Thermal Interface material Types
Every
thermal management solution requires a thermal interface material. It's
critical to understand the characteristics of various thermal interface
material types so you can make the best decision for your application.
Depending
on your application, you may prefer one type of TIM over another to improve
performance. Some are rigid, while others are adaptable. Some TIMs are solid,
whereas others can go through phases. There are numerous thermal interface
material types available for increasing heat transmission between surfaces, but
selecting the proper one is critical.
Types of Thermal Interface Material
Thermal grease
This is probably the first form of thermal interface
material that springs to mind for anyone who has built their own PC. As you may
expect, thermal grease is a lubricant that is specifically developed to have a
high heat conductivity. The majority of thermal greases are silicone-based,
with microscopic thermally conductive filler particles that boost the mixture's
overall conductivity. Silicone-free greases are available for applications that
are silicone-sensitive. A silicone-free solution would assist applications that
are concerned with the wettability and stickiness of surfaces that may come
into contact with a thermal grease.
Widely Available and Generally Used Application
Thermal grease is inexpensive and easy to come by, making it ideal for do-it-yourself projects, prototypes, and small production runs. It's pretty easy to construct a template for screening on thermal grease for applications that require consistency from one product to the next. This makes application-specific grease patterns straightforward and cost-effective. Other thermal interface materials necessitate die cutting to create bespoke forms, which is often more costly than a grease screen.
Interface Resistance is low, making it perfect
for flat surfaces
As greases are a form of pseudo-fluid, applying
pressure to thermal grease between two surfaces causes the grease to shear and
spread thin. In terms of thermal management, this is advantageous. The less
resistance your interface material will impose on heat transfers, the thinner
the material between the surfaces you're trying to transmit heat between.
Thermal grease is great for flat and smooth surfaces because of this. Rougher
or more complex surfaces with varying heights have small spaces that the grease
cannot completely fill, which is why gap fillers and other thermal interface
materials were designed.
Thermal greases necessitate mounting forces that are spring-loaded. The thermal grease can thin out and flow a little when it heats up. It's best to use a springy force to mount greased surfaces to ensure that both surfaces are continually in touch and compressing the grease.
What a shambles of greases!
The remarkable ability of thermal grease to get there and everywhere is a running joke at the test lab. It gets on your shirt if you look at it the wrong way. Thermal greases, like any other grease, can be difficult to clean up and maintain contained. Grease is held in tubes and syringes in smaller quantities, allowing for more precise administration. Thermal greases in bigger quantities come in larger containers with large covers, and applying grease from an open tub can be messy.
Grease can’t be reused
Thermal grease has several advantages, including
flexibility and ease of application, but it has the disadvantage of not being
reusable. There is no reliable method to gather the grease back up to the initial
thickness you applied without creating air pockets that undermine the whole
objective of a thermal interface material after it has been compacted and
thinned out.
Thermal grease has a tendency to outgas and dry out
more volatile compounds in the combination with prolonged use. The outgassing
chemicals are used to reduce viscosity and simplify the application process,
ensuring that the product is not an issue year down the line. When it comes to
rework, it's a problem. The grease has turned into a crumbly mass that cannot
be reapplied. The only method to restore previous performance is to reapply new
thermal grease.
Gap
Fillers
Another
prominent interface material is gap fillers. Gap fillers are elastomeric sheets
that contain specific thermal filler material to boost the material's overall
thermal conductivity. They're commonly constructed of silicone. These materials
come in a variety of sizes and shapes, making it quite simple to locate the
right gap filler for the job. Typically, gap fillers are cut to standard device
sizes or bespoke shapes for specific purposes.
Gap
Filler Materials Come in a Variety of Shapes and Sizes
Gap fillers
are the most diverse form of significant thermal interface material. A base
elastomer and a thermal filler are combined up with all gap fillers, which
might include silicone and silicone-free compounds. When it comes to gap
fillers, these are just a few of the alternatives accessible. Multiple sheet
thicknesses, sticky or adhesive options for each side of the sheet,
reinforcement materials like fiberglass, and carrier options for preserving the
material before application are all available within the same elastomer and
filler mix. Certain
materials have the ability to electrically isolate hot devices. Electromagnetic
interference can be absorbed by some gap fillers (EMI). You may have a hundred
different alternatives with just one material type if you combine all of these
options. This variety of alternatives is what makes gap fillers a popular
choice for thermal interface material.
Gap Fillers with Tolerance Stack-Up and Multiple
Devices
Gap fillers do have springy quality as they are made
of an elastomeric base material. This means it can be compressed and apply
pressure proportional to its deflection against the surfaces pressing against
it. Instead of an axial spring, it's an elastic surface that can be compressed
in varying amounts across its entire surface. This
is why gap fillers are so effective at accommodating multiple devices and
tolerance stack ups. Gap fillers will yield to varying heights, so if there's a
device where the tolerances stack up and there's some variation, the gap filler
can still connect the device to a heat sink. It doesn't have to be just one
device; it could be several devices connected to a single heat sink. It's
possible with gap fillers.
Thermal Interface Material with Some Reusability
Gap fillers can be reused in specific cases. These
thermal interface materials can spring back into position since they're
elastomeric. When we push too hard, we cause plastic deformation in the gap
filler, which prevents it from entirely recovering its original thickness. So
long as we stay within that range, we'll be able to use gap fillers once more. If the gap filler has an adhesive side, it may not
peel off easily, limiting its capacity to be reused. Adhesive or tacky surfaces
have an extraordinary ability to discover any and all particles floating
around, thus if the gap filler is not removed and replaced in a clean and
controlled environment, the surface may get unclean.
Thermal
Epoxy
Thermal
epoxy is the most durable thermal contact material. Thermal epoxy is
distinguished from regular epoxies by the use of thermally conductive fillers
in the resins. Thermally conductive ceramic particles are used in some epoxies,
while microscopic metallic particles are used in others. There are one-part and
two-part resins that can be mixed and applied to bind surfaces together, just
like conventional epoxies. The type of epoxy that is utilized is usually
determined by the materials that are being connected.
Using the
Strength of a Variety of Materials
Thermal epoxies generate a strong mechanical bond
between the surfaces they cure between, which is something most other thermal
interface materials don't do. As a result, thermal epoxy can function as a
thermal interface material as well as a mounting method. In some circumstances,
this can help reduce the quantity of mounting hardware used in a product or
application. This is why epoxy-bonded heat sinks are possible.
Some volatile compounds can be found in the resins and
hardeners that make up thermal epoxy. As a result, there may be some shipping
restrictions when exporting uncured epoxy. Uncured thermal epoxy may need to be
carried by ground since air shipping carries risks that air freight companies
do not want to deal with.
Possible Shipping Constraints
Thermal epoxy cannot be reused. Thermal epoxy, like
any other epoxy, will not simply break the polymeric connections that form and
attach to surfaces once set. This is why, before deciding whether thermal epoxy
is ideal for you, you should assess the amount of rework you may need to
undertake on your product. You'll have a hard time getting around your heat
sink and even harder time removing it if you need to perform maintenance on
your gadget with epoxied surfaces.
Phase
change material
A phase
change material is an intriguing form of thermal interface material. It is made
of a wax component with a certain melting point, which is usually between 50
and 65°C. As the material absorbs heat while changing from a solid to a liquid,
its temperature remains constant at its melting point. This allows for precise
temperature control between surfaces. Once the phase change material absorbs its
latent heat of fusion, or the energy required to totally melt the solid, it
will begin to warm up while in its liquid state.
Many phase change materials are deposited atop a
highly thermally conductive base material, which is also present in the application.
Some people employ a thermal film or aluminum foil to hold the material in
place before and during installation. Other phase change materials have films
on both sides, thus as the waxy substance is installed, the films from both
sides are eliminated, leaving only the phase change material between the
surfaces.
Reaching into every nook and cranny
When phase change material is heated above a certain
point, it melts and flows into any nooks and crannies between the surfaces it
is sandwiched between. Even the tiniest air pockets are removed using phase
change thermal interface materials, resulting in extremely low interface
resistance between surfaces. After the phase transition melts the first time,
you may expect consistently low thermal resistance between the surfaces you're
transmitting heat between.
Because phase change materials transform into liquids,
they can fit into places where conventional thermal interface materials can't.
This also implies that it can easily manage rougher surfaces. The use of phase
change material for heat transmission could benefit surfaces with flaws, rough
patches, or any other irregularities. However, for extreme height
discrepancies, gap fillers are still the best option. To fill the same volume
as gap fillers, a considerable amount of phase change material would be
required.
Spring forces
Phase change materials, like thermal greases, thin out
once they've been applied between surfaces for the first time. As the wax melts
and fills in any vacancies, the material becomes surface defects and no longer
adds to the material's thickness. This is why spring-loaded mounting methods
should be used with phase transition materials. While the phase change material
is still liquid, it will be compressed by a spring force. The force thins down
the material, lowering your contact resistance in the process. All of this aids
in the enhancement of thermal transmission between surfaces.
When replacing phase change material, it's simple
to clean up
Phase change material, like thermal grease, isn't
reusable, but it's also not a sloppy mess to clean up. When cool, phase change
materials, unlike greases, revert to a more solid form, making it easier to
scrape off surfaces. Typical cleaning fluids, such as isopropyl alcohol, can also
be used to remove the wax-like phase shift substance without the need to treat
the surfaces.
By
Siddhesh Gathe, Shubham Handibag, Harsh Mehta, Harshvardhan Kolekar, Harshwardhan Thakare
No comments:
Post a Comment