CN109048114B

CN109048114B - Sn-Cu-Ni lead-free solder containing Ga and Nd

Info

Publication number: CN109048114B
Application number: CN201811097247.4A
Authority: CN
Inventors: 薛鹏; 邹阳; 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: 2021-02-12
Anticipated expiration: 2038-09-20
Also published as: CN109048114A

Abstract

The invention discloses a Sn-Cu-Ni lead-free solder containing Ga and Nd, belonging to the field of brazing materials of metal materials. The Sn-Cu-Ni lead-free solder comprises, by mass, 0.45-1.1% of Cu, 0.05-0.5% of Ni, 0.003-0.008% of As, 0.014-0.020% of Sb, 0.4-0.6% of Ga, 0.04-0.06% of Nd and the balance of Sn, wherein the mass ratio of Ga to Nd meets the requirement that Ga: Nd is 10: 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, and can be used for wave soldering and reflow soldering of components in the electronic industry.

Description

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

Technical Field

The invention relates to a Sn-Cu-Ni lead-free solder containing Ga and Nd, belonging to the technical field of brazing materials in the fields of metal materials and metallurgy.

Background

The traditional Sn-Pb solder is widely applied to the field of electronic assembly and packaging due to the advantages of good wettability, low cost, low melting point and the like, but because Pb element is harmful to the environment and human body, the lead-free solder has to be used on many electronic products under the strict limitation of WEEE instruction and RoHS instruction issued by the European Union and the No. 39 instruction of the government of China. The Sn-based lead-free solder studied today is mainly Sn-Ag, Sn-Ag-Cu, Sn-Zn, Sn-Cu, Sn-Bi, etc. The Sn-Cu alloy solder is widely used due to low cost and good thermal fatigue resistance, particularly under the condition of wave soldering, the eutectic melting point reaches 227 ℃, but the wettability and the mechanical property of the Sn-Cu alloy solder are inferior to those of other lead-free solders. The researchers add metal Ni element in Sn-Cu solder, find that the Sn-Cu-Ni composite solder has better performance than the Sn-Cu solder, and add rare earth element in order to further improve the comprehensive performance of the Sn-Cu-Ni solder.

At present, Sn-Cu and Sn-Cu-Ni brazing filler metals have good comprehensive performance, moderate price and good application prospect, and are already applied to wave soldering. After retrieval, the invention patent of Sn-Cu and Sn-Cu-Ni series solder lead-free solder applied by intellectual property bureau of China reaches more than 280. However, in the using process, the thickness of the intermetallic compound at the brazing seam interface of the Sn-Cu-Ni brazing filler metal added with the rare earth element tends to increase gradually and thicken along with the time, particularly, tin whiskers which can cause short circuit of electronic components are easy to grow in a brazed joint along with the time, and the reliability of the brazed joint is greatly reduced. Therefore, in order to meet the needs of users, research and improvement are urgently needed for the problems of the Sn-Cu-Ni solder added with rare earth elements, and a new Sn-Cu-Ni solder with high reliability is developed.

Disclosure of Invention

The invention aims to provide a Sn-Cu-Ni lead-free solder which has good wettability, can effectively inhibit the growth of intermetallic compound thickness of a brazing seam interface and can effectively inhibit the growth of tin whiskers of a brazed joint, thereby greatly improving the reliability of the brazed joint, being suitable for wave soldering in the electronic industry and being used for welding methods such as reflow soldering and the like.

In order to achieve the purpose of the invention, the technical scheme of the invention is as follows:

the Sn-Cu-Ni lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.45-1.1% of Cu, 0.05-0.5% of Ni, 0.003-0.008% of As, 0.014-0.020% of Sb, 0.4-0.6% of Ga, 0.04-0.06% of Nd and the balance of Sn. Wherein the mass ratio of Ga to Nd is 10: 1.

The Sn-Cu-Ni lead-free solder containing Ga and Nd is prepared by a conventional method, namely, commercially available tin ingots, cathode copper, nickel plates, antimony ingots, bulk arsenic, metal gallium and metal neodymium are used, the raw materials of various elements are proportioned according to requirements, and a commercially available covering agent determined by optimized screening is added during smelting or is protected by inert gas for smelting and casting, so that strip-shaped solder or bar materials can be obtained. The wire material (or flux can be added to prepare the flux-cored wire) is obtained by extrusion and drawing. The Pb element is taken as an impurity element in raw materials such as tin ingots, cathode 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.%).

Considering that the metal neodymium has high melting point and is easy to oxidize, the metal praseodymium can be pre-smelted into intermediate alloy according to production requirements, and the intermediate alloy is added in the form of Sn-Nd so as to ensure the accuracy of the components of the metal neodymium in the brazing filler metal.

The solder has good soldering performance (such as wettability) and excellent mechanical property of soldering points (soldering seams), can effectively inhibit the growth of tin whiskers of soldered joints, is green and environment-friendly, has uniform tissue, is easy to process into various shapes such as strips, rods, wires and the like so as to meet the requirements of different production conditions, and is suitable for assembling and packaging components in the electronic industry.

Drawings

FIG. 1 is a graph showing the change in wetting force for different Nd contents of Sn-0.7Cu-0.05Ni-0.5 Ga-xNd.

FIG. 2 is a graph showing the change of the wetting time of Sn-0.7Cu-0.05Ni-0.5Ga-xNd with different Nd contents.

FIG. 3 is a graph of the "interface" morphology of the brazed joint after 30 days of room temperature aging.

Detailed Description

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

1) the synergistic effect of Ga and Nd in the element combination is found and verified, and when the mass ratio of Ga and Nd elements meets Ga: Nd-10: 1, the thickness increase of intermetallic compounds at the brazing seam interface can be effectively inhibited, and the growth of tin whiskers of a soldered joint can be effectively inhibited.

In the test process of the invention, researches show that the addition of Ga and Nd into Sn-Cu-Ni lead-free solder can effectively inhibit the growth rate of the thickness of intermetallic compounds at the brazing seam interface of the Sn-Cu-Ni lead-free solder. Further research finds and verifies that the mass ratio of the added Ga and Nd elements meets the requirement that Ga: Nd is 10: 1, the Ga and Nd have more obvious inhibition effect on the thickness increase speed of the brazing seam interface metal compound of the Sn-Cu-Ni lead-free solder, and the effect of inhibiting the growth and growth of tin whiskers of a soldered joint is also very obvious.

The prior invention indicates that the addition of Ga and Nd elements simultaneously can remarkably improve the wetting property of the Sn-Ag-Cu lead-free solder when the addition amount of the Ga and the Nd elements is in certain specific ranges. However, studies have not noticed that the negative effect of rare earth additions is the "tin whisker growth". However, once the solder joint grows up and tin whiskers grow, short circuit and burning of the electronic device are easily caused. Through a large number of comparison tests, screening and optimization, the inventor discovers that when Ga and Nd are simultaneously added into the Sn-Cu-Ni lead-free solder, the wettability of the solder can be obviously improved, the oxidation resistance of the solder can be improved, the requirement of wave soldering can be met, and the melting temperature of the Sn-Cu-Ni solder can be obviously reduced due to the addition of Ga, so that the Sn-Cu-Ni solder can be applied to a reflow soldering process. Tests show that the addition of Ga reaches 0.4 percent, and the addition of Nd reaches 0.04 percent

When in use, the melting temperature of the Sn-Cu-Ni-Ga solder can reach the performance of Sn-3.0Ag-0.7Cu lead-free solder, the solidus temperature is about 210 ℃, the liquidus temperature is about 218 ℃, and the temperature is reduced by 9 ℃ compared with the liquidus temperature 227 ℃ of Sn-Cu-Ni.

The Sn-Cu-Ni lead-free solder containing Ga and Nd has good wetting performance, which is shown in that the wetting force is obviously increased, and the 'wetting time' is greatly lower than 1s specified by the internationally recognized IPC standard (see attached figures 1 and 2). Moreover, as can be seen from fig. 3, after the aging time of the brazing seam interface sample reaches 30 days (in the test, it is acknowledged in the industry that the aging time is used for simulating the use time of the component), the thickness of the intermetallic compound of the brazing seam interface does not change significantly (the thickness is not increased), and the tin whisker does not grow, so that the effect of inhibiting the growth and the initiation of the tin whisker of the brazed joint under the synergistic effect of Ga and Nd is very significant, and the risk of crack initiation and growth and finally cracking of a welding spot (brazing seam) caused by the growth of the intermetallic compound can be reduced; the risk of short circuit and failure of electronic devices caused by the growth and growth of tin whiskers is inhibited or eliminated, and the reliability of the soldered joint is improved.

2) Researches show the strengthening effect of As and Sb on the Sn-Cu-Ni lead-free solder, and tests prove that the adding range of As and Sb is optimized.

As shown in the research, arsenic is used as an alloy additive to produce lead shot, printing alloy, brass (for condensers), grid plate of storage battery, wear-resistant alloy, high-strength structural steel, corrosion-resistant steel and the like. Dezincification is prevented when brass contains arsenic by weight. High-purity arsenic is a raw material for producing compound semiconductors, such as gallium arsenide and indium arsenide, and is also a doping element for semiconductor materials, such as germanium and silicon, and these materials are widely used as diodes, light emitting diodes, infrared emitters, lasers, and the like. Arsenic compounds are also used in the manufacture of pesticides, preservatives, dyes and pharmaceuticals, among others. The expensive cupronickel alloy is made by combining copper and arsenic. Arsenic is also used for manufacturing cemented carbide, and dezincification and the like can be prevented when brass contains a trace amount of arsenic. With respect to the role of antimony, it has been reported in the literature that antimony alloyed with lead and tin can be used to improve the performance of solder materials, bullets and bearings, and antimony has found its wide use in emerging microelectronic technologies.

Arsenic with the purity of 99.95% in YS/T68-2014 arsenic and antimony in antimony ingot with the purity of 99.90% in GB/T1599-. The rule of influence of adding As and Sb into Sn-Cu-Ni lead-free solder on inhibiting the thickness increase of intermetallic compounds at the brazing seam interface is discovered by a sequential experimental design method, and the adding range of As and Sb is preliminarily determined.

Although As has a remarkable strengthening effect on copper alloys, and Sb also has a good effect of adjusting the performance of tin-lead solder in Sn-Pb solder, based on the purpose of the invention, the invention aims to invent a high-reliability Sn-Cu-Ni solder, so that the aim of effectively inhibiting the thickness increase of intermetallic compounds at the brazing seam interface and effectively inhibiting the growth of tin whiskers of soldered joints is fulfilled, in the element combination, the adding amount of As is in a range of 0.003-0.008%, and the adding amount of Sb is in a range of 0.014-0.020%.

3) The addition ranges of Ga, Nd, As and Sb are optimized and determined.

Compared with the existing lead-free solder added with rare earth elements, in the alloy system related by the invention, the favorable addition range of the rare element Ga is very narrow and is only in the range of 0.4-0.6%; although the addition of Nd from 0.01% to 0.25% can have a beneficial effect on the wettability of Sn-Cu-Ni-Ga solders As shown in FIGS. 1 and 2, the change in solder properties after the addition of the strengthening elements As, Sb is highly "irregular". From the viewpoint of ensuring the performance of the brazing filler metal and the reliability of a brazed joint, the addition range of Ga is controlled to be 0.4-0.6%, the addition range of Nd is determined to be 0.04-0.06%, and Ga: Nd: 10: 1 is controlled, so that the brazing filler metal has good wetting performance, the thickness of intermetallic compounds at a brazing seam interface can be effectively inhibited from increasing, and the growth of tin whiskers of the brazed joint can be effectively inhibited.

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

Example 1

The Sn-Cu-Ni lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.45% of Cu, 0.5% of Ni, 0.003% of As, 0.020% of Sb, 0.4% of Ga, 0.04% of Nd and the balance of Sn. Wherein the mass ratio of Ga to Nd satisfies Ga: Nd: 10: 1.

The solidus temperature of the Sn-Cu-Ni lead-free solder containing Ga and Nd obtained by the component ratio is about 210 ℃, and the liquidus temperature is about 218 ℃ (both considering test errors). The brazing flux has excellent wettability on a red copper plate by matching with a commercially available RMA brazing flux, and the tensile strength of a brazing seam reaches 45MPa +/-5 MPa.

FIG. 3 shows that after aging for 720 hours (30 days), the intermetallic compound of the soldering seam interface of the Sn-Cu-Ni lead-free solder containing Ga and Nd has no obvious change and no tin whisker is generated, which shows that the reliability of the soldering joint (soldering seam) is obviously improved.

Example 2

The Sn-Cu-Ni lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 1.1% of Cu, 0.05% of Ni, 0.008% of As, 0.014% of Sb, 0.6% of Ga, 0.06% of Nd and the balance of Sn. Wherein the mass ratio of Ga to Nd satisfies Ga: Nd: 10: 1.

Example 3

The Sn-Cu-Ni lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.7% of Cu, 0.15% of Ni, 0.005% of As, 0.016% of Sb, 0.5% of Ga, 0.05% of Nd and the balance of Sn. Wherein the mass ratio of Ga to Nd satisfies Ga: Nd: 10: 1.

Example 4

The Sn-Cu-Ni lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.85% of Cu, 0.35% of Ni, 0.006% of As, 0.018% of Sb, 0.46% of Ga, 0.046% of Nd and the balance of Sn. Wherein the mass ratio of Ga to Nd satisfies Ga: Nd: 10: 1.

Example 5

The Sn-Cu-Ni lead-free solder containing Ga and Nd comprises the following components in percentage by mass: 0.65% of Cu, 0.3% of Ni, 0.004% of As, 0.017% of Sb, 0.55% of Ga, 0.055% of Nd and the balance of Sn. Wherein the mass ratio of Ga to Nd satisfies Ga: Nd: 10: 1.

Claims

1. The Sn-Cu-Ni lead-free solder containing Ga and Nd is characterized by comprising the following components in percentage by mass: 0.45-1.1% of Cu, 0.05-0.5% of Ni, 0.003-0.008% of As, 0.014-0.020% of Sb, 0.4-0.6% of Ga, 0.04-0.06% of Nd and the balance of Sn; wherein the mass ratio of Ga to Nd is 10: 1.