KR20090101336A - Process for coating a bumped semiconductor wafer - Google Patents

Abstract

A process is described that enables the active side of a bumped wafer to be coated with a front side protection (FSP) material or wafer level underfill (WLUF) without contaminating the solder bumps with the coating material and/or filler. In this process a repellent material is applied to a top portion of the solder bumps on the active side of the wafer, the front side of the wafer is then coated with the coating material, the coating material is hardened, and optionally the repellent material is removed from the solder bumps.

Description

PROCESS FOR COATING A BUMPED SEMICONDUCTOR WAFER}

The present invention relates to a method for manufacturing a bumped semiconductor wafer that can be used to protect the front side in a wafer level package (WLP) or wafer level underfill (WLUF) of a flip chip device.

Recent developments in packaging technology for semiconductor devices include as many steps as possible at the wafer level. Applying the material before dicing and singulating the wafer into individual dies can shorten the overall process time and, therefore, reduce manufacturing costs. Often, the active surface of the wafer has been laminated with solder bumps that are later used to attach individual dies to bonding pads on the substrate to form electrical connections between the two. Many packaging processes have emerged that require paste or coating to be applied to the bumping side of the wafer. Two examples of such processes include WLPs for memory devices and WLUFs for microprocessors and application specific integrated circuits (ASICs).

Memory packages manufactured by WLP technology require incremental front side protection (FSP) coatings. This is typically an adhesive or encapsulant that is applied to the active side (bump attachment side) of the wafer and cured prior to dicing and singulation. As the name suggests, the FSP coating protects the active side of the wafer in subsequent processing steps such as dicing, singulation, and attachment to the circuit board. Not all memory devices packaged by WLP require FSP coating, but the need is becoming more common with the development of this technology. Performance requirements, such as the need for thinner packages, faster signal transfer, and increased memory capacity, have resulted in larger die with lower bump heights. These changes, individually or collectively, result in an increase in package stress, which is usually mitigated by using FSP coating.

Flip chip devices, especially flip chip devices with large dies such as microprocessors or ASICs, are typically packaged using underfills or encapsulants around the solder bumps used to attach the active side of the die to the substrate or circuit board. . Early techniques in this package form used capillary underfill, which was applied as a liquid around a die already attached to the substrate. In recent years, a great deal of research has been done to allow the application of underfill at the wafer level, thus eliminating the time-consuming capillary underfill step.

Coating of bumped semiconductor wafers can be carried out using a variety of techniques well known in the art, including spin coating, stencil printing, and jetting. The spin coating process is not only fast, but also has the advantage of forming a very uniform coating thickness by selecting the coating material appropriately. In addition, since there is no squeegee or other physical medium scraping over the bumps, the coating may be applied to a thickness less than the height of the solder bumps, and the solvent may or may not be used in the coating formulation.

However, when using this method on the bump attachment surface, the coating material not only coats the die, but also the top of the solder bumps. The die must then be attached using thermo-compression bonding, and solder joints are formed by the application of heat and pressure when the die is mounted. Heat and pressure push the coating away from the top of the solder bumps so that a clean, non-foreign joint can be formed between the die and the substrate. This method is time consuming and expensive, and thermal-compression bonding devices are not widely available in the industry. In addition, thermal-compression bonding cannot be used in coating formulations containing significant amounts of fillers, since the effect is not sufficient when there are fillers in the solder bumps. In contrast, the coating on top of the solder bumps is removed before the die is attached to the substrate, whereby the solder bumps can form a clean joint and create an effective interconnect to adjacent substrates. This is particularly necessary when the coating contains fillers, since filler particles on the bumps are particularly harmful for joint formation.

Removal of excess coating and / or filler particles may be carried out after curing and / or hardening of the coating and is accomplished by physical or chemical means including lapping, grinding, or chemical etching. do. Unfortunately, such process steps are time consuming, can damage solder bumps or wafers, and can cause contamination. Thus, by coating the wafer to a predetermined thickness below the solder bump height without leaving significant coating residue on the solder bumps, a subsequent "pick and place" die attach apparatus is eliminated without subsequent coating removal steps. It is desirable to have a coating process that can use (apparatuses having high throughput and customary for industrial use).

Stencil printing is typically accomplished by applying a solvent-based coating formulation to a thickness sufficient to cover the solder bumps. The coating is then B-stage processed, which is the process of evaporating the solvent to partially cure and / or harden the coating. The coating shrinks substantially by evaporation of the solvent, and the thickness of the resulting coating is less than the height of the solder bumps. However, there is still a significant residual coating on top of the bumps, and if the coating contains fillers, filler particles may also be present on the bumps. The coatings and / or fillers must be removed by physical or chemical means to ensure clean solder joints are formed in the substrate through pick-and-place die bonding.

Alternatively, after dicing and singulation (separation of the die after dedusting), the die can be attached to the substrate using thermal-compression bonding, with the result that heat and pressure push the residual coating away from the solder joint to achieve good bonding and electrical Allows a connection to be made. As mentioned earlier, thermal-compression bonding devices are not currently widespread in the industry, and the process is a time-consuming method of attachment and ineffective when filler particles are present on the bumps. Accordingly, it is desirable to have a coating method that can apply a coating to a wafer at a prescribed thickness below the solder bump height, leaving no coating residue or filler particles on top of the solder bump. Such a method will enable package assembly using conventional pick-and-place die attach devices, and more readily use filled coating formulations.

1 and 2 illustrate two conventional wafer coating methods.

The present invention is a method for coating the active side of a semiconductor wafer on which solder bumps are laminated,

(a) preparing a semiconductor wafer having an active side and a front side on which solder bumps are stacked and a back side opposite the front side,

(b) applying a repellent material on top of the solder bumps,

(c) coating the front side of the wafer with a coating material,

(d) hardening the coating material, and

(e) optionally, removing the repellent material from the bumps

It includes, the coating method.

This method does not require the removal of remaining coatings from the bumps, and does not require the use of thermal-compression bonding to obtain a clean solder joint, without filling or filling the bumped wafer with a prescribed thickness that may be less than the solder bump height. It is possible to coat with a free coating.

In yet another embodiment, the invention is a semiconductor wafer made according to the method described above.

With reference to the accompanying drawings, the following detailed description will be able to more fully understand the present invention.

1 (Prior Art) is a diagram showing the steps for a traditional wafer spin coating process and the corresponding wafer cross section.

FIG. 2 (Prior Art) shows the steps for a traditional stencil print coating process and the corresponding wafer cross section.

3 shows one embodiment of the method of the present invention wherein the initial coating thickness is less than the tip of the solder bumps.

4 shows an embodiment of the method of the present invention wherein the initial coating thickness is thicker than the tip of the solder bumps.

Justice

The term "alkyl" as used herein refers to a branched or unbranched saturated hydrocarbon group having 1 to 24 carbon atoms, for example methyl ("Me"), ethyl ("Et"), n-propyl, iso Propyl, n-butyl, isobutyl, t-butyl, octyl, decyl, and the like. Preferred alkyl groups here contain 1 to 12 carbon atoms.

As used herein, the term "effective amount" of a compound, product, or composition means an amount of the compound, product, or composition sufficient to provide the desired result. As noted below, the exact amount required will vary from package to package depending on the particular compound, product or composition used, the mode of application thereof, and the like. Thus, although it is not always possible to specify the exact amount, the effective amount can only be determined by one skilled in the art using routine experimentation.

As used herein, the term “suitable” means a moiety that is compatible with the compounds, products, or compositions provided herein for the purposes described. Suitability for the described purposes can only be determined by one skilled in the art using routine experimentation.

As used herein, the term "substituted" is generally used to mean a carbon having a hydrogen atom or other atom that has been removed and replaced with an additional moiety or a suitable hetero atom. The term "substituted" is also used to mean a substitution that does not change the basic and novel utility of the base compound, product or composition used in the present invention.

As used herein, the term "B-stage processing" (and variations thereof) refers to partial curing or curing of the material when the material is dissolved or dispersed in a solvent by treating the material by heat or radiation. Without evaporating the solvent, or when the material does not contain a solvent, it is meant to partially cure the material, making it tacky or harder. If the material is a flowable adhesive, the B-stage processing will provide very low flowability without completely curing so that additional curing can be performed after the adhesive is used to bond one object to the other. Reduction in fluidity can be achieved by evaporation of the solvent, partial enhancement or curing of the resin or polymer, or both.

Detailed description of the invention

Semiconductor wafers suitable in the present invention may have any diameter and any thickness, and may include, for example, silicon, gallium arsenide, indium phosphide, or any other semiconductor material. Semiconductor wafers are fabricated with a top (front) surface that is active and on which electronic components and circuits are formed, and a bottom (rear) surface that is inactive facing the active surface.

The front side of the wafer is electrically active and there are raised bumps on the solder that will later form an electrical connection between the integrated circuit and the substrate. The solder bumps can be of any composition, size and arrangement.

The repellent material works by repelling or de-wetting the coating. The dewetting or repulsive effect may occur during the application of the coating to the wafer and / or during the hardening of the coating. The repellent material may be any material that can stick to the solder bumps and is not physically or chemically compatible with the coating to be applied, and therefore covers the solder bumps during coating application or subsequent hardening of the coating. Dewet the coating material from the broken portion. Incompatible, or repulsive properties can be achieved through chemical or physical means. One way to achieve incompatibility is to use materials with large differences in surface energy (greater than 5 nM / m).

In addition, there should be no polar reaction between the repellent material and the coating material. For example, if one of the materials is basic and the other is acidic, polar attraction will act between them resulting in ineffective dewetting. This may be the same even if the surface energy difference between the repellent material and the coating material is large.

Physical incompatibility can be achieved by using a repellent material that has a very flat surface when hardened, and the coating cannot physically attach to such a repellent material.

The melting point or softening point of the repellent material is selected by the practitioner to suit the particular coating, curing profile, and process to be used, and typically ranges from -40 ° C to 300 ° C. The repellent material may be solid or liquid at room temperature as long as it has a melting point lower than the temperature used in the solder reflow process. In some cases, the melting point or softening point is below the B-stage temperature of the coating, as long as it is high enough to cause partial evaporation of the solvent and / or partial hardening or solidification of the resin before the repellent material melts and / or evaporates. Can be selected. In other cases, by using a repellent material having a melting point or softening point that is between the B-stage temperature and the curing temperature of the coating material, the repellent material remains in place completely during the B-stage processing to protect the solder bumps, It may be desirable to melt and possibly volatilize upon thermal curing. Alternatively, if the coating is UV cured, the repellent material may have a low or high melting point depending on the downstream process used.

In one embodiment, the repellent material is a wax. Suitable waxes can be natural or synthetic. Examples of suitable waxes include, but are not limited to, paraffin, parowax, microcrystalline wax, petroleum wax blends, amorphous waxes, polyester waxes, soy waxes, beeswax, and blends thereof.

In another embodiment, the repellent material is a low surface energy compound such as silane, polysiloxane, or polyfluorinated compound.

In another embodiment, the repellent material is dissolved in a solvent and a solvent / repellent material formulation is applied to the solder bumps. In this example, the repellent material is applied at room temperature or at an elevated temperature below the boiling point of the solvent. In subsequent process steps, the solvent is volatilized by the application of heat, leaving a repellent material that coats the bumps.

The repellent material is applied on top of the solder bumps by any means that allows a controlled amount of material to be coated on the controlled portion of the solder bumps without damaging the solder bumps or wafers. In one embodiment, the solder bumps are pressed into pads that are immersed in the molten repellent coating. The pad may be a nonwoven or woven fabric, fabric, sponge, or similar material that absorbs the repellent material for delivery to the bumps. In yet another embodiment, the bumps are immersed in a reservoir of molten repellent material. In these two embodiments, the wafer is advanced into the reservoir or pad of the repellent material so that the top of the bump is covered with a controlled portion of the full height.

In another embodiment, the repellent material is coated as a film on a carrier such as paper, mylar, polyethylene, polypropylene, metal foil, and the like, and then laminated onto bumps to give controlled thickness and coating depth. . In another embodiment, the repellent material is melted and then printed on top of the bumps. In this embodiment, a stencil or mask with a pattern tailored to the bump pattern on the wafer may be used to ensure that the wax is deposited at a controlled height on top of the bump.

The portion of the bump to be covered varies with specific package requirements and manufacturing conditions, and may range from 5-100% of the total bump height. Typically, only a minimal amount of bump is covered with a repellent material when the underfill is applied. This allows the underfill to encapsulate as many solder bumps as possible while still exposing sufficient solder bump surface for good joint formation with the substrate. In contrast, in anterior protective applications, the amount of bumps covered with a repellent material can be minimized to enable a thick coating of the anterior protective material, or if a very thin layer of anterior protective material is needed to apply, Many parts can be covered.

The application of the repellent material can be carried out at any temperature suitable for the particular material selected and can be determined by the practitioner without undue experimentation. For example, if the repellent material is flowable at room temperature, it can be applied at room temperature. If the repellent material is hard at room temperature, it will need to be heated to allow the resilient material to soften or melt for application to the solder bumps without damaging the solder bumps. The repellent material may also be at temperatures above room temperature so that it is in a softened state that can be applied to the bumps by rubbing or light contact treatments that do not damage the bumps, and that the coating does not have to be significantly cooled to harden. It may be heated to a temperature lower than the melting point of the material. This method allows for a highly controlled coating without drips or runs that can result in the case of fully liquefied repellent material. In addition, the wafer itself may be at room temperature, or may be heated to assist the coating process, as required for the particular set of materials selected and the manufacturing conditions used.

The thickness or depth of the repellent material in the bumps may be selected by the practitioner to suit the needs of the particular manufacturing process and may range from several μm to 100 μm. Thin layers of repellent material are typically preferred when the wax residues are to be minimized. However, there may be cases where a thicker layer of repellent material is desired, for example, to preserve areas for expansion and collapse of solder bumps. This happens when the coating is a front side wafer protection material. If the repellent material is coated as a thick layer over the entire bump, after the repellent material is volatilized, a vacant area will be created around the bumps where the bumps can expand and collapse.

The depth or thickness of the layer of repellent material may be controlled in part by the viscosity at the application temperature. Materials with high viscosities at the application temperature tend to form thicker layers, while materials with low viscosities at the application temperature tend to form thinner layers with the application of less repulsive materials. The practitioner can change the amount of repellent material applied by changing various variables including the repulsive material formulation, application temperature, application pressure, or compressibility of the application medium.

Depending on whether the repellent material is in a flowable state at the time of application, there may be additional processing steps in which the repellent material solidifies before applying the coating to the wafer. If the repellent material is applied as a liquid, hardening of the repellent material may be necessary to prevent the coating from physically removing the repellent material to prevent contamination of the top portion of the bumps. Hardening of the repellent material also prevents the repellent material from flowing from the surface of the bump toward the active side of the wafer, preventing the coating from properly encapsulating the bottom portion of the bump. Typically, hardening can be accomplished by cooling the repellent material on the wafer.

The coating material can be any material that can be applied to the front side of the bumping die, including, but not limited to, adhesives, encapsulants, or front side protection materials. The choice of suitable coating agent depends on the coating purpose in the semiconductor package and the process to be used. Coatings typically contain some form of polymer or curable resin, which may include thermoplastics, thermosets, elastomers, thermoset rubbers, or combinations thereof. The coating may or may not contain a solvent. The polymer or curable resin will generally be a major component except for any filler present.

Other components typically used in coating compositions can be added at the choice of the practitioner, including but not limited to curing agents, fluxing agents, wetting agents, flow control agents, adhesion promoters, and air release agents. A curing agent is any substance or combination of materials that initiates, propagates, or accelerates the curing of a coating of an adhesive, and includes an accelerator, a catalyst, an initiator and a hardener. The coating composition may also contain a filler, in which case the filler is present in an amount up to 95% of the total amount of the composition.

Viscosity and thixotropy coefficient of the coating material are selected by the practitioner to suit the application method, manufacturing conditions and the repellent material to be used, and typically range from 100 to 60,000 cP when tested at 5 ° C. at 25 ° C. with a Brookfield CP 51 viscometer. . For example, when applying the coating via spin coating, the viscosity of the coating will be quite low. When the coating is applied by screen printing, it generally has a higher viscosity. In this situation, the coating will not dewet from the solder bumps immediately after coating of the wafer due to the high viscosity and impossibility of flow. However, when the wafer is exposed to heat to B-stage or cure the coating, the viscosity of the coating decreases before the coating cures, allowing flow of the coating and dewetting from the solder bumps. In this situation, the melting point or softening point of the repellent material is selected to be higher than the temperature at which the coating material flows so that the resilient material remains in place where dewetting of the solder bumps occurs.

The resins and polymers used for the coating may be solid, liquid, or a combination of both. Suitable resins include epoxy, acrylate or methacrylate, maleimide, bismaleimide, vinyl ethers, polyesters, poly (butadiene), siliconized olefins, silicone resins, siloxanes, styrene resins, and cyanate ester resins. Included. In one embodiment, the coating contains an epoxy resin, bismaleimide resin, and an acrylate resin.

In one embodiment, a solid aromatic bismaleimide (BMI) resin powder is included in the coating. Suitable solid BMI resins are those having the following structure:

Wherein X is an aromatic group; For example, aromatic groups include:

Bismaleimide resins having X as such bridging group are commercially available and can be obtained, for example, from Sartomer (USA) or HOS-Technic GmbH (Austria).

(여기서, n은 1∼3이고, X¹은 지방족 또는 방향족 기임)을 가지는 것들을 포함한다. X¹에 해당하는 예로는, 폴리(부타디엔), 폴리(카보네이트), 폴리(우레탄), 폴리(에테르), 폴리(에스테르), 단순 탄화수소, 및 카르보닐, 카르복 실, 아미드, 카바메이트, 우레아 또는 에테르와 같은 작용기를 함유하는 단순 탄화수소가 포함된다. 이러한 형태의 수지는 상업적으로 입수 가능하며, 예를 들면, National Starch and Chemical Company 및 Dainippon Ink and Chemical, Inc.로부터 구할 수 있다.In another embodiment, the maleimide resin used in the coating composition has a general structural formula

Wherein n is 1-3 and X ¹ is an aliphatic or aromatic group. Examples corresponding to X ¹ include poly (butadiene), poly (carbonate), poly (urethane), poly (ether), poly (ester), simple hydrocarbons, and carbonyl, carboxyl, amide, carbamate, urea Or simple hydrocarbons containing functional groups such as ethers. Resin of this type is commercially available and can be obtained, for example, from National Starch and Chemical Company and Dainippon Ink and Chemical, Inc.

In another embodiment, the maleimide resin is selected from the group consisting of:

Wherein C ₃₆ represents a straight or branched chain having 36 carbon atoms (with or without cyclic moiety);

Suitable acrylate resins include those having the following general structural formula:

Wherein n is 1 to 6, R ¹ is —H or —CH ₃ , and X ² is an aromatic or aliphatic group. Examples corresponding to X ² include poly (butadiene), poly (carbonate), poly (urethane), poly (ether), poly (ester), simple hydrocarbons, and carbonyl, carboxyl, amide, carbamate, urea or Simple hydrocarbons containing functional groups such as ethers are included. Commercially available materials include butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, available from Kyoeisha Chemical Co., Ltd. , n-lauryl (meth) acrylate, alkyl (meth) acrylate, tridecyl (meth) acrylate, n-stearyl (meth) acrylate, cyclohexyl (meth) acrylate, tetrahydrofurfuryl (meth ) Acrylate, 2-phenoxyethyl (meth) acrylate, isobornyl (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1 , 9-nonanediol di (meth) acrylate, perfluorooctylethyl (meth) acrylate, 1,10-decanediol di (meth) acrylate, nonylphenolpolypropoxylate (meth) acrylate, and poly Pentoxylate tetrahydrofurfuryl arc RELATED; Polybutadiene urethane dimethacrylate (CN302, NTX6513) and polybutadiene dimethacrylate (CN301, NTX6039, PRO6270) available from Sartomer Company, Inc .; Polycarbonate urethane diacrylate (ArtResin UN9200A) available from Negami Chemical Industries Co., Ltd .; Acrylated aliphatic urethane oligomers available from Radcure Specialities, Ind. (Ebecryl 230, 264, 265, 270, 284, 4830, 4833, 4834, 4835, 4866, 4881, 4883, 8402, 8800-20R, 8803, 8804); Polyester acrylate oligomers (Ebecryl 657, 770, 810, 830, 1657, 1810, 1830) available from Radcure Specialities, Ind .; And epoxy acrylate resins (CN104, 111, 112, 115, 116, 117, 118, 119, 120, 124, 136) available from Sartomer Company, Inc. In one embodiment, the acrylate resin is isobornyl acrylate, isobornyl methacrylate, lauryl acrylate, lauryl methacrylate, poly (butadiene) and methacrylate functional with acrylate functionality It is selected from the group consisting of poly (butadiene) with a.

Suitable vinyl ether resins include those having the following general structural formula:

Wherein n is 1 to 6 and X ³ is an aromatic or aliphatic group.

Examples corresponding to X ³ include poly (butadiene), poly (carbonate), poly (urethane), poly (ether), poly (ester), simple hydrocarbons, and carbonyl, carboxyl, amide, carbamate, urea or Simple hydrocarbons containing functional groups such as ethers are included. Commercially available resins include cyclohenandimethanol divinyl ether, dodecyl vinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether, dipropylene glycol divinyl ether, hexane available from International Specialty Products (ISP). Diol divinyl ether, octadecyl vinyl ether, and butanediol divinyl ether; Vectomer 4010, 4020, 4030, 4040, 4051, 4210, 4220, 4230, 4060, 5015, and the like, available from Sigma-Aldrich, Inc.

Examples of suitable poly (butadiene) resins include poly (butadiene), epoxidized poly (butadiene), maleic poly (butadiene), acrylated poly (butadiene), butadiene-styrene copolymers, and butadiene-acrylonitrile copolymers. Include. Commercially available materials include homopolymer butadiene (Ricon 130, 131, 134, 142, 150, 152, 153, 154, 156, 157, P30D) available from Sartomer Company Inc .; Random copolymers of butadiene and styrene available from Sartomer Company Inc. (Ricon 100, 181, 184); Maleated poly (butadiene) available from Sartomer Company Inc. (Ricon 130MA8, 130MA13, 130MA20, 131MA5, 131MA10, 131MA17, 131MA20, 156MA17); Acrylated poly (butadiene) available from Sartomer Company Inc. (CN302, NTX6513, CN301, NTX6039, PRO6270, Ricacryl 3100, Ricacryl 3500); Epoxidized poly (butadiene) (Polybd 600, 605) available from Sartomer Company Inc. and Epolead PB3600 available from Daicel Chemical Industries Ltd .; And acrylonitrile and butadiene copolymers (Hycar CTBN series, ATBN series, VTBN series and ETBN series) available from Hanse Chemical.

Suitable epoxy resins include bisphenols, naphthalenes, and aliphatic forms of epoxy. Commercially available materials include epoxy resins in bisphenol form (Epiclon 830LVP, 830CRP, 835LV, 850CRP) available from Dainippon Ink & Chemicals, Inc .; Epoxy (Npiclon HP4032) in naphthalene form available from Dainippon Ink & Chemicals, Inc .; Aliphatic epoxy resins (Araldite CY179, 184, 192, 175, 179) available from Ciba Specialty Chemicals; (Epoxy 1234, 249, 206) available from Union Carbide Corporation and (EHPE-3150) available from Daicel Chemical Industries, Ltd. Other suitable epoxy resins include cycloaliphatic epoxy resins, bisphenol-A type epoxy resins, bisphenol-F type epoxy resins, epoxy novolac resins, biphenyl type epoxy resins, naphthalene type epoxy resins, and dicyclopentadiene-phenol types. Epoxy resins, reactive epoxy diluents and mixtures thereof.

Suitable siliconized olefin resins are obtained by selective hydrosilylation reactions of silicone and divinyl materials and have the following general structure:

N ₁ is 2 or more, n ₂ is 1 or more, and n ₁ > n ₂ . These materials are commercially available and can be obtained, for example, from the National Starch and Chemical Company.

Suitable silicone resins include reactive silicone resins having the following general structure:

Wherein n is 0 or any integer, X ⁴ and X ⁵ are hydrogen, methyl, amine, epoxy, carboxyl, hydroxy, acrylate, methacrylate, mercapto, phenol, or vinyl functional group, R ² And R ³ may be —H, —CH ₃ , vinyl, phenyl or any hydrocarbon structure with more than two carbon atoms. Commercially available materials include KF8012, KF8002, KF8003, KF-1001, X-22-3710, KF6001, X-22-164C, KF2001 available from Shin-Etsu Silicone International Trading (Shanghai) Co., Ltd. , X-22-170DX, X-22-173DX, X-22-174DX, X-22-176DX, KF-857, KF862, KF8001, X-22-3367, and X-22-3939A.

Suitable styrene resins include resins having the following general structure:

Wherein n is at least 1, R ⁴ is —H or —CH ₃ , and X ⁶ is an aliphatic group. Examples corresponding to X ³ include poly (butadiene), poly (carbonate), poly (urethane), poly (ether), poly (ester), simple hydrocarbons, and carbonyl, carboxyl, amide, carbamate, urea or Simple hydrocarbons containing functional groups such as ethers are included. Such resins are commercially available and can be obtained, for example, from National Starch and Chemical Company or Sigma-Aldrich Co.

Suitable cyanate ester resins include those having the following general structure:

Wherein n is at least 1 and X ⁷ is a hydrocarbon group. Examples corresponding to X ⁷ include bisphenol, phenol or cresol novolac, dicyclopentadiene, polybutadiene, polycarbonate, polyurethane, polyether, or polyester. Commercially available materials include; AroCy L-10, AroCy XU366, AroCy XU371, AroCy XU378, XU71787.02L, and XU71787.07L available from Huntsman LLC; Primaset PT30, Primaset PT30 S75, Primaset PT60, Primaset PT60S, Primaset BADCY, Primaset DA230S, Primaset MethylCy, and Primaset LECY available from Lonza Group Limited; 2-allylphenol cyanate ester, 4-methoxyphenol cyanate ester, 2,2-bis (4-cyanatophenol) -1,1,1,3,3,3 available from Oakwood Products, Inc. Hexafluoropropane, bisphenol A cyanate ester, diallyl bisphenol A cyanate ester, 4-phenylphenol cyanate ester, 1,1,1-tris (4-cyanatophenyl) ethane, 4-cumylphenol cya Nate ester, 1,1-bis (4-cyanatophenyl) ethane, 2,2,3,4,4,5,5,6,6,7,7-dodecafluorooctanediol dicyanate ester , And 4,4'-bisphenol cyanate esters.

Suitable polymers for adhesive compositions are additionally polyamides, phenoxys, polybenzoxazines, acrylates, cyanate esters, bismaleimides, polyether sulfones, polyimides, benzoxazines, vinyl ethers, siliconized olefins, polyolefins, polys Benzoxazole, polyester, polystyrene, polycarbonate, polypropylene, poly (vinylchloride), polyisobutylene, polyacrylonitrile, poly (methyl methacrylate), poly (vinylacetate), poly (2-vinyl Pyridine), cis-1,4-polyisoprene, 3,4-polychloroprene, vinyl copolymer, poly (ethylene oxide), poly (ethylene glycol), polyformaldehyde, polyacetaldehyde, poly (b-propioacetone ), Poly (10-decanoate), poly (ethylene terephthalate), polycaprolactam, poly (11-undecanoamide), poly (m-phenylene-terephthalamide), poly (tetrameth) Ethylene-m-benzenesulfonamide), polyester polyarylate, poly (phenylene oxide), poly (phenylene sulfide), polysulfone, polyimide, polyetheretherketone, polyetherimide, fluorinated polyimide, polyimide Mid siloxane, poly-iosindolo-quinazolindione, polythioetherimide, poly-phenyl-quinoxaline, polyquinicsalon, imide-arylether phenylquinoxaline copolymer, polyquinoxaline, polybenzimidazole, poly Benzoxazoles, polynorbornene, poly (arylene ether), polysilane, parylene, benzocyclobutene, hydroxy (benzoxazole) copolymers, poly (silarylenesiloxanes) and polybenzimidazoles.

Other materials suitable for inclusion in the coating composition include rubber polymers such as block copolymers of monovinyl aromatic hydrocarbons and conjugated dienes, for example styrene-butadiene, styrene-butadiene-styrene (SBS), styrene- Isoprene-styrene (SIS), styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), and the like.

Other materials suitable for inclusion in the coating composition include ethylene-vinylacetate polymers, other ethylene esters and copolymers such as ethylene methacrylate, ethylene n-butylacrylate and ethylene acrylic acid; Polyolefins such as polyethylene and polypropylene; Polyvinylacetate and its random copolymers; Polyacrylates; Polyamides; Polyester; And polyvinyl alcohol and copolymers thereof.

Thermoplastic rubbers suitable for inclusion in the coating composition include carboxy-terminated butadiene-nitrile (CTBN) / epoxy adducts, acrylate rubbers, vinyl-terminated butadiene rubbers, and nitrile butadiene rubbers (NBR). In one embodiment, the CTBN epoxy adduct consists of about 20-80 wt% CTBN and about 20-80 wt% diglycidylether bisphenol A: bisphenol A epoxy (DGEBA). Various CTBN materials are available from Noveon Inc., and various bisphenol A epoxy materials are available from Dainippon Ink and Chemicals, Inc. And Shell Chemicals. NBR rubber is commercially available from Zeon Corporation.

Suitable siloxanes include elastomeric polymers comprising a backbone and pendant from the backbone, with one or more siloxane moieties conferring permeability and one or more reactive moieties capable of reacting to form new covalent bonds. Examples of suitable siloxanes include 3- (tris (trimethylsilyloxy) silyl) -propyl methacrylate, n-butyl acrylate, glycidyl methacrylate, acrylonitrile, and cyanoethyl acrylate; 3- (tris (trimethylsilyloxy) silyl) -propyl methacrylate, n-butyl acrylate, glycidyl methacrylate, and acrylonitrile; And elastomeric polymers prepared from 3- (tris (trimethylsilyloxy) silyl) -propyl methacrylate, n-butyl acrylate, glycidyl methacrylate, and cyanoethyl acrylate.

If a curing agent is required, the choice of curing agent depends on the chemical nature of the polymer used and the processing conditions used. As the curing agent, aromatic amines, cycloaliphatic amines, aliphatic amines, tertiary phosphines, triazines, metal salts, aromatic hydroxyl compounds, or combinations thereof can be used in the composition. Examples of such catalysts include imidazoles such as 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-ethyl-4-methyl Imidazole, 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-guanaminoethyl-2-methylimidazole, and imidazole Addition products of trimellitic acid; Tertiary amines such as N, N-dimethylbenzylamine, N, N-dimethylaniline, N, N-dimethyltoluidine, N, N-dimethyl-p-anisidine, p-halogeno-N, N-dimethyl Aniline, 2-N-ethylanilino ethanol, tri-n-butylamine, pyridine, quinoline, N-methylmorpholine, triethanolamine, triethylenediamine, N, N, N ', N'-tetramethylbutanediamine, N-methylpiperidine; Phenols such as phenol, cresol, xylenol, resorcin, and phloroglucin; Organometallic salts such as lead naphthenate, lead stearate, zinc naphthenate, zinc octolate, tin oleate, dibutyl tin maleate, naphthenate manganese, cobalt naphthenate, and acetyl acetone iron; And inorganic metal salts such as tin chloride, zinc chloride and aluminum chloride; Peroxides such as benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, acetyl peroxide, para-chlorobenzoyl peroxide and di-t-butyl diperphthalate; Acid anhydrides such as carboxylic anhydride, maleic anhydride, phthalic anhydride, lauric anhydride, pyromellitic anhydride, trimellitic anhydride, hexahydrophthalic anhydride, hexahydropyromellitic anhydride and hexahydrotrimellitic anhydride ; Azo compounds such as azoisobutylonitrile, 2,2'-azobispropane, m, m'-azocystyrene, hydrozones, and mixtures thereof.

In another embodiment, the cure accelerator is triphenylphosphine, alkyl-substituted imidazole, imidazolium salt, onium salt, quaternary phosphonium compound, onium borate, metal chelate, 1,8-diazacyclo [5.4. 0] undex-7-ene or a mixture thereof.

In yet another embodiment, the curing agent may be either a free radical initiator or a cationic initiator, depending on which of the radical curable resin or the ionic curable resin is selected. If a free radical initiator is used, the free radical initiator will be present in an effective amount. The effective amount is typically 0.1-10% by weight of organic compound (excluding any fillers that may be present). Suitable free radical initiators include peroxides such as butyl peroctoate and dicumyl peroxide, and 2,2'-azobis (2-methyl-propynnitrile) and 2,2'-azobis (2-methyl- Azo compounds such as butanenitrile).

If a cationic initiator is used, the cationic initiator will be present in an effective amount. The effective amount is typically 0.1 to 10% by weight of organic compound (excluding any fillers that may be present). Preferred cation curing agents include dicyandiamide, phenol novolac, adipic dihydrazide, diallyl melamine, diamino malonitrile, BF3-amine complexes, amine salts and modified imidazole compounds.

Metal compounds may also be used as cure accelerators for cyanate ester systems, including but not limited to metal naphthenates, metal acetylacetonates (chelates), metal octoates, metal acetates, metal halides, metal imidazole complexes, and Metal amine complexes.

Other cure accelerators that may be included in the coating formulations include triphenylphosphine, alkyl-substituted imidazoles, imidazolium salts, and onium borate.

In some cases, it may be desirable to use more than one type of transition agent in an adhesive composition. For example, both a cationic initiator and a free radical initiator may be preferred, in which case both free radical curable resins and ionic curable resins may be used in the composition. Such compositions contain an effective amount of initiator for each type of resin. Such compositions allow, for example, the curing process to be initiated by cationic initiation with UV irradiation and completed by free radical initiation when heat is applied in a later treatment step.

If the coating contains a solvent, a drying and / or B-stage processing step will typically be required. The time and temperature required to achieve this will vary depending on the solvent and coating composition used and can be determined by the practitioner without undue experimentation. Drying and / or B-stage processing can be carried out as a separate step from the curing of the coating (if the coating is cured) or as a separate process step.

Even if the coating contains no solvent, it may be desirable to B-stage or partially enhance the coating. This can be done prior to curing the coating to make it non-tacky so that additional processing can be performed before the coating is fully cured.

The coating may or may not require curing depending on the purpose and composition of the coating. If the coating needs to be cured, curing may be accomplished at an individual process step or with another processing operation such as solder reflow. Curing may be performed at the wafer level or at the die level, depending on the purpose of the coating, the composition of the coating, and the manufacturing process used.

When using the curing step, depending on the particular resin chemistry and the curing agent selected, the curing temperature is generally in the range from 80 to 250 ° C. and the curing can take place in a few seconds to within 120 minutes. The time and temperature of the curing profile for each coating composition can vary and different compositions can be designed to provide a curing profile suitable for a particular industrial manufacturing process.

Depending on the end application, one or more fillers may be included in the coating composition, which is usually added to improve flowability and reduce stress. To coat the active side of the wafer, the filler will be electrically nonconductive. Examples of suitable nonconductive fillers include alumina, aluminum hydroxide, silica, vermiculite, mica, ulastonite, calcium carbonate, titania, sand, glass, barium sulfate, zirconium, carbon black, organic fillers, and halogenated ethylene polymers, for example Examples include tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, vinyl fluoride, vinylidene chloride, and vinyl chloride. The filler particles can have any suitable size from nano size up to several mm. The selection of such sizes for any particular use is included in the expert's knowledge. The filler may be present in an amount from 0 to 95% by weight of the total amount of the composition.

In one embodiment, a fluxing agent is added to the coating composition. Fluxing agents mainly remove metal oxides and prevent re-oxidation of solder bumps. The choice of fluxing agent depends on the chemical properties of the resin and the metallurgical properties of the bumps used. However, some of the key requirements for fluxing agents are that they must not affect the curing of the coating resin, must not be excessively corrosive, must not be excessively released during reflow, and must be compatible with the resin. And / or the flux residue must be compatible with the resin.

Examples of suitable fluxing agents are compounds containing one or more hydroxyl groups (-OH), or carboxyl groups (-COOH) or both, such as organic carboxylic acids, anhydrides, and alcohols, such as rosin gum, dodecanedioic acid ( Commercially available from Aldrich under the tradename Corfree M2), sebacic acid, polysebacic acid anhydride, maleic acid, hexahydrophthalic anhydride, methyl nuxahydrophthalic anhydride, ethylene glycol, glycerin, tartaric acid, adipic acid, citric acid, malic acid , Glutaric acid, glycerol, 3- [bis (glycidyloxymethyl) methoxy] -1,2-propanediol, D-ribose, D-cellobiose, cellulose, 3-cyclo-hexane-1,1- Dimethanol; Amine fluxing agents such as aliphatic amines having 1 to 10 carbon atoms, for example trimethylamine, triethylamine, n-propylamine, n-butylamine, isobutylamine, sec-butylamine, t-butylamine, n-amylamine, sec-amylamine, 2-ethylbutylamine, n-heptylamine, 2-ethylhexylamine, n-octylamine, and t-octylamine; Epoxy resins using a crosslinking agent having fluxing properties. Other fluxing agents include organic alcohols. Fluxing agents also include (i) compounds with aromatic rings, (ii) one or more —OH, —NHR, where R is hydrogen or lower alkyl, or compounds with —SH groups, and (iii) electron-deodorization on aromatic rings. Or a compound with an electron-donating substituent, and (iv) a compound without an amino group. The fluxing agent will be present in an effective amount, with typical effective amounts ranging from 1 to 30% by weight.

In another embodiment, a coupling agent can be added to the coating composition. Typically, the coupling agent is a silane, for example an epoxy type silane coupling agent, an amine type silane coupling agent, or a mercapto type silane coupling agent. If a coupling agent is used, the amount used will be an effective amount, with a typical effective amount of up to 5% by weight.

In another embodiment, a surfactant can be added to the coating composition. Suitable surfactants include organic acrylic polymers, silicones, polyethylene glycols, polyoxyethylene / polyoxypropylene block copolymers, ethylene diamine-based polyoxyethylene / polyoxypropylene block copolymers, polyol-based polyoxyalkylenes, fatty acid alcohols Polyoxyalkylenes, fatty acid alcohol-based polyoxyalkylene alkyl ethers, and mixtures thereof. If used, surfactants are used in effective amounts, with typical effective amounts of up to 5% by weight.

In another embodiment, wetting agents may be included in the coating composition. The choice of wetting agent depends on the application requirements and the chemical nature of the resin used. If used, wetting agents are used in effective amounts, with typical effective amounts of up to 5% by weight. Examples of suitable wetting agents include Fluorad FC-4430 fluorosurfactant available from 3M, Clariant Fluowet OTN available from Rhom and Haas, BYK W-990, Surfynol 104 surfactant, Crompton Silwet L-7280, Triton X100, preferred Propylene glycol, gamma-butyrolactone, castor oil, glycerin or other fatty acids and silanes having an Mw greater than 240.

In another embodiment, flow control agents may be included in the coating composition. The choice of flow regulator depends on the application requirements and the chemical nature of the resin used. If used, flow regulators are present in effective amounts; The effective amount is 5% by weight or less. Examples of suitable flow regulators include Cab-O-Sil TS720, available from Cabot, Aerosil R202 or R972, available from Degussa, fumed silica, fumed alumina, or fumed metal oxides.

In another embodiment, an adhesion promoter may be included in the coating composition. The choice of adhesion promoter depends on the application requirements and the chemical nature of the resin used. When used, the adhesion promoter is used in an effective amount, and the effective amount is 5% by weight or less. Examples of suitable adhesion promoters include silane coupling agents such as Z6040 epoxy silane or Z6020 amine silane available from Dow Corning; A186 silane, A187 silane, A174 silane or A1289 available from OSI Silquest; Organosilane Sl264 available from Degussa; Johoku Chemical CBT-1 carbobenzotriazole available from Johoku Chemical; Functional triazoles; Thiazole; Titanate; And zirconates.

In another embodiment, an air release agent (antifoam) can be added to the coating composition. The choice of air release agent depends on the application requirements and the chemistry of the resin used. If used, an air release agent is used in an effective amount, with a typical effective amount of up to 5% by weight. Examples of suitable air release agents include Antifoam 1400, DuPont Modoflow, and BYK A-510 available from Dow Corning.

In some embodiments, such compositions are formulated with a tacky resin to enhance adhesion and introduce tack; Examples of the tacky resin include resins that are natural products and modified natural product resins; Polyterpene resins; Phenolic modified terpene resins; Coumarone-indene resin; Aliphatic and aromatic petroleum hydrocarbon resins; Phthalate esters; Hydrogenated hydrocarbons, hydrogenated rosin and hydrogenated rosin esters.

In some embodiments, the adhesive composition may include other components, such as diluents such as liquid polybutene or polypropylene; Petroleum waxes such as paraffin and microcrystalline wax, polyethylene grease, hydrogenated animal, fish and vegetable fats, mineral oils and synthetic waxes, naphthenic or paraffinic mineral oils and the like.

In some embodiments, a single functional reactive diluent may be included to gradually delay the increase in viscosity without adversely affecting the properties of the cured coating. Suitable diluents are p-tert-butylphenyl glycidyl ether, allyl glycidyl ether, glycerol diglycidyl ether, glycidyl ethers of alkyl phenols (commercially available as Cardolite NC513 from Cardolite Corporation), and butane Although diglycidyl ether (commercially available as BDGE from Aldrich), other diluents may be used.

Other additives such as stabilizers, antioxidants, impact modifiers, and colorants may also be added to the coating formulations in forms and amounts known in the art.

Common solvents that readily dissolve the resin and have a suitable boiling point in the range of 25 ° C. to 230 ° C. can be used in the present application. Examples of solvents that can be used include ketones, esters, alcohols, ethers, and other stable common solvents. Suitable solvents include γ-butyrolactone, propylene glycol methyl ethyl acetate (PGMEA), and 4-methyl-2-pentanone.

If the coating is curable, the coating can be cured by thermal exposure, ultraviolet (UV) or microwave irradiation, or a combination thereof. Curing conditions are adjusted to the coating formulation and can be readily determined by the practitioner. In addition, the composition may or may not be B-stage processed depending on the application requirements.

The front side or active side of the wafer is coated by any means suitable for uniformly applying the material to the bumped wafer, including but not limited to stencil printing, spin coating, curtain coating, Meniscus coating, or jet dispensing. Coating temperature, pressure, speed, and other coating conditions are determined by the method used and the coating applied and can be determined by the skilled practitioner without undue experimentation. The coating material is applied to the wafer to a thickness less than, equal to, or higher than the height of the solder bumps, depending on the application method used, the coating material used, and the requirements of the particular semiconductor package. In the case of a coating free of solvent, the coating thickness is typically equal to the height of the exposed portion of the bump. In the case of coatings containing solvents, the coating thickness is typically higher than the exposed portion of the bumps. That is, the coating partially or completely covers the repellent material. After the solvent is removed, the final coating thickness is typically equal to the exposed portion of the solder bumps.

The coating is hardened to enable subsequent processing steps such as backgrinding, application of backside protection, dicing, singulation, and die attach. The hardening method used depends on the coating selected and the manufacturing method used. In the case of thermoplastic coatings, the coated wafer is cooled to a temperature below the melting point of the thermoplastic material. In the case of B-stageable coatings, hardening is achieved by B-stage processing of the coating with either heat or UV radiation. Thermosetting coatings are hardened by exposure to heat or UV radiation causing curing of the coating. The conditions required for hardening the coating are readily determined by the skilled practitioner without undue experimentation.

Optionally, once the coating is hardened, the repellent material can be removed from the upper surface of the bumps. Typically, the removal is by heat melting and / or volatilization of the repellent material. When thermal B-stage processable and / or thermally curable coating materials are used, removal of the repellent material may be carried out in the same heating process as used for hardening the coating, or in a separate heating step. Depending on the metallurgical nature of the bumps, the package structure, the nature of the repellent material, and the attachment device used, it may not be necessary to remove the repellent material prior to die attach and solder bump reflow. In some cases, such as thermal compression bonding, the repellent material will be physically transferred by heat, pressure, or a combination of heat and pressure when the die is attached to the substrate to form a solder joint. The repellent material may also be removed by plasma cleaning (etching with ionizing gas) or cleaning in an ultrasonic bath with surfactant or soap.

After the coating is hardened, the wafers are diced and singulated to become individual dies by traditional processes. The coated die can be attached by any conventional means, including pick and place and thermal compression bonding. In the case of pick and place, a solder-on-pad or flux-on-pad can be implemented to assist in alignment and fluxing in the reflow process.

Example

Examples 1-5 were prepared using a coating formulation containing 13 weight percent bisphenol-A epoxy, 22 weight percent gamma-butyrolactone and 51 weight percent silica filler. The remaining 14% by weight of the coating formulation was a combination of a curing agent, an adhesion promoter, and other additives commonly used in adhesive formulations. The coating had a viscosity of 5100 cP and a thixotropic coefficient of 1.5. One of the wafers was coated using spin coating without using the method of the present invention (ie, without applying a repellent material on top of the bumps), which is referred to as Comparative Example 1. The method of the present invention was used in Examples 1-4. In Example 2, a wafer with 240 μm bumps was used and the entire surface of the bumps was covered with a repellent material. In Example 3, the bump was 130 μm and the repellent material was applied only to the top of the bump. In Example 4, the bump was 450 μm and the repellent material was applied to 200 μm above the bump height. In Example 5, five wafers were tested for surface energy properties and compared relative dewetting performance using the method of the present invention.

Comparative example  One - Repulsive  No substance

A 6 "silicon wafer formed with a thickness of 450 mu m and Sn / Ag / Cu bumps arranged at a height of 240 mu m and 300 mu m pitch was spin coated to a depth of 200 mu m using a solvent-based epoxy material. The spin coating was N _2. The atmosphere was run at room temperature under ambient conditions, where the profile of the speed cycle was 15 seconds at 350 rpm and then 5 seconds at 800 rpm.The solvent was removed by the B-stage step at 135 ° C. for 20 minutes, thereby hardening the non-tacky coating. Next, the wafer and bumps were examined by SEM with a backscattered electron detector The bumps were almost completely covered with a coating, which appeared black on the SEM image, and a very small amount of solder bumps. Only appeared white.

Example  2-method of the invention ( Repulsive  Substance use)

A 6 "silicon wafer was prepared according to the method of the present invention having a thickness of 450 mu m and Sn / Ag / Cu bumps arranged at a pitch of 240 mu m and 300 mu m in height. The repellent material used was a paraffin wax sold under the trade name Parowax. The melting point was 53 ° C. The application of the repellent material was carried out so that the entire surface of the bump was covered by pressing the bumped side of the wafer against a pad of paper saturated with paraffin wax at 135 ° C. The depth of the press was applied. The wax was hardened by cooling to room temperature to form a smooth coating on the bumps, then the wafers and bumps were subjected to SEM with a backscattered electron detector from 45 × 150 The wax covered the solder bumps and appeared black in the image The front side (bump side) of the wafer was spin coated with a solvent-based epoxy material. Spin coating was performed at room temperature under N ₂ atmosphere, where the profile of the speed cycle was 150 seconds at 350 rpm and then 5 seconds at 800 rpm The solvent was removed by a B-stage step of 20 minutes at 135 ° C. A hardened, non-stick coating was formed, measuring 190 μm (measured upwards from the surface of the wafer) The B-stage also melted the wax to expose the bumps, leaving a minimum amount of wax at the tip of the solder bumps. The wafers and bumps were then examined at a magnification of 45 × to 150 × using an SEM with a backscattered electron detector The bumps were almost completely exposed (shown as white in the SEM image), with very small amounts of wax or Coating residues were seen (black on SEM image).

Example  3-method of the present invention ( Repulsive  Substance use)

A 6 "silicon wafer was prepared according to the method of the present invention, formed by having a thickness of 450 mu m and Sn63 / 37 Pb bumps arranged at a pitch of 130 mu m and 190 mu m in height. The repellent material was pressed against the bumped side of the wafer by pressing a pad of paper saturated with paraffin wax at 135 ° C. to a depth of 50 μm (top of the bump from the top of the bump to the wafer). The depth of the press was controlled by the shim The wax was hardened by cooling to room temperature to form a smooth coating on the bump The wafer and bump were then SEM with backscattered electron detector The test was carried out at a magnification of 150 × with the wax covering the top of the solder bumps and appearing black in the image and the solder bumps appearing white. The front side (bump side) of the wafer was then spin coated with a solvent-based epoxy material Spin coating was performed at room temperature under an N ₂ atmosphere, with the profile of the speed cycle being 60 seconds at 800 rpm and then 30 at 1200 rpm. The solvent was removed by a 20-minute B-stage step at 135 ° C. to form a hardened non-stick coating having a thickness of 90 μm (measured upwards from the surface of the wafer). The wax was melted to expose the bumps, and a minimum amount of wax remained at the tip of the solder bumps. It was almost completely exposed (white in the SEM image), and very little wax or coating residue was seen (black in the SEM image).

Example 4 Method of the Invention (Using Repellent Material)

A single bumped silicon die formed by arranging Sn / Ag / Cu bumps having a measured thickness of 450 μm and a measured height of 475 μm at a 190 μm pitch was prepared according to the method of the present invention. The repellent material used was paraffin wax sold under the name Parowax, having a melting point of 53 ° C. The repellent material was applied to a depth of about 200 μm (measured downward from the top of the bump to the die) by manually pressing the bumped side of the die against a paper pad saturated with paraffin wax at 100 ° C. The depth of the press was adjusted by the shim. The wax was hardened by cooling to room temperature to form a smooth coating on the bumps. Subsequently, the die and the bumps were examined at a magnification of 35 × using a SEM equipped with a backscattered electron detector. The wax covered the tip of the solder bumps and appeared black on the burn, and the solder bumps appeared white. The front side (bump side) of the die was spin coated with a solvent-based epoxy material. Spin coating was performed at ambient temperature under ambient atmosphere, with the profile of the speed cycle being 150 seconds at 350 rpm and then 5 seconds at 800 rpm. The solvent was removed by a B-stage step at 135 ° C. for 20 minutes to form a hardened, non-stick coating. The B-stage process also melted the wax to expose the bumps, leaving a minimum amount of wax at the tip of the solder bumps. Subsequently, the wafer and the bump were examined at a magnification of 35 × using a SEM equipped with a backscattered electron detector. The bumps were almost completely exposed (white on the SEM image) and very small amounts of wax or coating residues were seen (black on the SEM image).

Example 5-Surface Energy Characteristics

The effectiveness of the repellent material in dewetting the coating from the bumps is affected by both dispersive (or nonpolar) and polar interactions between the coating and the repellent material. By conducting a full surface energy characterization of the material, the effects of these interactions were identified and quantified.

A Kruss Tensiometer was used to measure the contact angle for the calculation of surface energy. Contact angle measurements were performed on three repulsive materials (paraffin wax Parowax, Clarus CSX Microblend 35, and Accublend M300) using a liquid of known surface energy. The liquids used were deionized water, hexane, glycerol, hexyl ester bismaleimide, and methyl-ethyl ketone. The repellent material was cast into flat circular discs 2 cm thick. On the sample stage of the crus surface tension gauge, a sessile droplet (diameter <2 mm) was placed on the surface of the disk. All measurements were performed at room temperature. CCD video camera modules were used to image the droplets on the disk surface. Kruss' Drop Shape Analysis software was used to detect the baseline and measure the contact angle using the Tangent-1 method. The measured contact angles are shown in Table 1.

Table 1-Measurement of contact angle of various liquids on different repulsive materials surfaces

water Glycerol Hexane MEK SRM-1  Parowax 108.6 109.2 0 28.4 64.5  AccuBlend M-300 91.2 100.2 0 3.3 55.2  Microblend 101.6 94.2 0 3.12 54.9

Similarly, the solvent-based epoxy coatings (Material A) used in Examples 1-3 were tested for contact angles on substrates of the following known surface properties: glass, silicone, bismaleimide-triazine (BT), nylon 66, and polyethylene. The immobilized droplets of Material A (uncured) were placed on a Krus surface tension meter sample stage at room temperature and the contact angle was measured. The contact angles are shown in Table 2.

Table 2-Measurement of contact angle of material A on a substrate of known surface properties

 Glass Polished Silicone  BT  nylon  Polyethylene  Substance A 43.9 35.7 50.9 42 71.2

Surface properties were calculated using the contact angle measurements. The total surface energy was divided into nonpolar dispersible components (expressed as γ ^LW ) and polar components (γ ^{+ for} acid and γ ^-for basic). Using the contact angle θ between the measured liquid (L) and solid (S), the following equation was used to analyze the relationship between the contact angle and the solid / liquid surface properties:

은 공지된 것이고, 접촉각 θ은 측정된 것이며, 공지된 성질의 액체/고체를 사용하여 3회 이상 측정했다. 이로써, 미지의 고체/액체의 세 가지 표면 성질

을 계산할 수 있었다. 이러한 계산 결과를 표 3에 나타낸다.In this example, the surface properties of either solid or liquid

Is known and the contact angle θ is measured and measured three or more times using liquids / solids of known properties. This allows three surface properties of unknown solids / liquids.

Could be calculated. Table 3 shows the results of these calculations.

Table 3-Surface energy characterization for coatings and repellent materials

Total (mN / m) Polarity (mN / m) Dispersibility (mN / m) Acid (mN / m) Basic (mN / m)  Substance A 47.5 21.3 26.2 4.7 24.1  Parowax 26.7 5.8 20.9 2.9 2.9  AccuBlend M-300 32 11.9 20.1 5.8 6.1  Microblend 37.2 17 20.2 14.6 4.9

To test the correlation between dewetting (or repulsive) performance and surface energy properties, the effects of dewetting on dummy die with 240 μm bumps were examined using three repulsive materials. The top of the bump on the die was coated to cover the entire surface area of the bump by pressing the bumped side of the wafer against a pad of paper saturated with paraffin wax at 135 ° C. Samples were prepared using three waxes, Parowax, Accu-blend M-300, and Microblend, respectively. The depth of the press was adjusted by the shim. The wax was cooled to room temperature and then hardened to form a smooth coating on the bumps. Next, material A was spin coated on each of these dies. The spin coating profile included a speed cycle of 15 seconds at 350 rpm followed by 5 seconds at 800 rpm. The solvent was removed from the coating by a B-stage step at 135 ° C. for 20 minutes to form a hardened, non-stick coating.

The degree of dewetting of the coating material from the solder bump tip was measured by calculating the exposed bump area through digital gray scale analysis, based on a bump diameter of 240 μm at a sample area of 22 bumps. The average percentage of exposed bump area was as follows: Parowax 97.4%, Accublend M-300 53%, Microblend <1%.

Relative dewetting performance was consistent with the trend of surface energy (lowest to highest), and wax with lower surface energy had the greatest dewetting effect. Paraffin wax had the largest difference in total surface energy compared to material A. The smallest difference between the surface energy of the wax and material A was found to be the case of Microblend.

Since the dispersible components of surface energy were similar for all the repellent materials tested, the difference in dewetting performance was apparently due to the relatively acidic nature of the Microblend interacting with the properties of the more basic material A. Do. In comparison, Parowax and Accublend had less acidic components in their surface energy and, therefore, had a greater effect on repulsion of relatively basic substance A.

As will be apparent to those skilled in the art, various modifications and changes of the present invention can be made without departing from the spirit and scope of the invention. The specific embodiments described herein are for illustrative purposes only, and the invention is to be limited only by the appended claims and the equivalents of all scopes to which such claims are entitled.

Claims (14)

A method of coating the active side of a semiconductor wafer on which solder bumps are laminated, (a) preparing a semiconductor wafer having a front side that is active and has a stack of solder bumps and a back side opposite the front side, (b) applying a repellent material on top of the solder bumps, (c) coating the front side of the wafer with a coating material, (d) hardening the coating material, and (e) optionally, removing the repellent material from the bumps It includes, the coating method of the semiconductor wafer. The method of claim 1, And the repellent material is wax. The method of claim 1, Wherein the repellent material is applied at 5% to 100% of the total height of the solder bumps. The method of claim 1, And a difference of 5 mN / m between the surface energy of the repellent material and the surface energy of the coating material. The method of claim 1, Wherein said repellent material is nonpolar and said coating is polar. The method of claim 1, And the repellent material has a melting point of 40 ° C to 300 ° C. The method of claim 1, Wherein the repellent material is applied by dipping the top of the bump on the bumped wafer into a pad saturated with the repellent material. The method of claim 1, Wherein the repellent material is applied by immersing an upper portion of the solder bump on the wafer into a reservoir of repellent material in a liquid state. The method of claim 1, And the coating material is applied by spin coating. The method of claim 1, And the coating material is applied by stencil printing. The method of claim 1, And the coating material is selected from the group consisting of bismaleimide, epoxy, acrylate, and combinations thereof. The method of claim 1, The coating material of claim 1, wherein the coating material is B-stage processable. The method of claim 1, The coating method of the semiconductor wafer, wherein the coating material is UV curable. A semiconductor wafer having a front side that is active and has solder bumps laminated thereon and a back side opposite the front side, The front side is a) active, b) bump bumped, c) a semiconductor wafer coated by the following process: i) applying a repellent material on top of the solder bumps, ii) coating the front side of the wafer with a coating material, iii) hardening the coating material, and iv) optionally, melting and / or evaporating the repellent material.

Images