In materials science, the choice of raw materials can significantly influence the performance of high-tech products. When it comes to ceramics, especially those used in advanced electronic devices, two common forms of alumina come into play: traditional alumina and high purity alumina (HPA). While both are valued for their electrical insulating properties, thermal conductivity, and mechanical strength, there is a growing preference for high purity alumina, especially in cutting-edge applications where performance is critical.
Traditional Alumina and High Purity Alumina (HPA) Grades
Aluminum oxide (Al₂O₃), also know as alumina, is one of the most abundant and versatile ceramic materials used in various industries, from electronics to automotive components. Traditional alumina typically comes in different grades, often with impurities that affect its properties. In contrast, high purity alumina (HPA) refers to alumina with purity exceeding 99.99%, often >99.999%. This ultra-high purity, as high as 5N like in Polar Performance Materials’ HPA-M-HT (5N HPA with 2–6 µm particle size) and HPA-M5 (5N HPA with 3–5 µm particle size), is achieved through more advanced refining processes. For the case of Polar Performance Materials, this advanced manufacturing process has also been proven sustainable with NOx, SOx, and particulate matter (PM) emissions down by 87.9%, 97.9%, and 88%, respectively. More detailed information of the HPA sustainability production can be found in our blog: Can High Purity Alumina Be Produced Sustainably?
Why is High Purity Preferred in Advanced Applications?
Purity plays a critical role in determining the performance of alumina in high-end applications. Impurities in traditional alumina can alter its crystal structure, which in turn can reduce its strength, and impair its electrical and thermal conductivity. These characteristics are especially important in applications that demand high reliability and performance, such as electronics, aerospace, and e-mobility end-uses.
| Product Name | HPA-SDF | HPA-SDC1 | HPA-M1 | HPA-M3 | HPA-M5 | HPA-M-HT | HPA-LU-M | HPA-4N- SMB | 4N-SMBJ | 4N-HT-SMB |
| Grade | 5N | 5N | 5N | 5N | 5N | 5N | 4N to 5N | 3N to 4N | 4N | 4N |
| Total Impurity (ppm) | <21 | <25 | <21 | <21 | <21 | <21 | <23 | <105 | <105 | <105 |
| Na | < 10 | < 10 | < 10 | < 10 | < 10 | < 10 | < 10 | <50 | <50 | <50 |
| Si | <4 | <6 | <4 | <4 | <4 | <4 | <4 | <30 | <30 | <30 |
| Fe | <3 | <4 | <3 | <3 | <3 | <3 | <3 | <10 | <10 | <10 |
| Ca | <3 | <4 | <3 | <3 | <3 | <3 | <5 | <15 | <15 | <15 |
| Others | <1 | <1 | <1 | <1 | <1 | <1 | <1 |
High purity yields better electrical insulating properties.
High-purity alumina offers superior electrical insulation compared to traditional alumina. The absence of impurities minimizes the occurrence of defects and grain boundaries that can act as conductive pathways. As a result, HPA provides better dielectric strength and reduced electrical leakage, making it an ideal material for electronic substrates, insulators, and capacitors.
High purity improves material thermal conductivity.
While alumina, in general, exhibits good thermal conductivity, HPA takes this to another level. With fewer defects and more uniform crystal structures, HPA has higher thermal conductivity than that of traditional or lower grade alumina, which is vital for heat dissipation in high-power electronics like power semiconductors and light emitting diodes (LEDs). This is why HPA products with 5N purity, like HPA-M1, M3, M5, and HPA-LU-M, are commonly used as fillers in semiconductor epoxy mold compounds. They increase the thermal conductivity of the epoxy polymer matrix, improving heat dissipation in high reliability applications. In a similar rationale, high-purity alumina fillers can also be incorporated into thermal interface materials designed for thermal management in semiconductor packages, improving heat dissipation while maintaining electrical insulation.
High purity improves mechanical strength.
The purity of alumina also influences its mechanical properties. High-purity has a more uniform and consistent crystal structure, reducing grain boundary defects. This improves mechanical stability, fracture toughness, and resistance to deformation under stress. Impurities often lead to microstructural inconsistencies that introduce internal stresses. High purity reduces these inconsistencies, enhancing the material’s ability to resist cracking or mechanical failure under load. HPA is much stronger and more resistant to mechanical stress than traditional alumina, making it ideal for high-performance applications where durability is paramount. Whether used in aerospace or semiconductor packaging, HPA ensures long-term reliability and resistance to physical degradation.
Applications of High Purity Alumina and Traditional Alumina
The difference in purity between HPA and traditional alumina makes each suitable for distinct applications. Traditional alumina is often used in general-purpose applications, such as in abrasives and refractory linings, where the demands on purity are less stringent. High purity alumina, on the other hand, is preferred in advanced and specialized industries.
- Semiconductor and Electronics: For substrates, insulators, and packaging that require high reliability and performance. Prominent use of HPA in electronics is its role in improving sapphire substrates, particularly for LED manufacturing. Sapphire substrates, made from HPA-SDF, offer superior thermal conductivity and optical clarity, enhancing the efficiency and longevity of LEDs. Refer to our blog: Improving Sapphire Substrates for LED Manufacturing using High Purity Alumina.
- LED Manufacturing: For high-efficiency, high-power LEDs.
- Aerospace and High-Tech Industries: For components that demand strength, thermal stability, and minimal impurities.
In the energy storage sector, HPA is being used as a separator for lithium-ion batteries. High purity is needed to minimize metallic cation impurities and metal impurities, which should be less than a few ppm. Impurities can leach into the electrolyte, form dendrites, or serve as nuclei that accelerate dendrite formation. Metals in the ceramic layer, introduced either through raw materials or the manufacturing process, are a source of short-circuits due to their proximity to the polymer membrane. More details on this topic can be found on our blog: Maximizing Lithium-Ion Battery Separator Performance Using High Purity Alumina (HPA)
When it comes to high-performance applications where precision, reliability, and longevity are essential, the importance of purity in alumina cannot be overstated. High-purity alumina offers improved electrical insulation, thermal conductivity, and mechanical strength compared to traditional alumina, making it the material of choice for industries that require optimal performance. As technology continues to evolve, the use of HPA will only grow, ensuring that products perform at their best under the most demanding conditions.
Discover the benefits of using high-purity alumina for your applications. Contact us today!
