ALLOY

Description

[0001] The invention relates to an alloy that can be used in particular as a solder alloy.

[0002] WO 2004 / 096484 A2 discloses a hexagonal solder alloy which, in addition to tin as the main component, contains ≤10 wt.% silver, ≤10 wt.% bismuth, ≤10 wt.% antimony, ≤3 wt.% copper, and ≤1 wt.% nickel. Besides a balanced range of properties, the hexagonal solder alloy is characterized in particular by a low melting point, while at the same time enabling the production of stable solder joints even at high operating temperatures.

[0003] Starting with the solder alloy known from WO 2004 / 096484 A2, the applicant was able to obtain an alloy by replacing the nickel with germanium and selecting a low silver content. Surprisingly, when used as a solder alloy, this alloy exhibits no or only a slight tendency to form undesirable so-called blowholes when soldering in air. The alloy is also characterized by high stability against temperature cycling. Blowholes are crater-like, open cavities in the visible area of ​​the solder joint. These blowholes form during the solidification process of the previously molten solder metal. A low tendency to form blowholes is associated with high reliability of a solder joint. Patent documents EP 2 468 450 A1, WO 2011 / 102034 A1, and US 5 980 822 A disclose further solder alloy compositions with a low silver content.

[0004] The invention relates to a hexagonal alloy consisting of tin as the main component; 0.1 to 2.0 wt.%, preferably 1.3 to 1.7 wt.% silver; 2.0 to 4.0 wt.%, preferably 2.5 to 3.5 wt.% bismuth; 1.0 to 2.0 wt.%, preferably 1.2 to 1.8 wt.% antimony; 0.1 to 1.0 wt.%, preferably 0.5 to 0.9 wt.% copper; and 0.01 to 1 wt.%, preferably 0.02 to 0.25 wt.% germanium. Most preferably, this hexagonal alloy consists of tin as the main component; 1.3 to 1.7 wt.% silver; 2.5 to 3.5 wt.% bismuth; 1.2 to 1.8 wt.% antimony; 0.5 to 0.9 wt.% copper; and 0.02 to 0.25 wt.% germanium. The hexagonal alloy may also include elements other than tin, silver, bismuth, antimony, copper and germanium, which may have unintentionally entered it due to technical circumstances, e.g. as a result of an unintentional but unavoidable incorporation during manufacturing.In other words, such other elements may be present in the hexa-component alloy as unavoidable impurities (e.g., aluminum, arsenic, lead, cadmium, cobalt, iron, nickel, phosphorus, sulfur, zinc), but only in very small quantities totaling > 0 to 1000 ppm by weight. In any case, such unavoidable impurities are not intentionally added or introduced into the hexa-component alloy.

[0005] The solidus temperature of the alloy according to the invention is in the range of, for example, 200 to 235 °C, preferably 200 to 225 °C.

[0006] It has been shown that the alloy according to the invention can be used as a solder metal or in solder compositions, particularly for use in the electronics and microelectronics industries. When soldered in air, the alloy according to the invention exhibits only a slight to no tendency to form blowholes, both in number and size, and therefore does not require the use of a protective or inert gas during the soldering process. Furthermore, the alloy according to the invention is characterized by a pronounced resistance to temperature cycling of > 1500 temperature cycles between -40°C and +150°C.

[0007] The alloy according to the invention can be produced by conventional methods known to those skilled in the art, e.g., by melting together the elements forming the alloy according to the invention. It is possible to use an induction furnace, and the process can be carried out under vacuum or under a protective gas atmosphere. The materials used can have a purity level of, for example, ≥99.9 wt.% and higher. The melt is typically poured into a mold at room temperature, where it cools and solidifies.

[0008] The alloy according to the invention, in particular the hexagonal alloy, can be used directly as a solder metal. From a practical point of view, it can be suitably prepared for an intended soldering application, i.e., brought into a suitable form. Examples of suitable forms prepared accordingly and each free of flux include solder wires, solder rods, solder foils, solder powders, solder balls, and solder preforms. The alloy according to the invention can also be prepared as a solder metal in a solder composition containing flux, in particular as the sole solder metal component thereof. Examples of such solder compositions are flux-containing solder pastes, flux-containing solder preforms, and flux-containing solder wires, but especially flux-containing solder pastes and flux-containing solder preforms.Fluxes serve, among other things, to dissolve the oxide layer on the surfaces of the solder metal and the components to be soldered, thus ensuring better wettability during the soldering process. The same applies to oxides that form during soldering due to atmospheric oxygen. Fluxes also reduce surface tension.

[0009] A solder paste containing an alloy according to the invention can, for example, comprise or consist of 82 to 92 wt.% of an alloy according to the invention in the form of solder powder or solder balls and 8 to 18 wt.% of a flux. Such a solder paste can be produced by mixing the components of the flux and adding a solder powder made from an alloy according to the invention. The solder powder is preferably added in several portions to a given mixture of the flux components while stirring, generally without heating.

[0010] The flux is not subject to any special restrictions regarding its composition, and therefore a common soldering flux known to those skilled in the art can be used. Fluxes typically comprise one or more base resins (e.g., rosin, acrylic resin), an activator (e.g., hydrohalic acid salts of amines, organic carboxylic acids), a thixotropic agent (e.g., hydrogenated castor oil, beeswax, carnauba wax), and often an organic solvent.

[0011] In a preferred embodiment, the flux may, for example, comprise, based on its total weight, 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.

[0012] The at least one acidic resin i) can be selected from synthetic resins with acidic groups, such as, in particular, carboxyl groups. Natural resins, which may be unmodified or chemically modified, are preferred. The chemically modified natural resins may be, for example, those modified by hydrogenation, dimerization, and / or esterification of their carboxyl groups. In particular, the natural resins themselves are of the rosin resin type.

[0013] The at least one acidic resin i) has a total acid number, for example, in the range of 50 to 300 mg KOH / g. The term "acid number" used herein refers to an acid number that can be determined in mg KOH / g (milligrams of KOH per gram) according to DIN EN ISO 2114.

[0014] The at least one low molecular weight carboxylic acid ii) may preferably be selected from dicarboxylic acids. Examples include oxalic acid, adipic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, cortic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, and tridecanedioic acid.

[0015] 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 alkylamine, hydrogenated (tallow alkyl)dimethylamine and hydrogenated bis(tallow alkyl)methylamine.

[0016] In addition to components i), ii) and iii), the flux according to the preferred embodiment may optionally comprise one or more thickening agents, for example in a total quantity of 1 to 5 wt. Examples include ethylcellulose, hydrogenated castor oil and modified or unmodified glycerol tris-12-hydroxystearin.

[0017] Furthermore, according to the preferred embodiment, the flux may optionally comprise one or more organic solvents, for example in a total proportion 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, as well as mixtures thereof.

[0018] Examples of glycol ethers include mono-, di-, tripropylene glycol methyl ether, mono-, di-, tripropylene glycol n-butyl ether, mono-, di-, triethylene glycol n-butyl ether, ethylene glycol dimethyl ether, triethylene glycol methyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether and diethylene glycol monohexyl ether, as well as mixtures thereof.

[0019] Furthermore, according to the preferred embodiment, the flux may optionally comprise one or more halogenated compounds, for example in a total amount of 0.1 to 3% by weight. 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. Examples of electronic or microelectronic applications include the fastening and simultaneous electrical connection of electronic components to substrates by soldering.

[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, inductors, connecting elements (e.g., clips), base plates, and antennas.

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

[0023] The alloy according to the invention, or a solder composition containing the alloy according to the invention, can also be used to produce so-called solder deposits on substrates.

[0024] The alloy according to the invention can not only be solder metal as mentioned above, but it can also, for example, constitute the metal alloy of a solder joint or part of a solder joint. Such a metal alloy can, for example, also be formed during or after the completion of a soldering process, for example, through alloy formation from more than one alloy and / or with the participation of metal from metallic contact surfaces of electronic components or substrates connected by soldering.

[0025] The alloy according to the invention can not only be solder metal as mentioned above, but it can also, for example, constitute the metal alloy of a solder joint or part of a solder joint. Such a metal alloy can, for example, also be formed during or after the completion of a soldering process, for example, through alloy formation from several components, such as individual alloying elements and / or several alloys, and / or with the participation of metal from metallic contact surfaces of electronic components or substrates connected by soldering. Examples 1. Production of solder pastes and solder preforms

[0026] To produce solder alloys, the various pure elements (purity level of 3N) were crushed according to the composition listed in Table 1 (in wt.%), weighed out and melted together in an induction furnace under protective gas.

[0027] To produce the solder preforms listed in Table 1, the cast solder alloys were rolled down to a final thickness of 75 µm. Square solder preforms with an edge length of 1.5 mm were then cut from these sheets using a laser. The solder preforms were subsequently cleaned in ethanol with ultrasonic assistance for 20 minutes.

[0028] To produce the solder pastes listed in Table 1, the solder alloys were atomized as a melt under inert gas. The solder spheres formed by atomization were dispersed in 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-diaminepropane, 4 wt.% hydrogenated castor oil). The proportion of the solder alloy in each solder paste was 90 wt.%. 2. Identification of blowholes

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

[0030] In the case of the solder preforms, these were moistened on both the top and bottom sides with a drop of the aforementioned flux and placed on the copper plate.

[0031] In the case of the solder pastes, square solder deposits with an edge length of 1.5 mm were printed using stencil printing with a 120 µm thick stencil.

[0032] All solder deposits were soldered onto copper plates in a reflow process under atmospheric air. For this, the plates were heated to 250°C at a rate of approximately 1 K / s and held at this temperature for 70 seconds. The samples were then cooled, and the number of blowholes formed was counted under a microscope. The number of blowholes listed in Table 1 represents the mean values ​​from nine data points each. 3. Determination of temperature cycling resistance

[0033] To determine thermal shock resistance, the shear force of solder deposits was measured on both unloaded and thermally shocked samples. For this purpose, solder deposits were applied to tinned contact pads on printed circuit boards (FR4 material) and then populated with R1206 resistors measuring 3.2 mm x 1.6 mm x 0.8 mm. In the case of the solder preforms, the solder deposits were coated with a drop of the aforementioned flux on both the top and bottom surfaces before placement.

[0034] In the case of the solder paste, it was applied to the contact pads using a stencil with a square dimension of 1.5 mm edge length and a 120 µm thick stencil.

[0035] The soldering was performed using the aforementioned reflow profile.

[0036] After soldering, the samples intended for thermal cycling were transferred to a temperature cycling chamber and cycled between two chambers every 30 minutes; the first chamber was cooled to -40°C, the second chamber heated to +150°C. After 1500 cycles, the samples were removed and the quality of the solder joint was assessed using shear tests. For this purpose, the R1206 resistors were sheared at the longitudinal edge of the component using a shear chisel (3 mm wide; 150 µm distance of the chisel from the substrate) at a shear rate of 150 µm / s, and the force required was recorded. To determine the thermal cycling resistance, the respective shear forces after the thermal cycling test were compared to the shear force of an identical component without thermal cycling. The values ​​of this shear force reduction after thermal cycling are given as percentages in Table 1. Table 1: Overview of alloys according to the invention (1-16) and comparison alloys (R1-R13), as well as results regarding shear force reduction after temperature cycling TWB (in %) and number of blowholes formed. sample form Sn AG Cu Bi Sb Ni Ge Shear force reduction according to TWB Blowholes R1 Preform rest 3,8 0,7 3 1,5 0,15 - 43,5 81 R2 Preform 1 0,7 1 1 - 0,06 57,7 13 R3 Preform 1,5 0,7 1,5 3 - 0,25 63,7 3 R4 Preform 1,5 0,7 3 1,5 0,15 0,25 39,4 42 R5 Preform 1,5 0,03 3 1,5 - 0,03 36,6 133 R6 Preform 1,5 0,7 4,5 1,5 - 0,03 26,7 94 R7 Preform 1,5 0,7 3 0,7 - 0,03 40,9 82 R8 Preform 1,5 0,7 3 1,5 - 1,2 45,3 15 R9 paste 3,8 0,7 3 1,5 0,15 - 42,4 69 R10 paste 1,5 0,7 3 1,5 0,15 0,25 31,7 53 R11 paste 1,5 0,7 3 1,5 0,25 - 40,7 77 R12 paste 1,5 0,03 3 1,5 - 0,03 38,1 153 R13 paste 1,5 0,7 4,5 1,5 - 0,03 24,9 98 1 Preform rest 1,5 0,7 3 1,5 - 0,01 33,9 17 2 Preform 1,5 0,7 3 1,5 - 0,03 36,2 25 3 Preform 1,5 0,7 3 1,5 - 0,25 38,7 28 4 Preform 0,3 0,7 3 1,5 - 0,03 36,5 27 5 Preform 1,7 0,7 3 1,5 - 0,03 36,0 14 6 Preform 1,5 0,3 3 1,5 - 0,03 36,8 35 7 Preform 1,5 0,9 3 1,5 - 0,03 36,1 23 8 Preform 1,5 0,7 2,5 1,5 - 0,03 42,0 20 9 Preform 1,5 0,7 3,5 1,5 - 0,03 32,1 33 10 Preform 1,5 0,7 3 1,2 - 0,03 38,4 22 11 Preform 1,5 0,7 3 2 - 0,03 35,3 25 12 paste 1,5 0,7 3 1,5 - 0,01 31,6 20 13 paste 1,5 0,7 3 1,5 - 0,03 34,9 27 14 paste 1,5 0,7 3 1,5 - 0,25 36,5 31 15 paste 1,7 0,7 3 1,5 - 0,03 37,4 22 16 paste 1,5 0,7 2,5 1,5 - 0,03 39,2 23

Claims

1. A six-component alloy consisting of 90 to 96.8 wt.% of tin; 0.1 to 2.0 wt.% of silver; 2.0 to 4.0 wt.% of bismuth; 1.0 to 2.0 wt.% of antimony; 0.1 to 1.0 wt.% of copper; and 0.01 to 1 wt.% of germanium, wherein the six-component alloy may also include elements other than tin, silver, bismuth, antimony, copper and germanium as unavoidable impurities in very small quantities totaling > 0 to 1000 wt.ppm.

2. A six-component alloy consisting of 91.8 to 94.5 wt.% of tin; 1.3 to 1.7 wt.% of silver; 2.5 to 3.5 wt.% of bismuth; 1.2 to 1.8 wt.% of antimony; 0.5 to 0.9 wt.% of copper; and 0.02 to 0.25 wt.% of germanium, wherein the six-component alloy may also include elements other than tin, silver, bismuth, antimony, copper and germanium as unavoidable impurities in very small quantities totaling > 0 to 1000 wt.ppm.

3. The six-component alloy according to claim 1 or 2 with a solidus temperature in the range of 200 to 235°C.

4. The six-component alloy according to any of the preceding claims, prepared in each case as a flux-free solder product selected from the group consisting of solder wires, solder rods, solder foils, solder powders, solder balls, solder preforms, or in each case as a flux-comprising solder composition selected from the group consisting of solder pastes, flux-comprising solder preforms, and flux-comprising solder wires.

5. The six-component alloy prepared as a solder paste according to claim 4, comprising or consisting of 82 to 92 wt.% of a six-component alloy according to any of claims 1 to 3 in the form of solder powder or solder balls and 8 to 18 wt.% of a flux.

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

7. A use of a six-component alloy according to any of claims 1 to 6 in electronic or microelectronic applications or for the production of solder deposits on substrates.