JPWO2018181813A1 - Epoxy resin composition and electronic component device - Google Patents

Abstract

An epoxy resin composition containing an epoxy resin having a melting point or a softening point exceeding 40 ° C, a curing agent, and a compound having a glycidyl group and having a melting point of 40 ° C or less.

Description

  The present invention relates to an epoxy resin composition and an electronic component device.

  2. Description of the Related Art In recent years, as electronic devices have become smaller, lighter, and have higher performance, mounting density has been increasing. As a result, the mainstream of electronic component devices is changing from a conventional pin insertion type package to a surface mount type package such as an IC (Integrated Circuit) or an LSI (Large Scale Integration).

  The mounting method of the surface mount type package is different from that of the conventional pin insertion type package. That is, when the pins are mounted on the wiring board, the conventional pin insertion type package performs soldering from the back surface of the wiring board after inserting the pins into the wiring board, so that the package is not directly exposed to a high temperature. However, in a surface mount type package, since the entire electronic component device is processed by a solder bath, a reflow device, or the like, the package is directly exposed to a soldering temperature (reflow temperature). As a result, when the package absorbs moisture, the moisture due to the moisture absorption rapidly expands during soldering, and the generated vapor pressure acts as a peeling stress, and peeling occurs between the element, the insert such as a lead frame, and the sealing material. This may cause package cracks and poor electrical characteristics. For this reason, development of a sealing material that is excellent in adhesiveness to the insert and, consequently, excellent in solder heat resistance (reflow resistance) is desired.

  In order to respond to these requirements, various studies have been made on solid epoxy resins as main materials. For example, a method using a biphenyl-type epoxy resin or a naphthalene-type epoxy resin as a solid epoxy resin has been studied (for example, see JP-A-64-65116 and JP-A-2007-231159).

  In addition, the use of various epoxy resin modifiers is also being studied, and as one example, use of a silane coupling agent is being studied with an emphasis on improving the adhesion between an element and an insert such as a lead frame. . Specifically, the use of an epoxy group-containing silane coupling agent or an amino group-containing silane coupling agent (for example, see JP-A-11-147939) and the use of a sulfur atom-containing silane coupling agent (for example, JP-A-2000-2000) No. 103940).

However, it has been difficult to balance fluidity and reflow resistance only by using a biphenyl type epoxy resin or a naphthalene type epoxy resin.
Further, the use of an epoxy group-containing silane coupling agent or an amino group-containing silane coupling agent alone may not have a sufficient effect of improving the adhesiveness. In particular, the amino group-containing silane coupling agent described in JP-A-11-147939 has high reactivity, and when used in an epoxy resin composition for sealing, the fluidity during sealing decreases. Furthermore, the epoxy group-containing silane coupling agent and the amino group-containing silane coupling agent described in JP-A-11-147939 have problems in fluidity, such as gelation of the silane coupling agent itself.
In addition, when the sulfur atom-containing silane coupling agent described in JP-A-2000-103940 is used, the effect of improving the adhesion to a noble metal such as Ag and Au is not sufficient, and the effect of improving the reflow resistance is not sufficient. Is also inadequate.

As described above, at present, an epoxy resin composition that sufficiently satisfies both reflow resistance and fluidity has not been obtained.
The present disclosure has been made in view of such circumstances, and has an object to provide an epoxy resin composition having excellent reflow resistance while maintaining fluidity, and an electronic component device including a cured product of the epoxy resin composition. Things.

Means for solving the above problems include the following embodiments.
<1> An epoxy resin composition containing an epoxy resin having a melting point or a softening point exceeding 40 ° C., a curing agent, and a compound having a glycidyl group and having a melting point of 40 ° C. or less.
<2> The epoxy resin composition according to <1>, wherein the compound having a glycidyl group and having a melting point of 40 ° C. or less has a dicyclopentadiene skeleton.
<3> The epoxy resin according to <1> or <2>, wherein the content of the compound having a glycidyl group and having a melting point of 40 ° C or less is 5% by mass or more and less than 45% by mass with respect to the epoxy resin. Composition.
<4> The epoxy resin composition according to any one of <1> to <3>, further containing a curing accelerator.
<5> The epoxy resin composition according to any one of <1> to <4>, further containing an inorganic filler.
<6> The epoxy resin composition according to any one of <1> to <5>, further containing a silane compound.
<7> The epoxy resin composition according to any one of <1> to <6>, wherein the melting point or softening point of the epoxy resin is from 80C to 130C.
<8> The epoxy resin composition according to any one of <1> to <7>, wherein the compound having a glycidyl group and having a melting point of 40 ° C. or less has an epoxy equivalent of 165 g / eq to 365 g / eq.
<9> The content according to any one of <1> to <8>, wherein the content of the compound having a glycidyl group and having a melting point of 40 ° C. or less is 20% by mass or more and less than 45% by mass with respect to the epoxy resin. Epoxy resin composition.
<10> An electronic component device comprising: a device; and a cured product of the epoxy resin composition according to any one of <1> to <9>, which seals the device.

  According to the present disclosure, it is possible to provide an epoxy resin composition having excellent reflow resistance while maintaining fluidity, and an electronic component device including a cured product of the epoxy resin composition. Therefore, its industrial value is great.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including the element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, and does not limit the present invention.

In the present disclosure, the numerical ranges indicated by using “to” include the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described in stages in the present disclosure, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of the numerical range described in other stages. . Further, in the numerical range described in the present disclosure, the upper limit or the lower limit of the numerical range may be replaced with the value shown in the embodiment.
In the present disclosure, the content or content of each component in the composition is, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, the plurality of substances present in the composition Means the total content or content.
In the present disclosure, the term "layer" includes, when observing a region where the layer exists, in addition to a case where the layer is formed over the entire region and a case where the layer is formed only on a part of the region. included.
In the present disclosure, the term "lamination" refers to stacking layers, where two or more layers may be joined, or two or more layers may be removable.

<Epoxy resin composition>
The epoxy resin composition according to the embodiment of the present invention includes an epoxy resin having a melting point or a softening point exceeding 40 ° C. (hereinafter also referred to as “(A) specific epoxy resin” or “specific epoxy resin”) and a curing agent (hereinafter, “ (B) a compound having a glycidyl group and a melting point of 40 ° C. or lower (hereinafter also referred to as “(C) specific glycidyl compound” or “specific glycidyl compound”); It contains. The epoxy resin composition may contain other components as needed. In addition, as the (C) specific glycidyl compound, for example, a compound which is liquid at normal temperature (for example, 25 ° C.) can be mentioned.
With such a configuration, the epoxy resin composition is excellent in reflow resistance. The epoxy resin composition has good fluidity.

  The reason why the epoxy resin composition is excellent in reflow resistance while maintaining fluidity is not clear, but can be considered as follows. Specifically, the glycidyl group in the specific glycidyl compound is combined with the curing agent in the epoxy resin composition, so that the effect of improving the adhesive force and the effect of reducing the elastic modulus are obtained, and the high fluidity is maintained while maintaining high fluidity. It is considered that the reflow property is improved.

Examples of the epoxy resin composition include those which are solid at normal temperature and normal pressure (for example, 25 ° C. and 1 atm). The shape of the solid is not limited, and may be any shape such as a powder, a granule, and a tablet.
Further, the epoxy resin composition may be used as a sealing resin composition and further as a transfer molding resin composition.

(C) Specific glycidyl compound (C) The specific glycidyl compound is a compound having a glycidyl group in the molecular structure and having a melting point of 40 ° C or lower. The specific glycidyl compound may be used alone or in combination of two or more.
Since the epoxy resin composition contains the specific glycidyl compound, the epoxy resin composition is excellent in reflow resistance while maintaining fluidity.
The number of glycidyl groups in one molecule of the specific glycidyl compound is preferably from 1 to 6, more preferably from 2 to 4, from the viewpoint of obtaining an epoxy resin composition having excellent reflow resistance while maintaining fluidity.

The specific glycidyl compound preferably further has a dicyclopentadiene skeleton in the molecular structure from the viewpoint of obtaining an epoxy resin composition having excellent reflow resistance while maintaining fluidity. By including a specific glycidyl compound having a glycidyl group and a dicyclopentadiene skeleton in the molecular structure, the glycidyl group in the specific glycidyl compound binds to the curing agent in the epoxy resin composition, and further includes a dicyclopentadiene structure. Is presumed to further improve the adhesive force because of the interaction with the metal surface.
The number of dicyclopentadiene skeletons in one molecule of the specific glycidyl compound is preferably from 1 to 4, more preferably from 1 to 2, from the viewpoint of obtaining an epoxy resin composition having excellent reflow resistance while maintaining fluidity. .

Specific examples of the specific glycidyl compound include, for example, dicyclopentadiene dimethanol diglycidyl ether.
Specific examples of the specific glycidyl compound include, in addition to the above-mentioned compounds, a rubber-crosslinked bisphenol-type epoxy resin and a chelate-modified epoxy resin.

The molecular weight of the specific glycidyl compound is preferably from 100 to 600, more preferably from 200 to 400, from the viewpoint of obtaining an epoxy resin composition having excellent reflow resistance while maintaining fluidity.
In addition, the melting point of the specific glycidyl compound is 40 ° C or less, and from the viewpoint of obtaining an epoxy resin composition having excellent reflow resistance while maintaining fluidity, 0 ° C to 35 ° C is preferable, and 0 ° C to 30 ° C is more preferable. preferable.
The epoxy equivalent of the specific glycidyl compound is preferably from 165 g / eq to 365 g / eq, more preferably from 165 g / eq to 240 g / eq.

The content of the specific glycidyl compound in the epoxy resin composition is preferably from 5% by mass to less than 45% by mass based on the total amount of the specific epoxy resin (A). When the content is 5% by mass or more, the adhesiveness is improved as compared with the case where the content is less than 5% by mass, and the effect of improving the reflow resistance tends to be obtained. Further, when the content is less than 45% by mass, a decrease in hardness during molding tends to be suppressed as compared with the case where the content is 45% by mass or more.
The content of the specific glycidyl compound is more preferably from 10% by mass to less than 45% by mass, more preferably from 20% by mass to less than 45% by mass, more preferably from 25% by mass or more, based on the total amount of the specific epoxy resin (A). Less than 45% by weight is particularly preferred.
Further, the content of the specific glycidyl compound is preferably 1% by mass or more based on the whole epoxy resin composition.

(A) Specific epoxy resin The epoxy resin composition contains at least one kind of epoxy resin having a melting point or a softening point exceeding 40 ° C (that is, (A) a specific epoxy resin).
Here, the melting point or softening point of the epoxy resin is a value measured by a single cylinder rotational viscometer described in JIS K 7234: 1986 and JIS K 7233: 1986.
The specific epoxy resin may be one generally used in an epoxy resin composition, and is not particularly limited as long as it has a melting point or a softening point exceeding 40 ° C.
The melting point or softening point of the specific epoxy resin is preferably 45 ° C to 180 ° C, more preferably 50 ° C to 150 ° C, and more preferably 80 ° C to obtain an epoxy resin composition having excellent reflow resistance while maintaining fluidity. 130 ° C is more preferred, and 96 ° C to 113 ° C is particularly preferred.

Among the specific epoxy resins, those containing two or more epoxy groups in one molecule are preferable.
The epoxy equivalent of the specific epoxy resin is preferably from 100 g / eq to 1000 g / eq, more preferably from 150 g / eq to 1000 g / eq, from the viewpoint of obtaining an epoxy resin composition having excellent reflow resistance while maintaining fluidity, and more preferably 150 g. / Eq to 500 g / eq is more preferable, and 196 g / eq to 245 g / eq is particularly preferable.
The epoxy equivalent is measured by dissolving the weighed epoxy resin in a solvent such as methyl ethyl ketone, adding acetic acid and a tetraethylammonium bromide acetic acid solution, and then performing potentiometric titration with a perchloric acid acetic acid standard solution. In this titration, an indicator may be used.

  The specific epoxy resin is specifically selected from the group consisting of phenol compounds such as phenol, cresol, xylenol, resorcin, catechol, bisphenol A, bisphenol F and naphthol compounds such as α-naphthol, β-naphthol and dihydroxynaphthalene. A novolak-type epoxy resin obtained by epoxidizing a novolak resin obtained by condensing or co-condensing at least one phenolic compound with an aliphatic aldehyde compound such as formaldehyde, acetaldehyde, and propionaldehyde under an acidic catalyst ( A phenol novolak type epoxy resin, an orthocresol novolak type epoxy resin, etc.); an acidic catalyst comprising the above phenolic compound and an aromatic aldehyde compound such as benzaldehyde and salicylaldehyde. A triphenylmethane-type epoxy resin obtained by epoxidizing a triphenylmethane-type phenol resin obtained by condensation or co-condensation under the above conditions; co-condensing the phenol compound and the naphthol compound with an aldehyde compound under an acidic catalyst. Epoxy resin obtained by epoxidizing the novolak resin obtained by the above method; diphenylmethane type epoxy resin which is a diglycidyl ether such as bisphenol A and bisphenol F; biphenyl type which is a diglycidyl ether of an alkyl-substituted or unsubstituted biphenol Epoxy resin; stilbene type epoxy resin which is diglycidyl ether of stilbene phenol compound; diglycidyl ether of bisphenol S, epoxy resin containing sulfur atom such as thiodiphenol type epoxy resin; butanediol Epoxy resins which are glycidyl ethers of alcohols such as polyethylene glycol and polypropylene glycol; glycidyl ester type epoxy resins which are glycidyl esters of polycarboxylic acids such as phthalic acid, isophthalic acid and tetrahydrophthalic acid; aniline, diaminodiphenylmethane, A glycidylamine-type epoxy resin obtained by replacing active hydrogen bonded to a nitrogen atom such as isocyanuric acid with a glycidyl group; a dicyclopentadiene-type epoxy resin obtained by epoxidizing a cocondensation resin of dicyclopentadiene and a phenol compound Vinylcyclohexene diepoxide obtained by epoxidizing an olefin bond in the molecule, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 2 Alicyclic epoxy resins such as (3,4-epoxy) cyclohexyl-5,5-spiro (3,4-epoxy) cyclohexane-m-dioxane; para-xylylene-modified epoxy resin which is a glycidyl ether of para-xylylene-modified phenol resin; meta-xylylene-modified A metaxylylene-modified epoxy resin that is a glycidyl ether of a phenol resin; a terpene-modified epoxy resin that is a glycidyl ether of a terpene-modified phenol resin; a dicyclopentadiene-modified epoxy resin that is a glycidyl ether of a dicyclopentadiene-modified phenol resin; A cyclopentadiene-modified epoxy resin which is a glycidyl ether; a polycyclic aromatic ring-modified epoxy resin which is a glycidyl ether of a polycyclic aromatic ring-modified phenolic resin; Naphthalene type epoxy resin which is a glycidyl ether of phthalene ring-containing phenol resin; halogenated phenol novolak type epoxy resin; hydroquinone type epoxy resin; trimethylolpropane type epoxy resin; obtained by oxidizing olefin bond with peracid such as peracetic acid. Linear aliphatic epoxy resins; aralkyl type epoxy resins obtained by epoxidizing aralkyl type phenol resins such as phenol aralkyl resins having a biphenylene skeleton and naphthol aralkyl resins; and the like. Further, epoxidized silicone resin, epoxidized acrylic resin, and the like are also included as the specific epoxy resin. These epoxy resins may be used alone or in combination of two or more.

As the specific epoxy resin, among the above epoxy resins, from the viewpoint of fluidity and reflow resistance, a bisphenol F type epoxy resin having a bisphenol F skeleton, a stilbene type epoxy resin, and a sulfur atom-containing epoxy resin are exemplified. Preferably, a novolak type epoxy resin is preferable from the viewpoint of curability, a dicyclopentadiene type epoxy resin is preferable from the viewpoint of low hygroscopicity, and a naphthalene type epoxy resin is preferable from the viewpoint of heat resistance and low warpage. From the viewpoint of properties, a biphenylene type epoxy resin which is an epoxy resin having a biphenylene skeleton and a naphthol aralkyl type epoxy resin obtained by epoxidizing a naphthol aralkyl resin are preferable.
Specific epoxy resins include bisphenol F type epoxy resin, stilbene type epoxy resin, sulfur atom containing epoxy resin, novolak type epoxy resin, dicyclopentadiene type epoxy resin, naphthalene type epoxy resin, biphenylene type epoxy resin, and naphthol aralkyl type epoxy resin It is preferable to contain at least one of the following. It is preferable to use a resin having good flame retardancy as a specific epoxy resin to be non-halogen and non-antimony (that is, to use an epoxy resin having neither a halogen atom nor an antimony atom) from the viewpoint of improving high-temperature storage characteristics. .

  In addition, the specific epoxy resin can be selected and used according to the purpose and production conditions. For example, as the specific epoxy resin, a phenyl aralkyl type epoxy resin having a biphenylene skeleton-containing phenol aralkyl type epoxy resin, which is an epoxidized product of a phenol aralkyl resin having a biphenylene skeleton, and a methoxy naphthalene type epoxy resin having an methoxy naphthalene skeleton alone or in combination. Can be used.

  Bisphenol F type epoxy resin, stilbene type epoxy resin, sulfur atom containing epoxy resin, novolak type epoxy resin, dicyclopentadiene type epoxy resin, naphthalene type epoxy resin, biphenylene type epoxy resin, and naphthol aralkyl type epoxy to the entire specified epoxy resin The total content of the resin is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more.

  The content of the specific epoxy resin as a whole is preferably from 0.4% by mass to 28% by mass in the epoxy resin composition, from the viewpoint of balance of various properties such as moldability, reflow resistance, and electrical reliability. % By mass is more preferred. When the content of the specific epoxy resin in the epoxy resin composition is 28% by mass or less, reflow resistance tends to be better maintained than when the content exceeds 28% by mass. When the content is 0.4% by mass or more, the fluidity tends to be better maintained than when the content is less than 0.4% by mass.

(B) Curing agent The epoxy resin composition contains at least one kind of curing agent. The curing agent may be one generally used in an epoxy resin composition, and is not particularly limited.
(B) Examples of the curing agent include a phenol curing agent, an amine curing agent, an acid anhydride curing agent, a polymercaptan curing agent, a polyaminoamide curing agent, an isocyanate curing agent, and a blocked isocyanate curing agent. From the viewpoint of obtaining an epoxy resin composition having excellent reflow resistance while maintaining fluidity, the curing agent is preferably a phenol curing agent, an amine curing agent, and an acid anhydride curing agent, and more preferably a phenol curing agent.

  Examples of the phenol curing agent include a phenol resin having two or more phenolic hydroxyl groups in one molecule and a polyhydric phenol compound. Specifically, polyhydric phenol compounds such as resorcin, catechol, bisphenol A, bisphenol F, substituted or unsubstituted biphenol; phenol, cresol, xylenol, resorcin, catechol, bisphenol A, bisphenol F, phenylphenol, aminophenol, etc. Condensation of at least one phenolic compound selected from the group consisting of phenol compounds and naphthol compounds such as α-naphthol, β-naphthol and dihydroxynaphthalene with aldehyde compounds such as formaldehyde, acetaldehyde and propionaldehyde under an acidic catalyst Or a novolak-type phenol resin obtained by co-condensation; synthesized from the above phenolic compound, dimethoxyparaxylene, bis (methoxymethyl) biphenyl and the like. Aralkyl-type phenolic resin (phenol aralkyl resin, naphthol aralkyl resin, etc.); para-xylylene-modified phenolic resin; meta-xylylene-modified phenolic resin; melamine-modified phenolic resin; terpene-modified phenolic resin; synthesized by copolymerization of the above phenolic compound with dicyclopentadiene Dicyclopentadiene-type phenolic resin and dicyclopentadiene-type naphthol resin; cyclopentadiene-modified phenolic resin; polycyclic aromatic ring-modified phenolic resin; biphenyl-type phenolic resin; the above phenolic compound and aromatic aldehydes such as benzaldehyde and salicylaldehyde A triphenylmethane-type phenol resin obtained by condensing or co-condensing a compound with an acidic catalyst; a phenol resin obtained by copolymerizing two or more of these compounds. ; And the like. These phenol resins may be used alone or in combination of two or more.

  The curing agents exemplified above (that is, novolak type phenol resin, aralkyl type phenol resin, paraxylylene modified phenol resin, metaxylylene modified phenol resin, melamine modified phenol resin, terpene modified phenol resin, dicyclopentadiene type phenol resin, dicyclopentadiene type A naphthol resin, a cyclopentadiene-modified phenol resin, a polycyclic aromatic ring-modified phenol resin, a biphenyl-type phenol resin, a triphenylmethane-type phenol resin, and a phenol resin obtained by copolymerizing two or more of these. Species may be used alone or in combination of two or more. The content of the above-mentioned curing agent (when two or more kinds are used, the total thereof) is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 80% by mass or more based on the total amount of the curing agent.

The functional group equivalent of the curing agent is not particularly limited, and is preferably from 70 g / eq to 1000 g / eq, more preferably from 80 g / eq to 500 g / eq, from the viewpoint of balance between moldability, reflow resistance, and electrical reliability. preferable. The functional group equivalent refers to a value measured according to JIS K0070: 1992.
The softening point or melting point of the curing agent is not particularly limited, and is preferably from 40 ° C to 180 ° C from the viewpoint of moldability and reflow resistance, and from 50 ° C to 130 ° C from the viewpoint of handleability at the time of preparing the epoxy resin composition. Is more preferred. The method for measuring the softening point or melting point of the curing agent is the same as the method for measuring the softening point or melting point of the specific epoxy resin.

  In the epoxy resin composition, the equivalent ratio of (A) the specific epoxy resin and (C) the specific glycidyl compound to (B) the curing agent, that is, the amount of the epoxy resin and the specific glycidyl compound in the curing agent relative to the total amount of epoxy groups and glycidyl groups in the specific epoxy resin and the specific glycidyl compound (The number of functional groups in the curing agent / the total of the number of epoxy groups and the number of glycidyl groups in the specific epoxy resin and the specific glycidyl compound) is not particularly limited. In order to reduce the amount of each unreacted component, it is preferably set in the range of 0.5 to 2.0, and more preferably in the range of 0.6 to 1.3. In order to obtain an epoxy resin composition which is more excellent in moldability, solder resistance and reflow resistance, it is more preferably set in the range of 0.8 to 1.2. When the above ratio is 0.5 or more, the epoxy resin composition is more easily cured than when the ratio is less than 0.5, and the heat resistance, moisture resistance, and electric resistance of the cured product of the epoxy resin composition are improved. Properties tend to be good. On the other hand, as compared with the case where the ratio exceeds 2.0 by the ratio being 2.0 or less, the curing efficiency decreases due to an excessive amount of the curing agent component, and a large amount of functional groups remain in the cured product. There is a tendency that a decrease in electrical characteristics and moisture resistance of the package is suppressed. In particular, when the phenolic curing agent is used as the curing agent, the ratio is 2.0 or less, and the curing efficiency is reduced due to an excess of the phenolic resin component, and the curing is performed, as compared with the case where the ratio exceeds 2.0. There is a tendency that a decrease in electrical characteristics and moisture resistance of the package due to a large amount of phenolic hydroxyl groups remaining in the product is suppressed.

(D) Curing Accelerator The epoxy resin composition may contain at least one of (D) a curing accelerator, if necessary, in addition to (A) the specific epoxy resin, (B) the curing agent, and (C) the specific glycidyl compound. May be included. The curing accelerator is not limited as long as it is a compound that promotes the reaction between the specific epoxy resin (A) and the curing agent (B).
(D) As the curing accelerator, for example, 1,8-diaza-bicyclo (5,4,0) undecene-7,1,5-diaza-bicyclo (4,3,0) nonene, 5,6-dibutyl A cycloamidine compound such as amino-1,8-diaza-bicyclo (5,4,0) undecene-7; a maleic anhydride, a quinone compound (for example, 1,4-benzoquinone, 2,5- Tolquinone, 1,4-naphthoquinone, 2,3-dimethylbenzoquinone, 2,6-dimethylbenzoquinone, 2,3-dimethoxy-5-methyl-1,4-benzoquinone, 2,3-dimethoxy-1,4-benzoquinone, Phenyl-1,4-benzoquinone), diazophenylmethane, a compound having a π bond such as a phenol resin, and a compound having intramolecular polarization; Tertiary amines such as ruamine, triethanolamine, dimethylaminoethanol and tris (dimethylaminomethyl) phenol and derivatives thereof; imidazoles such as 2-methylimidazole, 2-phenylimidazole and 2-phenyl-4-methylimidazole And derivatives thereof; phosphine compounds such as tributylphosphine, methyldiphenylphosphine, triphenylphosphine, tris (4-methylphenyl) phosphine, diphenylphosphine, and phenylphosphine; Phosphorus compound having intramolecular polarization obtained by adding a compound having a π bond such as methane or phenol resin; tetraphenylphosphonium tetraphenylborate, triphenylphosphine Tiger tetraphenylborate, 2-ethyl-4-methylimidazole tetraphenyl borate, tetraphenyl boron salts and derivatives thereof such as N- methylmorpholine tetraphenylborate; and the like. These curing accelerators may be used alone or in combination of two or more.

  (D) The content of the curing accelerator is not particularly limited as long as the curing acceleration effect is achieved, and is preferably 0.005% by mass to 2% by mass in the epoxy resin composition, and 0.01% by mass. More preferably, it is from 0.5% by mass to 0.5% by mass. When the content of the curing accelerator in the epoxy resin composition is 0.005% by mass or more, the curability in a short time tends to be improved as compared with the case where the content is less than 0.005% by mass, When the content is 2% by mass or less, the curing rate is not too high as compared with the case where the content is more than 2% by mass, so that a good molded product tends to be easily obtained.

(E) Inorganic filler In addition to (A) the specific epoxy resin, (B) the curing agent, and (C) the specific glycidyl compound, the epoxy resin composition may further include, if necessary, at least one of (E) an inorganic filler. May be included. The inorganic filler can be used, for example, for the purpose of absorbing moisture, reducing the coefficient of linear expansion, improving thermal conductivity, and improving strength.

The type of the inorganic filler is not particularly limited. Specifically, spherical silica (for example, fused silica), crystalline silica, glass, alumina, calcium carbonate, zirconium silicate, calcium silicate, potassium titanate, silicon carbide, silicon nitride, aluminum nitride, boron nitride, beryllia, Examples include inorganic materials such as zirconia, zircon, fosterite, steatite, spinel, mullite, titania, talc, clay, and mica. An inorganic filler having a flame retardant effect may be used. Examples of the inorganic filler having a flame-retardant effect include aluminum hydroxide, magnesium hydroxide, a composite metal hydroxide such as a composite hydroxide of magnesium and zinc, zinc borate, and zinc molybdate.
Examples of the shape of the inorganic filler include powder, spherical beads, and fibers.

  These inorganic fillers may be used alone or in combination of two or more. Among them, spherical silica is preferable from the viewpoint of the filling property and the reduction of the linear expansion coefficient, and alumina is preferable from the viewpoint of the high thermal conductivity. The shape of the inorganic filler is preferably spherical from the viewpoint of filling properties and mold wear.

  The content of the inorganic filler in the epoxy resin composition is preferably 60% by mass or more, and more preferably 60% by mass or more, from the viewpoints of flame retardancy, moldability, hygroscopicity, reduction of linear expansion coefficient, strength improvement, and reflow resistance. 95 mass% is more preferable from a flame-retardant viewpoint, and 70 mass% to 90 mass% is even more preferable. When the content of the inorganic filler in the epoxy resin composition is 60% by mass or more, the flame retardancy and reflow resistance tend to be improved as compared with the case where the content is less than 60% by mass. When the content of the inorganic filler in the epoxy resin composition is 95% by mass or less, the fluidity tends to be improved and the flame retardancy tends to be improved as compared with the case where the content exceeds 95% by mass.

  The epoxy resin composition may further include, as necessary, a coupling agent, a flame retardant, and an anion described below, in addition to the above-mentioned components (A) the specific epoxy resin, (B) the curing agent, and (C) the specific glycidyl compound. Various additives such as an exchanger, a release agent, a colorant, and a stress relaxing agent may be included. In addition, various additives known in the art may be added to the epoxy resin composition as needed without being limited to the following additives.

(F) Coupling agent The epoxy resin composition may contain at least one coupling agent, if necessary, in order to enhance the adhesiveness between the resin component and the filler.
The coupling agent is not particularly limited as long as it is generally used in an epoxy resin composition. For example, the coupling agent has at least one of a primary amino group, a secondary amino group, and a tertiary amino group. Silane compounds, epoxy silanes, mercapto silanes, alkyl silanes, ureido silanes, vinyl silanes and other silane compounds (eg, the following silane coupling agents), titanium compounds (eg, the following titanate coupling agents), aluminum chelates And aluminum / zirconium-based compounds.
From the viewpoint of reflow resistance, it is preferable to use the silane compound as a coupling agent.

  Specific examples of the coupling agent include vinyltrichlorosilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, and β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane Γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, vinyltriacetoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-anilinopropyltrimethoxysilane, γ-anilinopropyltriethoxysilane, γ- (N, N-dimethyl) aminopropyl Trimethoxysilane, γ- (N, N-diethyl) aminopropyltrimethoxysilane, γ- (N, N-dibutyl) aminopropyltrimethoxysilane, γ- (N-methyl) anilinopropyltrimethoxysilane, γ- (N-ethyl) anilinopropyltrimethoxysilane, γ- (N, N-dimethyl) aminopropyltriethoxysilane, γ- (N, N-diethyl) aminopropyltriethoxysilane, γ- (N, N-dibutyl) ) Aminopropyltriethoxysilane, γ- (N-methyl) anilinopropyltriethoxysilane, γ- (N-ethyl) anilinopropyltriethoxysilane, γ- (N, N-dimethyl) aminopropylmethyldimethoxysilane, γ- (N, N-diethyl) aminopropylmethyldimethoxysilane, γ- (N, N-dibutyl) Aminopropylmethyldimethoxysilane, γ- (N-methyl) anilinopropylmethyldimethoxysilane, γ- (N-ethyl) anilinopropylmethyldimethoxysilane, N- (trimethoxysilylpropyl) ethylenediamine, N- (dimethoxymethylsilyl) Isopropyl) silane coupling agents such as ethylenediamine, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, γ-chloropropyltrimethoxysilane, hexamethyldisilane, vinyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane; Isopropyl triisostearoyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, isopropyl tri (N-aminoethyl-aminoethyl) titanate Tetraoctylbis (ditridecylphosphite) titanate, tetra (2,2-diallyloxymethyl-1-butyl) bis (ditridecylphosphite) titanate, bis (dioctylpyrophosphate) oxyacetate titanate, bis (dioctylpyrophosphate) Ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacryl isosteroyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl isostearyl diacryl titanate, isopropyl tri (dioctyl phosphate) titanate, isopropyl tricumyl phenyl titanate, tetraisopropyl bis (dioctyl phosphate) Phyto) titanate coupling agents such as titanate; These may be used alone or in combination of two or more.

  Among them, a silane coupling agent having a secondary amino group is preferable from the viewpoint of fluidity and flame retardancy. The silane coupling agent having a secondary amino group is not particularly limited as long as it is a silane compound having a secondary amino group in the molecule. Specific examples thereof include γ-anilinopropyltrimethoxysilane and γ-anilinopropyltrimethoxysilane. Ethoxysilane, γ-anilinopropylmethyldimethoxysilane, γ-anilinopropylmethyldiethoxysilane, γ-anilinopropylethyldiethoxysilane, γ-anilinopropylethyldimethoxysilane, γ-anilinomethyltrimethoxysilane, γ-anilinomethyltriethoxysilane, γ-anilinomethylmethyldimethoxysilane, γ-anilinomethylmethyldiethoxysilane, γ-anilinomethylethyldiethoxysilane, γ-anilinomethylethyldimethoxysilane, N- ( p-methoxyphenyl) -γ-aminopropyltri Toxysilane, N- (p-methoxyphenyl) -γ-aminopropyltriethoxysilane, N- (p-methoxyphenyl) -γ-aminopropylmethyldimethoxysilane, N- (p-methoxyphenyl) -γ-aminopropylmethyl Diethoxysilane, N- (p-methoxyphenyl) -γ-aminopropylethyldiethoxysilane, N- (p-methoxyphenyl) -γ-aminopropylethyldimethoxysilane, γ- (N-methyl) aminopropyltrimethoxy Silane, γ- (N-ethyl) aminopropyltrimethoxysilane, γ- (N-butyl) aminopropyltrimethoxysilane, γ- (N-benzyl) aminopropyltrimethoxysilane, γ- (N-methyl) aminopropyl Triethoxysilane, γ- (N-ethyl) aminopropyltriet Sisilane, γ- (N-butyl) aminopropyltriethoxysilane, γ- (N-benzyl) aminopropyltriethoxysilane, γ- (N-methyl) aminopropylmethyldimethoxysilane, γ- (N-ethyl) aminopropyl Methyldimethoxysilane, γ- (N-butyl) aminopropylmethyldimethoxysilane, γ- (N-benzyl) aminopropylmethyldimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, γ- ( β-aminoethyl) aminopropyltrimethoxysilane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, and the like.

  The content of the coupling agent in the epoxy resin composition is preferably 0.037% by mass to 4.75% by mass, more preferably 0.05% by mass to 5% by mass, and 0.1% by mass to 2.5% by mass. % By mass is more preferred. 3. When the content of the coupling agent in the epoxy resin composition is 0.037% by mass or more, the adhesiveness to the frame tends to be improved as compared with the case where the content is less than 0.037% by mass. When the content is 75% by mass or less, the moldability of the package tends to be improved as compared with the case where the content exceeds 4.75% by mass.

  The epoxy resin composition may be blended with at least one flame retardant, if necessary, to impart flame retardancy. The flame retardant is not particularly limited, and examples thereof include a known organic or inorganic compound containing a halogen atom, an antimony atom, a nitrogen atom, or a phosphorus atom, a metal hydroxide, and the like. Or two or more kinds may be used in combination. The content of the flame retardant is not particularly limited as long as the flame retardant effect is achieved, and is preferably 1% by mass to 30% by mass, more preferably 2% by mass to 15% by mass with respect to the specific epoxy resin (A).

In the epoxy resin composition, at least one kind of anion exchanger can be blended as required. In particular, since the epoxy resin composition uses the epoxy resin composition as a molding material for sealing, from the viewpoint of improving the moisture resistance and high-temperature storage characteristics of an electronic component device including an element to be sealed, Preferably, it contains an exchanger.
The anion exchanger is not particularly limited, and conventionally known ones can be used. Specific examples thereof include hydrotalcites; hydrated oxides of elements selected from magnesium, aluminum, titanium, zirconium, and bismuth; And the like. One type of anion exchanger may be used alone, or two or more types may be used in combination. Among them, the anion exchanger is preferably hydrotalcite represented by the following general formula (1).

Mg _1-X Al _X (OH) ₂ (CO ₃ ) _{X / 2} · mH ₂ O (1)
(In the formula (1), 0 <X ≦ 0.5, m is a positive number)

  The content of the anion exchanger is not particularly limited as long as it is a sufficient amount capable of capturing anions such as halogen ions, and is preferably 0.1% by mass to 30% by mass with respect to the specific epoxy resin (A). 1 mass%-5 mass% are more preferable.

  Further, in the epoxy resin composition, as other additives, release agents such as higher fatty acids, metal salts of higher fatty acids, ester waxes, polyolefin waxes, polyethylene and polyethylene oxide; coloring agents such as carbon black; silicone oil And a stress relieving agent such as silicone rubber powder; and the like, if necessary.

  The epoxy resin composition can be prepared by any method as long as the various raw materials can be dispersed and mixed. As a general method, after thoroughly mixing the raw materials with a mixer or the like, a mixing roll, an extruder, a raiker After mixing or melt-kneading with a planetary mixer or the like, a method of cooling, and defoaming and pulverizing as necessary can be mentioned. If necessary, the tablet may be formed into a tablet having a size and weight suitable for the molding conditions.

<Electronic component device>
An electronic component device according to an embodiment of the present invention includes an element and a cured product of the above-described epoxy resin composition that seals the element.
As electronic component devices, elements (active elements such as semiconductor chips, transistors, diodes, thyristors, capacitors, resistors, etc.) are mounted on supporting members or mounting substrates such as lead frames, wired tape carriers, wiring boards, glass and silicon wafers. , A passive element such as a coil, etc.), and a necessary part sealed with the epoxy resin composition described above.

  Here, the mounting substrate is not particularly limited, and specific examples thereof include an organic substrate, an organic film, a ceramic substrate, an interposer substrate such as a glass substrate, a liquid crystal glass substrate, an MCM (Multi Chip Module) substrate, and a hybrid. IC substrates and the like.

  Specific examples of the electronic component device include, for example, a semiconductor device. More specifically, an element such as a semiconductor chip is arranged on a lead frame (island, tab), and a terminal portion of the element such as a bonding pad is provided. The leads are connected by wire bonding, bumps, or the like, and then sealed by transfer molding or the like using the epoxy resin composition. DIP (Dual Inline Package), PLCC (Plastic Leaded Chip Carrier), QFP (Quad Flat) Package), SOP (Small Outline Package), SOJ (Small Outline J-lead package), TSOP (Thin Small Outline Package), TQFP (Thin Qu) a resin-packaged IC such as d Flat Package); a TCP (Tape Carrier Package) in which a semiconductor chip lead-bonded to a tape carrier is sealed with the epoxy resin composition; a wire formed on a wiring board or glass; A semiconductor device in which a semiconductor chip connected by bonding, flip chip bonding, soldering or the like is mounted on a bare chip such as COB (Chip On Board) or COG (Chip On Glass) sealed with the epoxy resin composition; on a wiring board or glass At least one of an active element (semiconductor chip, transistor, diode, thyristor, etc.) and a passive element (capacitor, resistor, coil, etc.) connected to the wiring formed by wire bonding, flip chip bonding, soldering, etc. A semiconductor chip is mounted on an interposer substrate formed with terminals for connecting a hybrid IC, MCM (Multi Chip Module); motherboard, and sealed with the epoxy resin composition, and the semiconductor chip and the interposer substrate are bonded to each other by bump or wire bonding. After connection with the formed wiring, BGA (Ball Grid Array), CSP (Chip Size Package), MCP (Multi Chip Package), and the like, in which the semiconductor chip mounting side is sealed with the epoxy resin composition. In addition, even if these semiconductor devices are stacked (laminated) type packages in which two or more elements are mounted on a mounting board in an overlapping manner, two or more elements are sealed with an epoxy resin composition at a time. The package may be a packaged mold package.

  In addition, as a method for obtaining an electronic component device such as a semiconductor device in which elements are sealed using the epoxy resin composition as a sealing material, a low-pressure transfer molding method is the most common, but an injection molding method, A compression molding method is also included. As a method for obtaining an electronic component device such as a semiconductor device in which elements are sealed, a dispensing method, a casting method, a printing method, or the like may be used.

  Hereinafter, the above-described embodiment will be specifically described with reference to examples, but the scope of the embodiment is not limited to these examples. Unless otherwise specified, “parts” and “%” are based on mass.

  The following components were blended in parts by mass shown in Tables 1 and 2 below, and were melt-kneaded at a kneading temperature of 135 ° C. by an extruder to prepare epoxy resin compositions of Examples and Comparative Examples. The blanks in the table indicate "no compounding".

(A) As the specific epoxy resin,
Epoxy resin 1: thiodiphenol type epoxy resin (manufactured by Nippon Steel & Sumitomo Chemical Co., Ltd., trade name: YSLV-120TE, epoxy equivalent 245, softening point 113 ° C)
Epoxy resin 2: an aralkyl type epoxy resin obtained by epoxidizing a phenol aralkyl resin having a biphenylene skeleton (trade name: CER-3000L, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent 240, softening point 96 ° C.)
Epoxy resin 3: Biphenyl type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: YX-4000, epoxy equivalent 196, melting point 106 ° C)
It was used.

(B) As the curing agent,
Curing agent 1: Phenol aralkyl resin having a hydroxyl equivalent of 176 and a softening point of 70 ° C. (trade name: MILEX XLC, manufactured by Mitsui Chemicals, Inc.)
Curing agent 2: Melamine-modified phenol resin having a hydroxyl equivalent of 120 and a softening point of 85 ° C (trade name: HPM-J3, manufactured by Hitachi Chemical Co., Ltd.)
It was used.

(C) Specific glycidyl compounds (compounds having a glycidyl group in the structure) include:
Liquid resin 1: dicyclopentadiene dimethanol diglycidyl ether (manufactured by ADEKA Corporation, trade name: EP-4088L, epoxy equivalent: 165, melting point: 25 ° C. or less)
Liquid resin 2: rubber-crosslinked bisphenol-type epoxy resin (manufactured by ADEKA Corporation, trade name: EPR-4030, epoxy equivalent 365, melting point: 25 ° C. or less)
Liquid resin 3: Chelate-modified epoxy resin (ADEKA Corporation, trade name: EP-49-10N, epoxy equivalent 220, melting point: 25 ° C or less)
It was used.

(D) As the curing accelerator,
Curing accelerator 1: Addition product of triphenylphosphine and benzoquinone Curing accelerator 2: A mixture of triparatolylphosphine / parabenzoquinone was used.

(E) As the inorganic filler,
Fused silica: spherical fused silica having a volume average particle size of 18 μm and a specific surface area of 1.5 m ² / g was used.

(F) As the coupling agent,
Coupling agent 1: γ-mercaptopropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., trade name: KBM-803)
Coupling agent 2: N-phenyl-γ-aminopropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., trade name: KBM-573)
Coupling agent 3: Methyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., trade name: KBM-13)
It was used.

In addition, as various additives,
Colorant: carbon black (manufactured by Mitsubishi Chemical Corporation, trade name: MA100)
Release agent: montanic acid ester (manufactured by Clariant Japan KK, trade name: HW-E)
Additives: magnesium aluminum hydroxide carbonate hydrate (anion exchanger, hydrotalcites, Sakai Chemical Industry Co., Ltd., trade name: HT-P)
It was used.

  The epoxy resin compositions of Examples and Comparative Examples were evaluated by the following various property tests (1) to (5). The evaluation results are shown in Tables 1 and 2 below. The molding of the epoxy resin composition was performed by a transfer molding machine under the conditions of a mold temperature of 180 ° C., a molding pressure of 6.9 MPa, and a curing time of 90 seconds, unless otherwise specified. Post-curing was performed at 175 ° C. for 6 hours as needed.

(1) Spiral flow Using a mold for spiral flow measurement according to EMMI-1-66, the epoxy resin composition was molded under the above conditions, and the flow distance (cm) was determined.

(2) Hot Hardness The epoxy resin composition was molded into a disk having a diameter of 50 mm and a thickness of 3 mm under the above conditions, and immediately after molding, a Shore D type hardness meter (manufactured by Kamishima Seisakusho Co., Ltd., product number: HD-1120 (type D )) Was used to measure the hot hardness.

(3) Flexural modulus at 260 ° C (high temperature bending test)
The epoxy resin composition was molded into a size of 10 mm × 70 mm × 3 mm under the above conditions and post-cured to prepare a test piece. The obtained test piece was subjected to a three-point bending test according to JIS K6911: 2006 using a bending tester (manufactured by A & D Co., Ltd., product name: Tensilon) while maintaining the temperature at 260 ° C. in a constant temperature bath. The flexural modulus (MPa) at 260 ° C. was determined from the equation.
In the following equation, “E” is the flexural modulus (Pa), “ΔP” is the value of the load cell (N), “Δy” is the displacement (mm), “l” is the span (= 48 mm), and “w”. "" Indicates a specimen width (= 10 mm), and "h" indicates a specimen thickness (= 3 mm).

(4) Adhesion test A palladium-plated copper plate was placed on a mold having a slit of 9 mm x 9 mm, and the epoxy resin composition was placed there under the conditions described above, with a bottom diameter of 4 mm, a top diameter of 3 mm, and a height of 4 mm. It was molded into a size, post-cured, and measured for shear adhesive strength (MPa) at room temperature (25 ° C.) at a shear rate of 50 μm / s using a bond tester (Series 4000 manufactured by Nordson Advanced Technology).

(5) Reflow resistance 20-mm x 14-mm x 2-mm 80-pin flat package (QFP) with a silicon chip of 8 mm x 10 mm x 0.4 mm (lead frame material: copper alloy, die pad top surface, and lead tip silver plating) A treated product (“Cu-Ag” in the table) and a palladium alloy-plated product (“PPF” in the table) were molded and post-cured using the epoxy resin composition under the above conditions, and were produced. After baking at 24 ° C. for 24 hours, humidifying at 60 ° C. and 60% RH for 40 hours, and then performing reflow treatment three times at 260 ° C. and 30 seconds, respectively, to obtain an interface between the resin and the frame. The presence or absence of peeling was observed with an ultrasonic flaw detector, and the reflow resistance was evaluated based on the number of peeling occurrence packages with respect to the number of test packages (20).

As is clear from Tables 1 and 2, the comparative example containing no specific glycidyl compound (C) is inferior in reflow resistance. On the other hand, Examples 1 to 7 containing the specific glycidyl compound (C) are excellent in reflow resistance as compared with Comparative Examples. Although the reason is not clear, as described above, it is presumed to be due to the effect of reducing the elastic modulus and the effect of improving the adhesive force.
From the results of Examples 1 to 3 and Comparative Example, it is understood that the polycyclic aromatic ring compound having a dicyclopentadiene structure has better reflow resistance.
From the results of Examples 4 to 7 and Comparative Example, the ratio of the liquid resin 1 to the entire epoxy composition was lower than that of Examples 4 and 5 in which the ratio of the liquid resin 1 to the entire epoxy composition was 1% by mass or less. It can be seen that Examples 6 and 7 in which the content is 1% by mass or more are more excellent in reflow resistance.

The disclosure of Japanese Patent Application No. 2017-072889 filed on March 31, 2017 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards mentioned herein are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference. Incorporated herein.

Claims (10)

  An epoxy resin composition comprising an epoxy resin having a melting point or a softening point exceeding 40 ° C, a curing agent, and a compound having a glycidyl group and having a melting point of 40 ° C or less.   The epoxy resin composition according to claim 1, wherein the compound having a glycidyl group and having a melting point of 40 ° C or less has a dicyclopentadiene skeleton.   The epoxy resin composition according to claim 1, wherein the content of the compound having a glycidyl group and having a melting point of 40 ° C. or less is 5% by mass or more and less than 45% by mass with respect to the epoxy resin.   The epoxy resin composition according to any one of claims 1 to 3, further comprising a curing accelerator.   The epoxy resin composition according to any one of claims 1 to 4, further comprising an inorganic filler.   The epoxy resin composition according to any one of claims 1 to 5, further comprising a silane compound.   The epoxy resin composition according to any one of claims 1 to 6, wherein the melting point or softening point of the epoxy resin is from 80C to 130C.   The epoxy resin composition according to any one of claims 1 to 7, wherein the compound having a glycidyl group and having a melting point of 40 ° C or less has an epoxy equivalent of 165 g / eq to 365 g / eq.   The content of the compound having a glycidyl group and having a melting point of 40 ° C. or less is 20% by mass or more and less than 45% by mass with respect to the epoxy resin according to any one of claims 1 to 8. Epoxy resin composition.   An electronic component device comprising: an element; and a cured product of the epoxy resin composition according to claim 1, which seals the element.