Composition usable as a temporary fixative

Abstract

A composition comprising: (A) 20-30% by weight of one or more thermoplastic polymers; (B) 45-69% by weight of an organic solvent; (C) 2-15% by weight of silicic acid particles; (D) 0.5-10% by weight of an organic thickener; (E) 1-10% by weight of a particulate inorganic filler material having a Mohs hardness in the range of 1 to 8; and (F) 0-1% by weight of one or more components different from components (A)-(E).

Description

[Technical field]

[0001] The present invention relates to a composition that can be used as a temporary fixing agent in the electronics field.

[0002] Compositions that can be used as temporary fixatives (prefixatives) in the electronics field are known, for example from EP 3276652, WO 2017 / 060140 and WO 2019 / 170213. Such compositions can be used to temporarily fix (prefix) a not yet fixedly joined structure consisting of one or more electronic components with one or more solder or sintered preforms. The structures thus temporarily fixed can subsequently be fixedly joined by corresponding heat or temperature treatments, i.e. soldering or sintering. For example, temporary fixatives can be used to temporarily fix solder preforms that are converted into solder deposits or to temporarily fix sintered preforms on electronic components or to temporarily fix solder preforms or sintered preforms between the respective electronic components. However, temporary fixatives can also be used, for example, to temporarily fix an electronic component on a solder deposit of another electronic component to which a solder deposit has been applied. The heat or temperature treatment of the temporarily fixed structure is usually carried out in an oven. In the case of a temporarily fixed structure comprising a sintered preform, the furnace may be, for example, a pressure sintering furnace, and in the case of a temporarily fixed structure comprising a solder preform or solder deposit, it may be a reflow furnace.

[0003] Finally, the temporary fixative can also be used, for example, on a solder deposit on an electronic component to adhere the temporary fixative to its outwardly facing free contact surface.

[0004] The term "fixedly bonded structures" is used herein to mean structures that are mechanically fixedly bonded. A mechanically fixed metal bond is, by definition, electrically conductive. In other words, the fixedly bonded contact surfaces of the structures are not only mechanically fixed, but also electrically conductively bonded.

[0005] The term "solder preform" as used herein refers to solder metal in the form of a shaped article, such as, for example, a solder metal film, a solder metal tape, a solder metal platelet, or a solder metal cylinder. The solder preform has separate contact surfaces, such as, for example, contact surfaces disposed on opposing sides of the solder preform. The thickness of the solder preform may be, for example, in the range of 10 to 750 μm.

[0006] The solder or solder metal is, for example, tin or a tin-rich alloy. Examples of tin-rich alloys include those with a tin percentage in the range of, for example, 90-99.5 Gew.% (weight %). Examples of alloy metals are copper, silver, indium, germanium, nickel, lead, bismuth, and antimony. The alloy may be lead-containing or lead-free. Lead-free alloys may be selected, for example, from the group consisting of SnAg, SnBi, SnSb, SnAgCu, SnCu, SnSb, InSnCd, InBiSn, InSn, BiSnAg, or SnAgCuBiSbNi. Lead-containing alloys may be selected, for example, from the group including SnPb and SnPbAg. The melting temperature of the solder may be, for example, in the range of 150-500°C, in particular 170-350°C.

[0007] The term "sintered preform" as used herein refers to a sintering agent that is not completely sintered, for example as a sintered metal film, but in particular to a dry, unsintered or simply presintered sintering paste. The sintering agent or sintering paste may be a metallic sintering agent or a metallic sintering paste. The metal of the metallic sintering agent or metallic sintering paste may in particular be copper or silver. In the case of a metallic sintering paste, the copper or silver is usually present in particulate form.

[0008] The term "solder deposit" is used herein to refer to solder fixedly bonded to a contact surface of an electronic component so as to be capable of being fixedly bonded to another electronic component via the contact surface of that component. A solder deposit on an electronic component can typically be produced by melting a soldering agent, such as a solder paste applied or a solder preform placed on the contact surface of the electronic component, and then cooling and hardening the solder metal. The hardened solder metal bonded to the contact surface of the electronic component is referred to as a solder deposit as described above. A solder deposit bonded to a contact surface of an electronic component has a free contact surface facing outward, which allows it to function as a solder material for establishing a solder bond with another electronic component. To this end, the solder can be melted to molten solder in an oven, such as a reflow oven, and then cooled and hardened after removal from the oven to form the desired fixed bond between the electronic components.

[0009] The term "electronics component" as used herein refers to a substrate commonly used in electronics and preferably to an active or passive electronic component that cannot be further broken down. Electronic components have contact surfaces, in particular metallic contact surfaces.

[0010] Examples of substrates include IMS substrates (insulated metal-substrates), AMB substrates (active metal copper circuit boards), DCB substrates (direct copper bonded substrates), ceramic substrates, PCBs (printed circuit boards), and lead frames.

[0011] Examples of active electronic components include diodes, light emitting diodes (LEDs), dies (semiconductor chips), insulated-gate bipolar transistors (IGBTs), integrated circuits (ICs), and metal-oxide-semiconductor field-effect transistors (MOSFETs).

[0012] Examples of passive electronic components include sensors, base plates, cooling bodies, connecting members (eg, clips), resistors, capacitors, inductors, and antennas. Summary of the Invention [Problem to be solved by the invention]

[0013] The problem is that in all of the embodiments mentioned at the beginning, undesirable position changes can occur between the preform and the electronic component during the movement or transportation of the structure that is not yet fixedly connected to one another, for example during transportation to an oven. The same situation also occurs during the movement or transportation of a structure consisting of an electronic component with a solder deposit and another electronic component to be connected to it. In the worst case, the electronic component can not only shift or tilt out of position relative to the preform or the electronic component to be connected or relative to the solder deposit, but can even fall off. This can be caused, for example, by vibrations during transportation or by acceleration or braking processes. The temporary fixing already described at the beginning by a temporary fixing agent takes care of this.

[0014] The object of the present invention is to provide a temporary fixative that can be used in the electronics field in the above sense, which has an advantageous viscous behavior in the sense that it has as little tendency to flow as possible after application. The required temporary fixative must have a high yield point, which allows it to be applied in a positionally and shape-stable manner. The viscous behavior of the required temporary fixative is particularly important when applying with methods that cause shear loads, such as dispensing or jetting. The temporary fixative should remain as shape- and positionally stable as possible after its application, and should contribute to the process safety of the temporary fixing process carried out industrially with it. In addition to this, the required temporary fixative must minimize wear of the tools or tool surfaces used in its application, thereby contributing to process safety or process stability. Furthermore, the required temporary fixative must not damage the surfaces that come into contact with it, especially during its application.

[0015] This problem can be solved by providing the composition described below. The present invention therefore relates to a composition that can be used as a temporary fixing agent, in particular as a temporary fixing agent in the electronics field. It should be noted that the term "composition according to the present invention" as used herein means the temporary fixing agent in its original state, i.e. before it is applied. In contrast, the term "temporary fixing agent" is used not only as a name for the original composition according to the present invention, but also as a name for a material formed by partial or complete loss of volatile substances that may occur during or after application. The aforementioned volatile substances may in particular be organic solvents that are inherently contained in the original composition according to the present invention.

[0016] The composition according to the invention comprises (A) 20 to 30% by weight, preferably 22 to 28% by weight, of one or more thermoplastic polymers, (B) 45 to 69% by weight, preferably 50 to 65% by weight, of an organic solvent; (C) 2 to 15% by weight, preferably 5 to 9% by weight, of silicic acid particles; (D) 0.5 to 10% by weight, preferably 1 to 4% by weight, of an organic thickener, (E) 1 to 10% by weight, preferably 5 to 8% by weight, of a particulate inorganic filler material having a Mohs hardness in the range of 1 to 8; (F) 0 to 1% by weight, preferably 0 to 0.5% by weight, of one or more components different from the components (A) to (E).

[0017] In a preferred embodiment, the composition according to the invention comprises (A) 22 to 28 weight percent of one or more thermoplastic polymers; (B) 50 to 65% by weight of an organic solvent; (C) 5 to 9% by weight of silicic acid particles; (D) 1 to 4% by weight of an organic thickener; (E) 5 to 8 weight percent of a particulate inorganic filler material having a Mohs hardness in the range of 1 to 8; (F) 0 to 0.5% by weight, particularly 0.1 to 0.5% by weight, of one or more components different from the components (A) to (E).

[0018] The composition according to the invention comprises (A) 20-30% by weight, preferably 22-28% by weight, of one or more thermoplastic polymers, examples of which include thermoplastic polyesters, polyurethanes, and (meth)acrylic copolymers, respectively, as well as hybrids of these polymer types.

[0019] As the thermoplastic polymer, a thermoplastic (meth)acrylic copolymer is preferred. "(meth)acrylic" means "methacrylic" and / or "acrylic". It is a copolymer of (meth)acrylic compounds, which may also contain copolymers other than the (meth)acrylic type, such as vinyl compounds, in a total weight percentage of <50% by weight based on the total (meth)acrylic copolymer. Examples of (meth)acrylic compounds that account for >50% by weight based on the total (meth)acrylic copolymer are (meth)acrylic acid, (meth)acrylic acid esters, and (meth)acrylamide, and examples of vinyl compounds include compounds such as vinyl esters, vinyl ethers, and styrene.

[0020] Preferably, the composition according to the invention, component (A) thereof consists of one or more thermoplastic (meth)acrylic copolymers.

[0021] The thermoplastic polymer(s) may have, for example, a glass transition temperature in the range of 40 to 100° C. The glass transition temperature can be determined by DSC (differential scanning calorimetry) at a heating rate of 10 K / min according to DIN EN ISO 11357-1.

[0022] Unless otherwise noted, all standards cited herein are current as of the filing date.

[0023] The thermoplastic polymer or polymers may have a weight-average molar mass Mw, for example, in the range of 30 000 to 180 000. The weight-average molar mass Mw can be determined by GPC (gel permeation chromatography, polystyrene standards, polystyrene gel as stationary phase, tetrahydrofuran as mobile phase) according to DIN 55672-1.

[0024] The thermoplastic polymer(s) may be acid group-free or may have acid groups, for example according to an acid number of <50 mg KOH / g, preferably <25 mg KOH / g, in particular <10 mg KOH / g. However, it is particularly preferred that the thermoplastic polymer does not have acid groups and does not have an acid number. As used herein, the expression "acid group" refers to a group that functions as a proton donor and converts HO in water. + By this we mean functional groups capable of forming ions, such as carboxy groups, sulfonic acid groups, etc. The determination of the acid number, such as the carboxy number, of organic polymers is well known to the person skilled in the art and is determined, for example, by DIN EN ISO 2114.

[0025] The thermoplastic polymer or polymers are soluble in the organic solvent (B), in other words, component (A) is present in the composition according to the invention in a dissolved state in component (B).

[0026] The composition according to the invention comprises (B) 45 to 69% by weight, preferably 50 to 65% by weight, of an organic solvent. The organic solvent or solvents (B) are in particular organic solvents boiling at ≦285° C. Examples thereof are aliphatics such as toluene and xylol; ketones such as methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate, isobutyl acetate and dimethyl succinate; glycol ethers such as diethylene glycol monobutyl ether; alcohols such as benzyl alcohol and in particular terpineol.

[0027] The composition according to the present invention contains (C) 2 to 15% by weight, preferably 5 to 9% by weight, of silicic acid particles. The silicic acid particles are used as an inorganic thickener. The silicic acid particles may be, for example, 50 to 500 μm. 2 / g. The unit is m 2 The specific surface area in g / g can be determined by BET measurement (static volumetric measurement according to chapter 6.3.1, gas used: nitrogen) as specified in DIN ISO 9277. The silica particles may have an average particle size (d50) in the range of, for example, 5 to 50 nm.

[0028] As used herein, the term "average particle size" refers to the average particle diameter (d50) as can be determined by laser diffraction. Laser diffraction measurements can be performed by suitable particle sizers, such as, for example, the Mastersizer 3000 from Malvern Instruments.

[0029] The composition according to the invention comprises (D) 0.5-10% by weight, preferably 1-4% by weight, of an organic thickener. The organic thickener may be one or more of various organic thickeners in combination with one another, such as are well known to the skilled artisan as organic thickeners, organic anti-sagging agents and / or organic thixotropic agents, in particular for solvent-based non-aqueous coatings. Examples include hydrogenated castor oil, modified fatty derivatives, cellulose derivatives such as ethylcellulose, diamides, polyamides, diureas and polyureas. Component (D) preferably consists of one or more cellulose derivatives, in particular ethylcellulose.

[0030] The organic thickener (D) may be completely or colloidally soluble in the organic solvent (B), in other words, component (D) may be present in the composition according to the invention in a completely or colloidally dissolved state in component (B).

[0031] The composition according to the invention comprises (E) 1-10% by weight, preferably 5-8% by weight, of a particulate inorganic filler material having a Mohs hardness in the range of 1-8. The particulate inorganic filler material may be particles of one or more different inorganic filler materials, each having a Mohs hardness in the range of 1-8. The particles of the inorganic filler material preferably have a Mohs hardness in the range of 1-6, in particular in the range of 1-4. Examples of suitable inorganic filler materials include zirconium silicate, quartz, titanium dioxide, mica, calcium silicate, kaolin, and α-boron nitride. α-boron nitride is a particularly preferred example, which may also be included in the composition according to the invention as the sole inorganic filler material of type (E). The one or more inorganic filler materials are present as particles, the average particle size (d50) of which may be, for example, in the range of 5-20 μm, preferably 5-10 μm.

[0032] Component (E) does not contain silicic acid particles.

[0033] The composition according to the invention may contain (F) 0-1% by weight, preferably 0-0.5% by weight, of one or more components different from components (A)-(E). Examples include fillers and additives, as are well known to the skilled artisan as additives, in particular for solvent-based, non-aqueous coating agents. In particular, mention may be made here of additives which influence the surface tension, such as wetting additives. Component (F) and therefore also the composition according to the invention preferably does not contain aluminum oxide particles.

[0034] The composition according to the present invention can be produced by mixing the components (A) to (E) and / or (A) to (F).

[0035] The viscosity behavior of the composition according to the invention is of course influenced by all its components, however, it has been shown to be important that the composition according to the invention simultaneously comprises components (C) and (D).

[0036] The composition according to the present invention is characterized by having a high yield point τ0 over a relative temperature range of, for example, 20 to 80° C. For example, the yield point τ0 of the composition according to the present invention is in the range of, for example, 200 to 300 Pa at 23° C., in the range of, for example, 90 to 200 Pa at 50° C., and in the range of, for example, 40 to 100 Pa at 75° C. The yield point τ0 at the relevant temperature can be specified by For example, it can be performed by rotational viscometry, for example with a cone diameter of 25 mm and a cone angle of 2°, a measurement gap of 104 μm, and a viscosity of 0.05 to 50 s within 15 minutes. -1 This can be done using the plate-and-cone measurement principle with a uniformly increasing shear rate over a range of

[0037] The composition or temporary fixing agent according to the present invention is adhesive, that is, it is adhesive both under the conditions of use as a temporary fixing agent, i.e., during application, and also during the production of the temporarily fixed structure, i.e., in the temperature range of, for example, 60 to 130° C. Factors that greatly influence the adhesive action in this phase are the glass transition temperature of one or more thermoplastic polymers (A) and the proportion of one or more organic solvents (B).

[0038] The composition according to the present invention can be successfully used as a temporary fixing agent, particularly in the electronics field.

[0039] The composition according to the invention can be used to temporarily fix a not yet fixedly bonded structure consisting of one or more electronic components with one or more solder preforms or sintered preforms. For example, the composition according to the invention can be used to temporarily fix a solder preform or sintered preform that converts into a solder deposit on an electronic component. In that case, the temporarily fixed structure comprises or consists of an electronic component and a solder preform that converts into a solder deposit, or comprises or consists of an electronic component and a sintered preform, each with a temporary fixing agent between the electronic component and the preform. Furthermore, the composition according to the invention can be used to temporarily fix a solder preform or sintered preform between a plurality of electronic components. In that case, the temporarily fixed structure can comprise or consist of a plurality of electronic components and solder preforms or sintered preforms between them, and a temporary fixing agent between the preform and at least one of the plurality of electronic components.

[0040] The composition according to the invention can also be used for temporarily fixing an electronic component on another electronic component having a solder deposit applied thereto, where the temporarily fixed structure comprises or consists of a first electronic component on the solder deposit of the other electronic component having a solder deposit applied thereto, and a temporary fixing agent between the first electronic component and the solder deposit, or more precisely between the first electronic component and the originally outwardly facing free contact surface of the solder deposit of the other electronic component.

[0041] Additionally, compositions according to the present invention can be utilized to apply a temporary fixative to the outwardly facing free contact surfaces of solder deposits on electronic components.

[0042] The application of the composition or temporary fixing agent according to the invention is carried out in all of the above-mentioned application types on at least one contact surface, which can be either a contact surface of an electronic component, a contact surface of the above-mentioned solder preform or sintered preform, or else the outwardly facing free contact surface of a solder deposit.

[0043] The composition according to the invention can be applied in any of the above-mentioned application forms by various application techniques, for example by immersion, dispensing or jetting, in particular by dispensing or jetting, whereby, as already mentioned, the application site or sites are the above-mentioned contact surfaces.

[0044] The application of the composition according to the invention is advantageously carried out in a heated state, for example in the temperature range of 45-75° C., i.e. the composition according to the invention leaves the application tool heated to the relevant temperature. As already mentioned at the beginning, in the preferred application by dispensing or jetting, the composition according to the invention is also subjected to further shear.

[0045] In particular, the preferred dispensing or jet application shows the advantageous behavior of the compositions according to the invention, i.e. they cause only little wear of the corresponding application tools, for example wearing parts such as nozzles, plungers or screw-type metering valves, which need only be replaced after a relatively long period of use.

[0046] The composition according to the invention can be applied, for example, in the form of a rod on the side of the preform, or in particular in the form of dots, for example hemispherical or nearly hemispherical dots. The height of the dots immediately after application can be, for example, in the range of 50 to 80 μm. The diameter immediately after application can be, for example, in the range of 200 to 1000 μm.

[0047] During the route of the application tool to the application site, the composition according to the present invention utilized as a temporary fixing agent may lose a portion of the organic solvent (B) originally contained therein due to evaporation loss.

[0048] The application of the composition according to the invention can be followed by drying first in order to partially or completely remove the organic solvent (B) contained therein. Alternatively, the application of the composition according to the invention can be followed by the preparation of the desired temporarily fixed structure according to any one of the above-mentioned embodiments, followed by drying. Drying can be carried out, for example, at an object temperature of 90 to 150° C. for 2 to 30 minutes. Furthermore, it is also possible not to dry at all. That is, it is also possible to leave it to passive drying without taking any active measures for drying.

[0049] As can already be seen from the above explanations regarding the adhesive action, the proportion of the organic solvent or solvents (B) is a factor that greatly influences the adhesive action. The skilled person can influence the adhesive action through the selection of the drying parameters. Furthermore, the temperature conditions under which the temporarily fixed structure is transported and / or stored are taken into consideration. This is generally done, for example, in the temperature range of 18-28° C. The skilled person will make similar considerations for electronic components to which a solder deposit is attached and to which a temporary fixing agent is applied on the free contact surface facing outwards of the solder deposit.

[0050] As a result of using the composition according to the present invention as a temporary fixing agent in the electronics field, the present invention also covers electronic components to which a solder deposit is attached and to which a temporary fixing agent made of the composition according to the present invention is applied on the free contact surface facing outward of the solder deposit. In this case, the organic solvent (B) originally contained in the composition according to the present invention may completely remain in the temporary fixing agent or may usually be partially or completely removed.

[0051] As a further result of using the composition according to the present invention as a temporary fixing agent in the electronics field, the present invention also relates to a temporarily fixed structure based on each of the above-described embodiments, in which the following examples (1) to (5) are particularly included. (1) A temporarily fixed structure comprising an electronic component and a solder preform, with a temporary fixative comprising the composition of the present invention applied between them. (2) A temporarily fixed structure comprising an electronic component and a sintered preform, with a temporary fixative comprising the composition of the present invention applied therebetween. (3) A temporarily fixed structure comprising a plurality of electronic components and one or more sintered preforms therebetween, wherein a temporary fixative comprising the composition according to the present invention is applied between at least one of the electronic components and the plurality of sintered preforms or at least one of the sintered preforms. (4) A temporarily fixed structure comprising a plurality of electronic components and one or more solder preforms therebetween, wherein a temporary fixative comprising the composition according to the present invention is applied between at least one of the electronic components and the plurality of solder preforms or between at least one of the solder preforms. (5) A temporarily fixed structure, in which a first electronic component is placed on a solder deposit of another electronic component having a solder deposit attached thereto, and a temporary fixative comprising a composition according to the present invention is applied between the first electronic component and the solder deposit.

[0052] In this case, the organic solvent (B) originally contained in the composition according to the present invention may completely remain in the temporary fixing agent in all of the temporarily fixed structures of Examples (1) to (5), or may usually be partially or completely removed.

[0053] To transfer the temporarily fixed state into a fixedly bonded state by soldering or sintering, the temporarily fixed structures, for example according to the above-mentioned examples (1) to (5), can finally be subjected to a corresponding heat or temperature treatment, during which the temporary fixing agent can be removed, with the exception of harmless inorganic residues remaining in the form of silicate particles and inorganic fillers.

[0054] example: To prepare an exemplary temporary fixing agent, a thermoplastic (meth)acrylic copolymer, α-terpineol, and ethyl cellulose were mixed in the amounts listed in Table 1 at 70-80°C until all components were dissolved. Then, inorganic filler material and silicic acid particles were added with stirring, and the mixture was allowed to swell for 10 minutes at 70-80°C. The temporary fixing agent showed Casson yield behavior.

[0055] Rheometer (Physika / MCR301, plate-and-cone measuring principle, cone diameter 25 mm, cone angle 2°, measuring gap 104 μm, 0.05 to 50 s within 15 min) -1The yield point τ0 was determined at three different temperatures (23°C, 50°C, and 75°C) using viscosity measurements at shear rates that increased uniformly over the range of 100°C.

[0056] [Table 1]

[0057] The temporary fixatives E1 and E2 according to the invention allow more dispensing processes before the screw-type metering valve of the dispenser wears out than the control compositions V1 to V3.

Claims

1. One or more thermoplastic polymers selected from the group consisting of (A) 20% to 30% by weight of a thermoplastic polyester, a thermoplastic polyurethane, a thermoplastic (meth)acrylic copolymer, and a thermoplastic hybrid of these polymer types; (B) 45% to 69% by weight of an organic solvent that can dissolve component (A) and boils at ≤285°C; (C) 2% to 15% by weight of silicic acid particles having a specific surface area in the range of 50 to 500 m2 / g and an average particle size (d50) in the range of 5 to 50 nm; (D) 0.5% to 10% by weight of one or more cellulose derivatives; (E) 1% to 10% by weight of a particulate inorganic filler material having a Mohs hardness in the range of 1 to 8 and selected from the group consisting of zirconium silicate, quartz, titanium dioxide, mica, calcium silicate, kaolin, and α-boron nitride; (F) 0% to 1% by weight of one or more components different from components (A) to (E) A composition comprising.

2. One or more thermoplastic polymers selected from the group consisting of (A) 22% to 28% by weight of a thermoplastic polyester, a thermoplastic polyurethane, a thermoplastic (meth)acrylic copolymer, and a thermoplastic hybrid of these polymer types; (B) 50% to 65% by weight of an organic solvent that can dissolve component (A) and boils at ≤285°C; (C) 5% to 9% by weight of silicic acid particles having a specific surface area in the range of 50 to 500 m2 / g and an average particle size (d50) in the range of 5 to 50 nm; (D) 1% to 4% by weight of one or more cellulose derivatives; (E) 5% to 8% by weight of a particulate inorganic filler material having a Mohs hardness in the range of 1 to 8 and selected from the group consisting of zirconium silicate, quartz, titanium dioxide, mica, calcium silicate, kaolin, and α-boron nitride; (F) 0% to 0.5% by weight of one or more components different from components (A) to (E) The composition according to claim 1, comprising.

3. The composition according to claim 1 or 2, wherein the component (E) is α-boron nitride.

4. Use of the composition according to claim 1 or 2 as a temporary fixing agent in the field of electronics.

5. Use according to claim 4 for temporarily fixing a yet-unfixed structure consisting of one or more electronics components having one or more solder preforms or sintered preforms, or for temporarily fixing an electronics component on another electronics component to which a solder deposit has been applied.

6. Use of the composition according to claim 1 or 2 for applying a temporary fixing agent on a free contact surface facing outward of a solder deposit on an electronics component.

7. Use according to any one of claims 4 to 6, wherein the composition is applied by dipping, dispensing, or jetting.

8. Use according to claim 7, wherein the composition is applied in a temperature range of 45 to 75 °C.