Solder paste

Abstract

A solder paste comprising 40 to 60% by weight of a solder powder having an absolute particle size of the powder particles in the range of 2 to 25 μm and 40 to 60% by weight of a flux.

Description

Technical Field

[0001] Solder pastes, especially soft solder pastes, are mainly used in the manufacture of electronic circuits and serve to create mechanical, electrical, and thermal connections between electronic components and substrates, more precisely, between their corresponding metal contact pads (metal contact surfaces, contact metal coatings) provided for this purpose. The metal contact pads are composed of bulk metal (e.g., pure metal or metal alloy) or may have a metal surface plating, and the metal itself or the metal of the metal surface plating may be selected from metals such as copper and copper-based alloys, tin and tin-based alloys, silver and silver-based alloys, gold and gold-based alloys, and nickel and nickel-based alloys.

[0002] Examples of electronic components in the meaning of the present disclosure include diodes, LEDs (light-emitting diodes), dies, IGBTs (insulated gate bipolar transistors, bipolar transistors with insulated gate electrodes), MOSFETs (metal oxide semiconductor field effect transistors), ICs (integrated circuits), sensors, heat sinks, resistors, capacitors, coils, connection elements (e.g., clips), base plates, antennas, etc.

[0003] Examples of substrates in the meaning of the present disclosure include lead frames, PCBs (printed circuit boards), flexible electronic devices, ceramic substrates, metal ceramic substrates such as DCB substrates (direct bond copper substrates), IMS (insulated metal substrates), glass substrates, etc.

[0004] Electronic components are usually brought into contact with or applied to the substrate via solder paste. The solder paste is heated, and the solder in the paste is melted by a reflow process to form a contact between the electronic component and the corresponding metal contact pad of the substrate. After the solder cools and solidifies, the electronic component and the substrate are firmly connected (attached) to each other with the solidified solder in between via their corresponding metal contact pads.

[0005] Solder paste generally contains flux, and the flux, among other things, dissolves any optionally present unwanted oxide film on the surfaces of solder powder, the metal contact pads of electronic components, and the metal contact pads of the substrate, and thus plays a role in ensuring improved wettability during the soldering process.

[0006] International Publication No. WO 2015 / 178374 (A1) discloses a solder paste for fixing solder balls. The solder paste contains solder powder and 75 to 93% by volume (volume percentage) of a solder flux.

[0007] In the electronics industry, development towards miniaturization leading to so-called fine pitch applications or even ultra-fine pitch applications with very small dimensions down to 100 μm or less is continuously being carried out. The term "pitch" represents the distance between the center of a metal contact pad and the center of an adjacent neighbouring metal contact pad. Such development results in an increase in the mounting density of electronic components and an increase in the requirements for solder paste.

[0008] An object of the present invention is to provide a solder paste that can be used even in fine pitch or ultra-fine pitch applications.

[0009] The present invention relates to a solder paste comprising 40 to 60% by weight (weight percentage) of solder powder having an absolute particle size in the range of 2 to 25 μm and 40 to 60% by weight of flux. The flux itself i) consists of 50 to 60% by weight of at least one optionally modified natural resin, ii) 15 to 30% by weight of at least one organic solvent, iii) 5 to 15% by weight of at least one thickener, iv) 5 to 10% by weight of at least one activator, v) and 0 to 10% by weight of at least one additive other than components i) to iv).

[0010] The total of the weight percentage of the solder powder and the weight percentage of the flux is 100% by weight. The same applies to the total of the weight percentages of the flux components i) to v).

[0011] The solder paste of the present invention contains 40 to 60% by weight of solder powder, particularly tin-based solder powder. The solder powder has an absolute particle size of powder particles in the range of 2 to 25 μm, preferably 2 to 15 μm.

[0012] The solder preferably has a liquidus temperature in the range of 200 to 250 °C, preferably in the range of 200 to 230 °C.

[0013] The term "tin-based solder" means a tin-based soldering alloy containing tin as a base and one or more other alloying elements. The tin content may be at least 80% by weight. Examples of other alloying elements include silver, copper, antimony, bismuth, indium, nickel, and cobalt. Lead is an example of an alloying element that is possible but not very preferred.

[0014] The solder paste of the present invention contains 40 to 60% by weight of flux. In each case, the flux contained in the solder paste of the present invention is based on its total weight, i) 50 to 60% by weight of at least one optionally modified natural resin, and ii) 15 to 30% by weight of at least one organic solvent, and iii) 5 to 15% by weight of at least one thickener, and iv) 5 to 10% by weight of at least one activator, and v) 0 to 10% by weight of at least one additive other than components i) to iv), and consists of.

[0015] As component (i), the flux contains 50 to 60% by weight, preferably 50 to 55% by weight of at least one optionally modified natural resin. It goes without saying that for those skilled in the art, "modified" represents chemical modification. The at least one optionally modified natural resin may be an unmodified natural resin or a modified natural resin. The modified natural resin means a natural resin modified by hydrogenation, dimerization, and / or esterification of its carboxyl group. In particular, the natural resin is a rosin-type (colophonium resin type) natural resin, that is, unmodified rosin or modified rosin (rosin modified by hydrogenation, dimerization, and / or esterification of its carboxyl group).

[0016] As component (ii), the flux contains 15 to 30% by weight, preferably 20 to 25% by weight of at least one organic solvent. 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, isobornyl cyclohexanol, glycol ethers, 2-ethyl-1,3-hexanediol, n-decyl alcohol, 2-methyl-2,4-pentanediol, terpineol, and isopropanol, and mixtures thereof. Glycol ethers are preferred examples. The glycol ethers may be partially or fully etherified. Specific examples include mono-, di-, tripropylene glycol methyl ether, mono-, di-, tripropylene 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, and mixtures thereof. In some preferred cases, the at least one organic solvent may contain or consist of one or more glycol ethers.

[0017] As component (iii), the flux contains 5 to 15 wt%, preferably 8 to 12 wt% of at least one thickener. Examples include ethyl cellulose, castor oil, hydrogenated castor oil, glycerol tris-12-hydroxystearate, modified glycerol tris-12-hydroxystearate, fatty acid amide, and polyamide. Castor oil and polyamide are preferred examples. The at least one thickener may preferably contain and / or consist of castor oil and / or one or more polyamide thickeners.

[0018] As component (iv), the flux contains 5 to 10 wt% of at least one activator. The function of the at least one activator is to remove the surface oxide of the solder powder that ultimately exists. Examples include carboxylic acids, preferably dicarboxylic acids such as oxalic acid, adipic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, and tridecanedioic acid. The carboxylic acid can be combined with at least one amine. Examples of amines include imidazole, 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. Further examples of activators include hydrochloride salts such as aniline hydrochloride, glutamate hydrochloride, diethanolamine hydrochloride, diethanolamine hydrobromide, triethanolamine hydrochloride, triethanolamine hydrobromide, and halogen-containing compounds such as trans-2,3-dibromo-2-butene-1,4-diol.

[0019] As component v), the flux contains 0 to 10% by weight of at least one additive other than components i) to iv). Examples of such additives include surfactants, antioxidants, and surface modifiers.

[0020] A further subject of the present invention is a method for manufacturing the solder paste of the present invention.

[0021] The method for manufacturing the solder paste of the present invention is - a step of mixing the components of the flux, and - a step of adding the solder powder as described above, and includes.

[0022] The addition of the solder powder is generally carried out without heating, while stirring, preferably in several portions, into the presented mixture of the flux.

[0023] The solder paste of the present invention can be used to connect (attach) electronic components to a substrate. When connecting an electronic component to a substrate, the metal contact pads of the substrate and the metal contact pads of the electronic component are brought into contact via the solder paste of the present invention. Accordingly, the present invention is also a method for connecting an electronic component to a substrate, the following steps: a) providing an electronic component having at least one metal contact pad; b) providing a substrate having at least one metal contact pad corresponding to (= corresponding to one single metal contact pad of the electronic component or two or more of those metal contact pads of the electronic component) at least one metal contact pad of the electronic component; c) providing the solder paste of the present invention to at least one metal contact pad of the electronic component and / or the corresponding at least one metal contact pad of the substrate; d) bringing at least one metal contact pad of the electronic component into contact with the corresponding at least one metal contact pad of the substrate via the solder paste; e) a step of heating the solder paste to a temperature higher than the liquidus temperature of the solder, and then cooling and solidifying the solder to form a strong connection between the electronic component and the substrate; relates to a method including

[0024] For those skilled in the art, steps a) and b) are self-evident and do not need further explanation. However, to prevent misunderstanding, those skilled in the art will understand that both the electronic component and the substrate may have one, two or more of the above metal contact pads. The term "corresponding" means that the metal contact pad of the electronic component is the same as or even identical (= corresponding) to the metal contact pad of the substrate in terms of size, shape, and arrangement, and that both the metal contact pad of the electronic component and the metal contact pad of the substrate are connected to each other.

[0025] In step c), the solder paste of the present invention is provided on at least one metal contact pad of the electronic component and / or the corresponding at least one metal contact pad of the substrate. That is, the solder paste of the present invention can be applied to at least one metal contact pad of the electronic component and / or the corresponding at least one metal contact pad of the substrate, particularly the corresponding at least one metal contact pad of the substrate. The application can be carried out by conventional methods known to those skilled in the art, for example, by printing, dispensing, spraying or transfer. Printing methods such as screen printing or stencil printing are preferred. It is advantageous that the solder paste of the present invention can cope with the problems associated with stencil printing using a stencil having openings with dimensions less than 100 μm.

[0026] The applicant of the present invention has discovered unexpected and advantageous features of the solder paste of the present invention. The solder paste of the present invention exhibits so-called self-aligning properties. That is, the solder paste of the present invention that protrudes beyond the non-metallic periphery of the metal contact pads can be drawn back between the metal contact pads of the electronic component and the corresponding metal contact pads of the substrate when heated during the final processing step e). In other words, when heated during step e), it can be drawn back from the non-metallic surface portion and can gather between the metal contact pads of the electronic component and the corresponding metal contact pads of the substrate. Usually, the solder paste should be applied on the metal contact pads, and any solder paste that spreads beyond the non-metallic and electrically insulating periphery of the metal contact pads is not allowed because it means a high risk of electrical short circuit occurring after the completion of step e). However, the above-mentioned drawing-back behavior of the solder paste of the present invention allows some inaccuracy when applying it on the metal contact pads. In other words, in step c), the solder paste of the present invention allows it to be applied on the metal contact pads with some degree of protrusion, for example, it can be spread onto the non-metallic periphery of the metal contact pads, for example, up to 50 μm, or preferably up to only 25 μm.

[0027] Step d) is a so-called pick-and-place step. In step d), at least one metal contact pad of the electronic component and the corresponding at least one metal contact pad of the substrate can be brought into contact with each other through the solder paste of the present invention applied in step c). In other words, a sandwich-like arrangement having the solder paste of the present invention therebetween, that is, between the metal contact pads of the electronic component and the corresponding metal contact pads of the substrate, can be produced from the electronic component and the substrate.

[0028] Step e) is the so-called solder reflow process. In step e), the solder paste is heated to a temperature higher than the liquidus temperature of the solder, and then soldered in a sandwich configuration. After subsequent cooling and solidification of the solder, a strong connection can be formed between the electronic component and the substrate through the solder paste. The sandwich configuration or the solder paste is preferably heated to a temperature 5 to 60 °C, preferably 10 to 50 °C higher than the liquidus temperature of the solder. A person skilled in the art will understand that during step e), the flux is removed, for example, by evaporation and / or decomposition. A person skilled in the art who has read the description of step c) will also understand that during the heating process in step e), the solder paste is withdrawn from the non-metallic surface portion and accumulates between the metal contact pads of the electronic component and the corresponding metal contact pads of the substrate.

[0029] The self-aligning performance and solder performance of the solder paste of the present invention can be confirmed by visual inspection of the soldered sandwich configuration after the completion of step e). Good self-aligning performance means that there are no solder beads (lumps of solder material) around the non-metallic part of the metal contact pad, that is, no solder beads remain around the non-metallic part of the metal contact pad. Good solder performance means that no solder bridges that electrically short-circuit between the metal contact pads of the substrate or between the metal contact pads of the electronic component are generated. When direct visual inspection by the human eye is not possible, an X-ray image of the soldered sandwich configuration can be taken, and the absence of the above solder beads and the non-occurrence of the above solder bridges can be inspected.

[0030] Due to the pull-back behavior or self-alignment characteristics of the solder paste of the present invention, this solder paste becomes particularly useful in the above fine-pitch applications or ultra-fine-pitch applications. This means that the solder paste of the present invention can be used to connect an electronic component having at least one pair (= positive electrode and negative electrode) of metal contact pads to a substrate having a corresponding one pair or a plurality of pairs of metal contact pads, and each metal contact pad of each individual pair of metal contact pads is spaced apart from each other by 50 μm or more and 100 μm or less. In other words, each individual pair of metal contact pads of the metal contact pads has a narrow gap of 50 to 100 μm therebetween. Here, in the case of fine-pitch applications or ultra-fine-pitch applications, the method of connecting an electronic component to a substrate is a special embodiment of the above-described disclosed method including steps a) to e). Here, the present invention is a method of connecting an electronic component to a substrate, comprising the following steps: a') providing an electronic component having at least one pair of metal contact pads having a gap of 50 to 100 μm therebetween; b') providing a substrate having at least one pair of metal contact pads corresponding to at least one pair of metal contact pads of the electronic component (= corresponding to one single pair of metal contact pads of the electronic component or two or more pairs of metal contact pads of the electronic component); c') providing the solder paste of the present invention to at least one pair of metal contact pads of the substrate and the narrow gap of 50 to 100 μm therebetween; d') contacting at least one pair of metal contact pads of the electronic component with the corresponding at least one pair of metal contact pads of the substrate via the solder paste; e') heating the solder paste to a temperature higher than the liquidus temperature of the solder, and then cooling and solidifying the solder to form a strong connection between the electronic component and the substrate; which is related to a method.

[0031] In step a’), an electronic component having at least one pair of metal contact pads with a narrow gap of 50 to 100 μm therebetween is provided. As already described, the individual pairs of metal contact pads of the metal contact pads have a narrow gap of 50 to 100 μm therebetween. The metal contact pads represent conductive metal surface portions, while the narrow gap portions represent non-conductive (electrically insulating) non-metal surface portions, i.e., non-metal gaps. Examples of such types of electronic components include mini-LEDs and micro-LEDs having a pair of metal contact pads separated from each other by a narrow gap of 50 to 100 μm. In an advantageous embodiment, the metal contact pads of the electronic component, in particular the metal contact pads of the mini-LED or micro-LED, can represent the surface of tin or a tin-based alloy, for example, in the form of a surface plating of tin or a tin-based alloy.

[0032] In step b’), a substrate having at least one pair of metal contact pads corresponding to the at least one pair of metal contact pads of the electronic component provided in step a’) is provided. The term “corresponding” means that the at least one pair of metal contact pads of the electronic component is similar or even identical (= corresponding) to the at least one pair of metal contact pads of the substrate in terms of size, shape, arrangement, and gap width, and that both the pair of metal contact pads of the electronic component and the pair of metal contact pads of the substrate are connected to each other. By way of example, in the case of the above mini-LED or micro-LED, the substrate has a pair of metal contact pads corresponding to the metal contact pads of the pair of metal contact pads of the mini-LED or micro-LED. In other words, here, the term “corresponding” means that the pair of metal contact pads of the mini-LED or micro-LED is similar or even identical (= corresponding) to the pair of metal contact pads of the substrate in terms of size, shape, arrangement, and gap width, and that both the pair of metal contact pads of the mini-LED or micro-LED and the pair of metal contact pads of the substrate should be connected to each other, and the connection should be made so as to align the narrow gaps, or more precisely, such a connection should be made so as to position the narrow gaps to coincide as much as possible.

[0033] In step c’), the solder paste of the present invention is applied, that is, the solder paste of the present invention is provided in at least one pair of metal contact pads of the substrate and a narrow gap of 50 to 100 μm therebetween. The application can be carried out by conventional methods known to those skilled in the art, for example, by printing, dispensing, spraying or transfer. Printing methods such as screen printing or stencil printing are preferred. However, it should be noted that due to the small structures prevalent in fine pitch or ultra-fine pitch applications, the application tool (dispenser, printing screen, printing stencil, etc.) cannot apply the solder paste absolutely accurately only on at least one pair of metal contact pads of the substrate without spreading over the non-metal gap forming region therebetween at all. However, here, in the embodiments of fine pitch application or ultra-fine pitch application, the application of the solder paste of the present invention onto the narrow non-metal surface portion is not simply intentionally accepted or tolerated, but rather, on the contrary, it is clearly permitted. Therefore, in this step c’), the solder paste of the present invention is applied on at least one pair of metal contact pads of the substrate and on the narrow gap of 50 to 100 μm therebetween. That is, the solder paste of the present invention is applied over the entire metal surface portion of the contact pads of the substrate and the narrow non-metal surface portion of 50 to 100 μm that forms the gap therebetween, that is, the portion of the narrow non-metal surface portion of 50 to 100 μm that forms the gap is not left uncovered but is instead filled with the solder paste.

[0034] It is significantly advantageous that the solder paste of the present invention exhibits the above self-aligning characteristics. When heated during step e’), the solder paste of the present invention within the non-metal gap region is drawn back and collected between at least one pair of metal contact pads of the electronic component and the corresponding at least one pair of metal contact pads of the substrate.

[0035] Step d’) is a so-called pick-and-place step in which at least one pair of metal contact pads of an electronic component and at least one corresponding pair of metal contact pads of a substrate can be brought into contact with each other via the solder paste of the present invention. In other words, a sandwich arrangement can be created with the solder paste of the present invention between the electronic component and the substrate, i.e., between the metal contact pads of at least one pair of metal contact pads of the electronic component and the metal contact pads of at least one corresponding pair of metal contact pads of the substrate.

[0036] Step e’) is a so-called solder reflow step. In step e’), the solder paste of the present invention is heated to a temperature higher than the liquidus temperature of the solder to solder the sandwich arrangement, so that after subsequent cooling and solidification of the solder, a strong connection can be formed between the electronic component and the substrate via the solder paste. The sandwich arrangement or the solder paste is preferably heated to a temperature 5 to 60 °C, preferably 10 to 50 °C, higher than the liquidus temperature of the solder. During the above heating process, the solder paste of the present invention undergoes the aforementioned advantageous pulling-back treatment. As a result, the non-metallic gap solder paste is removed, and the solder of the solder paste only exists between the metal contact pads of at least one pair of metal contact pads of the substrate and the metal contact pads of at least one corresponding pair of metal contact pads of the electronic component. A person skilled in the art will understand that during step e’), the flux is removed, for example, by evaporation and / or decomposition. A person skilled in the art who has read the description of step c’) will also understand that during the heating process in step e’), the solder paste is pulled back from the non-metallic surface portion (including the non-metallic surface portion of the gap) and accumulates between the metal contact pads of at least one pair of metal contact pads of the substrate and the metal contact pads of at least one corresponding pair of metal contact pads of the electronic component.

[0037] The pull-back behavior or self-alignment performance of the solder paste of the present invention, and the soldering performance can be confirmed by taking an X-ray image of the soldered sandwich configuration after the completion of step e'). Subsequently, the X-ray image can be visually inspected. Good self-alignment performance means that there are no solder beads in the non-metal surroundings or gap regions of the metal contact pads, that is, no solder beads remain there. Good soldering performance means that no solder bridges that electrically short-circuit between the metal contact pads of the substrate or between the metal contact pads of the electronic components are generated.

Example

[0038] 52 pbw (parts by weight) of hydrogenated rosin (hydrogenated colophonium resin) having an acid value of 240 mg KOH / g was melted at 170°C, and subsequently, 25 pbw of ethylene glycol dimethyl ether, 8 pbw of polyamide thickener, 4 pbw of succinic acid, 3 pbw of N,N,N',N'-tetramethylethylenediamine, 6 pbw of surfactant, and 2 pbw of antioxidant were added at 140°C to form a flux.

[0039] 50 pbw of the flux thus prepared was mixed with 50 pbw of solder powder (SnAgCu alloy composed of 96.5 wt% Sn, 3.0 wt% Ag, and 0.5 wt% Cu, type 6 powder according to IPC-TM-650 2.2.14.2) to form a solder paste.

[0040] The solder paste thus prepared was stencil printed onto a glass-reinforced epoxy laminate FR4 PCB substrate showing a pair of rectangular copper contact pads with dimensions of 55 μm × 80 μm. The copper contact pads had an ENIG (electroless nickel immersion gold) surface finish. Each pair of copper contact pads was spaced apart from each other by a narrow gap of 50 μm. The stencil openings were rectangles with dimensions of 70 μm × 130 μm. The solder paste was applied onto the copper contact pads of the substrate and onto the narrow 50-μm gap of the non-metallic surface portion between the copper contact pads. After the solder paste stencil printing process, mini-LED dies with dimensions of 100 μm × 150 μm were placed on each pair of the solder paste patterned in a rectangle. The back surface of each mini-LED die consisted of two tin alloy plated contact pads, and each contact pad was 30 μm × 50 μm. There was a narrow gap of 50 μm between the two contact pads. The placement of the LED dies was performed such that the narrow 50-μm gap between the tin alloy plated contact pads of the LED die exactly overlapped with the narrow 50-μm gap between the copper contact pads of the substrate and was filled with the solder paste applied by stencil printing.

[0041] The sandwich-like arrangement thus prepared, consisting of a mini-LED die and an FR4 PCB substrate with solder paste in between, was soldered by heating in a nitrogen atmosphere in a reflow oven at a peak temperature of 250°C. After the solder paste melted, the sandwich-like arrangement was taken out and cooled.

[0042] After the sandwich-like arrangement was cooled, the self-alignment performance of the solder paste was evaluated. For this purpose, an X-ray image of the soldered sandwich-like arrangement was taken from above using a Nordson X-ray (model: Q5) machine, and a visual inspection was performed for any solder beads remaining on the non-metallic gap between the copper contact pads of the FR4 PCB substrate. No solder beads were detected, which means that the solder paste showed very good self-alignment performance.

[0043] Regarding the solder performance, by visually inspecting the same X-ray image, it was evaluated whether a solder bridge occurred between the two tin alloy plated contact pads of the LED die. None occurred, which means that no unwanted electrical short circuit occurred in the contact pads of the LED die.

Claims

1. A solder paste comprising 40 to 60% by weight of a solder powder having an absolute particle size of the powder particles in the range of 2 to 25 μm and 40 to 60% by weight of a flux.

2. The flux is i) 50 to 60% by weight of at least one optionally modified natural resin, ii) 15 to 30% by weight of at least one organic solvent, iii) 5 to 15% by weight of at least one thickener, iv) 5 to 10% by weight of at least one activator, v) 0 to 10% by weight of at least one additive other than components i) to iv), and the solder paste according to claim 1.

3. The solder paste according to claim 1 or 2, wherein the solder powder is a tin-based solder powder.

4. The solder paste according to any one of claims 1 to 3, wherein the solder has a liquidus temperature in the range of 200 to 250°C.

5. The solder paste according to any one of claims 2 to 4, wherein the at least one organic solvent contains or consists of one or more glycol ethers.

6. The solder paste according to any one of claims 2 to 5, wherein the at least one thickener contains or consists of castor oil and / or one or more polyamide thickeners.

7. A method for connecting an electronic component to a substrate, comprising the following steps: a) providing an electronic component having at least one metal contact pad; b) providing a substrate having at least one metal contact pad corresponding to the at least one metal contact pad of the electronic component; c) providing the solder paste according to any one of claims 1 to 6 to the at least one metal contact pad of the electronic component and / or the corresponding at least one metal contact pad of the substrate; d) bringing the at least one metal contact pad of the electronic component into contact with the corresponding at least one metal contact pad of the substrate via the solder paste; e) heating the solder paste to a temperature higher than the liquidus temperature of the solder, and then cooling and solidifying the solder to form a strong connection between the electronic component and the substrate. A method comprising the above steps.

8. The method according to claim 7, wherein in step c), the solder paste is applied by spreading it slightly beyond the at least one metal contact pad and up to 50 μm onto its non-metallic surroundings.

9. A method for connecting an electronic component to a substrate, comprising the following steps: a') providing an electronic component having at least one pair of metal contact pads with a gap of 50 to 100 μm therebetween; b') providing a substrate having at least one pair of metal contact pads corresponding to the at least one pair of metal contact pads of the electronic component; c') providing a solder paste according to any one of claims 1 to 6 to at least one pair of metal contact pads of the substrate and the narrow gap of 50 to 100 μm therebetween; d') bringing the at least one pair of metal contact pads of the electronic component into contact with the corresponding at least one pair of metal contact pads of the substrate via the solder paste; e') heating the solder paste to a temperature higher than the liquidus temperature of the solder, and then cooling the solder to solidify it while forming a strong connection between the electronic component and the substrate. A method comprising the above steps.

10. The method according to claim 9, wherein the electronic component is a mini-LED or a micro-LED having a pair of metal contact pads separated from each other by a narrow gap of 50 to 100 μm.

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