JP2011237472A - Imaging lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of cracks on an antireflection film even if exposed to the high temperature environment such as reflow processing.SOLUTION: In a lens block 8, a convex lens part 20a made of a curable resin is formed on a surface of a glass substrate 16 and an antireflection film 100 is formed on the convex lens part 20a. The antireflection film 100 is constituted of a plurality of layers formed by alternatively laminating a high refractive index layer 102 and a low refractive index layer 104, and the outermost layer of the antireflection film 100 is the low refractive index layer 104. The outermost layer and at least one layer of layers provided closer to the convex lens part 20a than the outermost layer are a mixed film formed by mixing two kinds of different inorganic materials.

Description

  The present invention relates to an imaging lens, and more particularly to an imaging lens that can withstand reflow processing when electronic components are mounted.

  Conventionally, when an IC (Integrated Circuits) chip or other electronic component is mounted on a circuit board, a conductive paste (for example, solder) is previously applied (potted) to a predetermined position on the circuit board, and an electronic device is placed at that position. The circuit board is subjected to a reflow process (heat treatment at about 250 ° C.) with the component placed thereon, and the conductive paste is melted and the electronic component is mounted on the circuit board. Technology for manufacturing equipment has been developed. In recent years, in addition to electronic components, an imaging module (imaging unit) including an optical element is placed on a circuit board, and the reflow process as described above is performed, so that the electronic component and the imaging module are simultaneously mounted on the circuit board. However, production of electronic devices such as mobile phones integrated with an imaging module has also been performed. When an imaging module including an optical element is mounted on an electronic device by reflow processing, naturally, the optical element is also exposed to a high temperature by the reflow processing, and thus high heat resistance is required.

  In contrast, in the field of manufacturing optical elements such as imaging lenses, a technique for obtaining a hybrid optical element (lens) with high heat resistance by providing a lens portion made of a curable resin on a glass substrate has been studied. ing. As an example of a method of manufacturing an optical element to which this technology is applied, a so-called “wafer lens” in which a plurality of lens portions made of a curable resin is provided on the surface of a glass substrate is formed, and then cut for each lens portion (both dicing) A method for forming individual imaging lenses has been proposed. In some cases, it is also possible to form an imaging lens having a two-group configuration or a three-group configuration by cutting each lens unit in a state where a plurality of wafer lenses are laminated. In addition, an imaging module is manufactured by pasting together a wafer lens and a substrate on which a plurality of imaging elements such as a CCD image sensor and a CMOS image sensor are arranged, and then cutting each lens unit and each imaging element. Is also possible.

  It has also been studied to use the hybrid optical element as an optical element (imaging lens) of an imaging system and to provide a reflow process together with electronic components. In this case, in order to use as an imaging lens, an antireflection film is formed on the surface of the lens portion in order to increase the transmittance at each optical surface and to suppress the occurrence of problems such as ghosts due to reflected light. Is required. However, when the reflow process is performed when the imaging module is mounted on the circuit board constituting the electronic device, the imaging lens is exposed to a high temperature that greatly exceeds the normal usage environment. Since the antireflective film is formed by alternately laminating low refractive index layers and high refractive index layers usually made of an inorganic material, the antireflective film itself has high heat resistance and does not deteriorate even at high temperatures. However, when the lens portion of the imaging lens provided with the antireflection film is formed of a resin material, the coefficient of thermal expansion (line) between the inorganic material and the resin material constituting the lens portion when exposed to a high temperature. The problem that cracks (so-called film cracks) of the antireflection film occur due to the difference in physical properties such as (expansion coefficient), and therefore it is necessary to prevent this.

With respect to such a problem, the technique of Patent Document 1 prevents the occurrence of cracks in the antireflection film due to the reflow process to some extent by depositing (evaporating) the antireflection film at a temperature close to the temperature at which the reflow process is performed. Have succeeded in doing.
Although the technique of Patent Document 2 does not assume that it is exposed to a high temperature environment that greatly exceeds a normal use environment such as a reflow process, among the layers constituting the antireflection film, 2 high refractive index layers are used. We are investigating reducing the film stress and preventing the antireflection film from cracking in a high temperature environment by using a mixed film made of various materials.

JP 2009-244583 A Japanese Patent Laid-Open No. 10-73702

According to the technique of Patent Document 1, it is possible to suppress the occurrence of cracks in the antireflection film to some extent in the reflow process. However, the reflow process is generally performed in a processing time (stay time) of several minutes, whereas when the antireflection film is formed, it may take as long as 1 to 2 hours. For this reason, when the processing temperature during the formation of the antireflection film is set to the same level as the reflow temperature, it is necessary to expose the resin material constituting the lens part to high temperature for a long time. In some cases, the transmittance is lowered, or the resin material is softened and the optical surface shape is deformed. In addition, it is conceivable to select a curable resin having a high glass transition point that is less likely to be colored or softened. However, since a resin having a high glass transition point tends to be less brittle, chipping or peeling off occurs when molding an optical surface. In some cases, it is difficult to achieve the desired optical performance because the problem of the tendency to occur and the range of selection of the resin material are narrowed.
Therefore, there has been a demand for an antireflection film that does not cause cracks even in a high temperature environment regardless of the type of resin and the conditions for forming the antireflection film.

On the other hand, the technology of Patent Document 2 relates to an antireflection film provided on a lens portion made of a thermoplastic resin, and even when the lens is used in a relatively high temperature environment, the antireflection film cracks. As a configuration capable of suppressing the above, it is described that the high refractive index layer is a mixed film of titanium oxide and tantalum oxide. Specifically, it is assumed that it is used in an environment of about 70 ° C., and it is described that generation of cracks can be suppressed in the configuration. However, it has become clear that even if the same technique is applied to an imaging lens that undergoes reflow processing, cracks in the antireflection film cannot be sufficiently suppressed. The thermoplastic resin employed in Patent Document 2 cannot be used because it melts due to the reflow treatment and cannot maintain the lens shape, and is colored by heating and the transmittance is greatly reduced. Therefore, it is conceivable to change the thermoplastic resin to a curable resin, but certainly by using a curable resin, although melting and coloring of the resin due to reflow treatment can be suppressed, the problem of cracks in the antireflection film is sufficient. Could not be suppressed.
Therefore, a main object of the present invention is to provide an imaging lens capable of sufficiently suppressing the occurrence of cracks in the antireflection film even when exposed to a high temperature environment such as a reflow process.

In order to solve the above problems, according to the present invention,
In an imaging lens in which a lens portion made of a curable resin is formed on at least one surface of the glass substrate, and an antireflection film is formed on the lens portion,
The antireflection film is composed of a plurality of layers in which high refractive index layers and low refractive index layers are alternately stacked,
The outermost layer of the antireflection film is a low refractive index layer,
An imaging lens is provided in which the outermost layer and at least one of the layers provided closer to the lens portion than the outermost layer are a mixed film in which two different inorganic materials are mixed. Is done.

As a result of the study by the present inventors, although a certain amount of cracks can be suppressed by using a mixed film in which two kinds of materials are mixed as a high refractive index layer as in Patent Document 2, it seems to be a reflow process. However, it was revealed that sufficient effects could not be obtained when exposed to a high temperature environment significantly exceeding the normal use environment. As a result of further studies, the antireflective film is generally provided with a low refractive index layer on the outermost layer, and in order to obtain appropriate antireflective properties, the outermost low refractive index layer must be relatively thick. We focused on the fact that the largest stress (tensile stress) is likely to be applied to the outermost layer during heating. Therefore, it was studied to adjust the stress in the compression direction by using a low refractive index layer constituting the outermost layer as a mixed film. However, it was still not sufficient when it was subjected to reflow treatment, but by adjusting the stress using a layer provided between the outermost layer and the resin material as the base material as a mixed layer, the reflow treatment It was found that the antireflection film can be sufficiently suppressed even when exposed to.
Therefore, according to the present invention, even when the imaging lens is exposed to a high temperature condition that greatly exceeds the usage environment due to the reflow process, cracks in the antireflection film can be prevented.

It is sectional drawing which shows schematic structure of an imaging module. It is a perspective view which shows schematic structure of a wafer lens laminated body. It is sectional drawing which follows the II line | wire of FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Imaging module]
As shown in FIG. 1A, the imaging module 2 mainly includes a lens unit 4 and a sensor unit 6, and the lens unit 4 is disposed on the sensor unit 6. The lens unit 4 is an example of an imaging lens. The lens unit 4 mainly includes a lens block 8, a lens block 10, a spacer 12, and a cover package 14. The lens unit 4 is covered with the cover package 14 in a state where the lens blocks 8 and 10 and the spacer 12 are bonded and stacked. Yes.

The lens block 8 has a flat glass substrate 16.
A diaphragm 18 and a resin part 20 are formed on the upper part of the glass substrate 16, and a diaphragm 22 and a resin part 24 are formed on the lower part of the glass substrate 12.
A convex lens portion 20 a having a convex shape is formed at a substantially central portion of the resin portion 20.
In the resin part 20, parts other than the convex lens part 20a are non-lens parts 20b.
A concave lens portion 24 a having a concave shape is formed at a substantially central portion of the resin portion 24.
In the resin part 20, parts other than the concave lens part 24a are non-lens parts 24b.

The lens block 10 also has a flat glass substrate 26.
A resin portion 28 is formed on the upper portion of the glass substrate 26, and a diaphragm 30 and a resin portion 32 are formed on the lower portion of the glass substrate 26.
A concave lens portion 28 a having a concave shape is formed at a substantially central portion of the resin portion 28.
In the resin part 28, parts other than the concave lens part 28a are non-lens parts 28b.
A convex lens portion 32 a having a convex shape is formed at a substantially central portion of the resin portion 32.
In the resin part 32, parts other than the convex lens part 32a are non-lens parts 32b.

  The convex lens part 20a, the concave lens part 24a, the concave lens part 28a, and the convex lens part 32a in the resin parts 20, 24, 28, and 32 are lens effective parts that exhibit a lens function (optical function). When the lens blocks 8 and 10 are viewed from the object side (convex lens portion 20a side), the convex lens portion 20a, the concave lens portion 24a, the concave lens portion 28a, and the convex lens portion 32a are arranged concentrically. The optical axes 34 (see FIG. 3) are stacked vertically so as to coincide with each other.

The resin parts 20, 24, 28, 32 are made of a photocurable resin.
As the photocurable resin, an acrylic resin, an allyl ester resin, an epoxy resin, or the like can be preferably used.
The usable resin will be described below.
The photocurable resin may be the same type of resin for each of the resin portions 20, 24, 28, and 32, or may be a different resin.

(1) Acrylic resin The (meth) acrylate used for the polymerization reaction is not particularly limited, and the following (meth) acrylate produced by a general production method can be used. Ester (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, ether (meth) acrylate, alkyl (meth) acrylate, alkylene (meth) acrylate, (meth) acrylate having an aromatic ring, alicyclic structure The (meth) acrylate which has is mentioned. One or more of these can be used.

  In particular, (meth) acrylate having an alicyclic structure is preferable, and may be an alicyclic structure containing an oxygen atom or a nitrogen atom. For example, cyclohexyl (meth) acrylate, cyclopentyl (meth) acrylate, cycloheptyl (meth) acrylate, bicycloheptyl (meth) acrylate, tricyclodecyl (meth) acrylate, tricyclodecane dimethanol (meth) acrylate, isoboronyl (meth) ) Acrylates, di (meth) acrylates of hydrogenated bisphenols, and the like. In particular, it preferably has an adamantane skeleton. For example, 2-alkyl-2-adamantyl (meth) acrylate (see Japanese Patent Application Laid-Open No. 2002-193883), adamantyl di (meth) acrylate (Japanese Patent Application Laid-Open No. 57-5000785), diallyl adamantyl dicarboxylate (Japanese Patent Application Laid-Open No. 60-100537). ), Perfluoroadamantyl acrylate (JP 2004-123687), Shin-Nakamura Chemical 2-methyl-2-adamantyl methacrylate, 1,3-adamantanediol diacrylate, 1,3,5-adamantanetriol triacrylate, Saturated carboxylic acid adamantyl ester (JP 2000-119220), 3,3′-dialkoxycarbonyl-1,1 ′ biadamantane (see JP 2001-253835), 1,1′-biadamantane compound (US Patent) No. 3342880), It has an adamantane skeleton having no aromatic ring such as traadamantane (see JP-A-2006-169177), 2-alkyl-2-hydroxyadamantane, 2-alkyleneadamantane, di-tert-butyl 1,3-adamantanedicarboxylate, etc. Examples thereof include curable resins (see JP-A-2001-322950), bis (hydroxyphenyl) adamantanes, bis (glycidyloxyphenyl) adamantane (see JP-A-11-35522, JP-A-10-130371), and the like. It is done.

  It is also possible to contain other reactive monomers. In the case of (meth) acrylate, for example, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate Tert-butyl methacrylate, phenyl acrylate, phenyl methacrylate, benzyl acrylate, benzyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, and the like.

  Examples of the polyfunctional (meth) acrylate include trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dipentaerythritol penta (meth) ) Acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate, tripentaerythritol octa (meth) acrylate, tripentaerythritol septa (meth) acrylate, tripentaerythritol hexa (meth) acrylate, tripenta Erythritol penta (meth) acrylate, tripentaerythritol tetra (meth) acrylate, tripentaerythritol (Meth) acrylate.

(2) Allyl ester resin A resin having an allyl group and cured by radical polymerization. Examples thereof include the following, but are not particularly limited to the following.
Bromine-containing (meth) allyl ester not containing an aromatic ring (see JP 2003-66201 A), allyl (meth) acrylate (see JP 5-286896 A), allyl ester resin (JP 5-286896 A) , JP 2003-66201 A), a copolymer compound of an acrylate ester and an epoxy group-containing unsaturated compound (see JP 2003-128725 A), an acrylate compound (see JP 2003-147072 A), acrylic Examples include ester compounds (see JP 2005-2064 A).

(3) Epoxy resin The epoxy resin is not particularly limited as long as it has an epoxy group and is polymerized and cured by light or heat, and an acid anhydride, a cation generator, or the like can be used as a curing initiator. Epoxy resin is preferable in that it has a low cure shrinkage and can be a lens with excellent molding accuracy.

  Examples of the epoxy include novolak phenol type epoxy resin, biphenyl type epoxy resin, and dicyclopentadiene type epoxy resin. Examples include bisphenol F diglycidyl ether, bisphenol A diglycidyl ether, 2,2′-bis (4-glycidyloxycyclohexyl) propane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, vinyl Cyclohexene dioxide, 2- (3,4-epoxycyclohexyl) -5,5-spiro- (3,4-epoxycyclohexane) -1,3-dioxane, bis (3,4-epoxycyclohexyl) adipate, 1,2 -Cyclopropanedicarboxylic acid bisglycidyl ester etc. can be mentioned.

  A hardening | curing agent is used when comprising curable resin material, and there is no limitation in particular. Moreover, in this invention, when comparing the transmittance | permeability of the curable resin material and the optical material after adding an additive, a hardening | curing agent shall not be contained in an additive. As the curing agent, an acid anhydride curing agent, a phenol curing agent, or the like can be preferably used. Specific examples of the acid anhydride curing agent include phthalic anhydride, maleic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, 3-methyl-hexahydrophthalic anhydride, 4-methyl-hexahydrophthalic anhydride. Examples thereof include an acid, a mixture of 3-methyl-hexahydrophthalic anhydride and 4-methyl-hexahydrophthalic anhydride, tetrahydrophthalic anhydride, nadic anhydride, methyl nadic anhydride and the like. Moreover, a hardening accelerator is contained as needed. The curing accelerator is not particularly limited as long as it has good curability, is not colored, and does not impair the transparency of the thermosetting resin. For example, 2-ethyl-4-methylimidazole Imidazoles such as (2E4MZ), tertiary amines, quaternary ammonium salts, bicyclic amidines such as diazabicycloundecene and their derivatives, phosphines, phosphonium salts, etc. can be used, Two or more kinds may be mixed and used.

As shown in the enlarged view of FIG. 1A, an antireflection film 100 is formed on the resin portion 20 (particularly the convex lens portion 20a).
In general, when light is incident on a boundary surface having a different refractive index, a part of the incident light is reflected according to the refractive index ratio on both sides of the boundary surface. As the refractive index ratio of the boundary surface increases, the amount of light reflected at the boundary surface increases. For example, a plastic used as an optical element has a refractive index in the range of about 1.5 to 1.6. Therefore, when light is incident from a medium such as air, 4 to 5% of the incident light is reflected. Become. This surface reflection phenomenon is not only that the amount of transmitted light is simply reduced, but if such an optical element is used as it is for an imaging lens or the like, it causes a great cause of ghost or flare. Therefore, in order to reduce this surface reflection, a thin dielectric film having a wavelength order of light is provided as an antireflection film on the surface of the optical element, and the reflected light is reduced by the interference effect of light within the film. Well done. Many high-performance antireflection film structures have been proposed in which several layers of two or more types of dielectric films are stacked to achieve low reflectance in a wide wavelength range.

In this embodiment, the antireflection film 100 has a configuration in which a high refractive index layer 102 and a low refractive index layer 104 having a lower refractive index are alternately stacked, and the outermost layer is a low refractive index layer 104. Yes, the total number of layers is four. If the high refractive index layer 102 and the low refractive index layer 104 are alternately laminated, the number of layers of the antireflection film 100 can be changed as appropriate.
The high refractive index layer 102 is composed of a single film composed of a single inorganic material or a mixed film composed of two different inorganic materials, preferably a single film of Ta ₂ O ₅ or Ta ₂ O. ₅ and a mixed film of TiO ₂ . When the high refractive index layer 102 is composed of a mixed film of Ta ₂ O ₅ and TiO ₂ , the ratio of the number of elements of Ti to the number of elements of Ta in the mixed film is preferably 1 to 30%. In the mixed film, CeO ₂ , La ₂ O ₃ , ZrO ₂ , and HfO ₂ may be used instead of TiO ₂ .
Low refractive index layer 104 is also composed of a mixed layer composed of a single layer or two different inorganic material composed of a single inorganic material, preferably a single layer or SiO 2 of SiO _2, Al ₂ O ₃ mixed films. However, the low refractive index layer 104 provided as the outermost layer needs to be a mixed film. When the low refractive index layer 104 is composed of a mixed film of SiO ₂ and Al ₂ O ₃ , the ratio of the number of Al elements to the number of Si elements in the mixed film is preferably 1 to 5%. The In mixed _{film, MgF 2, Y 2 O 3} , La 2 O 3 may be used in place of the _Al 2 _{O 3.}
In the case where the high refractive index layer 102 and the low refractive index layer 104 are composed of a mixed film, the mixing ratio of the materials of the mixed film is determined from the elements in the film by a technique such as XPS (X-ray photoelectron analysis) from the film surface. This can be confirmed by measuring the ratio.

In the antireflection film 100, at least the low refractive index layer 104 serving as the outermost layer is composed of the mixed film, and at least one layer provided between the low refractive index layer 104 serving as the outermost layer and the resin portion 20 is used. However, what is necessary is just to be comprised with the said mixed film. Of the layers provided between the low refractive index layer 104 and the resin part 20 as the outermost layer, the layer closest to the resin part 20, that is, the layer adjacent to the resin part 20 is a mixed layer. Further, it is more preferable to improve the adhesion between the antireflection film 100 and the resin portion 20, and it is preferable that all the high refractive index layers 102 and the low refractive index layers 104 constituting the antireflection film 100 are composed of the mixed film. Particularly preferred.
In the present embodiment, the high refractive index layer 102 composed of a mixed film is formed directly on the resin portion 20.
The antireflection film 100 may be formed on the resin parts 24, 28, 32 other than the resin part 20, and is preferably formed on all of the resin parts 20, 24, 28, 32.

  As shown in FIGS. 1A and 1B, the sensor unit 6 mainly includes a sensor 36, a package 38, and a cover glass 40.

The sensor 36 is a light receiving sensor that receives light transmitted through the lens unit 4, and can photoelectrically convert the received light to output an electrical signal to an external device (not shown).
The package 38 has a bottomed box shape and is open at the top. As shown in FIG. 1B, a sensor 36 is disposed at a substantially central portion of the package 38.
The cover glass 40 is provided as a lid on the upper portion of the package 38, and the sensor 36 is sealed in a space surrounded by the package 38 and the cover glass 40.

  As shown in FIG. 1A, the spacer 12 is interposed between the lens blocks 8 and 10 and the sensor 36, and provides a constant interval between these members. The spacer 12 is formed with a circular opening 12b. An IR cut filter 42 is provided inside the opening 12b. The IR cut filter 42 is disposed above the cover glass 40 and shields infrared rays that are about to enter the sensor 36.

  Next, a method for manufacturing the imaging module 2 (particularly the lens unit 4) will be described.

  First, as shown in FIG. 2, a wafer lens 52, a wafer lens 54, and a spacer substrate 56 on which a plurality of convex lens portions 20a and the like are formed are prepared (manufactured).

As shown in FIG. 3, the wafer lens 52 has a wafer-like glass substrate 16. A diaphragm 18 and a resin part 20 are formed on the upper part of the glass substrate 16, and a diaphragm 22 and a resin part 24 are formed on the lower part of the glass substrate 16.
When the apertures 18 and 22 are formed, a light-shielding photoresist is applied to the glass substrate 16, and then developed by irradiating light through a mask having a predetermined pattern to form the apertures 18 and 22. As the light-shielding photoresist, a photoresist mixed with carbon black is used.
When the resin parts 20 and 24 are formed, a photocurable resin is dropped on the glass substrate 16 to press a molding die (not shown), and then the light is irradiated to cure the resin. Release from the mold.

The wafer lens 54 has a wafer-like glass substrate 26. A resin portion 28 is formed on the upper portion of the glass substrate 26, and a diaphragm 30 and a resin portion 32 are formed on the lower portion of the glass substrate 26.
The method of forming the diaphragm 30 and the resin portions 28 and 32 is the same as that of the wafer lens 52 (similar to the method of forming the diaphragms 18 and 22 and the resin portions 20 and 24 on the glass substrate 16).
The spacer substrate 56 is a glass flat plate having a wafer shape like the glass substrates 16 and 26. A large number of circular openings 56 a are formed in the spacer substrate 56. The opening 56a is formed at a position corresponding to the convex lens portion 20a, the concave lens portion 24a, the concave lens portion 28a, and the convex lens portion 32a.

Thereafter, the antireflection film 100 is formed on the resin portion 20 of the wafer lens 52 by vacuum deposition.
When the high-refractive index layer 102 and the low-refractive index layer 104 are composed of a mixed film, each material is mixed and fired at a desired ratio in advance, and then molded, whereby a mixed film deposition material can be produced. Moreover, it is also possible to form a mixed film by using each material alone and adjusting each film forming speed so that a desired mixing ratio can be obtained by two-source vapor deposition.

Specifically, the wafer lens 52 is mounted in a vacuum deposition apparatus, the pressure in the apparatus is reduced to a predetermined pressure (for example, 1.0 × 10 ⁻³ Pa), and the wafer lens 52 is heated from a heater above the vacuum deposition apparatus. Is heated to a predetermined temperature (for example, 200 ° C.).
Thereafter, the high refractive index layer 102 is formed using a vapor deposition source (vapor deposition material) constituting the high refractive index layer 102. For example, when a (Ta ₂ O ₅ + 5% TiO ₂ ) film is formed as the high refractive index layer 102, OA600 manufactured by Optran Co., Ltd. may be used as the evaporation source, and the evaporation source may be evaporated by electron gun heating. During the vapor deposition, it is preferable to form the film while introducing O ₂ gas until the pressure inside the vacuum vapor deposition apparatus becomes 1.0 × 10 ⁻² Pa and controlling the vapor deposition rate at 5 liters / sec.
Thereafter, the low refractive index layer 104 is formed on the high refractive index layer 102 using an evaporation source constituting the low refractive index layer 104. For example, in the case of forming a SiO ₂ film as the low refractive index layer 104, O ₂ gas is introduced until the pressure inside the vacuum vapor deposition apparatus becomes 1.0 × 10 ⁻² Pa, and the vapor deposition rate is 5 Å / sec. It is better to form the film while controlling the conditions.
Such an operation is repeated to form the antireflection film 100 on the resin portion 20 of the wafer lens 52. When the antireflection film 100 is formed on the other resin parts 24, 28, 32, the same operation as described above may be performed.

Thereafter, the wafer lens 52, the wafer lens 54, and the spacer substrate 56 are joined (adhered) while being aligned with each other, and the wafer lens laminate 50 (see FIG. 2) is manufactured. Thereafter, the wafer lens stack 50 is individually separated for each convex lens portion 20a by an end mill along a dicing line 61 (see FIG. 3), and a plurality of lens units 4 are manufactured. Thereafter, each lens unit 4 is incorporated in the cover package 14 and joined to the sensor unit 6. Thereby, the imaging module 2 can be manufactured.
Here, after manufacturing the lens unit 4 by dicing the wafer lens stack 50 into pieces, the imaging module 2 is manufactured by bonding to the sensor unit 6. However, in the state of the wafer lens stack 50, It is also possible to manufacture the imaging module 2 by bonding to a substrate having a plurality of sensor units 6 and dicing the wafer lens stack 50 and the substrate having the sensor units 6 simultaneously.

After the imaging module 2 is manufactured, when the imaging module 2 and other electronic components are simultaneously mounted on the circuit board, a predetermined mounting position of the circuit board on which a conductive paste such as solder has been applied (potted) in advance. The image pickup module 2 is placed together with other electronic components.
Thereafter, the circuit board on which the imaging module 2 and other electronic components are mounted is transferred to a reflow furnace (not shown) by a belt conveyor or the like, and the circuit board is heated at a temperature of about 230 to 270 ° C. for about 5 to 10 minutes. (Reflow processing).
As a result, the conductive paste is melted and the imaging module 2 is mounted on the circuit board together with other electronic components.

According to the above-described embodiment, the low refractive index layer 104 (outermost layer) disposed on the outermost side of the layers constituting the antireflection film 100 and the outermost layer and the resin portion 20 are provided. Further, at least one layer is composed of a mixed film. In this configuration, it has been experimentally confirmed that the compressive stress (stress in the direction in which the antireflection film 100 expands) increases in the layer formed of the mixed film as compared with a single material (the following implementation). See example). Therefore, during the reflow processing of the imaging module 2, the resin portion 20 (convex lens portion 20a) of the lens block 8 is thermally expanded, so that tensile stress (the direction in which the antireflection film 100 is pulled outward) is applied to the antireflection film 100. It is considered that the occurrence of cracks is suppressed by canceling the stress because the compressive stress by the mixed film is applied to the antireflection film 100 in advance. In particular, the low refractive index layer 104 that is relatively thick and is the outermost layer that is exposed to the largest tensile stress is a mixed film, and further, one layer between the outermost layer and the resin portion 20 is mixed. By being a film, a sufficient compressive stress can be applied to the entire antireflection film 100.
For the above reasons, even when the imaging module 2 (lens unit 4) is exposed to a high temperature environment such as a reflow process, the occurrence of cracks in the antireflection film 100 can be prevented.

(1) Preparation of sample A photocurable resin was dropped onto a flat glass substrate, and a mold whose surface corresponds to the lens surface was pressed. Thereafter, the glass substrate was irradiated with light from the back side (the side opposite to the surface on which the resin was dropped) to cure, and the mold was released. Thereafter, the glass substrate was heated at 200 ° C. for 8 hours. A plurality of such glass substrates (glass substrates on which resin portions (resin lens portions) were formed) were produced.
Thereafter, an antireflection film having a 4 to 5 layer structure was formed on the resin portion of each glass substrate. The film forming materials were variously changed as shown in Tables 1 and 2, and the samples of “Examples 1 to 12” and “Comparative Examples 1 to 6” were changed according to the configuration of the antireflection film (material of each layer). did.
The antireflection film was formed by vacuum deposition. In each sample, a mixed film material made of two kinds of materials was prepared by mixing the materials in a desired ratio in advance and molding after firing. In the vacuum deposition process, the apparatus was heated to 200 ° C. while evacuating the apparatus, and film formation was started when the apparatus internal pressure reached 1.0 × 10 ⁻³ Pa.
In Tables 1 and 2, the mixing ratio of the mixed film was verified by measuring the element ratio in the film from the film surface by a technique such as XPS (X-ray photoelectron analysis).

(2) Characteristics of each layer A material constituting each sample was formed on a thin glass substrate having a length of 50 mm and a width of 10 mm, and the stress and refractive index in the material were measured. The measurement results are shown in Tables 3 and 4. In the measurement of stress, an external force was applied to each glass substrate to bend the glass substrate, and the amount of warpage (warpage angle) was measured with an autocollimator and converted into stress.

From the results of Table 3, in the low refractive index layer, when the Al content is less than 1%, the film stress is small and film cracking is likely to occur during reflow treatment, and when the Al content exceeds 5%. It has a high refractive index and hardly exhibits an antireflection effect.
From the results of Table 4, in the high refractive index layer, when the Ti content is less than 1% or more than 30%, the film stress is small and film cracking is likely to occur during the reflow treatment.

(3) Evaluation of sample Each sample was reflowed (heat treatment at 260 ° C. for about 5 to 10 minutes) three times to evaluate the appearance and adhesion of the subsequent antireflection film.
Separately, each sample was left in an environment of a temperature of 60 ° C. and a humidity of 90% for 240 hours, and the appearance and adhesion of the subsequent antireflection film were evaluated.
Appearance inspection and adhesion inspection were conducted as follows.

(3.1) Appearance inspection For each sample, the appearance of the antireflection film was observed with a microscope. The observation results are shown in Table 5. In Table 5, the criteria for ◎, ○, △, × are as follows.
“◎”: No cracks are observed in the antireflection film and there is no problem in practical use. “○”: Several fine cracks are generated in part of the antireflection film, but there is no problem in practical use. : Although fine cracks are observed on the entire surface of the antireflection film, there is no problem in practical use. “×”: Cracks are observed on the entire surface of the antireflection film, causing problems in practical use.

(3.2) Adhesion test φ30mm preparing a planar test piece sample (forming an anti-reflection film as shown in Table 1 and 2.), The peeling tape the range of 100 mm ² of the antireflection film And the presence or absence of peeling of the antireflection film accompanying peeling of the tape was visually confirmed. The confirmation results are shown in Table 5. In Table 5, the criteria for ○, Δ, and × are as follows.
“◯”: No peeling is observed “Δ”: Some peeling is observed, but the area is within 0.03 mm ² “×”: The peeling exceeding 0.03 mm ² is recognized

(3.3) Summary From the results of Table 5, when comparing the samples of Examples 1 to 12 and Comparative Examples 1 to 6, the outermost layer is a low refractive index layer and the outermost layer and its inner layer are mixed. The samples of Examples 1 to 12 composed of a film had good results in both appearance inspection and adhesion inspection.
From the above, in the antireflection film, forming the outermost layer as a low refractive index layer and configuring the outermost layer and the inner layer thereof as a mixed film prevents the occurrence of cracks or adheres to the resin part of the film itself. It turns out that it is useful in improving the property.

2 Imaging module 4 Lens unit 6 Sensor unit 8, 10 Lens block 12 Spacer 14 Cover package 16 Glass substrate 18 Aperture 20 Resin part 20a Convex lens part 20b Non-lens part 22 Aperture 24 Resin part 24a Concave lens part 24b Non-lens part 26 Glass substrate 28 Resin portion 28a Concave lens portion 28b Non-lens portion 30 Aperture 32 Resin portion 32a Convex lens portion 32b Non-lens portion 34 Optical axis 36 Sensor 38 Package 40 Cover glass 42 IR cut filter 100 Antireflection film 102 High refractive index layer 104 Low refractive index layer

Claims (9)

In an imaging lens in which a lens portion made of a curable resin is formed on at least one surface of a glass substrate, and an antireflection film is formed on the lens portion,
The antireflection film is composed of a plurality of layers in which high refractive index layers and low refractive index layers are alternately stacked,
The outermost layer of the antireflection film is a low refractive index layer,
The imaging lens, wherein the outermost layer and at least one of the layers provided closer to the lens portion than the outermost layer are a mixed film in which two different inorganic materials are mixed. The imaging lens according to claim 1,
The material constituting the mixed film of the outermost layer is SiO ₂ and Al ₂ O ₃ ,
The imaging lens, wherein a ratio of the number of Al elements to the number of Si elements in the mixed film is 1 to 5%. The imaging lens according to claim 1 or 2,
Of the layers provided closer to the lens part than the outermost layer, at least one high refractive index layer is the mixed film,
The material constituting the mixed film of the high refractive index layer is Ta ₂ O ₅ and TiO ₂ ,
An imaging lens, wherein a ratio of the number of elements of Ti to the number of elements of Ta in the mixed film is 1 to 30%. In the imaging lens according to any one of claims 1 to 3,
Of the layers provided closer to the lens part than the outermost layer, at least one low refractive index layer is the mixed film,
The material constituting the mixed film of the low refractive index layer is SiO ₂ and Al ₂ O ₃ ,
The imaging lens, wherein a ratio of the number of Al elements to the number of Si elements in the mixed film is 1 to 5%. In the imaging lens according to any one of claims 1 to 4,
Of the layers provided closer to the lens unit than the outermost layer, the layer provided closest to the lens unit is the mixed film. The imaging lens according to claim 5,
The imaging lens, wherein the layer provided closest to the lens portion is a low refractive index layer. The imaging lens according to claim 5,
The imaging lens, wherein the layer provided closest to the lens portion is a high refractive index layer. In the imaging lens according to any one of claims 1 to 7,
An imaging lens, wherein all layers of a high refractive index layer and a low refractive index layer constituting the antireflection film are composed of the mixed film. The imaging lens according to claim 8,
All the high refractive index layers constituting the antireflection film are mixed films containing Ta ₂ O ₅ and TiO ₂ , and the ratio of the number of Ti elements to the number of Ta elements in the mixed film is 1 to 30. %
All of the low refractive index layers constituting the antireflection film are mixed films containing SiO ₂ and Al ₂ O ₃ , and the ratio of the number of Al elements to the number of Si elements in the mixed film is 1 to 5 %, An imaging lens.

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