Integrated Thermal Management Solutions with Customizable and Manufacturable Heat SinksJanuary 01, 2020 by Interplex
This article highlights Interplex Cell-PLX™ custom battery interconnect systems for battery modules across an extensive range of industries.
Thermal management of electronic devices has always been a key issue for assuring proper operation and sustainable performance across a wide range of ambient temperatures and operating conditions. Over recent years, the issues surrounding thermal management have become even more challenging, with high-current applications such as electric vehicle (EV) mobility and other automotive electrification developments requiring more efficient heat removal. Similarly, the proliferation of new high-performance applications across a wide range of industries — such as communications, industrial, transportation and consumer products — also requires innovative heat removal technologies, as more power is packed into smaller form factors.
This technical bulletin provides an overview of new heat sink design approaches, pioneered by Interplex, that give product engineers an expanded range of options for custom integration of thermal management solutions. These new approaches deliver on excellent heat dissipation while significantly reducing weight, provide for tight integration of the heat sinks, minimize product cost, and enable fast ramp-up to high-volume production.
Heat Sink Anatomy and Applications
Figure 1 – Heat Sink in Mass Production for Automotive LED Lighting
A heat sink is a heat exchanger that enables the transfer of heat generated by a device to surrounding media of lower temperature. By dissipating heat away from the device, its main function is to balance said device’s temperature at optimum levels for it to function as desired.
Heat sinks are used in a myriad of devices across industries for both electronic and mechanical applications. Some examples include LED headlights, HVAC systems and ECUs in the automotive industry, as well as busbars and power modules for energy applications.
Traditionally, thermal management has taken the form of extruded, forged or die-casted heat sinks connected to the heat-generating electronics. However, the accelerating growth of many different types of electronic devices, the rise of more powerful microelectronics, and the push toward smaller, more compact designs are making it much more difficult to accommodate the bulky size and weight of these conventional heat sink designs
New Manufacturing Methodology
The process flow diagram in Figure 2 shows how heat sinks can be fabricated by precision stamping and bending. The base plate, supports and fins can be customized, allowing for direct integration with the case or component. Dimensions can be scaled upwards and even significantly downwards by leveraging high-precision stamping techniques.
After pre-shaping the fins and defining their contours in the stamping process, bending is applied. The fins, tailored unique to the end application while featuring true 3D-design and alignment, are then joined to the base plate. This can be done in a number of ways — by use of welding or mechanical joining methods.
Figure 2 – Heat Sink Production Steps
How Fin Construction and Design Affects Heat Dissipation
Despite the long-held preconception that extruded, forged or die casted heat sinks are the only effective means for thermal dissipation, ultimately, it really is the measurable performance that matters. While in theory, a single body of matter transfers heat better than two bodies that are joined, in reality, designers must consider both economic and thermal efficiency needs of a product in its actual application.
An experiment was conducted to compare the practical performance of a laser-welded heat sink against an extruded one. By using an existing extruded heat sink design as a reference, a two-component design with the base plate separated from fins was designed and manufactured. The high-precision stamped fins were joined to the base plate with a partial fillet weld performed by a laser. The steady-state temperatures were measured and recorded after sufficient time had passed with the setup maintained at a set voltage and an accordingly stabilized ampere level.
The laser welded design allowed for reduced fin thickness and spacing, attaining material weight savings of 40% for the same 3-dimensional footprint (Figure 3). In terms of heat dissipation capabilities, it was able to achieve equivalent performance as the extruded design; even in a natural convection setting.
Figure 3 – Material Weight Savings of 40% are Achievable in the Laser Welded Design
Figure 4 below depicts the results of the experiment; as shown in this graph, the thermal properties of a heat sink can be modelled using a specific best-fit line equation. This equation is representative of thermal resistance, expressed in the unit K/W.
Figure 4 – Experimental Results Showcasing Effect of Joining Methods on Thermal Dissipation
Thermal resistance values can be used for heat sink comparability in benchmarked scenarios. When making such comparisons, the experiment’s setup and boundary conditions should be taken into consideration. Key factors influencing thermal performance include the relative sizes of the heat sink and the heat source device — if there are extreme differences, such as using a very small heat sink with a large heat source, the results of the best-fit equation may not be representative or meaningful.
Optimizing Heat Dissipation
The optimal configurations for fin thickness and fin spacing depend on the actual application scenario. In natural convection scenarios, larger fin spacing is more favorable; conversely, with forced air convection, heat dissipation performance can be improved with smaller fin spacing.
This is because radiative heat transfer between the fins comes into play in forced air convection scenarios at a certain temperature and fin spacing. With “stored” heat between the fins at close spacing, forced airflow removes more heat, on average, than with fins at a wider spacing. How much time the air particles reside in the heat sink before being displaced by airflow is also important — thus, flow speed and pressure also determine how much heat is removed from the system.
In addition to heat sink fin spacing, thermal dissipation performance can be further optimized by adjusting various other factors, such as:
Surface finish of the fin surface — varying levels of molecule friction result in different turbulent air flow behaviors
Modifying the macroscopic airflow path to take advantages of vorticity and stream dynamics
Maintaining proper planarity between the base plate and the fin interface
Alternative Types of Heat Sinks
As a custom application solutions specialist, Interplex is well-equipped to produce real 3D-designed heat sinks with optimal airflow dynamics for heat dissipation. For passive applications, a riveted design (Figure 5) with a 1:5mm fin thickness-to-spacing ratio performs better than a close-packed stackable design (Figure 6) with a 0.5:0.5mm ratio. The converse holds true in certain active airflow scenarios.
Figure 5 – Riveted Design (Mass Production)
Figure 6 – Stackable Design (Sample Phase)
As shown in Figure 7 and as described in the previous section, there are differences in the thermal performance for riveted versus stacked designs, depending on whether the airflow is passive or active. In general, stacked designs with closely spaced fins are more effective with active airflow, whereas riveted designs with wider fin spacing are more effective with passive airflow.
Figure 7 – Behavior of Heat Sinks with Different Fin Thickness-to-spacing Ratios
Vertically Integrated Capabilities
Interplex’s vertically integrated manufacturing capabilities bring various advantages to the table regarding the production of heat sinks. Customized applications are our forte, and our thermal solutions are trusted by top-tier customers worldwide. We provide customers with the valuable opportunity to produce optimized custom heat sink designs that are currently only achievable by additive manufacturing (AM). However, unlike AM, our manufacturing concept and capabilities can achieve mass production volumes, speed and economics.
Figure 8 – Examples of Various Achievable Heat Sink Fin Designs and Configurations
To meet the needs of product engineers, our thermal solutions can also be seamlessly integrated into the target sub-system. As shown in Figure 9, Interplex’s vertically integrated technologies enable integration of all key functions — ranging from a custom-designed assembly-friendly base plate, to providing full electrical infrastructure encompassing EMI shielding and electrical isolation on top of the heat sink’s thermal management capabilities.
Figure 9 – Comparison of Heat Sink Manufacturing Methods
As electronic devices employ the use of more powerful microelectronics and compact them into smaller spaces, the prevalence and importance of heat sinks becomes increasingly imperative. Optimizing heat sink performance has become a critical pathway to success across various applications and industries.
Interplex’s integrated capabilities enables the creation of fin dimensions beyond the limits of conventional extruding or forging. By analyzing application needs, convection scenarios and physical constraints, we can optimize the heat sink design for optimum performance. Every fin, pin or other solid-to-air transition geometry can be designed to achieve optimal thermal dissipation for active and passive scenarios.
Interplex is a leading multi-technological solutions provider trusted by top-tier companies across a multitude of industries. For 60 years and counting, we have played a major part in providing the highest quality customized solutions to tackle our valued customers’ most demanding problems.
Amidst fierce global competition, what makes us stand out and consolidate our leadership position is our technology. Our ability to design, develop and produce mission-critical products and solutions tailored to specific end applications stems from our long-standing commitment to technology and innovation. This encompasses numerous patents and trademarked products, underpinned by our reputation for developing new solutions a step ahead of emerging industry trends.