In traditional Si IGBT power modules, die-fixing materials such as Pb95Sn5 and Pb92.5Sn5Ag2.5 struggle to meet the reliability requirements of power supplies in high-temperature applications due to creep fatigue. Furthermore, substrate-fixing materials like Sn96.5Ag3Cu0.5, with melting temperatures lower than that of the solder used for die fixation, further limit the reliability of SiC power modules for high-temperature applications. These challenges are driving the market toward silver sintered materials, with the potential to extend to copper sintered materials, offering cost reductions.
Despite the cost advantages, the IDTechEx report "Thermal Management for EV Power Electronics 2024-2034: Forecasts, Technologies, Markets, and Trends" identifies barriers hindering the widespread commercialization of copper sintering, such as challenging manufacturing environments due to copper oxidation and costs comparable to or even higher than those of silver sintering in early 2024 due to smaller commercialization scales.
Conventional die and substrate fixturing materials typically consist of solder alloys, with bond line thicknesses ranging from 50 to 100 µm for die fixturing and from 100 to 150 µm for substrate fixturing. Despite their satisfactory performance, IDTechEx observes a growing preference for sintered silver (Ag), driven by leading automotive OEMs such as Tesla, BYD, and Hyundai. Compared to traditional solder alloys, sintered silver offers higher thermal conductivity (between 200 and 300 W/mK), potentially reducing the thermal resistance of the bond to the housing by more than 40%, along with significantly higher melting points and lower electrical resistivity.
With the adoption of SiC MOSFETs, IDTechEx anticipates that Ag sintering will capture almost or more than 50% of the market share in regions such as China in the near future, presenting significant market opportunities for thermal material suppliers.
Much of the sintered silver available on the market requires pressure during sintering to improve bonding characteristics and reduce porosity, significantly shortening sintering time. However, this method has drawbacks, such as decreased throughput and efficiency when bonding multiple chips, especially with complex architectures. It also requires additional steps and machinery, increasing costs. Therefore, manufacturers tend to avoid it and look for solutions that are easy to implement within their existing infrastructure: pressureless sintering. Pressureless sintering offers lower cost barriers and advantages in multi-chip sintering, but it is only reliable for surfaces with areas between 4 and 25 mm². Further details on the pressureless sintering process are included in the IDTechEx report, "Thermal Management for EV Power Electronics 2024-2034: Forecasts, Technologies, Markets, and Trends.".
The cost of sintered silver can vary significantly depending on factors such as customer relationships, order volume, and suppliers. The cost of sintered silver paste can easily be five to ten times higher than that of solder alloys. For example, IDTechEx learned of a sintered silver paste developed by a Japanese company that costs around $2–3 per gram, although this price has the potential to decrease significantly with increased volume and other material properties. Another supplier suggests that its sintered silver paste costs around $1,400/kg. Overall, driven by major players in the automotive industry, there is a noticeable trend toward replacing solder alloys with silver sintering pastes, creating market opportunities for material suppliers.
Copper sintering is being proposed as an alternative approach to address the cost factor. Compared to silver sintering, copper sintering aims to offer similar performance at a lower cost. One supplier informed IDTechEx that copper sintering technology can cost half as much as silver sintering. However, oxidation remains a significant challenge for copper sintering. Therefore, combining a controlled atmosphere with reduced solvents and binders is key to producing reliable materials. Copper sintering pastes are available with and without pressure under nitrogen or hydrogen. However, this presents challenges during processing, raising concerns about reliability.
IDTechEx is not aware of any automakers using sintered Cu materials by early 2024, but given the historical timeline for the adoption of sintered Ag, IDTechEx anticipates that large-scale commercialization will occur within five years and potentially as early as late 2024 or early 2025.
Author: Yulin Wang, Senior Technology Analyst at IDTechEx
