Traditional Packaging Materials

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I. Metal Packaging Materials

Metal packaging materials are the earliest developed packaging materials, known for their high thermal conductivity, mechanical strength, good processing performance, and electromagnetic shielding effects. Traditional metal packaging materials primarily include Cu, Al, W, Mo, as well as Kovar alloy (Fe-Co-Ni alloy) and Invar alloy (Fe-Ni alloy). Cu and Al exhibit high thermal conductivity and excellent heat dissipation performance, but their high thermal expansion coefficients make it difficult to match with silicon wafers. Thermal cycling generated by the chip during operation can cause significant stress. Additionally, Cu has a relatively high density. Kovar alloy and Invar alloy have thermal expansion coefficients that match silicon wafers well, but their lower thermal conductivity can significantly impact the performance of highly integrated packaging devices. Compared to Al, these materials have higher densities and inferior stiffness. W and Mo offer improved thermal conductivity compared to Kovar and Invar alloys, along with lower thermal expansion coefficients. However, their poor wettability with silicon wafers requires the application of Ag or Ni coatings, increasing process complexity and costs. Their higher densities also limit their use in aerospace applications.

II. Ceramic Packaging Materials

Ceramic packaging materials are primarily used for electronic packaging substrates, offering low dielectric constants, excellent high-frequency performance, high strength, good chemical stability, high thermal conductivity, low thermal expansion coefficients, excellent hermeticity, and good moisture resistance. Currently, the most widely used ceramic packaging material is Al2O3, accounting for 90% of all ceramic packaging materials. Other ceramic packaging materials include AlN, BeO, BN, SiC, among others. Al2O3 ceramic substrate materials have mature processing technology and are widely used due to their excellent comprehensive performance and low cost. However, their relatively low thermal conductivity and thermal expansion coefficient mismatch with silicon wafers limit their use in large-scale integrated circuits. During preparation, it is essential to maximize the content of Al2O3 and improve the sintering density of the powder to enhance its overall performance. This, however, leads to higher sintering temperatures and increased costs. AlN ceramic substrate materials exhibit excellent comprehensive performance, higher thermal conductivity compared to Al2O3, and a thermal expansion coefficient that matches silicon wafers well, making them a focus of research domestically and internationally. However, the high purity and sintering density requirements of AlN ceramic substrate materials make their preparation process difficult and costly, limiting their mass production. BeO ceramics have thermal conductivity similar to metals, making them suitable for high-power integrated circuit substrate materials. However, their high sintering temperatures significantly increase material production costs, and their toxicity limits their large-scale use. In summary, ceramic substrate materials excel in comprehensive performance, suitable for high-reliability, high-frequency, high-temperature, and strong hermeticity packaging applications. Nevertheless, they also have certain drawbacks and relatively high overall costs, currently limited to aerospace applications.

III. Plastic Packaging Materials

Plastic packaging materials are a rising star in the packaging industry, known for their low cost, simple processing, good insulation, and ease of realizing miniaturization and lightweighting of electronic products. They currently account for 90% of the entire packaging material field. Plastic packaging materials are primarily thermoplastic polymer materials, including epoxy, phenolic, polyester, and organic silicon polymer materials, with epoxy resins being the most widely used. However, plastic packaging materials have deficiencies such as poor hermeticity and sensitivity to humidity. Therefore, chips packaged with plastic require special attention during storage and require prolonged baking before reflow soldering. If the material absorbs water and is directly subjected to reflow soldering, the absorbed moisture will expand upon heating, potentially causing chip cracking. Additionally, moisture can affect the thermomechanical properties of the material, reducing its elastic modulus and strength at high temperatures. Furthermore, moisture can lead to corrosion and damage of internal metal layers, significantly reducing packaging reliability. Therefore, plastic packaging materials cannot adapt to harsh environments and are limited to civilian applications with low reliability requirements.