LTCC package materials refer to the base materials used to carry electronic components and their interconnections, and play the roles of mechanical support, sealing environment protection, signal transmission, heat dissipation and shielding. Including LTCC substrate, wiring, housing, frame, heat sink, cover plate, solder and other materials, there are generally three categories: LTCC substrate material, packaging metal material and soldering material.

LTCC substrate material

LTCC substrate materials include LTCC green tape and materials such as conductors and resistors matched with green tape. The conductor materials used in LTCC wiring and through-hole connections use noble metals such as Au, Ag, Pd, Pt or their alloys (binary or ternary alloys PdAg, PtAg, PtAu, PtPdAu, etc.) as the conductive phase, and its performance is stable. The technology is mature and can be sintered in air atmosphere.

LTCC substrate material

Cu is also a material with high electrical conductivity, high thermal conductivity, excellent welding performance, and suitable for low-temperature sintering.

However, since Cu is easily oxidized after being heated in the air, it is different from noble metal materials such as Au and Ag, and a neutral atmosphere (usually nitrogen) is required as a protective gas during sintering.

LTCC package metal material

The metal material for LTCC package is mainly selected according to the characteristics of the metal packaging material. It is necessary to comprehensively consider the thermal conductivity, thermal expansion coefficient, density, solderability, and process maturity of the metal material.

LTCC package metal material

The Fe-Ni-Co alloy containing 29% nickel and 18% cobalt is called Kovar alloy. Its thermal expansion coefficient is small, which matches the thermal expansion coefficient of commonly used LTCC substrates. With better processability and lower cost, it is a more commonly used metal shell material; but its thermal conductivity is not high, which also limits its application range as a metal shell package.

CuW and CuMo alloys combine many excellent properties of W, Mo and Cu, so they have good thermal conductivity, arc corrosion resistance, welding resistance, high-temperature resistance, oxidation resistance, etc., and the thermal expansion coefficient can be in a certain range. It is mainly used in large-scale integrated circuits and high-power microwave devices, such as thermal control boards, heat dissipation elements (heat sink materials) and lead frames.

However, due to the high density of CuW and CuMo, the scope of use is limited, and it is not suitable for application in portable electronic products and aerospace equipment. It is less used in LTCC package that requires lightweight electronic equipment.

Aluminum-silicon alloy material has the advantages of light weight, low thermal expansion coefficient, good thermal conductivity, high strength and rigidity, and can be plated with gold, silver, and nickel, and has good wetting between silicon and aluminum. It has excellent properties such as easy precision machining, non-toxicity, and low cost, and has become one of the electronic packaging materials with broad application prospects.

Al/SiC has the characteristics of high thermal conductivity, low expansion coefficient, high strength, low density, good electrical conductivity, etc., and is being paid more and more attention by more and more people. Al/SiC has been applied in batches in the packaging field as a substrate or heat sink material.

LTCC package solder material

LTCC package soldering materials are mainly used as connecting materials for welding LTCC substrates and metal base plates, metal enclosures, and pins, assembly of components on substrates, solder ball connections, and vertical interconnection of substrates. The melting point of welding materials for LTCC package is generally lower than 450 °C, which belongs to solder.

During the production process of LTCC package, processes such as metal and ceramic welding, component assembly, solder ball array production, and vertical interconnection are required. These assembly and packaging processes are often completed through multi-step welding. In order to ensure that the subsequent process does not affect the soldering results of the previous process (component remelting and displacement), the melting point of the solder used in different processes often has a certain temperature difference to form a temperature gradient.

Source: IBE Electronics