JP2002263886A - Curable flux, solder joint part, semiconductor package and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a curable flux which does not require cleaning and removing of a residual flux after solder joining, maintains an electrical insulation characteristic in spite of a high temperature and high moisture atmosphere and permits solder joining having high joining strength and reliability. SOLUTION: A resin (A) composed of at least one kind among phenol novolak, alkyl phenol novolac, resol and polyvinyl phenol and having at least one and more phenolic hydroxyl groups, resins (B) such as an epoxy resin and isocyanate resin acting as curing materials and a solvent (C) having a hydroxyl group and having a boiling point above 150 deg.C are formulated as essential components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a curable flux used for solder bonding, and more particularly, to a solder connection when a semiconductor package is mounted on a printed wiring board. On the board,
The present invention relates to curable flux when mounting by flip chip solder connection.

[0002]

2. Description of the Related Art In recent years, with the demand for higher functionality and lighter, thinner and smaller electronic devices, high-density integration and high-density mounting of electronic components have been progressing. Semiconductor packages have become smaller and have more pins than ever before.

[0003] With the miniaturization of the semiconductor package, the size of the conventional package using a lead frame has been limited in miniaturization. Recently, a chip mounted on a circuit board has recently been used. BGA (Ba
II Grid Array), CSP (Chip)
There has been proposed a new area mounting type packaging method called "Scale Package". In these semiconductor packages, various insulating materials such as plastics and ceramics, which are called semiconductor mounting substrates, having electrodes of a semiconductor chip and a function of a lead frame of a conventional semiconductor package, and terminals of a substrate composed of conductor wiring, As a method of electrical connection, a wire bonding method or TAB (Tape Automated Bonn) is used.
ding) method, and furthermore, FC (Flip Chip)
Although there are known methods such as BGA and C using FC connection method, which are advantageous for miniaturization of semiconductor packages,
The structure of the SP has been actively proposed.

For mounting a BGA or CSP on a printed wiring board, solder bonding using bumps formed of solder balls is employed. A flux is used for this soldering, and a solder paste is sometimes used in combination. In particular, the reason why solder balls are used is that the amount of solder supplied can be easily controlled and a large amount of solder can be supplied, so that the bumps can be made high. In addition, solder bonding is often used also as an electrical connection method between electrodes of a semiconductor chip and terminals of a semiconductor mounting substrate in a BGA or CSP manufacturing process.

[0005] In general, for solder joining, dirt such as oxides on the metal surface of the electrodes facing the solder surface is removed, and reoxidation of the metal surface at the time of solder joining is prevented, so that the surface tension of the solder is reduced. And a soldering flux is used to make the molten solder easily wet the metal surface. As the flux, a flux obtained by adding an activator or the like for removing an oxide film to a thermoplastic resin flux such as rosin is used.

However, if this flux remains after joining, the thermoplastic resin melts at high temperature and high humidity, and the active ions in the activator are also released. Problems arise. Therefore, at present, the above-mentioned problems are solved by cleaning and removing the residual flux after the solder bonding. However, there are disadvantages such as an environmental problem of the cleaning agent and an increase in cost due to the cleaning process.

Further, miniaturization of semiconductor packages and increase in the number of pins promotes miniaturization of bumps, and there is a concern that bonding strength and reliability may be reduced. Therefore, in order to obtain the reliability of the bump connection portion, studies are being made to fill the gap between the chip and the substrate with an insulating resin called underfill to seal and reinforce the bump connection portion. However, this requires a step of filling and curing an underfill, which is technically difficult, so that the manufacturing process is complicated and the manufacturing cost is increased.

[0008] To solve these problems, there is no need to wash and remove the residual flux after soldering, and it maintains electrical insulation even in a high-temperature, high-humidity atmosphere, and enables soldering with high bonding strength and high reliability. Flux has been proposed. However, this curable flux has problems such as insufficient flux effect and incomplete soldering.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in using a curable flux. In view of the foregoing, a curable flux having an improved flux effect, excellent solder bonding properties, and a resin reinforcing function has been proposed. An object of the present invention is to provide a solder joint, a semiconductor package, and a semiconductor device used.

[0010]

That is, according to the present invention, at the time of soldering, it acts as a flux for soldering, and at the same time, forms a meniscus around the soldering joint and heat-cures to form a core soldering joint. A curable flux characterized by resin reinforcement, comprising a resin (A) having at least one or more phenolic hydroxyl groups, a compound (B) acting as a curing agent thereof, and a hydroxyl group, and having a temperature of 150 ° C. or higher. Is a curable flux comprising, as an essential component, a solvent (C) having a boiling point of

Further, the present invention is the solder joint portion, wherein the curable flux acts as a flux for solder joint, and is reinforced by a heated and cured flux resin after the solder joint. .

Further, the present invention relates to a printed wiring board,
In a semiconductor package on which solder balls for electrical connection are mounted, the solder balls are solder-bonded by the curable flux, and after the solder bonding, the solder balls are further reinforced by a heated and cured flux resin. The semiconductor package is characterized in that the curable flux is applied onto a circuit pattern of a printed wiring board on which solder balls of the semiconductor package are mounted, acts as a flux at the time of solder ball joining, and after solder ball joining, By the flux resin which was further heated and cured,
A semiconductor device characterized by being reinforced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION As the resin (A) having at least one phenolic hydroxyl group used in the present invention, phenol novolak resin, alkylphenol novolak resin, resole resin, polyvinylphenol resin, resorcinol novolak resin, catechol novolak Resins, hydroquinone novolak resins and the like, and at least one of them is used.

Among them, the weight average molecular weight is 2,000
Those having a value of 0 or less are preferred. As a result, if the molecular weight is too large, the fluidity of the curable flux at the time of solder joining is reduced, and there is a possibility that solder joining may be hindered. However, it is sufficient that the melt viscosity at the time of solder joining is adjusted to obtain the optimum fluidity by using other compounding agents. At this time, there is no problem if the melt viscosity can be controlled to 50 Pa · s or less. For this purpose, a liquid curing agent may be blended or a solvent may be left.

In the curable flux of the present invention, the phenolic hydroxyl group of the resin (A) having at least one or more phenolic hydroxyl groups removes stains such as solder and oxides on metal surfaces by its reducing action. , Acts as a flux for soldering. The phenolic hydroxyl group is not particularly limited, but the resin (A) having at least one or more phenolic hydroxyl groups
It is preferable to use an electron-donating group having an electron donating group in order to enhance the effect as a flux of solder bonding.

In the curable flux of the present invention, the amount of the resin (A) having a phenolic hydroxyl group is preferably 20 to 80% by weight of the entire curable flux. If the content is less than 20% by weight, the effect of removing dirt such as solder and oxides on the metal surface is reduced, and solder joining may not be performed in some cases. On the other hand, if the content is more than 80% by weight, a sufficient cured product cannot be obtained, and the bonding strength and reliability may be reduced.

As the resin (B) acting as a curing agent of the resin (A) having a phenolic hydroxyl group used in the present invention, an epoxy compound or an isocyanate compound is used. Specifically, all are based on phenol-based compounds such as bisphenols, phenol novolaks, alkylphenol novolacs, biphenols, naphthols, and resorcinols, and skeletons such as aliphatic, cycloaliphatic, and unsaturated aliphatics. And an epoxy compound and an isocyanate compound modified. These may be used alone or in combination of two or more.

In the curable flux of the present invention, the compounding amount of the compound (B) acting as a curing agent is such that the epoxy group equivalent or the isocyanate group equivalent has at least one phenolic hydroxyl group. It is preferably from 0.5 to 1.5 times the group equivalent. If the ratio is less than 0.5 times, a sufficiently cured product cannot be obtained, the reinforcing effect is reduced, and the bonding strength and reliability may be reduced. On the other hand, if the ratio is more than 1.5 times, the effect of removing dirt such as solder and metal surface oxides is reduced, and there is a possibility that solder joining may not be performed.

In the curable flux of the present invention, a good cured product can be obtained by the resin (B) acting as a curing agent, so that it is not necessary to wash and remove after soldering, and it is possible to obtain electrical insulation even in a high temperature and high humidity atmosphere. It maintains solderability and enables soldering with high bonding strength and high reliability.

The solvent (C) used in the present invention has a boiling point of 150 ° C. or higher and has at least one hydroxyl group in the molecule, and is generally used as alcohols, alcohol esters, ketone alcohols. In some cases, solvents such as phenols and ether alcohols can be used, and there is no restriction. Specifically, glycerin, tributyl citrate, ethylene glycol monoester, monoacetin, diacetin, diethylene glycol, diethylene glycol monoethyl ether,
Solvents such as triethylene glycol, cresol, and xylenol are exemplified.

When the boiling point of the solvent (C) is lower than 150 ° C., the flux property is reduced due to the large evaporation of the additive during reflow, so that the solder joint may be incomplete. The boiling point of the solvent is preferably 200 ° C. or higher, more preferably 240 ° C. or higher. However, if the boiling point is too high and the residual amount of the solvent is too large at the time of soldering, the soldering will be hindered and the reliability after soldering will be reduced. Although it depends on the reflow conditions which differ depending on the solder composition, it is preferably 300 ° C. or less under the reflow conditions of 240 ° C. peak temperature when eutectic solder is used. More preferably, it is 270 ° C or lower.

In the curable flux of the present invention, the solvent (C) is added for the purpose of improving the action of removing dirt such as oxides on the surface of the solder and metal at the time of solder joining in the curable flux. And to realize stable solder jointability.

In the curable flux of the present invention, the amount of the solvent (C) to be added is not particularly limited as long as stable solder jointability can be realized.
It is preferably at most 50% by weight. If the amount is less than 3% by weight, there is a possibility that a sufficient improvement in solder jointability cannot be obtained. Also,
If it exceeds 50% by weight, the viscosity may be too low to make the coating film form difficult, or the effect of removing stains such as oxides on solder and metal surfaces may be reduced, and solder joining may not be possible. .

The curable flux of the present invention may be mixed with a solvent other than the solvent (C) in order to adjust the viscosity of the varnish and to improve the stability of the coating film and the workability. Can also. The solvent is not particularly limited as long as it has a relatively high dissolving power for the resin (A) having at least one or more phenolic hydroxyl groups and the compound (B) acting as a curing agent thereof. Specifically, commonly used alcohols, ethers, acetals, ketones, esters, alcohol esters, ketone alcohols, ether alcohols, ketone ethers, ketone esters and ester ethers, etc. Include solvents such as phenols and aprotic nitrogen compounds. The boiling point of this solvent is
Although it depends on the reflow condition which varies depending on the solder composition, the reflow condition at a peak temperature of 240 ° C. when eutectic solder is used is preferably 50 ° C. or more and 300 ° C. or less. There is no restriction on the amount of the mixed solvent to be added as long as good coating film stability and good control of the coating amount and stable solder bonding can be realized. However, in the varnish, 3% by weight or more and 50% by weight or less. Is preferred.

In addition to the above components, the curable flux of the present invention may contain a known curing catalyst, such as 2-methylimidazole, 2-phenylimidazole, or 2-phenyl-4, for promoting curing. -Methylimidazole, bis (2-ethyl-4-methyl-imidazole), 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-ethyl-4-methyl Imidazole, 2-undecylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-aminoethyl-2-methylimidazole, 1 -(Cyanoethylaminoethyl) -2-methylimidazole, 1- Anoechiru-2-phenyl-4,5
-Bis (cyanoethoxymethylimidazole) or triazine-added imidazole. Epoxy adducts or microcapsules of these can also be used. These may be used alone or in combination of two or more.

Furthermore, a silane coupling agent for improving adhesion and moisture resistance, an antifoaming agent for preventing voids, or a liquid or powdered flame retardant may be added.

The curable flux of the present invention can be obtained as a varnish of the curable flux by mixing the above components.

By setting the curable flux of the present invention as described above, the balance between melt viscosity, oxide removal properties and curability can be achieved, and at the time of solder joining, it acts as a flux for solder joining, and at the same time, A meniscus is formed around the joint, and it is further cured by heating and hardening in a form that reinforces the solder joint in a ring shape, significantly increasing joint strength and reliability compared to conventional soldering with flux. Can be improved.

The semiconductor package of the present invention is a semiconductor package on which solder balls for mechanically and electrically connecting to a printed wiring board are mounted. And is reinforced by a heated and cured flux resin after soldering.

When the curable flux of the present invention is used for a semiconductor package on which a solder resist is formed, a predetermined amount of the curable flux is previously set on a land portion on which solder balls for mechanically and electrically connecting are mounted. And mounting the solder ball on the curable flux in the land, or transferring a predetermined amount of the curable flux to the solder ball, and mounting the solder ball with the transferred curable flux on the land. .

A curable flux is applied to the entire surface of the circuit pattern of the semiconductor package on which the solder balls are mounted by a method such as screen printing or spin coating and dried, and then the solder balls are mounted on the circuit pattern. A solder ball may be placed on the land for use. Thereafter, the solder ball is solder-bonded to the land by solder reflow, and at the same time, a meniscus is formed around the solder joint, and then the curable flux is further cured by heating to apply resin reinforcement to the solder joint. Can be.

Further, a curable flux is applied on the circuit pattern of the printed wiring board on which the solder balls of the semiconductor package are mounted, acts as a flux at the time of solder ball joining, and is further heated and cured after solder ball joining. A semiconductor device reinforced with resin by the flux can be obtained.

[0033]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 105 g of a phenol novolak resin (trade name: PR-HF-3, OH group equivalent 105, manufactured by Sumitomo Durez Co., Ltd.) and diallyl bisphenol A type epoxy (Nippon Kayaku Co., Ltd.)
Made, trade name RE-810NM, epoxy equivalent 220) 2
20 g was dissolved in a mixed solvent of 10 g of diacetin (boiling point: 260 ° C.) and 40 g of butyl benzoate (boiling point: 250 ° C.) to prepare a curable flux varnish.

Copper plate (manufactured by Furukawa Electric Co., Ltd., trade name EF)
Each of the curable flux varnishes obtained above was applied to a thickness of 100 μm on TEC64T). On the copper plate on which the coating film is formed, a solder ball (Sn-P
Ten b-type eutectic solders (manufactured by Senju Metal Mining Co., Ltd.) were mounted and allowed to stand on a hot plate set at 240 ° C. After one minute,
The copper plate was released from the hot plate, and the wet spread ratio of the solder was calculated. The wetting and spreading ratio is determined by measuring the solder ball diameter H = 500 μm and the height of the spread solder D μm, and (H−D) / H
It was calculated by the following equation. The results are summarized in Table 1. Regarding the solder joint stability, the symbol “○” indicates that the wetting and spreading ratio is greater than 80, the symbol “Δ” indicates that the ratio is 60 or more and 80 or less, and the symbol “X” indicates that the ratio is less than 60.

Example 2 In place of diacetin, diethylene glycol (boiling point: 24
(5 ° C.) Except for using 10 g,
A curable flux varnish was prepared and evaluated.

Example 3 Instead of diacetin, glycerin (boiling point: 290 ° C.)
A curable flux varnish was prepared and evaluated in the same manner as in Example 1 except that g was used.

Comparative Example 1 Instead of diacetin, butyl benzoate (boiling point: 250 ° C.)
A curable flux varnish was prepared and evaluated in the same manner as in Example 1 except that 10 g was used.

Comparative Example 2 Instead of diacetin, triacetin (boiling point: 258 ° C.)
A curable flux varnish was prepared and evaluated in the same manner as in Example 1 except that 0 g was used.

Comparative Example 3 A curable flux varnish was prepared and evaluated in the same manner as in Example 1 except that 10 g of diethylene glycol dibutyl ether (boiling point: 254 ° C.) was used instead of diacetin.

Comparative Example 4 Instead of diacetin, methyl lactate (boiling point: 145 ° C.)
A curable flux varnish was prepared and evaluated in the same manner as in Example 1 except that g was used.

[0042]

[Table 1]

As can be seen from the evaluation results shown in Table 1,
This shows that when the solvent (C) of the present invention is used, it is possible to improve the solder joint stability as compared with the case where the solvent (C) is not used.

[0044]

The curable flux of the present invention does not require cleaning and removal of residual flux after soldering, maintains electrical insulation even in a high-temperature, high-humidity atmosphere, and has a curable flux around the solder joint. Since it hardens in a ring-shaped reinforcement form, it enables soldering with high bonding strength and high reliability, simplifying the process of mounting semiconductor packages on printed wiring boards, reducing manufacturing costs, and It is extremely useful for improving the reliability of solder joints. Furthermore, the soldering stability is large, which is extremely effective for improving the reliability.

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Claims (4)

[Claims] 1. A curability characterized by acting as a flux for soldering at the time of soldering, simultaneously forming a meniscus around the soldering joint, and further heating and curing to reinforce the core soldering joint with resin. A resin (A) which is a flux and has at least one or more phenolic hydroxyl groups;
A curable flux comprising, as essential components, a compound (B) acting as a curing agent and a solvent (C) having a hydroxyl group and a boiling point of 150 ° C. or higher. 2. A solder joint portion wherein the curable flux according to claim 1 acts as a solder joint flux, and is reinforced by a heated and cured flux resin after the solder joint. 3. A semiconductor package on which solder balls for mechanically and electrically connecting to a printed wiring board are mounted, wherein the solder balls are solder-bonded by the curable flux according to claim 1, and further heated and cured. A semiconductor package characterized by being reinforced with a flux resin. 4. The curable flux according to claim 1, which is applied on a circuit pattern of a printed wiring board on which solder balls of a semiconductor package are mounted, acts as a flux at the time of solder ball bonding, and further after the solder ball bonding. A semiconductor device, wherein the semiconductor device is reinforced by a heated and cured flux resin.