CN1302891C - Rare earth contained SnAgCuY tin based leadless solder and its preparation method - Google Patents

Abstract

The present invention relates to a rare earth contained SnAgCuy tin-base lead-free solder and a preparation method thereof which belong to the technical field of manufacturing electronic packaging lead-free solder in microelectron industry. The solder has the components, in weight percentages, 2 to 5% of Ag, 0.2 to 1 % of Cu, 0.025 to 1.0 of commercial rare earth Y and Sn in balancing amount. The rare earth contained SnAgCuy tin-base lead-free solder has the preparation method that a salt mixture with the weight ratio of potassium chloride to lithium chloride of (1 to 1.6): (0.8 to 1.2) is melted and poured on Sn; after the Sn is melted, weighed Ag and Cu are added in a Sn solution to make the Ag and Cu melted; then, the commercial rare earth Y is pressed into the salt mixture and the Sn-Ag-Cu alloy by a bell jar of which the wall is provided with holes; and the bell jar is rotated, temperature is preserved for 1 to 2 hours, and the surface salt mixture is removed after agitation, stationary placement and solidification. The solder has the advantages of few alloy components, strong practicability, low cost and no pollution, and the wetting technological property, the microscopic structure and the metallurgy quality are obvious improved.

Description

Rare earth-containing SnAgCuY tin-based lead-free solder

technical field

A rare earth-containing SnAgCuY tin-based lead-free solder and a preparation method thereof belong to the technical field of lead-free solder manufacturing for electronic assembly in the microelectronics industry.

Background technique

In the past ten years, a variety of lead-free solder alloys have been researched and developed at home and abroad, and hundreds of patents are involved. The current research on lead-free solder alloys mainly focuses on three temperature ranges and several alloy series. Among them, the most representative ones are lead-free solder alloys in the medium temperature range, such as Sn-Cu, Sn-Ag, Sn-Zn binary alloys, Sn-Ag-Cu, Sn-Ag-Bi, Sn-Zn-Bi Such as ternary alloys or more alloys.

The basic requirements for lead-free solder should include: the melting temperature should be close to the SnPb eutectic temperature, and the melting temperature interval should be small; there must be good wettability or brazing process performance, good wettability can reduce welding defects , improve brazing productivity; good physical and mechanical properties, such as strength, creep resistance, thermal fatigue resistance, metallographic structure stability, to meet the reliability requirements of electronic products; in addition, it should have good electrical conductivity, thermal conductivity, etc. Performance; chemical properties are also very important, so that the brazed joints have good corrosion resistance; lead-free solder should not contain new toxic components; the cost of solder should be low to facilitate popularization and application.

Judging from the research status at home and abroad, in the short term, the most widely used medium temperature section can realize lead-free substitution in production will be Sn-Cu, Sn-Ag binary alloy system and Sn-Ag-Cu ternary alloy system or More multi-alloy solders based on this. Sn-Cu solder will be mainly used for wave soldering, and Sn-Ag-Cu solder will be mainly used for reflow soldering. At present, there are many kinds of Sn-Ag-Cu solder alloys in the world. The representative SnAgCu patented solder alloys are: Sn-(3.5-7.7)Ag-(1-4)Cu-(0-10)Bi [US Patent USP5527628], Sn-(2-5)Ag-(0-2.9)Cuu-(0.1-3)Ni[US Patent USP 5863493], Sn-3.0Ag-0.5Cu[Japanese Patent JPP 3027441] and Sn -(2-5)Ag-(0.2-1)Cu-(0.025-1)RE[Chinese Patent ZL 02123528.7] etc.

The eutectic composition Sn-4.7%Ag-1.7%Cu of the SnAgCu solder reported in US Patent No. 5,527,628 has a melting point of 217° C., but the creep strength of the solder in this invention is not good. In addition, the lead-free solder Sn-(0.08-20%) Bi-(0.01-1.5%) Ag-(0.02-1.5%) Cu-0.01%P-(0-0.2%) mixed rare earth provided by US Patent 4,929,423, It is mainly used for pipe brazing, and has many alloy components, so its practicability is poor. U.S. Patent 6,361,742 introduces two kinds of SnAg and SnAgCuBi lead-free solders with rare earth additions, but the wettability of SnAg solders is poor, which will cause the dissolution of copper matrix in the brazing process, and SnAgCuBi not only has many alloy components, because The brazing filler metal contains Bi, which is easy to produce eutectic with low melting point, and the rare earth is a single rare earth element. Chinese patent 01128184.7 introduces a rare earth-containing lead-free solder suitable for electronic packaging and assembly soldering, wherein the rare earth is a mixed rare earth of La and Ce or a mixed rare earth of La and Ce plus one or two of Pr and Nd, Sn-(0.1-5%) Ag-(0.1-1%) Cu-(0.1-8%) Bi-(0.1-7.5%) In-(0-8%) Sb-(0.01-2%) rare earth. The patent pointed out that in order to further lower the melting point, a certain amount of In and Bi elements were added. However, with the acceleration of the lead-free process, some large companies have successively launched lead-free wave soldering machines and lead-free reflow soldering machines, and the peak temperature of soldering can reach about 250°C. Now, the melting point of lead-free solder is no longer a very prominent problem. In addition, Bi-containing solders are prone to undercut defects during brazing, and easily form eutectics with low melting points with lead, so they are more sensitive to lead pollution, and the brittleness of Bi is also an unfavorable factor. In addition, Bi is a by-product of lead, and the use of Bi-containing solder will inevitably increase the mining of lead ore, causing environmental pollution. The abundance of In in the earth's crust is very low, and it is expensive, which is not suitable for large-scale use. Therefore, adding some elements to lower the melting point of solder, such as In, Bi, etc., has become unnecessary without significantly improving the overall performance of the product.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides an alloy with few components, strong practicability, low cost, easy to control impurity lead content, good wettability, suitable strength and melting temperature, microstructure Rare earth-containing SnAgCuY lead-free solder with metallurgical quality superior to traditional SnAgCu solder and a preparation method thereof.

The SnAgCuY tin-based lead-free solder containing rare earth Y related to the present invention is characterized in that it contains 2 to 5% Ag, 0.2 to 1% Cu, 0.025 to 0.5% commercially available rare earth Y, and the rest is Sn.

The invention provides a preparation method of SnAgCuY tin-based lead-free solder containing rare earth Y, characterized in that:

(1) by weight ratio potassium chloride: the mixed salt of lithium chloride=(1～1.6): (0.8～1.2) pours on the weighed tin after melting at 450 ℃～550 ℃;

(2) Raise the temperature to 600°C to 800°C. After the tin is melted, add the weighed silver and copper into the molten tin liquid and stir to form an alloy;

(3) After it is melted evenly, the commercially available rare earth Y is quickly pressed into the above-mentioned molten alloy with a stainless steel bell jar with holes on the wall, and the bell jar is rotated;

(4) After the rare earth is completely melted, keep warm for 1 to 2 hours, stir to make the alloy homogeneous, leave the furnace to stand, and remove the mixed salt on the surface after solidification.

In the following, the improved performance of the rare earth Y-containing lead-free solder of the present invention is illustrated in the form of a graph through the test data of several examples, and compared with the traditional SnAgCu solder obtained under the same conditions.

Table 1 is a composition list of 9 kinds of tin-based lead-free solders containing rare earth Y and traditional SnAgCu solders. The compositions in the table are all weight percentages. phase temperature. The liquidus and solidus temperatures of the solder are measured by slow cooling curves. As can be seen from Table 1, examples 1 to 9 of the present invention have a melting temperature range close to or slightly lower than that of SnAgCu lead-free solder, especially under the same condition of Ag content, adding a trace amount of rare earth Y can generally reduce the melting temperature, As shown in Figure 3, it is suitable for the current lead-free soldering process conditions.

Table 2 is the comparison of shear strength and spreading area between Examples 1-9 of the present invention and traditional SnAgCu lead-free solder. As can be seen from the table, the shear strength of examples 1 to 9 of the present invention is equivalent to that of traditional SnAgCu solder, but the spreading process performance of most examples is improved, as shown in Figure 4, which is suitable for surface assembly in the microelectronics industry.

Fig. 1 and Fig. 2 are respectively the comparison of the microstructure of the tin-based lead-free solder containing rare earth Y of the present invention and the traditional SnAgCu solder. It can be seen that the microstructure of the solder with rare earth Y added is fine, while the crystal structure without added rare earth Y is coarse, with strong directionality and high brittleness. This also reveals the reason why the rare earth Y-containing lead-free solder can improve the metallurgical quality of the solder from a microscopic point of view.

Description of drawings:

Figure 1: Microstructure of SnAgCuY lead-free solder alloy containing rare earth Y.

Figure 2: Microstructure of a conventional SnAgCu lead-free solder alloy.

Fig. 3 Effect of Y on the melting temperature of Sn3.8Ag0.7Cu.

Fig. 4 Effect of Y on the spreading area of Sn3.8Ag0.7Cu.

Detailed ways

Example 1: 26 grams of potassium chloride and 20 grams of lithium chloride mixed salt were melted at 450°C and poured on 95.475 grams of tin. Raise the temperature of the furnace to 800°C to melt the tin and the mixed salt, then add 3.8 grams of Ag and 0.7 grams of Cu to the tin liquid while stirring continuously to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep warm for 1 hour, stirring constantly to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 360°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Example 2: 26 grams of potassium chloride and 20 grams of lithium chloride mixed salt are poured on 95.45 grams of tin after melting at 450°C. Raise the temperature of the furnace to 780°C to melt the tin and the mixed salt, then add 3.8 grams of Ag and 0.7 grams of Cu to the tin liquid while stirring continuously to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep it warm for 1.5 hours and keep stirring to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 380°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Example 3: 23.4 grams of potassium chloride and 18 grams of lithium chloride mixed salt are poured on 95.4 grams of tin after melting at 490°C. Raise the temperature of the furnace to 700°C, melt the tin and the mixed salt, add 3.8 grams of Ag and 0.7 grams of Cu to the tin liquid, and stir continuously at the same time to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep warm for 1 hour, stirring constantly to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 360°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Example 4: 26 grams of potassium chloride and 20 grams of lithium chloride mixed salt are poured on 95.25 grams of tin after melting at 510°C. Raise the temperature of the furnace to 720°C, melt the tin and the mixed salt, add 3.8 grams of Ag and 0.7 grams of Cu to the tin liquid, and stir continuously at the same time to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep it warm for 2 hours and keep stirring to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 400°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Example 5: 32.5 grams of potassium chloride and 25 grams of lithium chloride mixed salt are poured on 95 grams of tin after being melted at 500°C. Raise the temperature of the furnace to 720°C, melt the tin and the mixed salt, add 3.8 grams of Ag and 0.7 grams of Cu to the tin liquid, and stir continuously at the same time to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep it warm for 1.5 hours and keep stirring to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 380°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Example 6: 26 grams of potassium chloride and 20 grams of lithium chloride mixed salt are poured on 97.775 grams of tin after melting at 460°C. Raise the temperature of the furnace to 800°C, melt the tin and the mixed salt, add 2 grams of Ag and 0.2 grams of Cu to the tin liquid, and stir continuously at the same time to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep it warm for 2 hours and keep stirring to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 400°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Example 7: 26 grams of potassium chloride and 20 grams of lithium chloride mixed salt are poured on 96 grams of tin after melting at 550°C. Raise the temperature of the furnace to 600°C, melt the tin and the mixed salt, add 2 grams of Ag and 1 gram of Cu to the tin liquid, and stir continuously at the same time to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep it warm for 2 hours and keep stirring to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 400°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Example 8: 26 grams of potassium chloride and 20 grams of lithium chloride mixed salt were melted at 460 ° C and poured on 94.775 grams of tin. Raise the temperature of the furnace to 800°C to melt the tin and the mixed salt, then add 5 grams of Ag and 0.2 grams of Cu to the tin liquid while stirring continuously to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep it warm for 2 hours and keep stirring to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 400°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Example 9: 26 grams of potassium chloride and 20 grams of lithium chloride mixed salt were melted at 460 ° C and poured on 93 grams of tin. Raise the temperature of the furnace to 800°C, melt the tin and the mixed salt, add 5 grams of Ag and 1 gram of Cu to the tin liquid, and stir continuously at the same time to form an alloy; Y is quickly pressed into the above-mentioned molten alloy and stirred continuously until the rare earth is completely melted. Keep it warm for 2 hours and keep stirring to homogenize the alloy. Stand still and take out the furnace, and remove the mixed salt on the surface after the alloy is solidified. Lower the furnace temperature to 400°C to reheat and melt the solder block, and then pour it into strips on the angle iron for use.

Table 1 Solder alloy composition and melting temperature example Sn(wt%) Ag(wt%) Cu(wt%) Y (wt%) Liquidus temperature (℃) Solidus temperature (℃) comparative example 95.5 3.8 0.7 0 217.1 215.6 Example 1 95.475 3.8 0.7 0.025 217.1 213.9 Example 2 95.45 3.8 0.7 0.05 217.3 212.2 Example 3 95.4 3.8 0.7 0.1 216.7 210.4 Example 4 95.25 3.8 0.7 0.25 215.6 207.8 Example 5 95 3.8 0.7 0.5 216.9 215.6 Example 6 97.775 2 0.2 0.025 225.1 215.6 Example 7 96 2 1.0 0.5 219.9 213.0 Example 8 94.775 5 0.2 0.025 220.8 214.7 Example 9 93 5 1.0 0.5 216.0 213.0

Table 2 Shear strength and spreading area example Shear strength (MPa) Spread area(mm ² ) comparative example 67.2 57.7 Example 1 68.0 58.9 Example 2 62.9 59.7 Example 3 63.8 59.1 Example 4 67.3 60.8 Example 5 65.5 58.8 Example 6 65.5 57.5 Example 7 51.9 55.9 Example 8 43.4 60.0 Example 9 64.6 55.8

Claims (1)

1, a kind of SnAgCuY tin base leadless soldering-flux that contains rare earth is characterized in that: contain percentage by weight and be 2～5% Ag, and 0.2～1% Cu, 0.025～0.5% commercially available Rare Earth Y, all the other are Sn.

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