JEDEC JEP181 creates standard for electronics cooling files.
How Mature Is the Thermal Design Simulation Industry?
In the mid-1980s mechanical engineers were charged with testing thermal design. The engineers built physical prototypes using thermocouples. Based on an engineer’s preference or experience, a Type-K or Type-T thermocouple might have been used. Beyond this, several attachment methods existed and aluminum tape, Kapton tape, or epoxy could be used for connections. There was no clear set of best practices, and engineers did what made the most sense to them on a case-by-case basis in their own industry.
John Parry of Siemens wrote an article that asked “Can you measure an Industry’s Maturity by looking at their Thermal Design Standards?“ in which he presents the idea that the absence of best practices didn’t matter as much because most of the designs worked thermally with very few changes. Large fans and generous airflow usually addressed most issues that could occur, and when a failure did happen it was usually obvious—the bad component or system was the one with the melted wire casing, black soot spot, or smoky smell.
Product development isn’t so forgiving now—everything is electronic, everything is getting smaller, and everything needs to come to market faster. Smaller parts are in all our electronic devices and more are required for bitcoin mining, vehicle electrification, virtual reality and machine learning. Parry says the need for thermal design standards is clear and notes that Siemens has been involved with thermal design standards since around 1995 and the JESD51-2 standard for natural convection testing in still air.
Joint Electron Device Engineering Council
The Joint Electron Device Engineering Council (JEDEC) develops open standards for the microelectronics industry and has a history that stretches back to 1924 and the establishment of the Radio Manufacturers Association. Eventually, in 1958, after a series of name changes, the JEDEC was formed as a membership group for radio component developers. The council began to develop standards and test methods for the semiconductor industry and remains a leader for design and manufacturing best practices.
The new JEP181 standard is titled ECXML Guidelines for Electronic Thermal System Level Models – XML Requirements and outlines a new file format, ECXML, that is used to share thermal data between developers. Siemens started to develop JEP181 in conjunction with other electronics thermal simulation software vendors in 2005 as a supply chain tool and the Electronics Cooling eXtensible Markup Language (ECXML) format became the preferred file type for thermal designers. Parry’s argument is that since thermal design has blossomed into its own industry and has moved from a purely physical test environment to a mostly digital domain, it deserves its own standards for testing and communicating datasets and results.
What Is Gained from a New Standard?
Robin Bornoff of Siemens wrote a blog article with the incredibly bold title What STEP was for CAD, ECXML is for electronics thermal simulation. In the article, Bornoff describes an electronics design industry where dozens of tools are available for use. Suppliers are required to give data to their customers in a specific format, but the tools used to develop the products might not match the format required by the end users. Full use of thermal electronics simulation tools has been constrained and has slowed down because of this data translation requirement between companies or industries.
Most CAD designers understand the frustration of working with part and assembly files that have come from a different system. In the early ’90s, frustrations with converting between native formats were often so great that design engineers in my company would completely rebuild a drawing or model before navigating through the dense jungle of conversion. Perfect conversion was a completely different set of headaches and issues. ISO 10303 set a standard for product data and conversion between different software programs, mostly in the manufacturing environment. The ISO standard was released in 1994 and several revisions have been written since then with several different file formats added under the umbrella. Pulling a CAD file that you didn’t create into your assembly is always an adventure, but pulling a CAD file from a different system is a rougher adventure made much easier by the advent of the STP format.
Bornoff was the chair of the JEDEC JC15 ECXML working group that was made up of electronics design suppliers and thermal simulation software developers. The group built the guideline document that would later become the standard, with an eye on the format, the interpretation of the ECXML format by each software program that might import it, and a working example. JEP181 was published on September 17, 2020.
What’s in This New Standard?
The ECXML Guidelines for Electronic Thermal System Level Models – XML Requirements standard can be downloaded from the JEDEC website. The specification outlines several terms used in the electronic development industry and then shows different schematics for assembly models. Geometry is heavily defined with several variables to specify exactly what components are being used and their proximity to each other. Another layer of complexity is introduced when objects overlap, and the spec shows which object takes precedence over another and how the ECXML tool will build the data for the overlapping objects. These precedence listings are split out between five different software tools from four different suppliers.
One of the most interesting parts of the specification for me is the Loss Coefficient. The Loss Coefficient for the standard is defined as the pressure drop divided by one-half times the fluid density times the fluid velocity squared. This is a great starting point, so everyone knows how the loss coefficient is defined and calculated, but then we move into the different simulation tools.
Mentor’s FloTHERM, Future Facilities’ 6SigmaET, MSC’s scSTREAM, MSC’s HeatDesigner, and Ansys’ Icepak all have a bullet point beneath the developed equation. Each software tool explains how grille and flow resistance objects will be used. Most define 3D flow resistance as a loss per unit length, but Icepak requires the full resistance to be specified as one number and given a direction.
The specification ends with a long-annotated example that shows a computational wind tunnel with two resistors on a printed circuit board. All the components, boundary conditions and assumptions are laid out in the example and then the XML code is laid out in a heavily commented fashion. Commands and blocks of code are explained one by one as the XML works through its conditions, elements, boundaries, planes and materials. This last super example section should be a fantastic resource guide to someone coming from XML programming and jumping into thermal electronic design using the new ECXML format.
What Are the Takeaway Ideas Here?
If we’re trying to answer the question of the thermal electronic design industry’s maturity, this standard helps the industry to meet John Parry’s criteria as a fully mature industry with standards and best practices. If we take the idea a step further and ask ourselves if Robin Bornoff is right and that ECXML could be as big as the STEP format for thermal electronic design, I’d also say yes. The yes, however, comes with the caveat that we’re at the beginning of the standardization process when everything is bright and new and hasn’t been incrementally chipped away. If Siemens, MSC, Future Facilities and Ansys all use this format without straying every time a new electronic component is designed, there’s a great chance that the format will stick for at least a decade.
We know that technology is evolving faster than we could even imagine, so new electronic components or configurations might factor into a more complex specification and new thermal simulation companies might enter the arena as well. The idea that JEDEC is full of open standards is also promising, if the industry decides that its shifting council can recommend changes to the specification. Users likewise have this option, as the last page of the specification is the Standard Improvement Form, where any user can recommend a change or point out an error and fax or email the form to JEDEC.
