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Talk about traditional metal packaging materials

TraditionalMetal packageWhat are the materials? What are the characteristics of its packaging? The editor of Keweite will give you a detailed explanation below.

Traditional packaging materials include Al, Cu, Mo, W, steel, Kovar, Cu/W and Cu/Mo, etc. Their main properties are shown below.

1.1 Copper and aluminum pure copper is also called oxygen-free high-conductivity copper (OFHC), with a resistivity of 1.72μΩ·cm, second only to silver. Its thermal conductivity is 401W (m-1K-1). From the perspective of heat transfer, it is very ideal as a package shell. It can be used in packages that require high thermal conductivity and/or high electrical conductivity. However, its The CTE is as high as 16.5×10-6K-1, which can cause great thermal stress on the rigidly bonded ceramic substrate. In order to reduce the stress on the ceramic substrate, the designer can replace a single large substrate with several smaller substrates and separate the wiring. Annealed pure copper is rarely used due to its poor mechanical properties. Although the work-hardened pure copper has a higher yield strength, the low temperature during the manufacture or sealing of the shell will make it anneal and soften, causing permanent deformation of the bottom of the shell during mechanical shock or constant acceleration tests. Aluminum and its alloys are light in weight, low in price, easy to process, and have high thermal conductivity, 237W (m-1K-1) at 25°C. They are commonly used packaging materials and can usually be used as microwave integrated circuits (MIC)的壳。 The shell. But the CTE of aluminum is higher, 23.2×10-6K-1, which is very different from Si (4.1×10-6K-1) and GaAs (5.8×10-6K-1). The thermal cycle often produces greater thermal stress, leading to failure. Although designers can use methods similar to copper to solve this problem, the serious thermal mismatch between copper, aluminum, chips, and substrates brings great difficulties to the thermal design of the package and affects their widespread use.

1.2 The CTE of tungsten and molybdenum Mo is 5.35×10-6K-1, which is very compatible with Kovar and Al2O3. Its thermal conductivity is quite high, 138 W (mK-1), so it is often used as a hermetic package. The base is welded to the side wall of Kovar and is used in many medium and high power density metal packages. One of the main shortcomings of Mo as a base is poor flatness, and another shortcoming is its brittleness after recrystallization. W has a thermal expansion coefficient similar to that of Si and GaAs, and has good thermal conductivity. It can be used as a support material for chips. However, due to poor workability and solderability, it is often necessary to plate other metals on the surface, which makes the process complicated and poor reliability . W and Mo are expensive and not suitable for mass use. In addition, the density is relatively large, which is not suitable for aviation and aerospace applications.

1.3 Steel The thermal conductivity of No. 10 steel is 49.8 W (m-1K-1), which is about three times that of Kovar alloy. Its CTE is 12.6×10-6K-1, which is compatible with ceramics and semiconductors. The CTE is mismatched and can be compressed and sealed with soft glass. Stainless steel is mainly used in air-tight enclosures that require corrosion resistance. The thermal conductivity of stainless steel is relatively low. For example, the thermal conductivity of 430 stainless steel (Fe-18Cr, Chinese brand 4J18) is only 26.1 W (m-1K-1).

1.4 The CTE of Kovar Kovar (Fe-29Ni-17Co, Chinese brand 4J29) is close to that of Si, GaAs, Al2O3, BeO, and AIN. It has good weldability and workability, and can be harder than borosilicate. Glass matching sealing is the most widely used in low power density metal packaging. However, due to its low thermal conductivity, high resistivity and high density, its wide application has been greatly restricted. 1.5 Cu/W and Cu/Mo In order to reduce the CTE of Cu, copper can be compounded with substances with smaller CTE values, such as Mo and W, to obtain Cu/W and Cu/Mo metal-metal composite materials. These materials have high electrical and thermal conductivity, and at the same time integrate the low CTE and high hardness properties of W and Mo. The CTE of Cu/W and Cu/Mo can be adjusted according to the relative content of the components, and can be used as a package base, heat sink, or heat sink. It has been widely produced and used in high-power microwave tubes, high-power laser diodes and some high-power integrated circuit modules at home and abroad. Table 2 and Table 3 respectively list the properties of Cu/W and Cu/Mo composites from Ametek, USA.

Because Cu-Mo and Cu-W are incompatible or have very poor wettability, and the melting point of the two is very different, it brings some problems to the preparation of materials; if the prepared Cu/W and Cu/Mo are not dense If it is high, the air tightness cannot be guaranteed, which affects the packaging performance. Another disadvantage is that the Cu/W density is too large due to the high percentage of W, which increases the package weight. But the high density also makes Cu/W have an excellent shielding effect on the total radiation dose (TID) environment in space, because to obtain the same shielding effect, the thickness of aluminum used needs to be 16 times that of Cu/W.

I believe that through the above explanation, everyone has a deeper understanding of traditional metal packaging materials. If you are interested in this, you can directly communicate with Kevit’s online customer service. Welcome customers to come to consult and purchase!

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