CN101288923A - Low copper hypoeutectic Sn-Cu leadless solder - Google Patents

Abstract

The invention provides a low-copper hypoeutectic Sn-Cu lead-free solder, which is composed of the components according to weight percentage: 0.01 to 0.69 percent of Cu, 0.001 to 0.1 percent of Ni, 0.003 to 0.3 percent of Sb, 0.001 to 0.2 percent of Bi and/or In, 0 to 0.01 percent of P, 0 to 0.03 percent of Ge and the rest of Sn. The total amount of the microelements such as Ni, Sb, Bi, In, P and Ge added in the solder is not more than 0.5 percent. The solder of the invention has the advantages of excellent oxidation resistance, wettability and overflow property under high-temperature melting state, thus obviously reducing the waste of the solder, greatly improving the welding point formation and reducing the soldering defect. The invention is especially applicable to wave soldering, dip soldering, manual soldering and reflow soldering of electronic products.

Description

A kind of low copper hypoeutectic Sn-Cu leadless solder

Technical field

The present invention relates to the lead-free brazing that the little connection of electronic product in the field of electronic materials is used.

Background technology

For a long time, the tin-based solder that contains Pb is mainly used in little connection of electronic product.In recent years, the world has started the unleaded tide of electronic product, and wherein the Sn-Cu series leadless solder is because of better mechanical property, and cost is relatively low, and electronic product had favorable compatibility and is subjected to electron trade users' favor.

At present, the Sn-Cu lead-free brazing that electron trade is used mainly is eutectic or hypereutectic Sn-Cu alloy, and when at high temperature carrying out soldering, the non-oxidizability, wetability, the cross flow that exist liquid solder are relatively poor, and bridging easily takes place solder joint, draw defective such as point.Especially in immersed solder, wave-soldering process, except that producing the problems referred to above,, also can cause the violent rising of solder fusing point and make soldering that difficulty take place owing to the fluctuation of solder composition.In order to improve the performance of Sn-Cu lead-free brazing, carried out a large amount of research both at home and abroad, but most improvement that all concentrates on solid alloy tissue and mechanical property, and the research of liquid towards solder performance is less.For example Chinese patent ZL200410022637.7 has reported a kind of Sn-Cu leadless electronic brazing filler metal, though its physical property and mechanical performance are made moderate progress, but its processing performance is promptly still relatively poor aspect the non-oxidizability under molten condition, wetability, cross flow and the solder joint mouldability, this not only causes the serious waste of solder in the use, the more important thing is the reliability that causes that brazing defect is more, weld seam/point mass is relatively poor and have a strong impact on electronic product.

Summary of the invention

The objective of the invention is to improve the processing performance of Sn-Cu lead-free brazing, a kind of low copper hypoeutectic Sn-Cu leadless solder that has excellent anti-oxidation characteristics, wetability, cross flow and solder joint mouldability under high temperature fused state is provided.

A kind of low copper hypoeutectic Sn-Cu leadless solder that the present invention proposes is made up of following component by mass percent: Cu 0.01～0.69wt%, Ni 0.001～0.1wt%, Sb 0.003～0.3 wt%, Bi and/or In 0.001～0.2 wt%, P 0～0.01wt%, Ge 0～0.03 wt%, remainder is Sn.This solder is further characterized in that the total amount of trace elements such as the Ni that is added, Sb, Bi, In, P, Ge is no more than 0.5 wt% at the most in described solder.

The present invention does not adopt eutectic or hypereutectic Sn-Cu alloy, and Cu content component is designed to be lower than eutectic content, it be the reasons are as follows: by the Sn-Cu binary phase diagraml as can be known, Cu=0.7wt% is an eutectic point, eutectic temperature is 227 ℃, and eutectic structure is by β-Sn (232 ℃ of fusing points) and Cu ₆Sn ₅(η phase, fusing point are 415 ℃) formed, and Cu is with intermetallic compound Cu ₆Sn ₅Form is dispersed in the Sn matrix.Therefore, we know that Cu＜0.7wt% is a hypoeutectic, and Cu＞0.7wt% is a hypereutectic alloy.The applicant finds by further investigation, when Cu＞0.7wt% promptly consists of when hypereutectic Compound C u between the excessive refractory metal that exists in the Sn-Cu alloy ₆Sn ₅Can significantly reduce the flowability of liquid solder, simultaneously the Cu that can preferentially separate out at liquid solder and parent material interface ₆Sn ₅Compound will seriously reduce the wetability of solder, keeps the wetability of liquid solder and the penetrating power of butt welded seam as desire, then must the rising temperature.In the soldering connection procedure of modern electronic product, since enter weld seam/the temperature of liquid solder can not continue to rise and can only descend, and in the use of solder, especially in immersed solder, wave-soldering process, Sn is than the easy oxidation of Cu, so the Cu component always increases in the solder, this will further increase Compound C u between refractory metal ₆Sn ₅Content and make the liquid solder degradation.The present invention will be wherein the Cu component be limited to the hypoeutectic content range, its purpose one is that the liquid solder solidification temperature significantly rises when preventing Cu＞0.7wt%; The 2nd, reduce Cu in the liquid solder ₆Sn ₅The content of compound, the flowability of raising liquid solder; The 3rd, avoid preferentially separating out Cu at the interface of liquid solder and mother metal ₆Sn ₅Compound and cause wetting decline, and consequent grain coarsening and solder joint distortion.

In order further to improve the performance of liquid low copper hypoeutectic Sn-Cu leadless solder at high temperature, the present invention has selected multiple trace doped element.Wherein adding micro-Sb is for the reduction that remedies Cu content flowability to be improved.Add other various trace elements such as Ni, P, In, Ge, Bi etc., purpose is the surface modification of carrying out liquid solder.The applicant further finds: the key of electronics brazing quality depends on the physical-chemical reaction at surface or interface, and the trace element doping is effective measures of improving liquid solder surface or interfacial property.Add the antioxygenic property that micro-Ni, P, Ge element can significantly improve fusion Sn-Cu alloy, wherein Ni can also change liquid solder surface compound Cu ₆Sn ₅Form, Ni dissolves in Cu ₆Sn ₅Compound can delay the formation of acicular texture phase, impel the intermetallic compound englobement, thereby can reduce compound in the liquid solder to the influence of solder flowability, make unnecessary liquid solder can fully flow out gap between the solder joint, thereby prevent that solder joint from producing bridging.Add micro-Bi, In and can reduce the surface tension of liquid solder, improve the wetability of solder, improve the cross flow of liquid solder and the ability of infiltration weld seam.But, the variation of the amount of these several trace elements also can influence the performance of solder, research repeatedly through the applicant, think that Sb, Ni, Bi, In, the micro-total amounts such as P, Ge that limit interpolation are no more than 0.5wt% at the most, its purpose is in order to form skin covering of the surface as thin as a wafer on the one hand, reducing the thickness of skin covering of the surface, also is in order to reduce the generation of high melting compound, to make liquid solder have better non-oxidizability, wetability and cross flow on the other hand.

Therefore, the advantage of this solder is to have good non-oxidizability, wetability and cross flow under high temperature fused state, can significantly reduce the waste of solder, obviously improves the solder joint moulding, reduce soldering and connect defective, be specially adapted to wave-soldering, immersed solder, manual welding and the reflow welding of electronic product.

The specific embodiment

The preparation of low copper hypoeutectic Sn-Cu leadless solder of the present invention is by two sections meltings, again through casting, or further finish through pressure processing.In first section melting, mainly carry out refinement oxide and boiling refining; in second section melting, mainly outgas and the modification refining; under vacuum or protective atmosphere, carry out ingot casting at last; or further the gained ingot casting is shaped to goods such as rod, bar, silk, plate, band, paper tinsel, sheet, ball, grain through pressure processing, or be shaped to the metal dust of preparation solder(ing) paste through atomizing.

Provide embodiments of the invention below, provide comparison simultaneously with the liquid performance indications of two kinds of Sn-Cu lead-free brazings.

Annotate: oxidation rate, wetability, rate of spread test temperature are 270 ℃; RA type brazing flux is all used in wetability, rate of spread test; Solder joint appearance test adopts range estimation to estimate.

Claims (2)

1, a kind of low copper hypoeutectic Sn-Cu leadless solder, its component is: Cu 0.01～0.69wt%, Ni0.001～0.1wt%, Sb 0.003～0.3 wt%, Bi and/or In 0.001～0.2 wt%, P 0～0.01wt%, Ge 0～0.03 wt%, remainder is Sn.

2, a kind of low copper hypoeutectic Sn-Cu leadless solder as claimed in claim 1 is characterized in that: the total amount of the Ni of described interpolation, Sb, Bi, In, P, Ge trace element is no more than 0.5wt% at the most.