CN109048115B

CN109048115B - Sn-Ag-Cu lead-free solder containing Ga and Nd

Info

Publication number: CN109048115B
Application number: CN201811097248.9A
Authority: CN
Inventors: 薛鹏; 梁伟良; 王克鸿; 裴夤崟; 孙华为
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2018-09-20
Filing date: 2018-09-20
Publication date: 2020-11-13
Anticipated expiration: 2038-09-20
Also published as: CN109048115A

Abstract

The invention discloses a Sn-Ag-Cu lead-free solder containing Ga and Nd, belonging to the metal material class and the brazing material in the metallurgy field. The Sn-Ag-Cu lead-free solder comprises, by mass, 0.1-0.35% of Ag, 0.1-1.0% of Cu, 0.125-0.5% of Ga, 0.025-0.1% of Nd, 0.002-0.006% of Zr, 0.001-0.003% of Te and the balance of Sn, wherein the mass ratio of Ga to Nd is 5: 1, and the mass ratio of Zr to Te is Zr: Te ═ 2: 1. The solder has good wettability, can effectively inhibit the growth of tin whiskers of a soldered joint, greatly improves the reliability of the soldered joint, can be used for reflow soldering (reflow soldering) of components in the electronic industry and can also be used for wave soldering.

Description

Sn-Ag-Cu lead-free solder containing Ga and Nd

Technical Field

The invention relates to a Sn-Ag-Cu lead-free solder containing Ga and Nd, belonging to the metal material class and the brazing material in the metallurgy field.

Background

At present, representative lead-free solders comprise alloy systems such as Sn-Ag-Cu, Sn-Cu-Ni and the like, which are long in length, but have certain differences in solder cost, solder melting point and the like compared with tin-lead solders. The melting point and the raw material cost of the Sn-Zn solder are lower than those of Sn-Ag-Cu, Sn-Cu and Sn-Cu-Ni solder, particularly the melting point of the Sn-Zn solder is very close to that of tin-lead solder, but the Sn-Zn solder has poor wettability, so that the Sn-Zn solder is difficult to be applied to industrial production at present.

In recent years, Sn-Ag-Cu solders of various multi-element alloy systems, such As Sn-Ag-Cu lead-free solders containing Pr, Zr and Co (Chinese patent application, CN101579789A), Sn-Ag-Cu lead-free solders containing Nd, Li, As and In (Chinese patent application, CN101579790A), Sn-Ag-Cu lead-free solders containing Pr, Ni and Ga (Chinese patent application, CN101537546A) and Sn-Ag-Cu lead-free solders containing Nd, Ni and Co (Chinese patent application, CN101537547A) are developed on the basis of Sn-Ag-Cu at home and abroad, and have many improved performances compared with ternary Sn-Ag-Cu alloys, but all have obvious 'weaknesses', namely the silver content of all is 0.5-4.5%, no matter compared with Sn-Cu, Sn-Cu-Ni and Sn-Zn solders, also, the raw material cost is much higher than that of the conventional Sn-Pb solder.

Since silver is a worldwide "scarce" precious metal and its price fluctuates widely in addition to its own price, the need to investigate Sn — Ag — Cu lead-free solders of low silver or ultra-low silver to meet low-cost and high-quality production is a "hot problem" in recent years. Although the Sn-Ag-Cu lead-free solder containing Nd and Ga reduces the Ag content to 0.01-0.5%, the content of rare element Ga is still higher than 0.003-1.5%, and when the content of rare element Nd reaches 0.5% of the upper limit of 0.001-0.5%, a soldered joint is easy to generate a hidden trouble of tin whisker which has a great influence on electronic products. According to the 'Sn-Ag-Cu lead-free solder patent technical review' published by the State intellectual Property office patent examination cooperation Hubei Central Zhang prime sensor in 2017 and published in the technical and market, in recent years, China has few researches on Sn-Ag-Cu lead-free solder, so that the development of Sn-Ag-Cu lead-free solder with high performance, low cost, no tin generation and high reliability is urgently needed to meet the requirement of high-speed development of the electronic industry.

Disclosure of Invention

The invention aims to provide the Sn-Ag-Cu lead-free solder containing Ga and Nd, which is beneficial to saving rare and precious metal resources, has excellent wettability and brazing seam mechanical property, is suitable for reflow soldering (reflow soldering) in the electronic industry, can be used for wave soldering, meets the RoHS instruction requirements, has high performance, low cost, no tin whisker generation and high reliability.

The technical scheme for realizing the purpose of the invention is as follows:

the Sn-Ag-Cu lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.1-0.35% of Ag, 0.1-1.0% of Cu, 0.125-0.5% of Ga, 0.025-0.1% of Nd, 0.002-0.006% of Zr, 0.001-0.003% of Te, and the balance of Sn, wherein the mass ratio of Ga to Nd is 5: 1, and the mass ratio of Zr to Te is 2: 1.

The mass percentage of silver in the solder is only 0.01-0.35%, which is obviously reduced compared with the prior art, so that noble metal silver belonging to strategic resources can be saved; because a balance point with reasonable addition amount is found between Ga and Nd, the content of silver can be reduced to an ultra-low degree, the wettability of the brazing filler metal can be improved, the thickness increase of intermetallic compounds at a brazing seam interface can be effectively inhibited, the growth of tin whiskers of a brazed joint can be effectively inhibited, and the reliability of the brazed joint can be greatly improved; a balance point with reasonable addition amount is found between Zr and Te, and the shearing strength of the drill seam can be obviously improved. When the flux is matched with commercially available water-soluble soldering flux (namely medium-activity soldering flux, RMA soldering flux), the mechanical property of a soldering seam can reach 85MPa +/-5 MPa (shear strength), so that the flux can be suitable for wave soldering, reflow soldering and manual soldering in the electronic industry; the Pb element is taken as an impurity element in raw materials such as tin ingots, electrolytic copper and the like, and the total amount of Pb is controlled within the range of less than or equal to 0.07 wt.% so as to meet the regulation of the national standard GB/T20422-2018 Pb-free solder of the people's republic of China (the regulation of Pb in the standard is less than or equal to 0.07 wt.%).

Drawings

FIG. 1 is a schematic representation of the effect of different amounts of Nd on the wetting time of Sn-0.3Ag-0.7Cu lead-free solders in example 3 with a commercially available no-clean flux (GW9810A-6A flux) and under different test conditions when the mass ratio of Ga to Nd is 5 to 1.

FIG. 2 is a graph showing the effect of example 3 on the wetting time of Sn-0.3Ag-0.7Cu lead-free solders formulated with a commercially available water-soluble FLUX (FLUX 3355-11 water-soluble organic acid FLUX) and tested under different test conditions when the mass ratio of Ga to Nd is 5 to 1.

FIG. 3 is a microstructure view (300 times magnified) of Sn-0.3Ag-0.7Cu-0.5Ga-0.1 Nd.

FIG. 4 is a graph showing the morphology of the Sn-0.3Ag-0.7Cu-0.5Ga-0.1Nd/Cu interface after aging for 6 months at 150 ℃ (1000 times magnification).

FIG. 5 is a graph showing the morphology of the Sn-0.3Ag-0.7Cu-0.5Ga-0.1Nd/Cu interface after aging for 6 months at 150 ℃ (2000-fold magnification).

Detailed Description

The brazing filler metal is prepared by a conventional method, namely, commercially available tin ingots, silver plates, cathode copper, metal gallium, metal neodymium, zirconium copper alloy and tellurium copper alloy are used, the raw materials of various elements are proportioned according to the requirement, and a covering agent determined by optimized screening is added during smelting or inert gas protection is adopted for smelting and casting, so that bars can be obtained. The wire material (or flux can be added to prepare the flux-cored wire) is obtained by extrusion and drawing. Lead (namely Pb) element is taken as an impurity element in raw materials such as tin ingot, cathode copper and the like, and the total amount (mass percent) of the lead (namely Pb) element is controlled within the range of Pb being less than or equal to 0.07 wt.%, so as to meet the regulation of the lead-free solder of the national standard GB/T20422-2018 of the people's republic of China (Pb being less than or equal to 0.07 wt.% specified in the standard).

Considering that the metallic neodymium has high melting point and is easy to oxidize, the metallic neodymium can be smelted into intermediate alloy in advance according to production requirements, and the intermediate alloy is added in a Sn-Nd form to ensure the accuracy of the components of the neodymium in the brazing filler metal; zirconium copper and TTe0.5 tellurium copper with the mark of TZr0.4 in GB/T5231-2012 trade mark and chemical composition of processing copper and copper alloy are selected as raw materials, and zirconium and tellurium are added.

Referring to fig. 1, the effect of different amounts of Nd on the wetting time of sn0.3ag0.7cu lead-free solder is shown under different test temperature conditions in combination with a commercially available no-clean flux (GW9810A-6A flux) and under the precondition that the mass ratio of Zr to Te satisfies Zr: Te ═ 2: 1 and the Ga content and Nd content maintain Ga: Nd ═ 5: 1.

Referring to fig. 2, the effect of different amounts of Nd on the wetting time of sn0.3ag0.7cu lead-free solder is revealed under different test temperature conditions in combination with a commercially available water-soluble FLUX (FLUX of FLUX of FLUX of FLUX of FLUX.

Compared with the prior research, the invention has the creativity that:

1) the reasonable addition of Zr and Te is found to remarkably improve the mechanical property of the Sn-Ag-Cu lead-free solder with low silver (the silver content is less than or equal to 0.35wt percent in the specification), has no negative influence on the wettability of the solder, can effectively inhibit the growth of intermetallic compound thickness at a brazing seam interface and the growth of tin whiskers of a soldered joint when Ga and Nd are added simultaneously, can greatly improve the reliability of the soldered joint, is suitable for reflow soldering (reflow soldering) in the electronic industry, and is a novel Sn-Ag-Cu lead-free solder for wave soldering and other soldering methods.

When Ga and Nd elements are added simultaneously, and the addition amounts of Ga and Nd are in a certain specific range, the low-silver Sn-Ag-Cu lead-free solder has the wettability equivalent to that of the high-silver Sn2.5Ag0.7Cu lead-free solder. After the silver content is reduced from 2.5% to 0.35%, the liquidus temperature is increased from about 220 ℃ of Sn2.5Ag0.7Cu to about 225 ℃ of Sn0.35Ag0.7Cu. The addition of trace Ga and Nd elements improves the wettability of the Sn0.35Ag0.7Cu solder, and simultaneously, the solidus temperature and the liquidus temperature of the solder are both reduced to a certain extent, which is beneficial to the actual soldering production. Through test and measurement, the liquidus temperature of the solder determined in the embodiment of the invention is reduced by 7 ℃ compared with the liquidus temperature of the Sn0.35Ag0.7Cu solder, and the liquidus temperature of the Sn0.35Ag0.7Cu-Ga-Nd-Zr-Te solder is 218 ℃, which is equivalent to the liquidus temperature 217 ℃ of the Sn3.8Ag0.7Cu solder.

In the test process of the invention, through researching a Sn-Te binary phase diagram, the metal Te and Sn are completely not dissolved in solid solution, but the Te and Sn are easy to form a high-melting point intermetallic compound, and the melting point temperature of the intermetallic compound is 806 ℃; by researching the Sn-Zr binary phase diagram, the metallic Sn has high solid solubility in Zr element, and can form a plurality of high-melting-point intermetallic compounds, and the melting point temperature of the intermetallic compounds reaches 1988 ℃. According to the theory of metallurgy and metallurgy, the formation of trace amount of high-melting point intermetallic compound can be used as the nucleation mass point of liquid metal, which is beneficial to grain refinement and improves the mechanical property of brazing seams. However, since the liquidus temperature of the Sn0.35Ag0.7Cu solder is only 218 ℃ and the temperature difference from the liquid state to the solid state is not so large, a small amount of the high melting point intermetallic compound is required even if it can be used as a "nucleation site" of the liquid metal. Theoretical calculation and experimental verification such as finite element simulation prove that the addition amount capable of playing a positive role needs to control Zr element to be in the range of 0.002-0.006%, Te element to be in the range of 0.001-0.003%, and the mass ratio of Zr to Te to be in the range of Zr: Te-2: 1 is most effective.

2) Experiments verify and optimize the addition range and proportion relation of Ga and Nd elements.

Through a method of 'sequential experimental design', the Sn-Ag-Cu lead-free solder with the Ag content less than or equal to 0.5% (mass percent, the same below) is discovered, when the Ag content is less than or equal to 0.35%, the Sn-Ag-Cu lead-free solder can obtain the wetting performance equivalent to that of Sn2.5Ag0.7Cu and Sn3.8Ag0.7Cu lead-free solder, and the expected effect can be achieved by searching for new element combination and utilizing the special performance of a plurality of new trace elements which are not discovered, through proportion adjustment and component optimization.

The test results in fig. 1 and 2 show that, when compared with the sn0.3ag0.7cu lead-free solder, when the ratio of Ga to Nd is ensured to be 5: 1, the optimum addition range of the sn0.3ag0.7cu-Ga-Nd-Zr-Te lead-free solder Nd is 0.025-0.1%, and the optimum addition range of Ga is 0.125-0.5%, when the ratio of Ga to Nd is ensured to be 5: 1. Within this composition range, it is possible to ensure that the wetting time of the new solder is < 1 second (according to the US electronic industry Standard IPC/EIA J-STD-003B: 2004, the recommended value of the wetting time of solder for wave soldering on a substrate material is t₀Less than or equal to 1 s. It is recognized within the electronics industry that a smaller wetting time (at least less than one second) indicates a better solder wetting performance). When the addition amount of Nd is more than 0.1%, the wetting time is more than or equal to 1 second, which shows that the negative effect of the Nd on the wetting performance of the solder begins to appear, and the probability of the initiation and growth of tin whiskers is increased on a microstructure.

The brazing seam mechanical property test result shows that the shearing strength of the brazing seam (welding spot) of the brazing filler metal obtained in the embodiment of the application reaches 85MPa +/-5 MPa, and the brazing seam mechanical property is far higher than 50 MPa +/-10 MPa of the Sn3.8Ag0.7Cu0.05RE lead-free brazing filler metal while the brazing seam (welding spot) has the wettability equivalent to that of the Sn2.5Ag0.7Cu and Sn3.8Ag0.7Cu lead-free brazing filler metal, and the brazing seam mechanical property test result is mainly the result of strengthening the trace Zr and Te elements.

Various component optimization results show that the addition amount of Ga should be controlled within the range of 0.125-0.5%, the addition amount of Nd should be controlled within the range of 0.025-0.1%, the addition amount of Zr should be controlled within the range of 0.002-0.006%, the addition amount of Te should be controlled within the range of 0.001-0.003%, and the mass ratio of Ga to Nd should be controlled within the range of Ga: Nd: 5: 1; the mass ratio of Zr to Te should be controlled to be 2: 1. Under the 'synergistic action' of the four elements, the Sn-Ag-Cu lead-free solder containing Ga and Nd, which is obtained by the new element combination, has high soldering seam mechanical property, excellent wetting spreading property and excellent soldering seam reliability.

The following describes specific embodiments of the present invention based on the mass ratio of the "Sn-Ag-Cu lead-free solder containing Ga and Nd" of the present invention.

Example 1

The Sn-Ag-Cu lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.1% Ag, 1.0% Cu, 0.125% Ga, 0.025% Nd, 0.006% Zr, 0.003% Te, and the balance Sn.

The liquidus temperature of the Sn-Ag-Cu lead-free solder containing Ga and Nd obtained by the component ratio is about 218 ℃ (test error is considered), the solder joint has excellent wettability on a T2 copper plate by matching with a commercially available water-soluble soldering FLUX (FLUX of FLUX 3355-11 water-soluble organic acid), and the mechanical property of the solder joint can reach 85MPa +/-5 MPa (shear strength). After aging for 6 months at 150 ℃, the intermetallic compound of the brazing seam interface of the newly-invented lead-free brazing filler metal has no obvious change and no tin whisker is generated, which shows that the reliability of the welding spot (brazing seam) is obviously improved.

Example 2

The Sn-Ag-Cu lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.35% Ag, 0.1% Cu, 0.5% Ga, 0.1% Nd, 0.002% Zr, 0.001% Te, and the balance Sn.

The liquidus temperature of the Sn-Ag-Cu lead-free solder containing Ga and Nd obtained by the component proportion is about 218 ℃ (test error is considered), the solder joint has excellent wettability on a T2 copper plate by matching with a commercially available water-soluble soldering FLUX (FLUX of FLUX 3355-11 water-soluble organic acid), and the mechanical property of the solder joint can reach 85MPa +/-5 MPa (shear strength). After aging for 6 months at 150 ℃, the intermetallic compound of the brazing seam interface of the newly-invented lead-free brazing filler metal has no obvious change and no tin whisker is generated, which shows that the reliability of the welding spot (brazing seam) is obviously improved.

Example 3

The Sn-Ag-Cu lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.3% of Ag, 0.7% of Cu, 0.4% of Ga, 0.08% of Nd, 0.004% of Zr, 0.002% of Te and the balance of Sn.

Example 4

The Sn-Ag-Cu lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.25% of Ag, 0.65% of Cu, 0.3% of Ga, 0.06% of Nd, 0.003% of Zr, 0.0015% of Te and the balance of Sn.

Example 5

The Sn-Ag-Cu lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.15% Ag, 0.75% Cu, 0.2% Ga, 0.04% Nd, 0.005% Zr, 0.0025% Te, and the balance Sn.

Claims

1. The Sn-Ag-Cu lead-free solder containing Ga and Nd is characterized by comprising the following components in percentage by mass: 0.1-0.35% of Ag, 0.1-1.0% of Cu, 0.125-0.5% of Ga, 0.025-0.1% of Nd, 0.002-0.006% of Zr, 0.001-0.003% of Te, and the balance of Sn, wherein the mass ratio of Ga to Nd is 5: 1, and the mass ratio of Zr to Te is 2: 1.