Global electronics association IPC has published a new method for testing thermal properties of materials. The standard should finally give designers and thermal engineers a way to compare multiple technical data sheets side-by-side. Will IPC TM-650-2.4.54 replace ASTM D5470?
The provenance of performance data provided by suppliers of insulated metal substrates (IMS) and thermal interface materials (TIM) is often undefined and unclear. If the test method is not specified in the data sheet, it is impossible for a thermal designer to compare a vendor’s claimed material performance to what other vendors offer. Depending on what combination of baseplate material thickness, conductive dielectric and copper foil was used in the test, the provided data may not accurately represent real-world performance in applications.
‘There is a lot of costs associated with distrust of specification data,’ says Dale Hume, President at Thermtest, a Canadian lab equipment supplier. ‘I am sure that has an impact on the industry.’ Some companies pick the test method that gives them the best number. Material suppliers feel protected by ‘that little asteriks’ that they put on spec sheets that says the purchaser of the material has to verify all data as correct. ‘That has always been the industry’s out, but it’s not fair to the companies that are actually trying to make good measurements.’
One of the most used test method standards for thermal impedance and conductivity of materials and greases has been ASTM D5470 – ASTM was formerly the American Society for Testing and Materials, but is now an international standards organization. ASTM D5470 is prone to measurement errors in tests of samples with low thermal resistance (Rth). Repeatability and reproducibility errors are said to be in the 10 to 40% range. The ASTM D5470 standard was last updated in 2017. Another widely used thermal test standard is ISO 22007-2.
The thermal characteristics of IMS dielectric materials continue to improve, pushing Rth values lower and giving the ASTM method more trouble to deliver reproducible results. ASTM D5470 was primarily designed for thermal interface materials with a higher Rth. The ISO 22007-2 method makes a more reliable comparison between different materials possible, with high-performing low-Rth materials, but the measured conductivity is less representative of the performance in the target application.
Electronics association IPC recently published IPC TM-650-2.4.54, a ‘Test Method for Thermal Transmission Properties of Metal Based Printed Boards (MBPB)’. The new proposed standard aims to ‘address the issue of measurement uncertainty for materials with low thermal resistance (high thermal conductivity and/or thin thicknesses)’. The test is designed to be representative of real-world performance, ensuring minimal measurement inaccuracy from low to high Rth values.
Robert Art, Global Account Manager IMS/TIM at Ventec, will present the technical details at the Thermal Management Expo conference. Ventec worked with IPC on the TM-650-2.4.54 standard. Dale Hume will join the panel after Robert Art’s presentation. ‘In our own space the diversity of methods that are referred to in spec sheets are often just misunderstanding of what methods to use,’ Hume says. ‘It does cause confusion for sure if users of these test methods are not considering the complexity. Oversimplification of complex issues causes problems.’
Robert Art (Ventec) and Dale Hume (Thermtest) will present and discuss IPC TM-650-2.4.54 and thermal material testing methods at the Thermal Management Expo 2023 coming up May 2-3 in Novi, Michigan.
