JP3771751B2 - Connection method using conductive paste - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductive paste useful for forming a conductive connection between conductive members. The present invention further relates to a method of forming a conductive connection between conductive members using the conductive paste.
[0002]
[Prior art]
Conductive compositions for forming conductive connections between conductive members such as pads on a chip, pads associated with circuits printed on a circuit board are well known to those skilled in the art. In fact, conventional solder compositions made of eutectic gold, such as lead and tin alloys, have been known for a long time. However, such materials require a flux composition to remove oxides on the solder metal surface. These flux materials are acidic in nature and corrode electrically connected high value electrical components and are therefore usually removed using a solvent. However, the conventional solvent for removing the flux has environmental problems, and the use of this solvent complicates the manufacturing process. Therefore, the use of flux materials is decreasing in electrical assemblies that require the connection of expensive electrical components used in current electrical and electronic devices such as computers.
[0003]
A new conductive paste has been developed in view of the well-known drawbacks found in such fusion gold. Usually, these pastes include a conductive metal powder and a thermosetting resin material. After such a material is applied to the electrical component, it is heated to form an electrical connection. The thermosetting resin is cured during this heating. It is known to use non-oxidizing metals as conductive powders in these new pastes, eliminating the need to use flux, but such materials are characterized by the disadvantageous property of not remelting . Those skilled in the art are aware that thermosetting resins form a crosslinked structure when cured. A polymer having a crosslinked structure cannot be remelted or dissolved. Therefore, such electrically connected parts are very expensive, but if necessary, simply heat or remelt the conductive paste to disconnect the parts and use them before. Or cannot be easily reconnected using a new identical paste.
[0004]
A recent development that has made significant progress in the industry is described in US Pat. No. 5,062,896. This patent relates to a polymer-solder composite paste using eutectic metal alloy powder as a filler, which has a melting point of less than 200 ° C. and about 85-93 based on the total weight of the paste. Contained in a concentration by weight.
[0005]
The paste composition of said patent contains a thermoplastic polymer as the second component. The advantage of this patent lies in the presence of a thermoplastic polymer. The thermoplastic polymer contained in the patented paste makes the paste remeltable. Those skilled in the art know that thermoplastic polymers do not cure to form a three-dimensional network. The patent states that the thermoplastic polymer is preferably poly (imidosiloxane), which is essentially not crosslinked and can be remelted or re-dissolved.
[0006]
The third component included in the patent is a volatile organic solvent having a boiling point higher than the melting point of the alloy powder and lower than the maximum reflow temperature of the composite paste composition.
[0007]
Finally, the fourth essential component included in the patent is a temporary flux material, an aliphatic monocarboxylic acid, having a boiling point of about 140-200 ° C. However, aromatic monocarboxylic acids such as 2-methoxybenzoic acid can also be used. The content of the flux material is about 0.5 to 1.5% by weight.
[0008]
The paste composition of the above patent may contain any component such as a surfactant and provides a significant advancement in the industry, but remelts the composite of metal powder and polymer. Even though the problems associated with are resolved in this way, other problems associated with prior art materials are not resolved. That is, the problem associated with acidic fluids that are generated from the temporary flux material, which is the fourth essential component, and that have harmful corrosive effects on expensive electrical components that are electrically connected by paste, has not been solved.
[0009]
Since the paste of the said patent contains the metal which is easy to oxidize evidently from using the metal whose melting | fusing point is less than 200 degreeC, it must contain the flux component. Thus, the advances in the industry brought about by the patented paste do not solve all the problems associated with prior art conductive interconnect materials.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a novel conductive paste that can be remelted and does not contain a flux material that corrodes electrical components.
[0011]
[Means for Solving the Problems]
New conductive pastes have been developed that solve the problems associated with prior art conductive compositions used to electrically connect conductive members. That is, the conductive paste of the present application not only enables re-melting of the paste, but also does not contain a flux material, so that the problems associated with acidic flux are solved.
[0012]
According to the present invention, a conductive paste is provided. The paste contains a thermoplastic polymer, a conductive metal powder, and an organic solvent system.
[0013]
Furthermore, according to the present invention, a conductive composite material is provided. The composite material contains at least 30% by volume of conductive metal powder based on the total volume of the composite material.
[0014]
Furthermore, according to the present invention, a method for forming a flexible circuit by forming a circuit on a flexible substrate is provided. According to this method, electrical components such as integrated circuit chips and surface mount devices are connected to the flexible substrate by the conductive paste according to the present invention. This paste is converted into the conductive composite material of the present invention by the action of heat.
[0015]
Further in accordance with the present invention, a method of interconnecting multilayer structures (also referred to as multichip module laminates) is taught. In this method, a multilayer structure such as a thermoplastic polymer, for example polyimide, is fused from a pair of multilayer structures fused by appropriate heating and pressing using the conductive paste of the present application, vias or through holes or blind holes. Are electrically interconnected.
[0016]
Further in accordance with the present invention, a method for surface mounting an integrated circuit (IC) chip in a lead frame is disclosed. According to this method, conductive leads of a lead frame, or surface mount devices, such as capacitors or resistors, are electrically applied to circuit board pads by the paste composition of the present invention that is converted to a conductive composite material by heating. Connected.
[0017]
Finally, according to the present invention, a method is taught for directly bonding an uninsulated integrated circuit chip to a circuit board. According to this method, the terminal I / O pad of the bare integrated circuit chip is placed upside down so that it contacts the conductive pad on the circuit board surface. An effective amount of the paste of the present invention is placed between the chip I / O pads and the circuit board conductive pads. The paste is heated and converted to a conductive composite material, forming a conductive path between the chip and the circuit board.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The conductive paste of the present invention is a composition containing three components. The first of these components is a thermoplastic polymer. The polymer is selected, for example, from a thermoplastic polymer having a repeating structural unit containing at least one atom or group selected from the group consisting of sulfur, oxygen, nitrogen, silicon, alkyl groups and phenyl groups It's okay. The repeating structural unit of the thermoplastic polymer of the conductive paste may have two or more of the above atoms or groups.
[0019]
The thermoplastic polymer may be any of homopolymers, i.e., a polymer in which a single monomer repeats, a segmented copolymer, or a segmented copolymer having at least three different homopolymers, and mixtures thereof. But you can. The segmented copolymer contemplated in the thermoplastic polymer of the present invention contains at least two comonomers provided in the form of segments. The comonomer provided in the form of a segment is a copolymer having a repeating monomer unit of a first monomer and a block consisting of a repeating monomer unit of at least one different monomer adjacent to the first monomer unit. The lengths of these monomer units may form the same or different, and the length may vary from one to the length of many monomers. The segmented copolymer of the present invention preferably has a soft repeating monomer unit composed of nonpolar units and a rigid repeating monomer unit composed of polar units.
[0020]
Preferred homopolymers contemplated as thermoplastic polymers for the conductive pastes of the present invention include polysulfones, polyolefins, and polyacrylates.
[0021]
The segmented copolymers contemplated by the present invention include poly (imide urea), poly (ether siloxane), poly (imide siloxane), poly (styrene butadiene), poly (styrene isoprene), poly (acrylonitrile butadiene), poly ( There are copolymers such as ethylene vinyl acetate) and polyurethane.
[0022]
The preferred segmented copolymer described above is a thermoplastic elastomer. This polymer does not have the disadvantageous properties of thermoplastic polymers and elastomers, but combines the beneficial properties of both. That is, thermoplastic elastomers can remelt and change shape, unlike conventional elastomers. Similarly, unlike conventional thermoplastic polymers, thermoplastic elastomers exhibit good elastic recovery when stretched.
[0023]
All thermoplastic polymers that can be used as a component of the conductive paste have the requirement that they have good thermal stability. To that end, it is preferred that the decomposition temperature of the thermoplastic polymer be at least about 200 ° C. More preferably, the decomposition temperature of the thermoplastic polymer is at least about 300 ° C.
[0024]
The second component of the conductive paste of the present invention is a conductive metal powder. The conductive metal powder is preferably a metal powder containing no oxide and has a melting point of at least about 200 ° C. “Oxide free” means either that the metal does not produce an oxide or that it does not act as an electrical insulator. Accordingly, gold, silver, tin, nickel, ruthenium, rhodium, palladium, platinum, and iridium are preferred for use as “oxide-free” metals. Metals that do not contain oxides include metal elements that do not contain oxides, alloys of metal elements that do not contain at least two types of oxides, or single metal elements that do not contain oxides or at least two types of oxides A metal free of surface oxide coated with an alloy of a non-metallic element can be used. “Powder” means a single particle having a diameter or main dimension of less than 50 μm, or an aggregate of smaller particles.
[0025]
The metal containing no oxide is preferably silver or gold, whether used alone or as an alloy, or in pure form or as a coating.
[0026]
One skilled in the art will know that an anti-diffusion barrier layer is required to prevent metals that do not contain certain oxides from diffusing into a metal core that is susceptible to oxidation. For example, cobalt, preferably a cobalt alloy, and phosphorus are often added to a copper core and then coated with gold. This prevents the gold coating from diffusing into the copper even at high temperatures.
[0027]
This second component is not as preferable as the above-mentioned metal containing no oxide, but may be, for example, an organic polymer or an inorganic material core coated with a metal containing no oxide.
[0028]
In such embodiments with an organic polymeric material as the core, the organic polymer is preferably a polystyrene latex spherical particle.
[0029]
In still other embodiments cored with an inorganic material, the inorganic material is an oxide such as silica, alumina, zirconia, titania, borate, titanate, silicate, carbide, nitride, or other ceramic material The solid powder.
[0030]
The average particle size of the conductive metal powder is preferably about 20 μm or less. The average particle size of the metal powder used in the conductive paste of the present application is more preferably about 10 μm or less. More preferably, the average particle size of the metal powder is about 5 μm or less.
[0031]
The third component of the conductive paste of the present application is preferably an organic solvent type and having at least one polar organic solvent. The polar organic solvent used in the conductive paste of the present invention preferably has a boiling point in the range of about 130 to 300 ° C. at atmospheric pressure. More preferably, the boiling point at atmospheric pressure is in the range of about 150-250 ° C.
[0032]
Polar solvents that meet the above criteria are esters, ethers, amides, lactones, or sulfones, but are not limited thereto. Therefore, esters such as dimethyl adipate and ethyl benzoate, ethers such as acetophenone and 2-methoxyethyl ether, amides such as dimethylacetamide, lactones such as N-methylpyrrolidinone, sulfones such as dimethyl sulfoxide, Included within the range of polar solvents useful in the pastes of the present invention.
[0033]
The paste of the present invention preferably contains at least one of the above-mentioned solvents, but may contain a plurality of these solvents. That is, the solvent may be a mixture of a plurality of these solvents. In addition to one or more types of polar organic solvents, one containing one or more types of nonpolar solvents may be used.
[0034]
In a preferred embodiment using a combination of a nonpolar organic solvent and at least one polar solvent, the nonpolar solvent is preferably a liquid hydrocarbon. It is more preferable to use liquid aromatic hydrocarbons. The preferred aromatic hydrocarbons used as part of the polar solvent composition in the paste of the present invention are xylene and trimethylbenzene.
[0035]
Components such as a corrosion inhibitor and a surfactant may be optionally added to the conductive paste. However, it should be emphasized that the conductive paste contains no flux material.
[0036]
The second aspect of the present invention relates to a conductive composite material. The conductive composite material is made of a metal that does not contain an oxide. Preferably, the oxide-free metal is present at least about 30% by volume relative to the total volume of the composite material. The metal component of the composite material has the characteristics of the conductive metal powder used in the conductive paste. The preferred embodiment of the conductive metal powder is the same as the preferred metal powder in the conductive paste described above.
[0037]
More preferably, the oxide-free metal is present at least about 40% by volume relative to the total volume of the composite material.
[0038]
The second component of the conductive composite material is a thermoplastic polymer. The thermoplastic polymer used in this composite material is the same as the thermoplastic polymer component of the conductive paste. The thermoplastic polymer of the composite material includes the properties of the thermoplastic polymer of the conductive paste, including preferred embodiments.
[0039]
The conductive composite material of the present invention is formed by heating the conductive paste of the present invention. In order to improve or facilitate the adhesion of electrical components, an adhesion pressure is applied simultaneously with heating. Specifically, a conductive paste is injected between the conductive leads of two or more electrical components. The temperature of the paste is set to a temperature exceeding the boiling point of the solvent, and the solvent is evaporated from the paste. The pressure need not be atmospheric pressure. A vacuum may be used to lower the boiling point of the solvent.
[0040]
In an alternative embodiment, dynamic gas exchange is used in the step of removing the solvent in the process of converting the conductive paste to the composite material. This method is well known to those skilled in the art and is a method of removing the solvent by evaporation at atmospheric pressure at a temperature below the boiling point of the solvent. This step is usually performed in a stream of nitrogen or other inert gas.
[0041]
The method of forming the conductive interconnect is performed by one of two adhesion methods. In the first method, after injecting the paste, pressure is applied at a temperature higher than the glass transition temperature of the thermoplastic polymer. In this first method, the solvent evaporates and the thermoplastic polymer flows to form a conductive bond. In the second method, the paste is first dried (ie, the solvent is removed) at a temperature lower than the glass transition temperature of the thermoplastic polymer. Next, the temperature is raised to a temperature higher than the glass transition temperature of the thermoplastic polymer to complete the conversion to the conductive composite material. As mentioned above, this method is affected by time and temperature. Clearly, the higher the adhesion temperature, ie the temperature at which the paste is exposed, the shorter the required time. Optimal adhesion conditions depend on the specific structure to be formed and the glass transition temperature of the thermoplastic polymer.
[0042]
The conductive composite material may contain one or more optional components. These optional components include, for example, corrosion inhibitors and surfactants. The conductive composite material formed with the conductive paste of the present invention does not contain a fluxing agent like the paste.
[0043]
The criteria for selecting the formulation are fillers depending on (i) the conductivity of the polymer / metal composite, (ii) the hydrodynamic properties of the polymer / metal / solvent paste, and (iii) the intended application. It is determined based on the balance of wetting and adhesion properties of the polymer to the metal or other substrate.
[0044]
For conductivity, an ionic impurity acting as an “electron trap” during the metal / insulator / metal tunneling effect causes a linear current (I) versus voltage drop in the current range defined by the intended application. (V) Must be low enough to maintain the characteristics. Conductivity (σ) vs. temperature (T) is not as seen in disordered systems where conductivity decreases with increasing temperature, but behaves like a metal, ie, log (σ) to T ^1/4 It is necessary to follow the law. Finally, the resistivity at the temperature of liquid helium needs to be as low as possible. For good adhesion, the polymer pair wets the metal filler, wets the substrate material specified in the intended application, and the Young's modulus of the polymer is preferably greater than 0.1 GPa at 25 ° C. . The paste needs to have a non-Newtonian viscosity in the range of about 3000 to 5000 poise with respect to hydrodynamic behavior, the lowest initial normal stress difference and the low elastic recoil. Furthermore, the paste needs to decrease in viscosity when subjected to shear, as opposed to a normal viscoelastic non-Newtonian fluid that is stable in viscosity.
[0045]
Another aspect of the invention relates to a method for use in the manufacture of electrical components and devices by converting a novel conductive paste into the composite material of the invention. This method relates to bonding at least one flexible electrical component substrate to an electrical component. Such bonding uses the conductive paste of the present invention and is performed to assemble a flexible substrate to form a flexible or “flex” circuit.
[0046]
In this method, the conductive paste of the present invention is injected between the conductive surface of a flexible substrate on which a circuit is formed and the conductive surface of an electrical component. After injecting the paste in this way, heat and pressure are applied for a time sufficient for the conductive paste to convert to a conductive composite and form a bond. Preferably, the paste is at least about 0.35 kg / cm. ² And heated to a temperature higher than the glass transition temperature of the polymer. In the obtained product, an electrical connection is formed between the flexible substrate and the electrical component, and a flexible circuit is completed.
[0047]
A second application of the conductive paste and composite material of the present invention is its use in the process of making so-called “via-via” interconnections of multilayer structures. This method is shown in FIG. Layer 10 has vias 8 with copper plating 6. The layer 10 includes a metal wire 4 in the X direction and a metal wire 5 in the Y direction. Layer 10 has a ground plane 3 surrounded by a dielectric layer 2. Layer 10 also includes an adhesive surface 7.
[0048]
Layer 10 is electrically interconnected to second layer 50 by the conductive paste of the present invention. Specifically, the lump 12 of conductive paste is poured into the via 8 so as to rise from the top and bottom. These surfaces contain an adhesive dielectric 7. In order to electrically connect layer 10 to layer 50, one or more vias are similarly filled with a mass of conductive paste, and after performing the drying step, the layers are aligned, Pressure is applied at a suitable pressure and above the glass transition temperature of the polymer so that the paste in the layer via melts to form a conductive composite.
[0049]
Another important utility of the conductive paste and composite material of the present invention is in the method of surface mounting. The use of this conductive paste and composite material is shown in FIG. In FIG. 2, an insulated circuit board 20 such as an organic polymer or ceramic has a plurality of terminal points called pads in the industry. This is indicated by pads 22 and 24 in FIG. The pads 22 and 24 are electrically connected to the integrated circuit chip in the lead frame 25 by the conductive tubes 26 and 27, thereby electrically connecting the substrate 20 and the integrated circuit chip 25. This connection is made permanent by the conductive paste of the present invention. As shown in FIG. 2, the paste masses 21 and 23 injected between the leads to the lead tubes 26 and 27 and the pads 22 and 24 are heated to a temperature higher than the glass transition temperature of the polymer, When given a heavy load, preferably at least equal to the sum of the weights of the tip 25 and conductor tubes 26 and 27, the composite material of the present invention is formed.
[0050]
Yet another application of the conductive paste and composite material of the present invention is in a method of obtaining a “flip chip” connection, as described in US Pat. No. 4,434,434. Such connections are a major advance in computer technology. With "flip chip" connection, the integrated circuit chip can be attached directly to the circuit board by means other than wiring. Wiring is labor intensive, takes up space, and is therefore expensive and time consuming, but the use of conductive pastes in the manufacture of computers and other complex devices provides significant progress.
[0051]
In the method of the present invention, flip chip connection can be made by utilizing the conductive paste of the present invention. This method will be described with reference to FIG. 3, which shows a schematic diagram of this connection. The chip 30 "flips" or flips upside down to align the pads 34 on its surface with the pads 36 on the circuit board 32 (sometimes referred to as a substrate). A small amount of conductive paste 38 is injected between pads 34 and 36 so that an electrical connection is obtained. Thereafter, the entire apparatus is heated, preferably about 0.35 kg / cm. ² To make the electrical connection permanent, converting the paste into the conductive composite material of the present invention.
[0052]
Alternatively, the paste may be applied to the substrate pad, the chip pad, or both in a flip chip process. The paste is then dried, the two sides are aligned, pressed, heated to a temperature above the glass transition temperature of the thermoplastic polymer, and rapidly, in a substantially defect-free manner, the desired electrical Get a connected device.
[0053]
The above applications highlight the technological advances associated with the pastes and composites of the present invention. The unique combination of components that make up the paste composition makes it easy to convert the electrical and electronic components into permanent composites that are electrically connected at relatively mild temperature and pressure conditions without damaging the electrical and electronic components can do. In addition, despite the fact that the formation of the composite material is “permanent”, these connections can cause temperatures above the glass transition temperature of the thermoplastic component of the composition without damaging the parts connected by the composite material. The connection can be easily disconnected.
[0054]
The following examples illustrate the scope of the present invention. These examples are for illustrative purposes only, and the present invention is not limited to these examples.
[0055]
【Example】
Example 1
Based on the total weight of the solution, 28% by weight of poly (imide siloxane) was dissolved in acetophenone to produce a solution of poly (imide siloxane). To this solution was added metal silver flakes of particle size having a length and width of about 1-5 μm and a thickness of about 1 μm. The amount of silver particles was 87% by weight with respect to the total weight of silver and poly (imide siloxane). This 87% by weight concentration was calculated regardless of the weight of the acetophenone solvent.
[0056]
The resulting dispersion of silver particles in an acetophenone solution of poly (imidosiloxane) was mixed with high shear using a Mueller ™ high shear mixer to produce a paste.
[0057]
The paste composition was applied to a flip chip connection method (FCA), and applied to a gold-coated substrate in a circle having a diameter of 100 μm and a height of about 100 μm with a center-to-center distance of 200 μm. The feature array was 11 × 11. The resulting circular array was bonded to another substrate coated with gold at an adhesive load of about 1.1 kg and a temperature of 340 ° C. The resistance of the whole structure is ≦ 1μΩ ・ cm ² Met. The adhesive strength of an 11 × 11 array is about 210 kg / cm ² Met.
[0058]
Example 2
A solution prepared by dissolving 28% by weight of poly (imide siloxane) in N-methylpyrrolidone (NMP) was mixed with gold particles having a particle size of 1 to 5 μm in the same manner as Example 1 except for the solvent. The amount of gold particles added to the poly (imidosiloxane) solution was such that the gold particles were 92% by weight based on the total weight of gold and poly (imidosiloxane). This ratio was independent of the weight of the NMP solvent.
[0059]
As in Example 1, a paste was produced by mixing a dispersion of gold in an NMP solution of poly (imidosiloxane) with a Mueller ™ high shear mixer.
[0060]
This paste was used for FCA as in Example 1. Adhesive strength at an adhesive load of about 1.25 kg is about 225 kg / cm ² Met.
[0061]
Example 3
A mixture of 68% by weight of metal silver flakes having a particle size of 13% by weight of poly (imidosiloxane), length and width of about 3 to 10 μm, and a thickness of about 1 μm and 19% by weight of acetophenone was mixed in a high shear mixer. A paste was generated. As an example of surface mounting as shown in FIG. 2, this paste was deposited on a Cu pad from which the surface oxide on the epoxy substrate was removed. The paste is 1.65mm pitch, 1.27mm pitch with 14 pads arranged in 2 rows ² Of 28 patterns. A 28-pin VSOP (very small outline package) was attached to the uncured paste. The attachment portion was dried and then cured at 220 ° C. for 10 minutes. The adhesion strength of the component to the circuit board was about 0.27 kg per lead.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating the use of a paste and composite material of the present invention to provide via-via interconnection between two layers including a circuit.
FIG. 2 is a schematic diagram illustrating surface mounting of an integrated circuit chip in a lead frame to a circuit board using the paste and composite material of the present invention.
FIG. 3 illustrates using a paste and composite material of the present invention to make a “flip chip” connection between an integrated circuit chip and a circuit board to provide an adhesive and electrical connection between two components. It is a schematic diagram.
[Explanation of symbols]
2 Dielectric layer
3 Ground plane
4 Metal wire in X direction
5 Y direction metal wire
6 Copper plating
7 Adhesive surface
8 Bahia
10, 50 layers
12 Conductive paste
20 Circuit board substrate
21, 23 Conductive paste
22, 24 pads
25 Lead frame
26, 27 Conductor tube
30 chips
32 Circuit board
34, 36 pads
38 Conductive paste

Claims (15)

A method of making a flexible circuit,
A thermoplastic polymer exhibiting a decomposition temperature of at least 200 ° C., a powder comprising a metal having a melting point of at least 200 ° C. and containing no oxide, and a polar organic solvent system having a boiling point of about 130 to about 300 ° C .; In addition, the conductive paste does not include a flux component, and the metal powder has an average particle size of about 20 μm or less, and the amount of the metal powder is equal to the total volume of the thermoplastic polymer and the metal powder. Providing a conductive paste that is at least about 30% by volume relative to;
Contacting an electrical component and a flexible substrate on which a circuit is formed with the conductive paste; and heating the substrate to a temperature higher than a glass transition temperature of a polymer contained in the conductive paste. Including a step. In a method of electrically connecting a plurality of layers having one or more through vias to form a multilayer structure,
A thermoplastic polymer exhibiting a decomposition temperature of at least 200 ° C., a powder comprising a metal having a melting point of at least 200 ° C. and containing no oxide, and a polar organic solvent system having a boiling point of about 130 to about 300 ° C .; In addition, the conductive paste does not include a flux component, and the metal powder has an average particle size of about 20 μm or less, and the amount of the metal powder is equal to the total volume of the thermoplastic polymer and the metal powder. Providing a conductive paste that is at least about 30% by volume relative to;
Placing the conductive paste into the via;
Heating in air or under vacuum to remove the solvent in the conductive paste;
Aligning the vias of adjacent layers, and heating the aligned structure to at least about 150 degrees Celsius. A thermoplastic polymer exhibiting a decomposition temperature of at least 200 ° C., a powder comprising a metal having a melting point of at least 200 ° C. and containing no oxide, and a polar organic solvent system having a boiling point of about 130 to about 300 ° C .; In addition, the conductive paste does not include a flux component, and the metal powder has an average particle size of about 20 μm or less, and the amount of the metal powder is equal to the total volume of the thermoplastic polymer and the metal powder. Providing a conductive paste that is at least about 30% by volume relative to;
Electrically contacting the leads of the lead frame with corresponding pads of the circuit board substrate;
A method of performing surface mounting, comprising: depositing the conductive paste on the pad; and heating the assembly to a temperature higher than a glass transition temperature of a polymer contained in the conductive paste. In a method of forming an integrated circuit by connecting an integrated circuit chip to a circuit board,
A thermoplastic polymer exhibiting a decomposition temperature of at least 200 ° C., a powder comprising a metal having a melting point of at least 200 ° C. and containing no oxide, and a polar organic solvent system having a boiling point of about 130 to about 300 ° C .; In addition, the conductive paste does not include a flux component, and the metal powder has an average particle size of about 20 μm or less, and the amount of the metal powder is equal to the total volume of the thermoplastic polymer and the metal powder. Providing a conductive paste that is at least about 30% by volume relative to;
Depositing the conductive paste on the pads of the chip, the circuit board, or both to align the pads of the chip and the pads of the circuit board; and the assembly comprising: Heating to a temperature above the glass transition temperature of the polymer contained in the conductive paste. The method of claim 4, further comprising heating the paste at a temperature lower than the glass transition temperature of the polymer to dry the paste prior to the alignment step. The thermoplastic polymer is poly (imidourea), poly (ether siloxane), poly (imidosiloxane), poly (styrene butadiene), poly (styrene isoprene), poly (acrylonitrile butadiene), poly (ethylene vinyl acetate) and polyurethane. 6. A method according to any one of claims 1 to 5, characterized in that it is a segmented copolymer selected from the group consisting of: The metal containing no oxide is a metal selected from the group consisting of gold, silver, tin, nickel, ruthenium, rhodium, palladium, platinum, iridium, and alloys of these two or more metals. A method according to any one of claims 1 to 5. The polar organic solvent is selected from the group consisting of dimethyl adipate, ethyl benzoate, acetophenone, 2-methoxyethyl ether, dimethylacetamide, N-methylpyrrolidinone, dimethyl sulfoxide, and mixtures thereof, 6. A method according to any one of claims 1-5. The method according to claim 1, wherein the conductive paste is reconnectable. In a flexible circuit having an electrical component and a flexible substrate on which a circuit is formed,
Between the electrical component and the flexible substrate, a thermoplastic polymer exhibiting a decomposition temperature of at least 200 ° C., a powder comprising a metal having a melting point of at least 200 ° C. and containing no oxide, and about 130- Having an electrical connection formed by heating a conductive paste containing a polar organic solvent system having a boiling point of about 300 ° C. and not containing a flux component at a temperature higher than the glass transition temperature of the thermoplastic polymer;
The metal powder has an average particle size of about 20 μm or less, and the amount of the metal powder is at least about 30% by volume with respect to the total volume of the thermoplastic polymer and the metal powder. A flexible circuit. In an assembly structure having a first circuit having a first connection end and a second circuit having a second connection end,
A thermoplastic polymer exhibiting a decomposition temperature of at least 200 ° C. between the first connection end and the second connection end, a powder comprising a metal having a melting point of at least 200 ° C. and containing no oxide, and Electrical connection formed by heating a conductive paste containing a polar organic solvent system having a boiling point of about 130 to about 300 ° C. and containing no flux component at a temperature higher than the glass transition temperature of the thermoplastic polymer Have
The metal powder has an average particle size of about 20 μm or less, and the amount of the metal powder is at least about 30% by volume with respect to the total volume of the thermoplastic polymer and the metal powder. An assembly structure. The thermoplastic polymer is poly (imidourea), poly (ether siloxane), poly (imidosiloxane), poly (styrene butadiene), poly (styrene isoprene), poly (acrylonitrile butadiene), poly (ethylene vinyl acetate) and polyurethane. The structure according to claim 11, wherein the structure is a segmented copolymer selected from the group consisting of: The metal containing no oxide is a metal selected from the group consisting of gold, silver, tin, nickel, ruthenium, rhodium, palladium, platinum, iridium, and alloys of these two or more metals. The structure according to claim 11. The polar organic solvent is selected from the group consisting of dimethyl adipate, ethyl benzoate, acetophenone, 2-methoxyethyl ether, dimethylacetamide, N-methylpyrrolidinone, dimethyl sulfoxide, and mixtures thereof, The structure according to claim 11. The structure according to claim 11, wherein the electrical connection is reconnectable.

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