阅读说明：本技术 一种高空位浓度max相及其制备方法和一种有效抑制锡晶须生长的无铅焊料及其制备方法 (High-potential-concentration MAX phase and preparation method thereof, and lead-free solder capable of effectively inhibiting tin whisker growth and preparation method thereof ) 是由 刘玉爽 刘哲学 曹璐 李小雪 朱一鸣 王金婷 于 2021-09-29 设计创作，主要内容包括：本发明公开了一种高空位浓度MAX相及其制备方法,高空位浓度MAX相由M-(6)X八面体层与具有高空位浓度的A原子层交替堆垛而成。本发明还公开了一种有效抑制锡晶须生长的无铅焊料及其制备方法,无铅焊料包括以下质量百分比的组分：高空位浓度MAX相：2～10%；Sn或Sn合金90～98%。本发明利用高空位浓度MAX相增强相捕获Sn或Sn合金中高活动性的Sn原子,使基体相中的Sn原子扩散进入MAX相中后保持平衡状态,不再向外扩散,切断Sn晶须生长所需的原子来源,从根本上抑制Sn锡晶须生长。本发明的适用温度范围广,在高低温下均能有效抑制Sn晶须生长,工艺简单,对焊料性能无负面影响,且能提升焊料的力学性能。(The invention discloses a high-potential-concentration MAX phase and a preparation method thereof, wherein the high-potential-concentration MAX phase consists of M 6 The X octahedron layers and the A atomic layers with high concentration are stacked alternately. The invention also discloses a lead-free solder for effectively inhibiting the growth of tin whiskers and a preparation method thereof, wherein the lead-free solder comprises the following components in percentage by mass: high vacancy concentration MAX phase: 2-10%; and 90-98% of Sn or Sn alloy. The invention utilizes the MAX phase enhanced phase with high vacancy concentration to capture Sn atoms with high activity in Sn or Sn alloy, so that the Sn atoms in the matrix phase are kept in a balanced state after diffusing into the MAX phase, do not diffuse outwards any more, cut off the atom source required by the growth of Sn whiskers, and fundamentally inhibit the growth of Sn-tin whiskers. The invention has wide applicable temperature range, can effectively inhibit the growth of Sn whiskers at high and low temperatures, has simple process, has no negative influence on the performance of the solder, and can improve the mechanics of the solderAnd (4) performance.)

1. A high-dislocation-concentration MAX phase, characterized by: by M₆The X octahedron layers and the A atomic layers with high concentration are stacked alternately.

2. A high-dislocation-density MAX phase according to claim 1, characterised in that: the high-level concentration is between 5% and 50%; the vacancies in the A atomic layer are uniformly distributed.

3. A high-dislocation-density MAX phase according to claim 1, characterised in that: the MAX phase comprises Ti₂SnC、Nb₂SnC、Zr₂SnC、Lu₂SnC、Hf₂SnC、Hf₂SnN or Ti₃SnC₂(ii) a The A atom includes Sn.

4. A method for preparing a high-steric-concentration MAX phase according to any one of claims 1 to 3, wherein: the method comprises the following steps:

s1, weighing the MAX phase powder and the grinding balls, putting the MAX phase powder and the grinding balls into a ball milling tank, and putting the MAX phase powder and the grinding balls into a ball mill for high-energy ball milling;

s2, taking out the MAX phase powder subjected to the high-energy ball milling, and putting the MAX phase powder into a vacuum plasma cleaning machine for plasma treatment;

s3, adding the MAX phase powder subjected to plasma treatment into acid liquor after weighing, and performing magnetic stirring;

s4, transferring the mixture after the acid liquor etching to a centrifuge tube, and placing the centrifuge tube in a centrifuge for centrifugal cleaning;

s5, placing the centrifugally cleaned MAX phase powder into an oven for drying.

5. The method for preparing a high-steric-concentration MAX phase according to claim 4, wherein: the ball-material ratio used in the ball milling process is 5: 1-20: 1, the ball milling rotation speed is 400-600 r/min, and the ball milling time is 4-24 h; the plasma treatment power is 1000-3000W, the vacuum degree is 10-100 Pa, and the time is 5-30 min.

6. The method for preparing a high-steric-concentration MAX phase according to claim 4, wherein: the acid solution is hydrochloric acid solution with the concentration of 1-5 mol/L, the mass ratio of the acid solution to MAX phase powder is 10: 1-50: 1, the etching time of the acid solution is 2-24 hours, the magnetic stirring rotating speed is 200-500 r/min, the centrifugal rotating speed is 2000-10000 r/min, the centrifugal time is 1-5 hours, the drying temperature is 40-100 ℃, and the drying time is 2-8 hours.

7. A lead-free solder containing a high steric concentration MAX phase effective in suppressing tin whisker growth according to any one of claims 1 to 3, characterized in that: the composite material comprises the following components in percentage by mass: high vacancy concentration MAX phase: 2-10%; and 90-98% of Sn or Sn alloy.

8. The lead-free solder effective in inhibiting tin whisker growth as claimed in claim 7, wherein: the Sn alloy comprises Sn-Cu alloy, Sn-Ag alloy, Sn-In alloy, Sn-Zn alloy and Sn-Ag-Cu alloy.

9. The method for preparing the lead-free solder for effectively inhibiting the growth of the tin whiskers, according to claim 7, is characterized in that: the method comprises the following steps:

s01, weighing the MAX phase powder with high steric concentration, Sn or Sn alloy powder and grinding balls, putting the powder into a ball milling tank, and putting the powder into a ball mill for ball milling and mixing;

s02, taking out the mixed powder subjected to ball milling and mixing, and performing cold press molding to obtain a green body;

and S03, placing the green body in a sintering furnace, sintering under a protective atmosphere, and then cooling along with the furnace to obtain the Sn or Sn alloy/MAX composite lead-free solder with low whisker growth tendency.

10. The method for preparing the lead-free solder for effectively inhibiting the growth of the tin whisker as recited in claim 9, wherein: in S01, the ball-material ratio used in the ball milling process is 0.5: 1-2: 1, the ball milling speed is 50-200 r/min, and the ball milling time is 12-24 h; in S02, cold press molding pressure is 100-1000 MPa, and pressure maintaining time is 1-10 min; in S03, the protective atmosphere is argon, nitrogen or vacuum, the sintering temperature is 180-230 ℃, the heat preservation time is 1-5 h, and the heating rate is 5-15 ℃/min.

Technical Field

The invention relates to a high-potential-concentration MAX phase and a preparation method thereof, and a lead-free solder for effectively inhibiting tin whisker growth and a preparation method thereof, belonging to the technical field of materials.

Background

Tin (Sn) and Sn alloys are widely used in the electronics packaging industry as lead-free solders for solder joints of interconnect structures due to their superior solderability, ductility, electrical conductivity, and corrosion resistance. However, Sn whiskers are easy to grow in Sn-based solder, and can cause circuit failure in the forms of short circuit, metal vapor arc formation and the like, thereby causing great threat to the reliability of a circuit system. Up to now, accidents caused by spontaneous growth of Sn whiskers have been involved in almost all industrial fields including military, satellite, communications, aerospace, power, nuclear industry, transportation, medical, computing center, etc. In 1959, Arnold discovered that tin whisker growth can be effectively inhibited by adding a small amount of lead (Pb) to tin. In addition, the Sn-Pb alloy has the advantages of low melting point, good welding performance, lower cost and the like, and the Sn-Pb alloy solder is still widely applied to the industry until the beginning of the 21 st century.

However, Pb is a heavy metal known to be most toxic and extremely highly accumulated, and when entering into the human body, Pb and its compounds will cause damage to various systems such as nerves, digestion, hematopoiesis, kidneys, endocrine, etc., and the Pb has a particularly serious influence on the intelligence and physical development of children. Therefore, some countries have begun to restrict the use of Pb since the 90 s of the 20 th century. On 13.2.2003, the directive on the restriction of the use of certain harmful components in electronic and electrical equipment (RoHS for short) and the directive on the disposal of electronic and electrical equipment (WEEE for short) were issued by the european parlance and the european commission on official gazette, and it was required that the content of Pb in electronic products sold in the market of the european union should not exceed 0.1 wt% from 7.1.2006. Corresponding statutes have been issued successively in korea, sweden, ireland and turkish. Therefore, the problem of Sn whiskers that were once suppressed by the addition of Pb has attracted a lot of attention again, and development of a green and environmentally friendly method for suppressing tin whiskers is urgently required.

The existing lead-free inhibition method in tin-based solder mainly comprises non-lead alloying, conformal coating, heat treatment and the like. The non-lead alloying mainly refers to tin-bismuth (Bi) alloying, and experimental research shows that the Sn-Bi alloy can inhibit the growth of Sn whiskers at a lower temperature, but the Sn-Bi alloy has a stronger tendency to grow Sn whiskers in a higher temperature or thermal cycle environment, and a welding spot is always at a higher temperature in practical application, so that the application range of inhibiting the growth of Sn whiskers through the Sn-Bi alloying is limited. Although the coating of the conformal coating can avoid current failure, short circuit and the like caused by the growth of the Sn whisker in a short period, the coating is broken through and the short circuit and the like are caused when the Sn whisker is longer, so that the method has poor inhibition effect on the growth of the Sn whisker. The reflow or annealing heat treatment may retard the growth of Sn whiskers, but cannot fundamentally inhibit the growth of Sn whiskers, and the heat treatment process may cause solder joint failure, which adversely affects the reliability of the solder joint.

Chinese patent 202110023870.0 discloses a medium-entropy MAX phase material, a medium-entropy two-dimensional material, and a method for preparing the same, wherein the medium-entropy MAX phase material is reacted with an etchant, so that the etchant selectively etches away the a component in MAX, thereby obtaining the medium-entropy two-dimensional material, and the etchant is a hydrofluoric acid solution, an acid solution + fluoride salt system, or a halogen metal salt. Even if the method described in the patent is adopted, the MAX phase of partial etching (the A component is not completely etched) can be obtained by adjusting the etching time, but the MAX phase is actually obtained by etching the MAX phase from the outside to the inside by the etchant, so that the MAX phase/MXene composite structure is obtained, and the schematic diagram is shown in FIG. 1. The crystal structure of the MAX phase part is not changed, the vacancy concentration of the A atomic layer is not changed, the MXene part does not have the crystal structure of the MAX phase any more, and the MXene reacts with water, fluorine ions, oxygen and the like in the etching solution to generate a large number of functional groups such as-OH, -F, = O and the like on the surface. The schematic structure of the a atomic layer obtained by incomplete etching of the MAX phase is shown in fig. 2.

For the MAX phase/MXene composite structure in the patent, the MAX phase part can be used as a diffusion channel of A atoms, but cannot prevent the A atoms from continuously diffusing to the surface of the substrate; MXene has a different crystal structure from that of the MAX phase, a large number of functional groups are generated on the surface, and MXene cannot be recombined with A atoms to form the MAX phase or other stable structures at normal temperature and cannot prevent the A atoms from continuously diffusing to the surface of the substrate. Therefore, this patent can achieve partial etching of the MAX phase by adjusting the etching time, but cannot prevent Sn atoms with high mobility in the substrate from diffusing to the surface to form Sn whiskers.

Therefore, a new material and a preparation method thereof capable of solving the spontaneous growth problem of tin whiskers in lead-free solder are needed.

Disclosure of Invention

The invention aims to solve the technical problem that the invention provides a MAX phase with high space concentration, atoms in an A atomic layer of the MAX phase have strong activity, and the activity is in an A/MAX composite system (such as Sn/Ti)₂SnC), atoms in the simple substance a can diffuse through the a atomic layer in the MAX phase. If the concentration of the A vacancies in the MAX phase is increased, the atoms with high activity in the simple substance A will not diffuse outward after diffusing into the A atomic layer in the MAX phase. Therefore, the MAX phase having a high vacancy concentration can inhibit the diffusion of a atoms to the surface, cut the atom source necessary for whisker growth, and suppress whisker growth. Meanwhile, the MAX phase can also play a role in enhancing the mechanical property of the solder.

Meanwhile, the invention provides a preparation method of the MAX phase with high steric concentration, which comprises the steps of firstly carrying out high-energy ball milling on MAX phase powder to introduce more defects and enhance the activity of A atoms in the MAX phase; then carrying out plasma treatment on the MAX phase powder subjected to the high-energy ball milling so as to clean the MAX phase powder, and further activating the surface to improve the surface area; and finally, through chemical etching, the high-activity atoms in the A atomic layer are diffused outwards and react with acid, a large number of vacancies are left in the A atomic layer, and a MAX phase with high vacancy concentration is formed.

Meanwhile, the invention provides the lead-free solder for effectively inhibiting the growth of the tin whisker, and the lead-free solder can solve the problem of spontaneous growth of the tin whisker in the lead-free solder.

Meanwhile, the invention provides a preparation method of the lead-free solder for effectively inhibiting the growth of tin whiskers.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a high-potential concentration MAX phase consisting of M₆The X octahedron layers and the A atomic layers with high concentration are stacked alternately.

The high-level concentration is between 5% and 50%; the vacancies in the A atomic layer are uniformly distributed.

The MAX phase comprises Ti₂SnC、Nb₂SnC、Zr₂SnC、Lu₂SnC、Hf₂SnC、Hf₂SnN or Ti₃SnC₂(ii) a The A atom includes Sn.

The MAX phase is a generic term for a series of nano-layered carbide or nitride ceramics with hexagonal crystal structure, where M is a transition metal element, a is mainly a main group IIIA and IVA element, X is carbon or nitrogen, and n =1, 2, 3 …. MAX phase by M₆X octahedron layer and A atom layer are stacked alternately, X atom is in octahedron formed by M atom close stacking, strong covalent bond is formed between M atom and X atom, metal bond is formed between M atom and M atom, M is₆And interlayer weak ionic bonds are formed between the X octahedron layer and the A atomic layer, and the combination is weak.

A preparation method of a MAX phase with high steric concentration comprises the following steps:

s1, weighing the MAX phase powder and the grinding balls, putting the MAX phase powder and the grinding balls into a ball milling tank, and putting the MAX phase powder and the grinding balls into a ball mill for high-energy ball milling;

s2, taking out the MAX phase powder subjected to the high-energy ball milling, and putting the MAX phase powder into a vacuum plasma cleaning machine for plasma treatment;

s3, adding the MAX phase powder subjected to plasma treatment into acid liquor after weighing, and performing magnetic stirring;

s4, transferring the mixture after the acid liquor etching to a centrifuge tube, and placing the centrifuge tube in a centrifuge for centrifugal cleaning;

s5, placing the centrifugally cleaned MAX phase powder into an oven for drying.

The ball-material ratio used in the ball milling process is 5: 1-20: 1, the ball milling rotation speed is 400-600 r/min, and the ball milling time is 4-24 h; the plasma treatment power is 1000-3000W, the vacuum degree is 10-100 Pa, and the time is 5-30 min.

The acid solution is hydrochloric acid solution with the concentration of 1-5 mol/L, the mass ratio of the acid solution to MAX phase powder is 10: 1-50: 1, the etching time of the acid solution is 2-24 hours, the magnetic stirring rotating speed is 200-500 r/min, the centrifugal rotating speed is 2000-10000 r/min, the centrifugal time is 1-5 hours, the drying temperature is 40-100 ℃, and the drying time is 2-8 hours.

The lead-free solder for effectively inhibiting the growth of tin whiskers comprises the following components in percentage by mass: high vacancy concentration MAX phase: 2-10%; and 90-98% of Sn or Sn alloy.

The Sn alloy comprises Sn-Cu alloy, Sn-Ag alloy, Sn-In alloy, Sn-Zn alloy and Sn-Ag-Cu alloy.

A preparation method of lead-free solder for effectively inhibiting tin whisker growth comprises the following steps:

s01, weighing the MAX phase powder with high steric concentration, Sn or Sn alloy powder and grinding balls, putting the powder into a ball milling tank, and putting the powder into a ball mill for ball milling and mixing;

s02, taking out the mixed powder subjected to ball milling and mixing, and performing cold press molding to obtain a green body;

and S03, placing the green body in a sintering furnace, sintering under a protective atmosphere, and then cooling along with the furnace to obtain the Sn or Sn alloy/MAX composite lead-free solder with low whisker growth tendency.

In S01, the ball-material ratio used in the ball milling process is 0.5: 1-2: 1, the ball milling speed is 50-200 r/min, and the ball milling time is 12-24 h; in S02, cold press molding pressure is 100-1000 MPa, and pressure maintaining time is 1-10 min; in S03, the protective atmosphere is argon, nitrogen or vacuum, the sintering temperature is 180-230 ℃, the heat preservation time is 1-5 h, and the heating rate is 5-15 ℃/min.

The invention has the following beneficial effects:

(1) the high-potential concentration MAX phase of the invention is formed by M₆The X octahedron layer and the A atomic layer with high space concentration are stacked alternately and still have the crystal structure of the MAX phase material, the formation energy of the A vacancies in the MAX phase is low, and the A vacancy holding capacity is also high, so that the MAX phase crystal structure can not be damagedWhile introducing a higher density of a vacancies. With Ti₂SnC is taken as an example, and the research shows that the Sn vacancy forming energy is 1.72eV, and the structure can still be kept stable when the Sn vacancy concentration reaches 50 percent.

The atoms in the MAX phase A atomic layer have strong mobility and are in the A/MAX composite system (such as Sn/Ti)₂SnC), atoms in the simple substance a can diffuse through the a atomic layer in the MAX phase. If the concentration of the A vacancies in the MAX phase is increased, the atoms with high activity in the simple substance A will not diffuse outward after diffusing into the A atomic layer in the MAX phase. Therefore, the MAX phase having a high vacancy concentration can inhibit the diffusion of a atoms to the surface, cut the atom source necessary for whisker growth, and suppress whisker growth. Meanwhile, the MAX phase can also play a role in enhancing the mechanical property of the solder.

(2) The preparation method of the MAX phase with high steric concentration comprises the steps of firstly carrying out high-energy ball milling on MAX phase powder to introduce more defects and enhance the activity of A atoms in the MAX phase; then carrying out plasma treatment on the MAX phase powder subjected to the high-energy ball milling so as to clean the MAX phase powder, and further activating the surface to improve the surface area; and finally, through chemical etching, the high-activity atoms in the A atomic layer are diffused outwards and react with acid, a large number of vacancies are left in the A atomic layer, and a MAX phase with high vacancy concentration is formed.

(3) The growth of the Sn whisker is actually a process of diffusing unstable Sn atoms in a matrix to the surface of the matrix to finally form the Sn whisker. The research of the invention finds that in the A elementary substance/MAX phase composite system, the A atoms in the A elementary substance can diffuse through the A atomic layer in the MAX phase, namely, the MAX phase can be used as a diffusion channel of the A atoms. And the high-potential concentration enables the MAX phase to be in a state with higher energy, so that after the composite material is compounded with the Sn (or Sn alloy) matrix, on one hand, unstable Sn atoms in the matrix tend to diffuse towards the MAX phase to reduce the total energy, and on the other hand, after the Sn atoms enter the Sn atomic layer of the MAX phase, the Sn atoms occupy vacancies therein and keep an equilibrium state, and do not diffuse outwards to form Sn whiskers. Therefore, the MAX phase having a high steric concentration can inhibit diffusion of Sn atoms to the surface, thereby cutting off the Sn atom source necessary for Sn whisker growth.

The MXene in the prior art cannot play the same role, because the MXene does not have the crystal structure of the MAX phase, and a large number of functional groups such as-OH, -F, = O and the like are adsorbed on the surface of the MXene, Sn atoms cannot be combined with the MXene at normal temperature to form the MAX phase or other stable structures again, and the MXene cannot play a role in preventing the Sn atoms from diffusing to the surface, so that the MXene cannot play a role in inhibiting the growth of Sn whiskers.

Meanwhile, the MAX phase of the invention can also play a role in refining the solder structure and enhancing the mechanical property of the solder.

(4) The invention can solve the problem of spontaneous growth of tin whiskers in the lead-free solder, and the invention uses MAX with high steric concentration to cut off the atom source of whisker growth, thereby fundamentally inhibiting the growth of the Sn whiskers and having obvious inhibiting effect. The inhibition effect on the growth of the Sn crystal whisker is not influenced by temperature, and the applicable temperature range is wide. The MAX phase reinforced phase can inhibit the growth of whiskers, improve the mechanical property of the lead-free solder and has no negative influence on the performance of the solder.

(5) The invention provides a lead-free solder for effectively inhibiting the growth of Sn whiskers and a preparation method thereof. The invention has wide applicable temperature range, can effectively inhibit the growth of Sn whiskers at high and low temperatures, has good inhibition effect on the whiskers, has simple process, has no negative influence on the performance of the solder, and can improve the mechanical property of the solder.

Drawings

FIG. 1 is a schematic diagram of a MAX phase/MXene composite structure obtained by incomplete etching of a MAX phase in the prior art;

FIG. 2 is a schematic structural diagram of an A atomic layer obtained by incomplete etching of a MAX phase in the prior art;

FIG. 3 is a schematic diagram of the structure of the high-dislocation-density MAX phase of the present invention;

FIG. 4 is a schematic structural diagram of an A atomic layer obtained by etching the MAX phase of the present invention;

FIG. 5 is a diagram showing the growth of whiskers after 500h of culture in a high-temperature and high-humidity environment in comparative example 1;

FIG. 6 is a diagram showing the growth of whiskers after culturing for 500h in a high-temperature and high-humidity environment according to comparative example 2;

FIG. 7 is a diagram showing the growth of whiskers after culturing for 500h in a high-temperature and high-humidity environment in comparative example 3;

FIG. 8 is a graph showing the growth of whiskers after 500h of culture in high temperature and high humidity environment in example 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are merely illustrative of the invention and are not intended to be limiting.

Example 1:

as shown in FIG. 3, a high-dislocation-density MAX phase is composed of M₆The X octahedron layer and the Sn atom layer with high concentration are stacked alternately.

As shown in fig. 4, the high steric concentration is about 25%; the vacancies in the Sn atomic layer are uniformly distributed.

The MAX phase is Ti₂SnC。

A preparation method of a MAX phase with high steric concentration comprises the following steps: mixing 10g of Ti₂Putting SnC powder and 50g of grinding balls into a ball milling tank, and putting the ball milling tank into a ball mill for high-energy ball milling, wherein the ball milling speed is 500r/min, and the ball milling time is 12 hours; ball-milled Ti₂Putting the SnC powder into a plasma cleaning machine for plasma treatment, wherein the plasma treatment power is 1000W, the vacuum degree is 50Pa, and the time is 10 min; subjecting the plasma-treated Ti₂Adding SnC powder into 500g of hydrochloric acid with the concentration of 5mol/L, and carrying out chemical etching under magnetic stirring, wherein the etching time is 2 hours, and the rotating speed of the magnetic stirring is 500 r/min; after the etching is finished, carrying out centrifugal cleaning, wherein the centrifugal rotating speed is 5000r/min, and the centrifugal time is 2 hours; centrifugally cleaning the Ti₂The SnC powder is put into a drying oven to be dried, the drying temperature is 60 ℃, the drying time is 4 hours, and high-potential-concentration Ti is obtained₂SnC powder.

The lead-free solder for effectively inhibiting the growth of tin whiskers comprises the following components in percentage by mass: high vacancy concentration Ti₂SnC powder: 10 percent; and 90% of Sn.

A preparation method of lead-free solder for effectively inhibiting tin whisker growth comprises the following steps: 5g of Ti with high steric concentration₂Putting SnC powder, 45g of Sn powder and 50g of grinding balls into a ball milling tank, and putting the ball milling tank into a ball mill for ball milling and mixing, wherein the ball milling speed is 50r/min, and the ball milling time is 24 hours; taking out the mixed powder, and keeping the temperature at 1000MPa for 1 minute to obtain a green body; and (3) placing the green body in a sintering furnace, sintering in an argon atmosphere, wherein the sintering temperature is 230 ℃, the heat preservation time is 1 hour, and the heating rate is 10 ℃/min.

Example 2:

a high-potential concentration MAX phase consisting of M₆The X octahedron layer and the Sn atom layer with high concentration are stacked alternately.

The high bit concentration is about 15%; the vacancies in the Sn atomic layer are uniformly distributed.

The MAX phase is Ti₃SnC₂。

A preparation method of a MAX phase with high steric concentration comprises the following steps: mixing 5g of Ti₃SnC₂Putting the powder and 50g of grinding balls into a ball milling tank, and putting the ball milling tank and the grinding balls into a ball mill for ball milling, wherein the ball milling rotation speed is 400r/min, and the ball milling time is 6 hours; ball-milled Ti₃SnC₂Putting the powder into a plasma cleaning machine for plasma treatment, wherein the plasma treatment power is 3000W, the vacuum degree is 100Pa, and the time is 5 min; subjecting the plasma-treated Ti₃SnC₂Adding the powder into 200g of hydrochloric acid with the concentration of 2mol/L, and carrying out chemical etching under magnetic stirring, wherein the etching time is 6 hours, and the rotating speed of the magnetic stirring is 500 r/min; after the etching is finished, carrying out centrifugal cleaning, wherein the centrifugal rotating speed is 2000r/min, and the centrifugal time is 5 hours; centrifugally cleaning the Ti₃SnC₂Drying the powder in a drying oven at 100 deg.C for 2 hr to obtain Ti with high concentration₃SnC₂And (3) powder.

Effective tin whisker growth inhibitionThe lead-free solder comprises the following components in percentage by mass: high vacancy concentration Ti₃SnC₂Powder: 2 percent; and 98% of Sn alloy. The Sn alloy is Sn-Cu alloy powder.

A preparation method of lead-free solder for effectively inhibiting tin whisker growth comprises the following steps: 1g of high steric concentration Ti₃SnC₂Putting the powder, 49g of Sn-Cu alloy powder and 25g of grinding balls into a ball milling tank, and putting the ball milling tank into a ball mill for ball milling and mixing, wherein the ball milling rotation speed is 100r/min, and the ball milling time is 15 hours; taking out the mixed powder, and keeping the temperature at 100MPa for 10 minutes to obtain a green body; and (3) placing the green body in a sintering furnace, sintering in an argon atmosphere, wherein the sintering temperature is 180 ℃, the heat preservation time is 5 hours, and the heating rate is 5 ℃/min.

Example 3:

a high-potential concentration MAX phase consisting of M₆The X octahedron layer and the Sn atom layer with high concentration are stacked alternately.

The high-altitude concentration is 50%; the vacancies in the Sn atomic layer are uniformly distributed.

The MAX phase is Zr₂SnC。

A preparation method of a MAX phase with high steric concentration comprises the following steps: adding 5gZr₂Putting SnC powder and 100g of grinding balls into a ball milling tank, and putting the ball milling tank and the grinding balls into a ball mill for ball milling, wherein the ball milling speed is 600r/min, and the ball milling time is 24 hours; ball-milled Zr₂Putting the SnC powder into a plasma cleaning machine for plasma treatment, wherein the plasma treatment power is 2000W, the vacuum degree is 10Pa, and the time is 30 min; subjecting the plasma-treated Zr₂Adding SnC powder into 100g of hydrochloric acid with the concentration of 1mol/L, and carrying out chemical etching under magnetic stirring, wherein the etching time is 24 hours, and the rotating speed of the magnetic stirring is 200 r/min; after the etching is finished, carrying out centrifugal cleaning, wherein the centrifugal rotating speed is 10000r/min, and the centrifugal time is 1 hour; zr after centrifugal cleaning₂The SnC powder is put into a drying oven to be dried, the drying temperature is 50 ℃, the drying time is 5 hours, and high-potential concentration Zr is obtained₂SnC powder.

The lead-free solder for effectively inhibiting the growth of tin whiskers comprises the following components in percentage by mass: high altitudeConcentration of Zr₂SnC powder: 5 percent; and 95% of Sn alloy. The Sn alloy is Sn-Ag-Cu alloy powder.

A preparation method of lead-free solder for effectively inhibiting tin whisker growth comprises the following steps: 2.5g of high steric concentration Zr₂Putting SnC powder, 47.5g of Sn-Ag-Cu alloy powder and 100g of grinding balls into a ball milling tank, and putting the ball milling tank into a ball mill for ball milling and mixing, wherein the ball milling speed is 200r/min, and the ball milling time is 12 hours; taking out the mixed powder, and keeping the temperature for 8 minutes under 200MPa to obtain a green body; and (3) placing the green body in a sintering furnace, sintering in an argon atmosphere, wherein the sintering temperature is 230 ℃, the heat preservation time is 5 hours, and the heating rate is 15 ℃/min.

Example 4:

a high-potential concentration MAX phase consisting of M₆The X octahedron layer and the Sn atom layer with high concentration are stacked alternately.

The high-altitude concentration is 5%; the vacancies in the Sn atomic layer are uniformly distributed.

The MAX phase is Ti₂SnC。

A preparation method of a MAX phase with high steric concentration comprises the following steps: mixing 10g of Ti₂Putting the SnC powder and 50g of grinding balls into a ball milling tank, and putting the ball milling tank and the ball milling tank into a ball mill for ball milling, wherein the ball milling speed is 400r/min, and the ball milling time is 4 hours; ball-milled Ti₂Putting the SnC powder into a plasma cleaning machine for plasma treatment, wherein the plasma treatment power is 1000W, the vacuum degree is 50Pa, and the time is 10 min; subjecting the plasma-treated Ti₂Adding SnC powder into 100g of hydrochloric acid with the concentration of 1mol/L, and carrying out chemical etching under magnetic stirring, wherein the etching time is 12 hours, and the rotating speed of the magnetic stirring is 400 r/min; after the etching is finished, carrying out centrifugal cleaning, wherein the centrifugal rotating speed is 8000r/min, and the centrifugal time is 2 hours; drying the centrifugally cleaned Ti2SnC powder in an oven at 40 ℃ for 8 hours to obtain Ti with high concentration at high potential₂SnC powder.

The lead-free solder for effectively inhibiting the growth of tin whiskers comprises the following components in percentage by mass: high vacancy concentration Ti₂SnC powder: 10 percent; and 90% of Sn alloy. The Sn alloy is Sn-Ag alloy powder.

A preparation method of lead-free solder for effectively inhibiting tin whisker growth comprises the following steps: 5g of Ti with high steric concentration₂Putting SnC powder, 45g of Sn-Ag alloy powder and 25g of grinding balls into a ball milling tank, and putting the ball milling tank into a ball mill for ball milling and mixing, wherein the ball milling speed is 100r/min, and the ball milling time is 15 hours; taking out the mixed powder, and keeping the temperature at 500MPa for 5 minutes to obtain a green body; and (3) placing the green body in a sintering furnace, sintering in a nitrogen atmosphere, wherein the sintering temperature is 200 ℃, the heat preservation time is 4 hours, and the heating rate is 10 ℃/min.

Comparative example 1:

putting 50g of Sn powder and 50g of grinding balls into a ball milling tank, and putting the ball milling tank and the grinding balls into a ball mill for ball milling and mixing, wherein the ball milling rotating speed is 50r/min, and the ball milling time is 24 hours; taking out the mixed powder, and keeping the temperature at 1000MPa for 1 minute to obtain a green body; and (3) placing the green body in a sintering furnace, sintering in an argon atmosphere, wherein the sintering temperature is 230 ℃, the heat preservation time is 1 hour, and the heating rate is 10 ℃/min.

Comparative example 2:

5g of untreated Ti₂Putting SnC powder, 45g of Sn powder and 50g of grinding balls into a ball milling tank, and putting the ball milling tank into a ball mill for ball milling and mixing, wherein the ball milling speed is 50r/min, and the ball milling time is 24 hours; taking out the mixed powder, and keeping the temperature at 1000MPa for 1 minute to obtain a green body; and (3) placing the green body in a sintering furnace, sintering in an argon atmosphere, wherein the sintering temperature is 230 ℃, the heat preservation time is 1 hour, and the heating rate is 10 ℃/min.

Comparative example 3:

mixing 10g of Ti₂Putting SnC powder and 50g of grinding balls into a ball milling tank, and putting the ball milling tank into a ball mill for high-energy ball milling, wherein the ball milling speed is 200r/min, and the ball milling time is 12 hours; ball-milled Ti₂Putting the SnC powder into a plasma cleaning machine for plasma treatment, wherein the plasma treatment power is 1000W, the vacuum degree is 50Pa, and the time is 10 min; adding the Ti2SnC powder subjected to plasma treatment into 500g of hydrochloric acid with the concentration of 5mol/L, and carrying out chemical etching under magnetic stirring, wherein the etching time is 2 hours, and the rotating speed of the magnetic stirring is 500 r/min; after the etching is finished, carrying out centrifugal cleaning, wherein the centrifugal rotating speed is 5000r/min, and the centrifugal time is2 hours; centrifugally cleaning the Ti₂And (3) putting the SnC powder into an oven for drying, wherein the drying temperature is 60 ℃, and the drying time is 4 hours. 5g of Ti with high steric concentration₂Putting SnC powder, 45g of Sn powder and 50g of grinding balls into a ball milling tank, and putting the ball milling tank into a ball mill for ball milling and mixing, wherein the ball milling speed is 50r/min, and the ball milling time is 24 hours; taking out the mixed powder, and keeping the temperature at 1000MPa for 1 minute to obtain a green body; and (3) placing the green body in a sintering furnace, sintering in an argon atmosphere, wherein the sintering temperature is 230 ℃, the heat preservation time is 1 hour, and the heating rate is 10 ℃/min.

In order to evaluate the inhibition effect of the lead-free solder prepared by the method on the growth of the Sn crystal whisker, the prepared lead-free solder is cut and then is tested under different conditions, and the method comprises the following steps: (1) room temperature environment; (2) high temperature and high humidity environment (temperature: 60 ℃ C.; relative humidity: 90%); (3) the thermal cycle environment is (-50 ℃ to 85 ℃). After 500 hours of testing, no tin whisker growth was observed on the surface of all samples.

FIG. 5 is a graph of whisker growth in comparative example 1, comparative example 2, comparative example 3 and example 1, respectively, after 500h of culture in a high temperature and high humidity environment. The concentration of the A vacancies in MAX is measured by X-ray photoelectron spectroscopy, and the concentration of the A vacancies is converted according to M, A and the relative contents of the three elements of X. In comparative example 1, no MAX phase powder was added, and it was observed that a large amount of whiskers were grown on the surface thereof, since Sn atoms having high mobility in the matrix were directly diffused to the surface of the matrix to form Sn whiskers. Ti for solder preparation in comparative example 2₂The SnC powder was not treated, and it was observed that a large amount of whiskers were grown on the surface thereof due to Ti₂Sn vacancies in SnC are all in thermodynamic equilibrium state, and Sn atoms enter Ti₂And the Sn atomic layer of the SnC continues to diffuse outwards until Sn whiskers are formed on the surface of the substrate. Ti for solder preparation in comparative example 3₂The Sn vacancy concentration in the SnC powder is about 2 percent, the length and the number of whiskers on the surface of the SnC powder are obviously reduced, and a small amount of whiskers still grow because of Ti₂Sn vacancies with concentration exceeding thermodynamic equilibrium exist in SnC, and high-activity Sn atoms in the matrix enter Ti₂Sn atomic layer post occupation of SnCIt is stated that the Sn vacancy positions do not diffuse outwards any more, but because the initial concentration of Sn vacancies is low, the entering of Sn atoms makes the concentration lower to the thermodynamic equilibrium concentration quickly, and the Sn atoms can not be hindered to diffuse towards the surface any more to form Sn whiskers, so that a small amount of Sn whiskers are still formed. The concentration of Sn vacancies in example 1 was about 25%, and the large number of vacancies made it possible to accommodate a large number of highly mobile Sn atoms diffusing from the matrix to the Sn atomic layer, effectively suppressing the Sn whisker growth.

In order to evaluate the mechanical properties of the lead-free solder obtained by the method of the present invention, the hardness of comparative examples 1 to 3 and example 1 was examined, and the results are shown in Table 1. As can be seen from Table 1, the addition of MAX phase improves the hardness of the solder, and when 10wt% of Ti is added to the solder₂After SnC, the hardness increased by about 10.4%, and the vacancy concentration in the MAX phase did not have a significant effect on the mechanical properties of the solder.

TABLE 1

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.