Electronics Cooling is a challenging piece of Circuit Board Technology
Electronics cooling and thermal management are engineering challenges facing industry concerns when it comes to circuit board technology. Recently we came across an interesting product from a company at a trade show: a metal core printed circuit board (PCB) from SinkPad™ that allows high powered integrated circuit applications to stay cool. The high thermal conductivity path of the metal board allows high power to remain cool due to the superior heat transfer of the board. Light emitting diodes (LED) are ideal candidates for mounting on metal boards. However, their application is not limited to LED’s, but any high powered electronics application.
We will be presenting a white paper within a series of blogs that we will tie together and make available for downloading from our website. This is the first, in the series, describing the Sinkpad™ products.
Light Emitting Diodes (LED)require Thermal Management solutions
The increasing heat densities in modern high-power light-emitting diodes (LED) present difficult performance and reliability challenges at the junction of a device, as well as first and second level electrical power-delivery connections. There is also an adverse impact on power efficiency and emission wavelength stability. All means of reducing system thermal impedances must be considered for the successful thermal management of these high-power LED's. Both the system and board level thermal management practices should come under scrutiny for finding the right balance of performance, cost and reliability.
Engineers at SinkPad™ are working on addressing the existing shortcomings of widely available MCPCB offerings by developing a board design with an optimized thermal path for the energy dissipated at the diode junction on its way out to the environment. The solution optimizes the heat conduction path at the highest power density location to deliver the most-optimized board level thermal solution.
Licensed Engineers at Glew Engineering are working to demonstrate the improvement by thermal conduction analysis of the optimized SinkPAD™ board and compare it to a standard MCPCB solution. We are hoping to show substantial improvements in board level dependent components of thermal resistance, as well as some of the cost efficiencies that are related.
We will continue to discuss the applications and importance these boards play in electronics cooling technology in our upcoming blogs as well as the white paper.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.
Glass Breaking
We were recently asked to explain how glass breaks, or fractures, to some non-technical people. Glass is an amorphous material, without long range atomic order. This is different than crystalline material or polymers. The following is a summary written by mechanical engineers for the layperson.
One approach that an engineer, typically a mechanical engineer, uses to describe how materials behave under stress is to create a constitutive equation. This is a mathematical model that assumes that a material is a continuous media. The general field of this type of work is known as continuum mechanics. Even the notation in this field is complex, and relies on multi-dimensional matrices that use Einstein’s indicial notationThis type of analysis is usually taught in a Mechanical Engineering department at a university, but may also be in Materials Science, Civil Engineering, or Mathematics departments. This approach largely neglects the atomic nature of material, which is more the domain of Materials Science or Applied Physics departments.
Fracture toughness is a material property that attempts to characterize the ability of material to resist propagation for an existing crack. This value is relatively high for ductile materials, such as metals (~ 20 MPa×m0.5 for aluminum), and is relatively low for brittle materials, such as glass (< 1 MPa×m0.5). This generally implies that a material with glass properties would experience brittle fracture prior to the onset of a plastic, permanent, deformation.
Stress is simply force per area. For example, your car tires are inflated to 30 pounds per square inch. The stress in materials is given the same units, but is usually much higher than the load applied to the surface. The same force applied over as small area creates a greater stress or pressure; think of the pressure created by a stiletto heel versus a regular shoe.
Estimates of fracture toughness for materials with such properties in general follow the results of surface energy models based on the amount of energy required to generate a free surface starting from the bulk material. Simply, one assumes that there is a crack of a certain size. Then, one may calculate the energy required to create new surfaces when the crack propagates. Rapid crack propagation that results in failure is known as fracture.
Finite Element Analysis
Stress modeling would also help with calculating stresses concentrated at a tip of a crack for an estimate of an onset of crack propagation. Due to the fundamental nature of such stress field, both analytical and numerical models may be available for this engineering evaluation. Finite element analysis, FEA, is an example of numerical modeling. Fracture of glass generally occurs in a localized state of tension.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.
IC Thermal management
By now, you have identified the components, generated a schematic, placed the components and resolved routing. So what comes next?
Thermal Cooling
Proper identification of heat-sink requirements needed in electronics thermal management is usually relegated to this stage of design, but some design may be done during PCB routing. It may occur earlier in design cycle if it is a critical parameter, and one can argue that this should always be kept as an important consideration throughout the whole process. The mechanical engineer performs heat transfer analysis, usually by the FEA method, finite element analysis, as part of the design to facilitate IC thermal managment. The finite element analysis is a type of computer modeling in which the heat transfer, temperatures, and heat flux are calculated.
Heat sinks are the most common form of thermal cooling used in electronics cooling. Heat is transferred to an aluminum heat sink by thermal conductivity, usually through a thermal paste between the heatsink and the PCB. Then the heat sink cools by convection, either free convection or forced convection.
A power rating of the component, needed when sorting out power planes and traces, provides information on the amount of heat generated by the part. Barring special cases, almost all of the electrical power going into the component turns up as waste heat. Moving a photo album from a smartphone to a disk-drive on a server results in a certain amount of heat generation. Flipping those storage bits far away on a remote server can and should be done more efficiently in the future, but we have to deal with the waste energy now.
One must check the component temperature rating in order to identify the maximum allowed operating temperatures. There are internal component temperature differences which may lead to the distinction between a junction and a case temperature, which is very important in IC thermal management. The junction temperature is a chip temperature for all practical purposes, while the case temperature is just that, the temperature of the exterior of the component, and the exact location where this temperature is defined would depend on the heat sink mechanical attachment point (if such is needed). A board or a system designer usually is concerned with this case temperature, and a component manufacturer usually provides this value.
Finite element analysis (FEA) in Electronics cooling and thermal management
The heat flux in electronics thermal management and electronics cooling can be estimated by computer modeling with the finite element method. A heat flux travels in the direction of decreasing temperature, from a high temperature point to a low temperature point.The thermal conductivity of the solid material determines how much heat travels through a solid given a certain temperature difference for a fixed area.
Similarly, a designer is given some idea on the thermal resistance values for the components. A thermal resistance describes the magnitude of a heat current being pushed out per unit temperature difference. For low-power components all of the heat can be dissipated by the either surrounding air or through the board to which it mounts. Heat dissipation through the air is modeled as free convection, or in the case of a cooling fan, forced convection. At elecated temperatures, radiation cooling becomes relevant.
The FEA model uses thermal conductivity, convective heat transfer, and radiation in its calculations, similar to electrical resistance, capacitance and inductance that electrical engineers use in circuit modeling.
Higher power dissipation is the subject for our next entry.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.
Thermal Interface Materials
We last talked about the challenges for first level thermal interface material. Now we will discuss the third scenario where no integrated heat spreader is presented. This happens commonly in mobile computing platforms as well in many desktop systems. It is the configuration where the chip directly couples to a heat sink. The exact nomenclature is not yet settled throughout the industry may not have a level designation, and is referred to as just a TIM. Since thermal packaging with the integrated heat spreader became common, there was a need to designate the previously existing configuration, thus chip-to-heat sink thermal interface material became known as TIM 1.5.
This distinction at first seems arbitrary, but targeting maximum performance often comes at the cost of specialization, and this is also true with materials used for thermal management. The silicon surface itself is warped, and to make matters worse, this curvature changes with temperature. This will, in turn vary the volume of enclosure between the chips surface and the heat sink or heat spreader which creates a need for material that is resistant to this pump-out effect.
There are other failure modes, depending on the type of the material and chemical base that are used. These modes include an evacuation of the thermal interface material under constant pressure when above certain values, known as squeeze-out. Another type is known as dry-out, which is the loss of plasticity. Due to these types of failure modes, thermal interface material design is a continuing challenge for the semi-conductor industry.
For more information on Glew Engineering Consulting visit the
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blog or call 800-877-5892 or 650-641-3019.
Previously, we touched upon the importance of thermal interface materials for the proper temperature regime of the CPU in your favorite PC. If it is a server or a high-performance consumer desktop CPU, then it is likely to have a large, built-in piece of metal which helps with mating the CPU to the surface of the heat sink. This also protects the silicon chip from direct mechanical interaction with the system-level components. In this case, the thermal interface material that a system manufacturer applies during the product assembly is referred to within the industry as Thermal Interface Material level Two, or TIM2. This nomenclature mirrors electronic assembly hierarchy, where connections between the component and the board levels are referred to as second level. The built-in heat spreader is analogous to the organic, or ceramic, substrate to which the silicon chip is flip-chip mounted, and whose function is, to spread out dense, first-level electrical pathways coming off silicon. A situation that occurs is the metal lid spreads out a much more disorganized form of energy flux, a heat dissipated by CPU.
Thermal Interface Materials
Continuing the analogy, there is an equivalent of first level connections between the CPU and the substrate. The thermal interface material, internal to the CPU package, is referred to as Thermal Interface Material level One, or TIM1. As with the first level electrical connections, choice of materials and assembly methods are more involved, compared with those in the second level. These steps are either done at a CPU maker’s facility, or at specialized manufacturing service providers. The driving issue for the complexity of mechanical connection, just as with the first level electrical connections, is thermo mechanical. If first level electrical connections require extensive engineering of solder, inter-level dielectrics and under-fill systems, first-level thermal engineering of CPU packages require management of complex curvature that develops on the chip surface due to the coefficient mismatch of thermal expansion between the chip and the substrate.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.
Mechanical Engineers challenges in electronis packaging
In electronics packaging, first and second level connections present different challenges to engineering teams. Mechanical and packaging engineers working on first level connections deal with the delicate process of connecting a chip to a substrate: as in case with the silicon chips, sub-dividing a task of delivering power and signal traces into two connection levels eases engineering challenges for the final product use and streamlines manufacturing. Once the transfer of the chip to the substrate is completed, this first level-connected package is passed unto mechanical engineers for the second level connection. While there are various challenges at this stage, one of the main concerns for LED engineering teams is thermal management.
Electrical Technologies
In second level connections, a licensed mechanical engineer will take the assembled package and adopt it to specialized form-factors depending on the end user's needs. Delivering power to the LEDs is easy. Removing the thermally-dissipated power is the tougher part. Thermal power is wasted power and that keeps LED lighting from running efficiently.
Metal-core printed circuit boards (MCPCB's) are often used for high power LED product. These boards are made with very high metal content, and thus provide the necessary thermal conduction path for the heat generated at LED junction with the main focus on optimizing the thermal path. Therefore, LED packaging engineers are always on a lookout for improvement in thermal management. For example, SinkPad(tm) offers a PCB with highly optimized thermal performance. Glew Engineering will be writing about this interesting design solution in future blogs.
Typical cooling solutions, such as forced convection with a fan, cannot be used in these devices. LED engineers have to design good conduction paths for improving natural convection efficiency. Not only is the product reliability at stake, but also energy efficiency as s convert a higher fraction of electrical power into light at lower temperatures.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.
Printed Circuit Board Design
Suppose you decide that you want to design a product and need to make a custom printed circuit board (PCB) which needs to fit in a certain location within your product. If you are an experienced electrical engineer, then you may already know where to start. Sometimes the considerations are also thermal, which would require a mechanical engineer. However, if you are trained in another engineering discipline, or a non-technical sort, or just need some general knowledge, then the following blog may be useful to you.
Electronics Thermal Management
The need for a PCB assumes that you already have a circuit designed. One can use engineering experience, coupled with a SPICE model in software to understand how the circuit theoretically works. The actual mathematics and physics are very complicated, but have been reduced to modules that can be plugged into the software for analysis. Most components have SPICE model. IC thermal management is very important for reliability of components, but when they are integrated on a PCB, the thermal analysis needs extension and is usually known as "electronics thermal management." Thermal analysis requires other software to understand the generation and dissipation of the heat generated by components. Heatsinks, cooling fans, and other methods are used to keep PCB and the components within their operating temperature range. A mechanical Engineer takes into consideration strain relief, shock mounting, vibration effects, and related issues. PCBs can be tested thermally, and on shake tables. This is sometimes called "shake and bake."
The most basic aspect of PCB design involves making the devices fit on the board, and then connecting all of the relevant pins. Each electronic component manufacturer, be it a microcontroller or a programmable logic device, would already have a reference design which is always a good place to start. Once you settled on a circuit and component list, the next step is the design and routing of the board. Each component would have a certain footprint, such as DIP, SOIC, BGA, etc…, with a various number of pins. Your CAD system is more than likely to have the part in its library. If the part is new, one can usually make a new package footprint within the software being used. Choosing the number of layers of board depends on many factors, not the least of which is the number of outputs on the components with largest number of pin-outs, such as a central processing unit or a digital signal processor.
Interconnecting traces that are routed through the PCB requires both good engineering practice, and specific knowledge of the devices, frequencies, and sensitivies to interference, cross talk, and noise. Sensitive routes in some applications may require shielding which may also increase the number of layers needed. Power components would also require extra attention, if integrated within the same board along with low-power electronics. The most common configuration is the two layer board, which has a core FR4 (fire-retardant) layer and two metal layers on each side. This is often coated with the dielectric layer (solder mask) once routes are fabricated in the metal layers. At this stage, once the shape of the board, number of layers and component footprints are locked-in, one has to place the components and draw up the wires or routes. The unconnected routes would crisscross throughout the board forming a "rat's nest". Design packages make auto-placement and auto-routing much easier than in the past, but some clean-up and manual routing for some nets is still often required. Extra metal in boards may be required to dissipate heat and control warping of the boards, and the design engineer must be aware of the requirements.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.
Licensed Mechanical Engineers
The California Business and Professional Code (BPC) describes the branch of mechanical engineering at §6731.6.
Mechanical engineering is that branch of professional engineering described in Section 6734.2 that deals with engineering problems relating to generation, transmission, and utilization of energy in the thermal or mechanical form and also with engineering problems relating to the production of tools, machinery, and their products, and to heating, ventilation, refrigeration, and plumbing. It is concerned with the research, design, production, operational, organizational, and economic aspects of the above.
The California Business and Professional Code (BPC) describes that a person practices mechanical engineering 6734.2, when performing the duties described above at §6736.1.
Any person practices mechanical engineering when he professes to be a mechanical engineer or is in responsible charge of mechanical engineering work.
Mechanical engineers spearhead the structural, machinery, energy, fluid, and other related aspects of a project to ensure that processes, products, systems, subsystems and parts are designed, developed according to specifications. The licensed mechanical engineer will monitor the whole project or manufacturing process from initial concept work, through design and development to finished product assessment. Companies need to seek Licensed Mechanical Engineer and engineering firms that can initiate and manage the project coherently, whether it is a manufacturing process, product design, fluid delivery systems, energy analysis, or one of the many projects that falls to the mechanical engineer, the broadest of the engineering disciplines. The following are some of the attributes that a company should look for when engaging for a mechanical engineer.
Personal attributes
The personal characters that help mold the right qualities for an engineer will affect the mechanical engineer’s interpersonal relations, thus to some extent, his performance. Engineering is a discipline that requires a high level of personal and interpersonal skills. Whether you are engaging an industrial system engineer, a processing engineer for a refinery or petrochemical facility, or an electric engineer for power plant, the engineer should have the following attributes:
- Be able to think in mathematical and abstract dimensions. This will enable him or her to handle numeric calculations such as in product formulations, and analyzing costs of productions.
- Communication skills are essential for an engineer so that he or she can develop reports on performance.
- The Licensed Mechanical Engineer should have good attributes of a team player to integrate his team to offer optimal performance in order to reduce erroneous effects that can affect the quality of products, project schedule, cost, and performance of systems and subsystems leading to failures.
Educational qualifications
The basic qualification for a mechanical engineer is a bachelor’s degree, which is acceptable when obtained from a reputable and ABET accredited engineering college. (See BPC at §425(c) .) The period of obtaining a bachelor’s degree is substantial to impart the required knowledge and skills in a person pursuing mechanical engineering. This is generally the minimum required for licensing. Graduate degrees are helpful specialized knowledge, and mathematical modeling skills.
Line of specialization
The line of specialization is also another essential aspect, which helps determine how a person is knowledgeable in a particular field. There are mechanical engineers in the field of biomedical engineering, laser technology, energy, structural analysis, fluid flow, heat transfer, and nanotechnology, as well as manufacturing systems, and plants. There are engineers in design and development of heating systems, ventilation and air-conditioning systems. Therefore, the particular skills of the Licensed Mechanical Engineer experts need to be in line with the company’s engineering solutions. Many engineers are qualified in multiple areas.
The reliability engineering aspect needs to be emphasized so that a company can meet consumer demands, quality standards, realize returns on investment (ROI), and contribute to environmental care. This skill crosses all branches, but is also a specialty.
Experience of the engineer
Project exposure helps an engineer gain the experience in order to perform his or her duties and obligations. Experienced professional engineers, Licensed Mechanical Engineers, will most likely have diverse skill sets necessary to make them successful: administrative, interpersonal, management, financial, as well as the core technical expertise.
Software Tools
Sometimes it is important that an engineering firm use software tools that are compatible with the company that engages. This is not usually a sticking point, but it can make certain transitions proceed smoothly. This is sometimes the case with CAD (computer aided design) and FEA (finite element analysis) tools.
Fees
The fee structure of the professional engineer needs to be examined before engaging. The fees will help determine how much the company will invest in the engineering design, review, or process. Many engineering firms can combine and blend the work of principal engineers, senior engineers, staff engineers, and associate engineers, to help efficiently develop a project budget that is economical.
Professional Association
The Licensed Mechanical Engineer and engineering firm that a company engages should be a member of engineering associations and trade associations that bring together professional engineers.
Environmental management consciousness
The manufacturing process and project engineering requires a sense of environmental care. As companies go green, there is need to integrate environmental consciousness in their processes of manufacturing in order to scale down waste, energy use, hazardous emissions, C02e (CO2 equivalent) emissions, and other soft aspects of green engineering.
Summary
In summary, the Licensed Mechanical Engineer and engineering firm that a company engages should have all the qualities that will help to lead the company to the completion of a successful project.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.
Advantages of Using Licensed Mechanical Engineer
Mechanical engineers play a great role in the manufacturing process often tackling issues related to products designs, quality control, efficiency and reliability, production cost elements, and meeting environmental management standards. The reputation of a manufacturing company is highly determined by the quality of products and mechanical engineers are the key persons who analyze and control the quality of products. It is imperative that manufacturing firms seek the services of licensed mechanical engineering professionals who have been certified in their various fields of profession.
These engineers understand the forces and the thermal environments through, which products, subsystems or parts undergo in the manufacturing process. The design work of products, parts and systems is quite complex and any default in the process can result to economic and non-economical losses. The economic losses could be in form of lost revenues due to substandard products that have been declared inconsistent with the set standards.
Many products and parts defects such as witnessed in the electronic engineering like LED components shorten the lifespan of the lighting components. Products with defects are recalled and the company suffers financial losses. The licensed mechanical engineering experts have been certified to critically observe and monitor the manufacturing process to ensure that reliability is achieved.
A reliability engineer conducts failure analysis in systems, parts, and subsystems to ensure that the end products meet quality standards. A root cause failure analysis (RCFA) is conducted whenever failures in a part or system are noticed. The engineer also works on maintenance tasks and scheduling, which improves efficiency. They are able to design products, parts, systems and subsystems to achieve great functionality while at the same time meeting aesthetic aspect of the designs.
In the same way, a company can be faced with non-economic losses, such as bad reputation thus affecting the company growth aspects. A licensed mechanical engineering professional is well versed with environmental management be it in air conditioning, refrigeration, and compressors-HVAC or wind turbine projects. This ensures that product designs are done to meet environmental standards thus reducing pollution.
Moreover, engineers enhance efficiency of the manufacturing process. The cost element of a manufacturing process is greatly impacted by inefficiencies, which can drive a company to huge monetary losses. Inefficiencies lead to waste of resources, which in turn increased the cost of manufacturing, plunging a company into financial difficulties. With the licensed mechanical engineering experts, they thoroughly review the manufacturing process to ensure that it is efficient and reduces wastage of resources by integrating manpower, mechanical, as well as IT technologies to improve the process of manufacturing.
If a company witnesses variations in raw material utilization beyond the normal ranges, this is reviewed to ensure that the company’s manufacturing process is reverted to normal. Inefficiency technologies are upgraded or done away with. Mechanical engineers have advanced knowledge on materials, fluid mechanics, solid mechanics, thermodynamics, instrumentation and heat transfer aspects of the manufacturing process. They understand the mechanical systems, control and design aspects. Licensed mechanical engineering professionals make conversions of and use of resources in developing new products and adopt energy solutions that are efficient in line with the company manufacturing process.
Licensed Mechanical Engineers
Mechanical engineers also indulge in training and manpower development. Employees working in production department are equipped with apposite resource-use strategies and techniques to reduce wastage, enhance quality production, and identify parts, systems and product failures.
In a nutshell, by dealing with licensed mechanical engineering, it helps organizations enhance product reliability, increase efficiency in production, and improve environmental management. All these aspects enhance the reputation of a company while at the same time reducing costs for improved returns on investment.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.
- Mechanical engineers typically work with two types of connections when assembling electronic packages. These levels, known as first and second level connections, present mechanical engineering teams with different sets of challenges. The following blog will cover first level connection challenges and how they pertain to Light Emitting Diodes (LEDs).
In first level connections, mechanical engineers’ main responsibility is connecting a chip to an intermediate package, also known as a substrate. Due to the complexity of this process, many companies devote large resources to fund internal research and develop improved methodologies. The chip itself is fragile, especially an LED die, which may contain thin layers of epitaxial films about 20mm thick.
Mechanical engineers connect these fragile chips to useable carriers such as an fr-4 substrate, similar to high performance microprocessor packaging. When packaging engineers require high field reliability and/or minimized thermal mismatches for high power LEDs, ceramic substrates are used. Frequently, mechanical engineers use an intermediate carrier or submounts to ease wafer handling. Mechanical engineers do this prior to connecting devices to lead frames if the active layers are thin and fragile.
The structural assembly process requires a complex balancing act. The rigid mechanical connection between a crystalline semiconductor and a package, distributes signal and power connections to the usable spacing at board level. For example, when selecting first level package materials for a high performance silicon microprocessor, the dielectric layers need ultra low k materials for fast internal signaling. However, many material candidates cannot survive thermo-mechanical stresses during assembly and field use. In the case of LED lighting, epitaxial layers and general fragility of substrates, present a different set of challenges. A mechanical engineering team may find a material promising, but if it doesn’t survive in the connection, they will have to reject it. Also, there are difficult IC thermal management issues to solve.
LED lighting currently uses two types of first level connections, wire bonding and flip chip configuration. Wire bonding requires a LED die that faces up and connects to a package using wires. In contrast, a flip chip faces down and uses solder bumps to connect to the package. While wire bonding tends to be more reliable, mechanical engineers are also adopting flip chip configuration to help reduce material processing and optics engineering restrictions. Mechanical engineering teams can widen their portfolio of usable packaging configurations for producing optimal lighting solution.
Stay tuned for the following blog that will explore the challenges engineering teams face in second level connection assemblies.
For more information on Glew Engineering Consulting visit the
Glew Engineering website,
blog or call 800-877-5892 or 650-641-3019.