The Sn-Zn-Bi-Cr alloy lead-free solder
Technical field
What the present invention relates to is a kind of scolder that belongs to technical field of electronic materials, specifically, is a kind of Sn-Zn-Bi-Cr alloy lead-free solder.
Background technology
At present, the lead-free solder that can use mainly contains Sn-Ag system and Sn-Zn is or the ternary or the quaternary alloy scolder that derive from as base with these two kinds of alloys.But Sn-Ag is a scolder with traditional leaded Sn-Pb is that scolder is compared, and fusing point exceeds nearly 40 ℃, and price improves 2 times, and with the poor compatibility of existing equipment, technology, exist many shortcomings that self are difficult to overcome.In contrast to this, the Sn-Zn series lead-free solder because its fusing point is scolder near Sn-Pb, has higher mechanical strength, can compatible existing processes, equipment, and aboundresources, cheap, thereby get most of the attention.But there are two subject matters in present existing Sn-Zn series lead-free solder: the first since this to be Zn element reaction activity in the scolder bigger, selective oxidation easily takes place, make the easy oxidation of Sn-Zn series lead-free solder, corrosion resistance relatively poor; It two is that this is the reason of the relatively poor and alloy of scolder non-oxidizability itself, and its wetability is relatively low, and application has been subjected to some restriction.
Find by prior art documents, Young-Sun Kimetc. " Effect of compositionand cooling rate on microstructure and tensile properties of Sn-Zn-Bialloys ", Journal of a1loys and compounds, (composition and cooling velocity are to the influence of Sn-Zn-Bi alloy microstructure and ductility, " alloy and compound periodical ") Vol.352 (2003), 237-245, at Sn-Zn is to add three elements Bi in the alloy, the fusing point that can make scolder is more near the Sn-37Pb eutectic solder, and to make this be that the wetability of scolder improves.For example, add in Sn-8Zn or Sn-9Zn alloy, the Bi of 1-8% can make fusing point reduce to 186.1 ℃, and can improve its wetability.Wherein, fusing point is that 193 ℃ Sn-8Zn-3Bi solder is widely good by industry, and has obtained application in actual production.But then, still there are many problems in the Sn-Zn-Bi solder.The adding of Bi does not improve non-oxidizability and the corrosion resistance that Sn-Zn is a scolder, too much add Bi and the fragility increase also can occur, degradation phenomenon under the ductility causes bigger negative effect to the scolder mechanical performance, be difficult to the automobile that is applicable to that reliability requirement is high, the electronic product in fields such as aviation.
Summary of the invention
The objective of the invention is to overcome the deficiencies in the prior art part, a kind of Sn-Zn-Bi-Cr alloy lead-free solder is provided, make it on the basis that keeps advantages such as the original low melting point of Sn-Zn-Bi alloy, good wettability, chemical properties such as non-oxidizability, corrosion resistance and ductility and mechanical performance are greatly improved, and wetability also is further enhanced.
The present invention is achieved by the following technical solutions, and component of the present invention and mass percent thereof are: Cr is 0.005-1.5%, and Zn is 3-12%, and Bi is 0.5-12%, and surplus is Sn.
The mass percent of Cr is further defined to 0.01-1.0%.
The mass percent of Cr is further defined to 0.05-0.8% again.
Cr is stainless important composition element, has good anti-corrosion and non-oxidizability.In addition, Cr and Zn element can form the intermetallic compounds such as Znl3Cr, Zn7Cr of stability, can further play the Zn that stablizes in the scolder, reduce the effect of its reactivity.Owing to these two reasons, in the Sn-Zn-Bi scolder, introduce alloying elements cr, anti-oxidant, the corrosion resistance of scolder are improved significantly.The disperse of these intermetallic compounds in alloy simultaneously exists, but crystal grain thinning, and the metallurgical structure of change scolder has greatly improved the mechanical performances such as ductility of scolder.Have, Sn-Zn is that one of relatively poor reason of the wetability of scolder is because due to the oxide-film that a large amount of oxidations of Zn form on the surface again.Therefore, high antioxidant and corrosion resistance that Sn-Zn-Bi-Cr solder of the present invention is had have also further been improved the wetability of scolder to a certain extent.Parsing shows why this scolder has high non-oxidizability and corrosion resistance, is owing to formed the barrier layer of Cr between surperficial Zn oxide layer and base metal.In high temperature or corrosive environment, this barrier layer can reduce the activity of Zn, stops Zn to external diffusion, and then has reduced the oxide etch of Zn.
When the content of Cr in the Sn-Zn-Bi-Cr scolder during less than 0.005 (quality) %, be difficult to form the barrier layer of Cr at the near surface of scolder, antioxidant effect is obvious inadequately; When content is higher than 1.5 (quality) %, easily cause the segregation of intermetallic compound etc., this segregation makes the Cr barrier layer inhomogeneous, and sunburner has negative effect, also ductility descended wetability.When if the content of Cr is in 0.005-1.5 (quality) % scope in the control scolder, stop the Cr barrier layer of Zn oxidation even, thickness is moderate, does not have segregation phenomena to take place again, and non-oxidizability, ductility and the wetability of scolder all are improved.If the content of Cr is 0.05-0.8% in the scolder, effect so of the present invention will be in optimum state, can obtain excellent comprehensive performances.
Sn-Zn-Bi-Cr novel lead-free scolder provided by the invention can be with the preparation of a lot of methods, the direct smelting process of promptly available three kinds of direct mixed smeltings of metal, and the also available intermediate alloy such as Sn-Cr of producing earlier prepares the substep method of smelting of Sn-Zn-Bi-Cr alloy again.Because the alloy easy oxidization burning loss of Zn, Cr in the preparation, so be preferably in melting under vacuum or the protective conditions such as gas, fused salt during melting.Used raw material can be powdered pure metal, granular simple metal during melting, also can be block simple metal.When adopting the powdery metal melting, speed of melting is very fast, but scaling loss easily, and during the melting of reguline metal, smelting temperature is higher, and the time is longer, but is difficult for scaling loss, cuts both ways.
Characteristics of the present invention are by add the Cr element in the Sn-Zn-Bi alloy, make scolder when keeping advantages such as the original low melting point of Sn-Zn-Bi alloy, good wettability, the non-oxidizability of scolder, corrosion resistance improve more than 1 times, overcome the bigger shortcoming of former Sn-Zn-Bi alloy fragility, make ductility improve 5-100%, simultaneously because the improvement of non-oxidizability and corrosion resistance, wetability has also obtained further raising, and wetting time shortened 0.5-2.5 second by average 3 seconds of the Sn-Zn-Bi solder.Scolder provided by the invention can be used in a lot of fields, as makes welding rod, welding wire, weld tabs, soldered ball, welding powder, soldering paste etc.Particularly owing to the reduction of its fragility of scolder of the present invention, it is lower to be expected to be used for requirement scolder fusing point, and easily the products such as mobile phone of damage are fallen in landing.
The specific embodiment
Embodiment 1
Component of the present invention and mass percent thereof are: Cr:0.005%, and Zn:3%, Bi:0.5%, surplus is Sn.
Various performance measurements show: the fusing point of this scolder, tensile strength and Sn-3Zn-0.5Bi solder are basic identical, but at 85 ℃, humidity be under 85% the etching condition after experiment in 24 hours, corrosion pit reduces to some extent, after resistance to high temperature oxidation experiment in 250 ℃ * 25 hours, glossiness slightly is better than the Sn-3Zn-0.5Bi scolder.And fragility descends to some extent, and ductility improves about 5% than Sn-3Zn-0.5Bi scolder, and wetting time is 2.5 seconds.
Embodiment 2
Component of the present invention and mass percent thereof are: Cr:0.01%, and Zn:8%, Bi:3%, surplus is Sn.
Various performance measurements show: the fusing point of this scolder, tensile strength and Sn-8Zn-3Bi solder are basic identical, but at 85 ℃, humidity be under 85% the etching condition after experiment in 24 hours, corrosion pit further reduces, and after resistance to high temperature oxidation experiment in 250 ℃ * 25 hours, glossiness also is better than the Sn-8Zn-3Bi scolder.And fragility descends, and ductility improves 10-20% than Sn-8Zn-3Bi scolder.Wetting time is 2.0 seconds.
Embodiment 3
Component of the present invention and mass percent thereof are: Cr:0.05%, and Zn:8%, Bi:3%, surplus is Sn.
Various performance measurements show: the fusing point of this scolder, tensile strength and Sn-8Zn-3Bi scolder are basic identical.At 85 ℃, humidity be under 85% the condition after experiment in 24 hours, corrosion pit obviously reduces, and after resistance to high temperature oxidation experiment in 250 ℃ * 25 hours, keeps former glossy, anti-oxidant still substantially, corrosion resistance is better than the Sn-8Zn-3Bi scolder far away.And fragility obviously descends, and ductility improves 50-70% than Sn-8Zn-3Bi scolder.Wetting time is 0.5 second.
Embodiment 4
Component of the present invention and mass percent thereof are: Cr:0.3%, and Zn:8%, Bi:3%, surplus is Sn.
Various performance measurements show: the fusing point of this scolder, tensile strength and Sn-8Zn-3Bi scolder are basic identical.At 85 ℃, humidity be under 85% the condition after experiment in 24 hours, corrosion pit obviously reduces, and after resistance to high temperature oxidation experiment in 250 ℃ * 25 hours, keeps former glossy, anti-oxidant still substantially, corrosion resistance is better than the Sn-8Zn-3Bi scolder far away.And fragility obviously descends, and ductility improves 70-100% than Sn-8Zn-3Bi scolder.Wetting time is 0.5 second.
Embodiment 5
Component of the present invention and mass percent thereof are: Cr:0.8%, and Zn:12%, Bi:12%, surplus is Sn.
Various performance measurements show: the fusing point of this scolder, tensile strength and Sn-12Zn-12Bi scolder are basic identical.At 85 ℃, humidity be under 85% the condition after experiment in 24 hours, corrosion pit obviously reduces, and after resistance to high temperature oxidation experiment in 250 ℃ * 25 hours, keeps former glossy, anti-oxidant still substantially, corrosion resistance is better than the Sn-12Zn-12Bi scolder far away.And fragility obviously descends, and ductility improves 50-70% than Sn-12Zn-12Bi scolder.Wetting time is 2.0 seconds.
Embodiment 6
Component of the present invention and mass percent thereof are: Cr:1.0%, and Zn:12%, Bi:12%, surplus is Sn.
Various performance measurements show: the fusing point of this scolder, tensile strength and Sn-12Zn-12Bi scolder are basic identical.At 85 ℃, humidity be under 85% the condition after experiment in 24 hours, no corrosion pit, and after resistance to high temperature oxidation experiment in 250 ℃ * 25 hours, still basic maintenance is former glossy, anti-oxidant, corrosion resistance is better than the Sn-12Zn-12Bi scolder far away.Compare with the Sn-12Zn-12Bi scolder, fragility obviously descends, and ductility improves 10-20%, wetting time is 2.5 seconds.
Embodiment 7
Component of the present invention and mass percent thereof are: Cr:1.5%, and Zn:12%, Bi:12%, surplus is Sn.
Various performance measurements show: the fusing point of this scolder, tensile strength and Sn-12Zn-12Bi scolder are basic identical.At 85 ℃, humidity be under 85% the condition after experiment in 24 hours, do not have obvious corrosion pit, and after resistance to high temperature oxidation experiment in 250 ℃ * 25 hours, keep former glossy, anti-oxidant still substantially, corrosion resistance is much better than the Sn-12Zn-12Bi scolder.Compare with the Sn-12Zn-12Bi scolder, fragility descends, and that ductility improves is about 5%, wetting time is 2.5 seconds.