JPH08242064A - Printed wiring board - Google Patents

Abstract

PURPOSE: To obtain a metallic pad which has low resistance and is excellent in adhesion property with solder resist by forming a roughened surface by using needle-like crystal, etc., of eutectic metal in a metallic pad surface of a printed circuit board wherein solder resist is formed, thus charging an opening part thereof with a metallic film wherein a solder body is provided on a surface. CONSTITUTION: A first layer conductor circuit 2 is prepared on a glass epoxy copper-clad lamination board 1, photosensitive adhesive solution is applied for exposure and development, an opening which becomes a via-hole is formed and a roughened surface 4 is formed by roughening a surface of a resin interlayer adhesive layer 3. Liquid resist is applied and a resist layer 5 is formed, a first conductive circuit 7, a via-hole 6 and a metallic pad 8 are formed by masking and exposure and an eutectic roughened surface 9 is obtained in a surface of a conductor pattern and a pad by performing electroless plating. An Sn layer 10 is provided on a surface of a roughened surface, exposed by using liquid solder resist in close contact with a mask of a pattern covering a part of a pad, an opening part 15 which exposes a roughened surface is formed and an electrolytic copper plating film is filled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board having a metal pad for mounting an electronic circuit, and particularly to a printed wiring board having a metal pad having a low resistance and excellent adhesion to a solder resist.

[0002]

2. Description of the Related Art In mounting an electronic component such as an LSI on a printed wiring board, a metal pad portion for mounting the electronic component is formed. The metal pad portion is a portion wider than the wiring portion of the conductor circuit, and is electrically connected to the conductor circuit.

The surface of the printed wiring board usually has a resin coating film having a dye called a solder resist, and has the role of protecting the wiring and concealing the wiring pattern. This solder resist is formed so as to partially expose the metal pad, and a solder film is formed on this exposed portion.
As a method for forming such a solder film, electroless solder plating as disclosed in International Publication No. WO93 / 25060 has come to be used.

[0004]

However, the plating bath for such electroless solder plating is a strong alkali, and there has been a problem that the solder resist film and the metal pad are separated from each other. Further, since the solder film has high electric resistance, it has been required to reduce the amount of solder in the metal pad portion.

As described above, conventionally, no structure of a metal pad having a low resistance and an excellent adhesion to a solder resist has been proposed. An object of the present invention is to propose a printed wiring board having such a metal pad having low resistance and excellent adhesion to a solder resist.

[0006]

According to the present invention, a metal pad for mounting an electronic circuit is provided on the surface layer of a printed wiring board, and an opening is provided on the metal pad so that the metal pad is partially exposed. In a printed wiring board on which a solder resist is formed, a roughened surface such as needle crystals of eutectic metal is formed on the surface of the metal pad, and an opening on the roughened surface is filled with a metal film. And a solder body is provided on the metal film.

[0007]

In the present invention, it is necessary that a roughened surface is formed on the surface of the metal pad. The reason for this is to improve the adhesion with the solder resist. This is because the uneven portion of the roughened surface can penetrate into the solder resist like an anchor to improve the adhesion between the metal pad and the solder resist.

Further, it is necessary to fill the opening on the roughened surface with metal and to provide a solder body on it.
The reason for this is to reduce the amount of solder as much as possible to prevent the resistance value from increasing due to solder connection, and to place the solder body above the opening, or to project the solder body from the opening to the external terminal of the electronic circuit component. This is to facilitate the connection with. Also, the position of the solder body can be adjusted by adjusting the filling amount.

The roughened surface is preferably acicular crystals. The reason for this is that it easily penetrates into the solder resist. The needle crystals are preferably eutectic metal. The reason for this is that the eutectic alloy is likely to form needle crystals having a relatively low electric resistance. The needle crystals are preferably a eutectic alloy of Ni-P-Cu.
The reason for this is that a roughened surface having a very complicated shape can be easily formed, and the resistance value is not largely different from that of Cu. Further, since the eutectic compound has high strength, delamination due to thermal shock is unlikely to occur, and heat cycle characteristics are improved. Further, it is because it is not dissolved by an acid or an oxidizing agent and a high adhesion can be secured.

The contents of copper, nickel and phosphorus in the eutectic compound are 90 to 96%, 1 to 3% and 0.5 to respectively.
It is desirable to be about 2 wt%. This is because, in the above range, the crystals of the deposited film have a needle-like structure, and the anchor effect is excellent.

In the present invention, of the roughened surface on the pad, the portion exposed by the opening is preferably removed in advance or it is more preferable not to provide the roughened layer from the viewpoint of reducing the resistance value. Is. For this purpose, it is preferable to mask the portion exposed by the opening of the metal pad before dipping it in the electroless plating bath for forming the roughening layer.

The thickness of the roughened surface is preferably 0.5 to 5 μm. The reason for this is that if it is less than 0.5 μm, the anchoring effect is too low and the adhesion strength decreases, and if it exceeds 5 μm, the surface roughness becomes too large and the adhesion strength decreases. On the other hand, when it exceeds 5 μm, a void is formed between the roughened surface and the metal film, which leads to an increase in resistance.

As a method of forming the roughened surface, a printed wiring board provided with a pad is formed of at least a copper compound,
Electroless plating is performed by immersing in a plating bath containing a nickel compound and hypophosphite. In the electroless plating bath, in addition to the above compounds, a complexing agent and the like may be appropriately added. The copper compound, nickel compound, and hypophosphite concentration in the plating bath are 8 to 12 g / l and 0.8 to 1.2 g / l, respectively.
1, 18 to 22 g / l is desirable. The reason for this is that within the above range, the precipitated crystal structure becomes a needle-like structure, and the anchor effect is excellent.

As electroless plating conditions, a bath temperature of 60
It is desirable that the temperature is -80 ° C, the deposition rate is 1 to 1.5 µm / 10 minutes, and the bath ratio is 0.5 to 1.0 dm ² / l. The plating time is preferably 5 to 20 minutes. When it is out of the above range, the plating film forming the roughened surface to be deposited does not become dense and the heat cycle characteristics are significantly deteriorated.

It is desirable to have a Sn layer on the surface of the roughened surface. The reason for this is that Sn is not dissolved or discolored by a chemical such as an acid or an oxidizing agent, so that the roughened surface of the eutectic alloy can be protected. The Sn layer is preferably formed by substituting the metal on the surface of the eutectic alloy of Ni-P-Cu. The reason for this is that since it is a substitution reaction, the shape of the needle-like crystals is not impaired, and the adhesive force with the solder resist does not decrease.

In the present invention, the metal film filled in the opening of the solder resist is preferably Cu. The reason for this is that Cu is low in cost, and the metal pad is generally made of Cu, and it is easy to match the electric resistance and the coefficient of thermal expansion with the metal pad.

The solder body may be in the form of a film or a sphere, but is preferably sphere. The reason for this is that it is easy to mount semiconductor components. Flip-chip mounting is becoming the mainstream for semiconductor components, and a spherical solder body is most suitable for such flip-chip mounting. The metal to be filled is preferably formed by a plating method of either electroless plating or electrolytic plating.

Further, it is preferable that the solder body is projected from the surface of the solder resist. Conventional QFP
For those having leads as external terminals like this, the self-alignment effect can be expected, so place the solder body on the pad surface at a position lower than the solder resist surface,
It is better to make the pad part a dent, but in flip chip mounting, which uses solder bumps (solder balls), which are becoming the mainstream these days, the solder body was protruding more than the solder resist surface. Because it is better.

As a method for forming the solder body, there is a method in which a solder paste is printed on the opening of the solder resist by screen printing or the like to re-float, or electroless solder plating is carried out. It is better for fine pitch surface mounting.

The electroless plating method is preferably a method using displacement plating and disproportionation plating as disclosed in International Publication No. WO93 / 25060. The present invention is
It proposes a structure in which peeling of the solder resist does not occur even in such a strongly alkaline disproportionation plating bath.

A method using the displacement plating and the disproportionation plating will be described. First, a Cu—Sn substitution reaction based on the formation of a metal complex of thiourea occurs on the surface of a metal pad such as copper to form a Sn thin film layer having a thickness of 0.1 to 2 μm. Then, a disproportionation reaction based on selective precipitation occurs to form a Sn crystal layer. ^{_{2Sn (OH) 3 - → Sn}} + Sn (OH) 6 2- this way because coarser resulting precipitated crystals (1
100 μm), the crystalline particles are in an agglomerated state and become a porous body.

Further, the Sn porous body is replaced with Sn-Pb to form a Pb layer of 0.1 to 5 μm. This S
The n-Pb composite is reflowed as necessary to form a solder film or a solder ball.

The solder resist used in the present invention is preferably a composite of a thermoplastic resin and a sensitized thermosetting resin.

The thermosetting resin is phenol resin, amino resin such as melamine resin or urea resin, epoxy resin, phenoxy resin, epoxy modified polyimide resin, unsaturated polyester resin, polyimide resin, urethane resin, diallyl phthalate resin. Is desirable.

The thermoplastic resin may be polyethersulfone, polysulfone, polyetherimide, polystyrene, polyethylene, polyarylate, polyamideimide, polyphenylene sulfide, polyetheretherketone, polyoxybenzoate, polyvinyl chloride,
It is preferably polyvinyl acetate, polyacetal, or polycarbonate.

In the present invention, a photosensitive resin can be used in place of the thermosetting resin, and the photosensitive resin includes unsaturated double groups such as acryloyl group, methacryloyl group, allyl group and vinyl group. Those having one to several bonds in the molecule can be used, and epoxy acrylate, polyester acrylate, polyether acrylate, silcon acrylate, polybutadiene acrylate, polystyrylethyl methacrylate, vinyl / acrylic oligomer (branched acid, acid anhydride, A monomer having a hydroxy group or a glycidyl group, copolymerized with vinyl or an acrylic polymer, and then reacted with an acrylic monomer), polyethylene / thiol (a copolymer of olefin and mercaptan) and the like are preferably used.

Here, as the photoinitiator which is important as a photocuring factor for the photosensitive resin, benzoisobutyl ether, benzyl dimethyl ketal, diethoxyacetophenone, acyloxime ester, chlorinated acetophenone, hydroxyacetophenone, etc. Bond cleavage type,
Benzophenone, Michler's ketone, dibenzosuberone,
Any one or more of intramolecular hydrogen abstraction type such as 2-ethylanthraquinone and isobutylthioxanthone are preferably used.

As the photoinitiator aid, triethanolamine, Michler's ketone, 4,4-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, ethyl 4-dimethylaminobenzoate, 4-dimethylaminobenzoic acid (n-butoxy) Any one or more of ethyl, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, and a polymerizable tertiary amine are used. As a sensitizer, Michler's ketone or Irgacure
651, isopropyl thioxanthone and the like are preferable,
Some of the above photoinitiators act as a sensitizer. The composition ratio of the photoinitiator to the sensitizer is, for example, benzophenone / Michler's ketone = 5 parts by weight / 0.5 parts by weight Irgacure 184 / Irgacure 651 = 5 parts by weight / 100 parts by weight of the photosensitive resin.
Weight parts Irgacure 907 / isopropyl thioxanthone = 5 weight parts / 0.5 weight parts are preferred.

Epoxy acrylate, epoxy methacrylate, urethane acrylate, polyester acrylate, polystyryl methacrylate, etc. are preferably used as the photosensitive monomer or photosensitive oligomer constituting the photosensitive resin. More preferably, the solder resist is a composite of polyether sulfone and epoxy acrylate.

This composition is excellent in resolution, acid and oxidant characteristics, but conversely, it is weak in alkali. Therefore, by adopting a structure having a roughened surface in the pad portion as in the present invention, alkali This is because the problem of peeling due to is solved. The epoxy acrylate is 10 to 10% of epoxy resin.
A 50% acrylate is desirable. This is because an acrylation ratio in this range is excellent in resolution, acid resistance and oxidant characteristics.

The resist is a resin composite composed of a photosensitive resin and a thermoplastic resin in which a part of the thermosetting functional group of the thermosetting resin is replaced with a photosensitive group, and they have a pseudo-homogeneous compatible structure. It is desirable to be formed. The quasi-homogeneous compatible structure is a structure of the resin composite that the present inventors have newly proposed.

This is because a resin composite composed of a thermosetting resin and a thermoplastic resin, a resin composite composed of a photosensitive resin and a thermoplastic resin, or a part of the thermosetting functional group of the thermosetting resin is photosensitive. It is a resin composite consisting of a photosensitive resin substituted with a group and a thermoplastic resin, and the particle diameter of the constituent resin particles is 0.1 μm as measured by observation with a transmission electron microscope (hereinafter referred to as “TEM”). It is the following and refers to a resin composite having one glass transition temperature peak value of the resin measured by dynamic viscoelasticity. Here, the conditions for the dynamic viscoelasticity measurement in the present invention are: vibration frequency 6.28 rad / sec, temperature rising rate 5 ° C.
/ Min.

That is, the quasi-homogeneous compatible structure has the unique physical properties of a thermosetting resin such as an epoxy resin or the photosensitive physical properties of an acrylic resin and a thermoplastic resin such as PES. Refers to a more homogeneous structure that exhibits higher physical properties than the original physical properties, and has a single glass transition temperature peak value measured by dynamic viscoelasticity, and is used for thermosetting resins or photosensitive resins and thermoplastic resins. The interaction is extremely strong.

The composite having a pseudo-homogeneous compatible structure is
Even if the fracture surface is etched with a solvent that dissolves thermoplastic resin such as methylene chloride, it does not phase-separate into thermoplastic resin and thermosetting resin (including photosensitized resin). No unevenness occurs. This can be observed with a scanning electron microscope (SEM). This pseudo-homogeneous phase dissolution structure is represented by the following model.

Generally, the thermosetting resin has a minimum unit called a microgel having a diameter of 0.1 μm or less, and it is considered that this is an aggregate. The inside of the microgel is a mass of molecular chains in which monomers are chemically bonded and polymerized. The microgels are not chemically bound to each other. The destruction of the thermosetting resin is considered to occur at the interface between the microgels. Therefore, it is understood that the actual resin breaking strength is lower than the theoretical strength calculated from the chemical bond.

A composite of a thermoplastic resin and a thermosetting resin (including a photosensitized resin) is more complicated, and even if these resins are uniformly mixed and then cured, the thermosetting resin will have microgels which are different from each other. Aggregate and extrude the thermoplastic resin to form huge islands of thermosetting resin and sea of thermoplastic resin,
The phase is separated. In order to form a perfect homogeneity of the thermoplastic resin and the thermosetting resin, it is necessary to incorporate the thermoplastic resin into the microgel, which is impossible with the current curing technology. .

Therefore, the inventors of the present application accepted the existence of this microgel and proposed a structure in which the microgels were connected by a thermoplastic resin molecular chain, and named this "quasi-uniform structure". . The effect of the structure of the resin composite is that the thermoplastic resin (for example, P
It becomes particularly remarkable when the content of ES) is 15 to 50 wt% in terms of solid content. The reason is that the content of thermoplastic resin is 15 wt.
If it is less than%, the toughening effect is not sufficiently exerted because there are few thermoplastic resin molecules entangled in the resin component network, while if the content of the thermoplastic resin exceeds 50 wt%, it is thermoset due to a decrease in crosslinking points. This is because the interaction between the photosensitive resin or the photosensitive resin and the thermoplastic resin is reduced.

In the method of curing the resist for forming the resin composite as described above, firstly, when the thermosetting resin is used, the curing temperature of the thermosetting resin, the type of the curing agent, and the photosensitivity. With a curing rate exceeding a pseudo-homogeneous phase formation point determined by one or more factors selected from the presence or absence of imparting properties, on the other hand, when a photosensitive resin is used, a photocuring factor of the photosensitive resin, Such as initiators and sensitizers,
It is characterized in that it cures at a curing rate that exceeds the pseudo-homogeneous phase formation point determined by the photosensitive monomer and exposure conditions. The quasi-homogeneous phase formation point here means that the particle size of the resin particles forming the composite is 0.1 μm as measured by TEM observation.
It means the lower limit of the curing rate at which the following pseudo-homogeneous compatible structure can be obtained.

As the curing method, secondly, a quasi-homogeneous phase forming point which is determined by one or more factors of the crosslinking density or the molecular weight of the uncured thermosetting resin or the uncured photosensitive resin is exceeded. It is characterized in that it is cured at a non-phase separation rate. The quasi-homogeneous phase formation point here is a value measured by TEM observation of the particle size of the resin particles forming the composite.
It means the upper limit value of the phase separation rate at which a quasi-homogeneous compatible structure of 0.1 μm or less can be obtained.

Thirdly, the hardening method is characterized in that the hardening is carried out at a hardening speed exceeding the quasi-homogeneous phase forming point and at a phase separation speed not exceeding the quasi-homogeneous phase forming point. This means a method in which the factors that determine the curing rate and the phase separation rate influence each other.

Next, the interrelationship of the above-mentioned various factors that determine the curing rate or the phase separation rate will be described. First, regarding the factors that determine the curing rate, the curing rate increases as the curing temperature of the thermosetting resin increases, assuming that other factor conditions are constant. Therefore, when the thermosetting resin is cured below the lower limit of the curing temperature required to obtain a curing rate exceeding the pseudo-homogeneous phase formation point, the structure of the obtained resin composite becomes a pseudo-homogeneous compatible structure.

A curing agent having a shorter gel time has a higher curing rate. Therefore, when the thermosetting resin is cured with a curing agent that does not exceed the upper limit of the gelling time required to obtain a curing rate that exceeds the pseudo-homogeneous phase formation point, the structure of the resin composite obtained is pseudo. It has a uniform compatible structure.

The higher the photosensitivity, the faster the curing speed. Therefore, in a combination where other factor conditions form a quasi-homogeneous compatible structure, by imparting photosensitivity to the resin, the obtained resin composite has a more homogeneous quasi-homogeneous compatible structure.

As a method of imparting photosensitivity, there are a method of introducing a photosensitive group into a thermosetting resin or a thermoplastic resin, and a method of blending a photosensitive monomer. You may mix | blend a sensitizer. Further, a photosensitive resin such as an acrylic resin can be used instead of the thermosetting resin. In this case, it is necessary to cure the photosensitive resin at a curing rate exceeding a pseudo-homogeneous phase formation point determined by a photocuring factor such as an initiator, a sensitizer, a photosensitive monomer and exposure conditions.

Considering these facts, when the thermosetting resin or the photosensitive resin and the thermoplastic resin are compounded, if the above-mentioned variation factor is one, the value of the factor corresponding to the pseudo-homogeneous phase formation point is One point is decided. Therefore, when the above-mentioned fluctuation factors are two or more, various combinations of the values of the factors corresponding to the pseudo-homogeneous phase formation point are conceivable. That is, the particle size of the constituent resin particles is a value measured by TEM observation.
It is possible to select a combination that exhibits a curing rate of 0.1 μm or less.

Regarding the factors that determine the phase separation rate, if the other factor conditions are constant, the more the number of functional groups in one molecule of the uncured thermosetting resin or the uncured photosensitive resin, the more the phase separation occurs. Difficult to occur (phase separation speed slows down). Therefore, it can be obtained by curing using an uncured thermosetting resin or an uncured photosensitive resin having a crosslink density exceeding the lower limit of the crosslink density required to obtain a phase separation rate not exceeding the pseudo-homogeneous phase formation point. The structure of the resin composite has a pseudo-homogeneous compatible structure.

The larger the molecular weight of the uncured thermosetting resin or the uncured photosensitive resin, the less likely phase separation occurs (the phase separation speed becomes slower). Therefore, when the uncured thermosetting resin or the uncured photosensitive resin having a molecular weight exceeding the lower limit of the molecular weight required to obtain a phase separation rate not exceeding the quasi-homogeneous phase formation point is used for curing, the resulting resin composite is obtained. The body structure becomes a pseudo-homogeneous compatible structure. Considering these facts, when the thermosetting resin or the photosensitive resin is combined with the thermoplastic resin and the above-mentioned variation factor is one, the value of the factor corresponding to the pseudo-homogeneous phase formation point is determined by one point. . Therefore, when the above-mentioned variation factors are two types, various combinations of the values of the factors corresponding to the pseudo-homogeneous phase formation points are possible. That is, it is possible to select a combination showing a phase separation rate such that the particle size of the constituent resin particles is 0.1 μm or less as measured by TEM observation.

The resin composite obtained by the method of the present invention as described above has the physical properties peculiar to thermosetting resins such as epoxy resin or the peculiar physical properties of photosensitive resin such as acrylic resin. It is possible to exhibit higher physical property values than the original physical properties of thermoplastic resins such as PES and PES. That is, the PES-modified epoxy resin and PES-modified acrylic resin according to the present invention have higher resin strength than that of PES alone, and have an unprecedented toughening effect on epoxy resin or acrylic resin.

Thermosetting resin (photosensitized thermosetting resin), thermosetting resin or photosensitive resin prior to compounding at least one resin selected from photosensitive resin and thermoplastic resin The thermoplastic resin and the thermoplastic resin are uniformly mixed by being dissolved in a solvent as needed. Examples of such a solvent (phase solvent) include dimethylformamide (DMF), methylene chloride, and dimethylsulfoxide (DM).
SO), normal methyl pyrrolidone (NMP), diethylene glycol dimethyl ether (DMDG), etc. can be used.

It is also possible to heat-melt and mix the thermosetting resin or the photosensitive resin and the thermoplastic resin at a temperature lower than the phase separation start temperature and lower than the curing start temperature. Dissolving the resin in these solvents is advantageous because the viscosity can be adjusted and a film is easily formed.

In the present invention, when an epoxy resin is used as the thermosetting resin, an imidazole-based curing agent, a diamine, a polyamine, a polyamide, an organic acid anhydride, vinylphenol or the like can be used. On the other hand, when a thermosetting resin other than the epoxy resin is used, a known curing agent can be used.

These resins include coloring agents, leveling agents,
An antifoaming agent, an ultraviolet absorber, an additive such as a flame retardant, heat-resistant fine powder or other fillers may be appropriately mixed.
As the colorant, phthalocyanine green or the like is preferable.

The resist composition of the present invention is coated on a base film with a roll coater or a doctor bar, and then dried in a drying oven set at 60 to 100 ° C. to remove a predetermined amount of the solvent. It is preferable to form a film by setting it in a stage state in terms of film thickness uniformity and productivity.

The drying was carried out under the condition that the phases were not separated, and the dried product in the B stage was a single-phase mixture. It is desirable that the drying be performed in vacuum around room temperature of 30 ° C. or less. In the case of forming a film, it is advantageous to set the melting point of the resin mixture whose composition has been adjusted to be higher than room temperature and set the curing start time higher than this melting point.

The reason for this is that if the melting point of the resin composite is lower than room temperature, the resin composite after being processed into a film must be stored and used at room temperature or below, and the workability thereof is significantly impaired. Is. The reason for setting the curing start temperature to the melting point or higher is that, when the film is usually used, it is generally used by laminating under pressure, and the resin is softened by this heating to follow the substrate. This is to prevent the resin composite from being cured at this time.

If heat curing proceeds during lamination, problems such as a decrease in resolution are likely to occur. Of course, this is not the case in the case of a combination of a thermosetting resin and a thermoplastic resin.

The melting point of the resin depends on the skeleton structure, etc.
Although controllable, control by increasing or decreasing the molecular weight is advantageous in that the properties of the cured product are not significantly changed. Further, the curing start temperature can be easily controlled by selecting the structure and type of the curing agent. At this time, the thickness of the resist on the base film is adjusted to 15 to 150 μm by the doctor bar gap. Since this resist film is wound into a roll, it is desirable to form a protective film on the resist (cover film) to protect the uncured resist.

As the base film, polyethylene terephthalate, polypropylene and polyethylene fluoride (Tedlar film) films are preferably used. The thickness of this base film is 5-10.
0 μm is desirable. In order to prevent the plating resist from repelling the base film, the coated surface of the base film may be subjected to a mud treatment (unevenness).

In addition, in order to prevent dents or dents due to foreign matter on the resist layer when the sheets are brought into contact with each other when the resist film is formed, mud treatment may be performed on the opposite surface.

The printed wiring board having the metal pad of the present invention may be any printed wiring board, but is preferably a multilayer printed wiring board. Further, it is desirable that the surface has an adhesive layer, the surface is roughened, and the metal pad is formed on the roughened surface.

The above-mentioned adhesive is preferably an adhesive in which a heat-resistant resin fine powder is dispersed in a resin matrix, and the heat-resistant resin powder can be used in various shapes such as particle shape, hollow shape and crushed piece shape. In the case of particle shape, 1) average particle size
Particles of 10 μm or less, 2) Aggregate particles obtained by aggregating heat-resistant resin powder having an average particle size of 2 μm or less to have an average particle size of 2 to 10 μm, 3) Heat-resistant resin powder having an average particle size of 2 to 10 μm and average particles Mixture with heat resistant resin powder with a diameter of 2 μm or less, 4)
It is selected from pseudo particles formed by adhering at least one of a heat-resistant resin powder having an average particle size of 2 μm or less and an inorganic powder having an average particle size of 2 μm or less to the surface of the heat-resistant resin powder having an average particle size of 2 to 10 μm. Is desirable. The reason for this is
If the average particle size exceeds 10 μm, the anchor becomes deeper and 100
This is because a so-called fine pattern of μm or less cannot be formed. On the other hand, the reason why the pseudo particles of 2) to 4) are desirable is that a complicated anchor can be formed and the peel strength can be improved.

It is desirable that the surface of the heat-resistant resin powder is coated with silica sol or the like in order to prevent agglomeration. The blending amount of the heat resistant resin powder is preferably 5 to 100 by weight with respect to 100 solid resin content of the heat resistant resin matrix.
The reason for this is that if the weight ratio is less than 5, the anchor cannot be formed, and if it exceeds 100, the kneading becomes difficult, and the amount of the heat resistant resin matrix is relatively reduced, and the adhesive layer This is because the strength of is reduced.

Further, it is desirable that the anchor recesses formed in such an adhesive layer have an average depth of 15 μm or less, and by doing so, the conductor pattern L / S is formed.
= 50/50 μm or less.

Next, a method of manufacturing the printed wiring board of the present invention will be described. An example of a method for manufacturing a printed wiring board using the resist of the present invention will be described. 1) An adhesive layer is formed on the surface of a substrate such as a glass epoxy substrate, a polyimide substrate, a ceramic substrate, and a metal substrate by an ordinary method, and then the surface of the adhesive layer is roughened by an ordinary method using an acid or an oxidizing agent. After that, a catalyst is applied and fixed on the surface of the roughened adhesive layer. The adhesive is preferably an adhesive obtained by dispersing the heat resistant resin fine powder in the resin matrix described above.

2) After that, exposure, development and UV curing are performed, and then heat treatment is performed to form a plating resist printed in a predetermined pattern. On the base film,
When a resist for wiring board coated with a composition obtained by dispersing a heat-resistant fine powder in a heat-resistant photosensitive resin matrix is used, thereafter, exposure, development and UV curing are performed,
Then, heat treatment is performed to form a plating resist printed in a predetermined pattern.

3) If necessary, the catalyst is activated by acid treatment or the like, and then electroless plating is performed to form the required conductor pattern and metal pad. 4) In the case of a multilayer printed wiring board, steps 1) to 3) are repeated to form a multilayer. 5) A roughened surface made of a eutectic alloy is formed on the surface of the metal pad by the eutectic plating described above. 6) A liquid solder resist uncured resin composition is applied, or an uncured solder resist film is laminated to form a solder resist layer. Further, it is exposed to light and cured and developed to form an opening in a part of the metal pad.
In addition, when the solder resist is the above-mentioned complex having the pseudo-homogeneous phase dissolution structure, it is necessary to adjust the curing conditions.

7) A metal plating film is filled on the roughened surface of the eutectic alloy by electrolytic plating. By adjusting the plating time at this time, the filling amount is adjusted and the position where the solder body is formed is determined. For example, when the filling amount is up to the surface of the solder resist, the solder body is provided on the filling metal, so that the solder body projects from the surface of the solder resist. Also, if the filling amount is reduced, the solder body can be made lower than the solder resist surface, and as a result, the metal pad part will be in a depressed state, so that a self-alignment effect advantageous for mounting a semiconductor component having leads as external terminals can be obtained. It will be possible.

8) After filling the metal plating film, a solder body is formed. As a method of forming the solder body, there is a method of screen-printing a solder paste or the like or performing electroless solder plating as described above. By reflowing this solder film, the solder body can be made spherical with surface tension. The present invention will be described in more detail with reference to examples. The numbers in the examples are the numbers in the drawings.

[0069]

【Example】

(Example 1) (1) Glass epoxy copper clad laminate 1 (manufactured by Toshiba Chemical)
A photosensitive dry film (manufactured by DuPont) was laminated on the above, exposed to ultraviolet light through a mask film on which a desired conductor circuit pattern was drawn, and an image was printed. Then
After development with 1,1,1-trichloroethane and removal of copper in the non-conductor portion using a cupric chloride etching solution, the dry film was peeled off with methylene chloride. As a result, a wiring board having the first-layer conductor circuit 2 composed of a plurality of conductor patterns on the substrate was prepared (FIG. 1a).

(2) 200 g of epoxy resin particles (manufactured by Toray Co., Ltd., average particle size 3.9 μm) were dispersed in 5 l of acetone into an alumina particle suspension, which was stirred in a Henschel mixer to obtain 1 l of acetone. On the other hand, epoxy resin powder (manufactured by Toray, average particle size 0.5 μm) in an acetone solution in which 30 g of epoxy resin (manufactured by Mitsui Petrochemical) was dissolved
A suspension obtained by dispersing 0 g was added dropwise to attach the epoxy powder to the surface of the epoxy particles, the acetone was removed, and then the mixture was heated to 150 ° C. to prepare pseudo particles. This pseudo particle has an average particle size of about 4.3 μ.
m, and about 75% by weight is ± 2μ centered on the average particle size.
It existed in the range of m.

(3) of a cresol novolac type epoxy resin (manufactured by Nippon Kayaku, molecular weight 2500) dissolved in DMDG
70 parts by weight of 25% acrylate, 30 parts by weight of polyether sulfone (PES), 4 parts by weight of imidazole curing agent (manufactured by Shikoku Kasei, product name: 2E4MZ-CN), and caprolactone modified tris (acryloxy) as a photosensitive monomer. ethyl)
Isocyanurate (manufactured by Toagosei, trade name; Aronix M325) 10 parts by weight, benzophenone as a photoinitiator (manufactured by Kanto Kagaku) 5 parts by weight, photosensitizer Michler ketone (manufactured by Kanto Kagaku) 0.5 parts by weight, and further After mixing 40 parts by weight of the epoxy resin pseudo particles prepared in (2) above with the mixture, the mixture was mixed while adding NMP, and the viscosity was adjusted to 2000 CPS with a homodisper stirrer, followed by three rolls. The mixture was kneaded to obtain an adhesive solution.

(4) This photosensitive adhesive solution was applied onto the wiring board prepared in (1) above using a roll coater, left standing for 20 minutes in a horizontal state, and then dried at 60 ° C. It was (5) 100 μmφ on the wiring board that has been treated in (4) above.
Adhere the photomask film with the black circles of
It was exposed with an ultra-high pressure mercury lamp of 500 mj / cm ² . DMDG this
By spray developing with a (diethylene glycol dimethyl ether) solution, an opening to be a 100 μmφ via hole was formed on the wiring board (FIG. 1b). Furthermore, the wiring board was exposed to light of about 3000 mj / cm ² by an ultra-high pressure mercury lamp and heat-treated at 100 ° C. for 1 hour and then at 150 ° C. for 5 hours to form an opening having excellent dimensional accuracy equivalent to a photomask film. The resin interlayer adhesive layer 3 having a thickness of 50 μm was formed.

(6) The wiring board treated in the above (5) was adjusted to pH = 13 with potassium permanganate (KMnO).
₍₄ , 60 g / l) at 70 ° C. for 15 minutes to roughen the surface of the interlayer resin insulation layer to form a roughened surface 4, and then soak in a neutralizing solution (made by Shipley) and then wash with water ( Figure 1c). (7) A palladium catalyst (manufactured by Shipley) was applied to the substrate having the roughened surface of the adhesive layer to activate the surface of the adhesive layer 3.

(8) Cresol novolac type epoxy resin (manufactured by Nippon Kayaku, trade name EOCN-103) dissolved in DMDG (dimethyl glycol dimethyl ether)
S) sensitized oligomer (molecular weight 4000) in which 25% of epoxy group is acrylated, PES (molecular weight 170)
00), imidazole-based curing agent (Shikoku Kasei product name
2 PMHZ-PW), acrylated isocyanate which is a photosensitive monomer (trade name Aronix manufactured by Toagosei)
M215), benzophenone (manufactured by Kanto Chemical Co., Inc.) as a photoinitiator, and Michler ketone (sensitized by Kanto Chemical Co., Inc.) as a photosensitizer,
After mixing with the following composition using NMP, the viscosity was adjusted to 3000 cps with a homodisper stirrer, followed by kneading with a triple roll to obtain a liquid resist. Resin composition: Photosensitive epoxy / PES / M325 / BP
/MK/imidazole=70/30/10/5/0.5
/ 5

(9) This liquid resist was applied onto the resin insulation layer of (7) above using a roll coater and dried at 60 ° C. to form a resist layer having a thickness of about 30 μm (FIG. 1d). (10) L / S = on the wiring board subjected to the treatment of (9) above.
A mask film having a conductor circuit pattern of 50/50 drawn thereon was brought into close contact with it and exposed with an ultrahigh pressure mercury lamp of 1000 mJ / cm ² . By spray-developing this with triethylene glycol dimethyl ether (DMDG),
On the wiring board, a resist for plating from which the conductor circuit pattern portion was removed was formed. Furthermore, with an ultra-high pressure mercury lamp, 6000m
J / cm ² exposure, 1000 ° C. for 1 hour, then 15
Heat treatment was performed at 0 ° C. for 3 hours. The plating resist 5 is for patterning and forming the metal pad 8.

(11) The wiring board of (10) above is immersed in an electroless plating solution for additive having the composition shown below for 11 hours, and electroless copper plating having a plating film thickness of 25 μm is applied to the second conductor circuit. 7, via holes 6, and metal pads 8 were formed (FIG. 1e). Copper sulfate 0.06 mol / l formalin 0.30 mol / l sodium hydroxide 0.35 mol / l EDTA 0.35 mol / l additive a little temperature 70 to 72 ° C. pH 12.4

(12) After acid degreasing the substrate, applying a soft etching sulfuric acid active catalyst and activating it, the substrate is plated in the following electroless plating bath to form Ni-P-Cu on the surface of the conductor pattern and the pad. A roughened surface 9 having a eutectic thickness of 1 μm was obtained (FIG. 1f). Electroless plating bath Copper sulfate: 10.1 g / l Nickel sulfate: 1.0 g / l Sodium hypophosphite: 20.2 g / l Sodium hydroxide: Appropriate amount pH = 9.0

(13) Furthermore, this substrate is tin borofluoride-thiourea liquid (or tin chloride-thiourea is also available).
Is immersed in an electroless tin plating bath consisting of 1 minute at 50 to 60 ° C. to form a Sn layer 10 having a thickness of 0.05 μm on the roughened surface.
Was provided. (14) Cresol novolac type epoxy resin dissolved in DMDG Nippon Kayaku product name EOCN-103S)
25% acrylated photo-sensitive oligomer of epoxy group (molecular weight 4000), PES (molecular weight 1700
0), imidazole-based curing agent (trade name 2 manufactured by Shikoku Kasei
P4MHZ-PW), acrylated isocyanate which is a photosensitive monomer (trade name Aronix manufactured by Toagosei)
M215), benzophenone as a photoinitiator, a photosensitizer Michler (Kanto Kagaku), and a colorant (phthalocyanine green) were mixed with NMP with the following composition, and the viscosity was adjusted to 2000 cps with a homodisper stirrer. And kneaded with three rolls to obtain a liquid solder resist. Resin composition: Photosensitive epoxy / PES / M325 / BP /
MK / imidazole = 70/30/10/5 / 0.5 /
5

(15) This liquid solder resist was applied onto the wiring board of (13) using a roll coater and dried at 60 ° C. to form a solder resist layer having a thickness of 20 μm. (16) A mask film having a pattern in which a part of the metal pad was hidden was brought into close contact with the wiring board subjected to the treatment of (15), and exposed. This was spray-developed with diethylene glycol diethyl ether (DMDG) to form an opening 15 so that the roughened surface formed on the metal pad was exposed. Furthermore, it is 30 by the super high pressure mercury lamp.
Exposure was carried out at 00 mj / cm ² and heat treatment was carried out at 100 ° C. for 1 hour and then at 150 ° C. for 3 hours to obtain a solder resist 11 (FIG. 1g). This solder resist is TE
When observed by M, it was found to be 0.1 μm or less, and the glass transition temperature peak value of the resin measured by dynamic viscoelasticity was one. Here, the conditions of the dynamic viscoelasticity measurement in the present invention are a vibration frequency of 6.28 rad / sec and a heating rate of 5 ° C./min.

(17) A lead wire was attached to this substrate, immersed in a conventional electrolytic copper plating solution and energized to fill the opening 15 with the electrolytic copper plating film 15 (FIG. 1h). (18) Then, the substrate was treated with a degreasing solution at 70 ° C. for 5 minutes, washed with water, and then treated with an activating solution at room temperature for 10 seconds. (19) This was added to an electroless Sn displacement plating solution prepared by dissolving a thiourea or borofluoride solution having the following composition in water.
Immerse for minutes and replace the surface of the filled copper plating film with Sn to replace Sn
The electroless Sn displacement plating having a plating film thickness of 0.3 μm was applied. Tin borofluoride 0.1 mol / l Thiourea 1.0 mol / l Temperature 80 ° C. pH 1.2

(20) The substrate treated in (19) was immersed in the disproportionation plating bath shown below for 3 hours to form a Sn crystal layer, and the height of the layer was 100 to 150 μm. Sn plating was applied. As a result of SEM observation, the Sn crystal layer was an aggregate of crystals having an average particle size of 50 μm. Sodium hydroxide 5.2 mol / l tin chloride 0.4 mol / l formalin 1.0 mol / l additive a little temperature 80 ° C. pH 14-15

The substrates (21) and (20) were washed with water and immersed in a Pb displacement plating bath having the following composition for 6 minutes. Lead tetrafluoroborate 0.1 mol / l hydrogen borofluoride 1.0 mol / l temperature 80 ° C. pH 3.5

(22) The substrates of (21) were washed with water and dried. In this state, the solder body 13 is in the form of a film. Then, it was heated at 250 ° C. and reflowed to form a spherical solder body 14 (FIG. 1i). In this way, a printed wiring board having solder bodies 13 and 14 protruding from the surface of the solder resist 1 was obtained. No peeling was observed between the solder resist 11 and the metal pad 8 even with electroless solder plating at pH = 14.

Comparative Example 1 (1) A printed wiring board was formed by the steps (1) to (11) of the example. (2) A commercially available liquid solder resist was applied on a wiring board using a roll coater and dried at 60 ° C. to form a solder resist layer having a thickness of 20 μm. A mask film having a pattern in which a part of the metal pad 8 was hidden was brought into close contact with the wiring board subjected to this treatment and exposed. This was spray-developed with diethylene glycol diethyl ether (DMDG) to form an opening 15 so that a part of the metal pad 8 was exposed. (3) Electroless solder plating was performed by the steps (18) to (21) of the example. However, the metal pad 8
Peeling was observed between the solder resist 11 and the solder resist 11.

Comparative Example 2 (1) A printed wiring board was formed by the steps (1) to (11) of the example. (2) A commercially available liquid solder resist was applied on a wiring board using a roll coater and dried at 60 ° C. to form a solder resist layer having a thickness of 20 μm. A mask film having a pattern in which a part of the metal pad 8 was hidden was brought into close contact with the wiring board subjected to this treatment and exposed. This was spray-developed with diethylene glycol diethyl ether (DMDG) to form an opening 15 so that a part of the metal pad 8 was exposed. (3) Solder cream was printed on the opening 15 by screen printing and reflow was performed.

As described above, the structure of the metal pad 8 of the present invention is less likely to peel even in an electroless solder plating bath, can withstand a heat cycle, and can also reduce the resistance value of the connection portion. . Furthermore, by adjusting the height of the filling metal film, the solder body can be made to project or, conversely, the metal pad portion can be made to be a dent, and it is possible to design according to the mounted component.

[0087]

As described above, in the printed wiring board according to the present invention, the solder resist does not peel off even during electroless plating, and the amount of sag can be reduced, so that the increase in resistance value due to solder connection can be controlled. Further, since the height of the solder body can be adjusted, it is possible to design according to the application.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a printed wiring board of the present invention.

FIG. 2 is a cross-sectional structure diagram (solder body protrusion) of the printed wiring board of the present invention.

FIG. 3 is a cross-sectional structure diagram of the printed wiring board of the present invention (solder body spherical shape).

FIG. 4 is a cross-sectional structure diagram of a conventional printed wiring board.

[Explanation of symbols]

 1 Glass Epoxy Substrate 2 First Conductor Circuit 3 Adhesive Layer 4 Roughening Surface 5 Plating Resist 6 Via Hole 7 Second Conductor Circuit 8 Metal Pad 9 Cu-Ni-P Eutectic Roughening Surface 10 Sn Layer 11 Solder Resist 12 Filled metal film 13 Solder body 14 Spherical solder body 15 Opening

Claims (8)

[Claims] 1. A metal pad for mounting an electronic circuit is provided on a surface layer of a printed wiring board, and an opening is provided on the metal pad so that the metal pad is partially exposed and a solder resist is formed. In the printed wiring board according to the present invention, the metal pad surface is formed with a roughened surface, an opening on the roughened surface is filled with a metal film, and a solder body is provided on the metal film. Wiring board. 2. The printed wiring board according to claim 1, wherein the roughened surface is composed of needle crystals of a eutectic alloy. 3. The printed wiring board according to claim 1, wherein the roughened surface is a eutectic alloy of Ni—P—Cu. 4. The printed wiring board according to claim 1, wherein the roughened surface has a thickness of 0.5 to 5 μm. 5. The printed wiring board according to claim 1, wherein the roughened surface is composed of needle-like crystals of a eutectic alloy having a Sn layer on the surface thereof. 6. The metal film filling the opening is made of Cu.
The printed wiring board according to claim 1, wherein 7. The printed wiring board according to claim 1, wherein the solder body has a film shape or a spherical shape. 8. The printed wiring board according to claim 1, wherein the solder body is formed by protruding from a surface of a solder resist.