WO2021043708A1 - Alliage de brasage et pâte à braser contenant ledit alliage - Google Patents

Alliage de brasage et pâte à braser contenant ledit alliage Download PDF

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Publication number
WO2021043708A1
WO2021043708A1 PCT/EP2020/074193 EP2020074193W WO2021043708A1 WO 2021043708 A1 WO2021043708 A1 WO 2021043708A1 EP 2020074193 W EP2020074193 W EP 2020074193W WO 2021043708 A1 WO2021043708 A1 WO 2021043708A1
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WO
WIPO (PCT)
Prior art keywords
solder
alloy
rosin
lead
flux
Prior art date
Application number
PCT/EP2020/074193
Other languages
English (en)
Inventor
Daniel BUCKLAND
Ian Wilding
Ren GUANG
Maurice COLLINS
Original Assignee
Henkel Ag & Co. Kgaa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Henkel Ag & Co. Kgaa filed Critical Henkel Ag & Co. Kgaa
Priority to CN202080062342.XA priority Critical patent/CN114340836A/zh
Priority to EP20761287.0A priority patent/EP4025379A1/fr
Publication of WO2021043708A1 publication Critical patent/WO2021043708A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/26—Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
    • B23K35/262—Sn as the principal constituent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
    • B23K35/025—Pastes, creams, slurries
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C13/00—Alloys based on tin
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3457—Solder materials or compositions; Methods of application thereof
    • H05K3/3463—Solder compositions in relation to features of the printed circuit board or the mounting process
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3457—Solder materials or compositions; Methods of application thereof
    • H05K3/3485—Applying solder paste, slurry or powder

Definitions

  • the present invention concerns a lead-free solder alloy and a solder paste containing said alloy. More particularly, the present invention is concerned with a solder alloy containing gallium as a micro-alloying element and to a solder paste formed from said alloy and a solder flux.
  • solder alloys are used to make permanent electrical connections between two conductors and the associated soldering process is typically effected by heating the solder to above its melting point, surrounding the conductors to be connected with molten solder and allowing the solder to cool.
  • solder alloys are used to interconnect semiconductor devices, including integrated circuit chips fabricated on a silicon wafer: an array of solder bumps are deposited on the top side of the wafer, the chip is flipped such that the solder bumps align with matching pads on a substrate and the system is heated to flow the solder.
  • solders must still exhibit low melting points and sufficient conductivity for electronics applications. Whilst lead-free solders are known, these solders typically require processing temperatures that are 30 to 40°C higher than those historically used for production with tin-lead solders.
  • the established lead-free solder SAC 305 - comprising 96.5 wt.% tin (Sn), 0.5 wt.% copper (Cu) and 3 wt.% silver (Ag) - has a minimum processing temperature of approximately 232°C and its use thus requires specialized circuit board materials which can withstand these elevated temperatures. These high temperatures can thermally damage a printed circuit board (PCB) and many components attached thereto.
  • PCB printed circuit board
  • the replacement of Sn-Pb solders can impact the susceptibility of printed circuit boards - even when using circuit boards formed from specialized materials at elevated temperatures - to pad cratering. This is a fracture in the resin between copper foil on the PCB and the outermost fibreglass layer of a PCB and is considered a high strain rate event with minimal creep. Less compliant solders or those solders with higher yield points will increase pad cratering potential as they provide minimal load sharing. Further, many tin- based, lead-free solders have the propensity to grow tin filament whiskers when placed under compressive stress which may cause an electrical shortage: this is of particular concern in applications requiring high reliability, such as medical devices, aerospace applications and military applications.
  • solders installed within electronic circuit boards can be subjected to one or both of: significant temperature changes, for example within the range from -40° to 150°C; and, vibration loads.
  • significant temperature changes for example within the range from -40° to 150°C
  • vibration loads When subjected to the former, the difference of the coefficients of linear expansion of the mounted electronic components and the substrate can induce stress: additionally, repeated plastic deformation caused by temperature changes tends to cause cracks in a solder joint, and the stress repeatedly applied with the lapse of time concentrates in the vicinity of the tips of the cracks, so that the cracks tend to transversely develop to the deep portion of the solder joint. Where cracks become markedly developed, this can disconnect the electrical connection between the electronic components and the electronic circuit formed on the substrate. Vibration of the electronic circuit board can exacerbate the development of the cracks.
  • JP H08-252688 (Fujitsu Ltd.) describes a solder alloy for low-temperature bonding of parts within an electronic apparatus, said solder alloy consisting of: 37 to 58 wt.% Sn; 0.1 to 2.5 wt.% Ag; and, the balance Bi. It has been observed that small electronic devices - such as mobile phones or notebook computers - in which these Sn — Bi based solder alloys are used show low impact strength with fractures commonly occurring at the solder bonding interface.
  • JP 2002018589 (Senju Metal Industry Co.) describes a lead-free solder alloy which is obtained by adding 0.005 to 0.2 wt.% Ga to Sn which is the main component.
  • Sn which is the main component.
  • Cu, Sb, Ni, Co, Fe, Mn, Cr or Mo are added to the lead-free solders.
  • Bi, In or Zn are added to the lead-free solders to inhibit the oxidation thereof.
  • a lead-free solder alloy which consists essentially of or consists of: from 0.01 to 11 wt.% of zinc (Zn); from 0.01 to 6 wt.% of bismuth (Bi); from 0.01 to 2 wt.% of gallium (Ga); and, tin (Sn), wherein said weight percentages are based on the total weight of the alloy.
  • the tin constitutes the majority element of the solder alloy and is present to facilitate the wetting of the molten solder alloy to the metallic substrates to which it is to be adhered in use.
  • the zinc content in the alloy is not elevated above 11 wt.% as such a level is considered: i) to diminish the oxidation resistance of the alloy, leading to a shorter shelf life; ii) to worsen the wetting performance of the alloy; and, iii) to render the alloy more brittle due to the existence of rich primary Zn phase.
  • the melting temperature of the oxides is very high compared to the melting point of the solder alloys and the presence of the oxide is thus deleterious to the reflow and wetting properties of the alloy.
  • a bismuth content higher than 6 wt.% will result in enlarged pasty ranges and diminished mechanical strength of the alloy.
  • a gallium content of greater than 2 wt.% is considered deleterious to the ductility and wettability of the alloy.
  • the defined solder alloy is in particulate form and has an average particle size of from 0.05 to 150 pm, for example from 5 to 75 pm.
  • the particulate alloy may be further characterized in that: from 90 to 100% by volume of said particles are spherical; and, from 0 to 10% by volume of said particles are non-spherical.
  • a solder paste comprising, based on the weight of said paste: from 40 to 95 parts by weight of a particulate solder alloy having an average particle size of from 0.05 to 150 pm; and, from 5 to 60 parts by weight of solder flux, wherein said solder alloy consists essentially of or consists of: from 0.01 to 11 wt.% of zinc (Zn); from 0.01 to 6 wt.% of bismuth (Bi); from 0.01 to 2 wt.% of gallium (Ga); and, tin (Sn), wherein said weight percentages are based on the total weight of the alloy .
  • the solder flux of the paste comprises: a) at least one binder; b) at least one solvent; and, optionally c) additives.
  • Said at least one binder a) of the solder flux should preferably comprise: at least one rosin resin; at least one thermoplastic polymer; at least one thermosetting crosslinkable resin; or, a mixture thereof.
  • the solder flux should comprise either non-activated rosin (R) or mildly activated rosin (RMA).
  • the present invention provides a method of forming a solder joint, said method comprising: (i) providing two or more work pieces to be joined; (ii) providing a solder paste comprising a solder flux and solder alloy particles as defined herein above and in the appended claims; (iii) heating the solder paste in the vicinity of the work pieces to be joined to form a solder joint, wherein upon heating the solder paste the flux forms a residue which at least partially and preferably completely covers the solder joint.
  • the two or more work pieces to be joined typically comprise: an electronic component, such as a chip resistor or a chip capacitor; or, a copper pad typically disposed on a printed circuit board.
  • the term “consists essentially of’ is intended to mean that impurities may be tolerated within the powder in an amount of up to 0.25 wt.%, based upon the weight of the powder.
  • the constituent metals of the solder alloy may often be secondary or refined metals which are not absolutely (100%) pure.
  • impurities can be introduced into the solder powder from holding fixtures or from the solder pot itself.
  • impurities the typical impurities which might be present include: copper (Cu); gold (Au); cadmium (Cd); aluminium (Al); iron (Fe); sulphur (S); and, phosphorous (P).
  • lead free means that that the lead content is less than 0.01 wt%, preferably less than 0.001 wt%, based on the weight of the alloy.
  • the word “may” is used in a permissive sense - that is meaning to have the potential to - rather than in the mandatory sense.
  • ambient conditions refers to a set of parameters that include temperature, pressure and relative humidity of the immediate surroundings of the element in question.
  • ambient conditions are: a relative humidity of from 30 to 100% percent; a temperature in the range from 20 to 40°C; and, a pressure of 0.9 to 1.1 bar.
  • room temperature is 23°C ⁇ 2°C.
  • boiling point is the atmospheric boiling point, unless indicated otherwise, with the atmospheric boiling point being the boiling point as determined at a pressure of 100 kPa (0.1 MPa).
  • initial boiling point and boiling point range of the high boiling point hydrocarbon mixtures are as determined by ASTM D2887.
  • solidus temperature refers to the temperature below which the alloy exists as a solid phase and above which there is incipient melting of the alloy.
  • liquidus temperature is the lowest temperature at which the alloy is completely liquid. The range between the liquidus and solidus temperature is assigned the term "pasty range" in this application.
  • the liquidus and solidus temperatures mentioned herein refers to temperatures measured using Differential Scanning Calorimetry (DSC). Specifically DSC measurements were performed on a Netzsch DSC 204 F1 Phoenix (Netzsch Geratebau GmbH, Selb/Bayern, Germany) at a heating rate of 10 K/min for specimens of 4 mm x 2 mm x 0.5 mm. Samples were put into an AI 2 O 3 pan in the DSC apparatus at room temperature and cooled to -40°C at the highest possible rate and equilibrated for 10 minutes while employing a nitrogen gas flow of 20 mL.min- 1 . Measurements were performed between -40°C and 700°C.
  • DSC Differential Scanning Calorimetry
  • the term "average particle size” refers to the D 50 value of the cumulative volume distribution curve at which 50% by volume of the particles have a diameter less than said value.
  • the average particle size or D 50 value is measured in the present invention through an automated image analysis technique with a Malvern Morphologi G (Malvern Instruments Ltd). In this technique, the size of particles in suspensions or emulsions is measured using the diffraction of a laser beam, based on the application of either Mie theory or a modified Mie theory for non-spherical particles.
  • the average particle sizes or D 50 values relate to scattering measurements at an angle of from 0.02° to 135° relative to the incident laser beam.
  • spherical is used to denote particles that have an aspect ratio (i.e. , ratio of major axis to minor axis) of from 1 : 1 to 1.5: 1 , for example from 1.1 to 1.4: 1.
  • the shape of the particles may be determined by any suitable method known in the art including but not limited to optical microscope, electron microscope and suitable image analysis software.
  • solder flux encompasses a composition which is used to prevent oxidation during a soldering process but which may also provide some form of chemical cleaning prior to soldering.
  • soldder residue encompasses the residue formed as a result of heating of a solder flux during a soldering process. Without being bound by theory, it is considered that the solder flux residue forms when at least some of the solvent is evaporated from the solder flux.
  • epoxide denotes a compound characterized by the presence of at least one cyclic ether group, namely one wherein an ether oxygen atom is attached to two adjacent carbon atoms thereby forming a cyclic structure.
  • the term is intended to encompass monoepoxide compounds, polyepoxide compounds (having two or more epoxide groups) and epoxide terminated prepolymers.
  • monoepoxide compound is meant to denote epoxide compounds having one epoxy group.
  • polyepoxide compound is meant to denote epoxide compounds having at least two epoxy groups.
  • diepoxide compound is meant to denote epoxide compounds having two epoxy groups.
  • the epoxide may be unsubstituted but may also be inertly substituted.
  • Exemplary inert substituents include chlorine, bromine, fluorine and phenyl.
  • the first aspect of the present invention provides a lead-free solder alloy which consists essentially of or consists of: from 0.01 to 11 wt.% of zinc (Zn); from 0.01 to 6 wt.% of bismuth (Bi); from 0.01 to 2 wt.% of gallium (Ga); and, tin (Sn) wherein said weight percentages are based on the total weight of the alloy.
  • the tin constitutes the majority element of the solder alloy and is present to facilitate the wetting of the molten solder alloy to the metallic substrates to which it is to be adhered in use.
  • the lead-free solder alloy either consists essentially of or consists of: from 5 to 10 wt.%, preferably from 7 to 9 wt.% of zinc (Zn); from 1.5 to 5 wt.%, preferably from 2 to 4 wt.% of bismuth (Bi); from 0.01 to 1 wt.%, preferably from 0.1 to 0.5 wt.% of gallium (Ga); and, tin (Sn) wherein said weight percentages are based on the total weight of the alloy.
  • An illustrative lead-free solder alloy either consists essentially of or consists of:
  • Sn wherein said weight percentages are based on the total weight of the alloy.
  • Further exemplary alloys include: Snss.g/Zns ⁇ h/Gao.i; Snsss/Zns/Bh/Gao ⁇ ; Snss s/Zns/Bh/Gao ⁇ s; Sn88 /Zn8//Bi3/Gao.3; Snss.e/ZnsBh/Gao. ⁇ and, Snss.s/Zns/Bh/Gao.s-
  • the above-defined solder alloys may be produced by melt-blending the stated metals in accordance with known methods.
  • Multi-stage melt-blending is not precluded, wherein a master batch of Sn with an amount of at least one of the stated metals is first prepared by melt-blending, which master match is then optionally cooled before being melt blended in further stage(s) with either the remaining stated metals or the remaining amounts of the stated metals necessary to yield an alloy of the desired composition.
  • An illustrative multi stage melt-blending process might entail the first preparation of a master batch consisting of Sn, Zn and Bi, followed by the melt-blending of the micro-alloying element Ga into said master batch.
  • the or each means of melt blending must serve to homogeneously mix the constituent metals.
  • the composition of the melt - present in a bath or the like - should be verified through analytical means before the alloy is solidified to a particular morphology: the use of optical emission spectrometry might be mentioned in this context.
  • the molten solder alloys may be extruded into wires or cast into molds to form ingots or bars, which ingots may be hot compressed to convert the cast structure into a wrought microstructure.
  • the appropriate size and shape of the molds can be determined based on the intended use of the ingots and also on the alloy's density once cooled and solidified.
  • the bars or ingots provide for the convenient storage of the alloy and may subsequently be melted to produce solder baths which are useful where solder is to be applied by coating or through complete or partial immersion of a substrate therein: mention may in particular be made of hot-air leveling and wave soldering as described in inter alia US2006/0104855 (Rothschild).
  • the extrusion of solder alloys into wires which may be hollow and which may in turn be molded or shaped, provides forms which are useful in conventional manual soldering applications.
  • the solder alloy of the present invention may also be presented in the form of a powder.
  • the aforementioned ingots, bars, wires and others solid forms of the alloys can be transformed into powder by grinding, milling and other conventional diminution techniques.
  • the powder may be formed from the molten alloy by granulation or atomization. Granulation is conventionally performed by free-fall of the molten alloy through a plate having sized apertures or nozzles into a cold liquid, typically water: during the free- fall and by impact with the liquid surface, the melt stream is broken up into droplets which then solidify.
  • Atomization techniques which may be mentioned include but are not limited to: jet atomization of the melt, wherein the molten liquid is dispersed into droplets by the impingement of jets of gas, water or oil; centrifugal atomization; impact atomization; ultrasonic atomization; impulse atomization; and, vacuum atomization.
  • particles of the solder alloy should have an average particle size of from 0.05 to 150 pm, preferably from 5 to 75 pm and more preferably from 15 to 45 pm.
  • Very fine particles having an average particle size of less than 0.05 pm can be difficult both to produce and to process into solder pastes: such fine particles may increase cohesive force within the pastes and as a corollary increase viscosity and tackiness of the paste. Very fine particles can moreover be easily oxidized.
  • particles having an average particle size of greater than 150 pm can impede blending operations in the formation of a solder paste and moreover have limited utility where printing of fine circuit patterns on a substrate is required.
  • solder whether or not meeting the above described particle size parameters, should comprise or consist of spherical solder particles. Whilst the presence of some non-spherical particles in a solder paste may be tolerated and might, for instance, limit slump and outflow of the paste upon application, it is preferred that spherical particles constitute from 90 to 100% by volume of the solder particles and non-spherical particles constitute from 0 to 10% by volume of the solder particles. Importantly, spheres represent the physical object with the lowest surface area-to-volume ratio and hence, for a given oxide layer thickness, will contain the smallest amount of oxide. Further, non-spherical particles may jam the screen or the stencil through which the solder paste is printed or clog a needle through which solder paste is dispensed.
  • the solder flux and particles of solder alloy may be provided separately.
  • the solder flux may be applied separately in liquid, paste or film form, whereas the solder particles may be provided in the form of a powder, sheet, stick or wire, for instance.
  • the solder flux and solder particles may be provided together. It is not precluded, for instance, that the solder flux may be retained within the solder particles, for example within the voids in acicular particles or fibers of the alloy. However, it is preferred that the solder alloy particles be provided together with the solder flux in form of a solder paste.
  • a solder paste is a suspension of solder alloy particles in a flux- containing vehicle in which the shape and size of the particles and the rheology and tackiness of the flux vehicle are matched to the method of paste application most appropriate to the design of electronic component assembly.
  • the solder paste flux lowers the surface tension of solder to improve capillary flow and optimizes fillet geometries by promoting wetting; it also protects surfaces from re-oxidation during reflow.
  • the weight ratio of the solder particles to the flux is not particularly limited but it is conventional that the amount of the solder particles ranges from 40 to 95 parts by weight and that of the flux ranges from 5 to 60 parts by weight.
  • the solder paste may consist of, based on the weight of the paste: from 70 to 95 wt.% of solder alloy particles; and, from 5 to 30 wt.% of solder flux. It is noted that, as a result of the density difference, the flux may comprise a higher percentage by volume of the paste than it does by weight.
  • the solder flux of the present invention comprises: a) at least one binder; b) at least one solvent; and, optionally c) additives.
  • Said at least one binder a) may comprise: at least one rosin resin; at least one thermoplastic polymer; at least one thermosetting crosslinkable resin; or, a mixture thereof.
  • rosin resin in intended to encompass rosin acids, gum rosin, wood rosin, tall oil rosin, rosin esters, hydrogenated rosins, dimerized rosins, disproportionated rosin, polymerized rosin and modified rosin resin, the term “modified rosin” being used here to denote a rosin resin that is changed in some way other than by esterification, hydrogenation, or dimerization, for example by the Diels-Adler reaction and/or by ene-type reactions with a,b-olefinically unsaturated carbonyl compounds.
  • Exemplary modified rosins thus include rosin esters modified with maleic acid.
  • Exemplary thermoplastic polymers include but are not limited to polyamides, polybutylenes, polyimides and polyacrylates.
  • Exemplary crosslinkable thermosetting resins include but are not limited to epoxy resins, phenolic resins, polyesters and styrenated polyesters: such thermosetting resins may, of course, require an appropriate curative or hardener to be present in the solder flux.
  • pure rosin - abietic acid and the isomers and oligomers thereof - is a very weak acid that does not exhibit activity at ordinary temperatures but, under heating at 90°C or more, melts and exhibits activity to remove oxide films on a metallic base.
  • the activity of rosin can be enhanced by addition of an activator, a material that decomposes or otherwise changes upon heating to an activation temperature to produce a by-product that reacts with oxide on the substrate.
  • rosin fluxes are designated as non- activated (R), mildly activated (RMA), fully activated (RA) and super-activated (RSA).
  • R non- activated
  • RMA mildly activated
  • RA fully activated
  • RSA super-activated
  • the flux is a either a Type R flux (non-activated) or a Type RMA flux (Rosin Mildly activated) on the basis that that these fluxes leave virtually no flux residue.
  • RMA flux the flux residue is noncorrosive, tack free and exhibits a high degree of freedom from ionic contamination after cleaning.
  • RA flux residues should be removed from printed circuit boards, and RSA residues must be removed since they are corrosive in electronics applications.
  • activators which may be present in combination with the rosin resins, mention may be made of: monocarboxylic acids, such as formic acid, acetic acid, propionic acid, capronic acid, enanthic acid, caprilic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, myristic acid, palmitic acid and stearic acid; dicarboxylic acids, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid; oxycarboxylic acids such as oxysuccinic acid, citric acid, tartaric acid, hydroxyacetic acid, salicylic acid, (m-, p-) hydroxybenzoic acid, 12- hydroxydodecanoic acid, 12-isobutyric acid, (o-, m-, p-) hydroxyphenylacetic acid, 4-
  • the binder a) comprises: a1) an epoxy resin; a2) a hardener; and, optionally a3) a catalyst.
  • the epoxy resin may undergo cross-linking, meaning that the solder flux residue may comprise cross- linked epoxy resin.
  • Said epoxy resins a1) may be pure compounds but equally may be mixtures of epoxy functional compounds, including mixtures of compounds having different numbers of epoxy groups per molecule.
  • An epoxy resin may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted. Further, the epoxy resin may also be monomeric or polymeric.
  • polyepoxide compounds having an epoxy equivalent weight of from 100 to 700 g/eq, for example from 120 to 320 g/eq may be desirable and, generally, diepoxide compounds having epoxy equivalent weights of less than 500 or even less than 400 are preferred: this is predominantly from a costs standpoint, as in their production, lower molecular weight epoxy resins require more limited processing in purification.
  • polyepoxide compounds which may be utilized in the present invention (a1), particular mention may be made of: glycidyl ethers of polyhydric alcohols and polyhydric phenols; glycidyl esters of polycarboxylic acids; and, epoxidized polyethylenically unsaturated hydrocarbons, esters, ethers and amides.
  • the hardener a2) may comprise a phenolic group containing hardening agent and/or may be an anhydride-based hardener, typically a liquid anhydride-based hardener; and, the catalyst a3) may comprise a substituted aromatic amine catalyst, and / or a phosphene-based salt catalyst and / or an amide-based catalyst.
  • the solvents of the solder flux may be selected from: ketones; alcohols; ethers; acetals; esters; glycol ethers; amines; amides; and, hydrocarbons.
  • the solvents mentioned above may be used singly or in combination of plural kinds.
  • the ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, methyl n-amyl ketone, acetonylacetone, isophorone and acetophenone.
  • Examples of the alcohols include ethyl alcohol, isopropyl alcohol, n-butanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, hexylene glycol and texanol.
  • Examples of the ethers and acetals include n-butyl ether, n-hexyl ether, ethyl phenyl ether, 1,4-dioxane, trioxane, diethyl acetal, 1 ,2-dioxolan, tetrahydropyran and tetrahydrofuran.
  • esters examples include methyl formate, ethyl formate, propyl formate, isobutyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, benzyl acetate, isoamyl acetate, ethyl lactate, methyl benzoate, diethyl oxalate, dimethyl succinate, dimethyl glutamate, dimethyl adipate, methyl carbonate, ethyl carbonate, propyl carbonate, butyl carbonate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl acetate, ethylene glycol monopropyl acetate, ethylene glycol monobutyl ether acetate, ethylene glycol diacetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monompropyl ether acetate, propylene
  • glycol ethers examples include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol monobutyl ether, ethylene glycol dibutyl ether, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monoethyl ether, propylene glycol diethyl ether, propylene glycol monobutyl ether and propylene glycol dibutyl ether.
  • examples of the amines and the amides include dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, pyridine and pyrazine.
  • hydrocarbons examples include n-heptane, n-octane, n-decane, cyclohexane, benzene, toluene, xylene, ethylbenzene, diethylbenzene and pinene.
  • butyl carbitol ethylene glycol monohexyl ether; diethylene glycol mono hexyl ether; triethylene glycol monomethyl ether; ethylene glycol mono-2-ethylhexyl ether; diethylene glycol mono-2-ethylhexyl ether; diethylene glycol dibutyl ether; triethylene glycol butyl methyl ether; and, tetraethylene glycol dimethyl ether.
  • the solder flux or solder paste of the present invention may, of course, also contain additives and adjunct ingredients.
  • additives and adjunct ingredients are necessarily minor components of the present compositions and may conventionally be selected from: fillers; oxide sequestrants; catalysts; pigments, such as titanium dioxide, iron oxides or carbon black; rheological agents; thixotropic agents, such as hardened castor oil, amides and waxes; antioxidants; surfactants; impact modifiers; adhesion regulators; degassing agents; stress modifiers; tackifiers; and, mixtures thereof.
  • a filler - in an amount up to 5 wt.%, based on the total weight of the solder flux - may permit control of the mechanical and/or thermo-mechanical properties of the solder flux and/or the flux residue.
  • the presence of a filler may serve to decrease the disparity in the Coefficient of Thermal Expansion (CTE) between the solder flux residue and the solder joint, thereby increasing the resistance to thermal cycling fatigue.
  • CTE Coefficient of Thermal Expansion
  • certain fillers may also be included: to promote surface lubrication; to reduce isotropic shrinkage; to modify electrical and / or magnetic properties; to modify optical properties; and, for radiation absorption.
  • Exemplary fillers include but are not limited to: silica; aluminum oxide; aluminum nitride; zinc oxide; barium sulphate; calcium carbonate; polytetrafluoroethylene (PTFE); polyhedral oligomeric silsesquioxanes; glass fibers; glass flakes; glass beads; glass spheres; synthetic and natural fibers; mica; talc; kaolin; wallastonite; nanoclays; graphene; functionalized graphene; diamond; carbon nanotubes (CNT); graphite and carbon fibers; ferromagnetic metals and, boron nitride.
  • Fillers which impart thixotropy to the composition may also have utility: such fillers are also described as rheological adjuvants and include hydrogenated castor oil, fatty acid amides, or swellable plastics such as PVC.
  • the solder flux or solder paste may comprise at least one additive which acts to assimilate or sequester oxide from the molten solder, whether said oxide is disposed originally on the surface of the solder powder or is dispersed within the solder. By assimilating the oxide, the interference of this compound with wetting is minimized.
  • Suitable additives in this regard are broadly organic molecule having nucleophilic and/or electrophilic end groups. Specific mention may be made of organic compounds having terminal carboxylic acid groups and more particularly of dimer acids. The preparation and structure of the dimer acids by addition dimerization or polymerization of unsaturated fatty acids is described in inter alia Journal of American Oil Chemists Society, 39, 534-545 (1962) and US Patent No. 3,157,681.
  • liquid rubber in the solder flux - in an amount up to 5 wt.%, based on the weight of the solder flux - may also serve to negate the effects of the differences in Coefficient of Thermal Expansion (CTE) between work pieces and the solder joint, thereby increasing the resistance to thermal cycling fatigue.
  • the liquid rubber may increase the ductility of the solder flux residue, thereby increasing the mechanical properties of the solder joint and providing improved impact or “drop shock” resistance.
  • Suitable rubbers which may be mentioned include acrylonitrile-butadiene rubbers having one or more terminal groups selected from carboxyl, hydroxyl and / or amine groups, which copolymers may be obtained by emulsion polymerization.
  • concentration of tackifier compounds in toto is not rigidly limited and may be adjusted depending on inter alia solubility, the concentration thereof is preferably from 0.05 to 20 wt.%, based on the weight of the solder flux.
  • solder fluxes of the present invention are not precluded from containing other resin acids and the esters thereof.
  • “Resin acicf’ is a term of art that is used to refer to monocarboxyl ic diterpene acids, as discussed inter alia in Simonsen et al. The Terpenes, Vol.
  • Exemplary resin acids include, without limitation: communic acid (CAS # 1231-35-2); isopimaric acid (CAS # 5835-26-7); levopimaric acid (CAS # 79-54-9); neoabietic acid (CAS # 471-77-2); palustric acid (CAS # 1945-53-5); pimaric acid (CAS # 127, 27-5); and, sandaracopimaric acid (CAS # 471-74-9).
  • solder flux examples include but are not limited to: naphthotriazole-based derivatives; benzotriazole-based derivatives; imidazole- based derivatives; benzoimidazole-based derivatives; mercaptobenzothiazole-based derivatives; and, benzothiazolthio fatty acids.
  • These tackifier compounds exhibit a strong adhesive effect particularly to copper and are capable of imparting tackiness to other conductive substances.
  • the solder flux should comprise less than 1 wt.% of water, based on the weight of the composition, and is most preferably an anhydrous composition that is essentially free of water.
  • the composition of the solder flux is selected such that the solder flux residue has a Coefficient of Thermal Expansion (CTE) which differs from that of the material of solder joint by less than 100%, preferably less than 60%, more preferably less than 50%.
  • CTE Coefficient of Thermal Expansion
  • the composition of the solder flux is selected such that the solder flux or solder paste has a viscosity of from 250000 to 2000000 mPa.s, preferably from 300000 to 1500000 mPa.s.
  • suitable mixing devices might include: static mixing devices; magnetic stir bar apparatuses; wire whisk devices; augers; batch mixers; planetary mixers; C.W. Brabender or Banburry® style mixers; and, high shear mixers, such as blade-style blenders and rotary impellers.
  • the present invention also provides for the use of a solder paste as defined herein to form or strengthen a solder joint and / or interconnection.
  • the solder joint may be formed from said solder paste during a manufacturing method selected from: a surface mount technology (SMT) method; a die and component attach method; a package on package (POP) method; a chip scale package (CSP) method; a ball grid array (BGA) method; a flip chip method; a can shield attachment method; and, a camera lens attachment method.
  • SMT surface mount technology
  • POP package on package
  • CSP chip scale package
  • BGA ball grid array
  • HSA21231-45 Halide/halogen containing Solder flux based on gum rosin, polymerized gum rosin and glycol solvent, available from Henkel AG & Co. KgaA.
  • HSA20732-91 Halide/halogen-free Solder flux based on gum rosin post-reacted with acrylic acid, disproportionated resin and glycol ether solvent, available from Henkel AG & Co. KgaA.
  • HSA21235-36A Halide/halogen containing Solder flux based on gum rosin post-reacted with acrylic acid, disproportionated resin and glycol ether solvent, available from Henkel AG & Co. KgaA.
  • Ultimate tensile strength, yield strength, and elongation were measured as part of one continuous test.
  • the test was performed in accordance with ASTM E8 on a Satec HVL 60 Tension Testing Unit.
  • the lead-free solder specimen tested was a rod measuring 3 inches (7.62 cm) long and 0.250 inches (0.64 cm) in diameter.
  • the specimen was marked in the gauge length with ink and scribed with dividers. Elongation gauge marks were 4 times the diameter. The gauge marks for measuring elongation were approximately equidistant from the center of the length of the reduced section.
  • the specimen was affixed to the testing unit and stretched by gradual increase of force at a strain rate of 10 mm/min. When the sample started to lose its elasticity the load applied was noted and the yield strength (MPa) was determined. The specimen was further stretched with gradual force until breaking. The load at breaking was also noted and the ultimate tensile strength (MPa) was calculated, together with the Percentage Elongation at break based on the following formula:
  • microstructure of a given alloy was determined by Scanning Electron Microscopy (SEM) using a Hitachi TM1000 in back scatter electron (BSE) mode with a 15kV voltage.
  • SEM Scanning Electron Microscopy
  • BSE back scatter electron
  • Figure 1a is an SEM micrograph illustrating the microstructure of a comparative alloy Sn- 8Zn-3Bi.
  • Figure 1b is an SEM micrograph illustrating the microstructure of an alloy in accordance with an embodiment of the present invention Sn-8Zn-3Bi-0.1Ga.
  • Figure 1c is an SEM micrograph illustrating the microstructure of an alloy in accordance with an embodiment of the present invention Sn-8Zn-3Bi-0.25Ga.
  • Figure 1d is an SEM micrograph illustrating the microstructure of an alloy in accordance with an embodiment of the present invention Sn-8Zn-3Bi-0.5Ga.
  • the viscosity of the solder pastes was determined in accordance with IPC-TM-650 Test Methods Manual using a Malcom Spiral Pump Viscometer (available from Malcom Instruments Corporation).
  • the pastes to be tested were introduced at a volume sufficient to fill the viscometer receptacle to about 60% of its depth. Prior to testing, receptacles were introduced into the temperature controlled unit of the viscometer and allowed to stabilize at 25 ⁇ 0.25°C for 15 minutes. The viscosity of the pastes was evaluated at the shear rates stated below at a temperature of 25 ⁇ 0.25°C.
  • the Thixotropic Index (Tl) of the pastes was calculated as a ratio of a material’s viscosity measured at two different speeds different by a factor of ten. iv) Joint Shear Performance
  • a two-factor factorial design with nine replications was selected in the experiment.
  • the input variables are the solder alloy and the component substrate.
  • the peak temperature (205°C) and the duration of time above solder liquidus temperature (30 seconds) were not variables.
  • Test boards were assembled with a singular size (1206) of pure silver (Ag), tin (Sn) and copper (Cu) plated surface mount chip resistors.
  • 1206 means a component with a nominal length of 0.12 inch (3.0 mm) and a nominal width of 0.06 inch (1.5 mm).
  • x resistors There were x resistors on each board.
  • Y boards were assembled for each experimental run so a total of Z boards were assembled (3 Component Substrate x 2 Solder Alloy x 9 replication).
  • Each board was cut into two identical pieces.
  • the first half of the board represented the initial time zero and the components on this half of the board were sheared right after assembly.
  • the experimental results on the effect of reflow profile on shear force immediately after assembly were reported.
  • the other half of the test vehicles were then subjected to air-to-air thermal shock conditioning from -40 to 125°C with 30 minute dwell times (or 1 hour per cycle) for 500 cycles.
  • the experimental matrix is listed in Table 2.
  • the components were sheared using a Dage Series 4000 shear tester according to the parameters and conditions identified in Table 2 herein below.
  • Example 2 The alloy of Example 2 above (Sn-8ZN-3Bi-0.25Ga) was blended with the solder flux HSA21231-45 at an alloy loading of 86% by weight. A comparative paste was obtained based on SnZn with the solder flux HSA21231-45 at an alloy loading of 86%. Joint shear performance was measured in accordance with the test defined above and the results are indicated in Table 4 below.
  • Particle size and shape analysis was performed for the SnZnBiGa0.25 Type 4.5 powder. Particle size and shape analysis was performed by stenciling a small solder paste sample onto a glass slide. A drop of pine oil/resin solution was then gently mixed into the stenciled solder paste, spreading the resultant mixture over an area of approx. 20mm diameter. A glass cover slip was then gently placed on top of the mixture in order to remove any air pockets. The image analyzer system was switched on and focused on the samples under x20 magnification. An image of a representative area was then captured. After instructing the software to select all particles spurious ellipses were deleted or resized where possible. The particle measurements were repeated until >200 particles were measured. The particle size analysis numerical results are in tables 5 and 6 below and illustrated in figure 2. Similarly, the particle shape analysis numerical results are in table 7 below and illustrated in figure 3.
  • Reflow performance of Sn-8Zn-3Bi (comparative example) and Sn-8Zn-3Bi-0.25 (according to the present invention) at 88% metal loading (vacuum treated) were evaluated through stencil printing surface mount assembly process on a standard SPTV1.1 test board across ENIG, ImmSn & OSP-Cu metalisations. All boards were reflowed through a P100 Sn-Pb type reflow profile (Figure 4) under aneorobic conditions (O2 ppm ⁇ 1000ppm). Peak temperature 205°C, Ramp Rate 0.86°C/s with a time to peak of 202 seconds.
  • Figure 5 illustrates HSA21235-36A Sn-8Zn-3Bi 0805 P100 anaerobic 5a) ENIG 5b) ImmSn 5c) OSP-Cu
  • Figure 6 illustrates HSA21235-36A Sn-8Zn-3Bi-0.25Ga 0805 P100 Anaerobic 6a) ENIG 6b) ImmSn 6c) OSP-Cu.
  • the results and figures exemplify the solderability improvement arising from the Gallium addition to the alloy.
  • the SnZnBi alloy demonstrates much poorer solderability in terms of substrate and component wetting compared against Sn-Zn-Bi-Ga0.25 under equivalent conditions.
  • the Ga addition to SnZnBi creates a more roboust solder paste from an industry applications perspective.
  • HSA21235-36A flux formula’s wetting balance performance was evaluated on the GEN3 MUSTIII wetting balance with a SnZnBiGa0.25 solder bath held at 200°C. 1mm diameter wire of Cu (99.9% annealed), Ni (99.0%, annealed) & Zn (99.9% extruded) were evaluated against industry standard Acteic 2 & 5.
  • the wetting test had a 10s duration, 5mm immersion depth and a 20mm/s immersion speed.
  • Figure 7 illustrates MUSTIII Wetting Balance at 200 °C Ni 99.0%.
  • Figure 8 illustrates MUSTIII Wetting Balance at 200 °C Zn 99.9%.
  • Figure 9 illustrates MUSTIII Wetting Balance at 200 °C Cu 99.9%.
  • Figures 7 and 8 displays the relative wetting speeds and forces of the SnZnBiGa0.25 alloy on Cu, Ni and Zn substrates.
  • the SnZnBiGa0.25 alloy displayed poor wetting performance on Ni substrates as only negative wetting forces were adopted irrespective of flux.
  • the wetting performance on Zn shows some level of mutal compatibility between the two metals that can be significantly enhanced via flux chemistry optimisation.
  • the wetting performance on Cu appears poorer than what would be expected from conventional SAC305 alloys. However, there is evidence that this can be improved via flux chemistry optimisation.
  • Halide/halogen activators from flux formula HSA21231-45 promote wetting accross a range of substrates, whereas resin/solvent system of flux formula HSA20732-91 appeares to promote coalscence at expense of wetting. Hydribising these two into flux formula HSA21235-36A improves balance of wetting/coalescence performance and enhances overall reflow performance for the SnZnBiGa0.25 alloy system.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electric Connection Of Electric Components To Printed Circuits (AREA)

Abstract

La présente invention concerne un alliage de brasage sans plomb qui est consistué essentiellement ou est consistué : de 0,01 à 11 % en poids de zinc (Zn) ; de 0,01 à 6 % en poids de bismuth (Bi) ; de 0,01 à 2 % en poids de gallium (Ga) ; et d'étain (Sn), lesdits pourcentages en poids étant basés sur le poids total de l'alliage. L'invention concerne également une pâte à braser comprenant l'alliage de brasage sans plomb défini sous forme particulaire et un flux de brasage.
PCT/EP2020/074193 2019-09-06 2020-08-31 Alliage de brasage et pâte à braser contenant ledit alliage WO2021043708A1 (fr)

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CN114700649A (zh) * 2022-03-29 2022-07-05 郑州大学 一种铜铝钎焊连接钎缝导电性强且强度高的锌铝钎料
CN114799612A (zh) * 2022-05-27 2022-07-29 常州时创能源股份有限公司 一种光伏用钎焊焊料、其制备方法及应用

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CN113770589A (zh) * 2021-10-09 2021-12-10 浙江亚通焊材有限公司 一种高性能电子行业用无铅焊料
CN113770589B (zh) * 2021-10-09 2023-02-28 浙江亚通新材料股份有限公司 一种高性能电子行业用无铅焊料
CN114700649A (zh) * 2022-03-29 2022-07-05 郑州大学 一种铜铝钎焊连接钎缝导电性强且强度高的锌铝钎料
CN114700649B (zh) * 2022-03-29 2023-01-13 郑州大学 一种铜铝钎焊连接钎缝导电性强且强度高的锌铝钎料
CN114799612A (zh) * 2022-05-27 2022-07-29 常州时创能源股份有限公司 一种光伏用钎焊焊料、其制备方法及应用

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