CN118559279A - A high reliability lead-free solder alloy with thermal fatigue resistance and its application - Google Patents

Abstract

The invention discloses a high-reliability lead-free solder alloy with thermal fatigue resistance and application thereof, and relates to the technical field of welding materials. The lead-free solder alloy comprises the following components in percentage by mass: 1.0 to 4.0 percent of Ag, 0.1 to 1.0 percent of Cu, 1.0 to 8.0 percent of Sb, 0.05 to 4.0 percent of Bi, 0.5 to 6.0 percent of In, 0.5 to 1.2 percent of Ni, 0.001 to 0.2 percent of Co, 0.001 to 0.13 percent of trace elements and/or 0.001 to 0.09 percent of RE, and the balance of Sn and unavoidable impurities; wherein the microelements consist of P and/or Ge; RE is at least one of Ce, la and Nd. The solder alloy has good wettability, reliability, oxidation resistance, mechanical property and thermal fatigue resistance, and can meet the requirements of high-power semiconductor laser packaging.

Description

A high reliability lead-free solder alloy with thermal fatigue resistance and its application

Technical Field

The invention relates to the technical field of welding materials, and in particular to a high-reliability lead-free solder alloy resistant to thermal fatigue and application thereof.

Background Art

High-power semiconductor laser arrays have the advantages of small size, light weight, long life and high efficiency. They can be used as pump sources for solid lasers and directly as light sources for material processing. They have been widely used in military, fiber-optic communications, optical sensing, information storage, medical, laser printing, optical computing and other fields. High-power laser diodes or laser devices convert electrical energy into light energy with an efficiency of about 10%-50%. The rest is converted into waste heat. This waste heat must be dissipated in a short time, otherwise it will cause thermal stress to the laser diode, and eventually cause irreversible damage to the laser, resulting in a reduction in the life of the laser. Inefficient cooling and packaging design will lead to poor product quality because the temperature of the core of the device has a direct impact on the output wavelength and band gap. The actual situation has proved that every 3°C temperature change can cause a wavelength change of nearly 1nm for the diode laser, and the output power of the laser will also decrease with increasing temperature.

To help dissipate heat, the semiconductor laser chip and heat sink are soldered to the heat dissipation substrate. Typically, the solder used is SAC305, which has good thermal conductivity, mechanical ductility, and can achieve high-precision, high-reliability heat sink and pin welding in medium and low-power laser packages, ensuring the stable operation of the optical module during high-speed data transmission. With the increasing advancement of technology, many laser research and development companies have developed more complex high-power and high-performance laser arrays. CW (continuous wave laser) and QCW (quasi-continuous wave laser) powers exceeding 900W+ have appeared in different laser companies, such as Princeton Optronics. Traditional SAC305 solder can no longer meet the mechanical stress generated by repeated switching cycles or hard pulses in laser operation, resulting in cracking of the weld seam, increased thermal resistance, chip failure, and ultimately reduced laser life.

For example, Chinese patent CN103561903 A discloses an alloy composition, which may contain Bi, Sb, and In in a Sn-Ag-Cu solder alloy. The technology disclosed in the patent is that the composition of the solder alloy with a Cu content far from the eutectic leads to a decrease in temperature cycle characteristics: the decrease in temperature cycle characteristics when the Ag content is far from the eutectic is less than the composition of Cu far from the eutectic; by adding In to Bi and Sb instead of reducing the amount of Ag, the temperature cycle characteristics will be improved. However, the reduction in the amount of Ag will result in the inability to form sufficient IMC of Ag ₃ Sn, thereby reducing the bonding strength of the solder joint, while the wettability of the solder is reduced, and the oxidation resistance is not improved.

In addition, Chinese patent CN 115464299 A also discloses a solder alloy, in which trace amounts of Ge and P are added to the Sn-Ag-Cu-Sb solder alloy to improve the oxidation resistance of the solder, thereby reducing solder voids. The technology disclosed in this patent is that it is easier to combine with oxygen than tin, silver, and antimony. On the one hand, it can quickly remove the oxygen inside the solder, making the microscopic components of the solder more uniform. On the other hand, it can form an extremely dense oxide layer on the surface of the lead-free alloy to prevent the lead-free alloy from being further oxidized, so it can play a good deoxidation and anti-oxidation role. However, there is a lack of elements that can bring about solid solution strengthening, so the improvement of the mechanical properties of the solder is not obvious. In addition, the high-temperature reliability of the solder has not been further verified.

Summary of the invention

To solve the above technical problems, the present invention provides a high-reliability lead-free solder alloy with thermal fatigue resistance and its application, wherein the solder alloy has good wettability, reliability, oxidation resistance, mechanical properties and thermal fatigue resistance to meet the requirements of high-power semiconductor lasers, power devices and microelectronic circuit packaging. In its application, the disclosed solder alloy is particularly suitable for, but not limited to, forming a welding seam in the form of a strip, rod or flux-cored wire or a preformed solder sheet, solder ball, solder powder or solder paste (a mixture of solder powder and flux) in the field of high-power semiconductor lasers, power devices and microelectronic circuit packaging.

The specific technical solutions include the following:

In a first aspect, a high reliability lead-free solder alloy with thermal fatigue resistance is provided, comprising the following components in percentage by mass:

Ag (silver) 1.0-4.0%, Cu (copper) 0.1-1.0%, Sb (antimony) 1.0-8.0%, Bi (bismuth) 0.05-4.0%, In (indium) 0.5-6.0%, Ni (nickel) 0.5-1.2%, Co (cobalt) 0.001-0.2%, trace elements 0.001-0.13% and/or RE (rare earth elements) 0.001-0.09%, the balance is Sn (tin) and unavoidable impurities;

Wherein, the trace elements are composed of P (phosphorus) and/or Ge (germanium), the mass percentage of P in the high-reliability lead-free solder alloy with heat fatigue resistance is 0.001-0.08%, and the mass percentage of Ge in the high-reliability lead-free solder alloy with heat fatigue resistance is 0.001-0.05%; the RE is selected from at least one of Ce (cerium), La (lanthanum), and Nd (neodymium).

Furthermore, the mass percentage of Ag in the heat fatigue resistant high reliability lead-free solder alloy is 2.0-3.5%.

Preferably, the mass percentage of Ag in the thermal fatigue resistant high reliability lead-free solder alloy is 2.5-3.5%.

Furthermore, the mass percentage of Cu in the heat fatigue resistant high reliability lead-free solder alloy is 0.3-0.9%.

Preferably, the mass percentage of Cu in the thermal fatigue resistant high reliability lead-free solder alloy is 0.5-0.8%.

Furthermore, the mass percentage of Sb in the heat fatigue resistant high reliability lead-free solder alloy is 2.0-6.0%.

Preferably, the mass percentage of Sb in the thermal fatigue resistant high reliability lead-free solder alloy is 3.0-5.0%.

Furthermore, the mass percentage of Bi in the heat fatigue resistant high reliability lead-free solder alloy is 0.1-4.0%.

Preferably, the mass percentage of Bi in the thermal fatigue resistant high reliability lead-free solder alloy is 0.1-2.0%.

Furthermore, the mass percentage of In in the heat fatigue resistant high reliability lead-free solder alloy is 0.5-4.0%.

Preferably, the mass percentage of In in the thermal fatigue resistant high reliability lead-free solder alloy is 0.7-3.0%.

Furthermore, the mass percentage of Ni in the high-reliability lead-free solder alloy with thermal fatigue resistance is 0.5-1.0%; the mass percentage of Co in the high-reliability lead-free solder alloy with thermal fatigue resistance is 0.01-0.1%.

Preferably, the mass percentage of Ni in the heat fatigue resistant high reliability lead-free solder alloy is 0.5-0.7%.

Preferably, the mass percentage of Co in the thermal fatigue resistant high reliability lead-free solder alloy is 0.01-0.08%.

Further, the mass percentage of P in the high-reliability lead-free solder alloy with thermal fatigue resistance is 0.001-0.05%, and the mass percentage of Ge in the high-reliability lead-free solder alloy with thermal fatigue resistance is 0.001-0.03%. Preferably, the mass percentage of P in the high-reliability lead-free solder alloy with thermal fatigue resistance is 0.001-0.03%, and the mass percentage of Ge in the high-reliability lead-free solder alloy with thermal fatigue resistance is 0.001-0.015%.

Preferably, the mass percentage of the trace elements in the heat fatigue resistant high reliability lead-free solder alloy is 0.005-0.03%.

Furthermore, the mass percentage of the RE in the heat fatigue resistant high reliability lead-free solder alloy is 0.001-0.07%.

Preferably, the mass percentage of the RE in the thermal fatigue resistant high reliability lead-free solder alloy is 0.001-0.05%.

Preferably, the RE is a mixture of Ce, La and Nd.

Preferably, the liquidus temperature of the thermal fatigue resistant high reliability lead-free solder alloy is ≤220°C.

Preferably, the thermal fatigue resistant high reliability lead-free solder alloy is in the following forms: bars, rods, flux-cored wires, foils, strips, films, sheet preforms, powders, pastes, solder balls, and solder sheets.

In a second aspect, the application of the high-reliability lead-free solder alloy resistant to thermal fatigue as described in the first aspect is provided, and the high-reliability lead-free solder alloy resistant to thermal fatigue is used in module welding of high-power semiconductor lasers, power devices and microelectronic circuits.

The beneficial effects of the present invention are:

The present invention provides a high-reliability lead-free solder alloy with heat fatigue resistance and its application. The solder alloy exhibits suitable mechanical reliability and heat fatigue resistance, and shows improved shear strength even after thermal aging. The solder alloy can also obtain good connection strength when placed in an ambient temperature exceeding 150° C. for a long time as a welding part. Compared with the known SAC305 solder alloy, the solder alloy shows improved high-temperature mechanical properties and can be widely used in the packaging of high-power semiconductor lasers, power devices and microelectronic circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

FIG1 is a cross-sectional SEM image of a welded part of Example 21 of the present invention after a high temperature aging test;

FIG. 2 is a cross-sectional SEM image of the welded part of comparative example 15 of the present invention after high temperature aging test.

DETAILED DESCRIPTION

The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

It should be understood that the term “and/or” used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

In order to more fully understand the technical content of the present invention, the technical solution of the present invention is further introduced and illustrated in conjunction with specific embodiments below.

The different content ranges of the invention are defined in more detail in the following paragraphs describing the benefits of the compositional ranges of the solder alloys disclosed in the invention. Unless expressly stated to the contrary, any content range defined herein and any feature stated as being preferred may be combined with any other feature or features.

The solder alloy described in the present invention has a relatively low melting point, specifically a low liquidus temperature, typically less than 220°C, more typically less than 215°C, and even more typically less than 210°C liquidus temperature. This enables the solder alloy to be used in a low temperature reflow process (such as a reflow temperature from 215 to 235°C). Compared with conventional reflow processes, such a low temperature reflow process can reduce the risk of damage to the solder components. The term "solidus" used in this description refers to the temperature below which the material provided is completely solid. The term "liquidus" used in this description refers to the highest temperature at which crystals can coexist with molten materials. Above the liquidus temperature, the material is a homogeneous liquid in equilibrium. Below the liquidus temperature, solidification occurs to form more and more crystals. The solidus and liquidus temperatures are not aligned or overlapped. If there is an interval between the solidus and liquidus temperatures, it is called the "solidification range" or "mushy zone", and within this range, the material consists of a mixture of solid and liquid phases. The "solidification range" of the lead-free solder alloy described in this specification is relatively small, usually between 10-15°C. The narrower the temperature range, the faster the melting or solidification speed, the less leaching, dislocation, reoxidation, and voids of the components, the more conducive to the soldering operation, and the less energy consumption.

The lead-free solder alloy described in this specification can exhibit suitable high-temperature mechanical reliability and thermal fatigue resistance, and can generally withstand a use temperature of at least 150°C, for example, up to 175°C. Compared with the well-known SAC305, the solder alloy can show improved high-temperature mechanical properties, higher electrical and thermal conductivity, and the solder alloy exhibits improved thermal shock performance. For example, the solder alloy withstands a thermal cycle test of more than 500 cycles with a dwell time of 10 minutes from a low temperature of -50°C to a high temperature of +150°C. The solder alloy can be advantageously used in applications with high use temperatures, such as high-power semiconductor lasers, power devices, and microelectronic circuits.

The term “rare earth elements (RE)” as used herein includes elements selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

As used herein, the term "flux" includes a substance, usually an acid or base, used to promote the melting of metals, particularly to remove and prevent the formation of metal oxides.

Lead-free as used herein means that there is no intentional addition of lead. Therefore, the lead content is zero or within the range of incidental impurities.

In this specification, "%" concerning the composition of a solder alloy means "mass %" unless otherwise specified.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains 1.0 to 4.0 mass % of Ag. Ag can form Ag ₃ Sn intermetallic compounds (IMC) in the Sn matrix to achieve precipitation strengthening of the solder alloy, and improve the strength and cycle resistance of the solder alloy. In addition, Ag increases the wetting and spreading of the solder alloy and reduces the liquidus temperature. If the Ag content is less than 1.0 mass %, the wettability during soldering cannot be improved, the precipitated Ag ₃ Sn becomes less, the IMC network will not become stable, and the strength of the solder alloy cannot be improved. If the Ag content is greater than 4.0 mass %, the liquidus temperature of the solder alloy will rise and the solderability will decrease. Coarsened Ag ₃ Sn will precipitate in a plate-like form, the solder alloy will become brittle, and the impact drop resistance will also deteriorate. Preferably, the solder alloy includes 2.0 to 3.5 mass % Ag, more preferably 2.5 to 3.5 mass % Ag, and most preferably 3.0 to 3.2 mass % Ag.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains 0.1 to 1.0 mass % Cu. Cu can lower the melting point and prevent Cu corrosion. It forms IMCs of Cu ₆ Sn ₅ and Cu ₃ Sn with Sn solder, improves the mechanical strength and creep resistance of the solder alloy, and suppresses the strength degradation in a thermal cycle environment. If the Cu content is less than 0.1 mass %, the amount of Sn-Cu IMC generated is small, and the mechanical strength of the solder alloy is insufficient. Even if 2.0 mass % Bi is added later, the heat cycle resistance will deteriorate. If the Cu content exceeds 1.0 mass %, the liquidus temperature of the solder alloy rises, the solder cannot be completely melted at the usual reflow temperature or scum is generated when it is melted, resulting in poor wettability, more voids, and ultimately poor heat cycle resistance. In addition, a large amount of Cu ₆ Sn ₅ IMC is precipitated at the welding interface, so the drop impact resistance is poor. Preferably, the solder alloy comprises from 0.3 to 0.9 mass % Cu, more preferably 0.5 to 0.8 mass % Cu, and most preferably 0.7 to 0.8 mass % Cu.

The high reliability lead-free solder alloy resistant to heat fatigue of the present invention comprises 1.0 to 8.0 mass % of Sb. When the Sb content is less than 1.0 mass %, the solid solution strengthening effect of Sb dissolving in the Sn matrix to form the Sn (Sb) solid solution is not shown, and the shear strength of the welding interface is reduced. If more than 3.0 mass % of Sb is added to the solder alloy, the IMC phase of SnSb is precipitated from the supersaturated Sn (Sb) solid solution, which can improve the strength of the solder alloy without causing a decrease in ductility. In addition, Sb also enters the lattice of atomic arrangement and replaces Sn, causing the lattice of atomic arrangement to be strained, strengthening the Sn matrix, and improving the temperature cycle characteristics of the solder alloy. Based on this, the solder alloy of the present invention exhibits excellent mechanical properties (both high strength and high ductility) and heat fatigue resistance. However, when the Sb content exceeds 8.0 mass%, the solidus-liquidus temperature of the solder alloy is increased, and a coarse and brittle Sn ₃ Sb ₂ primary phase is solidified, which cannot suppress component failure caused by cracks in the solder alloy. Preferably, the solder alloy includes from 2.0 to 6.0 mass% Sb, more preferably includes 3.0 to 5.0 mass% Sb, and most preferably includes 3.0 to 4.0 mass% Sb.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains 0.05 to 4.0 mass % Bi. Bi can be dissolved in the Sn matrix to improve the strength of the solder alloy. Bi can also reduce the surface tension of the solder alloy in the molten state, thereby improving the wettability and spreadability of the solder alloy. Bi can also increase the creep resistance of the solder alloy. If the Bi content is less than 0.05 mass %, the solid solution amount of Bi is small and the strength cannot be fully improved. In addition. On the other hand, if the Bi content exceeds 4.0 mass %, the solidus temperature will drop. Bi will segregate in the grain boundaries and the strength of the solder alloy will decrease. At the same time, the solder alloy itself becomes brittle and hard, and the ductility and heat fatigue resistance are also significantly reduced, and the weld cannot suppress the further expansion of cracks caused by vibration or impact. Preferably, the solder alloy includes from 0.1 to 4.0 mass % Bi, more preferably includes 0.1 to 2.0 mass % Bi, and most preferably includes 0.5 to 1.0 mass % Bi.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains 0.5 to 6.0 mass % In. In can lower the melting temperature of the solder alloy and improve the strength of the solder alloy by solid solution strengthening. If the In content is less than 0.5 mass %, the solid solution amount of In in Sn is small, and the strength of the solder alloy will not be fully improved. In addition, the liquidus temperature of the solder alloy does not decrease. If the In content exceeds 6.0 mass %, the molten solder alloy becomes easily oxidized and the generation of voids in the weld cannot be suppressed. Preferably, the solder alloy includes from 0.5 to 4.0 mass % In, more preferably includes 0.7 to 3.0 mass % In, and most preferably includes 1.0 to 2.5 mass % In.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains 0.5 to 1.2 mass % Ni. It is uniformly dispersed in the Cu ₆ Sn ₅ phase, making the particle size of IMC fine, improving the bonding strength, impact resistance and thermal cycle resistance of the solder joint. The fine particle size allows the stress that generates cracks to be dispersed in many particle size directions, slowing down the further expansion of the cracks. Ni can also inhibit the diffusion and reaction of the plating components of semiconductor components and external substrates into the solder alloy during soldering. If the Ni content is less than 0.5 mass %, the bonding strength of the solder joint cannot be effectively improved. If the Ni content exceeds 1.2 mass %, the wettability of the solder alloy deteriorates, and the liquidus temperature increases sharply. If the soldering temperature is too high, the electronic components may be thermally damaged. Preferably, the solder alloy includes from 0.5 to 1.0 mass % Ni, more preferably includes 0.5 to 0.6 mass % Ni, and most preferably includes 0.1 to 0.3 mass % Ni.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains 0.001 to 0.2 mass % Co. Adding a trace amount of Co can refine the grains just like Ni. During solidification, a large number of Co solidification nuclei are generated in the solder alloy, the growth of the Sn phase precipitated around is suppressed, and the overall structure becomes finer. If the content of Co is less than 0.001 mass %, it cannot play the role of refining the alloy structure and improving the bonding strength. If the content of Co is higher than 0.2 mass %, the wettability of the solder alloy deteriorates and the melting point becomes higher. Preferably, the solder alloy includes from 0.001 to 0.1 mass % Co, more preferably includes 0.01 to 0.08 mass % Co, and most preferably includes 0.01 to 0.03 mass % Co.

The thermal fatigue resistant high reliability lead-free solder alloy of the present invention further comprises trace elements and/or RE (rare earth elements).

Among them, the trace elements consist of P and/or Ge.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains 0.001 to 0.05 mass % Ge. Ge is any element that can inhibit the oxidation of Sn and improve wettability. When the solder alloy is melted, Ge is highly enriched on the surface to form a dense protective film. If the content of Ge is less than 0.001 mass %, there is no obvious antioxidant effect. If the content of Ge exceeds 0.05 mass %, the surface tension of the molten solder alloy increases, the fluidity of the solder alloy deteriorates, and more voids are generated in the welding part. Preferably, the solder alloy includes from 0.001 to 0.03 mass % Ge, more preferably includes 0.001 to 0.015 mass % Ge, and most preferably includes 0.005 to 0.01 mass % Ge.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains 0.001 to 0.08 mass % of P. P is an element that can inhibit the oxidation of Sn and improve wettability. When the solder alloy is melted, P forms a tin phosphate film layer on the surface, which prevents the solder alloy from directly contacting the surrounding air to form tin oxide. If the content of P is less than 0.001 mass %, this anti-oxidation effect is not obvious. If the content of P exceeds 0.08 mass %, the surface tension of the molten solder alloy increases, the fluidity of the solder alloy deteriorates, and more voids are generated in the welding part. Preferably, the solder alloy includes from 0.001 to 0.05 mass % of P, more preferably includes 0.001 to 0.03 mass % of P, and most preferably includes 0.001 to 0.02 mass % of P. In addition, the total amount of Ge and P added should optimally meet the range of 0.005 to 0.03 mass %.

The heat fatigue resistant high reliability lead-free solder alloy of the present invention contains at least one rare earth element (RE) with a total amount of less than 0.09 mass % in addition to the above components. RE has a strong affinity for "Sn". A trace amount of rare earth preferentially combines with Sn. These preferentially precipitated and evenly distributed compounds can become heterogeneous nucleation centers for further crystallization, so that the organization is significantly refined and evenly distributed, thereby improving the shear strength, creep resistance and anti-electromigration performance of the solder alloy. If the total amount of RE added is less than 0.001 mass %, there is no obvious refinement effect on the organization. If the total amount of RE added is greater than 0.09 mass %, brittle rare earth compounds will be generated. At the same time, due to the large atomic radius, the lattice of the matrix alloy will be destroyed, resulting in a decrease in the bonding strength of the weld. The total content of RE elements is preferably less than 0.07 mass %, more preferably less than 0.05 mass %, and most preferably less than 0.02 mass %. Among them, the preferred RE element is at least one of Ce, Ld and Nd.

The balance of the heat fatigue resistant high reliability lead-free solder alloy of the present invention is Sn. In addition to the aforementioned elements, it may also contain inevitable impurities. Even if it contains inevitable impurities, it does not affect the aforementioned effects.

Now, the present invention will be further described through a summary of multiple non-limiting examples of these solder alloys and their properties, and the present invention is not limited to the following examples. In order to verify the effect of the present invention, Examples 1 to 25 and Comparative Examples 1 to 15 provide a high reliability lead-free solder alloy with thermal fatigue resistance, which is in the form of a preformed lead-free solder sheet, the components of the lead-free solder sheet are calculated by weight percentage as shown in Table 1 and Table 2, and the melting point, tensile strength, shear strength, oxide film thickness, temperature cycle results and high temperature aging results are measured for evaluation.

Performance evaluation test:

(1) Melting point. For the examples/comparative examples listed in Tables 1 and 2, their DSC curves were measured. According to the provisions of the ICTA Standardization Committee, the intersection of the extended line of the front baseline of the DSC curve and the tangent line at the maximum slope of the front edge of the peak represents the melting point. The DSC curves of the examples/comparative examples were obtained by placing 40 mg of the sample in a DSC instrument (model: JL-DSC001) from METTLER TOLEDO, heating it in the atmosphere at a rate of 10°C/minute. When the melting point is 214 to 217°C, it is evaluated as "◎". When the melting point is 217 to 220°C, it is a temperature that is not a problem in practical use, so it is evaluated as "０". When the melting point is lower than 214°C and higher than 220°C, it is evaluated as "×".

(2) Tensile strength. Measured according to JISZ3198-2 standard. For the examples/comparative examples listed in Tables 1 and 2, melt and inject into a mold to make test bars with a gauge length of 30 mm and a diameter of 10 mm. The produced test bars were stretched at a speed of 5 mm/min at room temperature using a universal material testing machine (Kezhun, KZ-50KN), and the average strength (Rm) of 5 test bars when they broke was measured. In the present invention, when the tensile strength is 56 MPa or more, it is sufficient strength, so it is evaluated as "◎". When the tensile strength is 52 MPa or more and less than 56 MPa, it is a strength that is not a problem in practical use, so it is evaluated as "０". When the tensile strength is less than 52 MPa, it is evaluated as "×".

(3) Shear strength. The examples/comparative examples listed in Table 1 and Table 2 were prepared with a size of 3×3×0.05 mm. A 4J29 alloy-Ni-plated-Au-plated plate with a thickness of 1.0 mm was used for soldering at a maximum temperature of 248°C, a holding time of 60 seconds, and nitrogen. At least 20 test substrates were prepared for each example/comparative example. The shear strength (MPa) was measured at 6 mm/min using a shear strength measuring device (STR 1000 manufactured by Kezhun Corporation). When the average shear strength of the 20 test substrates was above 35 MPa, it was judged to be a level of sufficient shear strength and was evaluated as "◎". When it exceeded 28 MPa and was below 35 MPa, it was judged to be a level that could be used practically without problems and was evaluated as "０". When it was below 28 MPa, it was evaluated as "×".

(4) Thickness of oxide film. The examples/comparative examples listed in Table 1 and Table 2 were processed into preformed ingots with a thickness of 10×10×0.5 mm, and heat-treated in a constant temperature bath at 150°C for 150 minutes. The oxide film thickness was measured by field emission Auger electron spectroscopy (FE AES) according to the method of ISO/TR 15969. A film thickness of 2.0 nm or less indicates that the example/comparative example has good antioxidant properties, and therefore, it is evaluated as "◎". When the film thickness exceeds 2.0 nm and is less than 2.8 nm, there is no practical problem, and therefore, it is evaluated as "０". When the film thickness exceeds 2.8 nm, it is evaluated as "×".

(5) Temperature cycle and high temperature aging results. The examples/comparative examples listed in Table 1 and Table 2 were prepared with a size of 3×3×0.05 mm. A 4J29 alloy-Ni-plated-Au-plated plate with a thickness of 1.0 mm was used for soldering at a maximum temperature of 248°C, a holding time of 60 seconds, and nitrogen. At least 20 test substrates were prepared for each example/comparative example. Among them, according to the method of JESD22-A104C standard, 10 test substrates were placed in a programmable hot and cold shock box (manufactured by Kezhun, TSTC-80-DC) for temperature cycle testing. The low temperature was set to -50°C, the high temperature was +150°C, the dwell time was 10 minutes, and the number of cycles was 500 cycles. Using a thrust shear machine (manufactured by Kezhun STR 1000), the residual shear strength (MPa) of 10 test substrates was measured at 6 mm/min. The average residual shear strength was above 15 MPa and was evaluated as "◎". When it exceeds 9 and is below 15MPa, it is judged to be a level that can be used practically without problems and is evaluated as "0". When it is below 9MPa, it is evaluated as "×". 10 test substrates are placed in a high-temperature aging box and kept warm at 150°C for 500 hours. Similarly, the residual shear strength of the 10 test substrates after aging is measured using a thrust shear machine. When the average shear strength is above 25MPa, it is judged to be a level that obtains sufficient shear strength and is evaluated as "◎". When it exceeds 20MPa and is below 25MPa, it is judged to be a level that can be used practically without problems and is evaluated as "0". When it is below 20MPa, it is evaluated as "×".

The specific compositions of the thermal fatigue resistant high reliability lead-free solder alloys of Examples 1-25 are shown in Table 1 below:

Table 1 Composition of thermal fatigue resistant high reliability lead-free solder alloys of Examples 1-25

Note: Bal. is the margin.

The specific compositions of the heat fatigue resistant high reliability lead-free solder alloys of Comparative Examples 1-15 are shown in Table 2 below:

Table 2 Composition of thermal fatigue resistant high reliability lead-free solder alloys of Comparative Examples 1-15

Note: Bal. is the margin.

Performance evaluation tests were conducted on the thermal fatigue resistant high reliability lead-free solder alloys of Examples 1-25 and Comparative Examples 1-15. The test results are shown in Tables 3-4 below.

Table 3 Performance evaluation test results of high reliability lead-free solder alloys resistant to thermal fatigue of Examples 1-25

Table 4 Performance evaluation test results of high reliability lead-free solder alloys resistant to thermal fatigue of comparative examples 1-15

The heat fatigue resistant and high reliability lead-free solder alloys of the embodiments and comparative examples listed in Table 1 and Table 2, except for metal indium, are all prepared by melting the master alloy.

The preparation method of the heat fatigue-resistant high-reliability lead-free solder (specifically in the form of preformed lead-free solder sheets) of the embodiments of the present invention and the comparative examples includes: firstly, melting each intermediate alloy (tin-silver alloy, tin-antimony alloy, tin-phosphorus alloy, tin-germanium alloy, tin-copper alloy, tin-bismuth alloy, tin-nickel alloy, tin-cobalt alloy, rare earth element intermediate alloy), mixing and melting the intermediate alloys, stirring evenly after all are melted, cooling to 320°C, and then casting, rolling, cleaning, punching or cutting into preformed lead-free solder sheets.

The preparation method of the tin-silver alloy comprises: placing the tin-silver metal in a high vacuum melting furnace, introducing argon protective gas, heating to 900° C., mixing and casting into a tin-antimony alloy after all the tin-silver metal is completely melted.

The preparation method of the tin-antimony alloy comprises: placing the tin-antimony metal in a high vacuum melting furnace, introducing argon protective gas, heating to 700° C., mixing and casting the tin-antimony alloy after all the metal is melted.

The preparation method of tin-phosphorus alloy includes: mixing tin and phosphorus, covering them with protective molten salt and putting them into a sealed box, then putting them into a muffle furnace and heating them to 800°C, and after all of them are melted, mixing them evenly, casting and cooling them into tin-phosphorus alloy.

The preparation method of the tin-germanium alloy comprises: placing the tin-germanium metal in a high vacuum melting furnace, introducing argon protective gas, heating to 1000° C., mixing and casting the tin-germanium alloy after all the metal is melted.

The preparation method of the tin-copper alloy comprises: placing the tin-copper metal in a high vacuum melting furnace, introducing argon protective gas, heating to 1050° C., mixing and casting the tin-copper alloy after all the metal is melted.

The preparation method of the tin-bismuth alloy comprises: placing the tin-bismuth metal in a high vacuum melting furnace, introducing argon protective gas, heating to 320° C., mixing and casting the tin-bismuth alloy after all the metal is melted.

The preparation method of the tin-nickel alloy comprises: placing the tin-nickel metal in a high vacuum melting furnace, introducing argon protective gas, heating to 1100° C., mixing and casting the tin-nickel alloy after all the metal is melted.

The preparation method of the tin-cobalt alloy comprises: placing the tin-cobalt metals in a high vacuum melting furnace, introducing argon protective gas, heating to 1150° C., mixing and casting the tin-cobalt alloy after all the metals are melted.

The preparation method of RE master alloy comprises: placing tin and rare earth metal in a high vacuum melting furnace, introducing argon protective gas, heating to 1000° C., mixing and casting into RE master alloy after all of them are melted.

As shown in Table 1, the mass percentage contents of Ag, Cu, Bi, Sb, In, Ni, Co and RE in Examples 1 to 25 are all within the range defined by the present invention. Therefore, it can be seen that the melting temperature of the solder alloy is not too high, the tensile strength and shear strength are high, the thickness of the surface oxide film is thinner, and it has excellent temperature cycle characteristics and thermal fatigue resistance, which meets the application of high-power semiconductor lasers, power devices and microelectronic circuits in high operating temperatures.

On the other hand, the difference between Comparative Examples 1 and 2 and Examples 1-4 is that the Ag content of Comparative Examples 1 and 2 is not within the scope of the present invention. Therefore, the tensile strength and shear strength of Comparative Example 1 are poor, the melting temperature of Comparative Example 2 is not within the expected range, and both Comparative Examples 1 and 2 have the problem of poor temperature cycling results and aging results.

The difference between Comparative Example 3 and Examples 5-7 is that the content of Cu in Comparative Example 3 is small, so the melting point is increased. The difference between Comparative Example 4 and Examples 5-7 is that the content of Cu in Comparative Example 4 is large, so the shear strength is poor.

Compared with Examples 8-11, the difference between Comparative Example 5 is that the Sb content of Comparative Example 5 is small, so its shear strength is poor, and the temperature cycling results and aging results are poor. Compared with Examples 8-11, the difference between Comparative Example 6 is that the Sb content of Comparative Example 6 is large, the melting point is increased, and the temperature cycling results and aging results are poor.

The difference between Comparative Example 7 and Examples 12-14 is that the content of In in Comparative Example 7 is small, so the melting point cannot be properly reduced, and the tensile and shear strengths are deteriorated. The difference between Comparative Example 8 and Examples 12-14 is that the content of In in Comparative Example 8 is large, the melting point is reduced too much, and the solder alloy is easily oxidized.

The difference between Comparative Example 9 and Examples 15-18 is that the Bi content of Comparative Example 9 is small, so the tensile and shear strengths of the solder alloy deteriorate. The difference between Comparative Example 10 and Examples 15-18 is that the Bi content of Comparative Example 10 is large, the solder alloy becomes brittle and hard, and the temperature cycling results and aging results deteriorate.

The difference between Comparative Example 11 and Examples 19-21 is that the Ni content of Comparative Example 11 is too high;

The difference between Comparative Example 12 and Examples 22-24 is that the Co content of Comparative Example 12 is too high, so the melting points of Comparative Examples 11 and 12 become higher and the temperature cycle results and aging results of Comparative Example 11 become worse.

Compared with Example 25, the difference between Comparative Example 13 is that Comparative Example 13 does not contain trace elements Ge, P and RE elements, resulting in low tensile and shear strengths of the solder alloy, easy oxidation, and poor temperature cycling results and aging results. Compared with Example 25, the difference between Comparative Example 14 is that the contents of Ge, P and RE elements in Comparative Example 14 exceed the upper limit, resulting in poor wetting of the solder alloy and low bonding strength, and poor temperature cycling results and aging results.

Comparative Example 15 is Sn96.5Ag3.0Cu0.5, the solder alloy strength is not high, it is easy to oxidize, and the temperature cycle results and aging results are not good.

Figure 1 is a cross-sectional SEM image of the welded part after high temperature aging test of Example 21 of the present invention. After aging at 150°C for 500h, it was observed in Example 21 that the IMC (white) growth thickness was small, only a small amount of white (Au, Ni) Sn ₄ compound existed at the edge of the weld, and the middle of the weld still retained the high reliability lead-free solder alloy component with thermal fatigue resistance.

Figure 2 is a cross-sectional SEM image of the welded part after high temperature aging test of Comparative Example 15 of the present invention. After aging at 150°C for 500h, it was observed that the IMC (white) growth rate was relatively fast in Comparative Example 15, and many white (Au, Ni) Sn ₄ compounds were also distributed in the middle of the weld, which could not inhibit the expansion of cracks at the weld.

In summary, compared with the traditional alloy Sn96.5Ag3.0Cu0.5, the high-reliability lead-free solder alloy with thermal fatigue resistance described in the present invention exhibits better melting point, oxidation resistance, mechanical properties and high-temperature reliability.

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims (10)

1. The high-reliability lead-free solder alloy with the thermal fatigue resistance is characterized by comprising the following components in percentage by mass:

1.0 to 4.0 percent of Ag, 0.1 to 1.0 percent of Cu, 1.0 to 8.0 percent of Sb, 0.05 to 4.0 percent of Bi, 0.5 to 6.0 percent of In, 0.5 to 1.2 percent of Ni, 0.001 to 0.2 percent of Co, 0.001 to 0.13 percent of trace elements and/or 0.001 to 0.09 percent of RE, and the balance of Sn and unavoidable impurities;

wherein the microelements comprise P and/or Ge, the P accounts for 0.001-0.08% of the high-reliability lead-free solder alloy with thermal fatigue resistance, and the Ge accounts for 0.001-0.05% of the high-reliability lead-free solder alloy with thermal fatigue resistance; RE is at least one of Ce, la and Nd.

2. The high-reliability lead-free solder alloy against thermal fatigue according to claim 1, wherein the Ag is 2.0-3.5% by mass of the high-reliability lead-free solder alloy against thermal fatigue.

3. The high-reliability lead-free solder alloy against thermal fatigue according to claim 1, wherein the Cu accounts for 0.3 to 0.9% by mass of the high-reliability lead-free solder alloy against thermal fatigue.

4. The high-reliability lead-free solder alloy against thermal fatigue according to claim 1, wherein the mass percentage of Sb in the high-reliability lead-free solder alloy against thermal fatigue is 2.0-6.0%.

5. The high-reliability lead-free solder alloy against thermal fatigue according to claim 1, wherein the Bi is 0.1 to 4.0% by mass of the high-reliability lead-free solder alloy against thermal fatigue.

6. The high-reliability lead-free solder alloy against thermal fatigue according to claim 1, wherein the In is 0.5 to 4.0% by mass of the high-reliability lead-free solder alloy against thermal fatigue.

7. The high-reliability lead-free solder alloy against thermal fatigue according to claim 1, wherein the Ni is 0.5 to 1.0% by mass of the high-reliability lead-free solder alloy against thermal fatigue; the mass percentage of Co in the high-reliability lead-free solder alloy with heat-fatigue resistance is 0.01-0.1%.

8. The high-reliability lead-free solder alloy against thermal fatigue according to claim 1, wherein the mass percentage of P in the high-reliability lead-free solder alloy against thermal fatigue is 0.001-0.05%, and the mass percentage of Ge in the high-reliability lead-free solder alloy against thermal fatigue is 0.001-0.03%.

9. The high-reliability lead-free solder alloy against thermal fatigue according to claim 1, wherein the RE accounts for 0.001 to 0.07% by mass of the high-reliability lead-free solder alloy against thermal fatigue.

10. Use of a high reliability lead free solder alloy against thermal fatigue according to any of claims 1-9 for module soldering of high power semiconductor lasers, power devices and microelectronic circuits.