JPS62291989A - Circuit transcription foil for injection molding and method of forming circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a circuit transfer foil for injection molding and a circuit transfer method.
More specifically, by using a circuit transfer foil in which a metal plating layer, which is the main conductive part, is provided on a circuit pattern printed by a printing method such as screen printing on a support film, a circuit can be formed at the same time as the object to be transferred, and The present invention relates to a circuit transfer foil and a circuit forming method that can manufacture a circuit that can be connected by soldering when connecting the electric circuit to another electric circuit.

[Technical background of the invention]

Conventionally, as a method for transferring electrical circuits such as wiring boards, a conductive thin film is formed over the entire surface of a support film, laminated onto the object to be transferred, and heat is applied to heat and press only the circuit portion (transfer portion). A method of forming a circuit by transferring only the circuit portion onto an object using a board (Japanese Unexamined Patent Application Publication No. 1983-1999)
No. 141789) is known.

According to such a circuit transfer method, (1) a heating plate that can heat and press only a predetermined portion is required, and the person performing the circuit transfer must purchase said heating plate; (2) the conductive thin film other than the transferred portion is Since the material will be discarded, the material will be wasted and the cost will be high. ■Because the circuit pattern is transferred by heating and pressurizing only the predetermined area using the heating plate, the conductive thin film has a good cut. There were disadvantages such as the need to be present.

In order to eliminate such drawbacks, the present inventor applied conductive paint onto a support film by screen printing, gravure printing,
We have developed a circuit transfer foil and a circuit transfer method that can transfer a circuit with good conductivity by printing a circuit pattern in advance using offset printing or pad printing and transferring this circuit pattern to a transfer target, and have filed a patent application. (Japanese Patent Application No. 7264, etc.).

According to this method, it is possible to easily transfer a circuit that has better conductivity compared to an electric circuit that uses a conventional conductive coating film as a conductive part without requiring special equipment. There is an advantage to having one. However, since the conductive part is a conductive resin layer, even if we pursue good conductivity, it will naturally be limited, and compared to metal electric circuits, the disadvantage is that the conductivity is inferior. It was extremely difficult.

Furthermore, electrical circuits are generally often connected to other electrical circuits, electrical components, electrical equipment, etc. by soldering, but electrical circuits that are transferred and formed using conductive resin as described above are The drawback was that it was impossible to connect circuits, electrical components, electrical equipment, etc. with solder. In other words, conductive layers such as conductive paints, conductive '7N, and films that serve as conduction paths in electric circuits as described above are generally made by adding an appropriate amount of conductive particles to the resin to impart conductivity to the resin. This is what I did. In a conductive coating film to which such conductive particles are added, when the amount of the conductive particles added is small, the conductivity tends to improve as the amount of the conductive particles added increases. It is known that when the amount of conductive particles added increases, the conductivity tends to decrease due to an increase in the contact resistance between the particles. Even in conductive coatings, if a large amount of conductive metal particles is added, soldering becomes possible, but as mentioned above, if the amount of metal particles added is such that soldering is possible, the electrical circuit There are disadvantages in that conductivity is not sufficient and the amount of metal particles added increases, resulting in increased costs.

Furthermore, if the amount of metal particles added to the conductive resin is increased, the adhesive strength will be significantly reduced, resulting in the disadvantage that it cannot be put to practical use.

Another disadvantage is that in order to transfer the circuit to an already molded object, two steps are required: a step of molding the object and a step of transferring the circuit.

[Summary of the invention]

The present invention has been made in view of the above-mentioned points, and it is possible to form a circuit well without requiring special equipment or expensive equipment, and without increasing costs due to waste of materials. It is an object of the present invention to provide a circuit transfer foil and a circuit forming method that can form a circuit having good conductivity similar to that of the present invention at the same time as molding a transfer target, and can also be soldered.

Therefore, the circuit transfer foil for injection molding according to the present invention is basically formed by adding 500 to 2,000 parts by weight of metal particles to 100 parts by weight of the resin on a predetermined portion of the support film. A contact portion is provided, and a conductive paint is basically made by adding 300 to 1000 parts by weight of conductive particles to 100 parts by weight of resin so as to contact the contact portion at least partially, and the supporting film is coated with a conductive paint. It is characterized in that a circuit pattern exhibiting easy peelability is printed immediately after heating and pressurizing, a metal plating layer is then provided on the circuit pattern, and an adhesive layer is laminated at least on the top surface of the metal plating layer.

Further, according to the circuit forming method of the present invention, contacts are formed with a conductive paint that is basically made by adding 500 to 2,000 parts by weight of metal particles to 100 parts by weight of the resin at a predetermined portion on the support film. A conductive paint, which is basically made by adding 300 to 1,000 parts by weight of conductive particles to 100 parts by weight of resin, is applied to the support film and heated so as to contact the contact part at least partially. Immediately after applying pressure, a circuit pattern that is easily peelable is printed, and then a metal plated eyebrow is provided on the circuit pattern, and a circuit transfer foil having an adhesive layer laminated on at least the top surface of the metal plated layer is injected onto the transfer target. Several supporting films are placed in contact with the inner wall of a mold for molding, a molten resin is press-fitted into the mold to form a transferred object, and then the supporting film is peeled off to form a transferred object. The feature is that the circuit is transferred at the same time as the molding.

The circuit transfer foil according to the present invention has the advantage that it has conductivity equivalent to that of metal, and that an electric circuit that can be soldered can be formed simultaneously with the molding of the transfer target. Also,
According to the circuit forming method of the present invention, a contact portion rich in metal particles is formed, and a circuit pattern is printed with a conductive paint using a printing method such as screen printing, gravure printing, or pad printing. By forming a metal plating layer on the circuit pattern as a conductive part and forming an adhesive layer on this metal plating layer, it is now possible to transfer and form the circuit at the same time as molding the object in injection molding. Compared to circuits using this type of transfer means, this method has the advantage that it is possible to form a circuit with better conductivity, and that connections with other electrical components can be made by soldering.

[Detailed description of the invention]

The circuit transfer foil used in the injection molding method according to the present invention includes the first
As shown in the figure, a contact portion 2 containing a large amount of metal particles is formed on a predetermined portion of a support film 1 by a printing technique such as screen printing, gravure printing, or pad printing.
A circuit pattern 3 in the form of an electric circuit is similarly printed using conductive paint by screen printing, gravure printing, pad printing, or the like. The contact portion 2 is formed as a lower layer of the circuit pattern 3 (see FIG. 2Cb)), but this is because when the circuit pattern 3 is transferred to the transfer object at the same time as molding, the contact portion 2 is formed as a lower layer of the transfer object. This is to expose it to the body surface.

A metal plating layer 4 is provided on such a circuit pattern 3, and an adhesive layer 5 is further laminated on the metal plating layer 4. In this embodiment, the adhesive layer 5 is formed only on the plating layer 4 formed on the circuit pattern 3, but the adhesive layer 5 may be formed to cover the entire surface of the support film 1. good.

In the case of the embodiment shown in FIG. 1, the adhesive N5 is provided only on the metal plating layer 4 by printing technology, similar to the circuit pattern 3 made of conductive paint.

Figure 2 (al is the A-A sectional view in Figure 1, Figure 2 (
bJ is a cross-sectional view taken along line 13-B, and as is clear from both figures, the contact portions 2 are formed only in predetermined portions so as to at least contact the circuit pattern 3.

The support film 1 on which the contact portions 2 and the circuit pattern 3 are formed by conductive paint is not fundamentally limited in the present invention, and has good adhesion to the contact portions 2 and the circuit pattern 3 at room temperature. With,
A synthetic resin film is used that easily separates from the contact portion 2 and the circuit pattern 3 immediately after heating and pressurizing, has heat resistance and flatness properties, and is not corroded by the solvent contained in the conductive paint. It can be used effectively. Specific examples of the support film 1 include plastic films such as polyester films, polyimide films, and polypropylene films, and aluminum foil.

The contact portion 2 has a higher content of metal particles than the circuit pattern 3 portion.

Since this contact part 2 is a part to be soldered, conductivity is not a big problem, and it must be possible to perform good soldering (solderability), have good adhesive strength with the circuit pattern 3, and It is required that the transfer body be easily peeled off from the support film 1 immediately after being formed.

As the base material of the conductive paint for solder that satisfies such conditions, it is preferable to use a resin that is the same as or similar to the resin used for the circuit pattern 2 described above. For example, one or more of acrylic, polyamide, epoxy, polyether, polyester resins, cyclized rubber, chlorinated rubber, rosin, etc., for example, MEK,
Ketone solvents such as MIBK and cyclohexanone, aromatic hydrocarbon solvents such as toluene and xylene, IPA
, alcohol solvents such as butanol, ether solvents, ester solvents, and others such as DMF, N-
It can be a resin solution dissolved in one or more solvents such as methylpyrrolidone.

Furthermore, it is clear that metal particles with good solderability are preferable as the metal particles added to this resin solution.

Such metal particles are generally metal particles that have a smaller ionization tendency than hydrogen. Examples of such metal particles include gold, silver, platinum, copper, nickel, tin,
It can be one or more of metal particles such as, or composites and alloy powders whose surfaces are coated with the metals described above.

Furthermore, the amount of metal particles added to the contact portion 3 is 10% of the resin.
The amount is 500 to 2000 parts by weight relative to 0 parts by weight.

If it is less than 500 parts by weight, the content of metal particles is too small and soldering becomes difficult, while if it exceeds 2000 parts by weight, the adhesion strength with the circuit pattern 3 or the support film 1 will be poor, It becomes brittle and cannot be put to practical use. Furthermore, there is also the drawback that the cost is high.

Further, the particle size of the metal particles varies depending on the method of forming the contact portion, but for example, in the case of a printing method (the particle size also differs depending on the printing method), it is usually preferably 10μ.
It is preferable that it is less than m. If it exceeds 10 μm, for example, coating streaks will occur in gravure printing, and clogging will occur in screen printing, making it difficult to form fine contact points.

The thickness of this contact portion 3 basically needs to be sufficient for soldering, but on the other hand, it must not be so thick as to significantly impair injection moldability or conductivity of the circuit. Therefore, the thickness of this contact portion 3 is preferably 1 to 15 μm.
It is better to be m.

Furthermore, this conductive paint for solder tends to have a high viscosity because it contains a large amount of metal particles. For this reason, it may be difficult to form by the above-mentioned printing means. In such a case, the contact portion 3 can be formed by a method other than printing.

In the case of forming by printing, the conductive paint preferably has a viscosity of 10 to 1000 voids. This is because if the number of voids is less than 10, printing tends to sag, and if it exceeds 1,000 voids, printing becomes difficult.

The viscosity of such a conductive paint can be adjusted by the amount of solvent, the type of resin used as the base material, the amount of metal particles added, or the addition of various reagents to the conductive paint.

After forming the contact portions 2 in this manner, a circuit pattern 3 is further printed on the support film 1 using a conductive paint for circuit pattern formation. The printing method for printing this circuit pattern 3 is not limited in the present invention. For example, it can be effectively printed using known printing methods such as screen printing and gravure printing.

The conductive paint used to print the desired circuit pattern 3 on the support film 1 described above coats the circuit pattern 3 with a metal plating layer 4.
It is necessary to contain an appropriate amount of metal powder to enable selective lamination.

That is, for example, in an electroless plating tank, when the support film 1 on which the circuit pattern 3 is printed is immersed, the conductivity and surface are such that metal ions are selectively and favorably deposited and adhered to the circuit pattern 3. Preferably, it has a state. Furthermore, it is possible to print a good and fine circuit pattern on the support film 1, and the adhesiveness with the contact portion 2 is good;
It is necessary that the transfer foil satisfies various conditions such as basic performance as a transfer foil, such as good peeling from the support film 1 immediately after heating and pressing.

In order to satisfy these conditions, the support film, the resin liquid (solvent and solute) that is the base material of the conductive paint,
Furthermore, it is important to select the type of conductive particles to be added to this resin liquid, and it is also necessary to consider the amount and particle size of the conductive particles. The resin serving as the base material for such a conductive paint is a resin component (solute) that has adhesive properties with the support film 1 at room temperature and can form an easily peelable circuit pattern immediately after heating and pressing, such as an acrylic resin. , polyamide-based, epoxy-based, polyether-based, polyester-based resin, etc., or one or more of cyclized rubber, chlorinated rubber, rosin, etc., for example, MEK, MTBK,
One or more of the following: ketone solvents such as cyclohexanone, aromatic hydrocarbon solvents such as toluene and xylene, alcohol solvents such as IPA and butanol, ether solvents, ester solvents, and other solvents such as DMF and N-methylpyrrolidone. It can be a resin solution dissolved in.

The conductive particles added to the resin solution described above are basically in accordance with the present invention, as long as they can be uniformly dispersed in the resin solution, can impart good conductivity, and can form the metal plating layer 4 well. It is not limited to. For example, it can be one or more of metal particles such as gold, silver, platinum, copper, nickel, aluminum, tin, and zinc, or composites and alloy powders whose surfaces are coated with the above metals.

Such conductive particles are used in an amount of 300 parts by weight per 100 parts by weight of resin.
Add ~1000 parts by weight. If the amount is less than 300 M parts, the metal density of the circuit pattern 2 may be too low and metal ions may not be deposited selectively on the circuit pattern 3. On the other hand, if it exceeds 1000 parts by weight, the metal ions may not be deposited uniformly on the circuit pattern 3. Although it becomes easier to deposit, there is a possibility that the coating film becomes too brittle.

The particle size of the conductive particles is preferably 10 μM or less.

This is because if the thickness exceeds 10 μm, problems tend to occur during screen printing.

Other additives such as antioxidants, dispersants, etc. can be optionally added to the conductive paint.

Although the circuit pattern 3 is printed on the support film 1 using such a conductive paint, this printing method is not limited in the present invention. For example, it can be effectively printed using known printing methods such as screen printing and gravure printing.

This conductive paint is preferably applied to the support film 1 by:
It is preferable to print to a thickness of 15 to 40 μm.

If the thickness of the conductive paint is thinner than 15 μm, good conductivity cannot be obtained, while if it exceeds 40 μm, a layer is formed that makes it difficult to print a circuit pattern by screen printing or the like.

Naturally, it is preferable that the line width or the distance between lines of the circuit pattern 2 be small. In the circuit transfer foil used in the present invention, in order to make it possible to form a circuit with the above-mentioned line width or line distance of 1 mm or less, the viscosity of the conductive paint to be printed is set to 10 to 1000 voids, most preferably 10 to 40 voids.
It is preferable to adjust to 0 poise. If the viscosity of the conductive paint is less than 10 poise, there is a risk that the wire will lose its shape and the circuit will be short-circuited, whereas if it exceeds 1000 poise, it will be difficult to print the circuit pattern on the support film 1. .

In the circuit transfer foil used in the present invention, as described above, a metal plating layer 4 is further provided on the circuit pattern 3 made of the conductive paint. This metal plating layer 4 constitutes the main body of the conductive part and also reinforces the circuit pattern 3. Therefore, it is made of metal that has good conductivity and good adhesion to the circuit pattern 3 of the conductive paint. It is desirable that there be. The plating performance of a given metal usually depends on the resin that is the base material of the conductive paint, the type and amount of conductive particles added to the conductive paint, the surface condition of the support film and the circuit pattern 3, etc. It is thought that it will be decided. Examples of the metal layer 4 that satisfies these various conditions include Cu, N+SSn, 8g, Au, etc.
, PL, and Nato.

This metal plating is not limited to one layer, but multiple layers can be deposited and adhered to each other.

The thickness of this metal plating layer 4 is preferably 3 to 20 μm.
It is good to be. If it is less than 3 μm, the environmental stability of the mesh will be poor and it will easily deteriorate, and furthermore, the reinforcing effect of plating the circuit pattern 3 during circuit formation cannot be expected to be very effective. Furthermore, it is not economically advisable to form a plating layer with a thickness exceeding 20 μm.

Such a circuit transfer foil can be laminated on the metal plating layer 4 described above or as a support film 1 containing the metal plating layer 4.
An adhesive layer 5 is provided all over.

For the adhesive layer 5, an adhesive is used that adheres to the object to be transferred at the molding temperature of the object and does not corrode the circuit pattern 3 of the conductive paint and the metal plating film 4. An effective example of such an adhesive 5 is, for example, a true-melt adhesive mainly made of thermoplastic resin that melts at around the injection molding temperature and made into a semi-cured state by adding a modifier such as a thermosetting resin. It can be used for. Specific examples of such true-melt adhesives include olefin-based, polyester-based, acrylic-based, urethane-based, and rubber-based adhesives, as well as EMA, saponified EVA,
One or more types of vinyl chloride-vinyl acetate copolymers can be mentioned.

The modifiers added to the above-mentioned true-melt adhesives are mainly added to improve the adhesive strength and heat resistance after bonding, and such modifiers include, for example, styrene resin. , coumaron indene resin, phenol resin, diarytupthalate, epoxy, etc. can be used.

Further, the thickness of this adhesive layer 5 is preferably 1 to 10 μm.
A rope is better. If it is less than 1μ, there is a risk that it will not adhere to the transfer target with good adhesive strength, while on the other hand, 101! It is unnecessary for the thickness to exceed m, and if it becomes extremely thick, there is a risk that the transferability will be impaired.

According to the circuit forming method of the present invention, the circuit transfer foil 6 described above is placed in one of the molds 7a of the injection mold 7 for producing the transferred object.
Then, the supporting film is laid so as to be in contact with the inner wall of the mold 7a, the mold 7a is covered with the mold 7b, and the molten resin 9 is injected from the resin injection port 8 to produce the transferred object. At the same time, the circuit is transferred. and,
By peeling off the support film 1 of the circuit transfer foil 6, the object to be transferred is formed, and at the same time, the adhesive layer 5,
A circuit in which the circuit pattern 3, the metal plating layer 4, and the contact portion 2 are buried in the object can be formed on the object.

In the method of forming a circuit simultaneously with injection molding as described above, the pressure and temperature within the injection mold 7 are particularly important. That is, if the pressure inside the mold is small, the circuit of the circuit transfer foil 6 may not be transferred well, and a portion of the circuit may remain on the support film 1 when the support film 1 is peeled off. When the pressure inside the mold is large, regardless of whether the circuit pattern 3 is protected by metal plating 4,
The drawn circuit does not collapse and forms a skin.

Furthermore, if the temperature of the injected resin is too high, there is a risk of damaging the conductive paint portion or the support film portion.

Among the above-mentioned injection conditions, the pressure within the mold is particularly important.

It has been found that a good pressure in the mold as described above is preferably 200-1000 Kg/cI1), taking into account the above. The pressure inside the mold is as follows: mold 7
It can be controlled by the viscosity of the molten resin injected into the molten resin and the injection pressure.

If the viscosity of the molten resin is too high, uneven pressure will be applied to the circuit transfer foil 6, causing a risk that parts with a small pressure load will remain on the support film 1, and the injection pressure will also increase.
There is also a risk of damaging the circuit. If the viscosity is too low, the applied pressure will be relatively small, making it difficult to transfer the circuit on the circuit transfer foil 6. Taking this into consideration, the viscosity of the resin for producing the transfer object when injected into the injection mold 6 is preferably 103 to 105 voids. If the above-mentioned viscosity is less than 103 poise, the pressure load on the circuit transfer foil 6 will be small and there is a risk that good transfer will not be performed.On the other hand, if it exceeds 105 poise, the pressure load will become uneven and the transfer There is a possibility that there will be good parts and bad parts.

The viscosity of the resin as described above changes depending on the temperature of the molten resin, but this temperature must not be such as to damage the conductive paint portion or the support film portion as described above. Therefore, it is desirable that the temperature at the time of injection of the resin having the above viscosity range is 400°C or less.

In addition, the injection pressure of the above molten resin is 400 to 2300 kg.
/cal is better. If the injection pressure of the resin in the above viscosity range exceeds 2300 Kg/cII+, the pressure inside the mold will become too large and may damage the circuit, while if it is lower than 400 Kg/-, the circuit transfer will be poor. This is because there is a possibility that it will not be carried out.

For example, AB is a resin that satisfies these conditions.
S, polyacecool, polysulfan, PP01 modified PPO, polycarbonate, polycarbonate, HIS
It can be P, PP, PMM8, etc.

4 and 5 show a circuit formed by the circuit forming method according to the present invention, and as is clear from these figures, a metal plating layer is formed in the transferred object 9 through the adhesive layer 5. 4 and the circuit pattern layer 3 are sequentially embedded and transferred, and the connecting portion 2 is exposed on the surface of the transfer target 9. Therefore, other electric circuits, electric equipment, electric parts, etc. can be connected to the connecting portion 2 by soldering.

Example 1 A conductive paint for contact parts having the following composition (viscosity 70 voids) was applied to a polyester film with a diameter of 1.5++ ui.
A contact portion with a thickness of 5 μm was formed.

Composition 1: Acrylic resin: 100 parts by weight Methyl isobutyl quinone: 150 parts by weight Copper particles: 800 parts by weight Next, a conductive paint for circuit patterns (viscosity: 70 voids) having the following composition was used, line width: 0.8 mm, distance between lines: 0.8
A circuit pattern was printed with mIrI to a thickness of 25 μm.

Composition 2 Thermoplastic polyester resin 100 parts by weight Aromatic solvent 120 parts by weight Silver-coated steel particles 600 parts by weight A plating layer of 5 μm thick is laminated on the metal by electroless plating on the circuit pattern thus produced. At the same time, an adhesive layer having the composition shown below was formed on the metal plated stone by screen printing to obtain a circuit transfer foil.

Composition 3 Polyamide resin 60 parts by weight Epoxy resin 40 parts by weight ABS resin (viscosity 4 ) Injection conditions: Injection temperature 220-240℃, injection pressure (gauge pressure) 800 Kg
/ ad, back pressure 5Kg/cnl, screw rotation speed 50
r, p, m,), the transfer target was molded.

Next, by peeling off the support film, a line width of 0.8 mm and a distance between lines of 0.8 mm were formed on the 1BS resin molded product.
A circuit with good accuracy was formed. The conductivity of this circuit was less than 0.1 Ω/C, and the contact strength was also good.

In the circuit obtained by transferring the circuit pattern at the same time as molding as in Example 1, the surface of the molded product and the surface of the circuit are on the same level (only the circuit part does not have a convex shape), so there is a problem in handling. There is also the advantage that circuit defects due to caution can be prevented.

Furthermore, when electrical components were connected to the contact portions using solder, the connection was successful.

〔Effect of the invention〕

As explained above, according to the circuit transfer foil for injection molding and the circuit forming method according to the present invention, a circuit pattern of conductive paint is printed by a printing means such as screen printing or gravure printing, and a metal is further added to the circuit pattern. In addition to forming a plating layer, an adhesive layer is also provided, and this is transferred to the transfer target at the same time as the transfer target to form a circuit, making it easy to create a circuit with conductivity similar to that of metal. It has the advantage of being cheap to manufacture. Further, since a contact portion having a high metal content is formed so as to be in contact with the circuit pattern, there is an advantage that electrical components, electrical circuits, and electrical equipment can be connected by soldering.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of a specific example of the circuit transfer foil used in the present invention, FIG. 2 is a sectional view of the circuit transfer foil, and FIG. FIG. 5 is a schematic diagram of the process of molding, FIG. 5 is a front view of a circuit formed on the transfer target, and FIG. 6 is a sectional view of FIG. 5.

■...Support film, 2...Contact part, 3...Circuit pattern, 4...Metal plating layer, 5...Adhesive layer, 6...Circuit transfer foil, 7...Injection Molding mold.

Applicant's representative Masaki Ame Miya ri, AL, B Figure 2 Figure 4 Figure 5 Procedural amendment (Marshal) ■Quote July 29, 1961

Claims (2)

[Claims] (1) Metal particles are placed on a predetermined portion of the support film using resin 1.
00 parts by weight to form a basic conductive paint, and add resin 1 to at least a portion of the contact part.
00 parts by weight and 300 to 1,000 parts by weight of conductive particles are added to the basic conductive paint, and a circuit pattern that is easily peelable is printed on the support film immediately after heating and pressing, and then the circuit pattern is printed. A circuit transfer foil for injection molding, characterized in that a pattern is provided with a metal plating layer, and an adhesive layer is laminated on at least the upper surface of the metal plating layer. (2) Metal particles are placed on a predetermined portion of the support film using resin 1.
00 parts by weight to form a basic conductive paint, and add resin 1 to at least a portion of the contact part.
00 parts by weight and 300 to 1,000 parts by weight of conductive particles are added to the basic conductive paint, and a circuit pattern that is easily peelable is printed on the support film immediately after heating and pressing, and then the circuit pattern is printed. A circuit transfer foil in which a metal plating layer is provided in the pattern and an adhesive layer is laminated on at least the upper surface of the metal plating layer is placed so that the support film is in contact with the inner wall of a mold for injection molding the transferred object. A method for forming a circuit, characterized in that a molten resin is press-fitted into the mold to form a transfer target, and then the support film is peeled off to mold the transfer target and simultaneously transfer the circuit.