Tubular solder, especially for soft soldering of aluminum

Abstract

Tubular solder consists of a solder material that is a tin-based alloy and a flux, where the flux is expressed as a percentage by weight 40 to 70% modified rosin, 25 to 40% triethanolamine, 1 to 5% of a fluoride as well as 0 to 15% water exhibits, and where the weight percentage of solder material is 90 to 99.5% and that of flux is 0.5 to 10%.

Description

[0001] The present invention relates to a tubular solder which is particularly suitable for soft soldering of aluminum.

[0002] Soldering is the joining of metal parts using a solder material, typically a metal alloy. The molten solder material is applied to one metal part, which is then joined to another metal part. Unlike welding, the metal parts themselves are not melted. Only the solder material is melted, which consequently has a lower melting point than the metal parts. The molten solder material diffuses into the surface of the metal parts and forms a strong bond between them.

[0003] Soft soldering refers to soldering processes at temperatures up to approximately 450°C, whereby solder materials that melt below this temperature are used. Above 450°C, hard soldering takes place.

[0004] The strength of the solder joint depends crucially on the solder material being able to thoroughly wet the surface of the metal part. However, good wetting requires that the surface be free of contaminants and surface layers.

[0005] This is a particular problem with aluminum. Aluminum is highly reactive and, upon contact with air, forms a compact, extremely stable oxide layer covering the entire surface. This oxide layer must be removed, otherwise soft soldering is impossible. Furthermore, the highly reactive aluminum must be prevented from forming another oxide layer during the soldering process.

[0006] It is known to use solder materials in combination with a flux for soft soldering aluminum. The flux's function is to remove the oxide layer and simultaneously prevent the oxide layer from re-forming during the soldering process.

[0007] It is also known to use solder tubes as a soldering agent. Solder tubes are a combination of solder material and flux, with the solder material in the form of a hollow wire that is at least partially filled with the flux.

[0008] Common tubular solders for soft soldering aluminum use organic systems containing halides as fluxes, for example, a mixture of 2-(2-aminoethylamino)ethanol and ammonium hydrogen difluoride (ammonium bifluoride). Since the halide-containing residues of these fluxes are highly corrosive, the soldered aluminum components must be carefully washed with water afterward to prevent corrosion. The necessity of a washing process requires additional effort. Furthermore, the soldered components often cannot be cleaned or cannot be completely cleaned, for example, due to their shape, resulting in an increased risk of corrosion.

[0009] Aluminum and aluminum-based alloys are increasingly being used in electronics and microelectronics, for example, as a replacement for copper, due to their light weight and relatively low cost. Components for these applications are often very small and have contours that are difficult or impossible to clean. For example, when soldering microelectronic components onto circuit boards, subsequent cleaning is not advisable because the gaps between the components and the circuit board are so small that optimal cleaning is no longer possible.

[0010] To solve this cleaning problem and the resulting risk of corrosion, US Pat. No. 3,655,461 A describes a flux based on a curable epoxy resin and a natural resin. The flux also contains a fluoroborate of a heavy metal and triethanolamine. The fluoroborate removes the oxide layer and, at the same time, causes the resin component to crosslink with the triethanolamine. As a result, a plastic layer is formed on the component as the fluoroborate is consumed, providing corrosion protection. A disadvantage, however, is that the flux is a two-component system, whereby the resin can only be added to the mixture of fluoroborate and triethanolamine immediately before the soldering process to prevent premature curing. The crosslinking reaction also occurs at temperatures as low as 100°C, i.e., temperatures commonly used in wire production.It is understood that such a system is unsuitable for use in a tube solder.

[0011] DE 10 2007 007 212 A1 describes, as an alternative to the known flux-filled solder wires, a solder consisting of a solder material and a non-corrosive flux. The solder material is a solid wire whose outer surface is coated with the flux. The flux contains, as its main component, a carrier resin substance, which can be a modified natural resin or a natural resin derivative, such as hydrogenated rosin, polymerized rosin, or rosin glycerol ester. Optional components include an activator, for example, salts that release hydrogen halides, and an extender, for example, a synthetic wax.

[0012] The flux also contains a plasticizer, for example an ester of an organic acid, which is intended to prevent premature detachment of the coating from the metal surface.

[0013] A problem with this type of tubular solder is the usually sticky consistency of the flux used. This can lead to flux delamination, resulting in the resulting tubular solder becoming defective on the outside and even causing further problems due to undesired flux dispersion before actual use. Furthermore, the activity of the flux described is too low to be able to remove the stable aluminum oxide layer.

[0014] EP 2 862 667 A1 describes a flux, particularly for use in soldering aluminum, which can remove disruptive metal oxide layers on the components to be soldered. The flux comprises a base material such as rosin, at least one amine, and an amine fluoride salt formed by the reaction of an amine and an acid. Aromatic amines such as a pyridine derivative, an imidazole derivative, a guanidine derivative, ethylamine, and picoperine are used as amines. It is further described that the flux can also be used for soldering tubes.

[0015] German patent DE 2042370 C relates to a liquid solder carrier for the production of screen-printable solder pastes. The liquid solder carrier consists of at least 0.01 wt.% of an active hydrogen-containing compound from the group of hydroxyl-substituted aliphatic or aromatic amines, for example, triethanolamine, 0 to 75 wt.% of rosin or rosin derivative, 0 to 75 wt.% of an organic solvent, and 0 to 20 wt.% of a thixotropic agent. The screen-printable solder pastes are produced by mixing powdered solder and the solder carrier, with the powdered solder being dispersed in the liquid carrier.

[0016] However, there remains a significant need for tubular solders, particularly for soft soldering of aluminum, which contain a flux that prevents corrosion, so that no washing of the soldered components is required after soldering.

[0017] This object is achieved according to the invention by a tubular solder made of a tin-based solder material and a flux, wherein the flux has a content (in wt.%) of 40 to 70% modified rosin, 25 to 40% triethanolamine, 1 to 5% of a fluoride and 0 to 15% water wherein the face proportion in weight percent of solder material is 90 to 99.5% and that of flux is 0.5 to 10%.

[0018] The flux according to the invention can remove the extremely compact and stable aluminum oxide layer that adheres to aluminum components, making soft soldering of these components possible. At the same time, it has a corrosion-inhibiting effect, eliminating the need for subsequent washing processes to remove flux residues.

[0019] The modified rosin can be any chemically modified rosin known for the production of fluxes. Examples include partially or fully hydrogenated rosin, dimeric or polymerized rosin, and rosin glycerol esters.

[0020] Triethanolamine and fluoride act as activators and support the removal of the aluminum oxide layer.

[0021] In principle, ionic fluorides can be used which have suitable solubility and temperature resistance and also do not show any undesirable reactions with the other flux components during melting.

[0022] An example of a suitable ionic fluoride is ammonium hydrogen difluoride.

[0023] The flux according to the invention contains 1 to 5 wt.%, preferably 2 to 4 wt.%, and in particular 2.5 to 3.5 wt.% of one or more fluorides. Ammonium hydrogen difluoride is preferably used as the fluoride.

[0024] Triethanolamine also acts as an activator and is present in the flux according to the invention in a content of 25 to 40 wt.%, preferably 25 to 35 wt.% and in particular 28 to 32 wt.%.

[0025] If necessary, water can be added to the flux according to the invention, for example to support the solubility of the fluoride such as ammonium hydrogen difluoride.

[0026] According to the invention, a solder material which is a tin-based alloy is used for the production of the tubular solder.

[0027] The alloy contains at least 90 wt% tin.

[0028] In addition, silver, copper or both metals may be present as additional alloy components.

[0029] Furthermore, the alloy can contain one or more microalloying elements if required. Examples of microalloying elements are nickel, germanium, and phosphorus.

[0030] Phosphorus can be present in a content range of 0.001 to 0.1 wt.%, germanium from 0.001 to 0.1 wt.%, and nickel <0.5 wt.%. For example, according to one embodiment, 0.004 wt.% phosphorus, 0.006 wt.% germanium, and / or 0.03 wt.% nickel can be present.

[0031] Below are some particularly advantageous examples of tin-based alloys that can be used according to the invention (in wt.%): 1. Tin, copper 0.3 to 4%; 2. Tin, copper 0.3 to 4%, silver 1 to 5%; 3. Tin, silver 1 to 5%; 4. an alloy according to examples 1 to 3, each additionally containing at least one microalloying element selected from the group consisting of nickel, germanium and phosphorus; 5. an alloy according to any one of examples 1 to 3, each containing the microalloying elements nickel, germanium and phosphorus.

[0032] According to one embodiment, the copper content in the above-mentioned alloys may be 0.3 to 2 wt.%.

[0033] A hollow wire is produced from the tin-based solder material used according to the invention in a manner known per se, which hollow wire contains one or more cores made of the flux according to the invention.

[0034] For example, the hollow wire can be produced from solder material by extrusion and filled with flux. The filling with flux can preferably occur during the extrusion process. The extruded strand is then drawn and / or rolled to the desired diameter and wound onto reels, for example, as a ready-to-use solder.

[0035] A particularly advantageous process is described in the German patent application DE 10 2009 033 406 A1 of the present applicant, to which reference is made.

[0036] The flux-cored solder consists of 90 to 99.5 wt.% tin-based solder material and 0.5 to 10 wt.% flux. A composition of 96.5 wt.% tin-based solder material and 3.5 wt.% flux is particularly preferred.

[0037] It has been shown that the modified rosin of the flux forms a layer that protects the joint of the soldered components from corrosion, so that there is no risk of corrosion due to flux residues or the risk of corrosion can at least be significantly reduced.

[0038] The tubular solder according to the invention effectively dissolves the disturbing oxide layer, which adheres particularly to components made of aluminum or aluminum alloys, prevents the formation of a new oxide layer and acts as a corrosion protection without the need for washing.

[0039] If necessary, unwanted flux residues can be easily removed with a solvent such as isopropanol.

[0040] The tubular solder according to the invention is not only excellently suited for soft soldering aluminum but equally for aluminum alloys, i.e. alloys whose main component is aluminum, as well as other oxide layer-forming metals and metal alloys, such as titanium, tantalum, their alloys and stainless steel.

[0041] However, it should be noted that aluminum and its alloys have a particularly strong and stable oxide layer, so that sufficient removal is particularly difficult here.

[0042] The flux according to the invention forms a protective resin layer without the need to add a further reactive component to the flux for curing and layer formation immediately before use. It is therefore ideally suited as a corrosion-protective flux core for a soldering iron.

Claims

[1] Tube solder made of a solder material which is a tin-based alloy and a flux, where the flux is in weight percent 40 to 70% modified rosin, 25 to 40% triethanolamine, 1 to 5% of a fluoride and 0 to 15% water and where the weight percentage of solder material is 90 to 99.5% and that of flux is 0.5 to 10%. [2] The solder tube of claim 1, wherein the tin-based alloy comprises at least 90 wt% tin. [3] Tube solder according to claim 2, wherein at least one further alloy component selected from silver and copper is additionally included. [4] Tubular solder according to one of the preceding claims, wherein the tin-based alloy comprises 0.3 to 4 wt.% copper in addition to tin. [5] A solder tube according to any one of the preceding claims, wherein the tin-based alloy comprises 1 to 5 wt% silver. [6] A solder tube according to any one of claims 1 to 5, wherein the tin-based alloy comprises at least one micro-alloying element selected from nickel, germanium and phosphorus. [7] Flux with a composition in weight percent of 40 to 70% modified rosin, 25 to 40% triethanolamine, 1 to 5% of a fluoride and 0 to 15% water. [8] A flux according to claim 7, wherein the fluoride is ammonium hydrogen difluoride. [9] Flux according to claim 7 or 8, wherein the modified rosin is partially or fully hydrogenated rosin, dimeric or polymerized rosin or rosin glycerol ester. [10] Use of a tubular solder according to any one of claims 1 to 6 or a flux according to any one of claims 7 to 9 for the soft soldering of aluminium and aluminium alloys.