WO2003068447A1

WO2003068447A1 - Solder paste formulations, methods of production and uses thereof

Info

Publication number: WO2003068447A1
Application number: PCT/US2003/004374
Authority: WO
Inventors: Kim-Chi Le; John Lalena; Martin Weiser
Original assignee: Honeywell International Inc.
Priority date: 2002-02-13
Filing date: 2003-02-12
Publication date: 2003-08-21
Also published as: AU2003211032A1; TW200414958A

Abstract

A solder paste formulation has been developed that comprises a) at least one metal-based material; b) at least one support material; and c) at least one stability modification material. Furthermore, a method of producing a solder paste formulation having a stability component, as described herein, comprises a) providing at least one metal-based material; b) providing at least one support material; c) providing at least one stability modification material; and d) combining the at least one metal-based material, the at least one support material and the at least one stability modification material such that the stability component of the solder paste formulation is increased over a reference stability component of a conventional or reference solder paste formulation comprising similar metal-based materials and similar support materials.

Description

SOLDER PASTE FORMULATIONS, METHODS OF PRODUCTION

AND USES THEREOF

FIELD OF THE INVENTION

The field of the invention is stability-enhanced and stability-modified solder paste formulations, methods of production and uses thereof.

BACKGROUND

Electronic components are used in ever increasing numbers of consumer and commercial electronic products. Examples of some of these consumer and commercial products are televisions, personal computers, Internet servers, cell phones, pagers, palm-type organizers, portable radios, car stereos, or remote controls. As the demand for these consumer and commercial electronics increases, there is also ^"a demand for those same products to become smaller, more functional, and more portable for consumers and businesses.

. As a result of the size decrease in these products, the components that comprise the products must also become smaller and better manufactured. Examples of some of those components that need to be reduced in size or scaled down are printed circuit or wiring boards, resistors, wiring, keyboards, touch pads, and chip packaging. Products and components also need to be prepackaged, such that the product and/or component can perform several related or unrelated functions and tasks.

When electronic and semiconductor components are reduced in size or scaled down, any defects that are present in the larger components are going to be exaggerated in the scaled down components. These components, therefore, are being broken down and investigated to determine if there are better building materials and methods that will allow them to be scaled down and/or combined to accommodate the demands for smaller electronic components. Electronic, semiconductor and communication/data-exchange components are composed, in some cases, of layers of materials, such as metals, metal alloys, solder materials and pastes, ceramics, inorganic materials, polymers, or organometallic materials. Many of the layers of materials are often thin (on the order of less than a few tens of angstroms in thickness). In order to improve on the quality of the layers of materials, the individual material that is forming the layer or part of the layer - such as solder materials and solder paste materials - should be evaluated and, if possible, modified and improved. In layered components, one goal appears to be decreasing the number of the layers while at the same time i ncreasing t he functionality and d urability of t he r emaining 1 ayers. T his t ask c an b e difficult, however, given that several of the layers and components of the layers should generally be present in order to operate the device. Thus, the defects that are present or could be present in the larger component should be identified and corrected, if possible, before the component is scaled down for the smaller electronic products.

In wafer humping and lid seal technologies, solder paste formulations are extremely important to the smooth flow of the production process and to the ability to produce semiconductor and electronic components that are reliable, efficient and reasonably defect free. Solder paste formulations must be able to endure prolonged exposure to temperature and humidity without undergoing a significant change in performance qualities or stability qualities. Solder paste formulations should also be able to withstand processing demands, such as remaining stable and viable during a pause or change in conditions during the processing steps, activity or inactivity, tack time, printability, cleanability, insulation and corrosion resistance.

Conventional solder paste formulations comprise a metal or alloy powder, a rosin compound, a rheological additive, a solvent or solvent mixture, a surfactant or surfactant mixture, and/or a buffer or neutralizing agent. One solder paste formulation manufactured by Flip Chip consists of a tin/silver/copper alloy powder, refined gum rosin, l-phenoxy-2- propanol, Thixatrol ST™, Igepal™ CO-430, 2,2,2-nitrilotriethanol and succmic acid. This solder paste formulation is based on a lead free platform with an organic system that serves as a carrier to produce the paste form of the solder. This solder paste formulation and similar formulations suffer from several physical and chemical defects and processing flaws, such as smearing after only a few prints and printing overtime, meaning that the formulations must be constantly replaced because of instability and loss of viscosity, which is directly related to instability, in the solder paste formulation. For example, in most reasonable and contemplated applications, this solder paste formulation starts to lose viscosity and show significant signs of instability less than 24 hours after introduction to the wafer production process. The exact formula of the Flip Chip solder paste formulation is shown in Table 1 :

Table 1: Formula for Flip Chip solder paste formulation, (conventional formulation)

Based on this conventional composition and the stability issues that result from this combination of materials, it is necessary to develop a solder paste formulation that is more stable than conventional solder paste formulations while being able to better withstand processing demands, such as remaining stable and viable during a pause or change in conditions during the processing steps, activity or inactivity, tack time, printability, cleanability, insulation and corrosion resistance. SUMMARY OF THE SUBJECT MATTER

A solder paste formulation has been developed that comprises a) at least one metal- based material; b) at least one support material; and c) at least one stability-modification material.

Furthermore, a method of producing a solder paste formulation having a stability component, as described herein, comprises a) providing at least one metal-based material; b) providing at least one support material; c) providing at least one stability-modification material; and d) combining the at least one metal-based material, the at least one support material and the at least one stability modification material such that the stability component of the solder paste formulation is increased over a reference stability component of a conventional or reference solder paste formulation comprising similar metal-based materials and similar support materials.

DETAILED DESCRIPTION

In order to enhance and/or modify the stability of solder paste formulations, a solder paste formulation has been developed that comprises a) at least one metal-based material; b) at least one support material; and c) at least one stability-modification material. Furthermore, a method of producing a solder paste formulation having a stability component, as described herein, comprises a) providing at least one metal-based material; b) providing at least one support material; c) providing at least one stability-modification material; and d) combining the at least one metal-based material, the at least one support material and the at least one stability modification material such that the stability component of the solder paste formulation is increased over a reference stability component of a conventional or reference solder paste formulation comprising similar metal-based materials and similar support materials.

As mentioned, solder paste formulations contemplated herein comprise at least one metal-based material. As used herein, the term "metal" means those elements that are in the d-block and f-blo^'ck of the Periodic Chart of the Elements, along with those elements that have metal-like properties, such as silicon and germanium. As used herein, the phrase "d- block" means those elements that have electrons filling the 3d, 4d, 5d, and 6d orbitals surrounding the nucleus of the element. As used herein, the phrase "f-block" means those elements that have electrons filling the 4f and 5f orbitals surrounding the nucleus of the element, including the lanthanides and the actinides. As contemplated herein, the metal- based material may comprise at least one metal, including copper, silver, tin, lead, low alpha lead, bismuth, aluminum, gallium, and alloys and combinations thereof. Preferred metals include indium, silver, lead, copper, aluminum, tin, bismuth, gallium and alloys thereof, silver c oated c opper, a nd s ilver c oated a luminum. T he t erm " metal" a lso i ncludes a Hoys, metal/metal composites, metal ceramic composites, metal polymer composites, as well as other metal composites.

Other solder paste formulations of the subject matter presented herein may comprise a metal-based material or metal powder that is not in alloy form, such as silver powder or a mixture of metal powders. Alloy powders that comprise at least two metal constituents are also contemplated, such as a bismuth/silver alloy and a similar alloy that comprises bismuth/silver/germanium. Conductive powders that comprise combinations of metals, conductive polymers, organometallic compounds, metallic composites, other conductive materials and/or mixtures thereof are also contemplated in the present subject matter, as long as the paste formulation has the properties of and acts as a solder material in electronic and semiconductor applications. The alloy, metal and metallic-like powders may also comprise any suitably-sized particles depending on the specific needs of the production scheme, the solder paste formulation, or the intermediate/final product that incorporates the solder paste formulation.

Other contemplated metal-based material may comprise any suitable solder material or metal, such as indium, lead, silver, copper, aluminum, tin, bismuth, gallium and alloys thereof, silver coated copper, and silver coated aluminum, as previously mentioned. Preferred s older m aterials m ay comprise i ndium t in ( InSn) c ompounds and a Hoys, i ndium silver (InAg) compounds and alloys, indium-based compounds, tin silver copper compounds and alloys (SnAgCu), tin bismuth compounds and alloys (SnBi), and aluminum-based compounds and alloys.

The metal-based material may comprise any suitable form, including powder, pellets, solder balls, liquid, semi-liquid and/or flakes. It should be understood that the metal-based material may comprise any form as long as the form can meet the following design goals: a) can be combined with other materials to form a paste formulation; b) can be readily produced or be commercially available; and c) can form a solder material in an electronic or semiconductor component.

Solder paste formulations contemplated herein also comprise at least one support material. The at least one support material is designed to provide a support or matrix for the at least one metal-based material in the solder paste formulation. The at least one support material may comprise at least one rosin material, at least one rheological additive or material, a 11 east o ne p olymeric a dditive o r m aterial a nd/or a 11 east o ne s olvent o r s olvent mixture, i some contemplated embodiments, the at least one rosin material may comprise at least one refined gum rosin.

Refined gum rosin is contemplated as the rosin-component of one of the present embodiments, however, any rosin compound or suitable compound that has rosin-like properties can be used in place of the refined gum rosin, such as those components that comprise abietic acid or comprise a phenanthrene ring. As used herein, the term "rosin" is defined as those compounds that are insoluble in water, soluble in alcohol, benzene, ether, glacial acetic acid, oils, carbon disulfide, and dilute solutions of fixed alkali hydroxides, hard at room temperatures and soft/sticky at temperatures above room temperature.

The at least one solvent or solvent mixture may include any suitable pure or mixture of organic molecules that are volatilized at a desired temperature and/or easily formed into an organic phase. The solvent may also comprise any suitable pure or mixture of polar and non- polar compounds. In some embodiments, the solvent comprises benzene, trichloroethylene, toluene, ethers, cyclohexanone, butryolactone, methylethylketone, and anisole. As used herein, the term "pure" means is composed of a single molecule or compound. For example, pure water is composed solely of H₂O. As used herein, the term "mixture" means that component that is not pure, including salt water. As used herein, the term "polar" means that characteristic of a molecule or compound that creates an unequal charge, partial charge or spontaneous charge distribution at one point of or along the molecule or compound. As used herein, the term "non-polar" means that characteristic of a molecule or compound that creates an equal charge, partial charge or spontaneous charge distribution at one point of or along the molecule or compound. Particularly preferred solvents include, but are not limited to, pentane, hexane, heptane, cyclohexane, benzene, toluene, xylene, halogenated solvents such as c arbon t etrachloride, and m ixtures t hereof. In s ome c ontemplated e mbodiments, t he a t least one solvent or solvent mixture may actually function as the stability modification agent or material, may function as the at least one support material or may function as both. In other contemplated embodiments, the at least one support material may comprise a first at least one solvent or solvent mixture and the at least one stability-modification material may comprise a second at least one solvent or solvent mixture.

The at least one polymeric material or composition may comprise polymers, such as polyethylene, polypropylene, polycarbonate, polyamides or Nylon-based compounds, polyethylene terphthalate or any polymer that can be dissolved in a solvent and will either provide a support material for the metal-based material or give a transparent appearance coating on the metal-based material surface. The polymeric composition may be colored or opaque, but in some embodiments, it may be preferable to have a transparent or close to transparent coating. In some embodiments, the polymeric composition should be transparent or relatively transparent, such that the solder parts, solder materials and/or solder compositions start out as bright and shiny as possible. In these embodiments, the polymeric composition and/or material is used to improve the processing of the metal-based material before it is combined with the support material and the stability-modification material. US Provisional Patent Application Serial No. 60/427597 filed on November 18, 2002, which is commonly owned and is incorporated by reference in its entirety.

Contemplated polymers may also comprise a wide range of functional or structural moieties, including aromatic systems, and halogenated groups. Furthermore, appropriate polymers m ay h ave m any c onfigurations, i ncluding a h omopolymer, a nd a h eteropolymer . Moreover, alternative polymers may have various forms, such as linear, branched, super- branched, or three-dimensional. The molecular weight of contemplated polymers spans a wide range, typically between 400 Dalton and 400000 Dalton or more.

Other contemplated polymer compositions or materials may comprise inorganic-based compounds, such as the silicon-based materials disclosed in commonly assigned US Patent 6,143,855 and pending US Serial No. 10/078919 filed February 19, 2002; (for example Honeywell NANOGLASS® and HOSP® products), gallium-based, germanium-based, arsenic-based, boron-based compounds or combinations thereof, and organic-based compounds, such as polyethers, polyarylene ethers disclosed in commonly assigned US Patent 6,124,421 (such as Honeywell FLARE™ product), polyimides, polyesters and adamantane-based or cage-based compounds disclosed in commonly assigned WO 01/78110 and WO 01/08308 (such as Honeywell GX-3™ product). Polymers, such as linear polymer, star polymers, cross-linked polymeric nanospheres, block copolymers, and hyperbranched polymers may be used in contemplated embodiments with the solder materials. Suitable linear polymers are polyethers, such as poly(ethylene oxide) and poly(propylene oxide); polyacrylates such as poly(methylmethacrylate); aliphatic polycarbonates such as poly(propylene carbonate) and poly(ethylene carbonate); polyesters; polysulfones; polystyrene (including monomer units selected from halogenated styrene and hydroxy-substituted styrene); poly(α-methylstyrene); and other vinyl-based polymers. Useful polyester polymers include polycaprolactone; polyethylene terephthalate; poly(oxyadipoyloxy- 1 ,4-phenylene) ; poly(oxyterephthaloyloxy- 1 ,4-phenylene) ; poly(oxyadipoyloxy-l,6-hexamethylene); polyglycolide, polylactide (polylactic acid), polylactide-glycolide, polypyruvic acid, polycarbonate such as poly(hexamethylene carbonate) diol having a molecular weight from about 500 to about 2500; and polyether such as poly(bisphenol A-co-epichlorohydrin) having a molecular weight from about 300 to about 6500. Suitable crosslinked, insoluble nanospheres (prepared as nanoemulsions) are suitably comprised of polystyrene or poly(methylmethacrylate). Suitable block copolymers are poly- gylcolids, polylactic acid, poly(styrene-co-α-methylstyrene, poly(styrene-ethylene oxide), poly(etherlactones), poly(estercarbonates) and poly(lactonelactide). Suitable hyperbranched polymers are hyperbranched polyester, e.g. hyperbranched poly(caprolactone), and polyethers such as p olyethylene o xide and p olypropylene o xide. A nother u seful p olymer i s e thylene glycol-poly(caprolactone). Useful polymer blocks include polyvinylpyridines, hydrogenated polyvinyl aromatics, polyacrylonitriles, polysiloxanes, polycaprolactams, polyurethanes, polydienes such as p olybutadienes and p olyisoprenes, p olyvinyl chlorides, p olyacetals and amine-capped alkylene oxides. Other useful thermoplastic materials include polyisoprenes, polytetrahydrofurans and polyethyloxazolines.

Other suitable polymers include those which contain one or more reactive groups, such as hydroxyl or amino. Within these general parameters, a suitable polymer for use in the compositions and methods disclosed herein is, e.g. a polyalkylene oxide, a monoether of a polyalkylene oxide, a diether of a polyalkylene oxide, bisether of a polyalkylene oxide, an aliphatic polyester, an acrylic polymer, an acetal polymer, a poly(caprolactone), a poly(valeractone), a poly(methlymethoacrylate), a poly(vinylbutyral) and/or combinations thereof. When the polymer is a polyalkylene oxide monoether, one particular embodiment is a Ci to about C₆ alkyl chain between oxygen atoms and a Ci to about C₆ alkyl ether moiety, and wherein the alkyl chain is substituted or unsubstituted, e.g., polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether, or polypropylene glycol monomethyl ether.

Contemplated polymers may also comprise at least two fused aromatic rings wherein each of the fused aromatic rings has at least one alkyl substituent thereon and a bond exists between at least two of the alkyl substituents on adjacent aromatic rings may be used in contemplated embodiments. Preferred polymers in this class of polymers include unfunctionalized polyacenaphthylene homopolymer, functionalized polyacenaphthylene homopolymer, the polyacenaphthylene copolymers. described below, poly(2- vinylnaphthalene) and vinyl anthracene, and blends with each other. Other useful c oating precursor compositions comprise adamantane, diamantane, fullerene and polynorbornene. Each of these precursor materials, including those listed above, may be blended with one another or other coating precursor material, such as polycaprolactone, polystyrene and polyester. Useful blends include unfunctionalized polyacenaphthylene homopolymer and polycaprolactone. Other contemplated coating precursor compositions include unfunctionalized polyacenaphthylene homopolymer, functionalized polyacenaphthylene homopolymer, polyacenaphthylene copolymer and polynorbornene.

Useful polyacenaphthylene homopolymers may have weight average molecular weights ranging from preferably about 300 to about 20,000; more preferably about 300 to about 10,000; and most preferably about 1000 to about 7000 and may be polymerized from acenaphthylene using different initiators such as 2,2'-azobisisobutyronitrile (AEBN); di-tert- butyl azodicarboxylate; di-phenylazodicarboxylate; l, -azobis(cyclohezanecarbonitrile); benzoyl peroxide (BPO); t-butyl peroxide; and boron trifluoride diethyl etherate. The polyacenaphthylene homopolymer may have functional end groups such as triple bonds or double bonds to the chain end or cationic polymerization quenched with a double or triple bond alcohol, such as allyl alcohol, propargyl alcohol, butynol, butenol or hydroxyethylmethacrylate.

Useful polyacenaphthylene copolymers may be linear polymers, star polymers or hyperbranched polymers. The comonomer may haye a bulky side group that will result in copolymer conformation that is similar to that of polyacenaphthylene homopolymer or a nonbulky side group that will result in copolymer conformation that is dissimilar to that of polyacenaphthylene homopolymer. C omonomers having a bulky side group include vinyl pivalate; tert-butyl acrylate; styrene; α-methylstyrene; tert-butylstyrene; 2-vinylnaphthalene; 5-vinyl-2-norbornene; vinyl cyclohexane; vinyl cyclopentant; 9-vinylanthracene; 4- vinylbiphenyl; tetraphenylbutadiene; stilbene; tert-butylstilbene; and indene; and preferably vinyl pivalate. Hydridopolycarbosilane may be used as an additional co-monomer or copolymer component with acenaphthylene and at least one of the preceding comonomers. An example of a useful hydridopolycarbosilane has 10% or 75% allyl groups. Comonomers having a nonbulky side group include vinyl acetate, methyl acrylate, methyl methacrylate, and vinyl ether and preferably vinyl acetate.

As used herein, the term "monomer" refers to any chemical compound that is capable of forming a c ovalent b ond w ith i tself o r a c hemically d ifferent c ompound i n a r epetitive manner. The repetitive bond formation between monomers may lead to a linear, branched, super-branched, or three-dimensional product. Furthermore, monomers may themselves comprise repetitive building blocks, and when polymerized the polymers formed from such monomers are then termed "blockpolymers". Monomers may belong to various chemical classes of molecules including organic, organometallic or inorganic molecules. The molecular weight of monomers may vary greatly between about 40 Dalton and 20000 Dalton. However, especially when monomers comprise repetitive building blocks, monomers may have even higher molecular weights. Monomers may also include additional groups, such as groups used for crosslinking.

The at least one stability modification materials that are added to the solder paste formulations described herein alter the physical and chemical properties of the formulation by enhancing and/or modulating the physical and chemical stability components of the solder paste formulation, such as viscosity, thermal stability, processing stability etc. For example, the at least one plasticizer compound or at least one humectant compound, such as a trihydric (polyhydric) alcohol and/or a glycerol-type of or glycerol-based compound, such as ethylene glycol, 1,2,3-propanetriol, triethylene glycol (by-product of ethylene glycol manufacture), are several classes of compounds among many that are directly related to the stability and viscosity when the solder paste formulation is originally produced and after the formulation has been used or included in a processing stage or production process and is a class of compounds that is contemplated as stability modification material or agent to the solder paste formulations of the subject matter presented herein. As mentioned earlier, in some contemplated embodiments, the at least one solvent or solvent m ixture m ay actually function a s the s tability m odification a gent o r m aterial, m ay function as the at least one support material or may function as both. In other contemplated embodiments, the at least one support material may comprise a first at least one solvent or solvent mixture and the at least one stability modification material may comprise a second at least one solvent or solvent mixture. It should be understood that the at least one solvent may be specifically recognized to modify the stability of the solder paste formulation, and once it is recognized that a specific at least one solvent will modify the stability of the solder paste formulation that the at least one solvent can be combined with the solder paste formulation to increase the stability component of the solder paste formulation versus a reference stability component of a solder paste formulation that has not been stability-modified.

Stability modification materials and compounds, such as humectants, plasticizers and glycerol-based compounds may also positively add to the stability of the solder paste formulation over time during storage and processing and are contemplated as desirable and often times necessary additives to the solder paste formulations of the subject matter presented herein. Also, the addition of dodecanol (lauryl alcohol) and compounds that are related to and/or chemically similar to lauryl alcohol contribute to the positive stability and viscosity results found in contemplated solder paste formulation and are also contemplated as desirable and sometimes necessary additives to contemplated solder paste formulations. Further, the addition or replacement of an amine-based compound, such as diethanolamine, triethanolamine or mixtures thereof may improve the wetting properties of the paste formulation to the point where it is inherently more printable in combination with the stencil apparatus, and therefore, more stable over time and during processing. Dibasic acid compounds, such as a long-chain dibasic acid, can be also used as a stability modification material.

It should be understood that many of the polymeric materials and monomeric materials previously described may be also used to form several of the humectants and plasticizers described herein as useful and potential stability-modulating compositions and/or materials.

In some contemplated embodiments, additives such as adhesion promoters and other adhesive additives may be added to the solder paste formulation to promote adhesion to other layers or to promote contemplated and desired decomposition upon heating to a particular temperature - such as the temperature required to melt solder material or make the solder material compliant, as long as the general objectives of the coating composition are met.

The phrase "adhesion promoter" as used herein means any component that when used with the thermally degradable polymer, improves the adhesion thereof to substrates compared with thermally degradable polymers. Preferably the at least one adhesion promoter is used with the thermally degradable polymer. The adhesion promoter may be a co-monomer reacted with the thermally degradable polymer precursor or an additive to the thermally degradable polymer precursor. Examples of useful adhesion promoters are disclosed in commonly assigned pending US Application Serial Number 158513 filed May 30, 2002 incorporated herein in its entirety.

A method of producing a solder paste formulation having a stability component, as described herein, comprises a) providing at least one metal-based material; b) providing at least one support material; c) providing at least one stability modification material; and d) combining the at least one metal-based material, the at least one support material and the at least one stability modification material such that the stability component of the solder paste formulation is increased over a reference stability component of a conventional or reference solder paste formulation comprising similar metal-based materials and similar support materials.

As contemplated herein, providing the at least one support material, providing the at least one metal-based material; and/or providing the at least one stability modification material may comprise a) buying one or more of the materials from a supplier; b) preparing or producing one or more of the materials in-house using chemicals provided by another source and/or c) preparing or producing the materials in house using chemicals also produced or provided in house or at the location. It is contemplated that one of the processing, manufacturing, physical and/or chemical variations comprises modulation or modification of the stability component of the contemplated solder paste formulation. The stability component may be measured by several different testing methods, such as thermal stability testing, processing stability testing, exposure to chemicals and/or print stability. Each solder paste formulation comprises a stability component, which identifies the degree of stability that the formulation or material has in response to a particular testing method or condition. In some cases, the stability component of a material may be zero or zero percent, meaning that the material is entirely unstable in view of a particular testing method or condition, such as applied heat over 150°C or over 300 printing cycles.

It is generally contemplated that the contemplated solder paste formulation (also known a s t he s ample m aterial) and t he r eference or e onventional s older p aste formulation (also known as the reference material) comprise the same base materials before variations are made to the sample material through the addition of at least one stability-modification material or agent, especially in view of the definition of the term "reference". As used herein, the term "reference" means a control, a standard and/or a generally excepted conventional solder paste formulation or material. For example, a reference material would be the "control" or base with which the sample material or material is compared. The reference is a sample of identical c onstitution and prepared under the same conditions for which all experimental, processing, manufacturing, chemical and/or physical variations are omitted. In chemical terms, the "reference" is analogous to a "blank", in that all of the properties of the variation or sample material are measured and calculated against the reference as if the properties of the reference equaled, in effect, zero. Therefore, when comparing relative properties of a reference material and a sample material, it is important that both the reference material and the sample material begin with the same base material before variations are incorporated into the sample material.

In some contemplated embodiments, the conventional or reference solder paste formulations comprise a stability component that is greater than about zero or zero percent and the difference between the stability component of the solder paste formulation described herein a nd t he r eference s tability component o f the r eference o r conventional s older p aste formulation or material is at least about 10%, meaning that there is at least about a 10% increase in the stability component of the contemplated solder paste formulation. In other embodiments, there is at least about a 20% increase in the stability component of the solder paste formulation described herein and the reference stability component of the reference or conventional solder paste formulation or material. In yet other embodiments, there is at least about a 25% increase in the stability component of the solder paste formulation described herein a nd t he r eference s tability component o f the r eference o r conventional s older p aste formulation or material. In even other embodiments, there is at least about a 35% increase in the s tability c omponent o f t he s older p aste formulation d escribed h erein a nd t he r eference stability component of the reference or conventional solder paste formulation or material.

The at least one metal-based material, at least one support material and/or at least one stability modification material may be combined using or implementing any suitable method, including mixing, coupling (and/or "interfaced"), blending, folding, or otherwise interacting these materials. As used herein, the term "interface" means a couple or bond that forms the common boundary between two parts of matter or space, such as between two molecules, two backbones, a backbone and a network, two networks, etc. An interface may comprise a physical attachment of two parts of matter or components or a physical attraction between two parts of matter or components, including bond forces such as covalent and ionic bonding, and non-bond forces such as Van der Waals, electrostatic, coulombic, hydrogen bonding and/or magnetic attraction. Contemplated interfaces include those interfaces that are formed with bond forces, such as covalent bonds through crosslinking; however, it. should be understood that any suitable adhesive attraction or attachment between the two parts of matter or components is preferred. As used herein, the term "coupled" means that the surface and layer or two layers are physically attached to one another or there's a physical attraction between two parts of matter or components, including bond forces such as covalent and ionic bonding, and non-bond forces such as Van der Waals, electrostatic, coulombic, hydrogen bonding and/or magnetic attraction.

The formulations described herein can be produced in a form of high viscosity, screen printable, electrically and/or thermally conductive paste or other similar formulation with high moisture resistance and high flexibility for compliance matching when introduced into or on a substrate, such as an organic laminate surface. The formulations disclosed herein may also be utilized in any suitable surface mount, semiconductor and/or electronic assembly. A typical introduction process for solder paste formulations is through the use of a stencil - but it should be appreciated that the stencil technology isn't the only introduction technology contemplated herein. Other introduction techniques include printing, jet printing, rolling, and manual application.

Some contemplated embodiments provide thick formulation pastes whose viscosity is formulated to be suitable for screen printing and advanced printing processes such as vacuum assisted printing and pressure assisted printing, into fine geometry holes for the printed wiring board and microelectronic substrate industries. The paste must be stable over process life, which means no settling, bleed, excessive viscosity changes or changes in tack and rheology, and no phase separation during processing either in the dispense process or after printing while sitting in the via-holes and during cure. The paste formulations may be used for any type of via-hole, blind or through-hole. The paste is also formulated to withstand all previously mentioned printing processes into via holes of any aspect ratio making it versatile for both substrate and board articles. The solder paste formulations have been formulated to be moisture stable in order to withstand plating bath conditions and environmental preconditioning, after curing, and to adhere to both laminate and copper surfaces present on the wafer, substrate or surface during these processes. In addition, the compliancy of the solder paste formulation has been adjusted to be compatible with the organic construction of the printed wiring board or laminate substrate in order to avoid post-processing or work-life failure of the solder paste formulation.

Other embodiments include the use of a specific particle distribution and as mentioned before, the use of a conductive polymer. The particle distribution advantageously provides for high packing for the conductive version which helps achieve conductivity. The conductive p olymer filler has a multitude o f functions: it c ontrols rheology for the s creen printing process, controls settling and phase separation for shelf-life and process stability, helps to control bleeding during printing and thermal processing, and it enhances both electrical and thermal conductivity. Because the conductive polymer functions in controlling rheological properties, the final formulation in either of the electrically and/or thermally or non-conductive versions show enhanced printing stability in either standard processes or in newer vacuum or pressure assisted processes. That is, there is no phase separation or settling during printing or in the via holes.

Solder materials, solder formulations and other related materials described herein may also be used to produce solder pastes, polymer solders and other solder-based formulations and materials, such as those found in the following Honeywell International Inc.'s issued patents and pending patent applications, which are incorporated herein in their entirety: US Patent Application Serial Nos. 09/851103, 60/357754, 60/372525, 60/396294, and 09/543628; and PCT Pending Application Serial No.: PCT/US02/14613, and all related continuations, divisionals, continuation-in-parts and foreign applications. Solder materials, coating compositions and other related materials described herein may also be used as components or to construct electronic-based products, electronic components and semiconductor components.

Electronic-based products can be "finished" in the sense that they are ready to be used in industry or by other consumers. Examples of finished consumer products are a television, a computer, a cell phone, a pager, a palm-type organizer, a portable radio, a car stereo, and a remote control. Also contemplated are "intermediate" products such as circuit boards, chip packaging, and keyboards that are potentially utilized in finished products.

Electronic products may also comprise a prototype component, at any stage of development from conceptual model to final scale-up/mock-up. A prototype may or may not contain all of the actual components intended in a finished product, and a prototype may have some components that are constructed out of composite material in order to negate their initial effects on other components while being initially tested.

As used herein, the term "electronic component" means any device or part that can be used in a circuit to obtain some desired electrical action. Electronic components contemplated herein may be classified in many different ways, including classification into active components and passive components. Active components are electronic components capable of some dynamic function, such as amplification, oscillation, or signal control, which usually requires a power source for its operation. Examples are bipolar transistors, field-effect transistors, and integrated circuits. Passive components are electronic components that are static in operation, i.e., are ordinarily incapable of amplification or oscillation, and usually require no power for their characteristic operation. Examples are conventional resistors, capacitors, inductors, diodes, rectifiers and fuses.

Electronic components contemplated herein may also be classified as conductors, semiconductors, or insulators. Here, conductors are components that allow charge carriers (such as electrons) to move with ease among atoms as in an electric current. Examples of conductor components are circuit traces and vias comprising metals. Insulators are components where the function is substantially related to the ability of a material to be extremely resistant to conduction of current, such as a material employed to electrically separate other components, while semiconductors are components having a function that is substantially related to the ability of a material to conduct current with a natural resistivity between conductors and insulators. Examples of semiconductor components are transistors, diodes, some lasers, rectifiers, thyristors and photosensors.

Electronic components contemplated herein may also be classified as power sources or power consumers. Power source components are typically used to power other components, and include batteries, capacitors, coils, and fuel cells. As used herein, the term "battery" means a device that produces usable amounts of electrical power through chemical reactions. Similarly, rechargeable or secondary batteries are devices that store usable amounts of electrical energy through chemical reactions. Power consuming components include resistors, transistors, ICs, sensors, and the like.

Still further, electronic components contemplated herein may also be classified as discreet or integrated. D iscreet components are devices that offer one p articular electrical property concentrated at one place in a circuit. Examples are resistors, capacitors, diodes, and transistors. Integrated components are combinations of components that that can provide multiple electrical properties at one place in a circuit. Examples are ICs, i.e., integrated circuits in which multiple components and connecting traces are combined to perform multiple or complex functions such as logic.

The solder paste formulation of the present invention provides printing times of greater than 300 hours after introduction of the solder paste to the production process before the paste formulation shows any measurable or significant signs of loss of desirable physical properties, such as viscosity and of instability with respect to storage and use. The dramatic increase in allowable printing times assists the consumer in setting up an automated printing line or other automated process that uses solder paste technology. The increase in allowable printing times also allows for the consumer to build pauses and stops in to the processing and production steps in order to take advantage of other related technologies and in order to conduct quality testing and related measurements.

At this point it should be understood that, unless otherwise indicated, all numbers expressing quantities of ingredients, constituents, interaction conditions and so forth used in this disclosure are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in this disclosure are approximations that may vary depending upon the desired properties sought to be obtained by the subject matter presented herein. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the subject matter presented herein are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

EXAMPLES

EXAMPLE 1

A contemplated formulation of one of the solder paste formulations of the present subject matter is shown in Table 2:

Table 2: Formula for a contemplated solder paste formulation. EXAMPLE 2; RHEOLOGY EXPERIMENT

Lead Free 510 (LF510) Development

Background:

LF510 indicates to be a stringy and smearing paste during printing operations.

Experiments:

Scanning Electron Microscopy (SEM) pictures showed that powder BM7001 has more fine particles than BM7008 ( LAL). Thoughts are smearing would be minimized when fine particles reduced. Sufficient wetting powder surfaces would improve rheology leads to less stringy paste. There are 4 pastes made with some changes to prove these ideas:

All pastes made at 88% solid.

Test Results: a) Viscosity: RVT/TF at 25oC +/- 1

a) Reflow

All 4 pastes reflow well. EXAMPLE 3

Dibasic Acid (DBA) Replacement in Low Alpha Lead pastes

Experiments:

DBA (dibasic acid) is a component in low alpha lead solder pastes.

General structure of DBA is HOOC(CH₂)nCOOH with n = 2-4 and is a mixture of acid from n=2 to n=4.

A contemplated Low Alpha Lead paste:

a). Glutaric acid can be used to replace DBA since it is at more than 50% in DBA Paste. b). Caprilic acid replacement (XKLC) reflowed with small balls but provide creamy and stable paste. Viscosity unchanged for 3 days at room temperature. 50/50 of Caprilic acid and Glutaric acid paste (XKLGC) made good reflow paste but stability the same as LAL600: 10-15 prints the most ( 1 hour). c). Replacement of Corefree Ml paste reflowed with some small balls. Addition of 0.84% Formamide made good reflow paste and viscosity stable up to 24 hours (XKLM1/8.7). (book#1009, pg.l9)

Corefree Ml has structure of HOOC(CH₂)nCOOH where n = 8-10. Viscosity, XKLG XKLC XKLGC XKLM1/8.7

RVT/TF @25oC 5 rpm 980 340 1540 780

Thus, specific embodiments and applications of solder paste formulations have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible m anner consistent with the context. In particular, the terms "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.

Claims

CLAIMSWe claim:

1. A solder paste formulation, comprising: at least one metal-based material; at least one support material; and at least one stability modification material.

2. The solder paste formulation of claim 1, wherein the at least one metal-based material comprises at least one metal.

3. The solder paste formulation of claim 2, wherein the at least one metal comprises copper.

4. The solder paste formulation of claim 2, wherein the at least one metal comprises tin.

5. The solder paste formulation of claim 2, wherein the at least one metal comprises silver.

6. The solder paste of claim 2, wherein the at least one metal comprises a lead-based material.

7. The solder paste of claim 6, wherein the lead-based material comprises low alpha lead.

8. The solder paste of claim 1, wherein the at least one metal-based material comprises powder.

9. The solder paste of claim 1, wherein the at least one support material comprises at least one rosin material, at least one rheological additive and at least one solvent.

10. The solder paste of claim 9, wherein the at least one support material further comprises at least one surfactant and at least one neutralizing agent.

11. The solder paste of claim 9, wherein the at least one rosin material comprises a refined gum rosin.

12. The solder paste of claim 1, wherein the at least one stability modification material comprises at least one humectant compound, at least one plasticizer compound, at least one dibasic acid compound, at least one solvent or solvent mixture, or at least one glycerol-based compound.

13. The solder paste of claim 12, wherein the glycerol-based compound comprises ethylene glycol.

14. A method for producing a solder paste formulation having a stability component, comprising: providing at least one metal-based material; providing at least one support material; providing at least one stability modification material; and combining the at least one metal-based material, the at least one support material and the at least one stability modification material, such that the stability component of the solder based formulation is increased over a stability component of a conventional or reference solder paste formulation.

15. The method of claim 14, wherein providing the at least one metal-based material comprises providing at least one metal.

16. The method of claim 15, wherein the at least one metal comprises copper.

17. The method of claim 15, wherein the at least one metal comprises tin.

18. The method of claim 15, wherein the at least one metal comprises silver.

19. The method of claim 15, wherein the at least one metal comprises a lead-based material.

20. The method of claim 19, wherein the lead-based material comprises low alpha lead.

21. The method of claim 15, wherein the at least one metal-based material comprises powder.

22. The method of claim 15, wherein providing the at least one support material comprises at least one rosin material, at least one rheological additive and at least one solvent.

23. The method of claim 22, wherein providing the at least one support material further comprises providing at least one surfactant and at least one neutralizing agent.

24. The method of claim 22, wherein providing the at least one rosin material comprises a refined gum rosin.

25. The method of claim 15, wherein providing the at least one stability modification material comprises at least one humectant compound, at least one dibasic acid compound, at least one solvent or solvent mixture, at least one plasticizer compound or at least one glycerol-based compound.

26. The method of claim 25, wherein the glycerol-based compound comprises ethylene glycol.