Metal treatment – Stock – Containing over 50 per cent metal – but no base metal
Reexamination Certificate
1998-04-23
2001-05-15
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Containing over 50 per cent metal, but no base metal
C148S400000, C420S558000, C420S570000, C420S589000
Reexamination Certificate
active
06231693
ABSTRACT:
This application is the U.S. national-phase application of PCT International Application No. PCT/EP96/03037.
The invention relates to an alloy, in particular a solder alloy, to a method for joining workpieces by soldering by means of a solder alloy, and to the use of an alloy for soldering.
Soldering is one of the most widely used joining techniques. Even wider use of soldering for joining workpieces has hitherto still been faced with some drawbacks.
Solder alloys known hitherto can be used successfully only if the surfaces or the workpieces to be joined are cleaned prior to application of the solder and are freed from any oxide layers present, to ensure good contact of the solder with the workpiece surfaces, and/or if a flux is used at the same time as the solder This means that the workpiece surfaces to be soldered require a complicated pretreatment and/or that the soldering operation involves a more complex procedure owing to the use of added flux. Furthermore there is the risk that after the soldering operation flux residues will remain on the soldered workpieces, which may lead to problems in further processing steps or which may impair the long-term durability of the soldered joints. Finally, some of the fluxes used are hazardous to health and/or the environment.
Known commercial soft solder alloys which comprise tin and/or lead and possibly silver and which can be processed at about 200° C. have the further drawback that they will wet many materials either not at all or only very poorly and that they cannot be used for joining workpieces having surfaces of such poorly wettable or entirely nonwettable materials. Such conventional soft solders cannot be used, for example, to solder work-pieces of ceramic materials, since ceramic surfaces are not wetted.
There have been previous attempts to overcome this drawback by admixing the soft solders with titanium. These so-called activated soft solders with a proportion of titanium as the so-called active metal exhibit significantly improved wetting even of surfaces which per se are poorly wettable, for example ceramics. A serious drawback of these activated soft solders, however, is that they require process temperatures of from 600 to 900° C. and can be processed only in a high vacuum or in a pure shielding gas. The need for processing under vacuum makes the soldering operation very complex; in many cases their use is entirely out of the question. Furthermore, the high processing temperature severely limits the choice of solderable materials.
In addition, for certain special cases, the method of eutectic copper bonding is known, but this is even more expensive and complicated.
It is therefore an object of the invention to propose an alloy, in particular a solder alloy, and a method for joining workpieces by soldering by means of a solder alloy, which method enables more versatile applicability of the soft-solder technique. In particular it is an object of the invention to propose an alloy, in particular a solder alloy, which can be processed even in oxygen-containing atmospheres such as, for example, in air, has a relatively low processing temperature and will wet even surfaces which per se are poorly wettable, such as ceramic surfaces, for example. In a further improvement of the invention, the solder alloy to be proposed should be amenable to processing without a flux.
The object is achieved by a novel alloy, in particular solder alloy, by a method for joining workpieces by soldering by means of said novel solder alloy and by the use of this novel alloy for soldering. The novel alloy is characterized in that it comprises
at least 1% by weight of an element or a mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements,
at least 0.01% by weight of an element or a mixture of elements of the lanthanide group,
optionally at least 0.5% by weight of silver or copper or indium or a mixture of silver and/or copper and/or indium and
optionally at least 0.01% by weight of gallium
and the remainder consists of tin or lead or of a mixture of tin and lead
and possibly of the usual impurities.
The proposed alloy therefore consists of at least three components, i.e. a first component which consists of an element or a mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements; a second component which consists of an element or a mixture of elements of the lanthanide group; and of a third remainder component, which consists of tin or lead or of a mixture of tin and lead.
Preferably the alloy according to the invention additionally comprises a further component which consists of silver or copper or indium or a mixture of silver and/or copper and/or indium; and/or another further component which consists of gallium. The fourth and possibly fifth components are advantageously present in the novel alloy, but are not absolutely necessary to achieve the advantages according to the invention.
The elements of subgroup IVa and/or Va of the Periodic Table of the Elements include, inter alia, the elements titanium, zirconium, hafnium, vanadium, niobium and tantalum, of which titanium is preferred. The elements of the lanthanide group include inter alia cerium, praseodymium, neodymium, gadolinium and ytterbium, of which cerium is preferred.
The function of the individual alloy components can be described as follows:
The third remainder component comprising tin or lead or a mixture of tin or lead is a conventional solder base.
The first component, which consists of an element or of a mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements, in particular of titanium, increases the wetting power of the alloy, in particular for ceramic surfaces. It further serves to reduce the surface tension of the alloy in the molten state.
The second component, which consists of an element or of a mixture of elements of the lanthanide group, in particular cerium, prevents, owing to its high affinity to oxygen, the oxidation of the first component which, in particular, consists of titanium. Owing to the high affinity to oxygen, oxygen from the environment, from oxide layers of the materials to be joined or from other sources will preferentially form compounds with the cerium and not with the titanium, so that the titanium will remain, at least largely, in nonoxidized form and will be able to deploy its positive effects.
Alloys having the novel composition can be used to join a multiplicity of metallic and nonmetallic materials, even oxidic and nonoxidic ceramic materials, to themselves or to other materials. Joining by soldering can advantageously be carried out in an oxygen-containing atmosphere, for example in air. Furthermore, in general it is not necessary to use a flux.
The processing temperature of the alloy according to the invention is preferably at most 500° C., in particular between 200 and 450° C. By means of the addition of further components such as the above-mentioned silver and/or copper and/or indium and/or gallium it can be tailored to the value desired for each particular application.
In contrast to the known, so-called activated soft solders, the processing temperatures of an alloy according to the invention are therefore drastically reduced. Furthermore, it is not necessary to use a vacuum or a shielding gas atmosphere to carry out the soldering operation.
The joining mechanism is based on:
the removal, by reactive alloy components, of any oxide coatings present on the surfaces of the workpieces to be joined;
the reduction of the surface tension in the molten state as a result of interactions of the alloy components with the surrounding media and
attachment via physical forces.
Solder alloys according to the invention are readily usable in a wide variety of sectors under a wide variety of processing conditions. They can be employed, for example, for producing soldered joints, without difficulty, between copper and steel or cast iron-carbon alloys. They also make it possible to solder copper onto a silicon workpiece, for example a semiconductor wafer. Alloys according to the i
Lugscheider Erich
Tillmann Wolfgang
Zhuang Hongshou
Ip Sikyin
Materials Resources International
Ratner & Prestia
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