CN101392337B

CN101392337B - Low melting point lead-free solder alloy

Info

Publication number: CN101392337B
Application number: CN2008102187801A
Authority: CN
Inventors: 张宇航; 赵四勇; 戴贤斌; 蔡志红; 韩振峰
Original assignee: Guangzhou Research Institute of Non Ferrous Metals
Current assignee: Guangzhou Research Institute of Non Ferrous Metals
Priority date: 2008-10-31
Filing date: 2008-10-31
Publication date: 2010-09-08
Anticipated expiration: 2028-10-31
Also published as: CN101392337A

Abstract

The invention discloses a lead-free solder alloy with a low melting point, which is composed of the following components: 53.0wt percent to 65.0wt percent of Bi, 0.02wt percent to 0.5wt percent of Cu, 0.01wt percent to 0.43wt percent of Ag, 0.01wt percent to 0.4wt percent of Ni, 0.001wt percent to 0.6wt percent of RE, and Sn as the rest. The invention is the lead-free solder alloy of a low melting point that can improve brittleness, enhance tractility and plasticity, be easy to be manufactured into thread-solder and have high reliability of welding spots. The lead-free solder alloy with a lowmelting point is applied to the welding of heat sensitive components and parts and the step soldering of electronic components and parts.

Description

A kind of low melting point lead-free solder alloy

Technical field

The present invention relates to the low and unleaded welding flux alloy of a kind of low-melting leadless welding alloy, particularly fusing point.

Background technology

In electron trade; solder is widely used in the welding of thermo-responsive components and parts in the electron trade; and the step brazing of electronic devices and components (secondary welding), also be applied in the industries such as TV tuner, fire alarm, temperature control element, air-conditioning protector.

Traditional low-temperature brazing filler metal is ternary or the quad alloy of forming with metals such as Sn, Pb, Bi, Cd, and wherein Pb, Cd belong to the poisonous metal element.Progress along with scientific development and society has proposed clear and definite requirement and index to the environmental-protecting performance of electronic product, in the electronic market, by the electronic devices and components of environmental certification, is not eliminated gradually.Particularly from July 1st, 2006, WEEE instruction (" Electrical and Electronic product abandonment thing ") that European Union formulates and RoHS instruction (" be limited in and use some objectionable impurities in the electric/electronic device ") are formally implemented, this instruction is defined in must sell lead-free product to the european consumer after this date, and this will seriously limit and influence the outlet of China to Electrical and Electronic products such as area such as Europe and national information of carrying out, household electrical appliances, medical treatment.China issued on February 28th, 2006, " the electronics and IT products pollution control management way " implemented on March 1st, 2007 determined the control of lead, mercury, cadmium, sexavalent chrome and the Polybrominated biphenyl (PBB) that contains in the electronics and IT products, polybromodiphenyl ether (PBDE) the six kinds of hazardous and noxious substances of etc.ing is adopted the mode of directory management, and propelling is by easy stages forbidden or limited its use.

Since the eighties in 20th century, obtaining certain progress aspect the lead-free solder that substitutes 183 ℃ of Sn-Pb eutectic alloys, as lead-free solders such as Sn-Ag, Sn-Ag-Cu, Sn-Zn, Sn-Bi, but to being applied to the low melting point lead-free solder alloy in the above-mentioned field, the leadless welding alloy fusing point of Sn-Ag, Sn-Ag-Cu, Sn-Zn series too high (all more than 200 ℃) is an alloy for Sn-Bi, and eutectic composition is Sn-58Bi, fusing point is 139 ℃, and application prospect is extensive.

For Sn-Bi is low-temperature brazing filler metal, in the alloy of eutectic composition, Bi content is bigger, because Sn-Bi is the feature of solidifying of alloy, the Bi element is understood a large amount of segregations in crystal boundary, the fragility of Bi itself, can cause alloy also to become very crisp, poor ductility, plasticity descends rapidly, is difficult to become brazing wire by the plastic forming processes.Volumetric expansion can take place in metal Bi when solidifying, so metal Bi can be used as " the cold alloy that rises ".When welding flux alloy when solidifying because a large amount of segregations in the Bi of crystal boundary element the phenomenon of " cold rising " take place, cause deformation and make the phenomenon that solder joint and pad are peeled off, cause the reliability variation of solder joint.

Summary of the invention

The objective of the invention is to overcome the defective of existing low temperature lead-free solder alloy, a kind of fragility of improving is provided, improve ductility and plasticity-, be easy to make thread scolder, and the high low melting point lead-free solder alloy of welding spot reliability.

Welding flux alloy of the present invention, by weight percentage, composed of the following components: Bi53.0～65.0, Cu 0.02～0.5, and Ag 0.01～0.43, and Ni 0.01～0.4, and RE 0.001～0.6, and surplus is Sn.RE is a mixed rare-earth elements.

Because the Bi content in the Sn-58Bi eutectic solder alloy is bigger, limited solid solution can only take place with Sn in Bi, and oversaturated Bi easily separately exists in and forms crisp hard phase outside the matrix, causes welding flux alloy hardening and fragility to increase, and solder joint is easily peeled off.Alloy of the present invention adds alloying elements such as Cu, Ag, Ni under the prerequisite little to the fusing point of alloy and cost impact.Because the effect of solution strengthening causes the matrix cystal dot matrix to distort, and forms bigger internal stress, produce strengthening effect, and Bi is distributed on the matrix disperse more; The alloy element of Tian Jiaing can form Sn-Cu, Sn-Ag and Sn-Ni intermetallic compound (IMCs) with Sn simultaneously, become " the activation particle " that promote the liquid alloy heterogeneous nucleation, increased nucleation rate, and the IMCs disperse that generates ground is distributed on the crystal boundary, and prevention crystal grain is further grown up, refinement crystal grain, the microstructure of alloy is more even, exquisiteness has been improved the plasticity of welding flux alloy, has improved the reliability of solder joint.

RE also can promote the forming core in the alloy graining process as a kind of surface active element, and welding flux alloy is played metamorphic homogenization, makes alloy structure refinement, evenly can improve the plasticity of welding flux alloy, reduces the difficulty that welding flux alloy becomes silk.Improve the timeliness military service intensity of brazed joint simultaneously, prolonged the work-ing life of solder joint.But along with the increase of RE content, can generate hard crisp rare earth intermetallic compound, worsen the performance of welding flux alloy, so RE content is 0.001～0.6%, be preferably 0.001～0.5%, further be 0.001～0.3%.

As required, also can add among a small amount of Zn, Al, P, Ga, Sb, In, Cr, Fe, Mn or the Co one or more.

Embodiment

In the preparation process of alloy of the present invention, because the increasing of the fusing point difference of Sn, Cu, RE, Ni, and the easy scaling loss of RE, in order accurately to control alloying constituent, guarantee alloy mass, adopted the form of master alloy to add various alloying elements, the preparation method is as follows:

The Sn-Cu master alloy: 99.95% smart Sn is joined in the plumbago crucible, heats up in the fusing back, to suitable temperature range, adds 99.95% pure Cu.The mass percent of smart Sn and pure Cu stirs by preparation in 90: 10, leaves standstill, and is cast into that to contain that Cu measures be 10% Sn-Cu intermediate alloy ingot.

The Sn-RE master alloy: 99.95% smart Sn is joined in the plumbago crucible, and heating up in the fusing back, to suitable temperature range, adds high-purity RE.The mass percent of smart Sn and RE stirs by preparation in 97: 3, leaves standstill, and is cast into that to contain that RE measures be the intermediate alloy ingot of 3% Sn-RE.

The Sn-Ni master alloy: 99.95% smart Sn is joined in the plumbago crucible, and heating up in the fusing back, to suitable temperature range, adds pure Ni.Smart Sn prepares by 97: 3 with the mass percent of Ni, stirs, and leaves standstill, and is cast into ni content and is 3.0% Sn-Ni intermediate alloy ingot.

Calculate the good Sn-Cu intermediate alloy ingot of weighing, Sn-Ni intermediate alloy ingot, Sn-RE intermediate alloy ingot by alloying constituent, the alloying constituent for preparing is adopted the crucible induction melting, the fused salt mixt of charcoal or LiCl and KCl covers.Be stirred well to fully fusing, leave standstill for some time, casting, product form such as the strip that obtains, spherical, paste.Or after melting finishes, the control melt temperature pours into ingot blank in the time of 190～230 ℃, the solidification cooling that as far as possible keeps alloy〉100 ℃/s, because rate of cooling increases, condensate depression increases, promote forming core, crystal grain thinning, the regional segregation tendency reduces very big condensate depression, make the composition of primary crystallization phase of alloy near the original composition of scolder, can access the composition uniform tissue like this.Ingot blank is carried out hot extrusion or the follow-up thread product that is drawn into Φ 0.8～2.0mm again at 60～90 ℃.Embodiment sees Table 1.

The elemental composition of table 1 embodiment

Annotate: surplus is Sn

To the welding flux alloy in the foregoing description, adopt the method for dsc (DSC) to measure fusing point.Measure the method for Plastic Deformation, the most frequently used is the mechanicl test method, can determine in test two plasticity index---unit elongation and relative reduction in area, unit elongation is represented the maximum deformation quantity before metal ruptures on the tensile axis direction, relative reduction in area is reflected in the plasticity index under unidirectional tensile stress and the three-dimensional action of pulling stress.According to the method among the JIS-Z-3198 of Japanese Industrial Standards, the unit elongation and the relative reduction in area of beta alloy on electronic universal drawing machine GP-TS2000/100KW.Test-results is as shown in table 2:

Fusing feature, unit elongation and the relative reduction in area of table 2 embodiment

Embodiment alloy in the last table and contrast Sn-58Bi alloy prepare under identical conditions and test.As can be seen from the table, the interpolation alloying element is not very big to the beginning temperature of fusion (being solidus curve) and fusing end temp (the being liquidus line) influence of alloy, and the assurance alloy is realized welding smoothly under cold condition.The unit elongation of embodiment alloy and relative reduction in area all are greatly improved than the Sn-58Bi alloy, illustrate that the alloy element that adds has played crystal grain thinning, have prevented a large amount of segregations of Bi, have improved the plasticity of alloy, have improved the reliability of solder joint.

The present invention is not limited to above-mentioned case study on implementation, and in actual application, the different performance requriementss and different use occasions of different field that can basis selected the alloying constituent in above-mentioned each case study on implementation; The perhaps heterogeneity proportioning except that above-mentioned case study on implementation, but all be no more than the scope of claims of the present patent application.

Claims

1. a low melting point lead-free solder alloy is characterized in that by weight percentage, and is composed of the following components: Bi 53.0～65.0, and Cu 0.02～0.5, and Ag 0.01～0.43, and Ni 0.01～0.4, and RE 0.001～0.6, and surplus is Sn.