JP2017033989A - Method for forming solder resist - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a solder resist capable of stably exposing conductor wiring even when a height of a surface of a solder resist layer from a surface of an insulation substrate is nonuniform.SOLUTION: The method for forming a solder resist includes the steps of: (A) forming a photosensitive solder resist layer 3 on a surface of a circuit substrate 1; (B) weakly partially exposing the solder resist layer; and (C) making the solder resist layer thin with an alkaline aqueous solution.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for forming a solder resist layer.

  The solder resist layer on the circuit boards inside various electrical devices is coated on the entire surface other than the part to be soldered to prevent solder from adhering to the wiring part that does not require soldering. It plays the role of electrical insulation and protection from the external environment.

  In a semiconductor package in which an electronic component such as a semiconductor chip is mounted on a circuit board, mounting by flip chip connection is an effective means for realizing high speed and high density. In flip chip connection, a part of the conductor wiring of the circuit board is used as a connection pad for flip chip connection, and, for example, solder bumps arranged on the connection pad and electrode terminals of the semiconductor chip are joined.

  As a method of providing a solder resist layer 3 in a wiring portion which does not require soldering and opening only a connection pad portion, a photosensitive substrate is formed on a circuit board in which a conductor wiring 2 is formed on an insulating substrate 1 as shown in FIG. Generally, a method is provided in which the solder resist layer 3 is provided, the portion other than the opening is exposed and cured with actinic rays, the uncured portion is removed by development, and the conductor wiring 2 serving as a connection pad is exposed. By this method, the shape of FIG. 2 is obtained. This method is called a photolithography method. However, in the shape of FIG. 2, the solder resist layer 3 is thick, which causes an inconvenience that electronic components cannot be correctly mounted. In addition, with the recent downsizing and multi-functionalization of electronic devices, when the distance between connection pads becomes less than 50 μm, it is very difficult to produce the structure of FIG. 2 by this method from the viewpoint of misalignment of exposure. there were.

  In the method described in Patent Document 1, a photosensitive solder resist layer 3 is provided on a circuit board on which a conductive wiring 2 is formed on an insulating substrate 1, and the portions other than the opening are exposed and cured with actinic rays, and cured. The unexposed solder resist layer 3 in the opening portion is thinned to expose the conductor wiring 2 serving as a connection pad. According to this method, the structure shown in FIG. 3 can be formed even when the distance between the connection pads is less than 50 μm, and the above-mentioned problems and difficulties in the conventional method can be solved. The thinning included in the method described in Patent Document 1 can uniformly reduce the thickness of the solder resist layer 3. When the entire surface of the solder resist layer 3 having a uniform thickness shown in FIG. 1 is thinned without being exposed, the solder resist layer having a uniform thickness as shown in FIG. 3 is obtained.

  For forming the solder resist layer 3, for example, if it is a liquid resist, a screen printing method, a roll coating method, a spray method, a dipping method, a curtain coating method, a bar coating method, an air knife method, a hot melt method, a gravure coating method, Brush coating and offset printing are generally used. For a dry film resist, a laminating method or a vacuum laminating method is generally used. It is ideal to form the solder resist layer 3 uniformly and smoothly as shown in FIG. 1, but in these forming methods, for example, as shown in FIG. 5, the thickness of the solder resist layer 3 is not uniform. As a result, the surface of the solder resist layer 3 may not be smooth and may be uneven as shown in FIG. .

  For example, when the solder resist layer 3 is formed by a roll coating method using a liquid resist, the thickness may be nonuniform as shown in FIG. When this is thinned, the problem that the part which the conductor wiring 2 used as a connection pad exposes, and the part which is not exposed will arise like FIG.

  Further, as shown in FIG. 7, when there is a difference in density between the conductor wirings 2 and the solder resist layer 3 is formed by a vacuum laminating method using a dry film-shaped solder resist, There may be a difference in height between the surface of the insulating substrate 1 and the surface of the solder resist layer 3 in the high portion. When this is thinned, as shown in FIG. 8, there is a portion where the conductor wiring 2 serving as the connection pad is exposed and a portion where the conductor wiring 2 is not exposed, and there is a problem that a portion where the solder resist layer 3 is not formed may be partially formed. To do.

International Publication No. 2012/043201 Pamphlet

  The subject of this invention is providing the formation method of the soldering resist layer which can expose a conductor wiring stably, even when the height of the soldering resist layer surface from an insulating board | substrate surface is non-uniform | heterogenous.

As a result of intensive studies to solve the above problems, the present inventors have
(A) forming a photosensitive solder resist layer on the surface of the circuit board;
(B) a step of partially weakly exposing the solder resist layer,
(C) A step of thinning the solder resist layer with an alkaline aqueous solution,
It has been found that the above-mentioned problems can be solved by a method for forming a solder resist layer characterized by including the above in this order.

  According to the method for forming a solder resist layer in the present invention, the conductor wiring can be stably exposed even when the height of the solder resist layer surface from the insulating substrate surface before processing is uneven.

It is a schematic sectional structure figure of a soldering resist layer. It is a schematic sectional structure figure of a soldering resist layer. It is a schematic sectional structure figure of a soldering resist layer. It is a schematic sectional structure figure of a soldering resist layer. It is a schematic sectional structure figure of a soldering resist layer. It is a schematic sectional structure figure of a soldering resist layer. It is a schematic sectional structure figure of a soldering resist layer. It is a schematic sectional structure figure of a soldering resist layer.

  Hereinafter, the formation method of the soldering resist layer of this invention is demonstrated in detail.

  A circuit board having a conductor wiring 2 formed on an insulating substrate 1 is prepared. For the formation of the conductor wiring 2, a subtractive method, a semi-additive method, an additive method, or the like may be used. A solder resist layer 3 is formed so as to cover the entire surface of the circuit board. As shown in FIG. 1, a structure in which the solder resist layer 3 is uniformly and smoothly formed is preferable. However, as shown in FIG. 5, the thickness of the solder resist layer 3 becomes uneven and a slope is formed. is there. Further, as shown in FIG. 7, when there is a difference in the density of the conductor wiring 2, there is a difference in the height between the surface of the insulating substrate 1 and the surface of the solder resist layer 3 between the low density portion and the high density portion of the conductor wiring 2. May be able to. When the solder resist layer 3 as shown in FIGS. 5 and 7 is thinned with an alkaline aqueous solution, a portion where the conductor wiring 2 serving as a connection pad is exposed and a portion where it is not exposed are formed as shown in FIGS. According to the invention, as shown in FIG. 4, it is possible to form a structure in which the conductor wirings 2 serving as all connection pads are exposed.

  As the solder resist according to the present invention, any solder resist can be used as long as it has photosensitivity and can dissolve or swell the surface of the solder resist layer with an alkaline aqueous solution to remove the solder resist layer 3. Further, it may be either a one-component or two-component liquid resist, or may be a dry film resist.

  The solder resist contains, for example, an alkali-soluble resin, a polyfunctional acrylic monomer, an epoxy resin, an inorganic filler, and the like. In addition, in this invention, since a soldering resist has photosensitivity, a photoinitiator is contained. Examples of the alkali-soluble resin include alkali-soluble resins having both photo-curing properties and thermosetting properties. For example, a secondary hydroxyl group of a resin obtained by adding acrylic acid to a novolak-type epoxy resin to form an epoxy acrylate. A resin to which an acid anhydride has been added may be mentioned. Examples of the polyfunctional acrylic monomer include trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, pentaerythritol triacrylate, and the like. Examples of the photopolymerization initiator include 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one. Epoxy resin is used as a curing agent. It is cross-linked by reacting with carboxylic acid of alkali-soluble resin to improve heat resistance and chemical resistance, but carboxylic acid and epoxy react at room temperature, so the storage stability is poor and alkaline In general, the development type solder resist often takes a two-component form that is mixed before use. Examples of the inorganic filler include talc, silica, barium sulfate, titanium oxide, and zinc oxide.

<Process (A)>
In the step (A), a photosensitive solder resist layer 3 is formed on the surface of the circuit board on which the conductor wiring 2 is formed on the insulating substrate 1. For forming the solder resist layer 3, for example, if it is a liquid resist, a screen printing method, a roll coating method, a spray method, a dipping method, a curtain coating method, a bar coating method, an air knife method, a hot melt method, a gravure coating method, A brush coating method or an offset printing method can be used. For a dry film resist, a laminating method or a vacuum laminating method is used.

<Process (B)>
In the step (B), the solder resist layer 3 formed on the surface of the circuit board on which the conductor wiring 2 is formed on the insulating substrate 1 is partially weakly exposed. Specifically, the portion of the solder resist layer 3 lower than the ideal height is weakly exposed to reduce the amount of thinning in the thinning process, thereby reducing the three-dimensional shape of the solder resist layer 3 that is close to ideal. Can be obtained.

  The weak exposure in the step (B) is a step of intentionally performing partial weak exposure in order to solve the problem of the present invention. The part of the solder resist that has been partially exposed to light is hardened and the thinning is suppressed. Even when the thickness of the solder resist layer 3 before thinning is uneven, the thickness of the solder resist layer 3 after thinning is reduced by partially weakly exposing a relatively thin portion of the solder resist layer 3. Can be improved. On the other hand, even if the thickness of the solder resist layer 3 before thinning is uniform, a portion having a small amount of thinning can be provided locally by a partially weak exposure process to create portions having different heights. it can.

  The partially weak exposure process in the present invention is different from a so-called normal exposure process known to those skilled in the art. That is, the normal exposure process is a pattern exposure, and in the exposed area, the solder resist is strongly cured and the solder resist is not removed by development, or the solder resist is reduced by thinning in the step (C). Means that the solder resist is removed by development in the unexposed region, or the solder resist is made thin by thinning in step (C). On the other hand, the weak exposure process according to the present invention only hardens the solder resist to such an extent that thinning is suppressed, and the solder resist after the weak exposure process can be developed and can be thinned. .

  As a means for partial exposure, a xenon lamp, a high-pressure mercury lamp, a low-pressure mercury lamp, an ultra-high-pressure mercury lamp, or a UV fluorescent lamp is used as a light source. A method of exposing only in a region through which light is transmitted and a method of partially scanning and exposing a laser beam or condensed beam light are easy, but any method known to those skilled in the art can also be used. As a means for weak exposure, any method known to those skilled in the art such as shortening the exposure time, weakening the light emission intensity of the light source, exposing through a neutral density filter, and increasing the scanning speed can be used. By combining the partial exposure method and the weak exposure method, the partial weak exposure method according to the present invention can be realized. When a protective film or the like is provided on the solder resist layer 3, it may be partially weakly exposed as it is or may be partially weakly exposed after being peeled off.

  According to the present invention, the portion of the solder resist layer 3 lower than the ideal height is weakly exposed to reduce the amount of thinning in the thinning process, thereby reducing the three-dimensional shape of the solder resist layer 3 that is close to ideal. A typical structure can be obtained. For example, when the solder resist layer 3 is formed by a roll coating method using a liquid resist, the solder resist layer 3 is thinner in the first half of the coating, and the solder resist layer 3 is thicker in the latter half. There is a case. In this case, it is possible to use a method in which only the first half portion is weakly exposed, thereby reducing the amount of thinning of the first half portion and making the thickness of the solder resist layer 3 after thinning substantially the same. On the other hand, when the solder resist layer 3 is formed by a laminating method using a dry film-shaped resist, the portion of the conductor wiring 2 having a high density has a higher surface height of the solder resist layer 3, and the density of the conductor wiring 2 is higher. In the lower portion, the surface height of the solder resist layer 3 may be lowered. In this case, by using the method of irradiating only the portion where the surface height of the solder resist layer 3 is low, the amount of thinning of the portion where the density of the conductor wiring 2 is low is reduced, and the solder resist layer 3 after thinning is reduced. A method can be used in which the thickness is substantially the same throughout.

  The time between the step (B) and the step (C) preferably takes a certain time in order to advance the curing of the solder resist by weak exposure. Since it differs depending on the type of solder resist and the weak exposure method, it cannot be specified unconditionally, but at room temperature, it is preferably 5 minutes to 72 hours, more preferably 10 minutes to 48 hours.

  The amount of exposure that is partially weakly exposed, that is, the amount of exposure energy for weak exposure varies depending on the type, film thickness, and process of the solder resist, and cannot be determined unconditionally, but the ideal height of the solder resist layer 3 For the purpose of finishing the height of the solder resist layer 3 after the thinning of the lower part (abnormal part) in comparison with the part having normal (normal part) to the same or within a permissible range, etc. What is necessary is just to determine the conditions of weak exposure. Specifically, the greater the difference in height between the normal part and the abnormal part of the solder resist layer 3, the greater the exposure energy amount of the weak exposure, and the greater the ratio of the thinning amount to the unexposed portion. More specifically, the exposure energy amount for weak exposure is preferably 1% or more and 50% or less of the standard normal exposure energy amount. Further, in the thinning step of the step (C), the amount of thinning under the same conditions is 10% or more and 95% or less, preferably 50% or more and 90% or less of the portion that is not weakly exposed. It is preferable to set the exposure energy amount.

<Process (C)>
In the step (C), the solder resist layer 3 is thinned with an alkaline aqueous solution. Specifically, the surface of the solder resist layer 3 is dissolved or swollen with an alkaline aqueous solution, and the surface of the solder resist layer 3 in the non-exposed portion is removed. In the case of a dry film-shaped resist, when a support layer film is provided on the solder resist layer 3, the thinning process is performed after peeling. In the method for forming a solder resist layer of the present invention, the amount of thinning can be appropriately adjusted within a range of 0.01 to 500 μm.

  In the thinning treatment with an alkaline aqueous solution, a water washing treatment may be performed as a pretreatment. By the pretreatment water washing, hydrophilic groups such as carboxyl groups in the solder resist layer 3 are reoriented, and the hydrophilicity of the layer surface is made uniform. Further, contaminants and foreign matters existing on the solder resist layer 3 can be removed. Examples of water used for the pretreatment washing include industrial water, tap water, ion exchange water, and distilled water. Examples of the pretreatment water washing method include immersion treatment, paddle treatment, spray treatment, brushing, scraping, and the like, and spray treatment is preferable in consideration of the removal of contaminants and foreign matters on the solder resist layer 3. Although spray conditions (temperature, spray pressure, time) can be appropriately adjusted, specifically, the temperature is preferably 15 to 30 ° C, more preferably 20 to 25 ° C. The spray pressure is preferably 0.02 to 0.5 MPa, more preferably 0.05 to 0.3 MPa.

  Further, a surfactant may be contained in the pretreated washing water. By using the surfactant, the surface of the solder resist layer 3 can be more quickly and stably hydrophilized. Surfactants include alkyl sulfate salts, polyoxyethylene alkyl ether sulfate salts, alkylbenzene sulfonate salts, fatty acid salts and other anionic surfactants; polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, sorbitan fatty acid esters, Polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkylamine, alkylalkanolamide, polyoxyethylene alkylphenyl ether, polyoxy Ethylene-polyoxypropylene block copolymer (so-called pluronic surfactant), fatty acid pentaerythritol ester It can be used amphoteric surfactants such as alkyl betaines, alkyl amine salts, cationic surfactants such as quaternary ammonium salts; nonionic surfactants such as acetylene glycol. As long as the pretreatment water washing treatment does not impair the quality of the solder resist layer 3, any type of surfactant can be used, but anionic, cationic and amphoteric surfactants are used in the solder resist layer 3. Nonionic surfactants are preferably used because they may be specifically adsorbed on the surface or may partially invade the surface of the solder resist layer 3 depending on the type. More preferred specific examples of the nonionic surfactant include acetylene glycol, Surfynol (registered trademark) 465, Surfynol (registered trademark) 485, Surfynol (registered trademark) manufactured by Nissin Chemical Industry Co., Ltd. ) 82 or the like.

  The amount of surfactant to be added to the pretreatment rinse water varies depending on the properties of various surfactants. In addition to the hydrophilicity of the surface of the solder resist layer 3, there is little foaming during the pretreatment rinse. In view of the removal efficiency of contaminants and foreign matters adhering to the solder resist layer 3 due to, a range of 0.001 to 0.1% by mass is preferable, a range of 0.001 to 0.05% by mass is more preferable, and 0 The range of 0.01 to 0.05% by mass is more preferable.

  Examples of the alkaline compound contained in the alkaline aqueous solution according to the present invention include alkali metal silicate, alkali metal hydroxide, alkali metal phosphate, alkali metal carbonate, ammonium phosphate, ammonium carbonate, and other inorganic alkaline compounds. Monoethanolamine, diethanolamine, triethanolamine, methylamine, dimethylamine, ethylamine, diethylamine, triethylamine, cyclohexylamine, tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide, trimethyl-2-hydroxyethylammonium hydroxide ( And an organic alkaline compound such as choline). Examples of the alkali metal include lithium, sodium, and potassium. The inorganic alkaline compound and organic alkaline compound may be used alone or in combination. Inorganic alkaline compounds and organic alkaline compounds may be used in combination.

  In order to make the surface of the solder resist layer 3 more uniform, sulfates and sulfites can be added to the alkaline aqueous solution. Examples of the sulfate or sulfite include alkali metal sulfates or sulfites such as lithium, sodium or potassium, and alkaline earth metal sulfates or sulfites such as magnesium and calcium.

  When the aqueous alkaline solution is an aqueous solution containing an inorganic alkaline compound, the inorganic alkaline compound is at least one selected from alkali metal carbonates, alkali metal phosphates, alkali metal hydroxides, and alkali metal silicates. Preferably it is a seed. The content of the inorganic alkaline compound is preferably 3 to 20% by mass. An alkaline aqueous solution having an inorganic alkaline compound content of less than 3% by mass is a liquid used for development after exposure by a conventional photolithography method, and when the unexposed solder resist layer 3 is completely removed. Although effective, in the process of reducing the thickness of the solder resist layer 3 to a uniform thickness in-plane without completely removing the solder resist layer 3, unevenness in thickness may easily occur. Moreover, when it exceeds 20 mass%, precipitation of an inorganic alkaline compound will occur easily and it may be inferior to the temporal stability of a liquid, and workability | operativity. As for content of an inorganic alkaline compound, 5-15 mass% is more preferable, and 7-15 mass% is further more preferable. Further, a surfactant, an antifoaming agent, a solvent and the like can be added as appropriate.

  In the thinning process of the solder resist layer 3, the presence of an inorganic filler that is insoluble in the alkaline aqueous solution contained in the solder resist layer 3 cannot be ignored. Although the size of the inorganic filler depends on the type, it has a particle size distribution ranging from submicron order called nanofiller to several tens of microns and a content of 20 to 70% by mass in the layer. Existing. The thinning process proceeds by dissolving and diffusing the alkaline compound into the solder resist layer 3, but the presence of the insoluble inorganic filler suppresses the penetration of the alkaline compound and slows the thinning rate. is there.

  The pH of the alkaline aqueous solution is preferably 12.5 or more, and more preferably 13.0 or more, for such permeation suppression by the inorganic filler. The higher the pH of the alkaline aqueous solution, the greater the swelling of the solder resist layer 3 when the alkaline compound penetrates, and the less the influence of the penetration inhibition by the inorganic filler.

  In the step (C), the conductor wiring 2 may be exposed by a thinning process. The exposed conductor wiring 2 may be called a connection pad. The height of the connection pad surface from the surface of the insulating substrate 1 may be different from the height of the surface of the conductor wiring 2 from the surface of the insulating substrate 1. Normally, when the solder resist layer 3 is formed on the circuit board having the conductor wiring 2, the surface of the connection pad is roughened by various polishing processes in consideration of the adhesion between the conductor wiring 2 and the solder resist layer 3. Is done. The anchor effect due to the roughening improves the adhesion between the conductor wiring 2 and the solder resist layer 3, and maintains high insulation reliability over a long period of time. Conventionally, when removing the solder resist layer 3 to expose the connection pad surface, it is common to use a low concentration sodium carbonate aqueous solution excellent in dispersion ability as a developer, and the solder pad residue on the connection pad surface The rest hardly occurs. However, when a thinning process is performed using a low-concentration sodium carbonate aqueous solution, the surface of the solder resist layer 3 cannot be uniformly processed, and in-plane unevenness occurs.

  Therefore, an alkaline aqueous solution containing an alkali metal silicate can be cited as an alkaline aqueous solution that does not leave a solder resist residue on the surface of the roughened connection pad while making the film uniformly in-plane. Alkali metal silicates are superior to other inorganic alkaline compounds in the ability to dissolve and diffuse the solder resist layer 3, and residue residues are unlikely to occur on the connection pad surface. The general formula of alkali metal silicate is shown in formula (i). Alkali metal silicate is a general term for chemicals that are formed by continuously changing the three components at various ratios. The mass ratio calculated from the molar ratio (mass ratio in the case of sodium salt = molar ratio × 1) 0.03, mass ratio in case of potassium salt = molar ratio × 1.568), the name changes. For example, in the case of a sodium salt, one having a mass ratio of 0.5 is sodium orthosilicate, one having a mass ratio of 1.0 is sodium metasilicate, and one having a mass ratio of 1.3 to 4 is generally sodium silicate. Call it. In the case of a sodium salt, sodium metasilicate is preferably used from the viewpoint of the stability of the aqueous solution and workability. In addition, since potassium salts are more soluble in water than sodium salts, various solutions can be used without the aqueous solution easily coagulating and separating.

M ₂ O.nSiO ₂ .xH ₂ O (i)
[M: sodium or potassium, n: molar ratio (SiO ₂ / M ₂ O)]

  Examples of the inorganic alkaline compound having the ability to dissolve and diffuse the solder resist layer 3 after the alkali metal silicate include an aqueous alkali solution containing an alkali metal phosphate. As the alkali metal phosphate, strongly alkaline trisodium phosphate or tripotassium phosphate in which three atoms of alkali metal are coordinated is preferably used. The concentration of the alkali metal phosphate is more preferably 5 to 15% by mass, and further preferably 7 to 15% by mass.

  Further, an aqueous solution containing potassium carbonate as an inorganic alkaline compound also dissolves and diffuses the solder resist layer 3 reasonably. Carbonate has a higher hydration power than silicates and phosphates, but as an alkali metal, potassium has a higher ionization tendency in an aqueous solution than sodium and has an advantageous effect on dissolution and diffusion of the solder resist layer 3. As for the density | concentration of potassium carbonate, 3-10 mass% is more preferable, and 5-10 mass% is further more preferable.

  The organic alkaline compound contained in the alkaline aqueous solution contains at least one selected from tetramethylammonium hydroxide (TMAH) and trimethyl-2-hydroxyethylammonium hydroxide (choline), and the content of the organic alkaline compound 5 to 25% by mass can be suitably used. If it is less than 5% by mass, in-plane unevenness may easily occur in the thinning process. On the other hand, if it exceeds 25 mass%, the thinning rate may be slow. As for content of an organic alkaline compound, 7-20 mass% is more preferable, and 10-20 mass% is further more preferable. Further, a surfactant, an antifoaming agent, a solvent and the like can be added as appropriate. When an alkaline aqueous solution containing an alkali metal salt is used, depending on the composition of the solder resist used, alkali metal ions may be taken into the solder resist layer 3 to reduce insulation reliability. When an alkaline aqueous solution containing a compound is used, an effect of suppressing a decrease in insulation reliability can be obtained.

  The temperature of the alkaline aqueous solution is preferably 15 to 35 ° C, more preferably 20 to 30 ° C. If the temperature is too low, the penetration rate of the alkaline compound into the solder resist layer 3 may be slow, and it takes a long time to reduce the desired thickness. On the other hand, if the temperature is too high, the dispersion of the alkaline compound proceeds simultaneously with the permeation of the alkaline compound into the solder resist layer 3, which may cause uneven film thickness in the surface, which is not preferable.

  The thinning treatment with an aqueous alkali solution can be performed by a method such as immersion treatment, paddle treatment, spray treatment, brushing, scraping, etc., but immersion treatment is preferred. In the treatment methods other than the immersion treatment, bubbles are likely to be generated in the alkaline aqueous solution, and the generated bubbles may adhere to the surface of the solder resist layer 3 during the thinning treatment, resulting in non-uniform film thickness. When spraying or the like is used, it is preferable to make the spray pressure as small as possible so that bubbles are not generated.

  Between the step (A) and the step (B), or between the step (B) and the step (C), the portion of the solder resist layer 3 other than the region to be thinned is selectively irradiated with an actinic ray to be cured. By including the process, that is, the above-described normal exposure process, a structure in which the solder resist layer 3 has a step as shown in FIG. 3 can be formed. The “region to be thinned” is, for example, a region around the connection pad including the connection pad that is a part of the conductor wiring 2 and between the connection pads. The “region other than the region to be thinned” is, for example, a region around the conductor wiring including the conductor wiring 2 other than the connection pad and between the conductor wirings 2 other than the connection pad. In the normal exposure process, exposure methods include xenon lamps, high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, reflection image exposure systems using UV fluorescent lamps as light sources, single-sided or double-sided contact exposure systems using photomasks, and proximity. A method, a projection method, a laser scanning exposure method, or the like can be used.

  After the step (C), the circuit board is sufficiently washed with water. By this circuit board cleaning with water, the solder resist layer 3 to be removed is completely dissolved and removed. There are immersion treatment, paddle treatment, spray treatment and the like as the washing treatment method, and the spray treatment is most suitable from the viewpoint of the dissolution diffusion rate of the solder resist layer 3 and the uniformity of liquid supply. Moreover, the temperature of the washing water is more preferably 25 to 45 ° C, further preferably 27 to 40 ° C.

  In the present invention, the solder resist is cured by a method of exposing the entire surface of the remaining solder resist after the step (C), a method of thermosetting (curing), etc., apart from the weak exposure and the normal exposure step. You can also.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this Example.

(Example)
<Process (A)>
Using a subtractive method on a copper clad laminate (area 170 mm × 200 mm, copper foil thickness 18 μm, base material thickness 0.4 mm), a circuit board having a conductor wiring 2 with a conductor wiring width of 50 μm and a conductor wiring width interval of 50 μm is manufactured. did. A part of the conductor wiring 2 is used as a connection pad. Next, using a roll coat method, a liquid solder resist (manufactured by Taiyo Ink Manufacturing Co., Ltd., trade name: PSR-4000 AUS320) is applied on the circuit board and then dried (drying temperature 70 ° C., drying time 30). Min), a solder resist layer 3 was obtained. When the height (initial film thickness) from the surface of the insulating substrate 1 to the surface of the solder resist 3 layer was measured, the average film thickness in the first half of the coating was 25 μm, and the average film thickness in the second half was 30 μm. The film thickness was measured at 10 locations in each sample, and the average value was calculated as the “initial film thickness”.

<Process (B)>
The second half of the circuit board on which the solder resist layer 3 was formed was covered with a light-shielding film, and only the first half was weakly exposed at an exposure amount of 20 mJ / cm ² with an ultrahigh pressure mercury lamp contact exposure machine. The weakly exposed part is hereinafter referred to as “weakly exposed part” and the rest is referred to as “non-weakly exposed part”.

<Process (C)>
The circuit board that has been completed up to the step (B) is allowed to stand at room temperature for 24 hours, and a solder resist thin film containing a solder resist thin film treating agent (trade name: SRP-100, manufactured by Mitsubishi Paper Industries Co., Ltd.) at a liquid temperature of 20 ° C. In order to harden the solder resist layer 3 after the film is made into a processing apparatus (Mitsubishi Paper Co., Ltd., trade name: SRFM-01) under the condition that the film thickness is reduced to 16 μm in the non-weakly exposed part, Sample 1 was obtained by exposing the entire surface with an exposure dose of 500 mJ / cm ² with a mercury lamp contact exposure machine, followed by thermosetting at 150 ° C. for 60 minutes.

  For sample 1, the height (film thickness after treatment) from the surface of the insulating substrate 1 to the surface of the solder resist 3 layer was measured. The average film thickness in the first half of the coating was 15 μm and the average film thickness in the second half was 14 μm. (Thickness difference after treatment 1 μm).

  The portion of the solder resist layer 3 having a small initial film thickness is partially weakly exposed in the step (B), so that the amount of thinning is reduced and the height of the solder resist layer 3 after the thinning treatment is uniform. I was able to approach.

(Comparative example)
<Process (A)>
In the same manner as in Example 1, a liquid solder resist (manufactured by Taiyo Ink Manufacturing Co., Ltd., trade name: PSR-4000 AUS320) was applied on a circuit board and dried (drying temperature 70 ° C., drying time 30 minutes), A solder resist layer 3 was obtained. When the height (initial film thickness) from the surface of the insulating substrate 1 to the surface of the solder resist 3 layer was measured, the average film thickness in the first half of the coating was 25 μm, and the average film thickness in the second half was 30 μm. The film thickness was measured at 10 locations in each sample, and the average value was calculated as the “initial film thickness”.

<Process (C)>
Solder resist thinning apparatus (trade name: SRP-100, manufactured by Mitsubishi Paper Industries Co., Ltd.) having a liquid temperature of 20 ° C. without partial weak exposure treatment in the step (B) ( In order to cure the solder resist layer 3, the entire surface was exposed at an exposure amount of 500 mJ / cm ² after being put into a 12 μm thin film on Mitsubishi Paper Industries Co., Ltd. (trade name: SRFM-01). Subsequently, a heat curing treatment was performed at 150 ° C. for 60 minutes to obtain Sample 2.

  For sample 2, when the height (film thickness after treatment) from the surface of insulating substrate 1 to the surface of the solder resist 3 layer was measured, the average film thickness in the first half of the coating was 13 μm, and the average film thickness in the second half was 18 μm. (Film thickness difference after treatment 5 μm).

  When partial weak exposure was not performed, the entire surface was thinned with the same thinning amount, so that the initial film thickness difference between the first half of the coating and the latter half was the film thickness difference after processing. For this reason, in the latter half, there is a case where the solder resist layer 3 remains partially on the conductor wiring 2 used as the connection pad.

  The method for forming a solder resist layer of the present invention can be applied to, for example, the use of manufacturing a wiring board suitable for mounting a semiconductor chip by flip chip mounting on a wiring board having a connection pad for connecting a semiconductor chip.

1 Insulating substrate 2 Conductor wiring 3 Solder resist layer

Claims (1)

(A) forming a photosensitive solder resist layer on the surface of the circuit board;
(B) a step of partially weakly exposing the solder resist layer,
(C) A step of thinning the solder resist layer with an alkaline aqueous solution,
A solder resist layer forming method, comprising: