JP3432410B2 - Liquid injection sealing underfill material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid injection / sealing underfill material used for liquid injection / sealing of a semiconductor having low stress and excellent adhesiveness.

[0002]

2. Description of the Related Art High integration and high density of IC chips and IC
The flip-chip mounting method has emerged due to the demand for smaller packages. The same mounting method enables miniaturization and thinning by connecting the IC chip surface and the printed circuit board with solder bumps instead of the conventional wire bonding connection. However, since the chips, the printed wiring board, and the solder have different coefficients of thermal expansion, thermal stress occurs during the thermal shock test. Especially, the thermal stress is locally concentrated on the solder bumps near the corners far from the center of the chip. As a result, cracks occur in the solder balls, and the operational reliability of the circuit is greatly reduced.

Therefore, for the purpose of relieving thermal stress, a liquid injection sealing underfill material (hereinafter abbreviated as an underfill material) is used for sealing. Specifically, the gap between the chip and the printed wiring board (stand gap: 30 to 15
A method of injecting an underfill material to 0 micron), curing it, and sealing it is adopted. In order for the underfill material to alleviate and absorb the above-mentioned thermal stress to the solder ball, the physicochemical properties are as follows: (1) Match the low thermal expansion coefficient (α1) of the underfill material to the solder ball. (2) High glass transition temperature (hereinafter referred to as Tg). That is, the temperature range of α1 is wide. (3) Adhesion at the interface of the underfill material-chip or the underfill material-printed wiring board is good. (4) It is necessary to absorb stress such as chip warp after sealing and have excellent connection stability at the bonding site. With the underfill material that satisfies some of these requirements, the sealing resin in the stand gap expands and contracts like external solder with respect to external temperature changes, and each interface is firmly bonded, and thermal stress is applied to the entire package. Connection reliability is maintained due to the distribution. In addition, the underfill material also serves to protect the circuit surface of the chip and the solder balls from the external environment. As described above, the reliability of flip-chip mounting largely depends on the underfill material.

With the rapid spread of flip chip mounting in recent years, a more reliable underfill material is desired (specifically, a moisture absorption treatment is performed under conditions such as JEDEC levels 3 and 4 and a temperature cycle test and Perform IR reflow test). Further, the stress property is important among the above characteristics in order to deal with a large chip or the like. Further, in order to improve productivity, it is preferable that the curing time of the underfill material is as short as possible. However, at present, few materials satisfy both properties of low stress and short-time curing.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of conventional underfill materials, and its object is to have excellent fast curing property, low stress, and adhesive property. This is to provide an underfill material having high reliability.

[0006]

That is, according to the present invention, the epoxy resin (a1) represented by the formula (1) and the bisphenol (a2) are mixed in an equivalent ratio [mol number / (a
2) the number of moles] is more than 1 and 5 or less, and the reaction product (a3) reacted at a temperature of 120 ° C. or higher is contained in the total epoxy resin in an amount of 30% by weight or more, and the liquid epoxy resin (A) at room temperature, It comprises a cyanate ester (B) and a spherical inorganic filler (C), and the weight ratio (A) / (B) of the epoxy resin (A) and the cyanate ester (B) is 0.5 ≦.
(A) / (B) ≦ 2, which is a liquid injection-sealing underfill material,

[0007]

[Chemical 1] (In the formula, R ₁ and R ₂ represent a divalent aliphatic group having 1 to 5 carbon atoms or a residue obtained by removing 2 hydrogens from an aromatic group having 6 or more carbon atoms, and may be the same as each other. May be different)

The average particle size of the inorganic spherical filler is 0.5.
A liquid injection-sealing underfill material having a maximum particle size of 50 μm or less and a μm to 12 μm. By using this material, the reliability and stress property of flip-chip mounting can be significantly improved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a production example of the reaction product (a3) contained in the epoxy resin (A) used in the present invention, the epoxy resin of the formula (1) and bisphenols are preferably used in a glass flask. Can be produced by heating at 120 ° C. or higher under a nitrogen stream. that time,
A catalyst may be added to facilitate the reaction. Examples thereof include organic phosphines such as triphenylphosphine and tributylphosphine, organic borate salts thereof, diaza compounds such as 1,8-diazabicycloundecene, and the like. If the temperature is lower than 120 ° C., the reaction does not proceed and a large amount of unreacted bisphenols is generated, which hinders the pot life as an underfill material for the reason described later.

Examples of the bisphenols used in the present invention include bisphenol A, bisphenol F, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol S, dihydroxydiphenyl ether, dihydroxybenzophenone and o-hydroxyphenol. , M-hydroxyphenol, p-hydroxyphenol, biphenol, tetramethylbiphenol, ethylidenebisphenol, methylethylidenebis (methylphenol),
Examples thereof include α-methylbenzylidene bisphenol and cyclohexylidene bisphenol, which may be used alone or in combination.

The epoxy resin (a1) represented by the formula (1)
And the bisphenol (a2) charge molar ratio is (a
Under the excess of 1), it is necessary that it is more than 1 and 5 or less. Generally, the epoxy resin (a1) represented by the formula (1) has extremely low reactivity. Therefore, if the charging ratio exceeds 5, the amount of unreacted epoxy resin (a1) increases and the curability as an underfill material decreases significantly, which is problematic in terms of productivity and industry.

Further, the epoxy resin and the cyanate ester react by heat. This reaction is known to be accelerated in the presence of phenolic hydroxyl groups. Therefore, when epoxy resin and an equivalent amount of phenols are simply mixed (including melt mixing), a large amount of free residual phenols are included, so the pot life as an underfill material (viscosity change when stored at room temperature is under The time within an allowable range that does not affect the workability of applying the fill material) is significantly reduced. However, when pre-reacted as in the present invention, since there is almost no free phenol, the catalytic effect of phenol (particularly at room temperature) is relaxed and the reaction product (a
The epoxy resin containing 3) reacts with the cyanate ester in a short time by heating and does not impair the pot life. More preferably, the reaction rate of bisphenols is 50.
% Or more. This is to reduce the amount of free phenols remaining as described above.

Examples of epoxy resins other than the reaction product (a3) are bisphenol A, bisphenol F, polyglycidyl ether obtained by the reaction of phenol novolac and epichlorohydrin, which is liquid at room temperature, vinylcyclohexene dioxide, dicyclohexyl. There are cycloaliphatic epoxies such as pentadiene oxide, alicyclic diepoxy-adipide, and naphthalene backbone epoxy resins such as 1,6-bis (2,3-epoxypropoxy) naphthalene. These may be used alone or in combination. Further, in order to obtain a highly reliable underfill material, it is preferable that the epoxy resin used contains as little ionic impurities as Na +, Cl− and the like.

It is essential that the ratio (a3) / (A) (weight ratio) of the reactive product (a3) in the total epoxy resin (A) is 30% by weight or more. This is because if it is less than 30% by weight, low stress properties as an underfill material cannot be exhibited.

The viscosity of the epoxy resin (A) at 25 ° C. is preferably 500 Pa · s or less.
When the viscosity of the epoxy resin (A) is higher than 500 Pa · s, the viscosity of the composition becomes high, and when the underfill material is flow-injected into the flip-chip mounting type package, air bubbles are trapped or the corner end is not filled well. Is likely to occur, leading to a decrease in reliability, which is not preferable. When measuring the viscosity of the epoxy resin, in the case of a liquid epoxy resin at room temperature, it is measured at 25 ° C with an E-type viscometer manufactured by Toki Sangyo Co., Ltd.

Next, the charge weight ratio (A) / (B) of the total epoxy resin (A) and the cyanate ester (B) is 0.5.
It is necessary that ≦ (A) / (B) ≦ 2. 0.5
When it is less than 2, the moisture-resistant adhesion is poor, and when it exceeds 2, the reactivity is lowered, which is not preferable in productivity and industrially.

Examples of the cyanate ester (B) used in the present invention include the formulas (2) and (3), and the cyanate ester represented by the formula (3) is 4,
4'-methylidene bis [2,6-dimethylphenylene cyanate], 4,4 '-(1-methylethylidene) bis [2-methylphenylene cyanate], 4,4'-(1
-Methylethylidene) bis [2,6-dimethylphenylene cyanate], 4,4'-methylenebis [2-methylphenylene cyanate], 4,4 '-(1-methyl-ethylidene) bis [2- (1,1- Dimethylethyl) phenylene cyanate] and the like.

[0018]

[Chemical 2]

[0019]

[Chemical 3] (In the formula, R ₁ and R ₂ : H or an alkyl group having 10 or less carbon atoms and at least one of R ₁ and R ₂ is an alkyl group. R ₃ : an alkylene group having 10 or less carbon atoms)

The cyanate ester resin alone is trimerized when hot. In general, since cyanate ester resin is crystalline, it is necessary to add 10 to 30 of these cyanate esters in advance in order to prevent crystallization of the underfill material during freezing storage.
About 3% by weight may be partially trimerized and blended.

In the present invention, in order to accelerate the trimerization of the cyanate ester resin, the reaction between the epoxy resin and the cyanate ester resin, and further the curing of the epoxy resin itself. A catalyst can be added. An example is cobalt,
Metal naphthenates such as zinc, iron, copper, chromium, manganese, nickel and titanium, salts of acetylacetonate and its derivatives, metal complexes such as organic acid salts of various carboxylate alkoxides, imidazoles, Examples include primary amines and acid anhydrides. These may be used alone or in combination.

Next, the spherical inorganic filler (C) used in the present invention is characterized by having an average particle diameter of 12 μm or less and a maximum particle diameter of 50 μm or less. Examples of the inorganic filler include aluminum nitride, alumina, and silica. From the viewpoint of heat dissipation and cost, silica particles are preferable, and low radiation is more preferable. The shape may be spherical, crushed, flake-shaped, or the like, but it is necessary to be spherical because the linear expansion coefficient can be reduced by increasing the filling of the filler.
The addition amount of the spherical inorganic filler is 50 to 50 based on the total composition.
80% by weight is desirable. If it is less than 50% by weight, the moisture resistance and the linear expansion coefficient of the cured product will be large, and if it exceeds 80% by weight, the viscosity of the resulting composition will be too high and the flow characteristics will be deteriorated, such being undesirable.

The flow characteristics of the underfill material also largely depend on the particle size distribution of the filler. Generally, a filler having a wider distribution and a larger particle size has a lower viscosity and a better fluidity of the composition. However, if a filler having a large particle size is used for the purpose of lowering the viscosity, the filler having a large particle size is settled during curing, and the linear thermal expansion coefficient in the gap becomes nonuniform, which is not preferable in terms of reliability. The underfill material is a gap between the organic substrate and the chip (stand gap: 30 to 150 μm).
Since it is necessary to flow the filler, the particle size of the filler must be smaller than the stand gap, and more preferably the maximum particle size is about 50% of the stand gap or less. On the other hand, if the particle size is too small, the specific surface area increases and the viscosity becomes high, so that the filling amount of the filler cannot be increased.
To satisfy the above requirements, the average particle size is 0.5 μm to 12
It is necessary for the filler to have a maximum particle size of 50 μm or less. It is more preferable to use a filler having a particle size distribution with an average particle size of 3 to 9 μm and a maximum particle size of 25 μm or less. Further, the fillers may be used singly or may be mixed so as to have a multimodal particle size distribution within the scope of the claims.

The underfill material of the present invention contains, in addition to the above-mentioned essential components, other resins, if necessary, a catalyst for promoting the reaction, a diluent, a pigment, a coupling agent, a flame retardant, a leveling agent, Additives such as antifoaming agents may be used. The underfill material is produced, for example, by dispersing and kneading each component, additive and the like with a three-roll, a two-heat roll and a vacuum mixer, and defoaming under vacuum.

[0025]

EXAMPLES Reaction Production Example 1 formula of product (1) In _{R 1 = R 2: -CH 2} CH 2 CH 2 - epoxy resin (epoxy equivalent 181) 100 g, catalyst bisphenol F (hydroxyl group equivalent 100) 45 g 1 g of tetraphosphonium tetraphenylborate was added thereto, and the mixture was reacted at 180 ° C. for 6 hours under a nitrogen stream. This product is referred to as a reaction product (1).

Production Example 2 of Reaction Product In Production Example 1, bisphenol F (hydroxyl group equivalent 10
The reaction was carried out in the same manner as in Production Example 1 except that 0) was changed to 12 g. This product is referred to as a reaction product (2).

Production Example 3 of Reaction Product In Production Example 1, bisphenol F (hydroxyl group equivalent: 10
The reaction was performed in the same manner as in Production Example 1 except that 0) was changed to 8 g. This product is referred to as a reaction product (3).

The present invention will be specifically described below with reference to Examples 1-4 and Comparative Examples 1-7. The formulations shown in Table 1 and Table 2 were weighed, kneaded and dispersed with a three-roll mill, and then vacuum defoaming treatment was performed to prepare a liquid injection sealing underfill material. The following tests were performed on the produced liquid injection sealing underfill material. The results are shown in Tables 1 and 2.

[Resin Property Test] (1) Viscosity measurement: The initial viscosity at 25 ° C. and the viscosity after standing at 25 ° C. for 24 hours were measured with an E-type viscometer manufactured by Toki Sangyo Co., Ltd. (2) Adhesion strength: A bismaleimide-triazine (BT) resin substrate on which a solder resist (PSR-4000 / CA-40 manufactured by Taiyo Ink Co., Ltd.) was formed as a chip, and a polyimide for a passivation film was formed on the surface as a chip. (Sumitomo Bakelite CRC-6050)
Was applied (6 × 6 × 0.38 mm square).
Liquid injection sealing underfill material is applied on an organic substrate, a silicon chip is mounted so that the polyimide application surface and the underfill material face each other, and the test piece is cured at 150 ° C x 30 minutes to obtain a die share at 240 ° C. The strength was measured by BT100 manufactured by DAGE. Further, the same test piece was subjected to a moisture absorption treatment at a humidity of 85% and a temperature of 85 ° C. for 72 hours, and similarly, the die shear strength was measured to obtain the adhesion after the moisture absorption treatment. (3) Warpage: Warpage was measured according to the following method as a measure of low stress. 150 x 6 x 0.3 mm (thickness) silicon chips on a 200 μm thick copper frame
Harden and adhere using an underfill material at ℃ for 30 minutes,
The maximum value of the displacement in the vertical direction was obtained in the longitudinal direction of the chip using a surface roughness meter.

[Reliability Test Using Package] (4) Fillability Test: Liquid injection-sealing underfill material was applied to a flip-chip mounting package on a hot plate at 80 ° C.
After injecting for 1 minute, it was cured in an oven at 150 ° C. for 30 minutes to obtain a semiconductor package. Ultrasonic flaw detector (hereinafter,
The filling property inside the package was confirmed by SAT). (5) T / C cycle test: T / C treatment (−65 ° C./5 minutes ← → 150 ° C.) on the semiconductor package manufactured in (4).
/ 5 minutes 1000 cycles), and the presence or absence of cracks between the semiconductor chip and the printed circuit board interface was confirmed by SAT and microscopic observation after cross-section polishing. (6) JEDEC Level 3 Treatment: The JEDEC Level 3 moisture absorption treatment (3
After performing 0 ° C. 60% 168 hours), IR reflow treatment (240 ° C./20 seconds) was performed 3 times, and the presence or absence of cracks between the semiconductor chip and the printed circuit board interface was confirmed by SAT. The number of flip chip mounting packages used for the reliability evaluation is 10 each. The size of the chip is 12
x 12 mm square, 0.3 mm thick, and the gap (stand gaff) from the substrate is 60 μm.

[0031]

[Table 1]

(1) Silica A: fused spherical silica having an average particle size of 7.9 μm and maximum particle size of 40 μm (2) silica B: synthetic spherical silica having an average particle size of 0.3 μm
m, maximum particle size 4 μm (3) Silica C: fused spherical silica having an average particle size of 15 μm,
Maximum particle size 40 μm (4) Epoxy resin (1): Bisphenol F type epoxy resin (equivalent 170) (5) Epoxy resin (2): R ₁ and R ₂ in the formula (1)
There are both -CH ₂ CH ₂ CH ₂ - compound represented by (6) cyanate ester (1): cyanate ester represented by formula (2). (7) Cyanate ester (2): a cyanate ester represented by the formula (3), wherein R ₁ and R ₂ are CH ₃ , and R ₃ is CH.
₂ things

[0033]

[Table 2]

In Comparative Example 1, since the reaction product was not added, the warpage was large. Comparative Example 2 has a very short pot life because of the presence of free phenol. Comparative Example 3 has a small amount of phenol added when synthesizing the reaction product, so that curing is not completed sufficiently under the prescribed curing conditions. Is a large amount of total epoxy resin, so that the curing is not completed sufficiently under a predetermined curing condition. In Comparative Example 5, the amount of the reaction product added is small, and thus the warpage as a measure of stress characteristics is high. The ratio is high and the warp value and the adhesiveness after moisture absorption are maintained. In Comparative Example 7, the maximum particle size of the filler is large and the flow characteristics are poor.

[0035]

The underfill material of the present invention seals the gap between the flip chip and the printed wiring board to perform a thermal cycle test and IR after JEDEC level 3 moisture absorption treatment.
Withstands reflow tests, has excellent low-stress properties, and enables highly reliable flip chip mounting, which has great industrial merits.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01L 23/29 H01L 23/30 23/31 (56) Reference JP-A-9-165566 (JP, A) JP-A-9- 12684 (JP, A) JP 10-130465 (JP, A) JP 7-118365 (JP, A) JP 9-176607 (JP, A) JP 7-161740 (JP, A) JP-A-9-12685 (JP, A) JP-A-7-22441 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08L 63/00-63/10 C08G 59/00 -59/72 H01L 23/28 H01L 23/29 H01L 23/31

Claims (2)

(57) [Claims] 1. An epoxy resin (a) represented by the formula (1):
1) and bisphenols (a2) are equivalent ratio [(a
The number of moles of 1) / the number of moles of (a2)] is more than 1 and 5 or less, and the reaction product (a3) reacted at a temperature of 120 ° C. or higher.
The ambient temperature in liquid epoxy resin containing 30 wt% or more in the total epoxy resin (A), the composed cyanate ester (B) and the spherical inorganic filler (C), the epoxy resin (A) and the cyanate ester (B) Weight ratio (A) /
A liquid injection-sealing underfill material in which (B) is in the range of 0.5 ≦ (A) / (B) ≦ 2. [Chemical 1] (In the formula, R ₁ and R ₂ represent a divalent aliphatic group having 1 to 5 carbon atoms or a residue obtained by removing 2 hydrogens from an aromatic group having 6 or more carbon atoms, and may be the same as each other. May be different) 2. The average particle size of the spherical inorganic filler is 0.5 μm.
The liquid injection-sealing underfill material according to claim 1, wherein the underfill material has a particle diameter of m to 12 µm and a maximum particle diameter of 50 µm or less.