JPH10173316A - Wiring substrate-forming transfer sheet and manufacture of wiring-substrate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer sheet with which a wiring substrate, having superior flatness when a semiconductor circuit pattern is transferred to an insulating substrate, can be manufactured without generation of transfer defects, dimensional errors and the disconnection of circuit, etc. SOLUTION: This transfer sheet is composed of a resin film 1, an adhesive layer 2 provided on the surface of the resin film 1, and a metal layer 3a on a circuit pattern formed on the adhesive layer. In this case, the metal layer 3a is adhered to the adhesive layer with the adhesive force (180 deg. peel strength) of 50g/20mm or higher, and at the same time, the adhesive layer is formed by the adhesive agent which decreases adhesive force by the irradiation of ultraviolet rays or by conducting heat treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer sheet used for manufacturing a wiring board, particularly a wiring board used for a package for accommodating a semiconductor element, and a method for manufacturing a wiring board using the transfer sheet. Things.

[0002]

2. Description of the Related Art Conventionally, ceramic wiring boards have been widely used as high-density wiring boards, for example, high-density multilayer wiring boards used in packages for housing semiconductor elements.
This ceramic wiring board is obtained by forming a wiring conductor made of a high melting point metal such as tungsten or molybdenum on an insulating substrate such as alumina, and a concave portion is formed in a part of the insulating substrate. The semiconductor element is housed in the recess, and the recess is hermetically sealed with an appropriate lid to form a package.

However, in such a ceramic multilayer wiring board, since the ceramics constituting the insulating substrate 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 is a problem that the yield is low because the hermetic sealing property of the resin may be impaired. Further, this multilayer ceramic wiring board is manufactured by printing metallized ink on a green sheet before sintering, sintering after laminating the printed sheet, and in the manufacturing process,
Since shrinkage is caused by baking at a high temperature, there is a problem that deformation such as warpage and dimensional variation are likely to occur in the obtained substrate.

[0004] Further, as the performance of various electronic devices increases, the density of wiring boards used for multilayer wiring boards and packages for accommodating semiconductor elements, etc. will further increase in the future, and wiring widths and wiring pitches will be reduced to 50 μm or less. And the via hole needs to be an interstitial peer hole (IVH), and the mounting method of the IC chip also changes from the wire bonding to the flip chip, so that the flatness of the substrate itself needs to be reduced. I have. Since the above-mentioned ceramic multilayer wiring board lacks dimensional stability, it is in fact impossible to sufficiently cope with such an ultra-high density circuit board or the flatness of the board required for flip chip mounting. is there.

As a wiring board other than the ceramic wiring board, a resin wiring board in which a circuit pattern made of a metal layer such as copper is formed on the surface of an insulating substrate containing an organic resin is known. This resin-made wiring board does not have defects such as chipping and cracking as in the case of a ceramic wiring board, and has the advantage that heat treatment at a high temperature, such as firing, is not required for multilayering.

However, resin wiring boards are generally
Since it is manufactured by pasting a metal foil such as a copper foil on an insulating substrate and then removing unnecessary portions of the metal foil by an etching method or a plating method to form a conductor circuit pattern, There was a problem. For example, the properties of the insulating substrate are changed by a chemical solution such as an etching solution, or the conductor circuit pattern formed by the metal foil is merely placed on the surface of the insulating substrate. Poor adhesion to the conductive substrate, voids and the like are likely to be generated at the interface between them, and in the case of multi-layering, the IVH must be formed by sequential lamination, which makes it impossible to perform batch lamination. is there. Further, since the conductive circuit pattern forms a convex portion on the insulating substrate, the flatness is low, and the flatness required for flip-chip mounting has not been satisfied.

A metal foil for forming a conductor circuit is attached to the surface of the resin film, and unnecessary portions of the metal foil are removed by an etching method or the like to form a conductor circuit pattern. A method has been proposed in which a conductive circuit pattern is transferred to an insulative substrate by pressure-bonding it to an insulative substrate and then peeling off the resin film to manufacture the above-mentioned resin wiring substrate. According to this method, since the insulating substrate does not come into contact with various chemicals, it is possible to prevent the characteristics of the substrate from being deteriorated due to the chemicals. In addition, since the conductive circuit pattern is embedded on the insulating substrate, there is an advantage that the adhesion between the two is good and the flatness is high.

[0008]

However, in the case where a resin wiring board is manufactured by transferring a conductive circuit pattern using the above-described transfer sheet, transfer defects and positional deviations (dimensional errors) of the conductive circuit pattern, There is a problem that disconnection or a decrease in flatness is likely to occur, and the yield is extremely low. In addition, such problems as poor transfer, dimensional errors, and reduced flatness are particularly remarkable when the conductive circuit pattern is a fine pattern of 50 μm or less, which hinders high-density wiring and flip-chip mounting. I have. In order to solve such a problem, it is conceivable to use an insulating substrate that is as flexible as possible. In this case, however, a new substrate such as deformation of the substrate during lamination or the like may be used. Problems occur.

Accordingly, an object of the present invention is to provide a transfer method capable of transferring a conductive circuit pattern to an insulating substrate without causing the above-described problems such as transfer failure, dimensional error, disconnection of a circuit, and deterioration of flatness. An object of the present invention is to provide a sheet and a method for manufacturing a wiring board using the transfer sheet. Another object of the present invention is to provide a method capable of manufacturing a wiring substrate having a fine conductor circuit pattern of 50 μm or less with good yield.

[0010]

According to the present invention, a resin film, an adhesive layer provided on a surface of the resin film,
In a transfer sheet for forming a wiring board, comprising a circuit pattern-shaped metal layer formed on the adhesive layer, the metal layer adheres to the adhesive layer with an adhesive force (180 ° peel strength) of 50 g / 20 mm or more. The transfer sheet is provided, wherein the transfer sheet is held while the pressure-sensitive adhesive layer is formed of a pressure-sensitive adhesive whose adhesive force is reduced by ultraviolet irradiation or heat treatment.

With this transfer sheet, it is possible to prevent a decrease in the adhesion between the conductor circuit pattern and the insulating substrate particularly when the resin film in the transfer sheet is peeled off from the insulating substrate. It is possible to effectively solve problems such as defects and disconnection of a circuit, and to obtain a wiring board having a flatness suitable for flip-chip mounting.

That is, in this transfer sheet, the pressure-sensitive adhesive layer is formed of a pressure-sensitive adhesive whose adhesive force is reduced by ultraviolet irradiation or heat treatment. Therefore, if the transfer of a conductive circuit pattern (metal layer) onto an insulating substrate is performed using this transfer sheet, the adhesive strength of the adhesive layer can be reduced as much as possible by irradiation with ultraviolet light or heat treatment. The peeling force of the resin film hardly acts on the metal layer embedded in the conductive substrate, so that the adhesion between the metal layer and the insulating substrate does not decrease, and the transfer of the metal layer forming the conductive circuit pattern is performed. It is possible to effectively prevent defects, dimensional errors, disconnections, reduction in flatness, and the like.

In such a transfer sheet, the metal layer provided on the resin film of the transfer sheet has a thickness of 50 g / 2.
It is also important that the adhesive layer is adhesively held with an adhesive force of 0 mm or more. That is, by holding the metal layer with such adhesive force, the metal layer is effectively prevented from being detached or displaced during formation of the conductive circuit pattern or during storage or transportation of the transfer sheet. Because

In the production of a wiring board using the above-mentioned transfer sheet, the above-mentioned transfer sheet is used, an insulating sheet is superimposed on the surface of the sheet on the metal layer side, and the transfer sheet and the insulating sheet are pressure-bonded. Embedding the metal layer on the surface of the insulating sheet, reducing the adhesive strength (180 ° peel strength) of the adhesive layer to less than 50 g / 20 mm by ultraviolet irradiation or heat treatment, and peeling off the resin film of the transfer sheet. Thus, the transfer can be performed by transferring the metal layer onto an insulating sheet.

Further, in the present invention, the formation of the insulating sheet in which the metal layer is embedded is performed by coating a curable insulating slurry for forming an insulating substrate on at least the metal layer side of the transfer sheet. It can be performed by applying the above-mentioned thickness and curing the insulating slurry. After forming the insulating sheet in this manner, the adhesive strength of the adhesive layer may be reduced and the resin film may be peeled off in the same manner as described above.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to specific examples shown in the accompanying drawings. FIG. 1 illustrates a process for manufacturing a wiring board using the transfer sheet of the present invention.
Briefly, the process consists of the following steps.

Step (a): First, an adhesive is applied to one surface of the resin film 1 to form an adhesive layer 2, and then a metal or alloy foil layer (hereinafter simply referred to as a metal foil) is formed on the adhesive layer 2. ) 3 is attached.

As the resin film 1, for example, polyester such as polyethylene terephthalate, polyimide, polyphenylene sulfide, polyvinyl chloride, polypropylene and the like are used. As described later, as an adhesive used for forming the adhesive layer 2, When an ultraviolet-curable resin film is used, the resin film 1 is particularly excellent in ultraviolet transmittance. The thickness of the resin film 1 is preferably in the range of 10 to 500 μm, especially 20 to 300 μm. If the film thickness is smaller than this range, the film 1 is likely to be deformed or bent. For example, when a circuit pattern is formed in the following steps,
Alternatively, at the time of transfer or the like, the formed circuit pattern is likely to be broken. If the thickness is larger than the above range, the flexibility of the film 1 is impaired, and it may be difficult to peel off the film 1 in a transfer step described later.

In the present invention, the pressure-sensitive adhesive used for the pressure-sensitive adhesive layer 2 may be a known photo-curing or thermosetting acrylic resin, a silicone resin, an epoxy resin, a styrene-butadiene, an SBS or a SIS. , Isoprene-based, chloroprene-based, acrylic butadiene-based elastomeric polymers, natural rubber, recycled rubber, etc., if necessary, polyterpene resin, gum rosin, rosin ester or rosin derivative, oil-soluble phenol resin, cumarone
Indene resin, those having a composition containing a tackifier such as petroleum hydrocarbon resin is used, these are solvent type,
Any type such as an emulsion type and a solventless type may be used. The thickness of the pressure-sensitive adhesive layer 2 varies depending on the type of the pressure-sensitive adhesive, but is usually preferably in the range of about 1 to 20 μm.

The metal foil 3 is for forming a so-called conductor circuit pattern, and is preferably made of a low-resistance metal such as gold, silver, copper, or aluminum, or an alloy thereof. Particularly preferred is copper or an alloy containing copper. Metal foil 3
Is preferably in the range of 1 to 100 μm, especially 5 to 50 μm. If the thickness is less than 1 μm, the resistivity of the formed conductor circuit becomes high, and
If the thickness is larger than μm, the deformation of the insulating substrate 5 during lamination, which will be described later, increases, or the amount of the metal layer (conductor circuit pattern) 3a embedded in the insulating substrate 5 increases, and the distortion of the insulating substrate 5 increases. This causes the substrate to be easily deformed after the resin is cured. Further, since it becomes difficult to perform the etching process, it tends to be difficult to obtain a fine circuit pattern with high accuracy.

In the present invention, the metal foil 3 is 50 g / 2
It is necessary that the adhesive layer 2 has an adhesive strength of 0 mm or more. That is, if the adhesive strength is lower than the above range, in the following steps, the metal foil 3 or the metal layer 3a in the form of a conductor circuit pattern formed from the metal foil 3 may fall off or be displaced. This is because it is difficult to form a fine circuit pattern.
The adhesive strength can be adjusted by the kind and composition of the above-mentioned adhesive, and for example, by adjusting the amount of the tackifier, the adhesive strength in the above-described range can be imparted. The adhesive strength can be calculated by measuring a 180 ° peel strength (JIS-Z-0237) with the metal foil 3 attached.

Step (b): Next, a metal layer 3a having a predetermined circuit pattern shape is formed from the metal foil 3 by a known resist method or the like to obtain a transfer sheet A of the present invention.
For example, a photoresist 4 is applied to the entire surface of the metal foil 3,
Exposure is performed through a mask having a predetermined pattern, and after development, the metal foil 3 in the non-pattern portion (the portion from which the photoresist has been removed) is removed by plasma etching, chemical etching, or the like. Thereby, a metal layer 3 a having a predetermined circuit pattern is formed from the metal foil 3. Further, the metal layer 3a can be formed by applying a resist 4 in a predetermined circuit pattern shape on the metal foil 3 by screen printing or the like and performing an etching process in the same manner as described above.
As shown in the figure, the resist 4 remains on the metal layer 3a, but adversely affects the characteristics of the insulating substrate described later and the adhesion between the metal layer 3a and the insulating substrate. For example, if a resist having the same composition as the constituent material of the insulating substrate is used, the remaining resist 4
Need not be removed. Therefore, in the example of FIG. 1, the following steps are performed without removing the resist 4. (However, when the resist 4 is removed, the resist 4 may be washed with an appropriate rinsing liquid and dried.) As the photoresist, either a negative type or a positive type can be used.

Step (c) or (c '): The insulating sheet 5 is laminated on the metal layer 3a side of the transfer sheet A formed as described above, and the metal layer 3 is embedded in the insulating sheet 5. Fix it. Step (c) is an example in which a part of the metal layer 3 is buried, and step (c ′) is an example in which the metal layer 3 is completely buried.

The insulating sheet 5 corresponds to an insulating substrate of a wiring board, and is made of a resin and an inorganic filler or a fibrous base material. As the resin, for example, PPE (polyphenylene ether), BT resin (bismaleimide triazine resin), epoxy resin, polyimide resin, fluororesin, phenol resin and the like are suitable. Preferably, the resin is in an uncured state. The inorganic filler and the fibrous base material are used for imparting a certain strength to the insulating substrate and for adjusting the expansion coefficient and the like to an appropriate range. Generally, silica (SiO ₂ ), alumina (Al ₂ O)
₃ ), zirconium oxide (ZrO ₂ ), zeolite, titanium oxide (TiO ₂ ), aluminum nitride (AlN),
Silicon carbide (SiC), barium titanate (BaTiO)
₃ ), strontium titanate (SrTiO ₃ ), calcium titanate (CaTiO ₃ ), aluminum borate, and the like are typical. It should be spherical. Further, fibrous particles having an average aspect ratio of 2 or more, particularly 5 or more can also be used. Examples of the fibrous base material include synthetic fibers such as paper, glass woven fabric, glass nonwoven fabric, and Teflon. The above resin and the inorganic filler are in a volume ratio of 60:40.
The resin and the fibrous substrate are preferably used in a volume ratio of 60:40 to 40: 6.
It is better to use at a rate of 0.

The embedding of the metal layer 3a into the insulating sheet 5 is performed, for example, by transferring the transfer sheet A and the insulating sheet 5 in a semi-cured state.
Can be performed by overlapping and press-bonding such that the metal layer 3a is interposed therebetween, and then, if necessary, by curing the insulating sheet 5.

In this case, as the semi-cured insulating sheet, a glass woven fabric, a non-woven fabric or a brigreg obtained by impregnating and drying a varnish-like curable resin on a base material such as paper or Teflon can be used. Of course, the composition of the prepreg corresponds to the composition of the insulating sheet 5 (insulating substrate) described above. Also, an insulating sheet can be formed by using an insulating slurry containing the thermosetting resin by a doctor blade method, extrusion molding, injection molding, or the like.

The mechanical pressure for crimping is generally 10
Or is a 500 kg / cm ² or so, if the pressure is small, (see step (c)) part of the metal layer 3a is embedded in the insulating sheet 5 together with the resist 4 remaining, if a high pressure, The entire metal layer 3a can be embedded in the insulating sheet 5 (see step (c ')).

Further, on the metal layer 3a side of the transfer sheet A, an insulating slurry containing the same thermosetting resin as described above is applied to a thickness larger than the thickness of the metal layer 3a by a doctor blade method, extrusion molding, injection molding or the like. And by applying to the thickness corresponding to the insulating substrate, by curing the insulating slurry,
The embedding described above can be performed. In this case,
As shown in step (c ′), the entire metal layer 3 a is embedded in the insulating sheet 5. The above-mentioned slurry is prepared by adding a solvent such as toluene, butyl acetate, methyl ethyl ketone, methanol, methyl cellosolve acetate, or isopropyl alcohol to a composite material of the above-mentioned thermosetting organic resin and inorganic filler constituting the insulating substrate. It is prepared by adjusting the viscosity by adding. Although the slurry viscosity depends on the molding method, it is generally 100 to 300.
0 poise (25 ° C.) is appropriate.

In the present invention, after the embedding and fixing of the metal layer 3a described above, ultraviolet irradiation or heat treatment is performed to cure the adhesive of the adhesive layer 2. Due to this curing, the adhesive force for adhering the metal layer 3a and the adhesive layer 2 is reduced, and when the film 1 is peeled in the following steps, the disconnection and transfer failure of the metal layer 3a (circuit pattern) are effectively prevented. Can be.

In the present invention, the reduced adhesion due to the above-mentioned curing is generally less than 50 g / 20 mm, preferably less than 30 g / 20 mm, and most preferably substantially zero. The degree of decrease in adhesive strength due to curing can be adjusted by the composition of the adhesive, etc. In general, the greater the amount of curing agent added and the greater the degree of cure shrinkage, the greater the adhesive strength. The drop is large. In addition, this adhesive force is measured as a 180 degree peel strength when the resin film 1 is peeled off as described above.

In the case where the adhesive is cured by irradiation with ultraviolet rays, an ultraviolet ray permeable resin is used as the resin film 1, and ultraviolet rays are irradiated from the back of the resin film 1. The condition of the ultraviolet irradiation varies depending on the kind of the adhesive, but it is generally preferable to set the intensity at 300 mJ / cm ² or more for about 1 to 10 minutes. In the case of curing by heating, it is desirable to perform heating at a temperature of at least the melting point or softening point of the resin film 1, for example, at a temperature of 70 to 130 ° C. for about 1 to 10 minutes.

Step (d) or (d '): According to the present invention, the metal film 3a having a circuit pattern is then separated from the insulating sheet 5 by peeling the resin film 1 together with the adhesive layer 2 from the insulating sheet 5. The desired single-layer wiring board is obtained by completely curing the insulating sheet 5 if necessary. At the time of peeling, since the adhesive strength of the adhesive layer 2 to the metal layer 3a is reduced, the adhesion between the metal layer 3a and the insulating sheet 5 is not reduced, and poor transfer or disconnection may occur. Absent.
In this case, as shown in step (d ′), the metal layer 3
a is completely embedded in the insulating sheet 5
Since no protrusion is formed by the metal layer 3a forming the circuit pattern, the obtained substrate has extremely excellent flatness, and is particularly suitable for manufacturing a multilayer wiring board by batch lamination and flip chip mounting.

The single-layer wiring board obtained above is further subjected to a heat treatment if necessary to completely cure the insulating sheet 5, and if necessary, a via hole is formed by a punching method or a method using a laser. The via holes are filled with a conductive substance such as a conductive resin, a conductive ink containing a metal filler, and a metal paste, and the via holes are laminated with a predetermined number of separately formed circuit boards, and then pressurized or heated. Then, the multi-layer wiring board can be formed by tightly contacting and integrating. The formation of the via hole and the filling of the conductive material are as follows.
It can be performed prior to the pressure bonding of the insulating sheet 5 and the transfer sheet A or at the stage of pressure bonding.

[0034]

【Example】

(Experimental Examples 1 to 15) An adhesive made of an ultraviolet curable acrylic resin was applied to the surface of a resin film made of polyethylene terephthalate (PET) having various thicknesses, and a copper foil having a thickness of 18 μm (average surface roughness) was applied. 0.8μm)
Was bonded to one side to prepare a transfer sheet. The 180 ° peel strength of the copper foil at this time was measured as the initial adhesive strength. Table 1 shows the thickness of the PET film and the initial adhesive strength. The transfer sheet was irradiated with ultraviolet light having an intensity of 500 mJ / cm ² for 1 minute from the PET film side to cure the pressure-sensitive adhesive.
The peel strength was measured, and the results are shown in Table 1 as the adhesive strength after curing. The adjustment of the initial adhesive strength was performed by adjusting the amount and thickness of the tackifier to be mixed with the adhesive. Then, the same insulating slurry as that used for forming the insulating substrate described later is printed as a resist on the surface of the copper foil in a conductive circuit pattern form, and immersed in a ferric chloride solution to form a non-patterned pattern. The portion was removed by etching, and a conductor circuit having a fine pattern with a line width of 30 μm and a space between wirings (wiring pitch) of 30 μm or less was formed from a copper foil, and a transfer sheet was obtained.

BT resin as an organic resin and spherical silica as an inorganic filler were mixed at a volume ratio of 30:70, butyl acetate was added to the mixture, and the mixture was sufficiently mixed by a mixer to have a viscosity (25 ° C.) of 100. A poise insulating slurry was prepared. Using this insulating slurry,
An insulating sheet having a thickness of about 125 μm was formed by the doctor blade method.

Next, the above-described insulating sheet is superimposed on the conductive circuit side of the transfer sheet prepared above, and is pressed by a vacuum laminator at a pressure of 30 kg / cm ² for 2 minutes to convert the conductive circuit into an insulating sheet. Completely embedded (Fig. 1
(C ')). After this, 500mJ from the PET film side
/ Cm ² for 1 minute to cure the adhesive, then peel off the PET film to transfer the conductor circuit to the insulating sheet.

After peeling off the PET film, the insulating sheet was heated at 200 ° C. for 5 hours to be completely cured,
Via holes were formed by laser, and the holes were filled with a copper paste containing Cu-Ag alloy powder to obtain a single-layer wiring board. For each of the 20 wiring boards, the occurrence rates of disconnection and transfer failure of the conductor circuit were determined with a binocular microscope. The flatness of the IC chip mounting area was measured by a surface roughness meter. The results are shown in Table 1.
The flatness indicates the difference (μm) between the height of the lowest part and the height of the highest part. The smaller the value, the higher the flatness.

[0038]

[Table 1]

From the above results, the initial adhesive strength was 50 g / 2.
In a sample lower than 0 mm, the copper foil was peeled off from the resin film at the time of etching, resulting in disconnection. The transfer sheet PE
If the thickness of the T film is unnecessarily small or unnecessarily large, disconnection or improper transfer is liable to occur, and it is found that the thickness is suitably in the range of 10 to 500 μm.

(Experimental Examples 16 to 23) PE having a thickness of 75 μm
A wiring board was prepared in the same manner as in the experimental example described above, except that a T film was used and the thickness of the copper foil (metal layer) used was variously changed. Table 2 shows the results.

[0041]

[Table 2]

From the above results, it can be seen that when the thickness of the metal layer (copper foil) forming the circuit pattern exceeds 100 μm, the flatness decreases. Further, when the thickness of the metal layer was smaller than 1 μm, the resistance as a circuit increased.

(Experimental Examples 24-28) PE having a thickness of 75 μm
The experiment described above was conducted using a T film and a copper foil (metal layer) having a thickness of 18 μm, replacing the pressure-sensitive adhesive with a thermosetting acrylic pressure-sensitive adhesive and changing various heat treatment conditions for curing the pressure-sensitive adhesive. A single-layer wiring board was prepared in the same manner as in the example.
Table 3 shows the results.

[0044]

[Table 3]

(Experimental Examples 29 to 34) A single-layer wiring board was prepared in exactly the same manner as in Experimental Example 11 except that the conditions for irradiation with ultraviolet light were changed. Table 4 shows the results. Experimental Example 34
Is an example in which no ultraviolet irradiation was performed.

[0046]

[Table 4]

(Experimental Examples 35 to 40) A varnish-like BT resin was impregnated and dried in a glass cloth so as to have a volume ratio of 50:50 to prepare a prepreg. This prepreg was used as an insulating sheet, and a single-layer wiring board was prepared in exactly the same manner as in Experimental Example 11 except that the ultraviolet irradiation conditions were changed. Table 5 shows the results.

[0048]

[Table 5]

(Experimental Examples 41 to 46) Except that the prepregs prepared in Experimental Examples 35 to 40 were used as insulating sheets, the heat treatment conditions were variously changed in the same manner as in Experimental Examples 24 to 28, and a single-layer wiring board was used. It was created. Table 6 shows the results.
In Experimental Example 46, no heat treatment was performed.

[0050]

[Table 6]

As is clear from the results of Tables 3 to 6, the adhesive strength of the adhesive layer was 50 g before peeling of the PET film.
/ 20 mm or more, circuit breakage occurred at the time of transfer. However, in the case of the present invention, which was less than 50 g / 20 mm by ultraviolet light or heat treatment, the circuit breakage occurrence rate and transfer failure occurrence rate were 2/20. The following are practically satisfactory. Particularly, the initial adhesive strength is 100 g / 20 mm or more, the adhesive strength after ultraviolet irradiation or heat treatment is 50 g / 20 mm or less, and the thickness is 10 to 30 mm.
By setting the thickness to 0 μm, the occurrence of disconnection of the circuit pattern and the occurrence of transfer failure can be reduced to zero, and a high-density multilayer wiring board capable of flatness flip-chip mounting can be obtained stably with a high yield by the batch lamination method.

[0052]

According to the present invention, when a wiring substrate is manufactured by the transfer method, the occurrence of disconnection of the circuit pattern and the occurrence of transfer failure can be reduced to zero.
H, a high-density multilayer wiring substrate having a fine wiring pitch of 50 μm or less, a small flatness and a flip-chip mountability can be stably obtained with good yield by a batch lamination method.

[Brief description of the drawings]

FIG. 1 is a view for explaining steps of an example of a production method of the present invention.

[Description of sign]

 A: Transfer sheet 1: Resin film 2: Adhesive layer 3: Metal foil 3a: Metal layer (conductor circuit) 4: Resist 5: Insulating sheet

Claims (5)

[Claims] 1. A transfer sheet for forming a wiring board, comprising a resin film, an adhesive layer provided on a surface of the resin film, and a circuit-patterned metal layer formed on the adhesive layer, wherein the metal layer Has an adhesive strength of at least 50 g / 20 mm (180 °
Transfer sheet, wherein the adhesive layer is adhesively held at a peel strength, and the adhesive layer is formed of an adhesive whose adhesive strength is reduced by ultraviolet irradiation or heat treatment. 2. The transfer sheet according to claim 1, wherein said metal layer has a thickness of 1 to 100 μm, and said resin film has a thickness of 10 to 500 μm. 3. A step of using the transfer sheet according to claim 1, and superposing an insulating sheet on a surface of the sheet on the metal layer side, wherein the transfer sheet and the insulating sheet are pressed to insulate the metal layer. The adhesive strength of the adhesive layer (180 ° peel strength) by embedding on the surface of the flexible sheet and irradiating with ultraviolet light or heat treatment
And a step of transferring the metal layer onto an insulating sheet by peeling off the resin film of the transfer sheet. 4. The transfer sheet according to claim 1, wherein a curable insulating slurry for forming an insulating substrate is applied to a surface of the transfer sheet on a metal layer side at a thickness of at least the thickness of the metal layer. Curing the insulating slurry to form an insulating sheet in a form in which the metal layer is embedded.
(Peel strength) to less than 50 g / 20 mm, and a step of transferring the metal layer onto an insulating sheet by peeling off the resin film of the transfer sheet. Manufacturing method. 5. The method according to claim 3, wherein the reduction in the adhesive strength of the adhesive layer is performed by irradiating the transfer sheet with ultraviolet light.