CN1946795A - Dual-Stage Underfill for Wafers - Google Patents

Abstract

A 100% non-volatile, one-part liquid underfill encapsulant is disclosed for application to the active side of a large wafer or integrated circuit chip. Upon coating, the encapsulant is converted to a liquefiable, tack-free solid by exposure to radiation, particularly in the UV, visible and infrared spectrum. The underfill-coated wafer exhibits outstanding shelf aging of months without advancement of cure. The large wafer can be singulated into smaller wafer sections and stored for months after which during solder reflow assembly, the wafer connects are fixed and the underfill liquefies, flows out to a fillet and transitions to a thermoset state on heat activated crosslinking.

Description

Dual-Stage Underfill for Wafers

field of invention

This invention relates to microelectronic chip assemblies, and more particularly to methods and materials for applying underfills to integrated circuit chips.

Background of the invention

Surface mounting of electronic components has been well developed in automated package assembly systems. An integrated circuit is composed of devices such as transistors and diodes, elements such as resistors and capacitors, connected by conductive connections to form one or more functional circuits. Devices are disposed on a wafer or silicon wafer having a surface for a series of fabrication steps to form identical integrated circuits separated by a repeating rectangular pattern of scribe or saw streets in the wafer surface Patterns, the scribe lines or rectangular areas serve as boundaries between dice, chips or dies. In later stages of the manufacturing process, individual dice from the wafer are attached to the substrate to form the IC package.

Conventional flip chip technology generally refers to any assembly in which the front side of an integrated circuit die is connected to a packaging substrate or printed circuit board (collectively referred to as a PCB). Flip-chip assemblies can be designed as packages with or without underfill. For flip-chip use, the chip has small bumps or solder balls (hereinafter "bumps" or "solder bumps") on the front side that correspond to the recesses on the surface of the circuit board. The chip is assembled by nesting the bumps on the board so that the solder bumps are sandwiched between the pads of the board and corresponding pads of the chip. After fluxing, the assembly is heated to the point where the solder reflows. After cooling, the solder hardens, allowing the flip chip to be mounted on the surface of the board.

Conventional underfills are used in a number of different ways and applied to mounted chips to provide protection to the chip from chemical attack, moisture, airborne contamination, etc., as well as mechanical shock, vibration and Temperature cycle changes encountered in transportation and use. Conventional capillary flip-chip underfill methods must have the following steps: chip and board alignment, flux dispensing, solder reflow, flux cleaning, underfill application, underfill flow, and curing.

Underfills used in chip packages serve the function of protecting the solder joints that interconnect the chip to the package or board from environmental factors such as moisture and contamination, and redistributing mechanical stress, thereby improving device lifetime. It provides the chip with protection from contamination such as moisture and resulting corrosion of the metal interconnects. However, wrong choice of adhesive can lead to flip-chip package failure in several ways, such as shrinkage, delamination, hydrolytic instability, corrosion, and contamination due to underfill.

Chip underfills are used to avoid stress between the attach parts due to different thermal expansion coefficients between the chip, interconnect, underfill, and substrate. If the substrate is organic, failure modes due to stress become more prevalent as the device size grows. Chip underfills must provide adhesion to substrates such as ceramic or organic PCBs (e.g. FR4 epoxy), where the substrate may or may not be coated with: solder mask; metal alloys or organic interconnects; and integrated circuit dies (chips), which are typically composed of silicon or other inorganic substances and may or may not be coated with a thin passivation layer.

In one of the two principal methods of packaging electronic components, the component is soldered on the same side as it is mounted on the board. These devices are said to be "surface mount". Two conventional underfills are used in practice for surface mount devices: capillary or "no-flow" types. Detailed descriptions of these techniques can be found in the literature. See, for example, John H. Lau's book Low Cost Flip Chip Technologies for DCA, WLCSP and PBGA Assemblies, McGraw-Hill, 2000. For both technologies, heat is typically applied to cure liquid thermoset formulations or to laminate solid films into assemblies. Vacuum is sometimes used to remove air bubbles from the system. Underfills are typically applied in surface mount (SMT) assembly lines for chip-in-package or chip-on-board. The use of conventional flow and no-flow underfills on SMT lines requires multiple steps, and the process is often the bottleneck on these microelectronic assembly lines.

A representative conventional no-flow underfill is disclosed in US Patent No. 6,180,696. The underfill material is first dispensed on a substrate or semiconductor chip, and then the solder bumps are reflowed while the underfill encapsulant cures. The underfills taught in US Pat. No. 6,180,696 include epoxy resins and/or mixtures of epoxy resins, organic carboxylic anhydride hardeners, cure accelerators, self-fluxing agents, viscosity control agents, coupling agents, and surfactants. The curing peak temperature of the underfill formulation is 180-240°C. The underfill must be stored at sub-zero temperatures (°C) to avoid accelerated curing.

Underfills are not the same as imageable photoresist substances that are applied to PC boards as a patterned formation, however, there is some similarity in the use of ubiquitous epoxy resins. Coatings for photoresists are known to employ a photoinitiator for curing the areas exposed to activating radiation through a mask, and a second thermally activated free radical curing component to effect polymerization in the non-irradiated or shadowed areas. A second cure mechanism commonly utilized relies on the addition of heat-activated peroxides to the formulation; however, temperatures in excess of 100°C are typically required to initiate peroxide-induced polymerization, thus precluding use involving, for example, heat-sensitive electronic components .

US Patent No. 5,077,376 discloses epoxy adhesives containing latent heat curing components. The '376 publication teaches the known storage stability problems of liquid epoxies that make it possible to contain latent hardeners such as dicyandiamide, dibasic acid dihydrazides, boron trifluoride-amine adducts, tris Epoxy resin compositions of polycyandiamine, melamine, and the like are widely used. However, this patent teaches that dicyandiamide, dibasic acid dihydrazide and melamine have the disadvantage that they require high temperatures of 150°C or higher for curing.

US Patent No. 5,523,443 discloses a post-cure conformal coating containing a UV-cured polymerizable system and a moisture-cure mechanism. The polymerizable coating system is a one-component system containing at least one alkoxysilyl-urethane-acrylate or methacrylate, acrylate or methacrylate or vinyl ether diluent, cationic or Free radical photoinitiator type polymerization initiator and metal catalyst.

U.S. Patent No. 5,249,101 (IBM, 1993) teaches that the brittleness of protective epoxy coatings for circuitry on circuitized surfaces of chip carriers having a modulus of elasticity greater than about 10,000 psi (69 MPa) can lead to cracking and delamination . U.S. '101 proposes coatings containing acrylated polyurethane oligomers, acrylated monomers, and photoinitiators to provide coatings with an elastic modulus of 10,000 psi or less and a chloride ion concentration of less than 10 ppm. Acrylated urethane underfills for chips do not require solder reflow due to their lack of adequate thermal insulation.

US Patent No. 5,494,981 discloses a curing combination of a cycloaliphatic epoxy resin, a cyanate ester resin, optionally a polyol, and Brönsted acid as an initiator. Upon curing, the composition provides interpenetrating polymer networks (IPNs). The IPNs are suitable for use as high temperature stable vibration damping materials, adhesives, adhesives for abrasives and protective coatings.

U.S. Patent No. 5,672,393 discloses acrylate sealing formulations that react at a high rate when exposed to radiation of wavelengths in the ultraviolet and visible Relatively low stress deposits with physical clarity and surface properties. The method necessitates exposing the formulation on the object to radiation to initiate photopolymerization and thermal polymerization, and the apparatus includes actinic radiation and thermal energy sources in close juxtaposition. The catalyst system includes a photoinitiator component and a thermal initiator component responsive to temperatures below 120°C.

US Patent No. 5,706,579 discloses a method of assembling an integrated circuit package made from a die, printed wiring board, and metal lid using a beta-stageable resin pre-applied to the lid and containing a thermally conductive filler material. With a lid properly placed over the die and substrate board, the package is heated to cause the resin to flow and form a connection to the die. Further heating causes the resin to cure and form a permanent thermal bridge between the die and lid.

US Patent No. 6,194,788 discloses an integrated thermoplastic, self-fusing two-component underfill for flip chips. The underfill consists of epoxy resin and acetate thinner with a self-fluxing acidic epoxy curing agent.

US Patent No. 6,323,062 (Alpha Metals, filed September 14, 1999) discloses the use of solvent-based subfills for flip chips. The method includes the steps of bonding a bumped wafer to an extensible carrier substrate by first sawing the wafer to form individual chips, extending the carrier substrate in a bidirectional manner to form vias between the individual chips, and then The underfill compound is applied to the bumped surface of the chip and around the edge of the chip. The underfill substance is not disclosed, but it teaches that the underfill can be dried after application, the underfill substance can be cut in the channels between the chips, and each individual chip coated with the underfill can be removed from the carrier. remove.

US Patent No. 6,383,659 discloses a b-staged film of a low Tg epoxy based underfill containing a thermoplastic polymer with a molecular weight of 5,000-200,000. The '659 patent also teaches self-polymerizing or phenol-curable epoxy resin compositions, typically containing imidazole, which exhibit limited storage stability, moisture resistance, and high temperature performance of cured compositions, and Difficulty controlling the progress of B-phase reactions.

The prior art described above exemplifies post-cure methods of forming coatings, but does not address storage of b-staged coatings containing post-cure chemicals on brittle substrates such as silicon wafers. Except in controlled environments, wafer deformation, cracking, and long-term ambient storage at temperatures easily reaching about 50°C may occur during transport or storage.

After the underfill is applied and cured, and then left for several months until the solder reflow step for the two-stage cure underfill, the problems encountered in underfill for wafers are: incipient wetting and sticking of the liquid coating. Attachment; coating cures at ambient temperature without delamination from wafer; long-term ambient temperature storage of coated wafers without loss of reflow capability due to cure or gel content growth; avoids delamination from wafer during partitioning or scribe ; ability to stencil in wafer saw wire; initial heat to thicken slowly during reflow by solder; ability for underfill to flow out and around die to form fillet when surround ring is not used ; the absence of voids in the underfill after the solder reflow step; and its long-term reliability (defect-free) in the device over its useful life.

All of these technical problems identified by underfills for wafers that are stored for long periods of time prior to assembly are not resolved by prior art underfill materials. Accordingly, it is an object to provide materials and methods for decoupling the application of the underlayer material from the flip-chip assembly whereby a liquid underfill is applied by conventional coating methods directly on the front side of a large die such as Wafers with a surface area of 100-500 mm ² and larger are then cured and the coated wafers or diced chips are stored for extended periods of time, eg several months. In this case, subsequent die attach methods must avoid problems related to the properties of aged underfills.

Summary of the invention

The present invention relates to a wafer-underfill assembly and method of applying a one-component, solvent-free, non-self-fusing underfill directly to the front side of a wafer at a coating thickness of typically about 0.003 inches to 0.070 inches (0.076 to 1.77 mm). The underfill is initially a liquid coating that partially or completely covers the solder bumps of the die. Underfills consist of filled, 100% solids (essentially non-volatile) liquid coatings. The underfill is cured to a thermally liquefiable solid state on the wafer by exposure to light radiation of about 50-2400 mJ/cm ² . The underfill can be applied in a grid pattern over the wafer saw wires, or can form a continuous coating that can withstand the wafer being diced into individual regions or dies. Coated wafers or coated individual areas can be stored at ambient conditions for an indeterminate delay time of many months prior to assembly or solder interconnection. In assembled chips employing a wrap-around encapsulant applied around the wafer's underfill, the thermally liquefiable solid underfill may have a thermal cure onset point of 150° C. or higher. In embodiments where the underfill is heated to liquefy and flow to the edge of the wafer, and to some extent flow up to form the fillet, the thermal cure activation temperature of the underfill must be above 170°C. The heat applied for reflowing the solder is sufficient to initiate melt flow of the underfill prior to activating the thermal cure system, which causes the underfill to gel into a thermoset solid state. In the thermoset cured state, the underfill exhibits a flexural modulus below 10 GPa.

One-component liquid underfills include a mixture of one or more ethylenically unsaturated monomers, one or more curable epoxies, one or more photoinitiators, A latent thermal curing agent, thermally conductive and electrically insulating filler, characterized in that the photocurable component accounts for 5%-30% of the total weight of the underfill adhesive, and the epoxy resin component accounts for 10%-45% of the total weight of the underfill adhesive. A preferred photocurable composition comprises 100% monofunctional ethylenically unsaturated acrylate or methacrylate monomers. Preferred photopolymerizable components are monofunctional cyclic ethers and/or cyclic acetals of acrylic acid.

Brief description of the drawings

Figure 1 shows the DSC curve of Example 6 showing the melting point, the onset of thermal curing and the peak temperature of the reaction.

Figure 2 shows the DSC curve of Example 7 showing the melting point, the onset of thermal curing and the peak temperature of the reaction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In terms of method, the underfill according to the invention is suitable for conventional coating methods such as application to the front side of the wafer by spin-molding, stencil coating, printing or the like. The rheology of the liquid underfill material is readily adapted to the chosen coating method. A liquid underfill is applied to the bumps or front side of a large wafer mounted on a substrate, undergoes light-induced radical polymerization, and rapidly forms a solid, self-supporting layer that remains adherent to the wafer. Light-curing solidification results in a tack-free solid underfill surface without wafer distortion. An underfill coating exhibiting a solid state at ambient remains thermally liquefiable after prolonged ambient storage and can be exposed for months at 50° C. without stressing the wafer.

The delay time for storage of wafers or individual areas coated with the photocurable, thermally liquefiable solid underfill prior to formation of solder interconnects is not limited, eg, weeks, months, up to a year, etc. Storage conditions during the delay may include exposure of the underfill to ambient temperature without refrigeration. Wafer underfills differ from conventional thermoplastic or thermoset materials that are cast from solvents or melt processed using heat and/or vacuum. However, according to the present invention, the underfill is a 100% solid material that photo-induced solidifies by addition polymerization on the front side of the wafer and remains in a thermoplastic state until the onset of the second thermally induced cure is significantly delayed. There is no further curing at room temperature, and the thermoplastic filler has the following specific key properties: no delamination, no void formation, sufficient reflow under solder reflow conditions, and long-term adhesion under repeated thermal cycling conditions in the thermoset state. adhesion without causing device failure or damage. Thermoset cured underfills have a flexural modulus of 1000-5000 MPa at 25°C and a coefficient of thermal expansion (CTE) of 15-about 60ppm/°C at temperatures below the glass transition temperature, more typically about 25(+ /-10)ppm/℃.

Wafer-level underfills consist of a 100% solids mixture. Volatile components such as solvents that would cause weight loss during prolonged ambient storage are absent. The absence of volatile components eliminates solvent removal steps and improves the control of shrinkage and delamination of light-induced solidified coatings from the front surface of the wafer. The exemption of VOCs prevents unacceptable shrinkage and stress, as well as outgassing during the solder reflow step, avoiding the formation of voids between the die or its area and the PCB. The underfill is non-self-fluxing. In other words, the ingredients used do not provide melting and are non-acidic.

In general method aspects, the invention involves applying a liquid underfill adhesive to an integrated circuit wafer, applying a controlled amount of light energy (ultraviolet, visible light, infrared, etc.), causing the underfill to solidify into a thermally liquefiable or The melt flow state may be used, optionally by scribing or sawing, to separate the wafer and preserve the coated wafer or die during the delay period. The electrical connection is made after a delay period and the applied photocurable solid underfill is heated to liquefy and flows to the edge of the device during solder reflow, curing from a heated liquid to a thermoset solid. During the delayed time in storage, the coatings of the invention remain in a liquefiable solid state without increasing the gel content. It is thus an aspect of the present invention to provide an ambient temperature stable integrated circuit die, the front side of which is attached to an underfill composition comprising a photocurable one-part composition, the one-part composition by weight Benchmarks include the following components:

light-curable acrylate components,

multifunctional epoxy resin,

at least one photoinitiator,

non-conductive fillers, and

A non-melting heat-activated epoxy curing agent, wherein the underfill has a flexural modulus of 1000-5000 MPa at 25°C in a thermosetting state, and at a temperature lower than the glass transition temperature of the underfill composition It has a thermal expansion coefficient of 15-50ppm/°C.

In another aspect, the invention relates to a two-stage process for curing an underfill composition for a wafer. The method includes applying an underfill composition in liquid form to the front side of a semiconductor wafer. Methods of application include application of liquid non-volatile (100% solids) coatings directly to the front side of the chip by spin molding, printing or stencil coating. The coated wafer is cured with a selected amount of UV radiation to form a solid coating. Optionally, the solid coated wafer can be scribed into partitions. The wafer or areas can be stored at ambient temperature followed by a second stage in which the electrical connection of the solder bumps to the PCB is established in a solder reflow step and then the solid underfill is thermally cured to a thermoset state.

The 100% solids underfill composition consists essentially of a photocurable acrylate component containing monofunctional ethylenically unsaturated monomers and/or oligomers, a multifunctional epoxy resin, a photoinitiator, a latent epoxy thermally initiated agents, and inorganic CTE-dilute fillers. The underfill is non-alkali-soluble in the solid state, and does not contain acid groups, such as free carboxyl groups, phosphate groups or sulfate groups, in liquid photocurable unsaturated monomers, oligomers and/or polymers. The weight percentages of ingredients used in the wafer composition are by weight, totaling 100%, and are as follows:

Ingredient % by weight

Light-curing acrylate component…………………………………………………………………………………………………………………………………5-30%

Liquid Multifunctional Epoxy Resin………………………………… 10-45%

Photoinitiator………………………………………………… 0.3-3%

Low CTE Filler……………………………………………40-70%

Latent curing accelerator……………………………………… 1-3%

The thermally liquefiable solid underfill composition is self-supporting, storage stable, and capable of maintaining adhesion to the front side of the wafer or regions at ambient temperature for extended periods of time prior to conversion to the thermoset state, thereby enabling the The application of the underfill is separate from the solder reflow chip mounting step. The present invention enables storage of chips under ambient conditions for later mounting on PCBs.

The photocurable component of the underfill composition includes an ethylenically unsaturated monomer or combination of monomers having at least 6 carbon atoms in its structure. The introduction of monomers with less than 6 carbon atoms leads to unacceptable volatility problems when photocured into a solid state, as well as shrinkage problems when converted to a thermally liquefiable photocured solid state, which tends to be harmful to adhesion Adds stress to the chip of the composition. Underfills containing more than 10 weight percent liquid multifunctional ethylenically unsaturated comonomers, based on the total weight of the photocurable components, can result in insufficient melt flow of the thermally liquefiable underfill during the solder reflow step of the chip mounting process. Therefore, it is a preferred aspect to have no polyunsaturated monomers in the underfill, or to limit it to no more than 10% by weight of the underfill photocurable composition.

The term photocurable component collectively refers to the ethylenically unsaturated monomers and/or oligomers, however employed. More preferably, the ethylenically unsaturated material comprises vinyl esters, vinyl ethers and/or α,β-unsaturated acrylates. Preferred photocurable components are ethylenically unsaturated acrylates as monomers, unsaturated oligomers or pendant unsaturated oligomers, and combinations thereof. The term oligomer refers to an unsaturated compound that is liquid at 25°C, or capable of dissolving in a photocurable liquid carrier. Non-functional or saturated thermoplastic polymer diluents such as polyacrylates, polyvinyl ethers, polyvinyl esters, polyesters, polyamides, polyolefins and functionalized derivatives can be used provided that the softening temperature of the diluent is not Can significantly hinder the melt flow of thermally liquefiable underfills at solder reflow temperatures. Such diluents can be used for different characteristics, such as precise control or enhancement of melt flow and/or cohesive strength.

When a wafer underfill containing a photocurable acrylate component polymerizes under the influence of UV radiation, the underfill transitions from a liquid to a solid state at ambient temperature. The solid remains thermoplastic, ie it remains in a thermally liquefiable state until thermally cured. The specified amount of the photocurable component is 5-30% by weight of the total weight of the underfill. The amount of multifunctional epoxy used relative to the weight of the photocurable components is critical to provide sufficient solidification upon photocuring and maintain melt flow during the solder reflow step. When the multifunctional epoxy material is above the range of 10-45% by weight, the tendency of the underfill to damage the wafer after photocuring also increases. Below this range, there is insufficient cohesive strength in the thermally liquefiable solid and creep increases in ambient temperature storage prior to solder reflow. The profile thickness of the underfill coating applied on the front side is most preferably such that a portion of the solder bump is exposed. Exposure means that the metal is exposed to air, or on the outermost protruding area of the solder bump, there may be a thin underfill residue below about 0.01 μm. In a preferred embodiment, the thickness of the underfill coating after photocuring is 50-90% of the solder bump profile. The profile is the depth of the portion of the solder bump that extends beyond the surface plane of the front side of the die.

The photocurable oligomers optionally used in this application are either liquids at ambient temperature, or solids that are soluble in liquid ethylenically unsaturated acrylate monomers. The oligomers contain one or more pendant or terminal ethylenically unsaturated groups. Typical oligomers contain 2 terminal unsaturated groups. The average number of unsaturated groups in the oligomeric photocurable acrylate component with a molecular weight of 500-3000 can be 1-2. Only di-, tri- or tetra- and higher ethylenically unsaturated monomers, dimers or trimers are excluded from the photocurable acrylate composition.

Embodiments of the underfill of the present invention exhibit sufficient melt flow under solder reflow conditions to flow out to the edge of the chip and completely fill the void between the underside of the chip and the PCB. In some cases, flow-out may include flowing up the edge of the die to form a fillet, the light-cured solid underfill adheres well to the wafer, and has properties for long-term storage and/or scribe lines without distortion Or sufficient cohesive strength necessary to break the wafer. After the delayed period of storage, when the weight ratio of the photocurable acrylate component to the epoxy functional component is 1:10-1:2, and the photocurable component contains the specified proportion of monofunctional and polyfunctional monomers and/or low In the case of polymers, the thermally liquefiable solids flow adequately under the heat encountered during the solder reflow step. Underfills typically lack sufficient cohesive strength and/or exhibit unacceptable surface tack at ratios of photocurable component to epoxy functional component below 1:10. At ratios above 1:2, the wafer exhibits warping, breakage and/or the underfill tends to delaminate or have insufficient flow for fillet formation.

Exemplary monoethylenically unsaturated monomers useful in the present application are monomers having at least 6 carbon atoms, including alkyl C ₃ -C ₁₂ alkane of acrylic acid or C ₁ -C ₄ alkyl substituted acrylic acid Alkyl esters, which are collectively referred to as (alk)acrylates. Specific examples of suitable monofunctional monomers include butyl acrylate, ethyl methacrylate, butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, trimethylcyclohexyl methacrylate, Cyclic ether acrylates and monocyclic acetal acrylates. Monocyclic acetal acrylates are known and disclosed in US Patent No. 4,076,727. Acetal acrylates are obtained by derivatizing polyols such as trimethylolpropane, trimethylolethane, glycerol, 1,2,4-butanetriol, 1,2,5-pentanetriol and 1,2 , 6-hexanetriol and aldehyde reaction, and with α, β-unsaturated carboxylate such as acrylic acid or ester for transesterification. An exemplary photocurable composition is a combination of cyclic ether-containing acrylates such as tetrahydrofurfuryl acrylate (THFA) and cyclic hydroxyalkyl formal acrylates. Preferred monofunctional acrylates are tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, pentaerythritol monomethacrylate, pentaerythritol monoacrylate, trimethylolpropane monomethacrylate, trimethylolpropane mono Acrylates, cyclic hydroxyalkylformal acrylates, and ketal acrylates. Acetal acrylates and ketal acrylates may include mixtures of isomers. Cyclic hydroxyalkyl formal acrylates and cyclic hydroxyalkyl ketal acrylates are readily prepared by esterification of acrylates or methacrylates with monohydroxy acetals derived from triols, so Such trihydric alcohols are, for example, trimethylolpropane and triethylolpropane. Structures of suitable triol starting materials that can react with aldehydes or ketones and be acrylated with acrylates or methacrylates include the following formulas:

Preferred cyclic hydroxyalkyl formal acrylates have the following structures (A-C)

Wherein, R ₁ is C ₁ -C ₄ alkylene, such as -CH ₂ -, -CH ₂ CH ₂ -, etc., R ₂ , R ₃ and R ₄ are H or C ₁ -C ₄ alkyl, such as -CH ₃ , -CH ₂ CH ₃ and so on.

The most preferred cyclic hydroxyalkyl formal acrylate is trimethylolpropane formal acrylate (structure B').

Other photocurable monomers used alone or in combination with any of the above monomers include acetoacetoxyethyl methacrylate, 2-acetoacetoxyethyl acrylate, 2-acetoacetoxypropyl methacrylate ester, 2-acetoacetoxypropyl acrylate, 2-acetoacetamidoethyl methacrylate, 2-acetoacetamidoethyl acrylate, 2-cyanoacetoxyethyl methacrylate, acrylic acid -2-cyanoacetoxyethyl ester, N-(2-cyanoacetoxyethyl)acrylamide, 2-propionylacetoxyethyl acrylate, N-(2-propionylacetoxyethyl base) methacrylamide, N-4-(acetoacetoxybenzyl)phenylacrylamide, ethylacryloyl acetate, acryloylmethyl acetate, N-ethacryloyloxymethylacetoacetamide , ethyl methacryloyl acetoacetate, N-allyl cyanoacetamide, methacryloyl acetoacetate, N-(2-methacryloyloxymethyl) cyanoacetamide, methyl Acrylic acid-ethyl-α-acetoacetoxy ester, N-butyl-N-acryloyloxyethyl acetoacetamide, monoacrylated polyols, and reaction products of hydroxyl-containing acrylates and anhydrides such as ortho Monomethacryloxyethyl phthalate. Comonomers which are copolymerizable with (alk)acrylate monomers, provided that the rate of polymerization is not slowed to a significant extent compared to acrylate monomers.

Rapid photocuring of acrylic monomers is a desirable feature. Photocurable ethylenically unsaturated monomers other than acrylates and alkyl acrylates are limited to about 6 carbon atoms or higher, examples include but are not limited to butyl vinyl ether, isobutyl vinyl ether , cyclohexyl vinyl ether p-(2-acetoacetyl)ethylstyrene, and 4-acetoacetyl-1-methacryloyloxypiperazine. Ethylenically unsaturated monomers containing epoxy-reactive groups, such as active hydrogen-containing groups, are not used in photocurable compositions.

Representative of known multifunctional ethylenically unsaturated compounds are ethylenically diunsaturated monomers such as ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, hexanediol diacrylate and triethylene glycol diacrylate. Representative triunsaturated monomers include trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate, glyceryl triacrylate, pentaerythritol triacrylate, and pentaerythritol trimethacrylate. Representative acrylic unsaturated photocurable materials are SR205, SR306, CD401, SR508, SR603, SR9036 from Sartomer, Exton, PA.

Other suitable photopolymerizable oligomer materials that may be included in the photocurable composition are, for example, bisphenol-based polyether acrylates, vinyl ether terminated oligomers, hydroxyl functional acrylates and methacrylates with ring Reaction products of oxides, acrylated polyethers, ethylenically unsaturated polyalkyl ethers, the aforementioned cyclic ether acrylates and cyclic ether acetal acrylates.

The photopolymerizable component may be a mixture of a monounsaturated acrylate monomer and an ethylenically unsaturated oligomer having a number average molecular weight of 500-5000, preferably 1000-4000. The liquid photocurable oligomer may include a urethane acrylate oligomer without isocyanate reactive groups. Urethane acrylate oligomers can also be combined with ethylenically unsaturated acrylate monomers. Acrylated polyurethanes can be aliphatic or aromatic. Examples of commercially available acrylated polyurethanes include those known under the tradenames: PHOTOMER (e.g., PHOTOMER 6010) from Henkel Corp. Hoboken, N.J.; Functional aromatic polyurethane acrylate), EBECRYL 284 (aliphatic polyurethane diacrylate with a molecular weight of 1200 diluted with 1,6-hexanediol diacrylate), EBECRYL 4827 (aromatic polyurethane diacrylate with a molecular weight of 1600) , EBECRYL 4830 (aromatic polyurethane diacrylate with a molecular weight of 1600 diluted by tetraethylene glycol diacrylate), EBECRYL 6602 (trifunctional aromatic polyurethane diacrylate with a molecular weight of 1300 diluted with trimethylolpropane ethoxy triacrylate) urethane acrylate), and EBECRYL 840 (aliphatic urethane diacrylate with a molecular weight of 1000); SARTOMER from Sartomer Co., Exton, Pa. (such as SARTOMER 9635, 9645, 9655, 963-B80, 966-A80 etc.) and UVITHANE (eg UVITHANE 782) from Morton International, Chicago, III.

Optionally included in the photocurable acrylate component are acrylate-modified epoxy materials having one or more photocurable unsaturated acrylate groups, such as diacrylate esters of bisphenol A epoxy resins , although such mixtures are not preferred. Typical acrylate-modified epoxies are obtained by reacting hydroxyl groups on acrylates with oxirane groups. No unreacted curable epoxy functionality remains. Commercially available examples of acrylated epoxides include the product from Radcure Specialties under the tradename CMD. Other suitable acrylic unsaturated epoxy oligomers or urethane acrylate oligomers are commercially available, eg CN929, CN136, CN970, CN104, CN120C60 from Sartomer. Proprietary acrylate-modified epoxy fluids can be formulated with additional mono- or multifunctional acrylates. The content of any additional mono- or polyfunctional acrylate monomers is within the total composition of the photocurable composition.

Representative diacrylate functional photocurable materials include SR205, SR306, CD401, SR508, SR603, SR9036. Representative trifunctional materials include SR350, SR444, CD501, SR9021. Tetrafunctional acrylates include SR295, SR355, SR399, SR9041.

The thermosetting multifunctional epoxy resin component of the underfill comprises at least one liquid resin containing at least two epoxy groups, having a viscosity at 25°C of less than about 10,000 poise, an average weight per epoxy (WPE) ranges from about 100 to about 1000, and the average molecular weight ranges from about 500 to about 3500. Epoxides which can be readily used are known and include diglycidyl ether of bisphenol A, 2,2-bis-4-(2,3-glycidoxy)-phenyl)propane. Commercially available suitable epoxy compounds are sold under the tradenames EPON 828, EPON 1004 and EPON 1001F from Shell Chemical Co. and DER-331 , DER-332 and DER-334 from Dow Chemical Co. Other suitable epoxy resins include cycloaliphatic epoxides, glycidyl ethers of phenol formaldehyde novolacs (eg DEN-431 and DEN-428 from Dow Chemical Co). Blends of free radical curable resins and epoxy resins are further described in US Patent No. 4,751,138 (Tumey et al.) and US Patent No. 5,256,170 (Harmer et al.). In a preferred embodiment, a combination of three epoxy resins is used, which are biphenyl epoxy resin with a WPE of about 192 g/eq., diglycidyl ether of bisphenol F with a WPE of about 172 g/eq., WPE A mixture of triglycidyl ethers of p-aminophenol at about 101 g/eq. These three epoxy resins are commercially available under the trade names RSS, EPICLON and ARALDITE, respectively.

The liquid wafer coating contains about 1-3% by weight of at least one photoinitiator capable of effectively setting the liquid underfill to a tack-free surface when exposed to conventional levels of actinic radiation. The type of photoinitiator chosen depends on the desired depth of cure, the type of contrast agent employed and the preferred wavelength of radiation employed. Commercially available photoinitiators that generate free radicals suitable for use in the present application include, but are not limited to, photoinitiators of the benzophenone, benzoin ether, and acylphosphine oxide classes, such as those sold under the tradename: ex Ciba IRGACURE(R) and DAROCUR(R) from Specialty Chemicals, Basel, Switzerland.

A preferred photoinitiator system is a mixture of 25% to 50% ketone-functional photoinitiator and 50% to 75% monoacylphosphine, diacylphosphine oxide or phosphonate containing photoinitiator. Examples of ketone photoinitiators include 1-hydroxycyclohexyl phenyl ketone, hydroxymethyl phenyl acetone, dimethoxyphenyl acetophenone, 2-methyl-1-[4(methylthio)-phenyl ]-2-morpholinoacetone-1,1-(4-isopropylphenyl)-2-hydroxyl-2-methylpropan-1-one, 1-(4-dodecyl-phenyl)- 2-Hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-2-(2-hydroxy-2-propyl)-one, diethoxyphenylphenethyl Ketone, 2,4,6-trimethylbenzoyldiphenylphosphine, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy) Phenyl]-2-hydroxy-2-methylpropan-1-one, 2-hydroxythioxanth-9-one. Representative acylphosphine oxide photoinitiators include ethyl-2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-triethylbenzoyldiphenylphosphine oxide , 2,4,6-triphenylbenzoyldiphenylphosphine oxide. Specific examples of photoinitiator compositions for deep curing of liquid underfills for wafers are 0.2-0.5% by weight of 1-hydroxycyclohexyl phenyl ketone based on the total weight of the underfill and 0.5- 0.7% by weight of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

Any source of actinic light dose that does not raise the coating temperature above 120°C can be used to photocure the underfill to a liquefiable solid gel state. Ultraviolet light is the easiest to use, but it can also be in other forms, such as Type RS fluorescent lamps, carbon arc lamps, xenon arc lamps, mercury discharge lamps, tungsten halide lamps, etc. Radiant energy can be emitted from a point source, or as parallel rays. However, a diverging beam of light can also be used as an actinic light source. The UV amount in the range of 100-2400mJ/cm ² can effectively provide the underfill with a curing depth of about 1.2-1.8mm, and the radiation polymerization can be completed at the underfill temperature below 100°C. The underfill composition light cures to a tack-free surface. The curing time can be adjusted by selecting the appropriate UV light source, the concentration of the underfill photocurable component, and the contrast agent.

In package assemblies, automated visual inspection of products requires the use of pigments to provide contrast between boards, underfills, and chips. Suitable are contrast agents such as carbon black and pigments such as those commercially available under the Sandorin(R) brand from Clariant AG. In one embodiment, an epoxy resin dispersed with 15 wt% carbon black was used to incorporate 0.1-0.2 wt% carbon black in the underfill to provide an effective contrast for automated visual inspection.

heat curing system

The epoxy curing system used in the present invention is a non-melting type containing a latent heat accelerator, wherein the curing start temperature of the heat accelerator is greater than 150°C, preferably greater than 160°C ± 5°C, more preferably 175°C ± 5°C °C and higher. The use of latent thermal curing agents for epoxies is used to initiate cure to the thermoset stage of the cured, aged underfill at temperatures encountered after solder reflow occurs. Dicyandiamide cannot be used alone as a thermal curing agent, but it can be used in combination with a potential heat accelerator in a small amount, but preferably does not contain dicyandiamide. Preferred latent thermal curing agents include amines, amine adducts; which include imidazole and urea derivatives such as 2,4,6-trimethyl-1,3-bis(3,3-dimethylureido) Benzene and 1,5-bis(3,3-dimethylureido)naphthalene. Thermal curing agents must be non-halogenated. Examples of curing agents can be obtained in a known method as taught in US Patent No. 5,543,486 by mixing an epoxy compound or an isocyanate compound with an amine compound, or by mixing an epoxy compound or an isocyanate compound, an amine compound, and an active hydrogen compound. Various blocked amines are suitable. Preferred thermal curing agents are blocked amines with tertiary amine and urea moieties. Exemplary imidazoles suitable for use in thermosetting compositions are 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole , 2-undecenyl imidazole, 1-vinyl-2-methylimidazole, 2-n-heptadecyl imidazole, 2-undecyl imidazole, 2-heptadecyl imidazole, 2-ethyl -4-methylimidazole,, 1-benzyl-2-methylimidazole, 1-propyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl- 2-Ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-guanidinoethyl-2-methyl Imidazole, 2-(p-dimethylaminophenyl)-4,5-diphenylimidazole, 2-(2-hydroxyphenyl)-4,5-diphenylimidazole, 2-phenyl-4-hydroxy Methylimidazole, 2-phenyl-4,5-bis(hydroxymethyl)-imidazole, bis(4,5-diphenyl-2-imidazole)-benzene-1,4,2-naphthyl-4, 5-diphenylimidazole, the addition product of imidazole and trimellitic acid, the addition product of imidazole and 2-n-heptadecyl-4-methylimidazole, phenylimidazole, benzyl imidazole, 1-(deca Dialkylbenzyl)-2-methylimidazole, 2-(2-hydroxy-4-tert-butylphenyl)-4,5-diphenylimidazole, 2-(2-methoxyphenyl)- 4,5-diphenylimidazole, 2-methyl-4,5-diphenylimidazole, 2,3,5-triphenylimidazole, 2-styryl imidazole, 2-(3-hydroxyphenyl) -4,5-diphenylimidazole, 1-benzyl-2-methylimidazole and 2-p-methoxystyrylimidazole. A preferred heat curing agent is available from Air Products and Chemicals under the name Curezol(R) 2-PHZ-S.

Alternative thermal curing agents may include blocked Lewis acids, for example latent acetoacetate metal-functional curing agents such as aluminum chelates including ethyl acetoacetate metal diisopropoxide, tris(acetyl Ethyl acetate) metal, alkyl acetoacetate metal diisopropoxide, monohexadecyl acetonate aluminum bis(ethyl acetoacetonate), tri(acetylacetonate) aluminum; cyclic aluminum oligomers Examples include cyclic alumina isopropoxide.

In order to provide sufficient reflow of the liquefiable photocurable solid, the thermal cure system does not progress in the photocurable solid coating on the wafer or die during the storage delay. The minimum temperature at which thermal curing begins is predetermined by selection of the thermal curing agent employed, and thermal curing occurs at temperatures greater than or equal to 150°C after initiation of solder reflow. Preferably, the lowest temperature range at which the thermal curing of the underfill glue begins is 150°C-225°C. Thermal cure onset temperature and peak cure rate can be readily determined by differential scanning calorimetry, which is known in the art. The starting temperature of thermal curing depends on the selection and amount of accelerator, and should not be higher than 280°C. Thermal curing cannot begin too close to the peak temperature, which is typically at or near 250°C for eutectic solders and at or near 300°C for lead-free solders. Typical solder reflow times are 3-4 minutes, and underfill exposure to peak temperature is typically less than 30 seconds. Thermal curing initiated at temperatures below 150°C results in underfill liquefaction and insufficient flow.

Non-conductive fillers are used to limit the CTE in underfills. These fillers are known and there are many suitable types. Microelectronics grade fused silica, crystalline quartz, boron nitride, aluminum and silicon, magnesia, magnesium silicate, and silica-coated aluminum can be selected based on desired properties and cost. The viscosity developed in the liquid underfill is a selection criterion. Due to the absence of solvents or non-reactive diluents, underfill embodiments according to the present invention are readily adaptable to methods employing relatively low viscosity coatings, such as the known spin-coating method. Spin-exposed underfill embodiments according to the present invention have a conventional viscosity that is relatively lower than the typical viscosity of underfills applied by stencil painting or printing.

In a preferred embodiment, the underfill is applied by stencil printing in a pattern covering at least 70% of the area of each wafer between the saw wires. The CTE range of the underfill in the thermoset state is 15-50ppm/°C, requiring a certain level of non-conductive filler, preferably spherical fused silica particles in an amount ranging from 40% to 70% by weight, preferably 45% to 60% by weight. weight%. It is more preferred to use 45-55% by weight of low CTE inorganic filler. Preferred low CET inorganic fillers have an average particle size of at least 10 μm and an average particle size of no greater than about 75 μm. The upper limit of filler diameter used must be less than the thickness of the underfill coating described above.

Optionally, the underfill may contain adhesion improving agents. The usual amount used is 3-8% by weight. Adhesion improvers are known and include organosilanes, organopolysiloxanes, organohydrogenpolysiloxanes, prehydrolyzed organosilanes, siloxanes and silsesquioxanes. Exemplary organosilanes contain epoxy functionality, such as mono(epoxyalkyl)trialkoxysilanes such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, Ethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; or preferably ethylenically unsaturated groups. Ethylenically unsaturated silicone compounds include mono- or polyalkenyl functional organosilanes such as 3-(meth)acryloxypropyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxy and polyalkenyl-functional siloxanes such as 1,1,3,3-tetramethyldisiloxane and 1,2,4-trivinylcyclohexane and/or 1,3,5 - Hydrosilylate of trivinylcyclohexane.

One method of applying the underfill to the wafer entails the use of known screen printing techniques. The wafer underfill according to the invention can advantageously be printed onto the wafer in such a way that it covers the surface area of the wafer other than the saw wire. Preferably, fillers applied by printing methods contain optional rheology control agents. Suitable known types are amorphous fumed silica or silanized amorphous fumed silica, commercially available, for example, from Cabot Corporation.

Optionally known flow regulators can be used. Thermoplastic flow modifiers increase the tendency of heat-liquefiable underfills to bleed during solder reflow. Representative flow improvers include polymethacrylate copolymers having an I.V. typically of 0.2-0.6, such as those commercially available under the trade name Elvacite(R). An example is Elvacite(R) 2013 from ICI Acrylics, which is a 64% butyl methacrylate/36% methyl methacrylate copolymer determined to have an I.V. of 0.2. Other flow conditioners known in the art include, for example, Lanco(R) Flow P10 from Lubrizol, Wickliffe, Ohio, U.S.A. and MODAFLOW(R) Powder available from Solutia, St. Louis, Mo. Flow improvers may be based on SAN or alpha-olefin polymers, among others. A preferred flow improver is a thermoplastic PMMA copolymer having a molecular weight of 60,000, such as Elvacite(R) 4026 from INEOS Acrylics, Inc. Suggested amounts of optional thermoplastic flow improvers are 1.0-10.0% by weight relative to the photocurable component. In order to adjust the fluidity of the underfill in the thermally liquefiable light-cured state, plasticizers such as carboxyl esters, or lubricants such as ethylenebisstearamide can be used in lesser amounts below 10% by weight .

Test Methods

1. Glass transition temperature (Tg)

Use b-stage or thermoset cure materials at a heating rate of 5°C/min using a thermodynamic analyzer, heating at a rate of 5°C/min using a dynamic mechanical analyzer, heating at a rate of 5°C/min using a differential scanning calorimeter , to measure the glass transition temperature.

2. Coefficient of thermal expansion

In the determination of the coefficient of thermal expansion above and below Tg, it is determined by using a conventional thermodynamic analyzer.

3. Viscosity

A Brookfield VDIII+ cone and plate rheometer is suitable, but a Haake(R) RheoStress I is used.

4. According to ASTM D1002 test shear (die shear) adhesion

5. Thermal and oxidative stability were determined by thermogravimetric analysis. The underfill exhibits a weight loss of less than 5% at 300°C in air.

Photopolymerization conditions

The following conditions using an AETEK UV processing unit are sufficient to allow liquid underfill to cure throughout the coating depth Lamp 1(W) Lamp 2(W) Belt speed (fpm) Curing energy (mJ/cm ² ) 400200200200200200125125200200200125125 40020020020020020012512500000 34304560657030704560707090 1170761515384349327712297274205176149116

production methods

Underfill Examples 1-4 were prepared by adding the ingredients to a Hauschild(R) cup and mixing at 3000 rpm for 30 seconds. The formulations were spin-coated onto Umicore(R) semiconductor wafers 4 inches (10.1 cm) diameter x 400 +/- [mu]m thickness. The coated wafers were photocured in one shot with an Aetec UV oven at 200W/200W settings at 30 fpm and _N2 atm. The film in the liquefiable gel state is not tacky. Storage of the underfill in the light-cured state for 8 months did not result in further curing activity, as confirmed by DSC. The thermal curing start temperature is 150°C±2°C, and the peak value of the exothermic curve appears at 166°C.

Example 1 Element parts by weight 1. Bisphenol A-epichlorohydrin-epoxy resin (residual amount of epichlorohydrin < 1 ppm) (RSL-1462, such as available from Shell Resins, Inc. (CAS #25068-38-6)) 2. Poly(propylene Acyl) unsaturated urethane acrylate oligomer (CN120C60, such as available from Sartomer) 3. epoxy acrylate oligomer (CN136, such as available from Sartomer) 4. epoxy curing agent 1 (Ancamine 2441, such as available from Air Products & Chem) 5. Epoxy curing agent 2 (Dyhard(R) 100s, such as available from SKWCHem.) 6. Trifunctional acrylate (SR351, such as available from Sartomer) 7. Photoinitiator Irgacure 184Irgacure8198. Fused silica (F5BLDX, such as Purchased from Denka) Total 19.0318.501.141.337.002.001.0050.00100.00

Example 2 Element parts by weight 1. Bisphenol A-epichlorohydrin-epoxy resin (residual amount of epichlorohydrin < 1ppm) (RSL-1462, such as purchased from Shell Resins, lnc. (CAS #25068-38-6)) 2. Epoxy curing Agent 1 (Ancamine 2441, as available from Air Products & Chem) 3. Epoxy Curing Agent 2 (Dyhard(R) 100s, as available from SKWCHem.) 36.282.182.54 4. Trifunctional Acrylate (SR351, as available from Sartomer) 5. Photoinitiator Irgacure 184 Irgacure 8196. Fused Silica (F5BLDX, as available from Denka) Total 6.001.501.5050.00100.00

Example 3 Element parts by weight 1. Bisphenol A-epichlorohydrin-epoxy resin (residual amount of epichlorohydrin < 1ppm) (RSL-1462, such as purchased from Shell Resins, lnc. (CAS #25068-38-6)) 2. Latent amine Accelerator (Ancamine 2441, as available from Air Products & Chem) 3. Dicyandiamide (Dyhard(R) 100s, as available from SKW CHem.) 4. Trifunctional Acrylate (SR351, as available from Sartomer) 5. Photoinitiator Irgacure 184 Irgacure8196. Fused silica (F5BLDX, as purchased from Denka) Total 36.292.182.546.002.001.0050.00100.01

Example 4 Element parts by weight 1. Bisphenol A-epioxyalcohol-epoxy resin (residual amount of epioxyalcohol < 1ppm) (RSL-1462, such as purchased from Shell Resins, lnc. (CAS #25068-38-6)) 2. Acrylate modification Proactive epoxy oligomer (CN136, such as available from Sartomer) 3. Latent amine accelerator (Ancamine 2441, such as available from Air Products & Chem) 4. Dicyandiamide (Dyhard(R) 100s, such as available from SKWCHem.) 5. Trifunctional acrylate (SR351, such as available from Sartomer) 6. Photoinitiator Irgacure 184 Irgacure8197. Fused silica (F5BLDX, such as available from Denka) Total 18.1519.502.182.546.001.501.5050.00101.37

Examples 5-7 were prepared and spin coated onto Umicore(R) semiconductor wafers 4 inches (10.1 cm) diameter x 400 +/- μm thickness. The coated wafers were photocured in one shot with an Aetec UV oven at 200W/200W settings at 30 fpm and _N2 atm. The photocurable films in the thermally liquefiable state of Examples 5-7 were not tacky.

Example 5

In the preparation of Example 5, ingredients 1-4 were mixed together in a 40 g Hauschild(R) cup and heated to 60° C. until the photoinitiator was completely dissolved. The samples were then mixed on a Hauschild(R) mixer at 3000 rpm for 30 seconds. Add remaining ingredients separately, mixing between additions. A bulk portion of silica was added with mixing.

Element describe parts by weight 1. CN1362. SR2033. Irgacure ® 1844. Irgacure ® 8195. RSL-14626. RSS-14077. Curezol ® 2PHZ-S8. Filling total Amino-modified, acrylated epoxy THFMA photoinitiator photoinitiator bisphenol A epoxy diglycidyl ether biphenyl epoxy resin imidazole latent curing agent fused silica 6.7012.400.300.5014.3514.351.4349.99100.02

The thermal curing initiation temperature of Example 5 was 167°C. Example 5 Tg-UV-B-stage 23.56°C Tg-heat curing 106.25°C CTE-below Tg 40.37ppm/℃ CTE - higher than Tg 107.7ppm/℃ Storage modulus (@25℃) 2,761Mpa Storage modulus (@175℃) 0.025Gpa

Example 6

Example 6 was prepared by adding the ingredients, except the 50% fused silica, to a 40 g Hauschild(R) cup and mixing at 3000 rpm for 30 seconds. The remainder of the fused silica was then added and mixed for 30 seconds at 3000 rpm. The mixture was heated in an oven at 45°C for 30 minutes to dissolve the photoinitiator. The solution mixture was mixed again for 30 seconds at 3000 rpm. raw material describe parts by weight SR203 Irgacure(R) 184 Irgacure(R) 819 RSS-1407 Curezol(R) 2PHZ-S Filler Total THFMA photoinitiator photoinitiator biphenyl epoxy resin imidazole latent curing agent fused silica 19.100.300.5028.661.4350.01100.00

Referring to Figure 1, it shows the DSC scan curve of Example 6.

The conditions used for the differential scanning calorimeter are:

Using a differential scanning calorimeter such as a Perkin-Elmer, model DSC 7

The heating and heating conditions are -20°C to 300°C, the rate is 5°C/min

All samples were tested in the light-cured state. The scanning shows that the melting temperature of the solid epoxy resin is 95.23°C, the curing start temperature is 191.65°C, and the peak reaction temperature of thermal curing is 193.71°C.

Example 7

Example 7 was prepared by adding the ingredients, except the 50% fused silica, to a 40 g Hauschild(R) cup and mixing at 3000 rpm for 30 seconds. The remainder of the fused silica was then added and mixed for 30 seconds at 3000 rpm. The mixture was heated in an oven at 45°C for 30 minutes to dissolve the photoinitiator. The solution mixture was mixed again for 30 seconds at 3000 rpm. raw material describe parts by weight SR285Irgacure 184Irgacure 819RSS-1407Curezol Filler Total % THFA Photoinitiator Photoinitiator Biphenyl Epoxy Resin Imidazole Fused Silica 19.050.300.5028.711.4450.01100.00

Figure 2 shows the DCS scan curve of Example 7.

The conditions used for the differential scanning calorimeter are:

Using a differential scanning calorimeter such as a Perkin-Elmer, model DSC 7

The heating condition is -20°C to 300°C, the rate is 5°C/min

All samples were tested in the light-cured state. The scan showed that the solid epoxy resin had a melting temperature of 99.5°C, a curing onset temperature of 189.62°C, and a peak reaction temperature of thermal curing of 192.6°C.

Example 8

Example 8 was prepared by adding the ingredients, except the 50% fused silica, to a 40 g Hauschild(R) cup and mixing at 3000 rpm for 30 seconds. The remainder of the fused silica was then added and mixed for 30 seconds at 3000 rpm. The mixture was heated in an oven at 45°C for 30 minutes to dissolve the photoinitiator. The solution mixture was mixed again for 30 seconds at 3000 rpm. raw material describe parts by weight CN136SR203 Irgacure(R) 184 Irgacure(R) 819RSL-1462RSS-1407Curezol(R) 2PHZ-S Filler Total Amine Modified, Acrylated Epoxy THFMA Photoinitiator Photoinitiator Bisphenol A Epoxy Diglycidyl Ether Biphenyl Epoxy Resin Imidazole FB5LDX (Fused Silica) 6.7012.400.300.508.6120.091.4349.99100.02 Example 8 Tg-light B-stage WAU 31.47°C Tg-heat curing 116.44°C CTE-below Tg 40.56ppm/℃ CTE - higher than Tg 120.5ppm/℃ Storage modulus (25℃) 3,313Mpa Storage modulus (175°C) 0.0268Gpa

Comparative example A (77-5) Element parts by weight 1. Mixture of acrylate-modified epoxy oligomer and tri(acryloyl) functional monomer (CN120C60, as available from Sartomer) 2. Tri(acryloyl) functional monomer (SR351, as available from Sartomer) ) 3. Dicyandiamide (Dyhard(R) 100s, as available from SKWCHem.) 4. Photoinitiator Irgacure 184 Irgacure 8195. Fused silica (F5BLDX, as available from Denka) Total 43.004.001.332.001.0050.00100.00

Comparative Example A delaminated from the wafer after 24 hours of ambient storage after photocuring, which was determined to be due to excessive shrinkage induced by photocuring. Comparative Example B 1. Bisphenol A-epichlorohydrin-epoxy resin (residual amount of epichlorohydrin < 1ppm) (RSL-1462, such as purchased from Shell Resins, lnc. (CAS #25068-38-6)) 2. Acrylate modification A mixture of epoxy oligomers and tri(acryloyl) functional monomers (CN120C60, such as available from Sartomer) 3. Latent amine accelerator (Ancamine® 2441, such as available from Air Products & Chem) 4. Bis Cyanamide (Dyhard(R) 100s, as available from SKWCHem.) 18.1520.51.091.27 5. Photoinitiator Irgacure 184Irgacure8196. Fused silica (F5BLDX, such as purchased from Denka) total 1.501.0050.00100.00

Comparative Example B also delaminated after 24 hours of ambient storage.

The present invention discovers specific industrial applicability of underfills for wafers and methods for their preparation, the compositions of the present invention can also be used in microelectronic applications other than underfills, e.g. for glob top, direct chip attach and other applications for thermosetting compositions. While a few preferred embodiments have been described, many modifications and variations are possible in light of the above teachings. It is therefore to be realized that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.

Claims (6)

1. stable integrated circuit (IC) wafer under the envrionment temperature, its front adheres to the underfill composition, and described underfill composition comprises the single-component composition of photocuring, and this single-component composition comprises following single-component mixture:

Liquid light-cured acrylate composition,

Polyfunctional epoxy resin,

At least a light trigger,

Non-conductive filler and

Non-melt thermal activation epoxy hardener, wherein said underfill down in 25 ℃ of modulus in flexurees that show 1000-5000MPa, and shows 15-50ppm/ ℃ thermal expansivity solid-state under the temperature below the described underfill composition second-order transition temperature.

2.100% solid is non-from molten single component liquid underfill, and it comprises:

The unsaturated photocuring composition of the simple function of 5%-30%,

The polyfunctional epoxy resin of 10%-45%,

At least a light trigger of 0.3%-3%,

The non-conductive filler of 40%-70%,

Described underfill in 20 ℃ of modulus in flexurees that show 1000-5000MPa, and shows 15-50ppm/ ℃ thermal expansivity under its temperature below second-order transition temperature under the thermoset state.

3. according to the underfill composition of claim 2, the wherein said branch that is light-cured into comprises and is selected from following at least a compound: vinylformic acid C ₃-C ₁₂Alkyl ester, C ₁-C ₄The vinylformic acid C that alkyl replaces ₃-C ₁₂Ester.

4. according to the underfill composition of claim 2, wherein said be light-cured into be divided into be selected from following at least a: tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, monomethyl vinylformic acid pentaerythritol ester, single vinylformic acid pentaerythritol ester, TriMethylolPropane(TMP) monomethacrylates, TriMethylolPropane(TMP) mono acrylic ester, ring-type hydroxyalkyl methylal acrylate and ketal acrylate.

5. according to the underfill of claim 2, wherein said photocuring composition is to be selected from following unsaturated oligomer: the bis-phenol polyether acrylate, the end capped oligopolymer of vinyl ether, the Resins, epoxy of acroleic acid esterification, the undersaturated poly alkyl ether of ethylenic, poly-(ring-type) ether acrylate and poly-ring-type (ether) acetal acrylate.

6. according to the underfill of claim 4, it further comprises monounsaturated acrylate monomer, and wherein said oligopolymer has 500-5,000 number-average molecular weight.