alloy

Abstract

An alloy comprising 90-96.8% by weight of tin, 0.1-2.0% by weight of silver, 2.0-4.0% by weight of bismuth, 1.0-2.0% by weight of antimony, 0.1-1.0% by weight of copper, and 0.01-1% by weight of germanium.

Description

[Technical field]

[0001] The present invention relates in particular to alloys that can be used as solder alloys.

[0002] WO 2004 / 096484 A2 discloses six-component solder alloys which, in addition to tin as the main component, contain ≦10% by weight (wt. %) silver, ≦10% by weight bismuth, ≦10% by weight antimony, ≦3% by weight copper and ≦1% by weight nickel. In addition to a well-balanced range of properties, the six-component solder alloys allow the production of solder connections which are characterized by a particularly low melting point but at the same time are stable even at high operating temperatures.

[0003] Based on the solder alloy known from WO 2004 / 096484 A2, the Applicant has been able to obtain an alloy by replacing nickel with germanium and selecting a low silver content. This alloy, surprisingly, has no or only a small tendency to form unwanted "blow holes" when used as a solder alloy during soldering in an air atmosphere. This alloy is also characterized by a high thermal cycle stability. "Blow holes" are crater-like open cavities in the visible area of ​​the solder joint. The formation of these blow holes occurs during the solidification process of the previously molten solder metal. The low tendency to form blow holes is accompanied by a high reliability of the solder joint.

[0004] The invention particularly relates to an alloy which can be used as a solder alloy and which comprises 90-96.8% by weight, preferably 91.8-94.5% by weight, of tin, 0.1-2.0% by weight, preferably 1.3-1.7% by weight, of silver, 2.0-4.0% by weight, preferably 2.5-3.5% by weight, of bismuth, 1.0-2.0% by weight, preferably 1.2-1.8% by weight, of antimony, 0.1-1.0% by weight, preferably 0.5-0.9% by weight, of copper and 0.01-1% by weight, preferably 0.02-0.25% by weight, of germanium. Preferably, the alloy according to the invention comprises 91.8-94.5% by weight of tin, 1.3-1.7% by weight of silver, 2.5-3.5% by weight of bismuth, 1.2-1.8% by weight of antimony, 0.5-0.9% by weight of copper and 0.02-0.25% by weight of germanium. The alloy according to the invention may also comprise elements other than tin, silver, bismuth, antimony, copper and germanium. In addition to the elements other than tin, silver, bismuth, antimony, copper and germanium, which are intentionally and deliberately included, the alloy according to the invention may also comprise elements which may enter the alloy according to the invention unnoticed due to the technical situation, for example as a result of unintentional but unavoidable contamination during production. In other words, such other elements may be present as unavoidable impurities in the alloy according to the invention, but only in very small amounts, for example >0-1,000 ppm by weight. In any event, such unavoidable impurities are not intentionally added or introduced into the alloy according to the present invention.

[0005] The alloy according to the invention is particularly preferably a 6-component alloy consisting of tin as the main component, 0.1-2.0% by weight, preferably 1.3-1.7% by weight, silver, 2.0-4.0% by weight, preferably 2.5-3.5% by weight, bismuth, 1.0-2.0% by weight, preferably 1.2-1.8% by weight, antimony, 0.1-1.0% by weight, preferably 0.5-0.9% by weight, copper, 0.01-1% by weight, preferably 0.02-0.25% by weight, germanium, etc. This 6-component alloy is very particularly preferably consisting of tin as the main component, 1.3-1.7% by weight, silver, 2.5-3.5% by weight, bismuth, 1.2-1.8% by weight, antimony, 0.5-0.9% by weight, copper, and germanium. The hexagonal alloy may also contain elements other than tin, silver, bismuth, antimony, copper, and germanium, which may be inadvertently mixed into the hexagonal alloy due to technical circumstances, for example as a result of unintentional but unavoidable mixing during production. In other words, such other elements may be present in the hexagonal alloy as unavoidable impurities (e.g., aluminum, arsenic, lead, cadmium, cobalt, iron, nickel, phosphorus, sulfur, zinc), but only in very small amounts, for example, >0-1,000 ppm by weight. In any case, such unavoidable impurities are not intentionally added or introduced into the hexagonal alloy.

[0006] The solidus temperature of the alloy according to the present invention is in the range of, for example, 200 to 235°C, preferably 200 to 225°C.

[0007] It has been shown that the alloy according to the invention can be used as a solder metal or in a solder composition, in particular for use in the field of electronics and microelectronics. When soldered in an air atmosphere, the alloy according to the invention has little or no tendency to form blowholes, both in terms of number and size, and therefore does not require the use of shielding gases or inert gases during the soldering process. The alloy according to the invention is further characterized by an outstanding thermal shock resistance of more than 1,500 temperature cycles between -40°C and 150°C.

[0008] The alloy according to the invention can be produced by conventional methods known to those skilled in the art, for example by melting together the elements forming the alloy according to the invention. It is possible to use an induction furnace and to work under vacuum or inert gas atmosphere. The materials used can have a purity of, for example, 99.9% by weight or higher. The melt is typically poured into a mould at room temperature, where it cools and solidifies.

[0009] The alloy according to the invention, in particular the 6-component alloy, can be used directly as it is as a solder metal. From a practical point of view, the alloy can be conveniently manufactured for the intended soldering operation, i.e. in a suitable shape for this purpose. Examples of suitable shapes prepared accordingly and free of flux include solder wire, solder rod, solder foil, solder powder, solder balls and solder preforms. However, the alloy according to the invention can also be prepared as a solder metal in a solder composition comprising a flux, in particular as the only solder metal component thereof. Examples of such solder compositions are solder paste comprising a flux, solder preform comprising a flux and solder wire comprising a flux, but in particular solder paste comprising a flux and solder preform comprising a flux. The flux serves, inter alia, to dissolve the oxide layer on the surface of the solder metal and of the component to be soldered, thereby ensuring better wettability during the soldering process. The same applies to the oxides generated by the oxygen of the air during the soldering process. The flux also reduces the interfacial tension.

[0010] A solder paste containing an alloy according to the invention may, for example, comprise or consist of 82-92% by weight of the alloy according to the invention in the form of solder powder or solder balls and 8-18% by weight of a flux. Such a solder paste may be produced by mixing the components of the flux and adding the solder powder of the alloy according to the invention. The solder powder is preferably added in several portions, with stirring, and generally without heating, to an already prepared mixture of the flux components.

[0011] The flux is not subject to any particular limitation regarding its composition, and therefore, it is possible to use conventional solder fluxes known to those skilled in the art. Typically, the flux may include one or more base resins (e.g., rosin, acrylic resin), activators (e.g., hydrohalides of amines, organic carboxylic acids), thixotropic agents (e.g., hydrogenated castor oil, beeswax, carnauba wax), and often organic solvents.

[0012] In a preferred embodiment, the flux can comprise, for example, i) 30 to 60 wt. % of at least one acidic resin, ii) 5 to 20 wt. % of at least one low molecular weight carboxylic acid, and iii) 0.4 to 10 wt. % of at least one amine, in each case based on the total weight.

[0013] The at least one acidic resin i) may be selected from synthetic resins, in particular those having acidic groups, such as carboxyl groups. In contrast, natural resins, which may be unmodified or chemically modified, are preferred. The chemically modified natural resin may be, for example, a modified natural resin, modified by hydrogenation, dimerization and / or esterification of its carboxyl groups. In particular, the natural resin itself is of the rosin resin type.

[0014] The at least one acidic resin i) has, for example, a total acid number in the range of 50 to 300 mg KOH / g. The term "acid number" as used herein relates to an acid number determinable in mg KOH / g (milligrams KOH / gram) according to DIN EN ISO 2114.

[0015] The at least one low molecular weight carboxylic acid ii) may preferably be selected from dicarboxylic acids, examples of which include oxalic acid, adipic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid.

[0016] Examples of the at least one amine iii) include N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetrapropylethylenediamine, N-coco-1,3-diaminopropane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane and 1,10-diaminodecane, bis(2-ethylhexyl)amine, bis(2-methylhexyl)amine, diethylamine, triethylamine, cyclohexylamine, diethanolamine, triethanolamine, hydrogenated tallow alkylamines, hydrogenated (tallow alkyl) dimethylamines and hydrogenated bis(tallow alkyl) methylamines.

[0017] In addition to components i), ii) and iii), the flux according to the preferred embodiment may optionally contain one or more thickeners, for example in a total amount of 1-5% by weight, examples of which include ethyl cellulose, hydrogenated castor oil, and modified and unmodified glycerol tris-12 hydroxystearin.

[0018] Furthermore, the flux according to the preferred embodiment may optionally contain one or more organic solvents, for example in a total amount of 20 to 46% by weight. Examples include diols, alcohols, ether alcohols, and ketones that are liquid at 25°C, in particular trimethylpropanol, 1,2-octanediol, 1,8-octanediol, 2,5-dimethyl-2,5-hexanediol, isobornylcyclohexanol, glycol ethers, 2-ethyl-1,3-hexanediol, n-decyl alcohol, 2-methyl-2,4-pentanediol, terpineol, and isopropanol, and mixtures thereof. Examples of glycol ethers include mono-, di-, and tripropylene glycol methyl ether, mono-, di-, and tripropylene glycol n-butyl ether, mono-, di-, and triethylene glycol n-butyl ether, ethylene glycol dimethyl ether, triethylene glycol methyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol monohexyl ether, and mixtures thereof.

[0019] Furthermore, according to a preferred embodiment, the flux may optionally contain one or more halogen-containing compounds, for example, in a total amount of 0.1 to 3 wt %. Examples include aniline hydrochloride, glutamic acid hydrochloride, diethanolamine hydrochloride, diethanolamine hydrobromide, triethanolamine hydrochloride, triethanolamine hydrobromide, and trans-2,3-dibromo-2-butene-1,4-diol.

[0020] The alloy according to the invention as a solder alloy or a solder composition containing the alloy according to the invention can be used in particular in electronic or microelectronic applications, for example the fastening of electronic components to a substrate by soldering and the simultaneous electrical connection.

[0021] Examples of electronic components include diodes, LEDs (light emitting diodes), dies, IGBTs (insulated gate bipolar transistors), MOSFETs (metal oxide semiconductor field effect transistors), ICs (integrated circuits), sensors, heat sinks, resistors, capacitors, coils, connecting elements (e.g., clips), base plates, and antennas.

[0022] Examples of substrates include lead frames, PCBs (printed circuit boards), flexible electronics, ceramic substrates, DCB substrates (direct bond copper substrates), and metal ceramic substrates such as IMS (insulated metal substrates).

[0023] The alloy according to the invention, or a solder composition containing the alloy according to the invention, may also be used to produce a solder deposit on a substrate.

[0024] The alloy according to the invention may not only be a solder metal as described above, but may also be, for example, a metal alloy of a solder joint or part of a solder joint. Such a metal alloy may also be formed, for example, during or only after the completion of the soldering process, for example, by alloying two or more alloys and / or by involving metals from metal contact surfaces of electronic components or substrates connected together by soldering.

[0025] The alloy according to the invention may be a solder metal as described above, but also may be, for example, a metal alloy of a solder joint or part of a solder joint. Such a metal alloy may also be formed, for example, during or only after the completion of the soldering process, for example, by alloying multiple components, such as individual alloying elements and / or multiple alloys, and / or by involving metal from metal contact surfaces of electronic components or substrates connected together by soldering. EXAMPLES

[0026] 1. Manufacturing of solder paste and solder preforms To produce the solder alloy, various pure elements (purity 3N) were ground, weighed according to the composition (weight %) shown in Table 1, and melted together in an induction furnace under a protective gas.

[0027] To produce the solder preforms listed in Table 1, the cast solder alloy was rolled with a roller to a final thickness of 75 μm. Subsequently, a square solder preform with a side length of 1.5 mm was cut out from these sheets using a laser. Subsequently, the solder preforms were washed in ethanol using ultrasound for 20 minutes.

[0028] To produce the solder pastes listed in Table 1, the solder alloy was atomized as a melt under an inert gas. The solder balls formed by atomization were dispersed in a flux (flux composition: 40 wt% rosin resin (acid value 240 mg / KOH), 40 wt% tripropylene glycol n-butyl ether, 12 wt% sebacic acid, 2 wt% N,N,N’,N’-tetramethylethylenediamine, 2 wt% N-coco-1,3-diaminopropane, 4 wt% hydrogenated castor oil). The proportion of the solder alloy in each solder paste was 90 wt% in each case.

[0029] 2. Determination of blowholes To determine the blowholes, the solder deposits of the alloys listed in Table 1 were applied to a copper plate.

[0030] In the case of the solder preform, the solder preform was wetted with 1 drop of the above flux and placed on the copper plate.

[0031] In the case of the solder paste, a square solder deposit with a side length of 1.5 mm was printed by stencil printing using a 120-μm-thick stencil.

[0032] All solder deposits were soldered to copper plates under air atmosphere in a reflow process. For this purpose, the samples were heated to 250 °C with a heating rate of about 1 K / s and held there for 70 seconds. Subsequently, they were cooled and the number of blowholes formed was counted under a microscope. The number of blowholes listed in Table 1 represents the average value of nine data points in each case.

[0033] 3. Determination of thermal shock resistance To determine the thermal shock resistance, the shear force of the solder deposit was measured on thermally shocked and non-shocked samples. For this purpose, the solder deposit was applied to the tin-plated contact pads of a printed circuit board (FR4 material) and then an R1206 resistor with dimensions of 3.2 mm x 1.6 mm x 0.8 mm was attached.

[0034] In the case of the solder preforms, the solder deposits were in each case wetted above and below with a drop of the aforementioned flux before attachment.

[0035] In the case of the solder paste, this was applied to the contact pads by stencil printing using a 120 μm thick stencil with square dimensions of 1.5 mm side length.

[0036] Soldering was performed using the reflow profile described above.

[0037] After soldering, the samples provided for thermal cycle loading stress were transferred to a thermal cycle chamber and cycled between the two chambers for 30 minutes. The first chamber was cooled to -40 ° C and the second was heated to 150 ° C. After 1,500 cycles, samples were taken and the quality of the soldered connections was evaluated by shear testing. For this purpose, R1206 resistors were sheared at the longitudinal edge of the component with a shear chisel (width 3 mm; distance of the shear chisel from the substrate 150 μm) at a shear rate of 150 μm / s, detecting the force required for this. To determine the thermal shock resistance, the respective shear force was related to the shear force of a structurally identical element without thermal cycling after the thermal shock resistance test. The value of this shear force reduction after thermal cycling is given in % in Table 1.

[0038] [Table 1]

Claims

1. A six-component alloy consisting of 90 to 96.8 wt. % tin, 0.1 to 2.0 wt. % silver, 2.0 to 4.0 wt. % bismuth, 1.0 to 2.0 wt. % antimony, 0.1 to 1.0 wt. % copper, and 0.01 to 1 wt. % germanium, or an alloy consisting of the six components and unavoidable impurities.

2. A six-component alloy consisting of 91.8 to 94.5% by weight of tin, 1.3 to 1.7% by weight of silver, 2.5 to 3.5% by weight of bismuth, 1.2 to 1.8% by weight of antimony, 0.5 to 0.9% by weight of copper, and 0.02 to 0.25% by weight of germanium, or an alloy consisting of the six components and unavoidable impurities.

3. An alloy or hexa-alloy according to claim 1 or 2 having a solidus temperature in the range of 200 to 235°C.

4. 3. The alloy or hexa-alloy of claim 1 or 2, prepared as a flux-free solder product selected from the group consisting of solder wire, solder rod, solder foil, solder powder, solder balls, solder preforms, or as a solder composition comprising a flux selected from the group consisting of solder paste, solder preforms comprising flux, and solder wire comprising flux.

5. 5. The alloy or hexa-alloy prepared as a solder paste according to claim 4, comprising or consisting of 82-92% by weight of the alloy in the form of solder powder or solder balls and 8-18% by weight of flux.

6. 6. The alloy or hexa-alloy prepared as a solder paste according to claim 5, wherein the flux comprises: i) 30-60 wt. % of at least one acidic resin; ii) 5-20 wt. % of at least one low molecular weight carboxylic acid; and iii) 0.4-10 wt. % of at least one amine, based on the total weight of the flux.

7. 3. Use of an alloy or a hexa-alloy according to claim 1 or 2 in electronic or microelectronic applications or for producing a solder deposit on a substrate.

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