JP3085649B2 - Transfer sheet and method of manufacturing wiring board using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer sheet for forming a conductive circuit such as a wiring board and a package for accommodating a semiconductor element, and a method for manufacturing a wiring board using the same.

[0002]

2. Description of the Related Art Conventionally, a ceramic wiring board has been frequently used as a high-density wiring board, for example, as a high-density multilayer wiring board used for a package containing a semiconductor element.
This ceramic wiring board is composed of an insulating substrate such as alumina and a wiring conductor made of a high melting point metal such as W or Mo formed on the surface thereof, and a concave portion is formed in a part of the insulating substrate. The semiconductor element is accommodated in the recess, and the recess is hermetically sealed by the lid.

However, since the ceramics constituting the insulating substrate of such a ceramic multilayer wiring board has a hard and brittle property, chipping or cracking of the ceramics is liable to occur in a manufacturing process or a transporting process. There are problems such as low yield because hermetic sealing properties may be impaired. In addition, a multilayer ceramic wiring board is manufactured by printing metallized ink on a green sheet before sintering, laminating and sintering the printed sheet, and in the manufacturing process, by firing at a high temperature. Due to the shrinkage of the firing, there is a problem that the resulting substrate is liable to be deformed such as warpage or dimensional variation, etc., and there is a strict demand for ultra-high density circuit boards and flatness of substrates such as flip chips. However, there was a problem that it was not possible to respond sufficiently.

Therefore, recently, in a printed circuit board, after a copper foil is adhered to the surface of an insulating substrate made of an organic resin, a conductor circuit is formed by an etching method and a plating method, and then the substrate is laminated to form a multilayer. It has been proposed to In addition, there is a method of forming a metal foil on a transfer sheet, forming a circuit pattern on the transfer sheet by an etching method or a plating method, and then transferring the circuit pattern to an insulating substrate.

[0005] In the future, the density of wiring substrates used for multilayer substrates and packages for housing semiconductor elements will be further increased, and the wiring width and wiring pitch must be reduced to 100 µm or less.
Further, since the mounting method of the IC chip is also changed from wire bonding to flip chip, it is necessary to reduce the flatness of the substrate itself.

However, a method of forming a conductive circuit by attaching a copper foil on the above-mentioned insulating substrate and then removing unnecessary portions by an etching method or a plating method involves inevitably removing the insulating substrate with a chemical such as an etchant. Because of the contact, the characteristics of the insulating substrate change, or the conductor circuit is merely placed on the surface of the insulating substrate.Therefore, poor adhesion of the conductor circuit to the substrate and voids at the interface between the copper foil and the insulating substrate may occur. Such a problem is liable to occur, and furthermore, there is a problem that the flatness of the insulating substrate is reduced due to the projections due to the conductor circuit even in the case of multilayering.

On the other hand, in the method of transferring a conductor circuit by applying pressure by using the above-described transfer sheet, since the conductor circuit is embedded in the insulating substrate by the pressure, the adhesion of the conductor circuit to the insulating substrate is excellent. This is advantageous.

[0008]

SUMMARY OF THE INVENTION In contrast to the above method,
A method in which a metal foil is adhered to a resin film, a circuit is formed on the resin film by etching or the like, and then this is heated and transferred to an insulating substrate without the insulating substrate coming into contact with various chemicals.
Although it is excellent in that it does not affect the characteristics of the insulating substrate, when transferring fine wiring, a dimensional error occurs between the wirings after the transfer, thereby causing a poor connection with the via hole. And so on. As a result of examining the cause, it was found that the resin film shrinks when a process such as etching is performed or a circuit is transferred by heating.

[0009]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that a metal layer is formed on the surface of a resin film via an adhesive layer, and the metal layer is formed on the surface of the insulating substrate. A transfer sheet for forming a conductor circuit by transfer, and when a predetermined heat treatment is applied to the resin film, the shrinkage of the resin film itself is suppressed, so that a metal layer is formed on the film after the treatment. By
In the transfer step of the wiring layer, it has been found that a wiring layer having excellent dimensional accuracy without dimensional error between wirings can be formed, and the present invention has been achieved.

That is, the transfer sheet of the present invention has a metal layer formed on the surface of a resin film via an adhesive layer, and transfers the metal layer to the surface of an insulating substrate to form a conductive circuit. The thickness of the metal layer is 1 to 100 μm
Wherein the resin film has a thickness of 10 to 500 μm,
Shrinkage after heating at 00 ° C. for 1 hour is 0.05% or less,
And the adhesion of the metal layer to the resin film is 50 to 70.
0 g / 20 mm, and furthermore, the metal layer has a thickness of 1 to 100 μm, and the resin film has a thickness of 20 to 500 μm. It is characterized by being heat-treated at 50 to 170 ° C.

Further, the method for manufacturing a wiring board according to the present invention is characterized in that a resin film having a thickness of 10 to 500 μm is formed at 70 to 170 ° C.
Heat treatment at 100 ° C., shrinkage after heating for 1 hour is 0.05
%, A step of forming a metal layer having an adhesive strength of 50 to 700 g / 20 mm and a thickness of 1 to 100 μm on the surface of the film via an adhesive layer, and forming a circuit pattern from the metal layer. Forming, and after laminating a transfer sheet and an insulating substrate on which a circuit pattern is formed by a metal layer, a step of forming a conductor circuit by peeling a resin film and transferring the metal layer to the insulating substrate, And the insulating substrate contains an organic resin.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The transfer sheet of the present invention has a resin film and a metal layer, and the metal layer is formed on the resin film via an adhesive layer. Known resin films such as polyester, polyethylene terephthalate, polyimide, polyphenylene sulfide, vinyl chloride, and polypropylene can be used. The thickness of the resin film is 10
５００500 μm is suitable, preferably 20-300 μm
m is good. This is because if the thickness of the resin film is smaller than 10 μm, the wiring circuit formed by deformation or bending of the film tends to cause disconnection, and the thickness of the resin film is 500 μm.
If it is larger, the flexibility of the film will be lost, and it will be difficult to peel off the sheet.

As the adhesive layer on the surface of the resin film, known adhesives such as acrylic, rubber, silicon, and epoxy can be used. Although the thickness of the adhesive layer is related to the adhesive strength, it is preferably 1 to 20 μm.

The metal layer is made of a metal suitable for forming a wiring layer as a wiring board.
A metal foil of a low-resistance metal containing at least one of gold, silver, copper, and aluminum is preferably used. The thickness of the metal layer is preferably 1 to 100 μm, and more preferably 5 to 50 μm. If the thickness of the metal layer is smaller than 1 μm, the resistivity of the circuit increases, and if it is larger than 100 μm, the deformation of the insulating substrate during lamination increases, or the amount of the metal layer embedded in the insulating substrate increases, and the insulating substrate increases. There is a problem that the distortion of the substrate becomes large and the substrate is easily deformed after the resin is cured. In addition, there is a problem that a fine circuit with high accuracy cannot be obtained because etching becomes difficult.

According to the present invention, it is important that the resin film used has a small shrinkage.
Shrinkage after heating for 1 hour is 0.05% or less, especially 0.01%
It must be: This shrinkage factor is important for transferring the metal layer as the wiring layer formed on the resin film to the insulating substrate, reducing the variation between the wiring pitches of the fine wiring and enabling the transfer with high dimensional accuracy. This is because if the above shrinkage is larger than 0.05%, the wiring layer cannot be transferred with higher dimensional accuracy.

Such a resin film having a small shrinkage is
It can be manufactured by performing a predetermined heat treatment. Specifically, the temperature of the heat treatment depends on the material of the film, but is preferably in the range of 70 to 170 ° C., preferably 100 ° C.
~ 170 ° C is good. If the processing temperature is lower than 70 ° C., the resin film shrinks greatly during the process, and the variation between wiring pitches tends to increase. On the other hand, if the processing temperature is higher than 170 ° C., deformation of the resin film occurs, and Variation increases.

Next, the resin film and the metal layer are bonded together. At this time, the adhesive strength of the adhesive layer of the resin film is preferably 50 to 700 g / 20 mm, preferably 10 to 700 g / 20 mm.
0 to 500 g / 20 mm is good. The above adhesive strength is 50g
If the thickness is smaller than / 20 mm, the metal layer is peeled off from the resin film during the etching process for forming the circuit, and the circuit is disconnected. On the other hand, if it is larger than 700 g / 20 mm, when transferring to an insulating substrate after circuit formation and peeling the resin film, deformation of the insulating substrate, disconnection of the circuit, and the like are caused.

Next, a method for manufacturing a wiring board according to the present invention will be described with reference to FIG. FIG. 1 is a diagram for explaining steps of a method for manufacturing a multilayer wiring board according to the present invention. First,
In the transfer sheet A, a conductor circuit 3 made of a metal layer is formed on the surface of the resin film 1 with the adhesive layer 2 interposed therebetween.
The metal layer 3 is formed of a metal foil made of at least one or two or more alloys selected from the group consisting of copper, aluminum, gold, and silver. Particularly, copper or an alloy containing copper is most desirable.

It is important that the resin film 1 used at this time has a low shrinkage of 0.05% or less after heating at 100 ° C. for 1 hour. As described above, such a low shrinkage film has a thickness of 70 to 170 mm.
It can be prepared by performing a heat treatment for about 10 minutes to 10 hours at a temperature of 100 ° C., particularly 100 to 170 ° C.

Then, a metal layer 3 made of a metal foil or the like is bonded to the resin film via an adhesive. At this time, the adhesive strength of the metal layer to the resin film is 50 for the above-described reason.
It is desirably about 700 g / 20 mm. In addition, as shown in FIG. 2, the adhesive force is a stress generated when the resin film 9 is peeled from the resin film 9 to which the metal layer 8 is adhered via the adhesive layer 7 in a direction of 180 ° from the metal layer 8. It is a representation.

Next, unnecessary portions of the metal layer 3 made of a metal foil adhered to the resin film 1 are removed by an etching method to form a conductor circuit. For example, in the etching method,
As shown in FIG. 1A, after a metal foil is adhered to the entire surface of the resin film 1 to form a metal layer 3,
As shown in (b), after a resist 4 is formed in a conductive circuit shape on the metal layer 3 by a method such as photoresist or screen printing, an unnecessary portion is removed by etching to obtain a desired conductive circuit 3. At this time, the resist 4 generally requires a process of removing unnecessary portions of the metal layer by etching and then removing the unnecessary portion with a resist removing solution or the like, and washing the resist 4. If it is made of an insulating material containing an organic resin, for example, an insulating material composed of an organic resin and an inorganic filler, there is no need to remove the resist, which is advantageous in that the process can be simplified. Further, the adhesive strength between the conductor circuit and the insulating substrate can be increased.

Next, from the transfer sheet A on which the conductor circuits 3 formed on the surface of the resin film 1 are formed, the conductor circuits 3
Is transferred to the insulating substrate 5. As a method of transferring,
As shown in FIG. 1D, the transfer sheet A and the insulating substrate 5 are laminated and a pressure of about 10 to 500 kg / cm ² is applied. At this time, a semi-cured sheet obtained by forming an insulating slurry containing an organic resin constituting the insulating substrate into a sheet shape by a doctor blade method or the like is used as the insulating substrate 5, so that the resist 4 and the conductor circuit 3 are formed by mechanical pressure. Can be embedded in the insulating substrate 5.

Then, as shown in FIG. 1D, the resin circuit 1 is peeled off together with the adhesive layer 2 and the conductive circuit 3 is transferred to the insulating substrate 5, so that the conductive circuit 3 is simply embedded with the insulating substrate 5 embedded therein. Layered circuit boards can be made. Thereafter, the wiring substrate can be manufactured by heat-treating the insulating substrate 5 to completely cure it.

As another method, as shown in FIG. 1C ', an insulating slurry 6 containing an organic resin is applied to the surface of the resin film 1 on which the conductive circuit 3 is formed, so that the thickness of the conductive slurry 3 is smaller than that of the conductive circuit 3. There is a method of forming the insulating substrate 5 by forming the insulating slurry 6 to be thicker, particularly to a thickness equivalent to one insulating layer, and then hardening or semi-hardening the insulating slurry 6.

Thereafter, as shown in FIG. 1 (d '), the resin film 1 is peeled off together with the adhesive layer 2 and the conductive circuit 3 is transferred, so that the surface of the insulating substrate 5 and the surface of the conductive circuit 3 are coplanar. Thus, a single-layer circuit board can be manufactured. Thereafter, a heat treatment is performed as desired to completely cure the insulating substrate, whereby a wiring substrate can be manufactured.

Since the insulating slurry used in the above method finally forms the insulating substrate of the wiring board, it is desirable that the insulating slurry be made of a material suitable for the insulating layer. According to the present invention, the slurry is made of an insulating material containing at least an organic resin. Examples of the organic resin include PPE (polyphenylene ether), BT resin (bismaleimide triazine), epoxy resin, polyimide resin, and fluororesin. , A phenolic resin, and the like, and particularly, a thermosetting resin that is liquid at room temperature as a raw material.

In the insulating slurry, it is desirable to combine an inorganic filler with an organic resin in order to increase the strength of the insulating layer or the wiring board as a whole.

Examples of the inorganic filler to be combined with the organic resin include SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ,
Known materials such as AlN, SiC, BaTiO ₃ , SrTiO ₃ , zeolite, CaTiO ₃ and aluminum borate can be used. Filler has an average particle size of 20 μm
In addition to the substantially spherical powder of 10 μm or less, optimally 7 μm or less, fibrous or woven fabric having an average aspect ratio of 2 or more, particularly 5 or more, can also be used. In the composite material of the organic resin and the inorganic filler, the volume ratio of the organic resin: the inorganic filler is 15:85 to 5: 5.
It is appropriate that the compounds are combined in a ratio of 0:50.

The insulating slurry is preferably prepared by adding toluene, butyl acetate, methyl ethyl ketone, methanol, methyl cellosolve acetate, isopropyl alcohol to a composite material of the above-mentioned organic resin and inorganic filler constituting the insulating substrate. And a fluid having a predetermined viscosity. From such a viewpoint, the viscosity of the slurry is suitably 100 to 3000 poise, although it depends on the molding method.

As a method for forming the insulating sheet using the slurry, a known method such as a doctor blade method, extrusion molding, injection molding, or the like is used.

In the case of multi-layering, FIG.
In the step (d), via holes are formed in the insulating substrate 5 of FIG. 1C by a punching method or a method using a laser, if desired, and a conductive ink containing a conductive resin or a metal filler is formed. Etc. may be filled in the via holes. Then, a desired number of the obtained circuit boards are stacked at a predetermined position, and the circuit boards are pressurized or heated to be closely adhered and integrated to produce a multilayer wiring board.

As described above, according to the transfer sheet and the method for manufacturing a multilayer wiring board using the transfer sheet of the present invention, the transfer of the conductor circuit formed of the metal layer formed on the transfer sheet to the insulating substrate requires the transfer sheet. Because the contraction is small,
Since the change in the size of the conductor circuit during the process, particularly during transfer, can be reduced, a wiring circuit having excellent dimensional accuracy can be formed. As a result, a wiring circuit can be formed with high accuracy even in a high-density and fine wiring of a conductive circuit without occurrence of a deviation from a through hole or the like formed in an insulating substrate in advance in a multilayer wiring substrate. it can.

[0033]

EXAMPLE A resin film of polyethylene terephthalate (PET) or polyimide resin having a thickness shown in Tables 1 and 2 was subjected to a heat treatment at the temperatures shown in Tables 1 and 2 for 30 minutes. Tables 1 and 2 show the results of measuring the shrinkage of the heat-treated resin film after holding it at 100 ° C. for 1 hour.

Then, an adhesive made of an acrylic resin was applied to the surface of each resin film to give the adhesive strength shown in Tables 1 and 2, and a copper foil having a surface roughness of 0.8 μm and a thickness shown in Tables 1 and 2 was obtained. Adhered to one side.

On the other hand, as an insulating slurry, BT resin as an organic resin and spherical silica as an inorganic filler are mixed at a volume ratio of 30:70, butyl acetate is added to the mixture, and the mixture is sufficiently mixed by a mixer. A slurry having a viscosity of 100 poise was prepared.

After printing the conductive slurry as a resist on the surface of the copper foil in a conductive circuit pattern,
This was immersed in a ferric chloride solution to remove non-pattern portions by etching. In the manufactured circuit, the conductor circuit had a line width of 50 μm, and the distance between wirings (wiring pitch) was 5 μm.
It is a fine pattern of 0 μm or less. Next, about 125 µ
m to form an insulating sheet, and further, a via hole is formed by laser, and Cu-
A copper paste containing Ag alloy powder was filled.

Then, the transfer sheet and the insulating sheet after the above-mentioned etching treatment are aligned, and 3
After applying a pressure of 0 kg / cm ² for 2 minutes, the resin film was peeled off and the conductor circuit was transferred to an insulating sheet. Then, the insulating sheet was completely cured by heating at 200 ° C. for 5 hours to obtain a single-layer wiring board.

With respect to the obtained wiring substrate, the presence or absence of disconnection of the circuit of the conductor circuit was observed with a binocular microscope, and the occurrence rate of disconnection for each of the 20 substrates was determined for each sample. The flatness of the IC chip mounting area was measured by a surface roughness meter. Further, the variation of the wiring pitch in the circuit was measured.
The results are shown in Tables 1 and 2.

[0039]

[Table 1]

[0040]

[Table 2]

As is clear from the results shown in Tables 1 and 2, Sample No. 1 which was not subjected to any heat treatment as a resin film.
8 and 44, the shrinkage ratio of the resin film was as large as 0.2%, and as a result, the variation in the wiring pitch was ± 15 μm,
It was as large as 19 μm.

On the other hand, the shrinkage of the resin film can be reduced by applying a heat treatment, but the heat treatment temperature of the sample No. 19, 45 or 170 ° C.
In Samples Nos. 24 and 48 higher than that, the shrinkage ratio exceeded 0.05%, and as a result, the variation in the wiring pitch was large.

On the other hand, in Samples Nos. 1, 2, and 33 having an adhesive strength of less than 50 g / 20 mm, the circuit was broken at the time of transfer, and Sample Nos. Having an adhesive strength of more than 700 g / 20 mm.
Disconnections also occurred at 8, 9, and 38. Samples Nos. 10, 39, and 500 having a resin film thickness of less than 10 μm
Even in samples Nos. 17 and 43 thicker than μm, many circuit breaks occurred. In samples Nos. 31 and 32 in which the thickness of the metal layer exceeded 100 μm, the flatness was increased.

On the other hand, according to the present invention, the resin film has a shrinkage of 0.05% or less and a thickness of 10 to 500.
In the case of the present invention using a product having an adhesive force of 50 to 700 g / 20 mm, the disconnection rate of the circuit was 2/20.
Hereinafter, the variation in the wiring pitch is ± 7 μm or less, which is practically satisfactory, and particularly, the adhesive strength is 100 to 500 g / 20 mm.
When the thickness is 20 to 300 μm and the shrinkage is 0.01% or less, there is no disconnection and the wiring pitch varies ±
A conductive circuit having an excellent dimensional accuracy of 5 μm was formed.

[0045]

As described in detail above, according to the transfer sheet of the present invention, by reducing the shrinkage of the tree film by a predetermined heat treatment in a series of transfer steps, the conductor of the metal layer formed on the surface of the resin film can be reduced. In transferring the circuit to a predetermined insulating substrate, a conductor circuit with high dimensional accuracy can be formed.

[Brief description of the drawings]

FIG. 1 is a view for explaining steps of a manufacturing method of the present invention.

FIG. 2 is a view for explaining a method for measuring the adhesive strength of a metal layer to a resin film in the present invention.

[Explanation of symbols]

 A transfer sheet 1 resin film 2 adhesive layer 3 metal layer (conductor circuit) 4 resist 5 insulating substrate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-100487 (JP, A) JP-A-61-210691 (JP, A) JP-A-63-73603 (JP, A) JP-A-8-108 70170 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 3/20

Claims (4)

(57) [Claims] 1. A transfer sheet for forming a conductive circuit by forming a metal layer on a surface of a resin film via an adhesive layer and transferring the metal layer to the surface of an insulating substrate, wherein the thickness of the metal layer is Is 1 to 100 μm, and the resin film has a thickness of 1
The shrinkage after heating at 0 to 500 μm and 100 ° C. for 1 hour is 0.
A transfer sheet having an adhesion of not more than 0.05% and the metal layer to the resin film of 50 to 700 g / 20 mm. 2. The transfer sheet according to claim 1, wherein said resin film is heat-treated at 70 to 170 ° C. 3. A step of heat-treating a resin film having a thickness of 10 to 500 μm at 70 to 170 ° C. to produce a film having a shrinkage of 0.05% or less after heating at 100 ° C. for 1 hour. Adhesive strength 50-700g via adhesive layer
/ 20 mm, a step of forming a metal layer having a thickness of 1 to 100 μm, a step of forming a circuit pattern from the metal layer, and a step of laminating a transfer sheet having a circuit pattern formed by the metal layer and an insulating substrate; Removing the resin film and transferring the metal layer to the insulating substrate to form a conductor circuit. 4. The method according to claim 3, wherein the insulating substrate contains an organic resin.