The Role of White Corundum Micropowder in Electronic Packaging Materials
Fellow colleagues, those working in materials and packaging know that while electronic packaging sounds impressive, it’s actually all about the details. It’s like putting a protective suit on a precious chip. This suit must withstand impact (mechanical strength), dissipate heat (thermal conductivity), and provide insulation and moisture resistance. Flaws in any of these are crucial. Today, we’ll focus on a commonly used, yet complex, material—white corundum micropowder—to explore how this tiny ingredient plays a crucial role in this protective suit.
Ⅰ. Let’s first get to know the protagonist: the “white warrior” of supreme purity.
White corundum, to put it simply, is extremely pure aluminum oxide (Al₂O₃). It’s related to the more common brown corundum, but its lineage is purer. Its exceptional purity gives it a white color, high hardness, high temperature resistance, and exceptionally stable chemical properties, making it virtually unaffected by anything else.
Grinding it into a micron or even nanometer-scale fine powder is what we call white corundum powder. Don’t underestimate this powder. In electronic packaging materials, especially epoxy molding compounds (EMC) or ceramic packaging materials, it’s more than just an additive; it’s a pillar filler.
II. What exactly does it do in the packaging?
Think of the packaging material as a piece of “composite cement,” with the resin being the soft, sticky “glue” that holds everything together. But glue alone isn’t enough; it’s too soft, weak, and breaks down when heated. This is where white corundum powder comes in. It’s like the “pebbles” and “sand” added to the cement, radically elevating the performance of this “cement” to a new level.
Primarily: Efficient “heat conduction channel”
A chip is like a small furnace. If heat can’t be dissipated, it can lead to frequency throttling and lag at best, or even outright burnout. The resin itself is a poor conductor of heat, trapping the heat inside—a truly uncomfortable situation.
White corundum micropowder has significantly higher thermal conductivity than resin. When a large amount of micropowder is evenly distributed in the resin, it effectively creates a network of countless tiny “thermal highways.” Heat generated by the chip is rapidly conducted from the interior to the surface of the package through these white corundum particles, and then dissipated into the air or heat sink. The more powder added and the more optimally matched the particle size, the denser and more fluid this thermal network becomes, and the higher the overall thermal conductivity (TC) of the packaging material. High-end devices are now striving for high thermal conductivity, and white corundum micropowder plays a leading role in this.
Special Skill: Precise “Thermal Expansion Controller”
This is a crucial task! The chip (usually silicon), the packaging material, and the substrate (such as a PCB) all have different coefficients of thermal expansion (CTE). Simply put, when heated, they expand and contract to varying degrees. If the expansion and contraction rates of the packaging material differ significantly from those of the chip, temperature fluctuations, the alternating cold and hot temperatures, will generate significant internal stress. This is like several people pulling a piece of clothing in different directions. Over time, this can cause the chip to crack or solder joints to fail. This is called “thermomechanical failure.”
White corundum powder has a very low thermal expansion coefficient and is very stable. Adding it to the resin effectively lowers the thermal expansion coefficient of the entire composite material, closely matching the silicon chip and substrate. This ensures that the materials expand and contract in unison during temperature fluctuations, significantly reducing internal stress and naturally improving device reliability and lifespan. This is like a team: only when they work together can they accomplish something.
Basic Skills: A Powerful “Bone Strengthener”
After curing, pure resin has average mechanical strength, hardness, and wear resistance. Adding high-hardness and high-strength white corundum powder is like embedding billions of hard “skeletons” within the soft resin. This directly brings three major benefits:
Increased modulus: The material is more rigid and less prone to deformation, better protecting the internal chip and gold wires.
Increased strength: Flexural and compressive strengths are increased, allowing it to withstand external mechanical shock and stress.
Abrasion and moisture resistance: The package surface is harder and more wear-resistant. Furthermore, the dense filling reduces the path for moisture penetration, improving moisture resistance.
Ⅲ. Just add it in? Quality control is key!
At this point, you might think it’s easy—just add as much powder as you can to the resin. Well, this is where the real skill lies. The type of powder to add and how to add it are extremely complex.
Purity is the bottom line: Electronic grade and ordinary abrasive grade are two different things. In particular, the content of metallic impurities such as potassium (K) and sodium (Na) must be controlled to extremely low ppm levels. These impurities can migrate in electric fields and humid environments, causing circuit leakage or even short circuits, a major threat to reliability. “White” is not just a color; it symbolizes purity. Particle size and grading are an art form: Imagine if all spheres were the same size, there would inevitably be gaps between them. We need to “grade” micropowders of varying sizes so that the smaller spheres fill the gaps between the larger spheres, achieving the highest packing density. A higher packing density provides more thermal conductivity pathways and better control of the thermal expansion coefficient. At the same time, the particle size should be neither too coarse, which would affect processing fluidity and surface finish; nor too fine, as this would create a large surface area and allow for excessive resin absorption, reducing the fill rate and increasing costs. Designing this particle size distribution is one of the core secrets of each formulation.
Morphology and surface treatment are crucial: Particle shape should ideally be regular, equal-area, with fewer sharp corners. This ensures good flow in the resin and minimizes stress concentration. Surface treatment is even more important. White corundum is hydrophilic, while resin is hydrophobic, making them inherently incompatible. Therefore, the micropowder surface must be coated with a silane coupling agent, giving it an “organic coating.” In this way, the powder can be closely combined with the resin, avoiding the interface becoming a weak point that causes cracking when exposed to moisture or stress.
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