Keeping Your Silicon Cool
A Parker Chomerics expert shares real-world solutions for the heat-dissipation challenges in onboard electronics.
Onboard electronics continue to evolve rapidly. Components are smaller. Systems are more complex. The sophisticated electronics components that make up modern vehicles require precision heat dissipation for reliable operation. To help components and systems designers deliver high-performance, cost-effective solutions, the following are several actual cases illustrating the types of thermal interface material (TIM) and their performance properties,
Challenge #1: The EV/HEV DC/DC Converter
Manufacturers of electric and hybrid vehicles must cope with the demands of increasing 12V and 24V accessories that are powered by a DC/DC converter rather than a traditional alternator. This power converter must be reliable, lightweight, and highly efficient, with low electromagnetic interference and low current/voltage ripple. The heat that the converter generates must be adequately dissipated through the housing. An EV component supplier came to Parker Chomerics with a specific list of TIM requirements for the converter they were developing.
The requirements included:
- High material flow rate for high volume dispensing
- Lower compressive force than competitive gap pads and gels
- Thin bond line for smaller assembly gaps
- Low thermal impedance for effective heat transfer
- Reliability in vertical testing and high vibration applications
- Provide good dielectric strength to avoid breakdowns
Therm-A-Gap GEL 30 provided the ideal solution. This highly conformable, pre-cured, single-component compound offered a 20 grams/minute flow rate with 3.5 W/m-K thermal conductivity. With a recommended minimum bond line thickness of just 0.004-inch (0.10 mm), GEL 30 provided a solution for tight tolerances and small assembly gaps within the converter. As a material originally formulated for the auto industry, GEL 30 was developed with vertical applications and long-term vibration exposure reliability in mind. The manufacturer could easily dispense the product in various patterns onto the heat sink. A 300cc cartridge solution was implemented and will eventually convert to high-volume manufacturing using a one-gallon pump unit and valve dispensing system.
Challenge #2: PCB with multiple fill locations
A premium automotive system manufacturer was searching for a high-performing TIM for their infotainment module. The TIM needed to be adaptable to filling multiple locations on their boards, and it needed to meet a specific temperature threshold.
Specifically, it needed to be capable of filling five locations on their printed circuit board (PCB), each having a different footprint and gap height. The manufacturer needed assistance to determine the best material and the correct amount of gel to dispense in each location, as well as equipment to best dispense in the high-volume application. Compounding the issue, the board with the material affixed would undergo a solder reflow process which would reach temperatures as high as 245°C (473°F). The upper operating temperature for silicone-based gels is 200°C (392°F).
Initially, the customer provided a production PCB for evaluation, which was then replicated for testing using an in-house 3D printer. The 3D printed prototype parts enhanced the five locations for dispensing, so they could be correctly identified for precise dispense location.
Using a precision dispensing system installed in the applications engineering lab, potential materials were evaluated. Therm-A-Gap TC50 dispensable thermal putty was ultimately selected for its high thermal conductivity (5.0 W/m-K) and easy dispensing onto the 3D printed parts for capabilities trials. The prototype parts were successful in representing the actual PCB. The customer’s engineering team witnessed the tests and preliminarily approved the material for use.
Experiments were run to study the effects of elevated temperatures on the thermal and mechanical properties of the TIM compound. TC50 samples were exposed to the 245°C solder reflow process, and the results concluded that the thermal impedance (TI) and viscosity did not deviate over the extended time exposure. Finally, the entire assembly (PCB with the interface material and a cover) was evaluated in the actual solder reflow profile. It was found that the material maintained its rheological structure along with its intended thermal properties and was approved for the program.
Challenge #3: Safety modules for ADAS
As vehicles are relying more on advanced driver-assistance systems (ADAS), automotive camera and motion sensor companies are expanding their technologies to meet stringent compliance requirements. For some ADAS modules, this requires high-performance, robotically dispensed, thermal interface materials. The TIM must provide soft compression, ease of dispensing, and a flow rate suited for high-volume manufacturing. Additionally, the material may need to be visible to optical cameras.
In this case, the customer initially expressed a preference for thermal gap pads over dispensables, due to previous negative experiences with dispensing. However, due to volume production requirements, it became apparent that pads would not be a feasible option. In addition, the thermal material needed to be higher in thermal performance than the pads they typically used ( > 3 W/m-K).
Through extensive testing, Therm-A-Gap GEL 45 was selected as the optimal TIM for this application. GEL 45 offers a high flow rate suited for high-volume manufacturing (55 grams/min) and has a thermal conductivity of 4.5 W/m-K. The product is also black, so it can be seen by optimal cameras on the assembly line. Finally, the camera manufacturer ran a battery of tests to ensure the amount of material dispensed was adequate to the heat and would not damage the PCB during assembly.
Challenge #4: Non-Silicone Thermal Interface for ADAS Modules
What if an application involves silicone contamination concerns? The positioning of optic lenses within automotive camera assemblies can present this issue. Additionally, semiconductor image sensors and chips within automotive camera assemblies often require enhanced heat dissipation efforts.
In its design of a multi-function camera vision system, a global manufacturer of automotive camera systems placed a camera sensor module with a circuit board near where there is an embedded chip emitting heat during power cycles. Because the camera lens is in such close proximity to the PCB, the concern of silicone contamination heightened the specification of the TIM.
As a result, the thermal material was required to be non-silicone-based and to comply with Paint-Wetting Impairment Substances (PWIS) automotive standards. While there are non-silicone thermal gap pads available, due to the high-volume production of the camera assembly, pads were not a feasible option; only a dispensable material could meet the necessary throughput requirements.
With the silicone-free requirement from the customer, it was determined that Therm-A-Gap GEL 25NS met and even exceeded the customer’s requirements, with 2.5 W/m-K thermal conductivity, and is yellow in color, which can be recognized by optical cameras on the assembly line.
Furthermore, a finite element analysis (FEA) simulation was conducted to predict the reacting force of the thermal material during and after its installation to the targeted location to ensure it would not cause deformation and/or damage to the PCB/IC during and after assembly.
For these applications, manufacturers need a dispensable material that is highly conformable, with a low compression force and long-term reliability and durability. They may need a non-silicone-based binder to eliminate factory and assembly silicone contamination concerns. The thermal interface material must also be easily dispensed into targeted areas, with no post curing, to speed the manufacturing process, and offer visibility to optical cameras. For more information, visit parker.com and download the recently updated “Thermal Interface Material Dispensing Guide for Thermally Conductive Gels, Cure-in-Place Potting Compounds and Thermal Greases.”
Scott Casper is senior applications engineer with Parker Hannifin Corp.’s Chomerics Division.
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