WO1993015870A1

WO1993015870A1 - Solder wire

Info

Publication number: WO1993015870A1
Application number: PCT/CA1992/000057
Authority: WO
Inventors: Karl Frederick Seelig
Original assignee: American Iron & Metal Company Inc./La Compagnie Americaine De Fer Et Metaux Inc.
Priority date: 1992-02-11
Filing date: 1992-02-11
Publication date: 1993-08-19

Abstract

Solder wire (10) having an outer metallic wall structure (12) of a metal composition, surrounding a core mass (16) of metal particles (18); suitably the metal particles (18) are dispersed in a solder flux (20) forming a cream or paste; the metal particles (18) and the metal composition together form a solder composition, at a soldering temperature; in this way metals and alloys which are hard and/or brittle and can not be manufactured, without varying degrees of difficulty, into a wire form, can be employed in a solder wire. Additionally solder wire can be manufactured containing a toxic metal such as lead, but which can be safely handled, by employing the toxic metal as a component of the core mass (16) and not as a component of the metallic wall structure (12).

Description

SOLDER WIRE TECHNICAL FIELD

* This invention relates to novel solder

5 wires, a process for producing the solder wires and a -* soldering method utilizing the solder wires.

BACKGROUND ART

Soldering is a technique for joining metal parts which is typically carried out utilizing a solid 10 wire of solder metal, which is heated to a temperature at which it melts, and a flux. The flux cleans the metal surfaces of the metal parts in the regions in which the metal parts are to be joined with the solder metal; typically the flux reduces metal oxide surface 15 coatings on the metal parts to leave a clean metal surface.

Flux-cored solder wires have also been developed in which a hollow wire of the solder metal is filled with the flux. 20 Traditionally lead and lead alloys have been the most popular choices for solder metals, because lead has a relatively low melting point; and lead alloys can be formed of suitably low melting point. In recent years concerns as to toxicity problems 25 associated with the handling of lead and lead alloys has lead to a search for alternative solder metals.

Many metals and alloys which have properties which would make them suitable as solder metals can not, as a practical matter, be employed in the form of

30 solder wires because they can not be worked or processed to produce an appropriate wire form.

Solder creams or pastes are also known in

_ which a solder metal or alloy, in a fine, part culate form is dispersed in a flux base carrier. Solder

35 creams and pastes are employed in forming soldered joints for electrical connections on electrical/electronic circuit boards. The solder cream or paste is printed in a required pattern on the circuit board. Electrical connecting elements are contacted with the printed pattern at desired sites of electrical connection and the sites are heated to melt the fine particles which coalesce to form the solder joint; the flux base carrier of the cream or paste performs its normal flux function.

Nevertheless there remain limitations as to the metals and alloys which can be employed as solders for different applications and it would be advantageous if a wider range of metals and alloys were available for different soldering requirements; and so as to make available substitutes for lead. DISCLOSURE OF THE INVENTION

In accordance with the invention there is provided a solder wire which permits great flexibility in the selection of the solder metals or alloys; more especially the invention permits the use of many metals in solder wires which heretofore could not be employed in solder wires because of their brittleness, high melting point, non-extrudability, non-drawability or other characteristics making them unsuitable for wire production. Furthermore the invention permits the use of lead or other potentially toxic metals in solder wires while reducing or eliminating contact between workers and the lead or other toxic metal.

In accordance with the invention a solder wire comprises an elongate rod having an outer metallic wall structure of a metal composition, surrounding a mass of metal particles; the metal composition is one which is formable into the outer wall structure, and which forms a solder composition with the metal particles, at a soldering temperature. In particular the outer wall structure has one or more longitudinally extending interior passages, which extend substantially the length of the rod and these passages are filled with the mass of metal particles so that air pockets or voids are substantially excluded from the interior of the rod.

Thus the rod may be in the form of a tubular member or housing having a single longitudinally extending interior passage filled with the mass of metal particles.

The mass of metal particles may consist solely of metal particles, or protective coated metal particles, or it may comprise such particles dispersed in, mixed with or coated with a solder flux. If the mass consists of the metal particles, then a separate flux is required when employing the solder wire to form a solder joint

In another aspect of the invention there is provided a process for producing a solder wire which comprises forming an elongate member having an outer metallic wall structure of a metal composition, and at least one longitudinally extending interior passage extending substantially the length of the member; filling the at least one interior passage with a mass of metal particles, and drawing said member to produce an elongate rod of reduced cross-sectional dimension; the metal composition being one which forms a solder composition with the metal particles, at a soldering temperature. In still another aspect of the invention there is provided a method of forming a solder joint between adjacent metal parts which comprises soldering the metal parts with the solder wire of the invention as described hereinbefore. DESCRIPTION OF PREFERRED EMBODIMENTS i) Wall Metal Composition

The metal composition of the outer metallic wall structure is, in particular, any metal or metal alloy desired in a solder composition, which can be formed into such wall structure. Furthermore, the metal composition should be such that the wall structure is stable and will neither collapse nor break during normal handling of the solder wire, which includes winding the wire on a spool.

More particularly the metal composition is selected from metals and metal alloys which are workable, more especially extrudable and drawable such that an elongate tubular member can be extruded from a billet of the metal composition, and such tubular member can be subsequently drawn, typically in successive drawing operations to a thin tubular rod.

Preferably the metal composition will not include a toxic metal such as lead, cadmium or arsenic. If these metals are required in the solder composition they can be included in the metal particles. In this way persons handling the solder wire avoid contact with toxic metals. ii) Metal Particles The metal particles employed in the core or interior of the wire are selected to produce a desired solder composition with the metal or metal alloy of the wall structure.

Typical metals for the metal particles include antimony, tin, copper, arsenic, cadmium, bismuth, lead, silver, indium, aluminium, zinc, gold, gallium and germanium and alloys of two or more of these metals. It will be recognized that this group includes metals and alloys which can be employed in the fabrication of the wall structure; and in this regard it should be understood that while there are restrictions on the selection of metals and metal alloys for forming the wall structure, there is no restriction on the choice of metals or metal alloys for the interior mass, other than that particles of the metal or metal alloy form a solder composition with the metal or metal alloy of the wall structure.

A particular advantage of the invention is that it permits use of metals or metal alloys in the final solder composition which can not be worked, such as by extrusion and drawing to form a solid or hollow solder wire. Such metals and alloys can be employed in the metal particles.

Furthermore toxic metals such as lead, cadmium and arsenic which may be desired in the solder composition can be omitted from the metal composition of the wall structure and included in the metal particles so that personnel handling the solder wire either during manufacture or as users in soldering operations, do not come into hand contact with the toxic metals. In the case of a lead/indium alloy the wall would necessarily be composed of lead.

In a further preferred embodiment the composition of the metal particles may be the same or similar to the metal composition of the wall structure, and in such case the metal particles may be exploited to alter, in a desired manner, the rheological characteristics of a solder flux in which they are dispersed, and which forms part of the mass in the interior of the solder wire. The metal particles suitably are of fine, particulate form having a particle size up to about 200 microns; in general less than 2%, by weight, of the particles will have a particle size less than 1 micron. iii ) Flux

The mass of metal particles suitably comprises such particles dispersed in, mixed with or coated by a flux. Suitable solder fluxes are well known to persons in the soldering art, and the present invention is not concerned with the precise nature of the flux. The flux will be selected, in accordance with known practice, having regard to the nature of the metals to be soldered and the nature of the solder composition.

Fluxes are typically creams or pastes based on resins, rosins, organic acids, inorganic acids, glycols, starches, amines, salts, oxides, reducing agents, wetting agents and combinations thereof. iv) Core mass

The mass of metal particles which forms the core of the solder wire may consist of the metal particles alone or dispersed in, mixed with or coated by, the flux.

The core mass should substantially fill the interior of the wire so that there are no voids defining air spaces which might interfere with the soldering or produce sites of weakness in the soldered joint. The core mass may suitably comprise a cream or paste of the metal particles and solder flux. v) Solder wire

The solder wire suitably has a diameter, determined for a wire of generally circular cross- section, less than 20 mm and typically less than 5 mm. The wire may have a single core or longitudinal passage filled with core mass, or it may have a multiplicity of cores or longitudinal passages filled with the core mass. Typically there may be 1 to 7 cores or longitudinal passages and especially 1, 3 or 5. In the case of a tubular solder wire having a single core passage filled with the core mass, the wall thickness of the tubular wire will suitably be at least 0.024 mm. The upper limit of the wall thickness is dictated by the requirements that the solder wire be handleable and have a flexibility such that it can be packaged, as by winding on a spool. The lower limit of the wall thickness is dictated by the requirements that the wall be a stable, self- supporting structure, under normal handling conditions, that the wall be continuous and free of openings to the interior core mass, and the limitations imposed by manufacturing techniques such as wire drawing.

The metal composition of the outer metallic wall structure and the metal particles of the core mass together form an alloy capable of forming a solder joint at a soldering temperature. It will be understood that the soldering temperature will depend on the composition of the alloy which is to be formed, and should be lower than the melting temperature of the metal parts to be soldered.

The solder wire of the invention has significant value in that it permits use of solder alloys that manufacturing procedures can not produce in wire form.

By way of example only the solder wire of the invention offers the following possibilities: i) tin-lead cored solder wires forming a 63/37 alloy (63% Sn; 37% Pb) for electronic soldering. Tin is employed as the metal of the outer metallic wall structure with the lead being incorporated in a flux cream in the core of the wire. Hand soldering can be carried out without the need for the soldering operator to come into contact with toxic lead; ii) alloys that are "lead free", are often too hard and/or brittle to be drawn into fine diameter wires can be utilized in solders by extruding an outer wall structure of, for example, tin, in accordance with the invention, and filling the interior surrounded by the wall structure with a flux cream containing particles of bismuth, bismuth alloys, zinc, zinc alloys, indium, indium alloys, and other metal combinations and drawing the wire to a desired diameter. The resulting product will melt at a lower temperature than tin-lead alloys, will provide good wetting of metal surfaces to be soldered, and is non- toxic. In this way a lead-free solder is provided suitable for use in the electronics industry or in other applications such as lamp manufacturing, for example, which solder can be employed at lower soldering temperatures than conventional tin-lead solders, thereby reducing exposure of heat sensitive materials to high temperatures; iii) indium alloy creams and pastes have a short shelf life and consequently are not used to a great extent. In accordance with the invention, lead or tin or their alloys can be employed to produce the outer wall structure of the solder wire, with a core mass containing particles of metal or alloys of indium. This has particular application where temperature or gold compatibility are required, or where thermal incompatibilities must be overcome. BRIEF DESCRIPTION OF DRAWINGS

The invention is illustrated in particular and preferred embodiments by reference to the accompanying drawings, in which:

Fig. 1 is a schematic view of a solder wire of the invention;

Fig. 2 in an end view of the solder wire of Fig. 1; and Fig. 3 is a schematic illustration of the manufacture of the solder wire of Fig. 1, in accordance with the invention. MODES FOR CARRYING OUT THE INVENTION With further reference to Figs. 1 and 2, a solder wire 10 has an elongate tubular wall 12 having a hollow core 14 filled with a core mass 16.

The core wall mass 16 comprises metal particles 18 dispersed in a flux 20. With further reference to Fig. 3, there is illustrated schematically the manufacture of solder wire 10.

In the manufacture of solder wire 10, a billet 30 of the metal composition which is to form tubular wall 23 is fed into an extruder 32 having a hollow die 34. Die 34 has an inlet 36 to die hollow interior 38, which inlet 36 communicates via line 40 with a source 42 of core mass 16. A pump 44 is included in line 40. The billets 30 are extruded in extruder 32 as a continuous tube 46 about die 34 while core mass 16 material is pumped by pump 44 from source 42 along line 40, through inlet 36 and thence into the hollow interior of tube 46. The continuous tube 46, filled with core mass 16 material is drawn to successively smaller cross-sectional dimension by a plurality of drawing machines 48, two of which are illustrated, and the finished wire 10 is wound on a spool 50. It will be understood that the method can be readily modified for specific circumstances. Thus while pump 44 operating at a pressure of 125 to 600 psi may be appropriate for pumping a dispersion of metal particles in a solder flux at 95°C into inlet 36 from source 42, a core mass consisting solely of metal particles 18, or a non-viscous, highly flowable core mass material, might be introduced into inlet 36 under gravity.

Furthermore, the billet 30 can be extruded about a die 36 resulting in a plurality of longitudinal passages, which are filled with core mass 16 material, rather than a single passage. EXAMPLE

A lead-free solder wire was produced based on bismuth and tin. A eutectic alloy containing 58%, by weight, bismuth and 42%, by weight, tin in particle form having a particle size of -200 to +325 mesh is formed into a paste with a standard No Clean paste flux, by melting the flux and mixing the metal particles into the molten flux. The metal particles and flux were mixed in the proportions: 80%, by weight, metal particles and 20%, by weight, flux.

The resulting mix was viscous and solidified at room temperature. The mix was introduced into source 42. Tin billets 30 were fed into extruder 32 and the mix was heated in source 42, to melt the flux. The mix flowed under gravity at a head pressure of 15-30 psi air, into inlet 36. The resulting continuous filled tube 46 was drawn in drawing machine 48 to a diameter of 0.8 mm.

The extrusion parameters in extruder 32 were selected so that the metal content of the tubular wall 12 and the metal particles 18 together provided an alloy of 11%, by weight, bismuth, balance tin. The flux content wire 10 was 3.8%, by weight.

The resulting solder wire 10 is suitable for the electronic industry, and in an experiment was employed as a solder using a hand-held soldering iron, and provided good wetting of metal parts to be soldered, forming a strong solder joint between the parts.

Claims

1- A solder wire comprising: an elongate rod having an outer metallic wall structure of a metal composition, surrounding a mass of metal particles; said metal composition being formable into said outer wall structure and forming a solder composition with said metal particles, at a soldering temperature.

2. A solder wire of claim 1, wherein said mass of metal particles comprises the metal particles dispersed in a solder flux, said particles having a particle size up to about 200 microns.

3. A solder wire of claim 1, wherein said mass consists solely of said metal particles.

4. A solder wire of claim 1, 2 or 3, wherein said wall structure defines a tubular housing having a single longitudinally extending interior passage filled with said mass.

5. A solder wire of claim 1, 2 or 3, wherein said wall structure defines a housing having a multiplicity of longitudinally extending interior passages filled with said mass.

6. A solder wire of claim 1, 2 or 3, wherein said metal composition is an extrudable, drawable metal or metal alloy.

7. A solder wire of claim 6, wherein said metal particles are of a metal or metal alloy which is non- extrudable.

8. A solder wire of claim 7, wherein said metal particles are of a metal or metal alloy which is non- drawable.

9. A solder wire of claim 1, 2, 3, 7 or 8, wherein said metal composition is of a first metal or metal alloy and said metal particles are of a second metal or metal alloy different from the first metal or metal alloy.

10. A solder wire of claim 1, 2, 3, 7 or 8, wherein said metal composition has a metallic composition substantially the same as that of said metal particles.

11. A process for producing a solder wire comprising: forming an elongate member having an outer metallic wall structure of a metal composition, and at least one longitudinally extending interior passage extending substantially the length of the member, filling said at least one interior passage with a mass of metal particles, and drawing said member to produce an elongate rod of reduced cross-sectional dimension, said metal composition forming a solder composition with said metal particles, at a soldering temperature.

12. A process according to claim 11, wherein the step of forming said elongate rod comprises extruding said metal composition to form an elongate tubular housing having a single longitudinally extending interior passage.

13. A process of claim 12, wherein said mass of metal particles comprises metal particles dispersed in a solder flux, said particles having a particle size up to about 200 microns.

14. A process of claim 11, wherein said mass consists solely of said metal particles.

15. A process of claim 11, wherein the step of forming produces an elongate tubular housing having a multiplicity of longitudinally extending interior passages.

16. A method of forming a solder joint between adjacent metal parts comprising soldering said metal parts with a solder wire of claim 1, 2, 3, 7 or 8.