JPH04318022A - Epoxy resin molding material for sealing electronic part - Google Patents

Abstract

PURPOSE:To provide an epoxy resin molding material having excellent soldering resistance (crack resistance) and moisture-resistant characteristics and used for sealing electronic parts. CONSTITUTION:The subject molding material comprises an epoxy resin having naphthalene skeletons, a compound having two or more of specific phenolic hydroxyl groups and >=60vol.% of an inorganic filler.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epoxy resin molding material for encapsulating electronic components, and is particularly directed to surface-mounted plastic package ICs.

0002

2. Description of the Related Art Epoxy resin molding materials have been widely used in the field of encapsulating electronic components such as transistors and ICs. The reason for this is that the epoxy resin has well-balanced properties such as electrical properties, moisture resistance, heat resistance, mechanical properties, and adhesiveness with insert products. In particular, the combination of an ortho-cresol novolak type epoxy resin and a phenol novolak curing agent has an excellent balance between these resins and has become mainstream as a base resin for molding materials for IC encapsulation.

0003

[Problems to be Solved by the Invention] In recent years, high-density packaging of electronic components onto printed wiring boards has progressed. Along with this, surface mount type packages have become mainstream for electronic components, replacing the conventional pin insertion type packages. IC, LSI
Surface mount ICs, such as the
The volume occupied by an element in a package has increased, and the thickness of the package has become extremely thin. Furthermore, the packaging method for these packages differs from that of conventional pin-insertion types. In other words, with pin insertion type packages, the pins are inserted into the wiring board and then soldered from the back of the wiring board.
The package was not directly exposed to high temperatures. However, since surface-mounted ICs are temporarily attached to the surface of a wiring board and processed using a solder bath or reflow device, they are directly exposed to soldering temperatures. As a result, if the IC package absorbs moisture, the absorbed moisture rapidly expands during soldering, causing the package to crack. This phenomenon is currently a major problem regarding surface-mounted ICs.

[0004] The above problems are unavoidable in IC packages sealed with current base resin compositions.
Methods such as drying thoroughly before use are taken. However, these methods are laborious and costly.

[0005] The present invention was made in view of the above situation.
The present invention aims to provide an epoxy resin molding material for encapsulating electronic components that can be soldered without any specific pretreatment when mounted on a wiring board.

[0006]

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the inventors have found that the above objects can be achieved by blending a specific epoxy resin having a naphthalene skeleton as a base resin. This discovery led to the completion of the present invention. That is, the epoxy resin molding material for electronic component encapsulation of the present invention contains as main components:

000
7] (A) The structural formula is

[Chemical formula 3] Epoxy resin shown as and

(B) Structural formula

[Chemical formula 4] Here, A is a phenol such as phenol, cresol, resorcinol, or naphthol, n is a positive real number, and is a compound having two or more phenolic hydroxyl groups, and (C) 60% by volume or more. It consists of an inorganic filler.

The epoxy resin (A) in the present invention has a naphthalene ring in its skeleton, and the purity of the epoxy resin, especially the amount of hydrolyzable chlorine, should be lower because it is related to corrosion of aluminum wiring on devices such as ICs. In order to obtain an epoxy resin molding material for encapsulating electronic components with good moisture resistance and excellent moisture resistance, the content is preferably 500 ppm or less. here,
What is the amount of hydrolyzable chlorine? Dissolve 1 g of the sample epoxy resin in 30 ml of dioxane, and add 5 ml of 1N KOH methanol solution.
ml was added and refluxed for 30 minutes, and the value determined by potentiometric titration was used as a scale.

As the epoxy resin (A), for example, 1
, 6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, etc., which are epoxidized using epichlorohydrin, but are not particularly limited.

In addition to the epoxy resin shown by the structural formula (A) above, the epoxy resin used in the present invention may be used in combination with epoxy resin molding materials commonly used for encapsulating electronic components. Good too. Examples of these include epoxidized novolac resins of phenols and aldehydes, such as phenol novolak epoxy resins and orthocresol novolac epoxy resins, and Glycidyl ester-type epoxy resins obtained by the reaction of polybasic acids such as glycidyl ether, phthalic acid, and dimer acid with epichlorohydrin; glycidylamine-type epoxy resins obtained by the reaction of epichlorohydrin with polyamines such as diaminodiphenylmethane and isocyanuric acid; There are linear aliphatic epoxy resins and alicyclic epoxy resins obtained by oxidation with peracids such as peracetic acid, and these can be used in combination as appropriate.

[0012] When these epoxy resins are used together, there are no particular limitations, but the blending ratio of the epoxy resin (A) of the present invention is preferably 30% by weight or more, more preferably 50% by weight or more of the entire epoxy resin. is preferred. The reason for this is that if it is less than 30% by weight, it will have little effect on the reflow resistance, which is the objective of the present invention, and in order to exhibit a particularly effective effect, 50% by weight or more is required. Furthermore, as the compound (B) of the present invention, for example, structural formula:

[0013]

Phenol/aralkyl resin or naphthol/aralkyl resin having a xylylene group synthesized from phenols or naphthols and dimethoxyparaxylene as shown in [Chemical formula 5]
There are aralkyl resins etc.

[0014] The epoxy resin (A) has a small molecular weight,
Since the melt viscosity is low, the viscosity differs greatly from that of component (B) in the kneading device, making it difficult to obtain a uniform molding material. Therefore, after heating and mixing the epoxy resin (A) and the compound (B) in advance, a curing accelerator, filler, etc. are added,
It is preferable to manufacture by kneading. The conditions for heating and mixing are preferably 80°C or higher, where the viscosity of the epoxy resin (A) is sufficiently low, and 140°C or lower, where the reaction between the epoxy group and the phenol group is relatively mild, and the heating and mixing time is (A). The necessary minimum amount is preferable so that both resins (B) are uniformly compatible with each other.

In the present invention, in addition to component (B), a compound having two or more phenolic hydroxyl groups in one molecule can be used in combination. Here, resins that can be used in combination include phenols such as phenol, cresol, xylenol, resorcinol, catechol, bisphenol A, and bisphenol F, and aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, and salicylaldehyde under acidic catalysis. There are novolac type phenol resins and polyparavinyl phenol resins obtained by condensation reaction with polyparavinyl phenol resins, which may be used alone or in combination of two or more types.

[0016] The equivalent ratio of the epoxy resin represented by (A) and the compound having a phenolic hydroxyl group represented by (B) used in the present invention is not particularly limited, but it depends on hardenability, heat resistance, etc. From this point of view, a range of 0.6 to 1.4 is desirable. Further, a curing accelerator that promotes the curing reaction between the epoxy resin and the compound having a phenolic hydroxyl group can be used. As this curing accelerator, for example, 1
,8-diazabicyclo(5,4,0)undecene-7,
Tertiary amines such as triethylenediamine, benzyldimethylamine, triethanolamine, dimethylaminoethanol, tris(dimethylaminomethyl)phenol, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2- Imidazoles such as heptadecylimidazole, organic phosphines such as tributylphosphine, methyldiphenylphosphine, triphenylphosphine, diphenylphosphine, phenylphosphine, tetraphenylphosphonium/tetraphenylborate, tetraphenylphosphonium/ethyltriphenylborate, tetrabutylphosphonium・Tetra-substituted phosphonium such as tetrabutylborate ・Tetra-substituted borate, 2-ethyl-4-
Examples include tetraphenylboron salts such as methylimidazole/tetraphenylborate and N-methylmorpholine/tetraphenylborate.

[0017] As a result of intensive studies on cracks during reflow, which is the object of the present invention, we found that 1,8-diaza-bicyclo(5,4,0)undecene-7 and its phenol derivatives or tetra-substituted It has been found that the use of phosphonium tetra-substituted borates as curing accelerators is particularly effective. Furthermore, as the tetra-substituted phosphonium/tetra-substituted borate, tetraphenylphosphonium/tetraphenylborate is preferable. The reason for this is that the curing accelerator has a large influence on the properties of the cured product, and 1,8-diaza-bicyclo(5
,4,0) When undecene-7 and its phenolic derivatives or tetra-substituted phosphonium/tetra-substituted borates are used, Tg (glass transition temperature), which is an index of heat resistance, is relatively high and water absorption is low. Therefore, it can be inferred that cracks no longer occur even if an IC package that has been humidified for a certain period of time is soldered. Therefore, in order to effectively exhibit the effects of the resin system of the present invention, a combination with the above-mentioned curing accelerator is preferred, but there is no particular limitation.

Further, as the filler, it is necessary to use an inorganic filler from the viewpoint of reducing hygroscopicity and improving strength. Inorganic fillers include crystalline silica, fused silica, alumina, zircon, calcium silicate, calcium carbonate, silicon carbide, silicon nitride, boron nitride, zirconia, zircon,
Examples include powders of forsterite, steatite, spinel, mullite, and titania, and beads made of spherical powders of these powders, and one or more of these may be used. For the same reason, the blending amount of the filler needs to be 60% by volume or more, and more preferably 65% by volume or more. However, when using a filler exceeding 65% by volume, it is better to have a lower melt viscosity of the compound (B) as a curing agent, and for this purpose, the weight average molecular weight of the compound (B) should be 2000.
The following are preferred.

Other additives include higher fatty acids, higher fatty acid metal salts, mold release agents such as ester waxes, coloring agents such as carbon black, epoxysilanes, aminosilanes, ureidosilanes, vinylsilanes, alkylsilanes, organic titanates, and aluminum. Coupling agents such as alcoholates and flame retardants can be used.

[0020] A general method for producing a molding material using the above-mentioned raw materials is to thoroughly mix a predetermined amount of raw materials using a mixer, etc., and then mix the raw materials with a mixing roll,
A molding material can be obtained by kneading, cooling, and pulverizing using an extruder or the like.

[0021] The most common method for sealing electronic parts using the molding material obtained in the present invention is low-pressure transfer molding, but injection molding and compression molding are also possible.

[0022]

[Effect] Damage to IC packages during reflow is caused by moisture absorbed during storage of the IC, which expands rapidly during reflow, resulting in cracks in the package and separation of the resin interface from the element or lead frame. . Therefore, a resin that is resistant to reflow is required to have low water absorption and high adhesive strength. The epoxy resin that is the main component of the present invention is a diepoxy resin with a naphthalene skeleton, and since the curing agent has a xylylene group in the skeleton, it has excellent moisture absorption properties and adhesive properties due to the hydrophobicity and flexibility of the base resin skeleton. It can be inferred that the composition could be obtained. It is thought that this effect improved the reflow crack resistance.

[0023]

EXAMPLES The present invention will be explained below with reference to Examples, but the scope of the present invention is not limited to these Examples.

Structural formula

Epoxy resin 80 with an epoxy equivalent of 150 containing [Chemical 6] as the main component
weight part,

Structural formula

A uniform solid resin obtained by melt-mixing 98 parts by weight of a phenol/aralkyl resin having a weight average molecular weight of 1810, a softening point of 70°C, and a hydroxyl equivalent of 167 at 120°C for 30 minutes and cooling it. and 20 parts by weight of a brominated bisphenol A epoxy resin with a bromine ratio of 50% by weight and an epoxy equivalent of 375, 1,8-diazabicyclo(5,4,0)undecene-7 (3 parts by weight), and carnauba wax (2 parts by weight). ), carbon black (1 part by weight), γ-glycidoxypropyltrimethoxysilane (2 parts by weight), and fused silica glass powder (80% by weight) and kneaded using a 10-inch diameter heating roll. Temperature 80-90℃, kneading time 7
The epoxy resin molding material of Example (1) was produced under conditions of ~10 minutes. In Example (2), for the phenol/aralkyl resin of Example (1), the amount added was changed to 49 parts by weight, and a new hydroxyl equivalent of 106, a weight average molecular weight of 660,
It was produced in the same manner as in Example (1) except that 31 parts by weight of a phenol novolak resin with a softening point of 85°C was added. Example (3) uses the phenol/aralkyl resin of Example (1).

Structural formula

[Chemical 8] Weight average molecular weight 1200, hydroxyl group equivalent 220
, was produced in the same manner as in Example (1) except that 129 parts by weight of a resin having a softening point of 108° C. was used.

Comparative Example (1) is a phenol novolac resin having a hydroxyl equivalent of 106, a weight average molecular weight of 660, and a softening point of 85° C.
It was produced in the same manner as in Example (1) except that parts by weight were used as the base resin and used without being melted and mixed in advance.

Comparative Example (2) uses the naphthalene skeleton diepoxy resin of Comparative Example (1) with an epoxy equivalent of 200 and a softening point of 7.
Orthocresol novolak type epoxy resin 80 at 3℃
It was produced in the same manner as Comparative Example (1) except that parts by weight were replaced.

Examples (1) to (3) and comparative example (1)
The characteristics of ~(2) are shown in Table 1, and the details of the test method are shown in Table 2. It can be seen that the examples have lower water absorption and superior adhesive strength than the comparative examples.

In order to clarify the effects of the present invention, the results of crack resistance during reflow and moisture resistance after reflow using an IC for evaluation will be shown. I used for crack resistance evaluation
C is a flat package with external dimensions of 19 x 14 x 2.0 (mm), and has 80 pins and 42 alloy leads on which an element of 8 x 10 x 0.4 (mm) is mounted. The test conditions were 85°C, 85% RH, and 215% humidity after a specified period of time.
It is heated for 90 seconds in a vapor phase reflow oven at ℃. Evaluation was performed by observing the appearance under a microscope and determining the presence or absence of package cracks. The IC used for moisture resistance evaluation was a 350 mil wide, 28 pin small outline package, mounted with a 5 x 10 x 0.4 (mm) test element with 10 μm wide aluminum wiring, and 25 μm gold wire. It is wire bonded using wire. The test conditions were 72 hours of humidification at 85°C and 85% RH, and 9 hours in a vapor phase reflow oven at 215°C.
After heating for 0 seconds, it was humidified for a predetermined period of time under the conditions of 2 atmospheres, 121° C., and 100% RH, and disconnection defects due to aluminum wiring corrosion were investigated. In addition, the molding of the IC package is 18
The molding was carried out under the conditions of 0°C, 90 seconds, and 70 kgf/cm2, and post-curing was performed at 180°C for 5 hours after molding. Table 3 shows the results of crack resistance during reflow and moisture resistance after reflow. As shown in Table 3 and Examples (1) to (3), by using the epoxy resin of the present invention, crack resistance during reflow and moisture resistance after reflow were significantly improved compared to conventional resin systems. can.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]
(Number of defects/Number of tests)

[0034]

Effects of the Invention The epoxy resin molding material obtained by the present invention can greatly improve crack resistance during reflow and moisture resistance after reflow compared to conventional ones. In the field of electronic components, especially ICs such as FP (Flat Package) and SOP (Small Outline Package), packages are becoming thinner and smaller, and together with the increase in the size of devices, there is a strong demand for package crack resistance. , it can be widely applied to these products and has great industrial value.

Claims (3)

[Claims] Claim 1: The main components are (A) an epoxy resin having the structural formula [Chemical 1] and (B) the structural formula [Chemical 2], where A is a phenol such as phenol, cresol, resorcinol, or naphthol. An epoxy resin molding material for encapsulating electronic components, characterized in that it contains a compound having two or more phenolic hydroxyl groups, where n is a positive real number, and (C) 60% by volume or more of an inorganic filler. Claim 2: The weight average molecular weight of the compound (B) is 2.
000 or less, and the inorganic filler (C) is fused silica powder, and the epoxy resin molding material for electronic component sealing according to claim 1, wherein the inorganic filler (C) is fused silica powder and is 65% by volume or more. 3. Claim 1, characterized in that it is produced by heating and mixing the epoxy resin (A) and the compound (B) in advance, adding a curing accelerator, a filler, etc., and kneading the mixture. Or the epoxy resin molding material for electronic component sealing according to 2.