CN1325680C - Sn-Ag-Cu-Cr alloy lead-free solder preparation method - Google Patents

Abstract

The invention discloses a method for preparing Sn-Ag-Cu-Cr alloy lead-free solder, which belongs to the technical field of electronic materials. The present invention comprises the following steps: (1) preparation of master alloy Sn-Cr: 1. at room temperature, fully mix all Cr raw materials and Sn raw materials of the same weight as Cr raw materials; 2. under vacuum or protective atmosphere conditions, Raise the temperature above the melting point of metal Cr, keep it warm after melting, and fully stir; ③Add the remaining Sn raw materials into the furnace, after melting, cool down, keep warm, and continue stirring at the same time; (2) Sn-Ag-Cu- Cr alloy smelting: ①Put Ag and Cu raw materials into the molten Sn-Cr master alloy, stir fully after melting, and keep warm; ②Cool down and keep warm under constant stirring; ③Cool to room temperature or cast as required Form an ingot to obtain a Sn-Ag-Cu-Cr alloy lead-free solder, the composition and mass percentage of which are 0.005-1% for Cr, 0-5% for Ag, 0-2% for Cu, and the balance is Sn. The invention has simple steps, uniform chemical composition and metallographic structure, and can obtain satisfactory Sn-Ag-Cu-Cr alloy lead-free solder.

Description

Preparation method of Sn-Ag-Cu-Cr alloy lead-free solder

technical field

The invention relates to a preparation method in the technical field of soldering, in particular to a preparation method of Sn-Ag-Cu-Cr alloy lead-free solder.

Background technique

So far, there are many types of lead-free solders that have been developed, but there are problems of one kind or another, and there are not many with practical application value. Among them, the Sn-Ag-Cu ternary alloy near the eutectic composition of Sn-3.5Ag-0.75Cu has a melting point of 217°C. Compared with other lead-free solders, it has good wettability, high mechanical strength, and high It is resistant to fatigue and thermal shock and has great practical value. It is currently recognized as the most lead-free solder that can replace the traditional Sn-Pb solder, and it may become the standard lead-free solder in the future. On the other hand, the Sn-Ag-Cu solder still has some unresolved problems besides its high melting point and high price. For example, under the conditions of low cooling rate or high Ag content, coarse and brittle Ag ₃ Sn and Cu ₆ Sn ₅ phases are easy to form, resulting in increased brittleness and decreased fatigue strength. In addition, the surface of Sn-Ag-Cu alloy lead-free solder products such as BGA solder balls is easy to oxidize and turn yellow when placed or in a corrosive environment, resulting in a decrease in soldering performance. In addition, when used for wave soldering, equipment such as stainless steel solder baths are severely corroded, and have to be replaced with high-cost titanium or titanium alloy materials. If the problems listed above are not resolved, the application of this type of solder will be seriously affected.

After searching the existing technical documents, it was found that Ren Xiaoxue, Li Ming, and Mao Dali wrote in "The Influence of Alloy Elements on the High-temperature Oxidation Resistance of Sn-Zn-Based Lead-Free Solder", (Electronic Components and Materials, Vol.23, No. 11, 2004, P40-44.) mentioned the preparation method of Sn-Zn-Cr, but it is very different from Sn-Ag-Cu-Cr in alloy composition, and the melting temperature of this preparation method is low, Not suitable for the preparation of Sn-Ag-Cu-Cr alloy lead-free solder. At present, there is no public report about the Sn-Ag-Cu-Cr alloy lead-free solder and its preparation method. Since the Cr element in the new lead-free solder of the Sn-Ag-Cu-Cr alloy has a melting point as high as 1857°C and is easily oxidized, it is difficult to form an alloy with metals Sn, Ag, and Cu by the usual method, and the melting is difficult.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a preparation method for Sn-Ag-Cu-Cr alloy lead-free solder, which has simple steps, uniform chemical composition and metallographic structure, and can obtain satisfactory Sn-Ag-Cu-Cr alloy lead-free solder.

The present invention is achieved through the following technical solutions, and the present invention comprises the following steps:

(1) Preparation of master alloy Sn-Cr

①According to the composition requirements of the Sn-Ag-Cu-Cr alloy solder with Cr being 0.005-1%, Ag being 0-5%, Cu being 0-2%, and the balance being Sn, first weigh block, granular or powder respectively Pure metal Cr and Sn, and at room temperature, fully mix all the Cr raw materials and the Sn raw materials with the same weight as the Cr raw materials.

②Under vacuum or a protective atmosphere of argon or hydrogen, raise the temperature above the melting point of metal Cr, that is, control it within the range of 1857-2100°C, keep it warm for 30 minutes after melting, and stir thoroughly. This method adopts smelting under protective atmosphere conditions such as vacuum or argon, and its purpose is to more effectively prevent the oxidation and burning of metals during the smelting process.

③Put the remaining Sn raw materials into the furnace, and after melting, lower the temperature to 800°C, keep the temperature for 60 minutes, and continue stirring at the same time. At this point, the intermediate smelting of Sn-Cr is completed, and the next step of final alloy smelting can be carried out.

(2) Sn-Ag-Cu-Cr alloy melting

①According to the composition requirements of the above-mentioned Sn-Ag-Cu-Cr alloy solder with 0.005-1% of Cr, 0-5% of Ag, 0-2% of Cu, and the balance of Sn, weigh block, granular or powder respectively Like pure metal Ag and Cu. Put the above-mentioned Ag and Cu raw materials into the Sn-Cr master alloy melted at 800°C, fully stir after melting, and keep the temperature for 30 minutes.

② Lower the temperature to 250°C and keep it warm for 2 hours under constant stirring. The purpose of this step is to further make the chemical composition and metallographic structure of the material more uniform.

③Cool to room temperature or cast into ingots as needed.

Since the Cr element in the new lead-free solder of the Sn-Ag-Cu-Cr alloy has a melting point as high as 1857°C and is easily oxidized, it is difficult to form an alloy with the low melting point metals Sn, Ag, and Cu by the usual method, and the melting is difficult. In this method, we use high-temperature melting to prepare the intermediate alloy Sn-Cr first, and then melt together with Ag and Cu to form the final melting method of Sn-Ag-Cu-Cr alloy solder. Thereby can overcome such as the high melting point metal Cr is difficult to completely melt, the chemical composition and metallographic structure of the solder are not uniform and so on.

Since Cr is easy to oxidize and burn during the preparation of the alloy, it is best to melt under the protection conditions of vacuum or inert or reducing gas or molten salt during melting. The raw materials used in smelting can be pure metal in powder form, pure metal in granular form, or pure metal in block form. When smelting powder metal, the smelting speed is faster, but it is easy to burn out. When smelting bulk metal, the smelting temperature is higher and the time is longer, but it is not easy to burn out. Each has its own advantages and disadvantages.

The invention adopts the method of preparing Sn-Cr intermediate alloy first to prepare Sn-Ag-Cu-Cr solder, the method has simple steps, uniform chemical composition and metallographic structure, and can obtain satisfactory Sn-Ag-Cu-Cr alloy lead-free solder . The feature of the present invention is that by adding Cr element into the Sn-Ag-Cu alloy, the solder can maintain the original good wettability and high mechanical strength of the Sn-Ag-Cu alloy, and at the same time improve the oxidation resistance and corrosion resistance of the solder. The corrosion resistance is more than doubled, the ductility of the solder is increased by 5-30%, the corrosion resistance to copper solder joints and stainless steel solder baths is reduced by more than 50%, and the disadvantage of poor creep resistance during use is overcome, making it The reliability of the solder is further improved.

Detailed ways

Example 1

The composition and mass percentage of the material of the invention are as follows: 0.005% of Cr, 5% of Ag, 0% of Cu, and the balance of Sn.

(1) Preparation of master alloy Sn-Cr

①According to the composition requirements of the Sn-Ag-Cr alloy solder with Cr being 0.005%, Ag being 5%, Cu being 0%, and the balance being Sn, first weigh bulk, granular or powdered pure metal Cr and Sn respectively, and At room temperature, all of the Cr raw material and the Sn raw material having the same weight as the Cr raw material were thoroughly mixed.

②Under vacuum conditions, raise the temperature above the melting point of metal Cr, that is, control it within the range of 1857°C, keep it warm for 30 minutes after melting, and stir thoroughly.

③Put the remaining Sn raw materials into the furnace, and after melting, lower the temperature to 800°C, keep the temperature for 60 minutes, and continue stirring at the same time. At this point, the intermediate smelting of Sn-Cr is completed, and the next step of final alloy smelting can be carried out.

(2) Sn-Ag-Cr alloy melting

① According to the composition requirements of the above-mentioned Sn-Ag-Cr alloy solder with 0.005% Cr, 5% Ag, 0% Cu, and the balance of Sn, weigh bulk, granular or powdery pure metal Ag. Put the above-mentioned Ag raw material into the Sn-Cr master alloy melted at 800° C., fully stir after melting, and keep the temperature for 30 minutes.

② Lower the temperature to 250°C and keep it warm for 2 hours under constant stirring.

③Cool to room temperature or cast into ingots as needed.

Implementation effect: through metallographic structure observation and ICP chemical composition analysis: the metallographic structure of the obtained alloy solder is uniform, the chemical composition of the top, middle and bottom of the ingot is consistent, basically the same as the composition of the ingredients, and various properties meet the requirements of the solder.

Example 2

The composition and mass percentage of the material of the invention are as follows: 0.5% of Cr, 0% of Ag, 2% of Cu, and the balance of Sn.

(1) Preparation of master alloy Sn-Cr

①According to the composition requirements of the Sn-Cu-Cr alloy solder with Cr being 0.5%, Ag being 0%, Cu being 2%, and the balance being Sn, first weigh bulk, granular or powdered pure metal Cr and Sn respectively, and At room temperature, all of the Cr raw material and the Sn raw material having the same weight as the Cr raw material were thoroughly mixed.

②Under the protective atmosphere of argon, raise the temperature above the melting point of metal Cr, that is, control it within the range of 2100°C, keep it warm for 30 minutes after melting, and stir thoroughly.

③Put the remaining Sn raw materials into the furnace, and after melting, lower the temperature to 800°C, keep the temperature for 60 minutes, and continue stirring at the same time. At this point, the intermediate smelting of Sn-Cr is completed, and the next step of final alloy smelting can be carried out.

(2) Sn-Cu-Cr alloy melting

① According to the composition requirements of the above-mentioned Sn-Cu-Cr alloy solder with 0.5% Cr, 0% Ag, 2% Cu, and the balance of Sn, weigh pure metal Cu in bulk, granular or powder form. Put the above-mentioned Cu raw material into the Sn-Cr master alloy melted at 800° C., fully stir after it is completely melted, and keep it warm for 30 minutes.

② Lower the temperature to 250°C and keep it warm for 2 hours under constant stirring.

③Cool to room temperature or cast into ingots as required.

Implementation effect: through metallographic structure observation and ICP chemical composition analysis: the metallographic structure of the obtained alloy solder is uniform, the chemical composition of the top, middle and bottom of the ingot is consistent, basically the same as the composition of the ingredients, and various properties meet the requirements of the solder.

Example 3

The composition and mass percentage of the material of the invention are as follows: 1% of Cr, 2.5% of Ag, 1% of Cu, and the balance of Sn.

(1) Preparation of master alloy Sn-Cr

①According to the composition requirements of the Sn-Ag-Cu-Cr alloy solder with 1% Cr, 2.5% Ag, 1% Cu, and Sn as the balance, first weigh the bulk, granular or powdered pure metal Cr and Sn respectively. , and at room temperature, fully mix all the Cr raw materials and the Sn raw materials with the same weight as the Cr raw materials.

②Under the condition of hydrogen protective atmosphere, raise the temperature above the melting point of metal Cr, that is, control it within the range of 1957°C, keep it warm for 30 minutes after melting, and stir thoroughly.

③Put the remaining Sn raw materials into the furnace, and after melting, lower the temperature to 800°C, keep the temperature for 60 minutes, and continue stirring at the same time. At this point, the intermediate smelting of Sn-Cr is completed, and the next step of final alloy smelting can be carried out.

(2) Sn-Ag-Cu-Cr alloy melting

①According to the composition requirements of the above-mentioned Sn-Ag-Cu-Cr alloy solder with 1% of Cr, 2.5% of Ag, 1% of Cu, and the balance of Sn, weigh the bulk, granular or powdered pure metal Ag and Cu respectively. . Put the above-mentioned Ag and Cu raw materials into the Sn-Cr master alloy melted at 800°C, fully stir after melting, and keep the temperature for 30 minutes.

② Lower the temperature to 250°C and keep it warm for 2 hours under constant stirring.

③Cool to room temperature or cast into ingots as required.

Implementation effect: through metallographic structure observation and ICP chemical composition analysis: the metallographic structure of the obtained alloy solder is uniform, the chemical composition of the top, middle and bottom of the ingot is consistent, basically the same as the composition of the ingredients, and various properties meet the requirements of the solder.

Example 4

The components and mass percentages of the material of the invention are as follows: Cr is 0.25%, Ag is 3.5%, Cu is 0.75%, and the balance is Sn.

(1) Preparation of master alloy Sn-Cr

①According to the composition requirements of the Sn-Ag-Cu-Cr alloy solder with 0.25% Cr, 3.5% Ag, 0.75% Cu, and the balance of Sn, first weigh the bulk, granular or powdered pure metal Cr and Sn respectively. , and at room temperature, fully mix all the Cr raw materials and the Sn raw materials with the same weight as the Cr raw materials.

②Under vacuum conditions, raise the temperature above the melting point of metal Cr, that is, control it within the range of 2100°C, keep it warm for 30 minutes after melting, and stir thoroughly.

③Put the remaining Sn raw materials into the furnace, and after melting, lower the temperature to 800°C, keep the temperature for 60 minutes, and continue stirring at the same time. At this point, the intermediate smelting of Sn-Cr is completed, and the next step of final alloy smelting can be carried out.

(2) Sn-Ag-Cu-Cr alloy melting

①According to the composition requirements of the above-mentioned Sn-Ag-Cu-Cr alloy solder with 0.25% of Cr, 3.5% of Ag, 0.75% of Cu, and the balance of Sn, weigh the bulk, granular or powdered pure metals Ag and Cu respectively. . Put the above-mentioned Ag and Cu raw materials into the Sn-Cr master alloy melted at 800°C, fully stir after melting, and keep the temperature for 30 minutes.

② Lower the temperature to 250°C and keep it warm for 2 hours under constant stirring.

③Cool to room temperature or cast into ingots as needed.

Implementation effect: through metallographic structure observation and ICP chemical composition analysis: the metallographic structure of the obtained alloy solder is uniform, the chemical composition of the top, middle and bottom of the ingot is consistent, basically the same as the composition of the ingredients, and various properties meet the requirements of the solder.

Claims (10)

1. the preparation method of a Sn-Ag-Cu-Cr alloy lead-free solder is characterized in that, may further comprise the steps:

(1) preparation of master alloy Sn-Cr

1. be 0.005-1% according to mass percent Cr, Ag is 0-5%, Cu is 0-2%, surplus is that the composition requirement of the Sn-Ag-Cu-Cr solder of Sn takes by weighing earlier bulk, granular or powdered pure Metal Cr and Sn respectively, and at room temperature, carry out thorough mixing with whole Cr raw materials with the Sn raw material of Cr raw material equivalent weight;

2. in vacuum or have under the protective atmosphere condition, temperature is risen to more than the fusing point of Metal Cr, the insulation of fusing back, and fully stir;

3. remaining Sn raw material is added in the stove, after waiting to melt, cooling, insulation continues to stir simultaneously;

(2) Sn-Ag-Cu-Cr alloy melting

1. be 0.005-1% according to above-mentioned mass percent Cr, Ag is 0-5%, Cu is 0-2%, surplus is that the composition requirement of the Sn-Ag-Cu-Cr solder of Sn takes by weighing bulk, granular or powdered pure metal A g and Cu respectively, above-mentioned Ag and Cu raw material are put into fused Sn-Cr master alloy, treat that all fully stir the fusing back, and insulation;

2. cooling, under continuous agitation condition, insulation;

3. be cooled to room temperature or be cast into ingot.

2. the preparation method of Sn-Ag-Cu-Cr alloy lead-free solder according to claim 1 is characterized in that, described temperature rises to more than the fusing point of Metal Cr, is meant: be controlled in the 1857-2100 ℃ of scope.

3. the preparation method of Sn-Ag-Cu-Cr alloy lead-free solder according to claim 1 is characterized in that, the step in the described step (1) 2. is incubated 30 minutes.

4. the preparation method of Sn-Ag-Cu-Cr alloy lead-free solder according to claim 1 is characterized in that, the step in the described step (1) 3. is cooled to 800 ℃.

5. according to the preparation method of claim 1 or 4 described Sn-Ag-Cu-Cr alloy lead-free solders, it is characterized in that, the step in the described step (1) 3., insulation is 60 minutes.

6. the preparation method of Sn-Ag-Cu-Cr alloy lead-free solder according to claim 1 is characterized in that, the step in the described step (2) 1., melt temperature is 800 ℃.

7. according to the preparation method of claim 1 or 6 described Sn-Ag-Cu-Cr alloy lead-free solders, it is characterized in that, the step in the described step (2) 1., insulation is 30 minutes.

8. the preparation method of Sn-Ag-Cu-Cr alloy lead-free solder according to claim 1 is characterized in that, the step in the described step (2) 2. is cooled to 250 ℃.

9. according to the preparation method of claim 1 or 8 described Sn-Ag-Cu-Cr alloy lead-free solders, it is characterized in that, the step in the described step (2) 2., insulation is 2 hours.

10. the preparation method of Sn-Ag-Cu-Cr alloy lead-free solder according to claim 1 is characterized in that, described protective atmosphere is argon gas or hydrogen.