SOLDER BRAZE ALLOY

Abstract: The invention, which permits active solder braze technology to be used in a more versatile manner, relates to a solder braze alloy and to a method for joining workpieces by soldering by means of a solder braze alloy. The novel alloy is characterized in that it comprises 1 - 10 % by weight of an element or a mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements and 0.1 - 20 wt. % of an element or a mixture of elements of the group of the rare earths and the remainder consists of zinc, lead, tin, bismuth or indium or a mixture predominantly of two or more of the elements zinc, lead, tin, bismuth and indium and optionally of the elements silver, copper, gallium, antimony, nickel, manganese, chromium, cobalt possibly of customary impurities. The alloy according to the invention can be processed as a solder even in oxygen-containing atmospheres, for example in air, has a relatively low processing temperature and exhibits good wetting even of inherently poorly wettable surfaces such as, for example, ceramic surfaces. In a development of the invention the solder braze alloy can be processed without a flux.

Description: Solder Braze Alloy The invention relates co a solder braze alloy and to a method for adjoining workpieces by soldering by means of a solder braze alloy. Soldering is one of the most common joining techniques. However, there are still some drawbacks which militate against even more widespread use of soldering for joining workpieces. Previously known solder braze alloys can be used to good effect only if the surfaces of the workpieces to be joined are cleaned prior to the solder braze being applied and are freed from any oxide layers present, in order to ensure good contact of the solder braze with the workpiece surfaces, and/or if a flux is used together with the solder braze. This means that the workpiece surfaces to be soldered have to undergo a laborious pretreatment and/or that the soldering operation, owing to the use of a flux additive, becomes a more complicated procedure. Furthermore there is the risk that after the soldering operation flux residues will remain on the soldered workpieces, which may lead to problems with further processing steps or which may impair the long-term durability of the solder braze joints. Finally, some cf the fluxes used constitute health and/or environmental hazards . Known commercial solder alloys comprising tin and/or lead and possibly silver, which can be processed at about 200°C, have the additional drawback that many materials are not wetted by them at all or only very poorly, and that they cannot be used to join workpieces having surfaces of such poorly wettable or entirely nonwettable materials. Using classic solders of this type it is not possible, for example, to solder workpieces made of ceramic materials, since ceramic surfaces are not wetted. In earlier attempts to overcome this drawback, titanium was added to the solders. These so-called active solders comprising a percentage of titanium as the so-called active metal exhibit considerably improved wetting even of inherently poorly wettable surfaces such as, for example, ceramic materials. A consideraole drawoack of tπese active solders, nowever, is that they require processing temperatures of from 600 to 900 °C and can be processed only a high vacuum or m pure shielding gas. The need of processing under vacuum means that the soldering process becomes very laborious; m many cases using them is out of the question. Furthermore, the nign processing temperature seriously limits the choice of solderaole materials . This drawback also relates to the classic active brazes wnich are processed at temperatures of at least 700°C, but m most cases aoove 850°C. A farther no r. technique, for certain special cases, is that of eutectic copper bonding, out tnis is even more laborious and complicated. It is therefore an object of tne invention to propose a solder braze alloy and a method for joining workpieces by soldering by means of a solder braze alloy, the method allowing soldering technology to be used a more versatile manner. In particular, t is the oo ect of the invention to propose a solder braze alloy wnich can be processed even in oxygen-containing atmospheres, for example air, nas a relatively low processing temperature and produces good wetting even on innerently poorly wettable surfaces such as, for example, ceramic surfaces In a development of the invention, the solder oraze alloy to be proposed is to be processable without a flux. The proposed solder braze alloys are to have li- quidus temperatures which, depending on the composition, can be oelow or above 450°C. This object is achieved by a novel solder braze alloy and a method for joining workpieces by soldering by means of this novel solder braze alloy. The novel alloy, which generally is an active solder braze alloy, is cnaracterized that it comprises 1 - 10 wt% of an element or a mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements and 0.1 - 20 wt% of an element or a mixture of elements of the group of the rare eartns and the remainder predominantly consists of z c, lead, tin, oismuth or indium or a mixture of two or more of the elements z c, lead, tin, oismuth and indium and possibly of customary impurities. The proposed active solder braze alloy therefore consists of at least three components, namely a first component which consists of an element or a mixture of elements of suogroup IVa and/or Va of the Periodic Table of the Elements; a second component wnich consists of an element or a mixture of elements of tne group of tne rare eartns; and of a tnird component making ip the remainder, which predominantly consists of zmc, lead, tm, bismuth or indium or a mixture of two or more of the elements zmc, lead, tin, bismuth and indium. Preferably, tne alloy according to the invention, whicn can be an active solder alloy or an active braze alloy, additionally comprises a further, fourth component wnich consists of silver or copper or a mixture of silver and copper; and/or another further, fifth component which consists of gallium. A sixth component of antimony and a seventh component of nickel, manganese, cnromium or cobalt can advantageously likewise be provided. The fourth and possibly fifth, sixth, seventh components are advantageously present in the novel alloy, but are not absolutely necessary to achieve the advantages of 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, among which titanium is preferred. The elements of the rare earths include, inter alia, cerium, praseodymium, neodymium, gadolinium and ytterbium, among which cerium is preferred. A mixture of elements of the rare earths, cerium being the mam component, is likewise preferred as the se- cond componen . The function of the individual active solder braze alloy components can be described as follows: The third component making up the remainder and comprising zmc, lead, t n, bismuth or indium or a mixture of two or more of tne elements zmc, lead, tin, bismuth and indium serves to set a suitable fusion temperature . The first component, which consists of an element or a mixture of elements of suogroup IVa and/or Va of the Periodic Table of tne Elements - particular of titanium - increases tne wetting power of the alloy, especially for ceramic surfaces. It further serves to reduce tne surface tension of tne alloy m the fased state. The second component, whicn consists of an element or of a mixture of elements of tne group of the rare earths, particular cerium, prevents, owing to its high affinity to oxygen, the oxidation of the first component which m particular consists of titanium. Owing to tne high affinity to oxygen, oxygen from the surroundings, from oxide layers of the materials to be joined or from otner sources preferably binds to the cerium but not to tne titanium, so that the titanium is preserved, at least largely, the nonoxidizeα form and is able to deploy its positive effects. Alloys of the composition according to the invention can be used to join a multiplicity of metallic and nonmetallic materials, including oxidic and nonoxidic ceramic materials, to themselves or to other materials. The solder joint can advantageously be effected m an oxygen- contammg atmosphere, for example m air. Furthermore, in general there is no need to use a flux. The liquidus temperature of the solder braze alloy according to the invention, depending on the composition, is below or above 450°C. The processing temperatures are between 120 and 550°C. In contrast to the known active solder brazes, the processing temperatures of an alloy according to the invention are therefore drastically lower. Furthermore, there is no need for a vacuum or a shieldmg-gas atmosphere for carrying 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 m the fused state owing to interactions of the alloy components witn the ambient media and bonding via physical forces. Active solder braze alloys according to the invention can be used to good effect m a wide variety of fields under a wide variety of processing conditions. They can be used, for example, for soldering copper to steel or cast iron-carbon alloys without any difficulty. They also allow copper to be soldered onto silicon workpieces - for example, a semiconductor wafer. For alloys according to the invention this means numerous applications in semiconductor electronics, both m microelectronics and m the field of power electronics . In addition to the option of soldering, for example, a copper sheet onto a silicon wafer it also becomes possible e.g. to solder a workpiece made of copper to a workpiece made of aluminium nitride. Aluminium nitride is a good insulator, whose insulating characteristics are comparable to those of the common insulator aluminium oxide, but which has a distinctly higher thermal conductivity than aluminium oxide. The solder braze alloy according to the invention can therefore be used to establish a joint having very good thermal conductivity between a power semiconductor and an aluminium nitride workpiece which dissipates the lost heat of the power semiconductor element into a base, the aluminium nitride workpiece however ensuring electrical insulation with respect to the base. Another possible approach, for example, is that of using an alloy according to the invention for soldering a copper sheet onto a base body made of silicon, aiummium nitride or flbre-remforced caroon. Then further metallic components can be soldered onto this copper sheet m a Known manner, using known, commercial solder brazes. An alloy solder braze according to the invention can also be used to solder aluminium workpieces to one another or to copper or steel components or components made of cast iron-carbon alloys sucn as cast iron or cast steel. This can advantageously be employed plumbing technology, e.g. for joining components when condensers or heat exchangers are being built or repaired, or for attaching, by means of a joint having good thermal conductivity, of temperature sensors to heating and hot-water systems. Solder braze alloys according to the invention can be prepared and used m a very wide variety of embodiments, for example as wires, rods, sheets, granular materials, powders, pastes, foils or shaped parts. Solder pastes are known as so-called metallization solder pastes, thick-layer solder pastes, thick-film solder pastes or screen-printing solder pastes and can be applied to printed circuits by screen-printing . Heating of an alloy according to the invention can suitably be effected by ail known heating methods, for example heating by means of soldering iron or flame, plate heating, hot-air heating, ultrasonic heating, resistance heating or induction heating. Solder braze alloys according to the invention can also be used m the reflow or flow- soldering method. The liquidus and solidus temperature and consequently the soldering temperature can be influenced by the addition of the further component (s) silver, copper, gallium, antimony, nickel, manganese, chromium, cobalt, which according to the invention can optionally be employed in addition. It is possible for optionally 0.5 - 10 wt% of silver or copper or a mixture of silver and copper, optionally 0.01 - 10 wt% of gallium, optionally 0.5 - 50 wt% of antimony and optionally 0.1 - 5 wt% of nickel, manganese, chromium, cobalt to be present . The function of the further components which according to the invention can be employed in addition can be described as follows: An addition of silver ensures a lowering of the surface tension m the fused state, a decrease in the soldering temperature and an increase of the strength of the finished solder joint. An addition of copper serves to increase the soldering temperature, to improve the wetting behaviour especially with respect to ferrous materials and to increase the strength of the finished solder joint. An addition of gallium results m improved removal of oxide layers and a reduction of the soldering temperature. Advantageously, the alloy also comprises antimony and iron, nickel, cobalt, manganese and chromium. In this context, the elements iron, nickel, manganese and chromium preferably likewise serve to adjust the fusion temperature and also to increase wettability, whilst cobalt additionally allows gram refinement to occur. The element antimony is used in a preferred embodiment, specifically to regulate the soldering temperature and to increase the strength of the solder joint. An essential feature, however, is the use of zmc, lead, tin, bismuth or indium or a mixture of two or more of the elements zmc, lead, tin, bismuth and indium, since this results in an increase of the strength and the fusion temperature of the alloy. Further advantageous refinements of the invention are the subject of the dependent claims. As stated, solder braze alloys according to the invention have a number of important advantages compared with the prior art. The most important point to be mentioned is that solder braze alloys according to the invention can be processed m all ambient atmospheres even without a flux, that they have relatively low processing temperature and can be used even with inherently very poorly wettable surfaces. In addition to those applications where solder joints are used even today for joining workpieces together, they will find an advantageous potential use even many areas where glued joints have hitherto been used for joining. The solder braze alloy according to the invention and the method according to the invention will be described below m more detail with reference to a working example. To produce a solder joint between a copper sheet and an aluminium nitride sheet, the copper sheet is first placed on an electric hotplate. Placed on top of the copper sheet, which does not require any special preparation - for example prior cleaning or polishing - is a foil made of a solder braze alloy according to the invention. The rolled foil, for example, consists of an alloy of 10% by weight of silver, 2% by weight of copper, 4% by weight of titanium, 0.1% by weight of cerium, 0.05% by weight of gallium, the remainder being tin. The aluminium nitride sheet is then placed on top of the foil. Then a mechanical compression force the direction towards the hotplate is applied to the stacked sheets, for example by placing a metal weight on top of the stacked sheets. If the hot plate is then heated by the hotplate heater being switched on, the stacked sheets warm up. In this working example of an alloy according to the invention the soldering temperature is about 350°C, the soldering time a few minutes. After the solder braze alloy foil has melted, the stacked sheets are allowed to cool down again, by the hotplate being switched off, so that the fused solder braze upon solidification firmly joins together the copper sheet and the aluminium nitride sheet. To establish the joint, preference is given - as m this working example - to additional mechanical support of the fused solder braze, to ensure even flow of the solder braze. Preferably, cooling of the stacked sheets proceeds relatively slowly if - as in the present working example - materials having markedly different thermal expansion coefficients are soldered together, since it would otherwise be possible, in the event of unduly rapid and especially uneven cooling, for cracks to form. The soldering operation as described can also be carried out with other solder braze alloys according to the invention. A solder braze alloy according to the invention consisting of 4% by weight of silver, 4% by weight of titanium, 0.1% by weight of cerium, 0.1% by weight of gallium, the remainder being tin, can be processed at 250°C, for example, whereas a solder braze alloy according to the invention consisting of 4% by weight of silver, 2% by weight of titanium, 2% by weight of t n, 2% by weight of indium, 0.1% by weight of cerium, 0.05% by weight of gallium, the remainder being lead, is processed at 400°C. In the domestic-appliance sector, an alloy consisting of 4 wt% of Ti, 4 wt% of Ag, 0.1 wt% of cerium, 0.1 wt% of Ga, the remainder being zmc, is particularly advantageous. With this alloy the fusion temperature is then in the range of from about 421 to 446°C.l As well as the soldering technique described, all other soldering techniques known to those skilled m the art can be carried out with an active solder braze alloy according to the invention. Any optimization, in terms of the specifically intended use, within the scope of the claims can readily be found experimentally by those skilled in the art .

Claims: CLAIMS 1. Solder braze alloy, characterized in that it comprises 1 - 10 wt% of an element or a mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements and 0.1 - 20 wt% of an element or a mixture of elements of the group of the rare earths and the remainder, at least predominantly, consists of zmc, lead, tin, bismuth or indium or a mixture of two or more of the elements zmc, lead, t n, bismuth and indium and possibly of customary impurities. 2. Alloy according to Claim 1, cnaracterized m that the element or the mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements is or comprises titanium and/or zirconium and/or hafnium and/or vanadium and/or niobium and/or tantalum. 3. Alloy according to Claim 2, characterized in that the element or the mixture of elements of subgroup IVa and/or Va of tne Periodic Table of the Elements is or comprises titanium. 4. Alloy according to Claim 1, cnaracterized m that it comprises 1 - 5% by weight of an element or a mixture of elements of subgroup IVa and/or Va of the Periodic Table of the Elements. 5. Alloy according to one or more of the preceding claims, characterized in that the element or the mixture of elements of the group of the rare earths is or comprises cerium and/or samarium and/or neodymium. 6. Alloy according to Claim 5, characterized in that the element is cerium. 7. Alloy according to one or more of Claims 1 to 6, characterized m that the alloy comprises 0.5 - 10% by weight of silver or copper or a mixture of silver and copper. 8. Alloy according to Claims 7, characterized in that the alloy comprises 0.5 - 5% by weight of silver or copper or a mixture of silver and copper. 9. Alloy according to one or more of Claims 1 to 8, characterized in that the alloy comprises 0.5 - 50% by weight of antimony. 10. Alloy according to one or more of Claims 1 to 9, characterized m that it comprises 0.1 - 5% by weight of nickel, cobalt, manganese or chromium or a mixture of two or more of the elements nickel, cobalt, manganese or chromium. 11. Alloy according to one or more of Claims 1 to 10, characterized m that it comprises 0.01 - 10% by weight of gallium. 12. Alloy according to Claim 1, characterized in that it consists of 4 wt% of titanium, 4 wt% of silver, 0.1 wt% of cerium, 0.1 wt% of gallium, the remainder being zmc. 13. Method for joining workpieces by soldering by means of a solder braze alloy, characterized in that a solder braze alloy according to any one of Claims 1 to 17 is used, the solder joint is effected m an oxygen-containing atmosphere such as a r and the solder joint is effected at a soldering temperature of between 120 and 550°C. 14. Method according to Claim 13, characterized in that the solder joint is effected at a soldering temperature of 200 - 450°C, and m particular at 421 - 446°C in the case of zmc solders. 15. Method according to either one of Claims 13 and 14, characterized in that the solder joint is effected without the use of a flux in an oxygen-containing atmosphere or under a shielding gas. 16. Method according to one or more of Claims 13 to 15, characterized m that at least one of the workpieces to be joined consists, at least at its solder joint face, of a metallic material, especially of aluminium, copper, steel or cast iron-carbon alloys such as cast iron or cast steel. 17. Method according to one or more of Claims 13 to 16, characterized in that at least one of the workpieces to be joined consists, at least at its solder joint face, of a nonmetallic material, especially of aluminium, nitride, silicon, fibre-reinforced carbon, an oxidic or a nonoxidic ceramic material.

Inventors: HILLEN FRANCK, LUGSCHEIDER ERICH, RASS INO J, HILLEN, FRANCK, LUGSCHEIDER, ERICH, RASS, INO, J.
Applicants: EUROMAT GMBH, HILLEN FRANCK, LUGSCHEIDER ERICH, RASS INO J, HILLEN, FRANCK, LUGSCHEIDER, ERICH, RASS, INO, J.
Application year: 1998
Main classification: B23K35
IPC codes: B23K35