to slide.
Poor thermal resistance can result in the failure of the entire system, so you’ll want to look at the size, piece proximity, and surrounding materials to determine the material you plan to use.
FACTOR #2: CONDUCTIVE STRENGTH OF THE ADHESIVE
After gathering a list of adhesives with the necessary thermal resistance to run your device, you’ll also want to determine whether their conductive strength meets your requirements.
Similar to thermal resistance, the conductive strength of an adhesive varies more on the type of material rather than the type of adhesive used. Certain adhesive foils have strong conductive properties while others are weaker than thermal grease or epoxy.
Thermally conductive adhesives vary in conductive strength based on their material, but the material’s ability will also vary based on its thickness (or density).
FACTOR #3: MATERIAL THICKNESS
Regardless of the type of adhesive you choose, the material thickness will affect its conductive ability.
Thicker Thermal Interface Materials (TIMs) cannot transfer heat as effectively as thinner conductive materials. The thick material collects heat slower at a greater quantity, which isn’t ideal for part conductivity.
On the other hand, epoxy or glue can have varying densities of conductive particles within each measurement, and like with grease or paste, you can apply thicker or thinner layers of it.
With adhesive film, you can adjust the thickness to change the conductive speed and effectiveness of the material. However, with epoxy or glue, you can adjust the density of conductive particles for a stronger charge.
FACTOR #4: SUBSTRATE COMPATIBILITY
With any adhesive application, you’ll want to start out by asking yourself, “Which surfaces do I need to bond together?”
Regardless of the thermally conductive adhesive you choose, you’ll need to consider the types of substrate your adhesive can bond with for effective applications.
While materials like glue or epoxy are limited to one type of adhesive connection, converters can laminate flexible materials together to create adhesive bonds with either substrate.
Thermal pads and films allow for adhesive lamination, but thermal grease and paste are ideal for situations in which you are looking to conduct electrical charges, but are also willing to make internal connections using additional types of adhesive or mechanical fasteners.
FACTOR #5: MANUFACTURABILITY
If your thermally conductive adhesive isn’t manufacturable, it won’t create a production-friendly part.
Part manufacturability can significantly impact the cost of your product. Difficult part manufacturability will lead to increased time on a machine press, elevating your labor cost. At the same time, more simple application methods can be built into production with more ease and automated in the future.
Consider your goals for scaling or automation and how they align with your current plan for production as you plan for manufacturability, and you’ll discover the types of adhesive materials that lend themselves to manufacturing in production.
How Can I Choose a Thermally Conductive Adhesive?
You might be overwhelmed by the prospect of finding material, but your first step is likely choosing the type of adhesive you’re interested in.
Now that you know different types of thermally conductive adhesives, you may understand how their properties lend themselves to different products. Once you’ve prioritized the factors most important to your project, you can select an adhesive type and begin the search for a converter or manufacturer that suits your product application.
Different manufacturers specialize in different types of adhesive, so knowing whether you want glue, epoxy, grease, paste, thermal pads, or film, will help you narrow down your pool of options into a more manageable list of experts to reach out to.
Your converter can help you coordinate the next steps like picking out an adhesive for an adhesive pad or film based on the design and application of your product.
