CN101791748A - Sn-Ag-Cu-Zn-Ge lead-free solder for inhibiting solid-state interface reaction and preparation method thereof - Google Patents

Abstract

A Sn-Ag-Cu-Zn-Ge lead-free solder used in the technical field of electronic packaging for suppressing solid-state interface reactions and a preparation method thereof. The solder components and their mass percentages are as follows: Ag is 0%-3.5%, Cu is 0%-0.7%, Zn is 0%-2%, Ge is 0%-0.3%, and the balance is Sn. The preparation method is as follows: firstly, put Sn grains into the KCl+LiCl eutectic protective salt melt, raise the temperature, add high-purity Ag wire and/or Cu wire, keep warm for the first time, and stir thoroughly to obtain a uniform Sn-TM solution ; Then, add a small amount of Zn foil and/or Ge particles to the alloy solution, keep warm for the second time, and stir thoroughly; after that, cool down and pour into the solder mold. The invention solves the disadvantages in the prior art that the lead-free solder is easy to react with the substrate metal due to its high Sn content, causing a large amount of substrate dissolution, and at the same time forming a large amount of intermetallic compounds at the interface, which seriously affects the reliability of the interface. The preparation of the present invention The lead-free solder has a simple process and is easy to produce.

Description

Sn-Ag-Cu-Zn-Ge lead-free solder for suppressing solid-state interfacial reaction and preparation method thereof

technical field

The invention relates to a solder used in the technical field of electronic packaging and a preparation method thereof, in particular to a Sn-Ag-Cu-Zn-Ge lead-free solder capable of suppressing solid-state interfacial reactions and a preparation method thereof.

technical background

SnPb is a traditional electronic packaging material. Due to the great threat of Pb to the natural environment and human health, countries around the world have legislated to gradually abandon SnPb solder. Therefore, seeking a substitute for SnPb eutectic solder has become an important task in the current electronics industry. So far, countries around the world have successively developed a series of lead-free solders, which are mainly based on Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Zn, Sn-Bi eutectic systems. . However, even the most promising Sn-Ag-Cu eutectic or near-eutectic solders have many properties that are difficult to compare with SnPb eutectic solders.

The most obvious difference between Sn-Ag, Sn-Cu and Sn-Ag-Cu (SnTM, TM=Ag and/or Cu) eutectic or hypoeutectic solder and SnPb eutectic solder is that the former Sn content is quite high. , reaching more than 95wt%. During the brazing process with Cu plating, which is the most common at present, the formation of intermetallic compounds is inevitable. The melting point of SnTM eutectic solder is about 220°C, while the working temperature of solder joints or joints is generally 100°C or even higher. Therefore, in the solid-state stage, the atoms in the solder and the Cu coating undergo interdiffusion, and a large number of atoms gather and react at the reaction interface, making the interfacial compound continue to grow.

Found through literature search to prior art, such as literature "Effect of Interfacial Reaction on the TensileStrength of Sn-3.5Ag/Ni-P and Sn-37Pb/Ni-P Solder Joints" (Chen Z et al, Journal of Electronic Materials, Vol.36, 2007, 17-25) The research results show that the mechanical properties of the solder joints deteriorate significantly with the aging time, that is, the growth of the compound, and at the same time, the fracture position is transferred from the inside of the solder to the compound interface. Compared with SnPb, the performance deterioration of SnTM solder joints is more obvious. Another example is that Chinese patent CN1603056 provides a kind of Sn-Cu-Ge lead-free solder, and CN1613597 provides a kind of Sn-Ag-Ge lead-free solder. The content of added elements is small, and has little effect on the interface reaction of brazed joints. Chinese patent CN1962157A provides an adaptive Sn-Ag-Zn lead-free solder, but the preparation process is relatively complicated.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses solid-state interfacial reactions and a preparation method thereof. By forming a diffusion barrier layer at the reaction interface, or forming fine compound pinning at the grain boundary, the diffusion of Cu atoms is limited, thereby inhibiting the growth of intermetallic compounds at the reaction interface. It solves the disadvantages in the prior art that the solder is easy to react with the metal of the substrate, causing a large amount of dissolution of the substrate, and at the same time a large amount of intermetallic compounds are formed at the interface, which seriously affects the reliability of the interface. The preparation process of the lead-free solder of the present invention is simple and easy to produce change.

The present invention is achieved through the following technical solutions:

The invention relates to a Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses solid-state interfacial reactions, and its components and mass percentages are:

Ag is 0%-3.5%;

Cu is 0%-0.7%

Zn is 0%-2%;

Ge is 0%-0.3%

The balance is Sn.

Only one of the contents of Ag and Cu can be 0, and only one of the contents of Zn and Ge can be 0.

The present invention relates to the preparation method of the Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses the solid interface reaction as described above, comprising the following steps:

First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire and/or Cu wire, keep it warm for 2-4 hours, and stir well to obtain a uniform Sn-TM solution;

Then, add a small amount of Zn foil and/or Ge grains to the alloy solution, keep the temperature for 2 hours, and fully stir;

After that, the temperature is lowered to 300°C and poured into lead solder molds.

In the present invention, after adding a trace amount of Zn element in the SnTM alloy solder, the melting effect can be achieved. At the same time, more importantly, the Zn element will form a Cu-Zn intermetallic compound at the Cu/Cu6Sn5 or Cu6Sn5/solder interface. layer. Cu is the main element for interfacial reactions, and the diffusion coefficient of Cu atoms in Cu-Zn compounds is 2 orders of magnitude lower than that in Cu6Sn5. Therefore, the continuous Cu-Zn compound layer formed at the reaction interface can act as a diffusion barrier for Cu atoms, slowing down the diffusion of Cu to the Cu6Sn5/solder interface, thereby inhibiting the growth of the compound layer and improving the reliability of the reaction interface. Ge is a congener element of Sn, which plays an important role in improving the wettability of solder. In addition, Ge and Cu can also form intermetallic compounds, but only limited solid solution with Sn and Ag. Therefore, when the content of Ge is sufficient, the interface or compound layer grain boundary will form fine Cu-Ge compounds, which play a pinning role for the diffusion of Cu. Therefore, the growth of the compound layer can also be suppressed; in addition, both Zn and Ge can significantly improve the oxidation resistance of the solder.

In the present invention, a small amount of Zn and Ge elements are added to the SnTM alloy solder, so that the solder can slightly lower the melting point of the solder while maintaining the original good wettability, high mechanical strength, and high ductility. reduce. At the same time, the corrosion of Cu pads is reduced, and the growth of solder/Cu interface reactants can be effectively inhibited, and the reliability of solder joints can be improved.

Compared with the reaction layer thickness of the traditional SnTM solder/Cu joint reaction interface after 20 days of thermal aging at 150°C, whether Zn and Ge are added at the same time or separately, it is beneficial to inhibit the solid-state reaction of the SnTM/Cu interface. The invention can inhibit the growth of the interface compound layer in the aging stage, and therefore is especially suitable for the interconnection of high-temperature electronic components, and increases the reliability of solder joints.

Detailed ways

The embodiments of the present invention are described in detail below: this embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are provided, but the protection scope of the present invention is not limited to the following embodiments.

Example 1

Each component and mass percent in this embodiment are: Ag 3.5%, Cu 0.7%, Zn 0.2%, Ge 0.1%, Sn balance. First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire and Cu wire, keep warm for 2-4 hours, and stir well to obtain a uniform Sn- TM solution; then, add a small amount of Zn foil and Ge particles to the alloy solution, keep warm for 2 hours, and stir well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted solder was prepared into a Sn-Ag-Cu-0.2Zn-0.1Ge/Cu brazing joint, and an aging test was carried out. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 2

Each component and mass percent in this embodiment are: Ag 3.5%, Cu 0.7%, Zn 1%, Ge 0.1%, Sn balance. First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire and Cu wire, keep warm for 2-4 hours, and stir well to obtain a uniform Sn- TM solution; then, add a small amount of Zn foil and Ge particles to the alloy solution, keep warm for 2 hours, and stir well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted brazing filler metal was prepared into a Sn-Ag-Cu-1.0Zn-0.1Ge/Cu brazing joint, and an aging test was carried out. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 3

Each component and mass percentage in this embodiment are: Ag 3.5%, Cu 0.7%, Zn 2%, Ge 0.1%, Sn surplus. First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire and Cu wire, keep warm for 2-4 hours, and stir well to obtain a uniform Sn- TM solution; then, add a small amount of Zn foil and Ge particles to the alloy solution, keep warm for 2 hours, and stir well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted brazing filler metal was prepared into a Sn-Ag-Cu-2.0Zn-0.1Ge/Cu brazing joint, and an aging test was carried out. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 4

Each component and mass percent in this embodiment are: Ag 3.5%, Cu 0.7%, Zn 1%, Ge 0.05%, Sn balance. First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire and Cu wire, keep warm for 2-4 hours, and stir well to obtain a uniform Sn- TM solution; then, add a small amount of Zn foil and Ge particles to the alloy solution, keep warm for 2 hours, and stir well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted brazing filler metal was prepared into a Sn-Ag-Cu-1.0Zn-0.05Ge/Cu brazing joint, and an aging test was carried out. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 5

Each component and mass percent in this embodiment are: Ag 3.5%, Cu 0.7%, Zn 1%, Ge 0.1%, Sn balance. First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire and Cu wire, keep warm for 2-4 hours, and stir well to obtain a uniform Sn- TM solution; then, add a small amount of Zn foil and Ge particles to the alloy solution, keep warm for 2 hours, and stir well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted brazing filler metal was prepared into a Sn-Ag-Cu-1.0Zn-0.1Ge/Cu brazing joint, and an aging test was carried out. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 6

Each component and mass percent in this embodiment are: Ag 3.5%, Cu 0.7%, Zn 1%, Ge 0.3%, Sn balance. First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire and Cu wire, keep warm for 2-4 hours, and stir well to obtain a uniform Sn- TM solution; then, add a small amount of Zn foil and Ge particles to the alloy solution, keep warm for 2 hours, and stir well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted solder was prepared into a Sn-Ag-Cu-1.0Zn-0.3Ge/Cu brazing joint, and an aging test was carried out. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 7

Each component and mass percent in this embodiment are: Ag 3.5%, Zn 1%, Sn surplus. First, put the Sn grains into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire, keep it warm for 2-4 hours, and stir well to obtain a uniform Sn-Ag solution; Then, add a small amount of Zn foil to the alloy solution, keep it warm for 2 hours, and stir it well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted solder was prepared into a Sn-Ag-1.0Zn/Cu brazing joint for aging test. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 8

Each component and mass percent in this embodiment are: Ag 3.5%, Ge 0.1%, Sn surplus. First, put the Sn grains into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire, keep it warm for 2-4 hours, and stir well to obtain a uniform Sn-Ag solution; Then, add a small amount of Ge particles into the alloy solution, keep it warm for 2 hours, and stir it well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted solder was prepared into a Sn-Ag-0.1Ge/Cu brazing joint for aging test. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 9

Each component and mass percent in this embodiment are: Cu 0.7%, Ge 0.1%, Sn surplus. First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Cu wire, keep it warm for 2-4 hours, and stir thoroughly to obtain a uniform Sn-Cu solution; Then, add a small amount of Ge particles into the alloy solution, keep it warm for 2 hours, and stir it well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted solder was prepared into a Sn-Cu-0.1Ge/Cu brazing joint for aging test. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Example 10

Each component and mass percent in the present embodiment are: Cu 0.7%, Zn 1%, Sn surplus. First, put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Cu wire, keep it warm for 2-4 hours, and stir thoroughly to obtain a uniform Sn-Cu solution; Then, add a small amount of Zn foil to the alloy solution, keep it warm for 2 hours, and stir it well. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

100 mg of the smelted solder was prepared into a Sn-Cu-1.0Zn/Cu brazing joint for aging test. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Comparative Example 1

Each component and mass percentage are in the present embodiment: Cu 0.7%, Sn surplus. First, put the Sn grains into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Cu wire, keep it warm for 2-4 hours, and stir thoroughly to obtain a uniform Sn-Cu solution. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

Take 100 mg of the smelted brazing filler metal, prepare it into a Sn-0.7Cu/Cu brazing joint, and carry out an aging test. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Comparative Example 2

Each component and mass percent in the present embodiment are: Ag 3.5%, Sn surplus. First, put the Sn grains into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire, keep it warm for 2-4 hours, and stir well to obtain a uniform Sn-Ag solution. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

Take 100 mg of the smelted brazing filler metal, prepare it into a Sn-3.5Ag/Cu brazing joint, and carry out an aging test. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Comparative Example 3

Each component and mass percent in this embodiment are: Ag 3.5%, Cu 0.7%, Sn surplus. Put the Sn particles into the KCl+LiCl eutectic protective salt melt at 400°C, and raise the temperature to 600°C, add high-purity Ag wire and Cu wire, keep it warm for 2-4 hours, and stir well to obtain a uniform Sn-Ag- Cu solution. After that, the temperature was lowered to 300°C and poured into stainless steel molds.

Take 100 mg of the smelted brazing filler metal, prepare it into a Sn-3.5Ag-0.7Cu/Cu brazing joint, and carry out an aging test. The microstructural evolution of the interface was observed by scanning electron microscopy, and the thickness of the compound layer at the reaction interface was analyzed. The thickness of the compound layer is shown in Table 1.

Table 1 The thickness of the interface compound after heat aging at 150℃ for 20 days

Claims (9)

1. A Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses solid-state interface reactions is characterized in that its components and mass percentages thereof are: Ag is 0%-3.5%, Cu is 0%-0.7 %, Zn is 0%-2%, Ge is 0%-0.3%, and the balance is Sn. 2. The Sn-Ag-Cu-Zn-Ge lead-free solder for suppressing solid-state interfacial reaction as claimed in claim 1, characterized in that only one of the contents of Ag and Cu is 0. 3. The Sn-Ag-Cu-Zn-Ge lead-free solder for suppressing solid-state interfacial reaction as claimed in claim 1, characterized in that only one of the contents of Zn and Ge is zero. 4. a preparation method of the Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses solid-state interfacial reaction as claimed in claim 1, is characterized in that, comprises steps as follows: First, put the Sn particles into the KCl+LiCl eutectic protective salt melt, raise the temperature, add high-purity Ag wire and/or Cu wire, keep warm for the first time, and stir thoroughly to obtain a uniform Sn-TM solution; Then, add a small amount of Zn foil and/or Ge particles to the alloy solution, keep warm for the second time, and stir thoroughly; Afterwards, cool down and pour into the solder mold. 5. the preparation method of the Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses solid-state interfacial reaction as claimed in claim 4 is characterized in that, described KCl+LiCl eutectic protective salt molten liquid, its temperature is 400°C. 6. The method for preparing Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses solid-state interfacial reaction as claimed in claim 4, characterized in that the temperature rise is up to 600°C. 7. The preparation method of the Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses the solid interface reaction as claimed in claim 4, characterized in that, the first heat preservation is 2-4 hours. 8. The preparation method of the Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses the solid interface reaction as claimed in claim 4, characterized in that, the second heat preservation is 2 hours. 9. The method for preparing Sn-Ag-Cu-Zn-Ge lead-free solder that suppresses solid-state interfacial reaction as claimed in claim 4, characterized in that the temperature drop is down to 300°C.