JP7754875B2 - Manufacturing method of circuit-embedded substrate - Google Patents

Description

The present invention relates to a method for manufacturing a circuit-embedded substrate.

A film heater in which a single thin metal wire is embedded in a film in an arbitrary pattern is known (see, for example, Patent Document 1). Referring to Fig. 10 , such a film heater 100 includes a film 200, a rectangular first electrode pad 500 and a second electrode pad 600 arranged parallel to each other and spaced apart along the Y direction on the periphery of the film 200, and a circuit 400 made of a single thin metal wire 300 embedded in the film 200.
The circuit 400 includes a heater section 450 having an arbitrary pattern, a first wiring section 430 and a second wiring section 440 drawn out from both ends of the heater section 450, and a first end section 410 and a second end section 420 extending from the first wiring section 430 and the second wiring section 440 in the opposite direction from the heater section 450 (the +X direction in the figure) and overlapping with a first electrode pad 500 and a second electrode pad 600, respectively. The circuit 400 is embedded by applying ultrasonic vibrations using an ultrasonic welding machine to melt the contact surface between the film 200 and the thin metal wires 300. For example, the circuit 400 can be embedded in the film 200 in the following order: first end section 410, first wiring section 430, heater section 450, second wiring section 440, and second end section 420.

The first end 410 and the second end 420 straddle the first electrode pad 500 and the second electrode pad 600, respectively, in the X direction. The upper surfaces of the first electrode pad 500 and the second electrode pad 600 are electrically connected to the thin metal wires 300 that contact the upper surfaces of the first end 410 and the second end 420. When a voltage is applied to the first electrode pad 500 and the second electrode pad 600, a current is generated in the circuit 400, causing the heater section 450 to generate heat.

Japanese Patent Application Laid-Open No. 2022-066706

In the conventional manufacturing method for the film heater 100, the electrode pads 500, 600 are first placed on the film 200, and the corners of the film 200 are then placed against a jig (not shown). The thin metal wires 300 are then embedded in the film 200 so that the first end 410 and second end 420 overlap the electrode pads 500, 600. Because the placement of the electrode pads 500, 600 and the embedding of the thin metal wires 300 are separate processes, the following misalignments occur: (1) misalignment of the electrode pads, (2) misalignment of the embedded thin metal wires, and (3) misalignment of the electrode pads and the embedded thin metal wires. In this manufacturing method, if the placement locations of the electrode pads 500, 600 are misaligned in the +Y direction in Figure 10(a), for example, the embedded position of the thin metal wires 300 will be relatively misaligned in the -Y direction in Figure 10(a). In other words, with conventional manufacturing methods, it was difficult to align the electrode pads 500, 600 with the circuit 400, making it difficult to increase the yield rate.

The present invention was made to solve the above-mentioned problems, and aims to provide a method for manufacturing circuit-embedded substrates that can improve the yield rate by increasing the alignment accuracy between the circuit and electrode pads.

The first invention to achieve the above object is:
a preparation step of preparing a film;
an arrangement step of arranging first electrode pads and second electrode pads parallel to each other at intervals along a first direction on a peripheral edge portion of a first main surface of the film;
a circuit forming process for forming a circuit including a functional section having an arbitrary pattern and made of one thin metal wire arranged on the first main surface, a first wiring section drawn out from one of both ends of the functional section, a second wiring section drawn out from the other of both ends of the functional section, and first and second wiring sections extending from the first and second wiring sections to opposite sides of the functional section, respectively, and partially overlapping the first and second electrode pads, respectively, to form a first end portion constituting a first misalignment absorption region and a second end portion constituting a second misalignment absorption region, by embedding the functional section, the first wiring section, the second wiring section, and portions of the first end portion and the second end portion that do not overlap the first and second electrode pads in the first main surface of the film using an ultrasonic welding machine;
a connecting step of electrically connecting the first electrode pads and the second electrode pads to the thin metal wires located on the first electrode pads and the second electrode pads, respectively;
The ultrasonic welding machine has a horn that applies ultrasonic vibrations to melt the contact surface of the film with the thin metal wire and embed the thin metal wire in the first main surface of the film, and the thin metal wire passes through the inside of the horn and is continuously drawn out from the tip of the horn onto the first main surface of the film,
This is a method for manufacturing a circuit-embedded substrate, in which the first misalignment absorption region and the second misalignment absorption region are composed of first and second curved end portions, and each have a width that absorbs misalignment in a first direction between the first electrode pad and the second electrode pad and the circuit.

With this manufacturing method, even if the embedded positions of the first and second electrode pads and the first and second ends are misaligned relative to each other in the first direction, the first and second ends have portions that overlap with the first and second electrode pads, respectively, because the first and second ends are curved and have widths that accommodate misalignment in the first direction between the first and second electrode pads and the circuit. This improves the alignment accuracy between the electrode pads and the circuit, thereby improving the yield rate.

The second invention is a method for manufacturing a circuit-embedded substrate according to the first invention, in which the bent shape is zigzag or U-shaped in plan view.

The manufacturing method for circuit-embedded substrates of the present invention can improve the alignment accuracy between the circuit and the electrode pads, thereby improving the yield rate.

1A to 1C are schematic perspective views showing an embodiment of a method for manufacturing a circuit-embedded substrate. FIG. 4 is a partially enlarged view showing an example of a first end portion and a second end portion. FIG. 10 is an enlarged view showing a state in which the electrode pad is misaligned in the +X direction. FIG. 10 is a partially enlarged view showing another example of the first end portion and the second end portion. FIG. 10 is an enlarged view showing a state in which the electrode pad is misaligned in the +X direction. 6 is an enlarged view showing a state in which the electrode pad is further displaced in the +X direction from FIG. 5 . FIG. 10 is an enlarged view showing a state in which the electrode pad is misaligned in the −X direction. FIG. 10 is an enlarged view showing a state in which an electrode pad is misaligned in the +X direction in a conventional film heater. 10 is an enlarged view showing a state in which an electrode pad is misaligned in the −X direction in a conventional film heater. (a) A schematic plan view showing a conventional film heater, (b) A cross-sectional view taken along the line AA in (a).

(Outline of circuit-embedded board)
Referring to FIG. 1( f ), the circuit-embedded substrate 1 includes a film 2, a circuit 4 consisting of a single thin metal wire 3 disposed on a first main surface 2 a of the film 2, a first electrode pad 5, and a second electrode pad 6. The circuit 4 includes a functional portion 45, a first wiring portion 43, a second wiring portion 44, a first end portion 41, and a second end portion 42. The functional portion 45 has an arbitrary pattern. The first wiring portion 43 is drawn out from one end 45 a of the functional portion 45. The second wiring portion 44 is drawn out from the other end 45 b of the functional portion 45. The first end portion 41 extends from the first wiring portion 43 toward the opposite side of the functional portion 45 (in the −Y direction) and overlaps the first electrode pad 5. The second end portion 42 extends from the second wiring portion 44 toward the opposite side of the functional portion 45 (in the −Y direction) and overlaps the second electrode pad 6.
In this embodiment, the first end portion 41 and the second end portion 42 have a zigzag shape (an example of a bent shape) in a plan view.

The functional section 45, first wiring section 43, and second wiring section 44 are embedded in the first main surface 2a of the film 2. The portions of the first end section 41 and the second end section 42 that overlap the electrode pads 5, 6 are not embedded in the first main surface 2a, while the remaining portions are embedded. In other words, the thin metal wires 3 located above the electrode pads 5, 6 are not embedded in the first main surface 2a, while the thin metal wires 3 not located above the electrode pads 5, 6 are embedded.

In this embodiment, the functional portion 45 is a heat-generating portion, and the circuit-embedded substrate 1 is a film heater. For example, applying a positive voltage to the first electrode pad 5 and a negative voltage to the second electrode pad 6 generates a current in the circuit 4 made of thin metal wires 3, causing the functional portion 45 to heat up. The functional portion 45 has two ends 45a, 45b connected to the first wiring portion 43 and the second wiring portion 44, respectively, and has a loop-shaped pattern. More specifically, the functional portion 45 has a pattern shape that extends from the connection portion 45a with the first wiring portion 43 in the +X direction, then extends in the +Y direction, the -X direction, the -Y direction, and the +X direction to reach the connection portion 45b with the second wiring portion 44. In this way, the functional portion 45 has connection portions 45a, 45b with the first wiring portion 43 and the second wiring portion 44, and has an arbitrary pattern that extends from the connection portions 45a, 45b in the XY plane.

Film 2 can be any shape, and in this embodiment is rectangular. Film 2 can be transparent, opaque, or colored and transparent. Examples of materials that can be used for film 2 include thermoplastic resins such as ethylene-based resins, propylene-based resins, polyolefin-based resins, thermoplastic polyester-based resins, polyamide-based resins, polyvinyl chloride, polycarbonate, and ABS resin. Films containing two or more of these may also be used. Film 2 can contain inorganic fine powders or organic fillers, dispersants, antioxidants, compatibilizers, UV stabilizers, antiblocking agents, antistatic agents, and the like, as appropriate. The thickness of film 2 is, for example, 0.05 mm to 1 mm.

The fine metal wires 3 can be made of conductive materials such as copper, iron, gold, copper-nickel, nickel-chromium, and iron-nickel-chromium. From the standpoints of electrical resistance, durability, and cost, it is preferable to use copper or a copper alloy made by combining copper with zinc, lead, tin, silver, aluminum, nickel, beryllium, zirconium, or other elements. The diameter of the fine metal wires 3 is, for example, 0.01 mm to 0.5 mm. By making the diameter as small as possible, for example, 0.01 mm to 0.2 mm, the fine metal wires 3 can be made less noticeable.

The circuit 4 may also be formed from a conductive wire consisting of thin metal wires 3 coated with an insulating coating layer. The insulating coating layer is made of an insulating resin, such as polyester, polyethylene, polyurethane, polyvinyl chloride, polyamide, polyimide, polyesterimide, polyamideimide, or fluororesin. The diameter of the conductive wire is, for example, 0.05 mm to 0.3 mm.

The two electrode pads 5 and 6 can be made of conductive materials such as copper, phosphor bronze, brass, Corson alloy, nickel, and molybdenum. These materials may be used as a base material plated with nickel, tin, gold, silver, copper, or the like. The electrode pads 5 and 6 each have a size of, for example, 5 mm x 10 mm and a thickness of, for example, 0.1 mm.
In this embodiment, the electrode pads 5 and 6 are rectangular, but are not limited to this. For example, they may be polygonal, circular, elliptical, or L-shaped.

(Method for manufacturing circuit-embedded substrate)
An embodiment of a method for manufacturing such a circuit-embedded substrate 1 will be described with reference to FIG.
The manufacturing method of the circuit-embedded substrate 1 includes a preparation step (not shown) of preparing the film 2, an arrangement step (FIG. 1(a)) of arranging the first electrode pads 5 and the second electrode pads 6 on the peripheral portion of the first main surface 2a of the film 2, a circuit formation step (FIGS. 1(b) to 1(e)) of forming the circuit 4 using an ultrasonic welder 7, and a connection step (FIG. 1(f)) of electrically connecting the first end 41 and the second end 42 of the circuit 4 to the electrode pads 5, 6.

In the preparation step, the film 2 may be fixed onto a stage (not shown). A jig (not shown) may also be used to facilitate alignment of the film 2. In the placement step, the first electrode pad 5 and the second electrode pad 6 are placed on the periphery of the first main surface 2a of the film 2. In other words, they are placed side by side in the X direction (first direction) along one side of the film 2 that is parallel to the X direction. The two electrode pads 5, 6 are rectangular and are placed parallel to each other with a gap in between along the X direction. The two electrode pads 5, 6 each serve as a terminal portion of the circuit-embedded substrate 1. The two electrode pads 5, 6 can be fixed onto the first main surface 2a using, for example, an adhesive.

Referring to Figure 1(b), the ultrasonic welding machine 7 used in the circuit formation process includes an oscillator (not shown) that generates ultrasonic vibrations, a horn 71 that propagates the ultrasonic vibrations from the oscillator, and thin metal wires 3. By applying ultrasonic vibrations, the horn 71 melts the contact surface of the film 2 with the thin metal wires 3 and embeds the thin metal wires 3 into the first main surface 2a of the film 2. The thin metal wires 3 pass through the inside of the horn 71 and are continuously drawn out from the tip 71a of the horn 71 onto the first main surface 2a of the film 2.

1(b), in the circuit formation process, first, a predetermined length of thin metal wire 3 is pulled out from horn 71 and embedded in first main surface 2a of film 2, and the thin metal wire 3 is then formed in a zigzag shape across first electrode pad 5 to form first end 41. At this time, the bent portion of the zigzag shape is embedded in first main surface 2a, and the thin metal wire 3 that overlaps first electrode pad 5 is not embedded in first main surface 2a but comes into contact with the upper surface of first electrode pad 5.
1(c), the fine metal wires 3 are pulled out a predetermined length from the buried end of the first end portion 41 in the +Y direction and embedded in the first main surface 2a to form a first wiring portion 43. Next, the fine metal wires 3 are pulled out a predetermined length from the buried end 43a of the first wiring portion 43 and embedded in the first main surface 2a in an arbitrary pattern extending in the XY plane to form a functional portion 45. The buried end 43a of the first wiring portion 43 becomes the starting end of the functional portion 45. In other words, the end 43a of the first wiring portion 43 becomes one of both ends 45a of the functional portion 45 (see FIG. 1(d)).
1(d), the thin metal wire 3 is pulled out by a predetermined length from the horn 71, and is embedded in the first main surface 2a, extending from the end 45b of the functional portion 45 in the −Y direction, to form the second wiring portion 44. The end 45b of the functional portion 45 is the starting end of the second wiring portion 44 and is the other of both ends of the functional portion 45.
1( e), the thin metal wire 3 is pulled out by a predetermined length from the buried end 44a of the second wiring portion 44 and buried in the first main surface 2a, and the second end 42 is formed by extending the thin metal wire 3 in a zigzag pattern over the second electrode pad 6. At this time, the bent portion of the zigzag pattern is buried in the first main surface 2a, and the thin metal wire 3 overlapping the second electrode pad 6 is not buried in the first main surface 2a but is in contact with the upper surface of the second electrode pad 6. After the second end 42 is formed, the thin metal wire 3 is cut at the buried end of the second end 42. For example, a cutter or nippers can be used as the cutting method.
Finally, in the connection step, as shown by point P in Fig. 1(f), the two electrode pads 5, 6 are electrically connected to the thin metal wires 3 located on (in contact with) the two electrode pads 5, 6. For the connection, known metal joining techniques such as welding (resistance welding, ultrasonic welding, laser welding, etc.), soldering, brazing, etc. may be used. Note that the electrode pads 5, 6 and the thin metal wires 3 may be electrically connected at multiple points.
In this manner, the circuit-embedded substrate 1 can be obtained.

(First embodiment of misalignment absorbing region)
2, the first end 41 and the second end 42 respectively constitute a first misalignment absorbing region 41a and a second misalignment absorbing region 42a. The first misalignment absorbing region 41a and the second misalignment absorbing region 42a are indicated by dashed lines in the figure. FIG. 2 shows a state in which there is no misalignment between the first electrode pad 5 and the second electrode pad 6 and the first end 41 and the second end 42.
The first misalignment absorption region 41a has a width _W41 , and the second misalignment absorption region 42a has a width _W42 . These widths _W41 and _W42 are equal to the width of the zigzag shape of the end portions 41 and 42, and are set larger than the widths W5 and W6 of the two electrode pads _{5 and 6.} Naturally, if the widths _W41 and _W42 of the misalignment absorption regions 41a and 42a are increased, the allowable magnitude of misalignment of the electrode pads 5 and 6 in the X direction also increases.
For example, when the widths W ₅ and W _{6 of the electrode pads 5 and 6} are each 5 mm and the spacing S between the electrode pads 5 and 6 is 10 mm, the widths W ₄₁ and W ₄₂ can each be set to 15 mm.

3 , even if the positions of the electrode pads 5 and 6 are shifted by d in the +X direction, the misalignment absorption regions 41a and 42a have widths _{W41 and} W42, respectively, which are greater than d, and therefore can absorb the misalignment of the electrode pads 5 and _6. Because the misalignment absorption regions 41a and 42a have widths _W41 and _W42 , respectively, the ends 41 and 42 overlap the electrode pads 5 and 6 even if the positions of the electrode pads 5 and 6 relative to the film 2 are shifted by d in the X direction. Therefore, the embedding positions of the ends 41 and 42 do not need to take into account the misalignment of the electrode pads 5 and 6. In other words, the ends 41 and 42 can be embedded in the same positions every time the circuit-embedded substrate 1 is manufactured.
In this way, it is possible to align the ends 41 and 42 with the electrode pads 5 and 6 without taking into consideration misalignment of the electrode pads 5 and 6, thereby improving the yield rate.

(Second embodiment of misalignment absorbing region)
4, the bent shapes of the first end 41 and the second end 42 may be U-shaped in a plan view. The first end 41 and the second end 42 respectively constitute a first misalignment absorbing region 41a and a second misalignment absorbing region 42a. FIG. 4 shows a state in which there is no misalignment between the first end 41 and the second end 42 and the first electrode pad 5 and the second electrode pad 6.

The first misalignment absorbing region 41a has a width _W41 , and the second misalignment absorbing region 42a has a width _W42 . These widths _W41 and _W42 are equal to the width of the U-shape of the end portions 41 and 42, and respectively satisfy the following formulas (1) and (2): where _S5 and _S6 are the spacings between the two thin metal wires 3 that straddle each electrode pad 5 and 6 in the Y direction.
W ₄₁ = (2×W ₃ )+S ₅ ...(1)
_W42 =(2× _W3 )+ _S6 ...(2)
Furthermore, when ultrasonically welding the fine metal wire 3 and the electrode pads 5, 6, the widths _W41 , _W42 of the first misalignment absorption region 41a and the second misalignment absorption region 42a can be set equal to the widths _W5 , W6 of the two electrode pads 5, _6. When soldering the fine metal wire 3 and the electrode pads 5, 6, it is necessary to fix the fine metal wire 3 by placing solder on both sides of the fine metal wire 3 (in other words, placing solder in positions that sandwich the fine metal wire 3), so _W5 ( _W6 ) > _W41 ( _W42 ).
With respect to the widths W5 and W6 of the electrode pads _{5 and 6} , the width (diameter) _W3 of the thin metal wire 3 and the intervals _S5 and _S6 are set to values that satisfy the following formulas (3) and (4), respectively.
_W5 = _2W3 + _S5 ...(3)
W ₆ =2W ₃ +S ₆ ...(4)
In other words, once the widths W5 and W6 of the electrode pads ₅ and ₆ and the width (diameter) _W3 of the thin metal wire 3 are determined, the intervals _S5 and _S6 can be calculated from the above formulas (3) and (4). For example, when the electrode pads 5 and 6 have a width _W5 (= width _W6 ) of 5 mm and the thin metal wire ₃ has a width (diameter) W3 of 0.5 mm, the interval _S5 (= _S6 ) is 5 - 1 = 4 mm.

5, even if the electrode pads ₅ and ₆ are each misaligned by d (= W5/ ₂ = _W6 /2) in the +X direction, there will be an overlapping portion between the thin metal wire 3 and the electrode pads 5 and 6 (a portion where the thin metal wire 3 straddles the electrode pads 5 and 6). In other words, the accuracy of alignment between the electrode pads 5 and 6 and the ends 41 and 42 is improved, thereby improving the yield rate.

6 and 7, even if the electrode pads 5 and 6 are misaligned by d+d/2 in each of the ±X directions, there will be overlapping portions between the fine metal wire 3 and the electrode pads 5 and 6 as long as the shapes of the first end 41 and the second end 42 satisfy the above formulas (3) and (4). In FIGS. 6 and 7, one fine metal wire 3 overlaps the edge portion of each of the electrode pads 5 and 6. As can be seen from FIGS. 6 and 7, the allowable range of misalignment of the electrode pads 5 and 6 in the X direction is d+d/2. Here, d= _W5 /2 (= _W6 /2), so _W5 /2+ _W5 /4= _3W5 /4 (= _3W6 /4).

8 and 9, the first end 410 and the second end 420 of the conventional film heater 100 are straight. In Figures 8 and 9, the electrode pads 500, 600 are misaligned in the X direction, but there are portions where the thin metal wire 300 overlaps the electrode pads 500, 600. The amount of misalignment of the electrode pads 500, 600 in Figures 8 and 9 is half the width of the electrode pads 500, 600 ( _W500 /2, _W600 /2). In other words, the allowable range of misalignment of the electrode pads 500, 600 in the X direction is half the width of the electrode pads 500, 600 ( _W500 /2, _W600 /2).

In this way, by changing the shape of the first end 41 and the second end 42 from the conventional straight line to a U-shape that satisfies the above formulas (3) and (4), the tolerance for misalignment of the electrode pads 5 and 6 in the X direction increases by 1.5 times. In other words, it becomes easier to align the first end 41 and the second end 42 with the electrode pads 5 and 6, thereby improving the yield rate.

In the above two embodiments, the embedded position of the fine metal wire 3 does not shift, but the electrode pads 5, 6 do. However, even in the opposite case, where the electrode pads 5, 6 do not shift, but the embedded position of the fine metal wire 3 shifts, the manufacturing method of the present invention achieves the same effects as the above embodiments. Furthermore, even in the case where both the positions of the electrode pads 5, 6 and the embedded position of the fine metal wire 3 shift, the manufacturing method of the present invention achieves the same effects as the above embodiments.

1: Circuit-embedded substrate 2: Film 2a: First main surface 3: Thin metal wire 4: Circuit 41: First end 41a: First misalignment absorbing region 42: Second end 42a: Second misalignment absorbing region 43: First wiring portion 44: Second wiring portion 45: Functional portion 5: First electrode pad 6: Second electrode pad 7: Ultrasonic welder 71: Horn 100: Film heater 200: Film 300: Thin metal wire 400: Circuit 410: First end 420: Second end 430: First wiring portion 440: Second wiring portion 450: Heater portion 500: First electrode pad 600: Second electrode pad 700: Adhesive layer

Claims (2)

a preparation step of preparing a film;
an arrangement step of arranging first electrode pads and second electrode pads parallel to each other at intervals along a first direction on a peripheral edge portion of the first main surface of the film;
a thin metal wire disposed on the first main surface;
a functional unit having an arbitrary pattern;
a first wiring portion drawn out from one of both ends of the functional portion;
a second wiring portion drawn out from the other of the two ends of the functional portion;
a circuit extending from the first wiring portion and the second wiring portion to a side opposite to the functional portion, partially overlapping the first electrode pad and the second electrode pad, respectively, and having a first end portion constituting a first misalignment absorbing region and having a first bent portion, and a second end portion constituting a second misalignment absorbing region and having a second bent portion ;
a circuit forming process in which the functional section, the first wiring section, the second wiring section, and portions of the first end section and the second end section that do not overlap with the first electrode pads and the second electrode pads are embedded in the first main surface of the film using an ultrasonic welding machine;
a connecting step of electrically connecting the first electrode pads and the second electrode pads to the thin metal wires located on the first electrode pads and the second electrode pads, respectively;
the ultrasonic welding machine includes a horn that applies ultrasonic vibrations to melt a contact surface of the film with the thin metal wire and embed the thin metal wire in the first main surface of the film, and the thin metal wire passes through the inside of the horn and is continuously drawn out from a tip of the horn onto the first main surface of the film,
the first misalignment absorption region and the second misalignment absorption region are respectively composed of the first end and the second end in a bent shape connected by the first bent portion and the second bent portion , and each have a width that absorbs misalignment in the first direction between the first electrode pad and the second electrode pad and the circuit , the first bent portion and the second bent portion are embedded in the first main surface, and thin metal wires overlapping the first electrode pad and the second electrode pad contact upper surfaces of the first electrode pad and the second electrode pad, respectively.
A method for manufacturing a circuit-embedded substrate.
The method for manufacturing a circuit-embedded substrate according to claim 1, wherein the bent shape is zigzag or U-shaped in plan view.