Embedded Computing is an important aspect of defense electronics systems, routinely fielded in aerospace, ground and naval applications. Many critical functions such as data processing, Electronic Warfare (EW), imaging and communications are made possible by specifically designed embedded computing systems. These Defense systems require significant functionality and speed, leading to increasingly higher levels of waste heat, which must be managed without affecting the systems’ durability or form factor. Complicating the thermal design, embedded computing systems are trending harshly towards higher power and smaller footprint electronics. ACT’s team of engineers are well versed on the system and component level challenges and provide a variety of solutions for these types of systems.
These types of systems are used heavily across all military platforms; however, the compact nature of embedded computing systems provide significant benefits to aircraft applications. Additional requirements such as acceleration may need to be considered, but can be satisfied with proper upfront design and analysis.
Read more in this article on ‘Acceleration Resistant HiK Heat Spreader’…
System-Level Thermal Management
The thermal management solution for an embedded system is often selected based on what’s occurring at the electronics interface.
There are three primary cooling methods used for system-level thermal management:
1. Conduction Cooled: uses conduction to spread heat to the external enclosure or chassis. An ultimate heat rejection method is implemented either on the sidewalls or the base of the chassis. This method of isolating the air or liquid external to the chassis can greatly extend the operating life of your system.
Benefits: Reliability, fully sealed
Challenges: Larger ∆T
2. Air Cooled or Air Flow-Through: relies on internal fans that push/pull air over fins that are local to the components or board in the system. Fins can be optimized based on the airflow and component location, but there are often restrictions on how much internal fin volume is available.
Benefits: Higher Power
Challenges: Fan reliability, open system, fin height restrictions
3. Liquid Cooled or Liquid Flow-Through: this method pumps liquid directly through cold plates that are in contact with the electronics boards. Direct liquid cooling provides the highest performance due to its high heat transfer coefficient but adds system-level risk.
Benefits: Highest power
Challenges: Reliability (leaks cause catastrophic damage)
ACT has analytical expertise and tools to assist your team in selecting the appropriate system-level solution to provide you with the best combination of size, power, reliability and cost for your program.
Sub-System Level Thermal Management
Mapping the thermal resistance network in your system can reveal many design points impacting thermal consideration. The three primary areas to invest in, to provide long-term benefits for your electronics systems, are the board-level heat spreader, chassis or enclosure, and the board-to-chassis interface. ACT offers design/analysis and hardware solutions for each area.
- HiK™ card frames increase thermal conductivity. In conduction systems, it’s paramount to get heat efficiently to the edge, and spread heat along the edge to lower heat flux into the chassis. Heat pipes can be strategically placed to accomplish both goals simultaneously. On air-cooled boards, the increased thermal conductivity will isothermalize the fin stack base and reduce hot spots, optimizing fin efficiency.
- HiK™ chassis or card guides include heat pipes implemented into the sidewalls to enhance thermal conductivity and reduce conduction gradients. These are particularly effective when the ultimate heat sink is located at the base of the chassis.
- Whether they are implemented at the board, chassis sidewalls or chassis base, having properly designed liquid cold plates drives performance. There are often significant manufacturing and packaging considerations to work through together, in parallel with the system-level design.
- The retainer clamp is a critical mechanical feature to allow for quick access and servicing of boards. While most COTS solutions provide this functionality, most offer a high thermal resistance over this short thermal path. The ICE-Lok® was designed to increase contact points and bypass metal to metal interfaces, leading to > 30% improvement in thermal performance at this interface.
Phase Change Material (PCM) Heat Sinks
- PCM Heat Sinks can absorb thermal energy (heat) with minimal temperature rise during the solid to liquid phase transition. During this phase transition, the latent heat (J/kg) is at least one (1) to two (2) orders of magnitude higher than the sensible energy that can be stored by the specific heat of a material in its solid or liquid phase.
ACT is known as a reliable and customer-focused heat pipe manufacturer and assembly partner. Some customers are surprised when they learn that we also have the capacity and experience to deliver complete solutions with an ever-growing list of options.
ACT offers the following value add services on conduction card assemblies:
| Mechanical Hardware | Test & Inspection Services | Finishing Options |
| * Heat Pipe Installation * Pin/Helicoil/Hardware * Ejector Clips * Thermal Interface * Material EMI Gasketing |
* Thermal Testing * Thermal Cycling * Shock/Vibration * First Article Inspection (FAI) |
* Coatings (Chem Film, Electroless Nickle, Matte Tin, etc.) * Part marking/engraving * Silk Screening * Laser Etching |
PAYLOAD LEVEL COOLING-SpaceVPX
Embedded computing systems are leveraged across many mission-critical platforms, but few with more challenging requirements than space vehicles. The power requirements for on-board processing, optoelectronics and other high heat flux components are very similar to terrestrial embedded computing applications; however, the space environment adds temperature extremes and other operational conditions that make the thermal design a major factor in system architecture.
Photo courtesy of BAE systems, showing ACT SCWHP embedded in a SpaceVPX Reconfigurable Computing Module (RCM)
When operating in the vacuum of space, heat must be transferred long distances to adequate radiator surface area. The conduction paths from component to card edge and from chassis to the radiator are often limited by the thermal conductivity of the base metal. Due to the high heat flux of the electronics and conduction being the primary bottleneck, copper-water heat pipes are an ideal solution- the challenge is making them so they can survive the mission! Through years of development, ACT has qualified and flown SCWHPs that feature more robust manufacturing techniques to survive the severities of space. An example of a 4U Space VPX board having three (3) SCWHPs transferring heat from components to the card edge is shown below.