JP2002299518A - Semiconductor package, manufacturing method thereof, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor package using a hardened flux together with a semiconductor device which allows solder jointing of high strength and reliability while neither rinsing out of a remaining flux after solder jointing nor filling of underfill is required, with an electric insulation characteristics being kept even in an atmosphere of high temperature and humidity. SOLUTION: Related to a semiconductor package on which a solder ball is mounted for mechanical and electrical connection, a prescribed amount of hardened flux is transferred at least onto a solder joint surface of the solder ball, so that a hardened flux resin layer is formed in advance. Related to a semiconductor device, the hardened flux resin layer formed at least on the solder joint surface of the solder ball of the semiconductor package acts as a flux at solder jointing, and after the solder jointing, it is further reinforced with a flux resin which is hardened by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor package having solder balls mounted thereon, a method of manufacturing the same, and a semiconductor device.

[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 been increasingly miniaturized and have more pins than ever before.

[0003] With the miniaturization of semiconductor packages,
In a package using a conventional lead frame, the miniaturization has reached its limit. Recently, a BGA (Ball (Ball)) has been used in which a chip is mounted on a circuit board.
Grid Array), CSP (Chip Sc)
area package) has been proposed. 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, Wire connection method and TAB (Tape Automated Bondin)
g) system, and furthermore, an FC (Flip Chip) system and the like are known. Recently, BGA and CSP structures using the FC connection system, which are advantageous for miniaturization of semiconductor packages, have 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, the thermoplastic resin melts at high temperature and high humidity, and the active ions in the activator are also released. Occurs. For this reason, at present, the above-mentioned problem is solved by cleaning and removing the residual flux after the solder bonding, but there are disadvantages such as an environmental problem of the cleaning agent and an increase in cost due to the cleaning process.

As described above, the functions of the flux are to remove the oxide of the solder and the metal surface, prevent re-oxidation, and improve the solder wettability (reduce the surface tension). The flux exists and the metal surface is exposed. If it does, the solder will get wet without restriction. Therefore, in general, a solder resist is used on the circuit surface of a semiconductor package or a printed wiring board in order to introduce solder only into a solder joint and to protect a conductor wiring pattern. However, if the solder resist remains in the solder joint, a problem such as a decrease in connection reliability or a failure in solder joint occurs. Therefore, extreme care must be taken in forming the solder resist.

Further, the miniaturization and the increase in the number of pins of the semiconductor package promote the miniaturization of solder balls, and there is a concern that the bonding strength and the 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 solder ball connection portion. However, this requires a step of filling and hardening an underfill, which is technically difficult, and has a problem that the manufacturing process is complicated and the manufacturing cost is increased.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of solder bonding at the time of mounting a semiconductor package, and has been made in view of the problem that the residual flux after solder bonding has been washed and removed, and underfill has been performed. Provided is a semiconductor package using a curable flux, a method of manufacturing the same, and a semiconductor device, which maintain electrical insulation even in a high-temperature, high-humidity atmosphere, and enable high-strength, reliable solder bonding. The purpose is to:

[0010]

That is, the present invention provides a mechanical,
In a semiconductor package on which solder balls for electrical connection are mounted, a curable flux resin layer is formed in advance by transferring a predetermined amount of curable flux onto at least the solder joint surface of the solder balls. A semiconductor package characterized by the above.

Preferably, the curable flux comprises a resin (A) having at least one or more phenolic hydroxyl groups and a resin (B) acting as a curing agent thereof as essential components. Package.

Further, according to the present invention, when the semiconductor package is mounted on a printed wiring board and solder ball bonding is performed, the curable flux resin layer formed at least on the solder bonding surface of the solder ball of the semiconductor package is used for solder bonding. A semiconductor device characterized by being reinforced by a flux resin that has been heated and cured after soldering.

Further, the present invention provides a step of applying a curable flux varnish to a predetermined thickness to form a curable flux film, and pressing the surface of the semiconductor package on which the solder balls are mounted on the curable flux film. A step of transferring the curable flux resin to the tip of the surface of the solder ball, and a step of drying and forming a curable flux resin layer on at least the tip of the solder joint surface of the solder ball. Semiconductor package manufacturing method.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention suppresses the oxidation of the surface of a solder ball by forming a curable flux resin layer on a semiconductor package on which the solder ball is mounted. Is melted at the time of reflow when mounted on a printed wiring board and acts as a flux for soldering, so that the step of supplying the flux can be omitted. Furthermore, at the same time, a meniscus is formed around the solder joint, and the solder joint has a structure reinforced with resin.

The curable flux used in the present invention preferably comprises, as essential components, a resin (A) having at least one or more phenolic hydroxyl groups and a resin (B) acting as a curing agent.

The resin (A) having at least one phenolic hydroxyl group used in the present invention includes a phenol novolak resin, an alkylphenol novolak resin, a biphenol novolak resin, a naphthol novolak resin, a resorcinol novolak resin, a resole resin, or It is preferable to select from at least one kind among the polyvinyl phenol resins, and it is more preferable that the weight average molecular weight is 20,000 or less. If the molecular weight is too large, the fluidity of the photosensitive flux at the time of solder joining may be reduced, which may hinder solder joining.
However, there is no problem if the melt viscosity at the time of solder joining can be controlled to 50 Pa · s or less by using other compounding agents. For this purpose, a liquid curing agent may be blended or a solvent may be added.

In the curable flux used in the present invention, the phenolic hydroxyl group of the resin (A) having a phenolic hydroxyl group removes dirt such as solder and oxides on the metal surface by its reducing action, and forms a solder joint. Acts as a flux.

The amount of the resin (A) having a phenolic hydroxyl group is preferably 20 to 80% by weight of the entire curable flux. When the content is less than 20% by weight, the effect of removing stains such as solder and oxides on the metal surface decreases,
Solder joining cannot be performed. 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. Melt viscosity, the curable flux in the present invention by the composition that balances the oxide removal property and the curability, the hardening flux in the present invention is cured in a form that reinforces the periphery of the solder joint in a ring shape, and the soldering with the conventional flux In comparison, the joining strength and reliability can be greatly improved.

As the resin (B) acting as a curing agent, of the resin (A) having at least one phenolic hydroxyl group used in the present invention, an epoxy resin or an isocyanate resin is used. Specifically, all of them are based on phenols such as bisphenols, phenol novolaks, alkylphenol novolaks, biphenols, naphthols and resorcinols, and skeletons such as aliphatic, cycloaliphatic and unsaturated aliphatics. Examples thereof include modified epoxy compounds and isocyanate compounds.

In the curable flux used in the present invention, a good flux-cured product can be obtained by the compound (B) acting as a curing agent. Therefore, it is not necessary to wash and remove the flux after soldering, and the high-temperature, high-humidity atmosphere is not required. However, it retains electrical insulation and enables soldering with high bonding strength and high reliability.

The amount of the resin (B) acting as a curing agent is such that the epoxy group equivalent or the ianate group equivalent is at least 0.5 times the phenolic hydroxyl equivalent or the carboxyl equivalent of the compound (A), and 1.5 or more. It is preferably at most twice.
If it is less than 0.5 times, a sufficient cured product cannot be obtained, the reinforcing effect is reduced, and the bonding strength and reliability are reduced. Also,
If the ratio is more than 1.5 times, the effect of removing dirt such as oxides on the surface of the solder and the metal is reduced, and there is a possibility that solder joining cannot be performed.

In the curable flux of the present invention, in addition to the above components, additives such as a curing catalyst, a silane coupling agent, an antifoaming agent, a flame retardant, and an organic solvent can be used. Specific examples of the curable catalyst include 2-methylimidazole,
2-phenylimidazole, 2-phenyl-4-methylimidazole, bis (2-ethyl-4-methyl-imidazole), 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxy Methylimidazole, 2-ethyl-4-methylimidazole, 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-cyanoethyl-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.

The curable flux used in the present invention can be obtained as a curable flux varnish by diluting the above components with an organic solvent such as alcohols, ethers and ketones.

As a method of supplying the curable flux resin to the solder balls mounted on the semiconductor package, for example, the obtained curable flux varnish is applied to a predetermined thickness to produce a curable flux film. When the surface of the semiconductor package on which the solder balls are mounted is pressed against the curable flux film and pulled up from there, the curable flux resin is transferred to the front end of the surface of the solder balls. in this case,
Pressure may be applied, but if the pressure is applied too much, the tip of the solder ball may be deformed flat. Therefore, a load of 10 g or less per solder ball is preferable. The semiconductor package in which the curable flux resin is transferred to the solder balls is dried under a suitable condition by a solvent to form a curable flux resin layer at least on the solder joint surface tip of the solder ball. Is obtained.

In the semiconductor device of the present invention, when the semiconductor package is mounted on a printed wiring board and solder balls are joined, the solder balls and the electrodes of the printed wiring board are aligned, and heating and pressing are performed. We perform joining, but, at this time,
At least a ring-shaped meniscus is formed around the solder joint, and the curable flux resin layer formed on at least the solder joint surface of the solder ball of the semiconductor package acts as a flux at the time of solder joint. , And is reinforced by a flux resin that forms a cured ring-shaped meniscus by heating.

[0026]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention.

Example 1 105 g of a phenol novolak resin (manufactured by Sumitomo Durez Co., Ltd., trade name: PR-51470, OH equivalent weight: 105);
Bisphenol A type epoxy resin (manufactured by Yuka Shell Epoxy, trade name: Epicoat-828, epoxy group equivalent: 19)
0) 190 g of ethyl lactate (reagent, boiling point 154 ° C) 5
0 g to prepare a curable flux varnish.

Copper plate 125 μm thick (Furukawa Electric Co., Ltd.)
Manufactured by EFTEC64T) with a land diameter of 30
An evaluation circuit including 0 μm and a land pitch of 0.8 mm was formed, and the lead frame was molded and sealed with a semiconductor sealing material (trade name: EME-7372, manufactured by Sumitomo Bakelite Co., Ltd.), and then polished from one side. Thus, the above-described circuit for evaluation was exposed to produce a 20 mm square evaluation package. For the finishing of polishing, a water-resistant abrasive paper No. 1000 specified in JIS-R6252 was used. After washing with isopropyl alcohol, this was dried at 80 ° C. for 30 minutes to obtain a solder joint evaluation package. Using a commercially available flux (MSP511, manufactured by Kyushu Matsushita Electric Co., Ltd.), solder balls having a diameter of 500 μm (Sn—Pb-based eutectic solder, manufactured by Senju Metal Mining Co., Ltd.) were placed on the land of the package circuit for evaluation.
Through a reflow oven set at a peak temperature of 240 ° C,
Soldered. A curable flux varnish is applied to a copper plate (Furukawa Electric Co., Ltd., trade name: EFTEC64T),
A film having a thickness of 100 μm was formed. The solder ball mounting surface of the evaluation package with solder balls obtained above is pressed against the curable flux film, pulled up 10 seconds later, the curable flux is transferred to the solder balls, and dried at 80 ° C. for 30 minutes to obtain the curable flux. Was fabricated on a solder ball. A printed circuit board for a temperature cycle (TC) test is mounted with an evaluation package in which a curable flux is formed on a solder ball, and a peak temperature of 24 is applied.
After passing through a reflow furnace set at 0 ° C,
The curable flux was cured by a heat treatment for 0 minutes, and ten package mounting substrates for evaluation were produced. The evaluation package mounting board is designed so that 80 solder ball joints are connected in series via the evaluation package and the test printed wiring board. After confirming the continuity of the obtained package for evaluation package, -5
T with 10 minutes at 0 ° C and 10 minutes at 125 ° C as one cycle
The C test was performed.

Comparative Example A comparison was made between a package for evaluation with a solder ball on which no curable flux was formed and a commercially available flux (MSP511, manufactured by Matsushita Electric Industrial Co., Ltd.) mounted on a printed circuit board for a temperature cycle (TC) test. Example 1 was used.

As a result of performing the above temperature cycle test,
In Example 1, the number of defects after 1000 cycles was 0 out of 10 samples. On the other hand, in Comparative Example 1, 1
Nine out of the zero samples are defective in disconnection, and the curing of the present invention is obvious.

[0031]

According to the semiconductor package of the present invention in which a curable flux is formed in advance on a solder ball, no flux supply step is required for mounting on a printed wiring board, and it is necessary to clean and remove the residual flux after soldering. Instead, the curable flux hardens in a form that reinforces the periphery of the solder joints in a ring shape, enabling high-strength and reliable solder joints. Simplify, reduce manufacturing costs,
Further, it is extremely useful for improving the reliability of solder bonding.

Claims (4)

[Claims] In a semiconductor package on which solder balls for mechanically and electrically connecting are mounted, a predetermined amount of a curable flux is transferred to at least a solder joint surface of the solder balls, so that a curable flux is prepared in advance. A semiconductor package having a flux resin layer formed thereon. 2. A curable flux comprising a resin (A) having at least one or more phenolic hydroxyl groups and a resin (B) acting as a curing agent thereof as essential components. The semiconductor package as described. 3. A method for mounting the semiconductor package according to claim 1 on a printed wiring board and joining the semiconductor package with a solder ball.
The curable flux resin layer formed on at least the solder joint surface of the solder ball of the semiconductor package acts as a flux at the time of solder joint, and after the solder joint, is further reinforced by a heated and cured flux resin. Characteristic semiconductor device. 4. A step of applying a curable flux varnish to a predetermined thickness to form a curable flux film, and pressing a surface of the semiconductor package on which the solder balls are mounted onto the curable flux film, and pulling up from the surface. Transferring the curable flux resin to the tip of the surface of the solder ball,
A method for manufacturing a semiconductor package, comprising a step of drying and forming a curable flux resin layer at least on a front end of a solder joint portion of a solder ball.