CN118559279A

CN118559279A - High-reliability lead-free solder alloy resistant to thermal fatigue and application thereof

Info

Publication number: CN118559279A
Application number: CN202410663556.2A
Authority: CN
Inventors: 汪迎春; 徐明聪; 林逸敏; 黄倍宏; 陈泽云; 邹建; 熊杰然
Original assignee: Bolin Electronic Package Material Co ltd
Current assignee: Bolin Electronic Package Material Co ltd
Priority date: 2024-05-27
Filing date: 2024-05-27
Publication date: 2024-08-30

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

High-reliability lead-free solder alloy resistant to thermal fatigue and application thereof

Technical Field

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

Background

The high-power semiconductor laser array has the advantages of small volume, light weight, long service life, high efficiency and the like, can be used as a pumping source of solid laser, can be directly used as a light source for material processing, and has been widely applied to the fields of military, optical fiber communication, optical sensing, information storage, medical treatment, laser printing, optical calculation and the like. High power laser diodes or laser devices convert electrical energy to optical energy at an efficiency of about 10% -50%. The remainder is converted into waste heat. This waste heat must be dissipated in a short period of time, otherwise thermal stresses are generated to the laser diode, eventually causing irreversible damage to the laser, resulting in reduced laser life. Inefficient cooling package designs can result in poor product quality because the temperature of the device core has a direct effect on the output wavelength and bandgap. The practical situation proves that every 3 ℃ temperature change can lead to the wavelength change of the diode laser near 1nm, and the output power of the laser can also be reduced along with the temperature rise.

To aid in heat dissipation, the semiconductor laser chip and heat sink are soldered to a heat dissipating substrate. In general, the solder used is SAC305, which has good thermal conductivity and mechanical ductility, so that high-precision and high-reliability heat sink and pin welding can be realized in a middle-low power laser package, and stable operation of the optical module in a high-speed data transmission process is ensured. 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. Conventional SAC305 solders have failed to meet the mechanical stresses created by repeated switching cycles or hard pulses in laser operation, resulting in solder joint cracking, increased thermal resistance, chip failure, and eventually reduced laser life.

For example, chinese patent CN103561903 a discloses an alloy composition which may contain Bi, sb, in a Sn-Ag-Cu based solder alloy. The technique disclosed in this patent is that the composition of the braze alloy in which the Cu content is far from the vicinity of the eutectic causes a decrease in the temperature cycle characteristics: and the decline of the temperature cycle characteristic is less than that of Cu when the Ag content is far away from the composition near the eutectic; by adding In to Bi and Sb instead of reducing the amount of Ag, the temperature cycle characteristics are improved. However, the decrease in the amount of Ag may result in insufficient IMC of Ag ₃ Sn being formed, so that the bonding strength of the solder joint is lowered, while the wettability of the solder is lowered, and the oxidation resistance is not improved.

In addition, chinese patent CN 115464299A also discloses a solder alloy, in which trace amounts of Ge and P are added to the Sn-Ag-Cu-Sb series solder alloy to improve oxidation resistance of the solder, thereby reducing solder voids. The technology disclosed in the patent is that compared with tin, silver and antimony, the technology is easier to combine with oxygen, on one hand, oxygen in the solder can be rapidly removed, so that the micro-components of the solder are more uniform, and on the other hand, an extremely compact oxide layer can be formed on the surface of the lead-free alloy to prevent the lead-free alloy from being further oxidized, so that the technology has good deoxidizing and antioxidant effects. However, the mechanical properties of the solder are not significantly improved because of the lack of elements that can bring about solid solution strengthening. In addition, the high temperature reliability of the solder was not further verified.

Disclosure of Invention

In order to solve the technical problems, the invention provides a high-reliability lead-free solder alloy with thermal fatigue resistance and application thereof, and the solder alloy has good wettability, reliability, oxidation resistance, mechanical properties and thermal fatigue resistance so as to meet the requirements of high-power semiconductor lasers, power devices and microelectronic circuit packages. In its application, the disclosed solder alloy is particularly useful for, but not limited to, forming bars, rods or flux-cored wires or soldered joints in the form of preformed tabs, solder balls, 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 method specifically comprises the following technical scheme:

In a first aspect, a high reliability lead-free solder alloy is provided that is resistant to thermal fatigue, comprising the following components in mass percent:

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

Wherein the microelements comprise P (phosphorus) and/or Ge (germanium), the P accounts for 0.001-0.08% of the high-reliability lead-free solder alloy with heat-fatigue resistance, and the Ge accounts for 0.001-0.05% of the high-reliability lead-free solder alloy with heat-fatigue resistance; RE is at least one selected from Ce (cerium), la (lanthanum) and Nd (neodymium).

Furthermore, the Ag accounts for 2.0-3.5% of the mass of the high-reliability lead-free solder alloy with heat resistance and fatigue resistance.

Preferably, the Ag accounts for 2.5-3.5% of the mass of the high-reliability lead-free solder alloy with heat resistance and fatigue resistance.

Further, the Cu accounts for 0.3 to 0.9 percent of the mass of the high-reliability lead-free solder alloy with heat resistance and fatigue resistance.

Preferably, the Cu accounts for 0.5-0.8% of the mass of the high-reliability lead-free solder alloy with heat resistance and fatigue resistance.

Further, the mass percentage of the Sb in the high-reliability lead-free solder alloy with heat and fatigue resistance is 2.0-6.0%.

Preferably, the mass percentage of the Sb in the high-reliability lead-free solder alloy with heat resistance and fatigue is 3.0-5.0%.

Further, the Bi accounts for 0.1 to 4.0 percent of the mass of the lead-free solder alloy with high reliability of thermal fatigue resistance.

Preferably, the Bi accounts for 0.1-2.0% of the mass of the lead-free solder alloy with high reliability of thermal fatigue resistance.

Further, the In accounts for 0.5-4.0% of the mass of the high-reliability lead-free solder alloy with thermal fatigue resistance.

Preferably, the In accounts for 0.7-3.0% of the mass of the high-reliability lead-free solder alloy with thermal fatigue resistance.

Further, the Ni accounts for 0.5 to 1.0 percent of the mass of the high-reliability lead-free solder alloy with heat resistance and fatigue resistance; the mass percentage of Co in the high-reliability lead-free solder alloy with heat-fatigue resistance is 0.01-0.1%.

Preferably, the Ni accounts for 0.5-0.7% of the mass of the high-reliability lead-free solder alloy with heat resistance and fatigue resistance.

Preferably, the mass percentage of Co in the high-reliability lead-free solder alloy with heat and fatigue resistance is 0.01-0.08%.

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

Preferably, the trace elements account for 0.005-0.03% of the high-reliability lead-free solder alloy with thermal fatigue resistance.

Further, RE accounts for 0.001-0.07% of the mass of the high-reliability lead-free solder alloy with heat resistance and fatigue resistance.

Preferably, RE accounts for 0.001-0.05% of the mass of the high-reliability lead-free solder alloy with heat resistance and fatigue resistance.

Preferably, RE is a mixture of Ce, la and Nd.

Preferably, the liquidus temperature of the high-reliability lead-free solder alloy with the thermal fatigue resistance is less than or equal to 220 ℃.

Preferably, the high reliability lead-free solder alloy resistant to thermal fatigue is in the form of: strips, bars, flux-cored wires, foils, strips, films, sheet preforms, powders, pastes, solder balls, tabs.

In a second aspect, there is provided the use of a high reliability lead free solder alloy of thermal fatigue resistance as described in the first aspect for module soldering of high power semiconductor lasers, power devices and microelectronic circuits.

The invention has the beneficial effects that:

The present invention provides a high-reliability lead-free solder alloy resistant to thermal fatigue, which exhibits suitable mechanical reliability and thermal fatigue resistance, and exhibits improved shear strength even after thermal aging, and its use. The solder alloy can also obtain good connection strength as a solder part when being placed at an ambient temperature exceeding 150 ℃ for a long time. The solder alloy exhibits improved high temperature mechanical properties compared to known SAC305 solder alloys and is widely applicable to packaging of high power semiconductor lasers, power devices and microelectronic circuits.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a SEM image of a cross-section of a weld after a high temperature aging test of example 21 of the present invention;

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

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely, and it is apparent that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

It should be understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.

In order to more fully understand the technical content of the present invention, the following description and description of the technical solution of the present invention will be further presented with reference to specific embodiments.

The different content ranges of the present invention are defined in more detail in the following paragraphs, describing the benefits of the compositional ranges of the solder alloys of the present disclosure. Any content range defined herein can be combined with any other feature or features indicated as being preferred unless clearly indicated to the contrary.

The solder alloys described herein have a relatively low melting point, particularly a low liquidus temperature, typically less than 220 ℃, more typically less than 215 ℃, and even more typically less than 210 ℃. This enables the solder alloy to be used in low temperature reflow processes (e.g., reflow temperatures from 215 to 235 ℃). Such a low temperature reflow process may reduce the risk of damage to the solder elements compared to conventional reflow processes. The term "solidus" as used in this specification means below this temperature, the substance provided is entirely solid. The term "liquidus" as used herein refers to the highest temperature at which crystals can coexist with molten materials. Above the liquidus temperature, the material is a liquid that is homogeneous and in equilibrium. Below the liquidus temperature, solidification occurs to form more and more crystals. The solidus and liquidus temperatures are not aligned or overlap. If a region exists between the solidus and liquidus temperatures, it is referred to as a "solidification range" or a "pasty region (Mushy Zone)", and within this range, the substance consists of a mixture of both solid and liquid phases. The lead-free solder alloys described herein have a small "solidification range", typically between 10-15 ℃. The narrower the temperature range, the faster the melting or solidification speed, the less leaching, dislocation, reoxidation, and void formation of the component, the more advantageous the brazing operation and the less energy consumption.

The lead-free solder alloys described herein may exhibit suitable high temperature mechanical reliability and thermal fatigue resistance, and are generally capable of withstanding service temperatures of at least 150 ℃, e.g., up to 175 ℃. The solder alloy may exhibit improved high temperature mechanical properties, higher electrical and thermal conductivity, and improved thermal shock properties compared to known SACs 305. For example, the solder alloy withstands a thermal cycle test of more than 500 cycles of residence time from a low temperature of-50 ℃ to a high temperature of +150 ℃. The solder alloy may be advantageously used in applications with high use temperatures, such as high power semiconductor lasers, power devices, and microelectronic circuits.

The term "rare earth element (RE)" as used in this specification includes an element selected from the group consisting of: sc, Y, la, ce, pr, nd, pm, sm, eu, gd, tb, dy, ho, er, tm, yb and Lu.

The term "flux" as used in this specification includes a substance, often an acid or a base, that is used to promote metal melting, particularly removal, and to prevent metal oxide formation.

The term lead-free as used herein means lead which is not intentionally added. Thus, the lead content is zero or within a range not exceeding incidental impurities.

In the present specification, "%" related to the composition of the solder alloy is "% by mass" unless otherwise specified.

Wherein the high-reliability lead-free solder alloy of the present invention resistant to thermal fatigue contains 1.0 to 4.0 mass% of Ag. Ag ₃ Sn intermetallic compounds (INTERMETALLIC COMPOUNDS, IMC) can be formed in the Sn matrix by Ag, so that the precipitation strengthening of the solder alloy is realized, and the strength and the cycle resistance of the solder alloy are improved. In addition, ag increases wetting and spreading of the solder alloy, lowering the liquidus temperature. If the Ag content is less than 1.0 mass%, the wettability during brazing cannot be improved, the amount of Ag ₃ Sn deposited becomes small, the network of the IMC does not become stable, and the strength of the solder alloy cannot be improved. If the Ag content exceeds 4.0 mass%, the liquidus temperature of the solder alloy increases and the solderability decreases. Coarsened Ag ₃ Sn precipitates in the form of a plate, and the solder alloy embrittles and the impact drop resistance is deteriorated. Preferably, the solder alloy includes 2.0 to 3.5 mass% Ag, more preferably includes 2.5 to 3.5 mass% Ag, and most preferably includes 3.0 to 3.2 mass% Ag.

The high-reliability lead-free solder alloy of the present invention resistant to thermal fatigue contains 0.1 to 1.0 mass% of Cu. Cu can lower the melting point and prevent Cu corrosion. The IMCs of Cu ₆Sn₅ and Cu ₃ Sn are formed with the Sn solder, improving the mechanical strength and creep resistance of the solder alloy, and suppressing the strength deterioration in the thermal cycle environment. If the Cu content is less than 0.1 mass%, the amount of the generated Sn-Cu IMC is small, and the mechanical strength of the solder alloy is insufficient. Even if 2.0 mass% of Bi is added later, the heat cycle resistance is deteriorated. If the Cu content exceeds 1.0 mass%, the liquidus temperature of the solder alloy increases, and when the solder is not completely melted or dross is generated at a normal reflow temperature, wettability becomes poor, voids become large, and eventually heat cycle resistance becomes poor. In addition, since IMC of Cu ₆Sn₅ is deposited in large amounts at the weld interface, drop impact resistance is deteriorated. Preferably, the solder alloy includes from 0.3 to 0.9 mass% Cu, more preferably includes 0.5 to 0.8 mass% Cu, and most preferably includes 0.7 to 0.8 mass% Cu.

The high-reliability lead-free solder alloy of the present invention, which is resistant to thermal fatigue, contains 1.0 to 8.0 mass% of Sb, and when the Sb content is less than 1.0 mass%, does not exhibit a solid solution strengthening effect in which Sb dissolves in a Sn matrix to form Sn (Sb) solid solution, and the shear strength of the solder 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 a supersaturated Sn (Sb) solid solution, and the strength of the solder alloy can be improved without causing a decrease in ductility. In addition, sb also enters the lattice of the atomic arrangement to be displaced with Sn, so that the lattice of the atomic arrangement is strained, the Sn matrix is enhanced, and the temperature cycle characteristics of the solder alloy are improved. Based on this, the solder alloy of the present invention exhibits excellent mechanical properties (both high strength and high ductility) and thermal fatigue resistance. However, if the Sb content exceeds 8.0 mass%, the solidus temperature of the solder alloy increases, and the primary phase of Sn ₃Sb₂, which is strongly brittle, is solidified, so that element failure due to cracking of the solder alloy cannot be suppressed. Preferably, the solder alloy includes from 2.0 to 6.0 mass% Sb, more preferably 3.0 to 5.0 mass% Sb, and most preferably 3.0 to 4.0 mass% Sb.

The high-reliability lead-free solder alloy of the present invention resistant to thermal fatigue contains 0.05 to 4.0 mass% of Bi. Bi can be solid-dissolved in the Sn matrix, improving the strength of the solder alloy. Bi also reduces the surface tension of the solder alloy in the molten state, thereby improving the wettability and spreadability of the solder alloy. Bi also increases the creep resistance of the solder alloy. If the content of Bi is less than 0.05 mass%, the solid solution amount of Bi is small and the strength cannot be sufficiently improved. In addition, the method comprises the following steps. On the other hand, if the Bi content exceeds 4.0 mass%, the solidus temperature decreases. Bi segregates in grain boundaries and the strength of the solder alloy decreases. At the same time, the solder alloy itself becomes brittle and hard, and ductility and thermal fatigue resistance are also significantly reduced, and the soldered joint cannot suppress further propagation of cracks due to vibration or impact. Preferably, the solder alloy includes from 0.1 to 4.0 mass% Bi, more preferably 0.1 to 2.0 mass% Bi, and most preferably 0.5 to 1.0 mass% Bi.

The high-reliability lead-free solder alloy of the present invention resistant to thermal fatigue contains 0.5 to 6.0 mass% of 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 content of In is less than 0.5 mass%, the solid solution amount of In Sn is small, and the strength of the solder alloy is not sufficiently improved. In addition, the liquidus temperature of the solder alloy does not drop. If the In content exceeds 6.0 mass%, the molten solder alloy becomes easily oxidized, and voids In the solder joint cannot be suppressed. Preferably, the solder alloy includes In from 0.5 to 4.0 mass%, more preferably includes In from 0.7 to 3.0 mass%, and most preferably includes In from 1.0 to 2.5 mass%.

The high-reliability lead-free solder alloy of the present invention resistant to thermal fatigue contains 0.5 to 1.2 mass% of Ni. Uniformly dispersed in Cu ₆Sn₅ phase to make the particle size of IMC fine and raise the joint strength, impact resistance and heat-resisting cycle property of soldered joint. The fine grain size distributes crack stress in a plurality of grain size directions, and further propagation of cracks is slowed down. Ni can also suppress diffusion and reaction in the solder alloy during soldering of the plating components of the semiconductor element and the external substrate. If the Ni content is less than 0.5 mass%, the joint strength of the braze joint cannot be effectively improved. If the content of Ni exceeds 1.2 mass%, wettability of the solder alloy becomes poor, and liquidus temperature increases sharply, and electronic components having an excessively high soldering temperature may be thermally damaged. Preferably, the solder alloy includes from 0.5 to 1.0 mass% Ni, more preferably 0.5 to 0.6 mass% Ni, and most preferably 0.1 to 0.3 mass% Ni.

The high-reliability lead-free solder alloy of the present invention resistant to thermal fatigue contains 0.001 to 0.2 mass% of Co. The addition of a trace amount of Co can refine the crystal grains as in Ni, and a large amount of Co solidification nuclei are formed in the solder alloy during solidification, so that the growth of the Sn phase precipitated around is suppressed, and the entire structure becomes finer. If the Co content is less than 0.001 mass%, the effect of refining the alloy structure and improving the bonding strength cannot be exerted. If the Co content is more than 0.2 mass%, the wettability of the solder alloy becomes poor and the melting point becomes high. Preferably, the solder alloy includes from 0.001 to 0.1 mass% Co, more preferably 0.01 to 0.08 mass% Co, and most preferably 0.01 to 0.03 mass% Co.

The high reliability lead-free solder alloy of the present invention that is resistant to thermal fatigue also includes trace elements and/or RE (rare earth elements).

Wherein the microelements are composed of P and/or Ge.

The high-reliability lead-free solder alloy of the present invention resistant to thermal fatigue contains 0.001 to 0.05 mass% of Ge. Ge is any element that can suppress oxidation of Sn and improve wettability. When the solder alloy is melted, ge is highly enriched on the surface, and a compact protective film is formed. If the content of Ge is less than 0.001 mass%, no remarkable antioxidation is achieved. 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 soldered portion. Preferably, the solder alloy includes from 0.001 to 0.03 mass% Ge, more preferably 0.001 to 0.015 mass% Ge, and most preferably 0.005 to 0.01 mass% Ge.

The high-reliability lead-free solder alloy of the present invention resistant to thermal fatigue contains 0.001 to 0.08 mass% of P. P is an element capable of suppressing oxidation of Sn and improving wettability. When the solder alloy melts, P forms a tin phosphate film layer on the surface, preventing the solder alloy from directly contacting ambient air to form tin oxide. If the content of P is less than 0.001 mass%, such an antioxidation effect is not remarkable. 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 soldered portion. Preferably, the solder alloy includes from 0.001 to 0.05 mass% P, more preferably includes 0.001 to 0.03 mass% P, and most preferably includes 0.001 to 0.02 mass% P. In addition, the total amount of Ge and P added should preferably be in the range of 0.005 to 0.03 mass%.

The high-reliability lead-free solder alloy of the present invention, which is resistant to thermal fatigue, contains at least one of rare earth elements (RE) in a total amount of 0.09 mass% or less in addition to the above-described components. RE has strong Sn-philic capacity, trace rare earth is preferentially combined with Sn, and the compounds which are preferentially separated out and uniformly distributed can become heterogeneous nucleation centers for further crystallization, so that the structure is obviously refined and uniformly distributed, and the shearing strength, creep resistance and electromigration resistance of welding spots of the solder alloy are improved. If the total amount of RE added is less than 0.001 mass%, there is no significant refining effect on the structure. If the total amount of RE added is more than 0.09 mass%, a brittle rare earth compound is produced. Meanwhile, the crystal lattice of the matrix alloy is damaged due to the large atomic radius, so that the bonding strength of the welding line is reduced. The total content of the RE element is preferably 0.07 mass% or less, more preferably 0.05 mass% or less, and most preferably 0.02 mass% or less. Wherein, the preferable RE element is at least one of Ce, ld and Nd.

The balance of the high-reliability lead-free solder alloy resistant to thermal fatigue of the invention is Sn. Besides the aforementioned elements, unavoidable impurities may be contained. Even when unavoidable impurities are contained, the aforementioned effects are not affected.

The invention will now be further described by a summary of several non-limiting examples of such solder alloys and their properties, without being 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 provided a high-reliability lead-free solder alloy resistant to thermal fatigue in the specific form of a preformed lead-free tab whose composition in weight percent is shown in tables 1 and 2, and evaluated in terms of melting point, tensile strength, shear strength, thickness of oxide film, temperature cycle result and high-temperature aging result.

Performance evaluation test:

(1) Melting point. For the examples/comparative examples listed in tables 1 and 2, the DSC curves thereof were determined. The intersection of the line of elongation of the front baseline of the DSC curve with the tangent at the maximum slope of the front edge of the peak represents the melting point, as prescribed by the ICTA standardization committee. The DSC curve of the example/comparative example was obtained by placing 40mg of the sample in a METTLER TOLEDO-company DSC instrument (model: JL-DSC 001) and heating it in the atmosphere at 10℃per minute. When the melting point was 214 to 217 ℃, the evaluation was "excellent". When the melting point is 217 to 220 ℃, the temperature is a temperature which is practically free from problems, and therefore, the evaluation is "good". The melting point was evaluated as "X" when it was lower than 214℃and higher than 220 ℃.

(2) Tensile strength. Measured according to JIS Z3198-2 standard. For the examples/comparative examples listed in tables 1 and 2, test bars having a gauge length of 30mm and a diameter of 10mm were produced by smelting and injecting into a mold. The produced test bars were stretched at room temperature and a speed of 5 mm/min by a universal material tester (KZ-50 KN), and the average strength (Rm) at the time of breaking of 5 test bars was measured. In the present invention, since the tensile strength was sufficient when 56MPa or more, the tensile strength was evaluated as "good". When the tensile strength is 52MPa or more and less than 56MPa, the tensile strength is practically no problem, and therefore, the tensile strength is evaluated as "good". When the tensile strength was less than 52MPa, the test was evaluated as "X".

(3) Shear strength. Examples/comparative examples listed in tables 1 and 2 were prepared with dimensions of 3X 0.05 mm. At least 20 test substrates were fabricated for each example/comparative example using a 4J29 alloy-Ni-plated Au plate having a thickness of 1.0mm and soldering at a maximum temperature of 248℃for 60 seconds under nitrogen. The shear strength (MPa) was measured under a condition of 6 mm/min by a shear strength measuring apparatus (STR 1000, manufactured by Kequal Co., ltd.). When the average value of the shear strengths of the 20 test substrates was 35MPa or more, it was determined that a sufficient level of shear strength was obtained, and the test substrate was evaluated as "excellent". When the pressure exceeds 28MPa and is 35MPa or less, it is judged that the level can be used practically without any problem, and the evaluation is "good". Below 28MPa, the evaluation was "x".

(4) Thickness of the oxide film. The examples/comparative examples listed in tables 1 and 2 were processed into preformed ingots having a thickness of 10X 0.5mm, and heat-treated in a constant temperature bath at 150℃for 150 minutes. The oxide film thickness was measured by the method of ISO/TR 15969 using the Auger electron spectroscopy (FEAES). Film thickness of 2.0nm or less indicates that the oxidation resistance of the examples/comparative examples was good, and thus was evaluated as "". When the film thickness exceeds 2.0nm and is 2.8nm or less, there is no problem in practical use, and therefore, the evaluation is "good". When the film thickness exceeded 2.8nm, the evaluation was "X".

(5) Temperature cycling and high temperature aging results. Examples/comparative examples listed in tables 1 and 2 were prepared with dimensions of 3X 0.05 mm. At least 20 test substrates were fabricated for each example/comparative example using a 4J29 alloy-Ni-plated Au plate having a thickness of 1.0mm and soldering at a maximum temperature of 248℃for 60 seconds under nitrogen. Wherein 10 test substrates were placed in a programmable cold and hot shock box (TSTC-80-DC, manufactured by Ke-Zhi Co., ltd.) to perform a temperature cycle test according to the JESD22-A104C standard method. Setting the low temperature to-50 ℃ and the high temperature to +150 ℃, and keeping the temperature for 10 minutes, wherein the cycle number is 500 cycles. The residual shear strength (MPa) of 10 test substrates was measured by a thrust shear (STR 1000, manufactured by Kequal Co., ltd.) at 6 mm/min. The average residual shear strength was 15MPa or more, and was evaluated as "good". When the pressure exceeds 9 and is 15MPa or less, it is judged that the level can be used practically without any problem, and the evaluation is "good". Below 9MPa, the evaluation was "x". 10 test substrates were placed in a high temperature aging oven and incubated at 150℃for 500 hours. Similarly, the residual shear strength after aging of 10 test substrates was measured by using a thrust shear machine, and when the average value of the shear strengths was 25MPa or more, it was determined that a sufficient level of shear strength was obtained, and the test was evaluated as "excellent". When the pressure exceeds 20MPa and is 25MPa or less, it is judged that the level can be used practically without any problem, and the evaluation is "good". Below 20MPa, the evaluation was "x".

Specific compositions of the high reliability lead-free solder alloys of examples 1 to 25 for thermal fatigue resistance are shown in table 1 below:

TABLE 1 high reliability lead free solder alloy compositions for thermal fatigue resistance of examples 1-25

Note that: bal is the balance.

Specific compositions of the high-reliability lead-free solder alloys of comparative examples 1 to 15 against thermal fatigue are shown in table 2 below:

TABLE 2 high reliability lead free solder alloy compositions for thermal fatigue resistance of comparative examples 1-15

Note that: bal is the balance.

Performance evaluation tests were conducted on the high-reliability lead-free solder alloys of examples 1 to 25 and comparative examples 1 to 15 for thermal fatigue resistance, and the test results are shown in tables 3 to 4 below.

TABLE 3 high reliability lead free solder alloy Performance evaluation test results of thermal fatigue resistance of examples 1-25

TABLE 4 high reliability lead free solder alloy Performance evaluation test results of thermal fatigue resistance of comparative examples 1-15

The high-reliability lead-free solder alloys of the thermal fatigue resistance of each of examples and comparative examples shown in tables 1 and 2 were prepared by melting a master alloy except for indium.

The preparation method of the high-reliability lead-free solder (the specific form is a preformed lead-free soldering lug) with the heat resistance and the fatigue resistance of the embodiment and the comparative example comprises the following steps: firstly, smelting intermediate alloys (tin-silver alloy, tin-antimony alloy, tin-phosphorus alloy, tin-germanium alloy, tin-copper alloy, tin-bismuth alloy, tin-nickel alloy, tin-cobalt alloy and rare earth element intermediate alloy), mixing and smelting the intermediate alloys, after all the intermediate alloys are melted and stirred uniformly, cooling to 320 ℃, casting, rolling, cleaning, blanking or cutting into preformed lead-free soldering lugs.

The preparation method of the tin-silver alloy comprises the following steps: and (3) putting tin-silver metal into a high-vacuum smelting furnace, introducing argon shielding gas, heating to 900 ℃, uniformly mixing after all molten tin-silver metal is formed, and casting into the tin-antimony alloy.

The preparation method of the tin-antimony alloy comprises the following steps: and (3) putting the tin-antimony metal into a high-vacuum smelting furnace, introducing argon shielding gas, heating to 700 ℃, uniformly mixing after all molten tin-antimony alloy, and casting into the tin-antimony alloy.

The preparation method of the tin-phosphorus alloy comprises the following steps: and mixing tin and phosphorus, covering protective molten salt on the mixture, placing the mixture into a sealing box, then placing the sealing box into a muffle furnace, heating to 800 ℃, uniformly mixing the mixture after the mixture is completely melted, and casting and cooling the mixture to obtain the tin-phosphorus alloy.

The preparation method of the tin-germanium alloy comprises the following steps: and (3) putting tin-germanium metal into a high-vacuum smelting furnace, introducing argon shielding gas, heating to 1000 ℃, uniformly mixing after all the tin-germanium metal is melted, and casting into the tin-germanium alloy.

The preparation method of the tin-copper alloy comprises the following steps: and (3) putting tin-copper metal into a high-vacuum smelting furnace, introducing argon shielding gas, heating to 1050 ℃, uniformly mixing after all molten tin-copper alloy is cast into the tin-copper alloy.

The preparation method of the tin-bismuth alloy comprises the following steps: and (3) putting the tin-bismuth metal into a high-vacuum smelting furnace, introducing argon shielding gas, heating to 320 ℃, uniformly mixing after all the metals are melted, and casting into the tin-bismuth alloy.

The preparation method of the tin-nickel alloy comprises the following steps: and (3) putting tin-nickel metal into a high-vacuum smelting furnace, introducing argon shielding gas, heating to 1100 ℃, uniformly mixing after all molten tin-nickel metal is formed, and casting the tin-nickel alloy.

The preparation method of the tin-cobalt alloy comprises the following steps: and (3) putting tin-cobalt metal into a high-vacuum smelting furnace, introducing argon shielding gas, heating to 1150 ℃, uniformly mixing after all molten tin-cobalt alloy is cast into the tin-cobalt alloy.

The preparation method of the RE intermediate alloy comprises the following steps: and (3) putting tin and rare earth metal into a high vacuum melting furnace, introducing argon shielding gas, heating to 1000 ℃, mixing uniformly after all the tin and rare earth metal are melted, and casting into RE intermediate alloy.

As can be seen from Table 1, ag, cu, bi, sb, in, ni, co and RE contents in examples 1 to 25 are within the scope of the present invention. Therefore, the melting temperature of the solder alloy is not too high, the tensile strength and the shearing strength are high, the thickness of the surface oxide film is thinned, and the solder alloy has excellent temperature cycle characteristics and thermal fatigue resistance, thereby meeting the application of high-power semiconductor lasers, power devices and microelectronic circuits in high use temperature.

On the other hand, comparative examples 1 and 2 are different from examples 1 to 4 in that the contents of Ag of comparative examples 1 and 2 are not within the scope of the present invention, and thus, the tensile strength and shear strength of comparative example 1 are poor, the melting temperature of comparative example 2 is not within the desired range, and both comparative examples 1 and 2 have problems of poor temperature cycle results and aging results.

Comparative example 3 is different from examples 5 to 7 in that the Cu content of comparative example 3 is small and thus the melting point is raised. Comparative example 4 is different from examples 5 to 7 in that the comparative example 4 has a large Cu content and thus has poor shear strength.

Comparative example 5 is different from examples 8 to 11 in that the content of Sb of comparative example 5 is small, and thus, the shear strength thereof is poor, and the temperature cycle result and the aging result are poor. Comparative example 6 is different from examples 8 to 11 in that the Sb content of comparative example 6 is large, the melting point is high, and the temperature cycle result and the aging result are poor.

Comparative example 7 is different from examples 12 to 14 In that the In content of comparative example 7 is small, and thus, the melting point cannot be properly lowered and the tensile and shear strengths are deteriorated. Comparative example 8 is different from examples 12 to 14 In that the content of In of comparative example 8 is large, the melting point is lowered too much, and the solder alloy is easily oxidized.

Comparative example 9 is different from examples 15 to 18 in that the content of Bi of comparative example 9 is small, and thus, the tensile and shear strength of the solder alloy is deteriorated. Comparative example 10 is different from examples 15 to 18 in that the content of Bi of comparative example 10 is large, the solder alloy becomes brittle and hard, and the temperature cycle result and the aging result are deteriorated.

Comparative example 11 is different from examples 19 to 21 in that the Ni content of comparative example 11 is excessive;

comparative example 12 is different from examples 22 to 24 in that Co content of comparative example 12 is excessive, and thus melting points of comparative example 11 and comparative example 12 become high and temperature cycle results and aging results of comparative example 11 become poor.

Comparative example 13 is different from example 25 in that comparative example 13 does not contain trace elements Ge, P and RE, resulting in a solder alloy having low tensile and shear strength, being susceptible to oxidation, and being inferior in temperature cycle result and aging result. Comparative example 14 is different from example 25 in that the content of Ge, P and RE elements in comparative example 14 exceeds the upper limit value, resulting in deterioration of solder alloy wetting and lower bonding strength, and deterioration of temperature cycle results and aging results.

Comparative example 15 is Sn96.5Ag3.0Cu0.5, which is low in solder alloy strength, easy to oxidize and poor in temperature cycle result and aging result.

FIG. 1 is a SEM image of a cross-section of a weld after a high temperature aging test of example 21 of the present invention. After aging at 150 ℃ for 500 hours, a smaller IMC (white) growth thickness was observed in example 21, with only a small amount of white (Au, ni) Sn ₄ compound present at the edge of the weld, and the high reliability lead-free solder alloy composition that is resistant to thermal fatigue remained at the intermediate positions of the weld.

Fig. 2 is a cross-sectional SEM image of a weld of comparative example 15 of the present invention after a high temperature aging test. After aging at 150℃for 500 hours, a faster growth rate of IMC (white) was observed in comparative example 15, and many white (Au, ni) Sn ₄ compounds were distributed in the middle of the weld joint, and the crack growth at the weld joint could not be suppressed.

In conclusion, compared with the traditional alloy Sn96.5Ag3.0Cu0.5, the high-reliability lead-free solder alloy with thermal fatigue resistance provided by the invention has more excellent melting point, oxidation resistance, mechanical property and high-temperature reliability.

While the invention has been described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various changes and substitutions of equivalents may be made and equivalents will be apparent to those skilled in the art without departing from the scope of the invention. Therefore, the protection scope of the invention is subject to the protection scope of the claims.

Claims

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.