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For more than 100 years, the car has simply been used as a device for transporting a driver and passengers from point A to point B at speed with minimum effort.
With the introduction of Advanced Driver Assistance Systems (ADAS) and other semi-autonomous driving technologies, a different concept of the vehicle is emerging. In the future, the car will be a media playback center, telephone, office and extension of the home’s living room which also happens to be able to convey passengers from A to B.
This is having a profound effect on the characteristics and on the sheer number of electronics systems in new vehicles and this in turn will dramatically extend the demands on the EMI shielding devices used to attenuate the radiated emissions that could affect circuits in the car. EMI shielding materials will need to perform over a wide range of frequencies, in more applications as electronic systems take over more and more aspects of the car’s driving operations, while adding as little as possible to the weight of the vehicle.
The time for OEMs to consider the options for achieving EMC in new car designs is at the start of a new design project, before the electrical and mechanical features of the vehicle’s systems have been decided. This gives design engineers the opportunity to bring considerations of EMI and shielding devices into the design process and enable optimization of the size, cost and performance of EMI shielding in the final system.
Top challenges of next generation 5G networksThe first challenge for automotive design engineers is the range of frequencies that need to be attenuated will be far greater in new cars than it was in the past. Until recently, the main frequencies of interest were the AM and FM bands used by radio and frequencies below 3GHz used by Bluetooth radio and mobile phone networks.
With the future introduction of 5G mobile phone network coverage, frequency coverage of EMI shielding materials will need to be extended. A higher frequency range is not the only issue. Cars are also going to support a much greater number of wireless communications systems within the vehicle.
The second challenge is that the effectiveness of EMI shielding is likely to be more tightly specified in the future as automotive manufacturers move towards a strict view of the functional safety of the electronics systems in cars, codified in the ISO 26262 functional safety standard.
So, what does this mean for the specification of EMI shielding materials?
Parker Chomerics maintains an intensive research and development program aimed at producing new filler materials for electrically conductive elastomer products. An important goal for this research program is to produce EMI gaskets that can cover the broader frequency range of interest in autonomous vehicles, while maintaining the desirable mechanical characteristics. Parker Chomerics CHO-SEAL conductive elastomers are widely used in automotive systems and offer useful properties, including resistance to high temperatures and contaminants, and the ability to provide environmental sealing to protect circuits from the ingress of liquids.
These elastomer gaskets resist compression set, accommodate low closure force, and help control air flow. They are available in standard sheet form, extruded or custom shapes.
In addition, Parker Chomerics CHOFORM Form-In-Place automated EMI gasket material can be dispensed directly onto castings, machined metal and conductive plastic and is widely used in tightly packed electronic housings. This advanced technology allows dispensing of precise positioned gaskets in very small cross sections and can free up valuable packing space of up to 60%. CHOFORM offers excellent shielding effectiveness which exceeds 100dB between 200 MHz and 12GHz.
New opportunities for weight savingThe development of autonomous and semi-autonomous vehicles is leading to a huge increase in the number of electronics modules per vehicle. This increases the scope for car makers to reduce weight by replacing conventional metal housings with lighter conductive plastic housings. While the weight saving on each module might appear small, when multiplied across the 100 or more electronics modules, the total weight saving becomes invaluable.
Parker Chomerics PREMIER™ PBT-225 is a single-pellet conductive plastic for use in automotive housings. PREMIER PBT-225 offers excellent resistance to hydrolysis when exposed to extreme temperatures and provides for easy processing and uniform filler dispersion. As a result, EMI housings made from PBT-225 offer tightly controlled electrical and mechanical performance throughout complex geometries. A weight saving of 30% is also possible when replacing an equivalent metal or aluminium housing with PBT-225.
By collaborating early in development projects with Parker Chomerics, automotive system designers can ensure that their electronic and mechanical design is optimized for shielding purposes.
Learn more about Parker Chomerics EMI shielding and thermal solutions for the automotive Industry.
This blog post was contributed by Mel French, marketing communications manager, Chomerics Division Europe.
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Honeycomb air ventilation panels are used in applications where superior electromagnetic interference (EMI) shielding must be incorporated with heat dissipation in the form of airflow. Every vent panel has a variety of design features, each providing benefits to end customers based on specific application needs. These design features can include framing, plating/painting, gasketing, and vent size control.
An often overlooked but highly important phenomenon to consider when designing EMI vent panels is that of polarity.
What this means is that honeycomb vents can have differences in shielding effectiveness, sometimes as great at 50 dB, depending on the direction of the electromagnetic waves.
For example, a basic aluminum honeycomb vent may provide shielding of 70 dB in the horizontal direction while only providing shielding of 25 dB in the vertical direction. This characteristic is due to the manufacturing process of standard aluminum honeycomb vent panels.
Basic aluminum honeycomb is created using thin ribbons of aluminum that are bonded using a non-conductive adhesive. Polarity is associated with seam leakage caused by the non-conductive bonds from cell to cell created during the manufacturing process of adhering aluminum ribbons together to make the honeycomb. While thin, this non-conductive gap is the cause of difference in shielding effectiveness (SE). It is important to note that polarity is only an issue for aluminum vents, not for steel, stainless steel, and brass honeycomb due to a different manufacturing process (steel and brass honeycomb use a welding process, eliminating the non-conductive gap). The below graph demonstrates the significant difference in shielding effectiveness in the horizontal and vertical directions.
Fortunately, there are several solutions to combat this polarity issue:
Layered ventsWith the addition of a second layer of honeycomb, offset at a 90-degree angle, the polarization effect can be dramatically reduced. The Chomerics term for these layered vents is Omni Cell. By rotating the second layer of honeycomb 90 degrees, RF wave interaction in both the X and Y axes are combated by the seam orientation of each layer of honeycomb. This means that while the electromagnetic waves may pass through one layer of the honeycomb, the offsetting layer will not allow them to pass through the entire vent assembly. Of note, airflow through the vent is not significantly impacted, allowing for enough heat dissipation.
While the maximum shielding effectiveness of the Omni Cell vents is nearly identical compared to that of a single layer vent, the directional consistency is instantly noticeable. There is no longer a difference in the horizontal and vertical shielding effectiveness, with the offsetting layers eliminating the polarity effect.
PlatingElectroless nickel plating is an ideal plating option to combat polarity on aluminum vents. The nickel plating covers the non-conductive bonds and eliminates seam leakage between aluminum ribbons. The nickel plating electrically connects the aluminum ribbons which overcome the non-conductive adhesive. Not only does nickel plating effectively eliminate the polarity effect, it increases the durability of the vents and improves their lifespan in harsh environments.
As with Omni Cell vents, the polarization effect is eliminated with the vent exhibiting nearly no difference in shielding between horizontal and vertical testing. A properly plated vent will also increase the SE of the entire honeycomb array, creating conductive contact between every individual aluminum ribbon in the assembly. The nickel plating also improves the electrical connection of the honeycomb to the frame if the plating process is done after assembly.
Based on the above graphs, a conclusion can be made about the techniques used in eliminating the polarity effect. Since the plating process can eliminate the polarization effect AND increase the SE, this approach is most common. Omni Cell construction is effective if it meets the desired shielding effectiveness level. It is rare to see a nickel plated Omni Cell vent.
Individual project specifications such as airflow requirements, shielding performance, environmental exposure, budget and a myriad of others will drive the design process of EMI shielding honeycomb ventilation panels, but it is important to know about principles such as polarity in making final considerations.
Article contributed by Ben Nudelman, market development engineer, Parker Chomerics Division.
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As the defense industry continues to push the boundaries on advanced electronic systems and state-of-the-art communication devices, the requirements governing these programs must follow suit. Among the many technical requirements is Electromagnetic Compatibility, defined as the ability of a device to withstand both anticipated and unanticipated electronic interference (EMI) as well as minimize the interference being radiated.
It’s important to note that electromagnetic compatibility is a requirement across a variety of platforms in military technology including, but not limited to: missile and missile defense, ground vehicles, man-portable communication, electronic warfare/radar, stationary shelters, and avionics. Additionally, commercial technology such as aircraft and satellites often adopt military standards for electromagnetic shielding.
Missiles and missile defenseInnovation and improvements in war-fighting over the past several decades have led to the improvement of key weapons systems, most notably the missile defense arsenal. As weapons improve range, minimize collateral damage, and attempt to outpace anti-missile efforts, a greater focus has been placed on electronic controls and built in fail-safe measures. These measures are developed to the highest EMI standards for the safety of military personnel, with elastomer gaskets and conductive paints serving to ensure weather sealing and minimization of interference.
Ground vehicles
Humvees and tanks are built for durability in all environments, with safety of the crew a top priority. To ensure proper function of the engine components, weapons systems, and data transmission, these vehicles must meet EMI standards. Expanded aluminum gaskets for turret and antenna mounts are just one example of shielding efforts on both the interior and exterior of the vehicle
Man-portable communication
Defense research and development continues to optimize the gear used by servicemen and women, both in combat and support roles. The first line of communication is the direct unit carried by those who serve, whether built into helmets/headsets or carried in the form of hand-held devices. Each device is tested and retested, verifying that interference will not present hazards at the most inopportune times. EMI shielded displays on these devices ensure minimal interference with maximum information transmission.
Electronic warfare/radarRadar and electronic warfare modules come in all sizes, from under-wing units on fighter jets to stationary units the size of a small island. Each unit, whether stationary or mobile, must pass stringent electronic emissions and susceptibility standards to ensure that billions of dollars of development and manufacturing yield the most advanced technology.
Stationary sheltersGround control shelters have become mobile mission control hubs, storing a great deal of technology inside. EMI shielding caulks and compounds at the seams ensure that only the proper information is relayed as expected.
On-board electronics equipment such as flight recorders, navigation units, flight-control systems, and radios are perfect examples of components that must comply with EMI shielding specifications. These devices are mission-critical, with the slightest interference potentially causing communication delays or misinformation presented to the crew or ground control staffs. Commercial aircraft observe similar safety requirements, while including additional electronics such as in-flight entertainment units that utilize custom shielded display units.
EMI shielding is a crucial consideration in the safe and effective operation of defense electronic systems. Nearly every device developed for military and aerospace applications must utilize gaskets, coatings, adhesives, or a variety of other sub components in meeting rigorous military electronics standards. Additional technical information and specific metrics on defense requirements for electromagnetic compatibility can be found in MIL-STD 461G.
Article contributed by Ben Nudelman, market development engineer, Parker Chomerics Division.
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From the Parker O-Ring Handbook and Material Offering Guide to finite element analysis and blogs, our engineering experts run the gamut of all sealing solutions. So it's no surprise that the top blogs over the last six years fall into categories that highlight their recommendations on O-ring design tips, installation basics, and O-ring sealing alternatives.
Bookmarking these blog favorites are sure to come in handy for your future sealing challenges. Simplify your research by checking out these top ten sealing solutions and design blogs by Parker O-Ring & Engineered Sealing Division.
For further expert tips and advice, be sure to chat with our engineers by visiting our website or check out our Parker O-Ring eHandbook and Sealing Solutions eGuide.
Selecting the Right O-Ring Seal Squeeze Ratio:
One of the decisions equipment designers need to make when installing O-ring seals in their applications is how much the O-ring will be squeezed by its mating hardware to create an effective seal.
Racetrack Grooves: Can O-Rings be used in Non-Circular Groove Patterns?
Can O-rings be used in rectangular or non-circular groove patterns? This question comes up weekly, and the answer is a resounding “Yes!” however there are definite guidelines we want to follow.
Sealing Fundamentals | Face Seal:
The physics of creating a face seal is relatively simple. In most sealing systems, the objective is to prevent fluid from leaking from a high-pressure location to a lower pressure location through a sealing gap. Sealing fundamentals should be followed for trouble free application.
Why is Shore A Harness Important?
O-rings are the simplest, most readily available type of seal used across every industry and market. They are arguably the best seal for many applications, but perhaps daunting to an engineer with no experience in seal design.
O-Ring Squeeze - More is Not Always Better:
Conventional wisdom says that the more an O-ring seal is squeezed (i.e. deformed relative to it’s “unsqueezed” state), the tighter the seal. More squeeze equals greater force between the O-ring and its mating hardware — which means that liquids, gases and dry powders are otherwise prevented from flowing between the rubber seal and mating hardware.
The proper method of applying a lubricant to an O-ring always seems to be an area of concern for many of our customers and there are many methods used in the marketplace.
O-Rings and Seals for Automotive Transmission Fluid:
Efficiency gains in the automotive industry are not limited to engine designs. Transmissions are also undergoing significant changes to increase fuel mileage. To reduce friction and cope with more gears (or even an infinite number of gears with a Continuously Variable Transmission (CVT)), new Ultra Low Viscosity (ULV) transmission fluids and CVT fluids have been developed. Fortunately, Parker has already performed a significant amount of testing in these new fluids.
3 Guidelines to Ensure Proper Seal Installation:
If O-ring damage happens with high frequency, you could be wasting time and money on seal replacement. Luckily, there are some easy steps that can be followed to help prevent this from occurring. Parker’s recommended guidelines for installation include always using lubrication, good gland design, and ensuring correct sizing.
TetraSeal: An Alternate Sealing Solution When An O-Ring Isn't Working:
It isn’t all that uncommon for a groove to be cut in a flange and a novice designer learns the hard way that standard O-rings cannot fit in just any groove geometry. For hardware that has already been machined, frustration ensues as the caller learns the O-ring solution requires tooling. Parker offers a TetraSeal® solution, which often does not require tooling and can be made of many of the same materials used for O-rings.
What O-Rings Do You Recommend for an E85 Rated Assembly?
There are nearly 20 million flex fuel vehicles on U.S. roads today, and over 2,900 ethanol fuel stations. With the increased use of alcohol/fuel blends there is also an increased demand for seals that are compatible with alcohol/fuel blends. Parker offers a variety of compounds to meet this crucial need in the automotive industry.
Samantha J. Sexton, marketing communications manager, Parker O-Ring & Engineered Seals Division
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Did you know that up to 80% of conductive coating failures can be directly attributed to inadequate surface preparation? Not properly preparing your surfaces for spraying or adherence is almost certainly the best way to set yourself up for failure. And on top of that, many different surfaces require vastly different preparations – it’s hard to keep up with which goes with which!
Conductive paints such as the new PRO-SHIELD family are generally comprised of micron sized metal particles of nickel, copper, silver plated copper or silver blended into water or solvent based paint system. Similar to selective plating processes, a masking fixture is used to control the location of the conductive paint that is sprayed onto the required areas of the part. The fully cured conductive paint thickness ranges from 0.0005” (0.0125 mm) to 0.002” (0.05 mm) depending on the paint type and EMI shielding requirement.
The paint can be applied in a manual paint booth where an operator applies the paint with a paint gun or with a paint robot. The automated process offers advantages over manual spray methods, especially in higher volume applications where cost is of most importance. With the automated process, the spray pattern can be programmed to apply the optimal amount of conductive paint across the entire shielded surface. Manual paint application typically has lower set-up cost than automated painting and is a good match with lower volume applications or for qualification testing and prototyping.
Surface preparation guideThe Parker Chomerics' PRO-SHIELD conductive paints and coatings surface preparation guide will help you determine the best surface preparation guidelines for your conductive paints, adhesives, and inks, including our new PRO-SHIELD family of conductive paints and coatings. From Acrylic to zinc and any surface in between, our guide to conductive paint surface preparation covers it all.
Did you know the best way to properly prepare a copper surface for a silicone adhesive is to first clean with methyl ethyl ketone (MEK), followed by toluene? Be sure to let the surface air dry, then roughen the surface with 220 grit sandpaper and apply any commercially available silicone primer. Now you’re all set to add your silicone conductive coating or adhesive.
Be sure to check out our PRO-SHIELD Guide for Preparing Surfaces for Conductive Paints and Coatings for more information.
This blog was contributed by Jarrod Cohen, marketing communications manager, Parker Chomerics Division.
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The world of thermal interface materials continues to evolve as the cooling requirements for applications in the automotive, consumer, medical and aerospace markets continue to demand lower prices and higher performance. As each new product generation requires higher power in smaller packages the challenges associated with thermal management become more intense.
The criteria which engineers use to select these thermal interface materials will by necessity include the thermal conductivity. However other properties of the material such as its hardness, dielectric strength, dielectric constant, compression set, cut-through resistance, toughness, tensile strength and resistance to chemical and environmental attack is equally important, as well as their suitability for rework or repair.
So which is the best product for your application? Here are the top four thermal interface materials.
Dispensable gels
Highly conformable, dispensable, one and two component, pre-cured, or cure-in-place silicone, such as Chomerics THERM-A-GAP® gels are ideal for filling large and uneven gaps in electronics assemblies. The viscoelastic paste is a form stable, cured silicone material that takes considerably less force to deform during assembly than traditional form stable gap fillers. This characteristic helps avoid placing excessive stress on component solder joints and leads that can result in either premature failure of the device or damage to the circuit board on which it is placed.
Parker Chomerics has also developed pre-cured and cure-in-place non-silicone gels to resolve the issues of silicone contamination in some applications. This unique material has similar thermal and physical properties to the silicone gel without the problems silicone can sometimes cause.
Gap filling pads
Chomerics THERM-A-GAP® silicone based gap filler pads have supported the utilization of equipment enclosures or chassis as heat dissipaters in place of costly and heavy dedicated heat sinks. By fitting a piece of soft gap filling material between a device requiring thermal management and an enclosure, heat can be channeled away effectively. Because of the typically large surface area of the equipment enclosure coupled to the fact that it provides a direct thermal path to the lower temperature of the ‘outside world’, adopting this approach can also negate the need for fans where they were previously required for a specific design.
Gap filling pad materials are available in a wide range of thicknesses that now extends beyond 5mm, allowing even very large gaps to be bridged. Their extremely soft nature means that large mechanical tolerances can be taken up with relatively low assembly forces being used. Accurate blending of silicon-based gap fillers, using a range of materials with different thermal conductivities, results in a choice that allows designers to select a material that accurately meets the thermal requirements of their specific design.
Insulator pads
These are generally very thin materials (around 0.25mm) that comprise a silicone elastomer blended with a thermally conductive filler. Fiber glass cloth is commonly used to reinforce the material and provide some resistance to cut through that would reduce the electrical isolating properties of the material. There is a wide choice of CHO-THERM® insulator pad materials available.
These use a variety of different fillers that provide a wide range of thermal and electrical performance levels. Options such as low-tack adhesive coatings, pressure sensitive adhesives, and tabbed release liners, which aid assembly, may also be specified.
Adhesive tapes
Thermally conductive tapes, such as Chomerics THERMATTACH® provide effective alternatives to mechanical fasteners such as screws, clips and rivets for bonding heat sinks to either ceramic or metal device packages.
The benefits include, lower assembly times, smaller footprints, and reduced material costs.
Learn more about Parker Chomerics Thermal Interface Materials
This blog was contributed by Mel French, marketing communications manager, Parker Chomerics Division Europe.
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Fundamental design checkpoints of new products generally focus on the designs of mechanical, electrical and software systems. On the whole, EMI/EMC design falls by the wayside for many companies, including preparation for certification testing.
If any of the above answers give you cause for concern, then you now realize that testing your product early in the design cycle to make sure it works appropriately in an EMI/EMC environment is just as important as the basic mechanical and electrical design to make it function.
In this blog we’ll discuss the basics of EMI/EMC pre-compliance testing – something all electronic products should undergo much earlier than full certification testing. Typically EMI/EMC compliance testing certification occurs very late in the development process and test failures are almost always encountered. If you did pre-compliance testing earlier on, fixing these test failures is far easier and less costly.
What is EMI/EMC anyway?EMI and EMC stand for electromagnetic interference and electromagnetic compatibility respectively. EMI is the unwanted electromagnetic energy either radiating in free space or conducting down I/O and/or power cables. This unwanted energy can come from any electronic device and is considered interference when the energy makes another device malfunction. EMC is the ability of electronic devices to all operate in harmony in an environment, including unwanted EMI. This can also include wanted electromagnetic energy in the form of intentional radiation off antennas such as WiFi.
All electronic products, whether it be your tablet or your TV, must eventually pass EMI/EMC compliance tests to be certified before they can be brought to market. This certification testing is performed to demonstrate that a device will not electromagnetically interfere with another electronic device in close proximity and in turn, not be interfered with from the other devices.
To get your device certified, there are four basic types of EMI/EMC phenomena a device must pass:
Emissions is concerned with the amount of unintentional electromagnetic energy emitted from your device. As stated earlier, it can happen in the form of radiated electromagnetic energy or conducted electromagnetic energy conducting down interface cables and/or power cables. The intentional radiation of any antenna is also considered a radiated emission and also must undergo certification testing to ensure the radiated energy is effectively controlled.
Immunity is concerned with how susceptible your device is to electromagnetic energy being emitted from surrounding devices. For example, if you were a patient in a hospital hooked up to a medical device, would you want that device to malfunction by electromagnetic energy from other devices in close proximity? Unless you've got your malpractice lawyers on speed dial, this wouldn't be optimal. The device malfunction can be created by either radiated or conducted electromagnetic emissions (EMI).
Here again, a device cannot be placed on the market (sold) without having proven to meet the EMI/EMC regulations. Regulatory bodies, like the Federal Communications Commission (FCC) in the United States (US), set up EMI regulations that devices are tested against. As you would expect, standards vary from one device to another – meaning intentional and unintentional radiated emissions have different requirements. Similar radiated and conducted emissions requirements exist globally. Much of the standards development activity is now handled by the International Electrotechnical Commissions (IEC).
Immunity regulations are not as widespread globally. Although immunity requirements are most prevalent in Europe, similar requirements are being adopted in many other countries. For example, medical device approval in the US by the Food and Drug Administration (FDA) requires compliance to both emissions and immunity regulations.
In addition, countries such as Taiwan and Japan have adopted many of the IEC standards which include both emissions and immunity. In some cases these standards are adopted with minor changes which are typically called “country specific deviations."
So what do you recommend?EMI/EMC testing is very expensive, but what makes it the most expensive is failing test requirements at the end of the design cycle when a device is ready to be released. At that point making changes to a device is the most painful and you risk having to do design revisions and throwing off your entire schedule. That’s why it’s important to do some pre-compliance testing for your device during the design cycle well in advance of sending it in for certification compliance testing.
The further any device design is down the path to completion, the more painful it is to make changes to correct test failures. In addition, it becomes less likely that the problem can be solved at the board level or internal to a device in general. At that point the focus typically becomes a packaging solution. This is primarily due to the complex integration of components and sub subsystems that are purchased to be integrated into your design. You have little to no control over the EMI/EMC performance of these integrated parts.
Get to the point alreadyBased on this unknown, a packaging approach to address EMI/EMC issues is a sound way to end up with a solid design. Materials such as EMI gaskets, shielded windows and shielded vents can be incorporated into a design at any time. Typically, the earlier the better in pre-compliance testing will have the least impact with regard to cost and time.
Another important reason to use a packaging approach to your EMI/EMC design is that you not only need to be concerned with what your device may radiate (emissions) but you also need to be concerned with keeping outside unwanted electromagnetic interference out of your device so that your device does not malfunction (immunity).
This blog was contributed by Jarrod Cohen, marketing communications manager, Parker Chomerics Division
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Wherever drinking water is obtained from any of its sources, pumped and processed, materials with low extraction levels and without any harmful ingredients are required. Sealing compounds for use in drinking water and heating applications are subject to diverse approval regulations. These regulations serve to assure the safety of water from the time of intake, via treatment, processing and transportation through to the consumer. Practically every country in the world has its own drinking water regulations specifying particular tests and including lists of approved ingredients. These regulations are complemented by physical and microbiological examinations.
The Parker Engineered Materials Group has developed a number of compounds, each of which meets a wide range of the required approvals, thus permitting the global utilization of the sealing systems.
The peroxide-crosslinked plasticizer-free EPDM compound EJ820 was specifically developed for use in drinking water applications. The material conforms to all standard national and international drinking water approvals such as KTW, W270, W534, EN681-1 including the supplementary requirement, W534, NSF61, KIWA, WRAS, ACS. The material’s low compression set guarantees long life and thus permanent and reliable sealing of all fittings, valves and pipe systems. In addition, EJ820 exhibits enhanced resistance against autoxidation.
Parker materials cover a broad range of drinking and service water applications
Parker Compound E1244 E1512 E1549 E1561 E1583 EJ820 N1510 P5000 nobrox® Base Polymer EPDM EPDM EPDM EPDM EPDM EPDM NBR TPU
Posted by: Dr. Stefan Reichle, Market Unit Manager Industry, Engineered Materials Group Europe, Prädifa Technology Division
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There are a variety of thermal pads and gap fillers to choose from -- so many choices that it can become so overwhelming. How can you decide what's best for your application? And how does quality come into play? Read on, we answer these questions and much more.
Back to the basics: what are thermal gap fillers?
Thermal interface materials are used to improve performance and reliability of electronic devices by dissipating heat from a heat source to a heat sink. Both the semiconductor component and the mating heat spreader inherently have uneven surfaces.
The contact area can consist of more than 90% air voids, representing a significant resistance to heat flow. Thermally conductive gap fillers are used to eliminate these air gaps by conforming to the rough and uneven mating surfaces of both the heat sink and the semiconductor.
THERM-A-GAPTM gap fillers are a family of soft, thermally conductive silicone elastomers for applications where heat must be conducted over a large and/or variant gap, always between a semiconductor component and a heat dissipating surface. Gap fillers are supplied either in pad-form which can cover a wide range of thickness (0.25mm to 5mm), or as fully cured dispensable gels.
How to identify quality thermal gap fillers in four steps (summary):
Now, let's review each step in more detail.
Step 1: Identify thermal performance
First, it's a good idea to Identify the amount of heat [Watts] that you need to dissipate to determine the thermal conductivity performance of a gap filler. This is usually displayed in Watts per meter Kelvin, or W/m-K. The higher the number, the more heat the material can theoretically dissipate. Gap filler materials offer a high tack surface which reduces contact resistance.
Step 2: Choose low mechanical stress
Generally speaking, the softer the gap filler, the better it is at filling voids and surface irregularities under low pressure. You can tell the hardness of the gap filler as it's usually measured in Shore A or Shore 00. The lower the hardness rating, the softer the material. Gap pads and gels are also good at absorbing shock and vibration to help with reliability.
Step 3: What's my assembly?
Gap filler pads are offered on a variety of carriers for ease of assembly and end-use. They include:
Thermal gap filling gels are single-component products that require no mixing or refrigeration, and can be dispensed directly on to parts.
Step 4: Make sure there's reliability data
THERM-A-GAPTM products have been examined for physical and thermal reliability after being subjected to multiple environmental stress tests (elevated temperature, random vibration, heat and humidity, etc.) with varying gap thickness. The results have indicated superior long-term physical integrity and thermal reliability. Discover these test reports for THERM-A-GAP G579 and THERM-A-GAP GEL30 now.
This blog was contributed by Callie King, applications engineer, Parker Chomerics Division.
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Polyurethanes have been around for decades as a seal material for high pressure reciprocating mobile hydraulic applications. Original equipment manufacturers select it as their “go to” seal material for mobile equipment due to fluid compatibility, cost effectiveness, long service life, and reliable sealing. These capabilities are attributable to the molecular chemistry of polyurethane that produces desirable performance characteristics such as:
Seal manufacturers are closely dialed in to the need for equipment manufacturers to extend the overall useful life of mobile equipment. In addition, there are global expectations and owner/operator use trends pushing the envelope and driving the need for polyurethane materials capable of sealing higher temperatures and higher pressures, including:
Given the trends mentioned above, how will prolonged exposure at elevated temperatures – still within range – affect seal performance and ultimately, seal life? Seals are assigned a temperature rating by manufacturers, but how much is too much when it comes to heat exposure?
What do temperature ratings mean?Manufacturers like Parker quantify thermal capabilities of their engineered sealing materials by assigning them “Temperature Ratings” – from X to Y (min to max), but what does that really mean for equipment designers?
Temperature ratings for sealing materials are generally based upon the typical physical characteristics of the material alone. A material's suitability for a specific application, however is dependent on actual use conditions which take into account wide ranging variables which include but are not limited to: hardware attributes and configuration, seal profile geometry, fluid compatibility, and expected duration and frequency of service exposure at pressure, temperature, and speed (i.e. ambient, continuous operating, intermittent, excursion).
Assuming one has taken into account actual use conditions, specified a profile geometry, and selected a compatible material, let's next consider whether one can reasonably expect that seal performance will be constant at all temperatures within the material's broad stated range.
Supported by exhaustive mechanical test lab data representing millions of cycles and decades of experience designing sealing systems, our application engineers know that best sealing performance with polyurethane can be expected when an application’s continuous operating temperature falls well within the maximum and minimum temperature limits for a compound. This is illustrated in Figures 1 and 2.1
As a practical example, the four scenarios in Figure 1 represent expected seal performance of Parker’s high performance Resilon® 4300 polyurethane material along its stated thermal range of -65°F to 275°F as configured in the application types and profiles shown (i.e., rod/piston, rod wiper, static O-ring/head seal, bumper/damper). Figure 2 is the key showing expected performance at each color coded interval.
A closer look at what this meansThe purple range represents conditions where performance is compromised due to compound stiffness. In this extremely low temperature range, the polyurethane material is hardening and approaching glass transition and brittle point.
The blue range represents values where performance is compromised due to stiffness and compound rigidity. Polyurethane lip seals may require a low temperature energizer to offset compromised resiliency.
The green range represents the recommended continuous operating temperature range for best performance.
The yellow range represents extended or continuous exposure under system pressure in temperatures roughly spanning 225 to 240°F. In this scenario, continuous dynamic cycling and increased frictional heat buildup compromises three critical performance characteristics of polyurethane: tensile – most closely associated with wear resistance; modulus – most closely associated with extrusion resistance; and compression set – most closely associated with resiliency (sometimes referred to as sealing force or the ability of sealing lips to “bounce-back” after being compressed).
In thermal conditions represented in the red area, the reference material Resilon 4300, is capable only for short duration before tensile, modulus, and compression set are irreversibly compromised.
In summary, temperature ratings of polyurethane seal materials are primarily based on laboratory and service tests and should be used as a guide only. They do not take into account all of the variables that may be encountered in actual use. Seal designers will have more certainty and a better judgment of the fit of the seal material to the application. when the application’s sealing demands are in alignment with the described expected performance scenarios shown in Figure 2, there will be more certainty and a better judgment of the fit of the seal material to the application when all variables are considered and then matched to expected performance.
1It is always advisable to test material under actual service conditions before specifying.
This article was contributed by Shannon Johnson, marketing communications manager, Engineered Polymer Systems Division.
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