In the mid- to high-voltage power semiconductor sector, which enables EVs, telecom networks, energy infrastructure, and industrial innovation, wide band gap (WBG) semiconductors like gallium nitride (GaN) and silicon carbide (SiC) are on their way to surpassing silicon (Si) for power discretes, power modules, and RF devices. Their projected annual growth rate of more than 13% over the next several years is proof of WBG’s performance superiority for high-power, high-temperature, high-frequency applications where they offer exceptional efficiency, excellent thermal conductivity, and higher breakdown voltages, making them indispensable for cutting-edge technologies in high-stakes markets.
To fully harness the performance potential of WBG semiconductors, the die attach materials that bond the semiconductors to their packages must be able to cost-effectively accommodate WBG’s high heat and ensure efficient power transfer. Because of its proven thermal and electrical conductivity advantages, sintering (where particles are bonded through heat and pressure into a solid metal layer) has become the preferred die/substrate attach method over traditional soldering, as it can provide exceptionally high thermal conductivities and cope with the high-temperature operating environments (>200° C) WBG devices experience in some applications. Silver sintering is arguably the industry standard, but new developments in copper pressure-assisted sintering materials are challenging silver sintering’s dominance and have the potential to reshape the WBG semiconductor market.
Silver’s high thermal conductivity (430 W/m-K) and electrical performance are why it has traditionally been favored for sintering WBG devices, even though it comes at a price premium. Copper, however, offers similar thermal conductivity at close to 400 W/m-K and electrical conductivity only slightly lower than silver. This performance parity at lower cost, combined with other advantages of copper, is driving copper-based sintering materials development that rivals – and in some cases exceeds – silver’s advantages. These include:
Copper sintered joints exhibit excellent mechanical strength, maintaining structural integrity through thermal cycling, which is critical for high-reliability applications like automotive and aerospace, where prolonged exposure to high temperatures, humidity, and stress are the norm. Compared to silver, copper demonstrates resistance to electromigration, helping to minimize the possibility of degraded long-term performance. Finally, copper’s higher tensile strength and lower coefficient of thermal expansion (CTE) increase its potential for better reliability than silver-based materials.
Copper is notoriously more economical than silver, with the ability to deliver lower cost-of-ownership in high-volume production operations. In addition to its cost advantage, copper is a sustainable material. Copper mining has a lower environmental impact than silver, is more abundant, and recyclable. Finally, copper sintering processes have been shown to require less energy than silver sintering.
Historically, the challenges with copper-based materials have centered on their sintering difficulty. Older-generation formulations required higher temperatures and higher pressures than silver materials to achieve complete sintering, which introduced potential damage to dies and substrates. However, advances in sintering environments and innovative formulation approaches are mitigating these concerns, enabling thorough copper sintering without the need for excessive pressure and temperature. For instance, Henkel’s new pressure-assisted copper sintering material is engineered to overcome many shortcomings of conventional copper sintering formulas.
This groundbreaking material, leveraging proprietary copper filler technology, offers a compelling cost-of-ownership advantage versus silver-filled formulas, delivering thermal conductivity exceeding 300 W/m-K, reduced pressure (10-15 MPas) and temperature requirements (200° C – 250° C) for lower die stress, and faster processing time to accommodate mass production. The new pressure-assisted sintering formula is especially well-suited for current and next-generation SiC applications like power modules, ensuring high reliability and performance comparable to silver-based sintering solutions without the risk of die or substrate damage from the pressure and temperature required with other materials to achieve complete sintering.
As WBG semiconductors evolve, higher-performance, cost-effective sintering materials that can enable current and next-generation devices with high thermal and electrical capability, as well as more delicate processing parameters to mitigate potential device damage and preserve high yields, will help close the price-performance gap. New copper sintering formulations have the potential to leapfrog silver-based materials and offer manufacturers an innovative, competitive, sustainable, and cost-efficient advantage that can deliver the long-term reliability and exceptional performance necessary for the power sector.
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