Due to the unique technical requirements of the electronics industry, electronic ceramics differ greatly from conventional engineering ceramics in terms of microscopic structure, chemical composition, and electrical properties. For instance, high mechanical strength, high temperature and humidity resistance, radiation resistance, high dielectric strength, and insulation resistance, as well as the ability to change dielectric constants over a wide range, are all characteristics closely associated with electronic ceramics.
Among various types of electronic ceramics, alumina electronic ceramic substrates stand out for their cost-effectiveness, in addition to their excellent properties. As a result, they are currently one of the most widely used substrates in the market. The manufacturing process of alumina ceramic substrates consists of two main parts: substrate preparation and cutting, and surface processing techniques. While both parts are essential, the latter plays a critical role in ensuring the accuracy of circuits deposited onto the substrates during electronic component production. After all, a "rough" surface cannot guarantee the accuracy required for these circuits.
Typically, people use a "rough grinding + fine polishing" method to make alumina electronic substrates smooth. However, different processing methods and abrasive choices can significantly affect the surface processing results. Below, we will summarize the factors that influence the preparation of alumina ceramic substrates and their grinding and polishing processes.
Alumina electronic ceramic substrates are made by sintering a mixture of 96% to 99% alumina with a suitable amount of mineral raw materials. Common molding methods include tape casting, dry pressing, slip casting, and extrusion. Among these, tape casting is a relatively newer technique compared to traditional ceramic molding methods and is an important method for thin ceramic materials.
After tape casting and trimming, the substrate can be produced with a smooth surface through appropriate debinding and sintering processes. Common sintering methods include:
The thickness and surface quality of the ceramic substrate are crucial indicators. However, sintering often causes deformation and shrinkage, necessitating further precision processing. Given that the mechanisms for effective thinning and ultra-smooth polishing of alumina ceramic substrates are complex, several factors influence the processing outcomes, including processing method, abrasives, and process parameters. Researchers, such as Chen Jianxin and others, have conducted numerous studies on this topic. Below is a summary of the key factors influencing alumina ceramic substrate processing.
There are two main processing methods: single-side grinding and double-side grinding.
Single-side grinding uses high-precision planar processing equipment with high mechanical strength and stable accuracy. The fine, ring-shaped grooves allow the grinding fluid to stay on the grinding wheel surface, resulting in a higher material removal rate under the same grinding fluid flow.
On the other hand, double-side grinding is used for two parallel crystals or other mechanical parts. The wide cross-shaped grooves mostly fill with abrasives and allow them to escape the grinding area, so only a small part of the abrasives is involved in the grinding process, resulting in a lower material removal rate. Overall, single-side grinding is more suitable for rapid thinning of alumina ceramic substrates.
For mechanical removal, abrasives must be chosen with a hardness greater than that of the workpiece. Unlike fixed abrasives, the abrasive particles in the grinding fluid exist in a free form, and the workpiece is processed by these free abrasives.
The relative hardness of the abrasives and their shapes significantly affect the grinding results. Harder abrasives achieve higher material removal rates, but the damage caused during processing is also greater. Softer abrasives result in lower material removal rates but cause less damage, leading to better surface quality. Below is a comparison of several commonly used abrasives.
The particle size of the abrasives affects the depth of cutting into the workpiece surface and the pressure exerted. For the same abrasive concentration in the grinding fluid, larger particles result in fewer abrasive particles in the grinding area. Due to the uneven distribution of particle sizes, smaller particles may not be fully engaged, leading to larger depth of cut and higher material removal rate. However, this may also cause scratches, pits, and sub-surface damage.
Smaller particles allow for more even distribution and a more uniform depth of cut, leading to lower material removal rates but better surface quality.
Grinding pressure determines the action of abrasive particles on the workpiece surface. Lower pressure results in a smaller material removal rate and roughness, while higher pressure increases both. However, when the grinding pressure exceeds a certain level, coarse abrasives may cause deep scratches and worsen surface quality.
Grinding speed impacts the trajectory and uniformity of abrasive particles. Increasing speed raises the number of abrasive tracks per unit time, increasing material removal rate. However, higher speeds may increase vibrations of the grinding wheel, leading to uneven abrasive action and increased surface roughness.
Studies by Chen Jianxin and others found that increasing the flow of grinding fluid initially increases material removal rate and roughness, but beyond a certain point, the accumulation of abrasives leads to reduced efficiency and better surface finish.
The concentration of abrasives in the grinding fluid significantly affects the grinding efficiency and results. Increasing concentration improves material removal rate but may lead to saturation at very high concentrations, causing abrasive clumping and reduced quality.
Based on grinding, experiments were performed with both double-side and single-side polishing using SiC abrasives with particle sizes of W1 and W0.5. The results showed improvements in surface smoothness after polishing.
Tags: Black Silicon Carbide, White Fused Alumina, Brown Fused Alumina, Pink Fused Alumina, Black Fused Alumina
