KR20070083541A - Low voiding no flow fluxing underfill for electronic devices - Google Patents

Abstract

A no flow fluxing underfill having a hardener component comprising a phenolic component and an anhydride component in a molar ratio of phenolic component to anhydride component of between about 0.1:1 and about 2:1; or between about 0.8:1 and about 1.2:1. An underfill preparation method involving blending an epoxy component and a phenolic component, heating the blend, and cooling the blend, prior to incorporation of an anhydride component.

Description

LOW VOIDING NO FLOW FLUXING UNDERFILL FOR ELECTRONIC DEVICES

The present invention relates to an underfill composition and a method for attaching an element in an electronic device having a solder joint.

Electrical components such as resistors, capacitors, inductors, transistors, integrated circuits, and chip carriers are typically mounted on a circuit board according to one of two structures. In the first structure, the parts are mounted on one side of the substrate, and lead from the parts is led through holes in the substrate and soldered on the opposite side of the substrate. In the second structure, the parts are soldered to the same substrate side on which they are mounted. This latter device is referred to as "surface-mounted".

Surface-mounting of electronic components is used to manufacture small circuit structures and is well suited for process automation. One type of surface-mount device, referred to as an area array package, includes electronic components such as integrated circuits with numerous bonding leads attached to pads mounted on the bottom surface of the device.

Examples of grid array packages include flip chips, chip scale packages (CSPs) and ball grid arrays (BGAs). In connection with the use of a lattice array package, a circuit board or device includes a small solder bump or ball (hereinafter referred to as “bump”) located at a position corresponding to a pad on the bottom surface of each device and a pad on the surface of the circuit board. Or "solder bump"). (a) contacting the device with the substrate such that the solder bumps are sandwiched between the pad on the substrate and the corresponding pad on the device, and (b) heating this assembly to a temperature that allows the solder to reflow (ie melt), ( c) The device is mounted on a substrate by cooling the assembly. During cooling, the solder hardens so that the element is mounted on the substrate. Tolerance is important in the lattice arrangement technique because the spacing between the elements and the substrate as well as the spacing between the individual elements is typically small. For example, the flip chip spacing from the substrate surface to the bottom of the die is typically about 15 to about 75 microns, and is expected to reach about 10 microns in the near future.

One of the problems associated with grating arrangement techniques is that chips, solders, and circuit board construction materials often have significantly different coefficients of thermal expansion. Due to the different expansion, heating of the assembly during manufacture and use can lead to severe stresses. Also, when the element falls (for example in the case of cordless phones and portable computers), significant stress occurs. Stress applied on the solder joint can result in failure to degrade device performance or render the device completely incapable.

In order to minimize thermomechanical fatigue due to different thermal expansions, thermoset epoxy has been used as an underfill material that occupies the space below the chip between the lower surface of the chip and the substrate that surrounds the periphery of the lattice array element and is not occupied by solder. Such epoxy systems provide some level of protection by forming physical barriers that resist or reduce stresses on solder joints due to different expansion and / or drop impacts of device components.

Several trends are becoming increasingly important in the art of grating array surface-mount devices. These trends include (1) increasing the flip chip and BGA die size, (2) increasing the number of electrical junctions, (3) reducing the gap-height between the die and the substrate, and (4) driving the drive to increase throughput. (5) incorporating a vulnerable low-K dielectric layer into the silicon die. In order to address this issue, great attention has been paid to the use of so-called "non-flow underfill (NUF)". This is typically a thermoset epoxy based material containing a fluxing agent.

Non-flow underfill is applied directly to the substrate prior to placement of the device. When heat is applied, for example in a reflow oven, the fluxing agent begins to remove metal oxides on the solder balls and on the pads, thereby preventing the wetting of the solder and the formation of solder joints at temperatures above the liquidus temperature of the solder. It becomes possible. At the same time, the underfill begins to polymerize (cure), forming a strong adhesive layer between the die (or BGA / CSP) and the substrate. This adhesive layer acts to distribute the thermal stress between the components, increasing the reliability of the device.

Conventional NUF materials can often negatively affect device reliability, such as lack of sufficient fluxing ability (which results in poor electrical yields), excessive volatility, gas-emission, or bubble or void formation in the underfill layer. Present undesirable properties. These defects are closely related to the chemicals used in the NUF. For example, typical commercial NUFs are liquid epoxy resins, anhydride hardeners (volatile at elevated reflow temperatures), as well as smaller amounts of acidic curing accelerators and additives (eg carboxylic acids), or upon curing. It consists of additives (eg active hydrogen compounds such as alcohols) which react in situ with anhydrides to form acidic species. In particular, the anhydride compounds contained in the NUF material have relatively high volatility, thus contributing to the formation of voids. The voids increase the reliability of the underfill by allowing the solder "crosslinking" to occur, especially at the high reflow temperatures required for lead-free soldering applications, or by acting as a stress-focuser that results in the growth of underfill cracks during thermal cycles. Lowers.

Non-flow underfills have been prepared by mixing the epoxy resin and the curing agent until the mixture is homogeneous and then dissolving or mixing any remaining ingredients such as wetting agents, antifoams and CTE modifiers.

The possibility of designing an improved NUF with reduced pore formation potential and increased fluxing activity is characterized by: (a) good pot life and shelf life, (b) acceptable viscosity to make the material dispensable, (c) high T _g , (d) strong adhesion to die passivation and solder mask, (e) high fracture toughness K _1C , (f) moisture resistance, and the like.

Summary of the Invention

Accordingly, it is an object of the present invention to provide an underfill composition having reduced volatility and potential for void formation; Underfill compositions having increased fluxing activity; Underfill compositions having good pot life and shelf life; An underfill composition having a low viscosity to make the material dispenseable; Underfill compositions having high T _g ; An underfill composition having strong adhesion to the die protective film and the solder mask; Underfill compositions having high fracture toughness K _1C ; And an underfill composition having moisture resistance.

Thus, in summary, the present invention includes an epoxy component and a hardener component comprising a phenolic component and an anhydride component in a molar ratio of phenolic component to anhydride component from about 0.1: 1 to about 2: 1. An underfill composition for use in the manufacture of an article.

The invention also relates to a process for the preparation of an underfill composition comprising an epoxy component, an anhydride component and a phenolic component for use in the manufacture of an electronic product. The method blends the epoxy component with at least about 80% by weight of the phenolic component to form an epoxy / phenolic blend; Blending the anhydride component into the epoxy / phenolic blend in an amount such that the underfill composition has a molar ratio of phenolic component to anhydride component from about 0.1: 1 to about 2: 1.

In another aspect, the present invention relates to a method of making an underfill composition comprising an epoxy component, an anhydride component and a phenolic component for use in the manufacture of an electronic product. The method blends the epoxy component with at least about 80% by weight of the phenolic component to form an epoxy / phenolic blend; The epoxy / phenolic blend is heated to a temperature above the softening point of the phenolic component; Cool the epoxy / phenolic blend; Blending the anhydride component into the epoxy / phenolic blend to form the underfill composition.

Other objects and aspects of the invention will be in part apparent and in part pointed out hereinafter.

The underfill composition of the present invention comprises an epoxy component, an anhydride component, a phenolic component, a latent catalyst and other additives described below.

Epoxy

The main epoxy component is selected from epoxy resins that are considered thermoset rather than thermoplastic. In general, thermoplastics are minimally crosslinked, softened and deformable when heated. In contrast, thermosets become highly crosslinked, hard and stiff when heated. Because of these differences, thermosets typically tend to provide the package with greater strength (eg, greater mechanical shock resistance and thermal cycle resistance) than thermoplastics. Thermoplastics may be selected to be included in the underfill to provide some level of reworkability, even if they do not provide such strength to the underfill.

Structural differences (ie crosslinking) between thermosets and thermoplastics are also reflected in the temperature-related nature of the epoxy component. Of particular importance is the glass transition temperature (T _g ) of the cured epoxy component. The glass transition temperature is the temperature at which a polymer deforms from a solid-like form exhibiting an elastic strain profile to a rubber-like form exhibiting a viscous strain profile. In addition, the strain in T _g is typically associated with a significant increase in coefficient of thermal expansion (CTE) and a significant decrease in storage and volume modulus. Typically, T _g of the heat-curable material is greater than T _g of the thermoplastic material. For example, a cured thermosetting material, such as diglycidyl ether of bisphenol A (also referred to herein as a "bis-A epoxy resin"), may vary from about 70 to about 220 ° C, depending on the curing agent and / or hardener, etc. T _g , but on the other hand thermoplastics such as INCHEMREZ PHENOXY PKHJ have a T _g of about 95 ° C. Generally, the epoxy component has a T _g of at least about 70 ° C. when cured. In one embodiment, the epoxy component is selected to have a T _g of about 60 to about 90 ° C when cured. In another embodiment, the epoxy is selected to have a T _g of about 90 to about 150 ° C when cured.

The melting temperature (T _m ) or softening point of the epoxy component (the temperature at which the viscous flow turns into a plastic flow for materials without a particular melting point) is from about -50 to about 0 ° C. The softening point can be determined by JIS K 7234..1986 or ASTM D 6493-99. Melting temperatures can be determined by differential scanning calorimetry (DSC) according to standard ISO 11357-5 or ASTM E 794-01. The epoxy component is typically considered to be relatively pure. For example, the epoxy component preferably contains less than about 500 ppm hydrolyzable chloride (ASTM D1726).

The epoxy resin component can include any suitable type of molecule that includes one or more epoxide groups (ie, at least monofunctional). Bifunctional and / or polyfunctional resins, alone or in combination with monofunctional resins, may be selected to increase the glass transition temperature of the underfill solution by increasing the crosslinking density. Suitable epoxy resin components typically include epoxy resins having a number of repeat units (ie degree of polymerization) of about 1 to about 7. Preferably, the number of repeat units is about 1 to about 3.

The epoxy resin component typically comprises about 25 to about 75 weight percent of the underfill solution. Although not typical, the concentration of the epoxy resin component may be at concentrations outside the above-mentioned range without departing from the scope of the present invention. Depending on the particular application, the concentration of the epoxy resin component may be as small as about 15 wt% or less of the underfill solution, or may be as high as 80 wt% or more. Preferably, the epoxy resin component comprises about 50 to about 70 weight percent of the underfill solution.

Depending on the desired properties of the underfill solution and / or the cured underfill, the epoxy resin component may comprise a single epoxy resin or a combination of epoxy resins. In one embodiment, when the epoxy resin component, or blend, is used, the epoxy resins may be selected from among glycidyl ether of bisphenol A, glycidyl ether of bisphenol F, naphthalene epoxy, cycloaliphatic epoxy, epoxy-functional reactive diluent, and the like. Is selected. For example, it is diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, triglycidyl ether of trifenomethane, polyglycidyl ether of novolac, polyglycidyl ether cresol novolac , Polyglycidyl ethers of naphthalene phenol, and methyl, ethyl, propyl and butyl-substituted transformations thereof. For example, it may be desirable to incorporate trifunctional epoxy resins to increase the amount of crosslinks in the cured underfill to increase the T _g of the underfill. Polyglycidyl ethers of cresol novolac may be incorporated as part of the epoxy resin component to improve high temperature performance. Bis-A epoxy resins are typically incorporated to increase the glass transition temperature and / or viscosity of the underfill solution. Diglycidyl ethers of bisphenol F (which may be referred to herein as "bis-F epoxy resins") are typically incorporated to reduce viscosity.

Specific examples of suitable epoxy resins for incorporation into the NUF composition of the present invention include the following: Bis-F epoxy resins: Epalloy 8229, 8230, 8230E, 8240 and 8240E (Moors Town, NJ) CVC Specialty Chemicals Inc., Epiclon® 830, 830-S, 830-LVP, 835, and 835-LV (Dainipon Ink and Materials, Tokyo, Japan) Chemicals, Inc., Dainipppon Ink & Chemicals, Inc., Epon Resin 862 (Resolution Performance Products, Houston, TX), RE-304S (Nippon Kaya, Tokyo, Japan) Nippon Kayaku Co. Ltd .; Bis-A epoxy resin: Epaloy 7190 (CVC Specialty Chemicals, Inc., Moorestown, NJ), EPON 824, 826, and 828 (USA) Resolution in Houston, Texas Performance Products), Epiclon 840, 840-S, 850, 850-S, 850-CRP and 850-LC (Dainippon Ink and Chemicals, Inc., Tokyo, Japan), DER 330 and 331 (Michigan, USA) Dow Chemical, Midland, RE-310S (Nippon Kayaku Co., Ltd., Tokyo, Japan); Naphthalene epoxy resins: HP-4032 and HP-4032D (Dinipon Ink and Chemicals Inn, Tokyo, Japan) Cycloaliphatic epoxy: ERL-4221 (Union Carbide Corp., Danbury, Conn.), Arladite CY 179 (Huntsman Advanced, Salt Lake City, Utah, USA); Huntsman Advanced Materials; Trifunctional epoxy resins: Epikote 1032 (Japan Epoxy Resins Co., Tokyo, Japan). Ltd.), and Tactix 742 (Huntsman Advanced Materials, Salt Lake City, Utah, USA).

In view of the foregoing, sample combinations of epoxies include the following:

(a) 90% bisphenol F epoxy and 10% naphthalene epoxy; (b) 50% bisphenol F epoxy and 50% bisphenol A epoxy; (c) 80% bisphenol F epoxy and 20% alicyclic epoxy; And (d) 80% bisphenol F epoxy, 10% trifunctional epoxy, 10% cycloaliphatic epoxy.

The glass transition temperature and other properties (eg modulus) of the cured epoxy resin component largely depend on the "equivalent weight" of the epoxy resin component, based on the equivalents of the various epoxy resins that make up the epoxy resin component. The equivalent of epoxy resin is equal to the molecular weight of the epoxy resin molecule divided by the number of epoxide groups contained in the molecule. For example, Bis-A epoxy resins available under the tradename EPON 828 in resolution have a molecular weight of about 380 g / mole and include two epoxide groups per molecule, corresponding to about 190 equivalents. Typical bis-F epoxy resins available under the trade name EPON 862 in resolution are difunctional and have an equivalent of about 170. In general, the greater the equivalent, the more flexible the cured epoxy is, because the greater the spacing between the crosslinking sites. Thus, as typically required in underfill, to increase the rigidity and glass transition temperature, epoxy resins having smaller equivalents or higher functional groups can be incorporated as part of the epoxy resin component. In addition to affecting the physical properties of the epoxy resin, the equivalent plays a role in determining the amount of fluxing hardener included in the underfill solution. For example, the smaller the total equivalent of the epoxy resin component (ie, the equivalent of the epoxy resin component based on the relative amounts of the different epoxy resins that make up the epoxy resin component generally), the epoxide for the given amount of epoxy resin component. Since the number of crosslinking sites increases, the amount of flux hardening agent required to cure the epoxy resin component during solder reflow increases.

anhydride

The first component of the curing agent used in the NUF composition of the present invention is an anhydride compound. Examples of suitable anhydride compounds include methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, dodekenyl succinic anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride. One of the functions of the anhydride component is to react with the epoxy resin to produce a highly crosslinked thermoset polymer. Another function is to react with the phenolic component to form a 1-esterified carboxylic acid, which thus functions as an active fluxing agent that removes metal oxides and facilitates the formation of solder joints. do.

The anhydride component comprises about 15 to about 90% of the total hardener component, including the anhydride and phenolic components. The anhydride component comprises about 30 to about 60% of the total underfill composition.

phenol

The second component of the curing agent used in the NUF composition of the present invention is a phenolic compound. Examples of suitable phenolic compounds are solid phenolic novolac compounds such as H-1, H-2, H-3, H-4, H-5, MEH-7500, -7800, -7851 (Tokyo, Japan) Meiwa Plastic Industries, Ltd., Rezicure 3000, 3010, 3020 and 3020 (Schenectady International Inc., Schenectady, NY, USA) .)), GP 2074 and GP 5833 (Georgia-Pacific Resins Inc., Atlanta, GA, USA), Durite SD-1731 (Lewisville, KY, USA) Borden Chemical Inc.), Tamanol PA and 758 (Arakawa Chemical Industries, Ltd., Osaka, Japan). Other examples include semi-solid or liquid phenolic resins, in particular semi-solid or liquid alkyl-substituted phenolic resins such as MEH 8000H, -8005, -8010 (Maywa Plastic Industries Limited, Tokyo, Japan) and YLH903 (Japan Epoxy Resin's Co., Ltd., Tokyo, Japan). The phenolic component acts as a hardener for the epoxy resin and generally reacts with the anhydride component to form the 1-esterified carboxylic acid, according to the following scheme:

This carboxylic acid acts as an active fluxing agent and reacts with some epoxy to form the following product:

The phenolic component comprises about 10 to about 85% of the total hardener component. The phenolic component comprises about 5 to about 60% of the total underfill composition.

Latent catalyst

In order to supplement the curing action of the anhydride / phenolic compound, the NUF composition of the present invention uses a latent catalyst. Preferred catalysts are “potential” in that at low temperatures (up to about 40 ° C.) the reaction and / or polymer cure rates are very slow, resulting in only a slight increase in underfill viscosity. Among the latent catalysts, polymer-bonded catalysts and phosphonium salt based catalysts, in particular tetraaryl phosphonium salts, tetraalkyl phosphonium salts, mixed tetra (aryl / alkyl) phosphonium salts are preferred. At high temperatures (above 150 ° C.), the reaction and polymerization rates are faster, allowing the underfill to achieve a fully cured state within a faster time (typically less than 1-2 hours). Examples of suitable latent catalysts are solid quaternary phosphonium salts, such as tetraphenylphosphonium-tetraphenylborate, tetrabutyphosphonium, such as available from Hokko Chemical Industries, Tokyo, Japan. Tetraphenylborate, tetraphenylphosphonium tetra-p-tolylborate, and the like. Further examples of suitable latent catalysts include polymer-linked imidazoles, such as Intelimer® 7002, 7004 or 7024 (Lubrizol Dock Resins, Linden, NJ). It includes. This group of latent catalysts consists essentially of imidazole catalysts that are "contained" or enclosed in the crystalline polymer matrix. When the polymer matrix is heated to a temperature above its melting point (typically 60 to 80 ° C.), the active catalyst is released, allowing rapid curing of the epoxy resin. The amount of latent catalyst is such that the peak curing temperature has a value of 150 to 220 ° C. in a ramped DSC (10 C / min) according to ISO 11357-5. The latent catalyst is incorporated at a composition ratio of about 0.2 to about 2 weight percent of the total underfill composition.

Toughening agent

Toughening agents are optionally included in the underfill compositions to improve fracture toughness and to act as stress reducing agents. Toughening agents are, for example, dispersed submicron particles of maleic anhydride functionalized polybutadiene, acrylic or polysiloxane core-cell polymers, or CTBN (carboxyl-terminated butadiene-nitrile resin). If present, the toughening agent is at a concentration of about 20% by weight or less of the underfill composition.

Composition ratio

Phenolic hardener and anhydride components are used in the molar ratio of phenolic compound / anhydride compound from about 0.1: 1 to about 2: 1. If the composition ratio of the phenolic component is too high, the product becomes too viscous. Too high a composition ratio of the anhydride causes the product to become too volatile and voids are formed. In one preferred embodiment, these are used as near stoichiometric mixtures. That is, the molar ratio of these two components is about 0.8: 1 to about 1.2: 1. In one preferred embodiment, this molar ratio is about 0.9: 1 to about 1.1: 1. Mixtures having a molar ratio of about 1: 1 also belong to this embodiment. These ratios have been found to provide a good balance, avoiding premature curing but forming sufficient carboxylic acid reaction product to perform the fluxing function in the underfill product.

The epoxy resin and hardener component are incorporated in an amount such that the molar ratio of epoxy resin to total hardener is from about 0.6: 1 to about 1.4: 1. Total Hardener is the cumulative sum of phenol and anhydride. In one preferred embodiment, these are used as near stoichiometric mixtures. That is, the molar ratio of epoxy resin to hardener component is about 0.8: 1 to about 1.2: 1. In one preferred embodiment, this molar ratio is about 0.9: 1 to about 1.1: 1. Mixtures having a molar ratio of about 1: 1 also belong to this embodiment.

Other additives

Although not required, other additives may also be included in the underfill, such as wetting agents, antifoams, flow promoters, dispersion aids, flame retardants, coupling agents, stress reducers and fillers. Wetting agents are typically added to improve the bond of the underfill to the surface of the integrated circuit device and the printed circuit board by improving the film-formability of the underfill and / or reducing the surface tension of the underfill. Suitable wetting agents include modified silicone resins, carbon fluorides, and acrylic resins. The most commonly used type of wetting agent in underfill is silane. One such commercially available silane-type wetting agent is available under the trade name BYK 306 from BYK Chemie, Bezel, Germany. If a humectant is present, the concentration of the humectant in the underfill solution is typically maintained at a concentration similar to the minimum concentration that achieves effective wetting, because high concentrations can actually reduce adhesion. Generally, the concentration of the wetting agent is from about 0.005 to about 2.0 weight percent of the underfill solution. Preferably, the concentration of the humectant is from about 0.1 to about 0.5 weight percent of the underfill solution. Note that the BYK 306 wetting agent contains only 12% by weight wetting agent and the rest are solvents. Thus, adding about 0.5 wt% BYK 306 to the underfill solution is equivalent to adding about 0.06 wt% wetting agent and about 0.44 wt% solvent.

Antifoaming agents, if present, are typically added before or during mixing of the epoxy resin component, fluxing curing agent and solvent to aid in degassing of the underfill solution. In other words, the antifoaming agent tends to minimize the formation of pockets of air trapped in the underfill solution. Such trapped air pockets typically tend to form voids in the cured underfill that degrade the underfill's adhesion and thermal stress compensation effects. Suitable antifoams include a group of polyether modified siloxanes and methylalkyl siloxanes. Most commonly used defoamers include modified polysiloxanes. Specific examples of such defoamers include BYK 525, BYK 530 and BYK 535 available from BYK Chemie, Bezel, Germany. Another type of antifoam including modified polydimethylsiloxanes is commercially available under the trade name SAG 100 from Crompton, Middlebury, Connecticut. If an antifoam is present, the concentration of the antifoam in the underfill solution is typically maintained at a concentration similar to the minimum concentration that achieves effective degassing, since high concentrations can reduce adhesion. Generally, the concentration of antifoaming agent is about 1% by weight or less of the underfill solution. Preferably, the concentration of antifoaming agent is from about 0.05 to about 0.5 weight percent of the underfill solution.

The cured epoxy resin typically has a linear coefficient of thermal expansion (CTE) of about 50 to about 80 ppm / ° C. and serves to reduce the CTE mismatch between the solder and the substrate material. In order to further reduce any CTE mismatch between the integrated circuit and the solder and the circuit board, the underfill solution may include a coefficient of thermal expansion modification, often referred to as a filler. CTE modifying components have CTEs that are more compatible with substrates (eg flip chip and circuit boards) to reduce thermal stress during thermal cycles. The CTE modifying component is electrically insulating and preferably has a CTE of less than about 10 ppm / ° C. Exemplary CTE modifying component materials include beryllium oxide (about 8.8 ppm / ° C), aluminum oxide (about 6.5 to 7.0 ppm / ° C), aluminum nitride (about 4.2 ppm / ° C), silicon carbide (about 4.0 ppm / ° C), dioxide Silicon (about 0.5 ppm / ° C.), low expansion ceramic or glass powder (about 1.0 to about 9.0 ppm / ° C.) and mixtures thereof. The CTE modifying component, if present, preferably comprises silicon dioxide.

The maximum particle diameter of the CTE modifying component (ie the maximum cross-sectional length of the particles) is preferably below the height of the solder bumps to minimize any negative impact on the integrity of the solder joint. Typically, the average particle diameter of conventional CTE modifying materials is from about 0.5 to about 15 microns. Nanoparticle fillers, typically having a median particle size of about 10 to about 500 nm, may also be used. The amount of filler in the underfill may vary depending on the particular application, but if present, the amount of CTE modifying component suspended or dispersed in the underfill solution is typically about 10 to about 90% of the underfill solution.

To reduce the surface tension of the underfill solution to allow the underfill solution to flow more easily during application of the solution and / or during placement of the electronic component on the substrate on which the underfill solution is deposited, May be included. The leveling agent may also enhance the ability of the underfill solution to wet the surface to be combined with the underfill solution. Conventional levelers fall into four categories: (1) fluorine-based surfactants; (2) organomodified silicon; (3) organo-titanate and organo-zirconates (Kenrich Petrochemicals, Inc.); and (4) acrylics. Leveling agents, if present, typically comprise from about 0.01% to about 1.2% by weight of the underfill solution, for example, in one embodiment, the underfill solution is about 0.5% by weight of the underfill solution. Include in concentration.

Silane coupling agents may be included in the underfill solution to improve the adhesion of the underfill to various substrates. Typically, silane coupling agents include organomodified silicon molecules. If present, the concentration of the silane coupling agent is from about 0.5 to about 2 weight percent of the underfill solution. In one embodiment, the silane coupling agent comprises about 0.5% by weight of the underfill solution.

Process for producing underfill composition

In general, an underfill solution is prepared by mixing the various components together. Typically, the manufacturing process involves mixing selected components, for example in a planetary mixer. If desired, certain solvents may be added to aid mixing. Preferably, the mixing process is carried out in vacuo to reduce or eliminate the trapping of gas in the underfill solution.

In preparing the NUF compositions of the present invention, the invention has been found to facilitate the formation of compositions having reduced pore formation potential, increased fluxing activity, good pot life and shelf life (viscosity stability) and other advantages. Include the order. In particular, the solid phenolic component is first mixed with the epoxy resin component. In a preferred embodiment, the entire amount of phenolic component is blended with the epoxy component during this initial blending operation. In another embodiment, less than the total amount of phenolic components, such as at least about 80% by weight, of the phenolic components are blended with the epoxy component during the initial blending operation, and later the remaining phenolic components are blended with the other components. This initial blending operation yields an epoxy / phenolic blend.

Prior to addition of the anhydride component, this epoxy / phenolic blend is heated to a temperature above the softening point of the phenolic component, typically above about 80 ° C., often above about 100 ° C., using high-shear mixing. do. The temperature of the blend is maintained at a temperature above about 80 or 100 ° C. while the temperature is lower than the temperature at which the risk or tendency for epoxy polymerization to occur is significantly higher. Thus, for many embodiments, the temperature is maintained at less than about 170 ° C. Once a homogeneous mixture is obtained at this temperature, the epoxy / phenolic blend is allowed to cool. If it cools below about 40 ° C., anhydride is added. This heating is not necessary when a liquid or semi-solid phenolic resin is used as the phenolic component. If other additives are present, they are added at this point. These components are then mixed using conventional high-shear dispersion techniques. However, the timing of adding any other additives such as coupling agents and toughening agents is not critical. In particular, they can be added before the heating step.

After a homogeneous mixture is obtained, the mixture is degassed under vacuum and packed. The product is preferably stored at a temperature of less than about -20.

According to the aforementioned protocol, it has been found that premature reactions between phenolic and anhydride components are avoided or at least significantly reduced. Thus, this results in a dramatic decrease in the viscosity of the blend, an increase in pot life, and a reduction in the consumption of the components through premature reactions, if not otherwise (1) H. Lee and K. Neville, "Handbook of Epoxy Resins, 1982-reissue, pages 5-18 (1982, McGraw-Hill, NY) and (2) W. Blanc, Z. He and M. Picci: "Catalysis of the Epoxy-Carboxyl Reaction," Proceeding, Int. Waterborne, High-Solids and Powder Coatings Symposium February 21-23, 2001 New Orleans, LA] will have less hardener components available for reaction with epoxy. By increasing the efficiency of the hardener component, a lower total constituent of the hardener is used, which in particular has the advantage of higher crosslink density and T _g .

While not wishing to be bound by any theory, it is believed that pre-dissolving the phenolic component in the epoxy reduces the risk of the phenolic component reacting excessively with the anhydride component. In addition, the risk of the phenolic component reacting with the epoxy component is reduced because the predissolution is carried out in the absence of a catalyst, using high-shear mixing, at a temperature not too high. It is also contemplated that the anhydride will not be consumed because the anhydride is not blended until the epoxy / phenolic blend is cooled, and because of the nature of the catalyst.

The invention is further illustrated by the following examples.

Example 1

To prepare the underfill composition, 9.6 parts of Paraoid® EXL 2330 core-cell rubber, liquid diglycidyl ether of bis-phenol F (DGEBPF), were prepared using a high-shear centrifugal laboratory mixer. Pre-dispersed in 38 parts. This pre-blend was then placed in a glass container with additional 62 parts of DGEBPF, 30.2 parts of solid phenolic novolac resin, and 1.9 parts of Silquest® A-189 mercaptopropyl-trimethoxysilane. Put in. The mixture was heated to 125 ° C. on an electric hotplate and homogenized for 25 minutes using a uniaxial mixer equipped with high strength centrifugal rotors. The pale pink to orange viscous opaque mixture is allowed to cool to about 40 ° C., and when the mixture is cooled, 48.8 parts of methylhexahydrophthalic anhydride (MHHPA) is fumed with 0.76 parts of tetraphenylphosphonium tetraphenylborate (TPP-K). Along with 0.08 parts of silica (R-972 from Degussa) was added, along with 0.84 parts of TPM-K / fumed silica blend. The mixture was mixed vigorously for another 10 minutes at room temperature and then degassed for 90 minutes under vacuum (less than 25 mm Hg).

Example 2

An underfill composition was prepared according to the protocol of Example 1, except that 0.48 parts of Intellimer 7024 polymer-bonded imidazole was used instead of the TPP-K / fumed silica blend.

Comparative Example 1

The composition of Example 1 was changed except that the composition ratio of the solid phenolic novolac resin was reduced to 14 parts, the composition ratio of MHHPA was increased to 81.0 parts, and the composition ratio of the TPP-K / fumed silica blend was increased to 1.04 parts. Accordingly an underfill composition was prepared.

Comparative Example 2

100 parts of DGEBPF, 14.0 parts of solid phenolic novolac resin, 9.6 parts of Pararoid EXL 2330 core-cell rubber, 1.9 parts of Silquest A-189 mercaptopropyl-trimethoxysilane and 81.0 parts of MHHPA were placed in an underfill. The composition was prepared. This mixture was homogenized at 125 ° C. for 25 minutes using a uniaxial mixer equipped with a high strength centrifugal rotor. After cooling to room temperature, 0.19 parts of Curazol 2E4MZ (Air Products) were added to the mixture and stirred at the same time. This blend was then degassed for 90 minutes under vacuum (<25 mmHg).

Comparative Example 3

Core-cell rubbers (9.6 parts of Pararoid EXL 2330) were pre-dispersed in 38 parts of DGEBPF using a high-shear centrifugal laboratory mixer. The pre-blend was then placed in a glass container with additional 62 parts of DGEBPF, 1.9 parts of Silquest A-189 mercaptopropyl-trimethoxysilane and 103.7 parts of MHHPA. In a separate step, 16.2 parts of hydrogenated bis-phenol A (Aldrich) were ground together with 1.6 parts of fumed silica and added to the mixture, which was added to a room temperature using a single screw mixer equipped with a high-strength centrifugal rotor. (See: Attempts to produce a homogeneous single phase blend of hydrogenated bisphenol-F and an epoxy resin via melt blending have been achieved by high melting point of hydrogenated bisphenol-A and its incompatibility with epoxy resin.) Due to full phase separation, which was not successful). Finally, using a method of vigorously mixing for 10 minutes, 1.04 parts of TPP-K and 0.1 part of fumed silica were added to the mixture. This blend was then degassed for 90 minutes under vacuum (<25 mmHg).

Comparative Example 4

An underfill composition was prepared according to the protocol of Comparative Example 3, except that 4.1 parts of glycerol (Aldrich) was used instead of hydrogenated bis-phenol A and the TPP-K / fumed silica blend was increased to 1.34 parts.

Comparative Example 5

An underfill composition was prepared according to the protocol of Example 1, except that 0.74 parts of cured 2MA-OK imidazole salt (Air Products) and 0.07 parts of fumed silica were used in place of the TPP-K / fumed silica blend. It was.

Comparative Example 6

An underfill composition was prepared according to the protocol of Example 1, except that 0.20 parts of Curazole 2E4MZ imidazole (Air Products), an imidazole, was used in place of the TPP-K / fumed silica blend.

Comparative Example 7

An underfill composition was prepared according to the protocol of Example 1, except that 0.76 parts of triphenylphosphine and 0.08 parts of fumed silica were used in place of the TPP-K / fumed silica blend.

Comparative Example 8

Except that the epoxy resin, solid phenolic resin, A-189 silane, Pararoid 2330 toughening agent and MHHPA were melt-blended together at 125 ° C. for 25 minutes, cooled to 40 ° C. and then added with TPP-K catalyst. , An underfill composition was prepared according to the protocol of Example 1.

Example 3

The underfill compositions of Example 1 and Comparative Examples 1-7 were evaluated for the following properties:

(1) First Brookfield Viscosity (ISO 2555)

(2) characteristic temperature T _peak and T _g (ISO 11357-5)

(3) fluxing ability

(5) void formation

(6) weight loss rate

To assess the fluxing capacity, about 0.5 ml of each NUF composition was dispensed onto a 7 × 3 cm strip of copper / OSP-coated FR4 laminate. Three 35.4-mil diameter eutectic 63Sb37Pb solder spheres were placed into the liquid and applied to a standard JEDEC eutectic reflow profile (220 ° C. peak, time above liquidus = 60 seconds). After reflow, the spheres were examined to demonstrate collapse and wetting on the copper, as evidenced by an increase in the sphere diameter. X-ray images generally consist of dark color centers surrounded by lighter "halo". Calculated according to the percentage increase in sphere diameter (100 × [(Rf / Ri) -1], where Rf is the diameter of the dark center image after reflow and Ri is the diameter of the x-ray image before reflow ) Is considered to represent the fluxing ability of the NUF.

For pore formability analysis, the underfill was placed under a 13 x 13 mm glass die with 24 eutectic bumps of 50-mil pitch. This die was attached to an FR-4 organic substrate equipped with Cu pads. This assembly was subjected to standard JEDEC eutectic reflow and then examined with an ultrasound scanning microscope to assess the degree of pore formation.

Perkin-Elmer Model Pyris 1 using a sample size of 7-8 mg, heating from 25 ° C. to 275 ° C. at a heating rate of 10 ° C./min, and a nitrogen atmosphere. The weight loss rate was analyzed using a Thermo-Gravimetric Analyzer.

The results of these assessments are set forth in Table 1 below.

Viscosity-First, cP Viscosity after 4 hours at 23 ° C DSC T _{peak *} ( ^* first or largest peak) TGA weight loss rate,% DSC T _g Fluxing (% Diameter Growth) Voids (% area under the die) Example 1 (preferred) 7,800 9,840 185 11.9 101 130 0 Example 2 (preferred) 10,270 13,190 182 8.3 98 138 0 Comparative Example 1 1,200 1,430 191 20.6 109 140 One Comparative Example 2 2,980 3,320 185 16.1 108 143 0 Comparative Example 3 <1,000 1,020 191 19.6 109 96 ^* (irregular shape) 2 Comparative Example 4 <1,000 1,030 191 20.1 108 127 One Comparative Example 5 5,300 30,000 182 8.0 88 113 ^* (irregular shape) 0 Comparative Example 6 19,800 > 50,000 188 8.4 97 105 ^* (irregular shape) 0 Comparative Example 7 16,500 > 50,000 184 9.1 96 121 0 Comparative Example 8 21,000 46,000 186 9.2 99 140 2

Embodiments of the present invention (Examples 1 and 2) exhibit excellent fluxing ability, relatively low TGA weight loss rate, low pore formation, and stable room temperature viscosity (good pot life).

Comparative Example 1, which has a lower concentration of solid phenolic novolac and an increased anhydride concentration, shows an increased pore formability, and a higher TGA weight loss rate compared to the preferred embodiment. However, this material has a lower viscosity.

Comparative Example 2 has a composition similar to Comparative Example 1, but it is prepared using a conventional blending process (adding all materials except catalyst, heating and mixing together) and 2E4MZ catalyst. This material has a higher weight loss rate compared to the preferred embodiment. However, this material has a lower viscosity.

Comparative Examples 3 and 4 show that aliphatic polyols (glycerol, hydrogenated bisphenol A) have a higher tendency of pore formation at similar molar concentrations of active hydrogen.

Comparative Example 5 shows that another conventional latent catalyst (imidazole adduct) is not as effective as phosphonium salt or polymer-linked imidazole in maintaining low viscosity.

Comparative Examples 6 and 7, in contrast to the preferred embodiments of Example 1 and 2 and Comparative Example 2, are cursols which are conventional catalysts when the molar ratios of anhydride / phenolic hardeners are similar, i.e. close to 1. It is shown that 2E4MZ or TPP organophosphine is not suitable.

Comparative Example 8, with high viscosity and poor pot life, illustrates the advantages of the order of addition in achieving the desired material properties, as disclosed in the preferred embodiments.

The present invention is not limited to the above embodiments and can be variously modified. The foregoing description of the preferred embodiments is directed to those skilled in the art, the principles and practical aspects of the invention, to enable those skilled in the art to modify and apply the invention in numerous forms that may best suit the requirements of the particular application. It is only intended to familiarize you with the application.

Throughout this specification (including the appended claims), when the words “comprise” or “comprising” are used, unless otherwise stated, these words are to be interpreted as inclusive and not as exclusive, unless otherwise stated. It is to be understood that the phraseology is used on an understanding basis, and that each of these words is so interpreted throughout this specification.

Claims (45)

Blending the epoxy component with at least about 80% by weight of the phenolic component to form an epoxy / phenolic blend; Heating the epoxy / phenolic blend to a temperature above the softening point of the phenolic component; Cooling the epoxy / phenolic blend; Blending an anhydride component into the epoxy / phenolic blend to form an underfill composition A method for producing an underfill composition comprising an epoxy component, an anhydride component and a phenolic component, for use in the manufacture of an electronic product comprising a. The method of claim 1 wherein the step of cooling the epoxy / phenolic blend comprises cooling to a temperature of less than about 40 ° C. The method of claim 1, wherein blending the epoxy component with at least about 80% by weight of the phenolic component to form an epoxy / phenolic blend comprises blending substantially the entire amount of the phenolic component with the epoxy component. 3. The method of claim 2, wherein blending the epoxy component with at least about 80% by weight of the phenolic component to form an epoxy / phenolic blend comprises blending substantially the entire amount of the phenolic component with the epoxy component. The method of claim 1 wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.1: 1 to about 2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. The method of claim 1 wherein blending of the epoxy component and blending of the anhydride component achieves a molar ratio of epoxy component to total hardener of about 0.6: 1 to about 1.4: 1, wherein the total hardener is a phenolic component and an anhydride component. The cumulative sum of. The method of claim 2, wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.1: 1 to about 2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. 3. The method of claim 2, wherein through blending the epoxy component and blending the anhydride component, a molar ratio of epoxy component to total hardener is achieved between about 0.6: 1 and about 1.4: 1, wherein the total hardener is a phenolic component and an anhydride component. The cumulative sum of. 4. The method of claim 3, wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.1: 1 to about 2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. 4. The molar ratio of epoxy component to total hardener of about 0.6: 1 to about 1.4: 1 is achieved by blending the epoxy component and blending the anhydride component, wherein the total hardener is a phenolic component and an anhydride component. The cumulative sum of. The method of claim 1 further comprising blending the additive into an epoxy / phenolic blend, wherein the additive is a wetting agent, antifoaming agent, flow promoter, dispersion aid, flame retardant, coupling agent, stress reducer, CTE modifier, and their The method selected from the group consisting of combinations. The method of claim 1 further comprising blending the additive into an epoxy / phenolic blend, wherein the additive is a wetting agent, antifoaming agent, flow promoter, dispersing aid, flame retardant, coupling agent, stress reducer, CTE modifier, and their Selected from the group consisting of combinations, wherein the blending of the additives is carried out after cooling of the epoxy / phenolic blend. The method of claim 2 further comprising blending the additives in an epoxy / phenolic blend, wherein the additives are wetting agents, antifoams, flow promoters, dispersing aids, flame retardants, coupling agents, stress reducers, CTE modifiers, and their The method selected from the group consisting of combinations. The method of claim 2 further comprising blending the additives in an epoxy / phenolic blend, wherein the additives are wetting agents, antifoams, flow promoters, dispersing aids, flame retardants, coupling agents, stress reducers, CTE modifiers, and their Selected from the group consisting of combinations, wherein the blending of the additives is carried out after cooling of the epoxy / phenolic blend. 6. The method of claim 5 further comprising blending the additives in an epoxy / phenolic blend, wherein the additives are wetting agents, antifoams, flow promoters, dispersing aids, flame retardants, coupling agents, stress reducers, CTE modifiers, and their The method selected from the group consisting of combinations. 7. The method of claim 6 further comprising blending the additive into an epoxy / phenolic blend, wherein the additive is a wetting agent, antifoaming agent, flow promoter, dispersion aid, flame retardant, coupling agent, stress reducer, CTE modifier, and their Selected from the group consisting of combinations, wherein the blending of the additives is carried out after cooling of the epoxy / phenolic blend. The method of claim 1 further comprising blending the latent catalyst into an epoxy / phenolic blend. The method of claim 1, further comprising blending the latent catalyst into an epoxy / phenolic blend, wherein the blending of the latent catalyst is performed after cooling of the epoxy / phenolic blend. 3. The process of claim 2 further comprising blending the latent catalyst into an epoxy / phenolic blend. The method of claim 2 further comprising blending the latent catalyst into an epoxy / phenolic blend, wherein the blending of the latent catalyst is performed after cooling of the epoxy / phenolic blend. 6. The process of claim 5 further comprising blending the latent catalyst into an epoxy / phenolic blend. 6. The process of claim 5 further comprising blending the latent catalyst into an epoxy / phenolic blend, wherein the blending of the latent catalyst is performed after cooling of the epoxy / phenolic blend. 7. The process of claim 6 further comprising blending the latent catalyst into an epoxy / phenolic blend. 7. The method of claim 6 further comprising blending the latent catalyst into an epoxy / phenolic blend, wherein the blending of the latent catalyst is performed after cooling of the epoxy / phenolic blend. The method of claim 1 wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. The method of claim 2, wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. The method of claim 6, wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. The method of claim 12, wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. 18. The method of claim 17, wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. The method of claim 18, wherein blending the anhydride component into the epoxy / phenolic blend to form the underfill composition causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. Blending the anhydride component in an epoxy / phenolic blend in an amount. The method of claim 1, wherein heating the epoxy / phenolic blend to a temperature above the softening point of the phenolic component comprises heating to a temperature above about 80 ° C. 3. The method of claim 2, wherein heating the epoxy / phenolic blend to a temperature above the softening point of the phenolic component comprises heating to a temperature above about 80 ° C. 4. Blending the epoxy component with at least about 80% by weight of the phenolic component to form an epoxy / phenolic blend; Blending the anhydride component into the epoxy / phenolic blend in an amount such that the underfill composition has a molar ratio of phenolic component to anhydride component from about 0.1: 1 to about 2: 1. A method for producing an underfill composition comprising an epoxy component, an anhydride component and a phenolic component, for use in the manufacture of an electronic product comprising a. 34. The method of claim 33, wherein the phenolic component is a semi-solid or liquid phenolic resin. 34. The method of claim 33, wherein blending the anhydride component into the epoxy / phenolic blend causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. Blending into an epoxy / phenolic blend. 35. The method of claim 34, wherein blending the anhydride component into the epoxy / phenolic blend causes the underfill composition to have a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. Blending into an epoxy / phenolic blend. 34. The method of claim 33, further comprising blending the latent catalyst into an epoxy / phenolic blend. 35. The method of claim 34, further comprising blending the latent catalyst into an epoxy / phenolic blend. An underfill composition for use in the manufacture of an electronic product produced by the method of claim 1. Epoxy component; And Hardener component comprising a phenolic component and an anhydride component in a molar ratio of phenolic component to anhydride component from about 0.1: 1 to about 2: 1 Underfill composition for use in the manufacture of electronics, comprising. 41. The underfill composition of claim 40, wherein the hardener component comprises a phenolic component and an anhydride component in a molar ratio of phenolic component to anhydride component from about 0.8: 1 to about 1.2: 1. The underfill composition of claim 40 further comprising a latent catalyst. 42. The underfill composition of claim 41 further comprising a latent catalyst. 41. The underfill composition of claim 40 further comprising a latent catalyst selected from the group consisting of polymer-bonded catalysts and phosphonium salt based catalysts. 42. The underfill composition of claim 41 further comprising a latent catalyst selected from the group consisting of polymer-bonded catalysts and phosphonium salt based catalysts.