JP2017120866A - Solder bump-forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder bump-forming method which enables the formation of a minute solder bump while suppressing missing bump.SOLUTION: A solder bump-forming method according to the present invention is a method for forming solder bumps on a plurality of electrode pads 12 formed on a surface of a wiring board 1. The method comprises: a temporary resist film formation step for forming a temporary resist film 2 by coating the wiring board 1 with a photosensitive resin composition to form a coating film of which the haze value at 385 nm 65% or more, exposing the coating film to light and then developing the coating film, where the temporary resist film has an opening corresponding to each electrode pad 12 provided therein, an end portion of the opening is taper in sectional shape, and a taper angle θ in the sectional shape is 75° or smaller; a solder bump formation step for forming the solder bumps by filling a solder paste in each opening followed by a reflow process; and a temporary resist film delamination step for delaminating the temporary resist film 2 from the wiring board 1.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for forming solder bumps.

Due to the demand for high-density mounting of electronic components, the mounting method of electronic components has changed from a face-up mounting method using a wire bonding method to a face-down mounting method using solder bumps. Conventionally, a so-called plating method or vapor deposition method has been employed as a method for forming solder bumps. However, these methods have problems in that, in addition to requiring large and expensive equipment, it is difficult to control the height of the solder bumps and the solder composition.
In order to solve these problems, a solder bump forming method (so-called film method) using a dry film and a solder paste has been proposed (for example, Patent Document 1).

JP 2000-208911 A

  Due to the demand for high-density mounting of electronic components, solder bumps tend to be miniaturized and narrow pitch. In order to meet this requirement, the film method requires further miniaturization of the opening of the dry film. However, in the method described in Patent Document 1, when the size of the opening advances, when the solder paste enters the opening, the inside of the opening cannot be completely filled with the solder paste, and an appropriate amount of printing cannot be obtained. There is. Further, since the solder paste is not in contact with the bottom electrode of the opening during printing, molten solder is clogged in the opening of the film during heating, and so-called missing bumps are generated in which solder bumps are not formed on the wiring board.

  Then, an object of this invention is to provide the formation method of the solder bump which can form a minute solder bump, suppressing a missing bump.

In order to solve the above-mentioned problems, the present invention provides the following solder bump forming method.
The solder bump forming method of the present invention is a solder bump forming method for forming solder bumps on a plurality of electrode pads formed on the surface of a wiring board, and a photosensitive resin composition is applied onto the wiring board. Then, a coating film having a haze value at 385 nm of 65% or more is formed, and after developing the coating film, an opening corresponding to the electrode pad is provided, and an end of the opening is formed. A temporary resist film forming step of forming a temporary resist film having a tapered cross-sectional shape and a taper angle of 75 ° or less in the cross-sectional shape; and filling the opening with a solder paste and performing a reflow process. And a solder bump forming step for forming a solder bump, and a temporary resist film peeling step for peeling the temporary resist film from the wiring board. It is the law.

In the method for forming a solder bump of the present invention, it is preferable that a haze value at 385 nm of the coating film is 75% or more and a taper angle in the cross-sectional shape is 70 ° or less.
In the method for forming a solder bump of the present invention, it is preferable that a haze value at 385 nm of the coating film is 80% or more and a taper angle in the cross-sectional shape is 60 ° or less.
In the method for forming solder bumps of the present invention, the coating film is preferably exposed by a direct drawing exposure apparatus.

  ADVANTAGE OF THE INVENTION According to this invention, the formation method of the solder bump which can form a minute solder bump can be provided, suppressing a missing bump.

It is the schematic which shows the wiring board used for this invention. In this invention, it is the schematic which shows the state which formed the coating film of the photosensitive resin composition on the wiring board. In this invention, it is the schematic which shows the state which has exposed the coating film of the photosensitive resin composition. In this invention, it is the schematic which shows the state which gave the development process to the coating film after exposure processing, provided the opening part, and formed the temporary resist film. In this invention, it is the schematic which shows the method of filling a solder paste from the temporary resist film. In this invention, it is the schematic which shows the state which filled the solder paste in the opening part. In this invention, it is the schematic which shows the state which gave the reflow process and formed the solder bump. In this invention, it is the schematic which shows the state which peeled the temporary resist film from the wiring board.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the contents of the embodiment. In the drawings, there are portions enlarged or reduced for easy explanation.

[Method of forming solder bumps]
The method for forming solder bumps of this embodiment is a method for forming solder bumps in which solder bumps 3 are formed on a plurality of electrode pads 12 formed on the surface of a wiring board 1, as shown in FIGS. The method includes a temporary resist film forming step, a solder bump forming step, and a temporary resist film peeling step described below.
First, a wiring board used in the method for forming solder bumps of this embodiment will be described.

(Wiring board)
As shown in FIG. 1, the wiring substrate 1 includes an insulating base material 11, an electrode pad 12, and a solder resist film 13. The wiring substrate 1 may be a multilayer substrate including the internal electrodes 14 and the interlayer insulating layer 15. The electrode pad 12 may be provided on the internal electrode 14 via the interlayer insulating layer 15, but may be electrically connected to the internal electrode 14 by a blind via.
As the insulating substrate 11, a known material can be used as appropriate, and examples thereof include a glass epoxy substrate, a polyimide substrate, and a silicon substrate.
The electrode pad 12 is formed on the surface of the wiring board 1 and is used for electrical connection with other electronic components. Although the material of the electrode pad 12 is not specifically limited, Copper, silver, tin, gold | metal | money, nickel, palladium etc. are mentioned. The electrode pad 12 may be formed of a single layer or may be formed of a plurality of layers using a plurality of materials.
The solder resist film 13 is formed on the surface of the wiring board 1 and prevents a short circuit between the wirings of the wiring board 1. As the solder resist film 13, a known one can be used as appropriate. Note that the solder resist film 13 is a permanent resist that exists semipermanently on the surface of the wiring substrate 1 and is different from the temporary resist film 2 described below.
As the interlayer insulating layer 15 on the internal electrode 14, a known one can be used as appropriate.

  The temporary resist film 2 refers to a temporary resist film that exists only during the execution of the solder bump forming method of the present invention. The temporary resist film 2 needs to have a certain resistance to the molten solder and be peelable after the solder bumps are formed. The temporary resist film 2 is formed using a photosensitive resin composition described below.

(Temporary resist film formation process)
In the temporary resist film forming step, the temporary resist film 2 provided with openings 21 corresponding to the electrode pads 12 is formed on the wiring substrate 1. Specifically, the temporary resist film 2 provided with the opening 21 corresponding to the electrode pad 12 can be formed by the following method.
In the temporary resist film forming step, first, as shown in FIG. 2, a photosensitive resin composition is applied to the entire surface of the wiring substrate 1, and then preliminarily dried to form a coating film 2a.
The photosensitive resin composition will be described later.
Examples of the method for applying the coating film 2a include screen printing, spray coater, bar coater, applicator, blade coater, knife coater, roll coater, and gravure coater.
Preliminary drying conditions vary depending on the type of the photosensitive resin composition and are not particularly limited. For example, the preliminary drying may be performed at a temperature of about 60 to 80 ° C. for about 15 to 60 minutes. By such preliminary drying, the solvent and the like in the photosensitive resin composition are volatilized to form a tack-free coating film 2a.
Although the thickness of the coating film 2a is not specifically limited, Usually, it is 5 micrometers or more and 200 micrometers or less, Preferably, they are 10 micrometers or more and 70 micrometers or less.

  In the present embodiment, the haze value at 385 nm of the coating film 2a needs to be 65% or more. With this haze value, the taper angle in the cross-sectional shape of the end of the opening can be made 75 ° or less. Further, from the viewpoint of reducing the taper angle, the haze value at 385 nm of the coating film 2a is preferably 75% or more, and more preferably 80% or more.

In addition, the haze value in 385 nm of the coating film 2a can be calculated | required as follows.
That is, a photosensitive resin composition is applied to a glass substrate and dried to obtain a sample (application conditions are the same as application conditions to an electronic substrate). Then, using an integrating sphere with a Hitachi spectrophotometer U-4100, the transmittance at a wavelength of 385 nm at a distance of 0 mm and 350 mm from the integrating sphere of the obtained sample is measured. And from these measured values, a haze value (%) can be calculated by the following mathematical formula (F1).
Haze value (%) = [(T _total− T _flat ) / T _total ] × 100 (F1)
T _total : transmittance at a distance of 0 mm from the integrating sphere T _flat : transmittance at a distance of 350 mm from the integrating sphere

Moreover, the following methods are mentioned as a method of adjusting the haze value in 385 nm of the coating film 2a to the range mentioned above.
The haze value can be adjusted by changing the composition of the photosensitive resin composition described later. For example, if a filler is added to the photosensitive resin composition, the haze value tends to increase. Moreover, it exists in the tendency for a haze value to become large, so that the compounding quantity of this filler is increased. Further, the haze value varies depending on the type and blending amount of the antifoaming agent in the photosensitive resin composition.

In the temporary resist film forming step, next, as shown in FIG. 3, the coating film 2a is exposed using an exposure apparatus.
Here, the exposure apparatus is not particularly limited, but a direct drawing exposure apparatus is preferably used from the viewpoint of adjusting the taper angle with higher accuracy.
The direct drawing exposure apparatus and the light source thereof are not particularly limited. For example, a combination of a direct drawing exposure machine “DiIMPACT Mms80” manufactured by Oak Co., Ltd.) and a short arc UV lamp (ultraviolet light having a wavelength of 300 to 500 nm), Hitachi Via Mechanics Co., Ltd. Examples include a combination of direct drawing exposure and ultraviolet laser having a wavelength of 405 nm.
The exposure amount in this exposure step can be appropriately set according to the type of photosensitive resin composition and the type of exposure apparatus. For example, the exposure amount is preferably at 10 mJ / cm ² or more 500 mJ / cm ² or less, more preferably 10 mJ / cm ² or more 200 mJ / cm ² or less.

In the temporary resist film forming step, the exposed film 2a is then developed by removing the non-exposed areas with a dilute alkaline aqueous solution. Thereby, the temporary resist film 2 which provided the opening part 21 in the coating film 2a can be formed.
Examples of the developing method include a spray method and a shower method.
Examples of the dilute alkaline aqueous solution include an aqueous sodium carbonate solution of 0.5 mass% to 5 mass%.

The coated film 2 a after development can be cured by heat treatment (sometimes referred to as “post-cure”) as necessary to improve the adhesion between the temporary resist film 2 and the solder resist film 13. Note that post-cure need not be performed.
When performing the post cure, the heat treatment condition varies depending on the type of the photosensitive resin composition and is not particularly limited. For example, the heat treatment temperature is preferably 130 ° C. or higher and 170 ° C. or lower. Moreover, it is preferable that the heat processing time is 10 minutes or more and 30 minutes or less. Furthermore, as the heat treatment furnace, a hot-air circulating dryer or the like can be employed.

As described above, as shown in FIG. 4, the temporary resist film 2 in which the opening 21 corresponding to the electrode pad 12 is provided and the cross-sectional shape of the end of the opening 21 is tapered can be formed.
In the present embodiment, the taper angle θ in the cross-sectional shape of the end portion of the opening 21 of the temporary resist film 2 needs to be 75 ° or less. If the taper angle θ is 75 ° or less, the opening 21 can be sufficiently filled with the solder paste 3a. Further, from the viewpoint of facilitating the filling of the solder paste 3a, the taper angle θ is preferably 70 ° or less, and more preferably 60 ° or less.
The taper angle θ can be obtained as shown in FIG. That is, the end of the opening 21 of the temporary resist film 2 is observed, the distance x in the plane direction of the wiring substrate 1 from the upper end to the lower end of the end of the opening 21 in the temporary resist film 2, and the temporary resist film 2 The thickness y is measured. Then, the taper angle θ can be calculated from these x and y values.

(Solder bump formation process)
In the solder bump forming step, first, the solder paste 3a is filled into the opening 21 of the temporary resist film 2.
As the solder paste 3a, a known solder paste can be used as appropriate.
As a method for filling the solder paste 3a, for example, a method using a squeegee can be employed. Specifically, as shown in FIG. 5, the solder paste 3a and the squeegee 9 on the temporary resist film 2 are arranged, and the squeegee 9 is moved on the temporary resist film 2 while sliding, as shown in FIG. In addition, the solder paste 3 a can be filled in the opening 21 of the temporary resist film 2.

In the solder bump forming step, next, a reflow process is performed to form solder bumps 3 as shown in FIG.
What is necessary is just to set the conditions of a reflow process suitably according to melting | fusing point of solder. For example, when using a Sn—Ag—Cu-based solder alloy, preheating may be performed at a temperature of 150 to 200 ° C. for 60 to 120 seconds, and a peak temperature may be set to 230 to 270 ° C.

(Temporary resist film peeling process)
In the temporary resist film peeling step, the temporary resist film 2 is peeled from the wiring board 1 as shown in FIG.
As a method for removing the temporary resist film 2, a method in which the temporary resist film 2 is dissolved and removed with an alkaline aqueous solution can be employed.
What is necessary is just to select alkaline aqueous solution suitably according to the photosensitive resin composition to be used. Examples of such an alkaline aqueous solution include an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution. Moreover, it is preferable that the density | concentration of such alkaline aqueous solution shall be 1-5 mass%, for example.

(Effect of embodiment)
According to the above embodiment, the following effects can be obtained.
(1) If the haze value at 385 nm of the coating film 2a is adjusted to a predetermined value or less, the cross-sectional shape of the end portion of the opening 21 in the temporary resist film 2 can be tapered, and the taper angle θ can be 75 ° or less. Furthermore, the taper angle θ can be further reduced by further increasing the haze value at 385 nm of the coating film 2a. Thus, according to the present embodiment, the taper angle θ in the temporary resist film 2 can be adjusted by a simple method.
(2) By setting the taper angle θ in the temporary resist film 2 to 75 ° or less, the entrance of the opening 21 of the temporary resist film 2 becomes larger. Therefore, it becomes easy to fill the solder paste 3a, and the amount of the solder paste 3a per electrode pad 12 can be increased. Even when the electrode pad 12 is very small, the missing bump can be sufficiently suppressed.

(Photosensitive resin composition)
Next, the photosensitive resin composition used for this embodiment is demonstrated.
The photosensitive resin composition used in the present embodiment contains (A) a carboxyl group-containing photosensitive resin, (B) a photopolymerization initiator, and (C) a reactive diluent. D) An epoxy compound is contained.

((A) component)
The (A) carboxyl group-containing photosensitive resin used in the present embodiment is not particularly limited, and examples thereof include a photosensitive carboxyl group-containing resin having one or more photosensitive unsaturated double bonds. As a carboxyl group-containing photosensitive resin, acrylic acid or methacrylic acid (hereinafter referred to as “(meth) acrylic acid”) is included in at least a part of the epoxy group of the multifunctional epoxy resin having two or more epoxy groups in one molecule. And a radical polymerizable unsaturated monocarboxylic acid epoxy resin such as epoxy (meth) acrylate, and then a polybasic acid or a polybasic acid in addition to the resulting hydroxyl group. Polybasic acid-modified radically polymerizable unsaturated monocarboxylic oxide epoxy resin such as polybasic acid-modified epoxy (meth) acrylate obtained by reacting the anhydride.

  Any polyfunctional epoxy resin can be used as long as it is a bifunctional or higher functional epoxy resin. Moreover, although an epoxy equivalent is not specifically limited, For example, it is 1000 or less, Preferably it is 100 or more and 500 or less. Examples of the polyfunctional epoxy resin include biphenyl type epoxy resin, naphthalene type epoxy resin, dicyclopentadiene type epoxy resin, rubber-modified epoxy resin (for example, silicone-modified epoxy resin), ε-caprolactone-modified epoxy resin, phenol novolac. Type epoxy resin (for example, epoxy resin such as bisphenol A type, bisphenol F type, bisphenol AD type), cresol novolac type epoxy resin (for example, о-cresol novolac type epoxy resin), bisphenol A novolak type epoxy resin, cyclic aliphatic Multifunctional epoxy resin, Glycidyl ester type polyfunctional epoxy resin, Glycidylamine type polyfunctional epoxy resin, Heterocyclic polyfunctional epoxy resin, Bisphenol modified novolac type epoxy resin, Multifunctional modified epoxy resin Examples thereof include a borak type epoxy resin and a condensate type epoxy resin of a phenol and an aromatic aldehyde having a phenolic hydroxyl group. Moreover, what introduce | transduced halogen atoms, such as Br and Cl, to these resin can also be used.

  The radically polymerizable unsaturated monocarboxylic acid is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, crotonic acid, and cinnamic acid. Among these, acrylic acid and methacrylic acid are preferable. The reaction method of the epoxy resin and the radically polymerizable unsaturated monocarboxylic acid is not particularly limited. For example, the epoxy resin and the radically polymerizable unsaturated monocarboxylic acid can be reacted by heating in an appropriate diluent. it can.

  The polybasic acid and the polybasic acid anhydride are those for introducing a free carboxyl group into the resin by reacting with the hydroxyl group generated by the reaction of the epoxy resin and the radical polymerizable unsaturated monocarboxylic acid. The polybasic acid or its anhydride is not particularly limited, and either saturated or unsaturated can be used. Polybasic acids include succinic acid, maleic acid, adipic acid, citric acid, phthalic acid, tetrahydrophthalic acid, 3-methyltetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, 3-ethyltetrahydrophthalic acid, 4-ethyltetrahydro Phthalic acid, hexahydrophthalic acid, 3-methylhexahydrophthalic acid, 4-methylhexahydrophthalic acid, 3-ethylhexahydrophthalic acid, 4-ethylhexahydrophthalic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid , Endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, trimellitic acid, pyromellitic acid, diglycolic acid, and the like. Examples of polybasic acid anhydrides include these anhydrides. These compounds may be used alone or in combination of two or more.

  The polybasic acid-modified unsaturated monocarboxylic oxide epoxy resin described above can also be used as a carboxyl group-containing photosensitive resin. Further, if necessary, by reacting the carboxyl group of the polybasic acid-modified unsaturated monocarboxylic oxide epoxy resin with a glycidyl compound having one or more radical polymerizable unsaturated groups and an epoxy group, a radical is obtained. It is good also as a carboxyl group-containing photosensitive resin which introduce | transduced the polymerizable unsaturated group further and improved photosensitivity.

  In this carboxyl group-containing photosensitive resin with improved photosensitivity, the radical polymerizable unsaturated group is bonded to the side chain of the polybasic acid-modified unsaturated monocarboxylic oxide epoxy resin skeleton by the reaction of the glycidyl compound. It becomes a resin having high photopolymerization reactivity and having excellent photosensitive properties. The compound having one or more radically polymerizable unsaturated groups and an epoxy group is not particularly limited, and examples thereof include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and pentaerythritol triacrylate monoglycidyl ether. In addition, you may have multiple glycidyl groups in 1 molecule. The above-mentioned compound having one or more radically polymerizable unsaturated groups and an epoxy group may be used alone or in combination of two or more.

  The acid value of the carboxyl group-containing photosensitive resin is not particularly limited. For example, it is preferably 30 mgKOH / g or more, particularly preferably 40 mgKOH / g, from the viewpoint of reliable alkali development. On the other hand, the acid value is preferably 200 mgKOH / g or less, and particularly preferably 150 mgKOH / g or less, from the viewpoint of preventing dissolution of the exposed area with an alkali developer.

  Further, the mass average molecular weight of the carboxyl group-containing photosensitive resin is not particularly limited, but for example, is preferably 3000 or more, and particularly preferably 5000 or more, from the viewpoint of toughness of the cured product and dryness to touch. preferable. On the other hand, the mass average molecular weight is preferably 200000 or less, particularly preferably 50000 or less, from the viewpoint of smooth alkali developability.

  Examples of commercially available carboxyl group-containing photosensitive resins include cyclomer (ACA) Z-251 (manufactured by Daicel Ornex Co., Ltd.), ZCR-1601H, ZAR-2000, ZFR-1122, FLX-2089 (and above). , Nippon Kayaku Co., Ltd.) and Lipoxy SP-4621 (Showa Denko). These resins may be used alone or in combination of two or more.

((B) component)
The (B) photopolymerization initiator used in the present embodiment is not particularly limited, and known ones can be used as appropriate. Examples of the photopolymerization initiator include an α-hydroxyketone photopolymerization initiator and an oxime ester photopolymerization initiator having two or more carbazole skeletons in one molecule.
Examples of the α-hydroxyketone photopolymerization initiator include 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, and 1- [4- (2-hydroxyethoxy). ) -Phenyl] -2-hydroxy-2-methyl-1-propan-1-one and 2-hydroxy-1- {4- [4- (2-hydroxy-2)
-Methyl-propionyl) -benzyl] -phenyl} -2-methyl-propan-1-one. These may be used alone or in combination of two or more. Examples of commercially available α-hydroxyketone photopolymerization initiators include Irgacure 184, Darocur 1173, Irgacure 2959, and Irgacure 127 manufactured by Ciba Specialty Chemicals.

  Examples of the oxime ester photopolymerization initiator include 1,8-octanedione, 1,8-bis [9-ethyl-6-nitro-9H-carbazol-3-yl]-, 1,8-bis (O-acetyl). Oxime) and 9- (2-ethylhexyl)-(9-ethyl-6-nitro-9H-carbazol-3-yl)-(4-((1-methoxypropan-2-yl) oxy) -2- And methylphenyl) methanone-O-acetyloxime.

  The blending amount of the photopolymerization initiator is not particularly limited. For example, the photosensitivity and resolution can be reliably improved even in a coating film containing a colorant with respect to 100 parts by mass of the carboxyl group-containing photosensitive resin. It is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more from the viewpoint of solder heat resistance, and 0.6 parts by mass or more from the viewpoint of gold plating resistance. Is particularly preferred. On the other hand, the blending amount of the photopolymerization initiator is preferably 4.0 parts by mass or less from the viewpoint of reducing outgas from the coating film with respect to 100 parts by mass of the carboxyl group-containing photosensitive resin. From this point, it is more preferably 3.0 parts by mass or less, and particularly preferably 2.0 parts by mass or less from the viewpoint of reliably preventing a decrease in brightness.

((C) component)
The (C) reactive diluent used in this embodiment is, for example, a photopolymerizable monomer and a compound having at least one polymerizable double bond per molecule. The reactive diluent can improve the photocurability of the photosensitive resin composition.

  Examples of reactive diluents include 2-hydroxyethyl (meth) acrylate, phenoxyethyl (meth) acrylate, diethylene glycol mono (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 1,4 -Butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, neopentyl glycol adipate di (meth) acrylate, hydroxypivalic acid Neopentyl glycol di (meth) acrylate, dicyclopentanyl di (meth) acrylate, caprolactone modified dicyclopentenyl di (meth) acrylate, ethylene oxide modified phosphoric acid di (meth) acrylate, Rilylated cyclohexyl di (meth) acrylate, isocyanurate di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate, pentaerythritol tri (meth) Acrylate, propylene oxide modified trimethylolpropane tri (meth) acrylate, tris (acryloxyethyl) isocyanurate, propionic acid modified dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and caprolactone modified dipenta Examples include erythritol hexa (meth) acrylate. These may be used individually by 1 type, and may mix and use 2 or more types.

  The compounding quantity of a reactive diluent is not specifically limited, For example, it is preferable that it is 2 mass parts or more and 500 mass parts or less with respect to 100 mass parts of carboxyl group-containing photosensitive resin, and 10 mass parts or more and 300 mass parts or less. It is particularly preferred that

((D) component)
The (D) epoxy compound used in the present embodiment is a compound having an epoxy group. By this epoxy compound, the crosslinking density of the cured product of the alkali-soluble transparent resin composition can be increased.
Examples of the epoxy compound include an epoxy resin. Examples of the epoxy resin include bisphenol A type epoxy resin (for example, bisphenol A type liquid epoxy resin, bisphenol A type modified flexible epoxy resin, nuclear hydrogenated bisphenol A type liquid epoxy resin), and novolak type epoxy resin (for example, phenol). Novolac type epoxy resin, o-cresol novolak type epoxy resin, p-tert-butylphenol novolak type), bisphenol F type and bisphenol S type epoxy resin (epoxy resin obtained by reacting bisphenol F and bisphenol S with epichlorohydrin), An alicyclic epoxy resin (an alicyclic epoxy resin having a cyclohexene oxide group, a tricyclodecane oxide group, a cyclopentene oxide group, etc.), a dicyclopentadiene type epoxy resin, and Adamantane type epoxy resins.

  The compounding amount of the epoxy compound is preferably 1 part by mass or more and 75 parts by mass or less from the viewpoint of obtaining sufficient curability with respect to 100 parts by mass of the carboxyl group-containing photosensitive resin. The following is more preferable.

((E) component)
In addition to the components (A) to (D) described above, (E) an antifoaming agent may be blended in the photosensitive resin composition used in the present embodiment, if necessary.
Although it does not specifically limit as an antifoamer, For example, antifoamers, such as a silicone type, a hydrocarbon type, an acrylic type, are mentioned. These may be used individually by 1 type, and may mix and use 2 or more types.
In the case of using such an antifoaming agent, the blending amount thereof is 0.01 parts by mass with respect to 100 parts by mass of the carboxyl group-containing photosensitive resin from the viewpoint of adjusting the defoaming property and the haze value to a predetermined range. The amount is preferably 10 parts by mass or less, and more preferably 0.05 parts by mass or more and 5 parts by mass or less.

((F) component)
In addition to the above-described components (A) to (E), the photosensitive resin composition used in the present embodiment may contain a filler (F) as necessary.
Examples of the filler include barium sulfate, silica, alumina, talc, and mica. These may be used individually by 1 type, and may mix and use 2 or more types.
When such a filler is used, the blending amount thereof is 1 part by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the carboxyl group-containing photosensitive resin from the viewpoint of adjusting the haze value to a predetermined range. Is preferably 5 parts by mass or more and 50 parts by mass or less.

  In the photosensitive resin composition used in the present embodiment, in addition to the above-described components (A) to (F), various additive components, for example, a solvent, a colorant, a latent curing agent, You may mix | blend antioxidant, a coupling agent, other additives (for example, mercaptocarboxylic acid ester) etc. suitably.

The solvent (non-reactive diluent) is for adjusting the viscosity and drying property of the photosensitive resin composition. Solvents include ketones (eg, methyl ethyl ketone, cyclohexanone), aromatic hydrocarbons (eg, toluene, xylene), alcohols (eg, methanol, isopropanol, cyclohexanol), alicyclic hydrocarbons (eg, cyclohexane) , Methylcyclohexane), petroleum-based solvents (eg, petroleum ether, petroleum naphtha), cellosolves (eg, cellosolve, butylcellosolve), (eg, carbitol, butylcarbitol), and esters (eg, ethyl acetate, Butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, ethyl diglycol acetate, diethylene glycol monomethyl ether acetate, diethylene glycol Roh ether acetate) and the like. These may be used individually by 1 type, and may mix and use 2 or more types.
As a compounding quantity of a solvent, it is preferable that it is 1 to 200 mass parts with respect to 100 mass parts of carboxyl group-containing photosensitive resin, and it is more preferable that it is 5 to 50 mass parts. If these compounding quantities are in the said range, the viscosity and drying property of the photosensitive resin composition can be adjusted, without affecting the various characteristics of the obtained photosensitive resin composition.

The colorant is not particularly limited, such as a pigment or a dye, and any of a white colorant, a blue colorant, a yellow colorant, and a black colorant can be used. Examples of the colorant include inorganic colorants such as titanium oxide as a white colorant, carbon black as a black colorant, and acetylene black, phthalocyanine types such as phthalocyanine green, phthalocyanine blue, and lionol blue, anthraquinone types, and the like. Organic colorants and the like. These may be used alone or in combination of two or more.
Examples of the latent curing agent include dicyandiamide (DICY) and its derivatives, melamine and its derivatives.
Known antioxidants and coupling agents can be used as appropriate.

  When using these colorants, latent curing agents, antioxidants, coupling agents and other additives, the blending amount is 0.01 parts by mass with respect to 100 parts by mass of the carboxyl group-containing photosensitive resin. The amount is preferably 10 parts by mass or less, and more preferably 0.05 parts by mass or more and 5 parts by mass or less. If the blending amount is less than the lower limit, the effects of the respective additives tend to be difficult to achieve. On the other hand, if the upper limit is exceeded, various characteristics of the resulting photosensitive resin composition tend to be lowered.

  The manufacturing method of the photosensitive resin composition of this embodiment mentioned above is not limited to a specific method. For example, after blending each of the above components in a predetermined ratio, it can be produced by mixing or mixing at room temperature with a kneading means such as a three roll, ball mill, or sand mill, or a stirring means such as a super mixer or a planetary mixer. . Further, prior to the kneading or mixing, if necessary, preliminary kneading or premixing may be performed.

[Modification of Embodiment]
The present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the above-described embodiment, the coating film is exposed by the direct drawing exposure apparatus in the temporary resist film forming step, but the present invention is not limited to this. For example, a photomask having a light-transmitting pattern other than the circuit pattern land may be brought into close contact with the pre-dried coating film of the photosensitive resin composition, and exposed to ultraviolet rays from above. .

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these examples.

((A) component)
Carboxyl group-containing photosensitive resin: trade name “Lipoxy SP-4621”, manufactured by Showa Denko KK, solid content: 62.5% by mass
((B) component)
Photopolymerization initiator: 9- (2-ethylhexyl)-(9-ethyl-6-nitro-9H-carbazol-3-yl)-(4-((1-methoxypropan-2-yl) oxy) -2- Methylphenyl) methanone-O-acetyloxime, trade name “NCI-831”, manufactured by ADEKA (component (C))
Reactive diluent: Dipentaerythritol hexaacrylate, trade name “Miramer M600”, manufactured by MIWON (component (E))
Antifoaming agent A: silicone-based antifoaming agent, trade name “KS-66”, Shin-Etsu Chemical Co., Ltd. antifoaming agent B: trade name “Floren AC-1180HF”, manufactured by Kyoeisha Chemical Co., Ltd. (component (F))
Filler A: Barium sulfate, trade name “Barium sulfate B-30”, Sakai Chemical Industry filler B: Silica, trade name “ACEMATT OK-412”, Evonik Degussa Japan (other components)
Additives: Trade name “Trimethylolpropane tristhiopropionate (TMTP)”, Sakai Chemical Co., Ltd. solvent A: Diethylene glycol monomethyl ether acetate, trade name “EDGAC”, Sanyo Chemicals Co., Ltd. solvent B: Hydrocarbon solvent, Product name "Solvesso S-150", manufactured by Ando Parachemy

[Example 1]
First, a wiring board having the following conditions was prepared.
Electrode pad diameter: 60 μm and 100 μm 2 types of electrode pad pitch: 100 μm
Insulation substrate: Made of glass fiber reinforced epoxy resin (FR-5)
Insulating base material thickness: 0.2mm
Conductor thickness: 18 μm
Next, carboxyl group-containing photosensitive resin 40 parts by mass, photopolymerization initiator 0.4 parts by mass, reactive diluent 7 parts by mass, antifoaming agent A 1.6 parts by mass, filler A 10 parts by mass, filler B 1.5 parts by mass. Part, 0.6 parts by weight of additive, 15 parts by weight of solvent A and 15 parts by weight of solvent B are premixed in a stirrer, and then mixed and dispersed at room temperature using a three-roller to obtain a photosensitive resin. A composition was obtained.
Then, the surface of the wiring board was treated with dilute sulfuric acid (5% by mass), and the obtained photosensitive resin composition was applied by a screen printing method. After coating, preliminary drying was performed at 80 ° C. for 20 minutes in a BOX furnace. After preliminary drying, using a short arc UV lamp (ultraviolet light having a wavelength of 300 to 500 nm) with an exposure apparatus (Oak direct drawing exposure machine “DiIMPACT Mms80”), an exposure amount of 15 mJ / cm ^{2 is} directly applied on the coating film. Drawing exposure. After the exposure, development was performed using a 1% by mass aqueous sodium carbonate solution at a development temperature of 30 ° C. and a spray pressure of a development pressure of 0.2 MPa to form a temporary resist film on the substrate. The thickness of the temporary resist film was 40 μm.
Next, solder paste (made by Tamura Corporation, alloy composition 96.5% Sn, 3% Ag, 0.5% Cu) is filled in the opening of the temporary resist film, and the solder paste is subjected to reflow treatment. (Preheating was performed at a temperature of 150 to 200 ° C. for 60 to 120 seconds, and a peak temperature was 240 ° C.) to form solder bumps.
Thereafter, the temporary resist film was dissolved with a 3% aqueous potassium hydroxide solution (temperature: 50 ° C.) to remove the temporary resist film 2. In this manner, a bumped wiring board in which a plurality of solder bumps were formed on the electrode pads of the wiring board was produced.

[Examples 2 to 4]
A photosensitive resin composition and a bumped wiring board were obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
[Comparative Examples 1 and 2]
A photosensitive resin composition and a bumped wiring board were obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.

<Evaluation of solder bump formation method>
Evaluation of the solder bump formation method (haze value, taper angle, missing bump, void area ratio) was performed by the following method. The obtained results are shown in Table 1.
(1) Haze value A photosensitive resin composition is applied to a glass substrate and dried to obtain a sample (the application conditions are the same as the application conditions to the substrate, and the thickness of the cured temporary resist film is 40 μm) Set). And the transmittance | permeability in wavelength 385nm is measured in the distance 0mm and 350mm of the obtained sample from the integrating sphere using the integrating sphere with Hitachi spectrophotometer U-4100. And haze value (%) was computed from these measured values by the following numerical formula (F1).
Haze value (%) = [(T _total− T _flat ) / T _total ] × 100 (F1)
T _total : transmittance at a distance of 0 mm from the integrating sphere T _flat : transmittance at a distance of 350 mm from the integrating sphere (2) taper angle The taper angle θ in the cross-sectional shape of the end of the opening in the temporary resist film is shown in FIG. Measurements were made as indicated. That is, the end of the opening in the obtained temporary resist film is observed with an electron microscope, the distance x in the planar direction of the substrate from the upper end to the lower end of the end of the opening in the temporary resist film, and the temporary resist film The thickness y was measured. The taper angle θ was calculated from these x and y values. The measurement was performed three times, and the average value was defined as the taper angle θ.
(3) Missing bumps Using a bumped wiring board as a sample, the presence of missing bumps was confirmed at a magnification of 20 using a stereo microscope DSZ-44F manufactured by CARTON OPTICAL. In addition, each 100-micrometer location where the diameter of an electrode pad is 60 micrometers was observed. And the missing bump was evaluated according to the following criteria.
○: There is no missing bump.
Δ: There are some missing bumps.
X: There are missing bumps.
(4) Void area ratio Using a bumped wiring board as a sample, a solder bump on an electrode pad having a diameter of 60 μm was observed using an X-ray transmission device (product name: XD7600 Diamond, manufactured by Nordson Corporation). The void area ratio determined in (1) was calculated.
Void area ratio [%] = SP / SV × 100
SP: Total area of solder bumps by X-ray transmission image SV: Area of void part in solder bumps by X-ray transmission image

As is apparent from the results shown in Table 1, when the solder bump forming method of the present invention is used (Examples 1 to 4), the missing bump is suppressed even when the electrode pad diameter is as small as 60 μm. However, it was confirmed that minute solder bumps can be formed.
On the other hand, when the taper angle θ in the temporary resist film is too large (Comparative Examples 1 and 2), it was found that missing bumps are likely to occur and the void area ratio is large.

  The solder bump forming method of the present invention is useful as a technique for producing a mounting substrate.

DESCRIPTION OF SYMBOLS 1 ... Wiring board 2 ... Temporary resist film 21 ... Opening part 2a ... Coating film 3 ... Solder bump 3a ... Solder paste (theta) ... Taper angle

Claims (4)

A solder bump forming method for forming solder bumps on a plurality of electrode pads formed on a surface of a wiring board,
A photosensitive resin composition is applied onto the wiring substrate to form a coating film having a haze value of 385 nm or more at 65% or more, and the coating film is exposed and developed to correspond to the electrode pad. A temporary resist film forming step in which an opening is provided, a cross-sectional shape of an end of the opening is tapered, and a temporary resist film having a taper angle of 75 ° or less in the cross-sectional shape is formed;
A solder bump forming step of filling the opening with a solder paste, performing a reflow process, and forming a solder bump;
A temporary resist film peeling step for peeling the temporary resist film from the wiring board;
A method for forming solder bumps, comprising: In the formation method of the solder bump of Claim 1,
The haze value at 385 nm of the coating film is 75% or more,
The taper angle in the said cross-sectional shape is 70 degrees or less. The formation method of the solder bump characterized by the above-mentioned. In the formation method of the solder bump of Claim 1,
The haze value at 385 nm of the coating film is 80% or more,
The taper angle in the said cross-sectional shape is 60 degrees or less. The formation method of the solder bump characterized by the above-mentioned. In the formation method of the solder bump of any one of Claims 1-3,
The method for forming a solder bump, wherein the coating film is exposed by a direct drawing exposure apparatus.

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