JP2018153817A - Joint structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joint structure which comprises an electrode layer and a connection metal member sequentially provided on a flexible insulating substrate and keeps strength enhanced as the whole.SOLUTION: A joint structure 10 comprises a flexible insulating substrate 12, an electrode layer 14 formed on the flexible insulating substrate 12, and a connection metal member 16 welded to the electrode layer 14, and is provided with a melting spot 20 reaching from the surface of the connection metal member 16 to the surface of the flexible insulating substrate 12, wherein, an interface between the flexible insulating substrate 12 and the electrode layer 14 has, in the periphery of the melting spot 20, a joint reinforcement part 18 where the flexible insulating substrate 12 is engaged with the electrode layer 14.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bonded structure.

  A temperature sensor in which a thin film thermistor is formed on a substrate made of a ceramic material such as alumina is known. Such a temperature sensor is very small and highly responsive, but when the substrate is thinned to about 0.1 mm, it becomes very brittle and easily broken. On the other hand, a film type thermistor sensor using a resin film as a substrate is very thin and flexible.

  In the film type thermistor sensor, the thermistor material layer on the resin film and the lead frame are connected. Conventionally, a patterned electrode connected to a thermistor material layer is formed on a resin film, and the patterned electrode and the lead frame are soldered together.

  In the conventional film type thermistor sensor, the joint portion melts in a high temperature environment exceeding the melting point (about 200 ° C.) of the solder, and it becomes difficult to maintain the joint between the pattern electrode and the lead frame. Resistance welding and laser welding are widely used to produce electronic components for high temperature applications. In resistance welding, an electrode is pressed against a lead frame and energized between the electrodes while applying pressure to generate heat, thereby joining the pattern electrode and the lead frame. In laser welding, the pattern electrode and the lead frame are joined using the energy of laser light.

  Various methods have been proposed for joining the pattern electrode and the lead frame (see Patent Documents 1 to 4).

  Patent Document 1 discloses that a via hole is formed in an insulating film disposed on the opposite side of the pattern electrode, and a metal material embedded in the via hole and a lead frame are welded.

  Patent Document 2 discloses that a terminal portion is provided at a base end portion of a pattern electrode formed on the surface of an insulating film, and a lead frame is connected to the terminal portion with a conductive resin adhesive or the like.

  In Patent Document 3, an oscillation wavelength is set to irradiate a laser beam from a side opposite to a component through a flexible printed circuit (FPC) without mounting the component on the FPC without adversely affecting the quality. A method of irradiating 532 nm laser light is disclosed.

  Patent Document 4 discloses a method in which a groove is provided in an electrode patterned on an insulating layer or an insulating substrate, and laser welding is performed at a contact portion between the side surface and the groove with a lead embedded in the groove. .

JP 2014-116550 A (Claim 1) JP 2014-52228 A (paragraph 0025) JP 2009-94349 A (Claim 1) Japanese Patent No. 5560468 (Claim 1)

  However, the method according to the above-mentioned patent document is not satisfactory as a method of joining a connecting metal member such as a lead frame to an electrode layer such as a pattern electrode provided on the surface of a flexible insulating substrate. It was.

  That is, in the method described in Patent Document 1, a predetermined size is required for the via hole in order to avoid an adverse effect on the pattern electrode. For this reason, the structure is complicated and the manufacturing cost is high. The method using an adhesive such as a conductive adhesive described in Patent Document 2 cannot sufficiently increase the bonding strength between the lead frame and the pattern electrode.

  When laser light having an oscillation wavelength of 1064 nm is irradiated from the opposite side of the component through the FPC, the adhesive layer between the conductor and the film is adversely affected. In Patent Document 3, laser light having an oscillation wavelength of 532 nm is used. It has been. Copper, gold, and the like have a high absorption rate for laser light having an oscillation wavelength of 532 nm. For this reason, it is necessary to use copper or gold for the joint between the component and the FPC.

  In the method of Patent Document 4 in which a lead is embedded in a groove formed in the electrode, an electrode having a groove for embedding the lead is formed. In order to form such an electrode, it is necessary to remove the plating resist after forming a plating layer by applying a plating resist to the portion to be the groove to protect it. For this reason, the manufacturing process becomes complicated.

  When the pattern electrode is very thin, the pattern electrode evaporates due to heat during laser welding. Even if a part of the pattern electrode evaporates, if the pattern electrode is very thin, the lead frame does not melt deeply and sufficient bonding strength cannot be obtained.

  When the pattern electrode on the resin film and the lead frame are resistance-welded, the electrode contacts only one-side spot welding on the lead frame side. Since at least a space for two electrodes is required, miniaturization is difficult. Further, the electrode and the resin film between the welding spots are damaged by heat generated by the current flowing in the pattern electrode.

  Accordingly, the present invention includes a joining structure provided with an electrode layer and a connecting metal member sequentially provided on a flexible insulating substrate, and provided with a melting spot that reaches the surface of the flexible insulating substrate from the surface of the connecting metal member. In the body, apart from the bonding strength between the electrode layer and the connecting metal member, by improving the strength of the interface between the flexible insulating substrate and the electrode layer, a bonding structure having a further increased strength as a whole element is obtained. The purpose is to provide.

  A first aspect of the present invention includes a flexible insulating substrate, an electrode layer formed on the flexible insulating substrate, and a connecting metal member welded to the electrode layer, the connecting metal A bonding structure provided with a melting spot that reaches the surface of the flexible insulating substrate from the surface of a member, and an interface between the flexible insulating substrate and the electrode layer is around the melting spot, It has a junction strengthening part in which the flexible insulating substrate and the electrode layer are engaged with each other.

  A second aspect of the present invention is an invention based on the first aspect, wherein the flexible insulating substrate is a polyimide resin sheet.

  A third aspect of the present invention is the invention based on the first or second aspect, wherein the electrode layer protects the metal thin film formed on the surface of the flexible insulating substrate and the metal thin film. And a thick metal film.

  A fourth aspect of the present invention is the invention based on the third aspect, wherein the connecting metal member is made of a metal having a melting point higher than that of the metal thick film.

  A fifth aspect of the present invention is the invention based on any one of the first to fourth aspects, wherein the joint strengthening portion includes a plurality of convex portions, and the height of the convex portions is 0.1 to 0. 0.5 μm, and the distance between adjacent convex portions is 0.1 to 1.5 μm.

  A sixth aspect of the present invention is the invention according to any one of the first to fifth aspects, wherein the joint strengthening portion has a width of 3 to 30 μm and exists around the melting spot. To do.

  A seventh aspect of the present invention is an invention based on any one of the first to sixth aspects, wherein the joint strengthening portion is provided in a range of 50 μm or more and 200 μm or less from the center of the melting spot. It is characterized by that.

  An eighth aspect of the present invention is the invention based on any one of the first to seventh aspects, wherein a plurality of the melting spots are provided, and the distance between the centers is adjacent by 500 μm or more. And

A ninth aspect of the present invention is the invention based on the eighth aspect, wherein the melting spots are provided at a density of 1.25 points or more per 1 mm ² .

  A tenth aspect of the present invention is the invention based on any one of the third to ninth aspects, wherein the metal thin film is a pattern electrode provided in contact with a thin film thermistor of a temperature sensor. To do.

  An eleventh aspect of the present invention is the invention according to any one of the third to tenth aspects, wherein the metal thick film is partially provided on a surface of the metal thin film. .

  In the bonding structure according to the first to eleventh aspects of the present invention, the interface between the flexible insulating substrate and the electrode layer is joined to the flexible reinforcing substrate and the electrode layer around the melting spot. By having this, the bonding strength between the flexible insulating substrate and the electrode layer is increased, and the strength of the entire bonded structure can be increased.

  The bonded structure according to the first to eleventh aspects of the present invention includes an electrode layer and a connecting metal member that are sequentially provided on a flexible insulating substrate. When the number of welding spots is increased, the strength between the electrode layer and the connecting metal member increases. By forming the joint strengthening portion, the strength between the flexible insulating substrate and the electrode layer is increased. As a result, even when the strength between the flexible insulating substrate and the electrode layer is lower than the strength between the electrode layer and the connecting metal member, the strength of the entire bonded structure can be increased.

  In the joint structure according to the second aspect of the present invention, since the flexible insulating substrate is a polyimide resin sheet, the thickness of the entire joint structure can be reduced and the heat resistance can be increased.

  In the bonded structure according to the third aspect of the present invention, the electrode layer includes a metal thin film formed on the surface of the flexible insulating substrate and a metal thick film for protecting the metal thin film, thereby protecting the metal thin film. In addition, the electrode layer and the connecting metal member can be firmly bonded.

  In the joint structure according to the fourth aspect of the present invention, since the connecting metal member is made of a metal having a melting point higher than that of the metal thick film, the metal thick film is melted to firmly bond the electrode layer and the connecting metal member. be able to.

  In the joint structure according to the fifth aspect of the present invention, the joint reinforcing portion includes a plurality of convex portions, the height of the convex portions is 0.1 to 0.5 μm, and the distance between adjacent convex portions is 0. 0. Since it is 1-1.5 micrometers, the joint strength of a flexible insulated substrate and an electrode layer can be raised more.

  In the bonded structure according to the sixth aspect of the present invention, the bonding strength between the flexible insulating substrate and the electrode layer can be further increased by the presence of the bonding reinforcing portion having a width of 1 to 30 μm around the melting spot. it can.

  In the bonded structure according to the seventh aspect of the present invention, the bonding strength portion is provided within the range of 50 μm or more and 200 μm or less from the center of the melting spot, thereby increasing the bonding strength between the flexible insulating substrate and the electrode layer. It can be further enhanced.

  In the joined structure according to the eighth aspect of the present invention, a plurality of melting spots are provided, and the distance between the centers is adjacent by 500 μm or more, thereby avoiding interference between the joining strengthened portions of the adjacent melting spots. be able to.

In the bonded structure according to the ninth aspect of the present invention, the melting spot is provided at a density of 1.25 points or more per 1 mm ² , thereby further ensuring the bonding strength between the flexible insulating substrate and the electrode layer. Can be increased.

  In the bonded structure according to the tenth aspect of the present invention, the metal thin film is a pattern electrode provided in contact with the thin film thermistor of the temperature sensor, whereby the bonded portion in the temperature sensor can be strengthened.

  In the junction structure according to the eleventh aspect of the present invention, the thick metal film is partially provided on the surface of the metal thin film, so that the thickness of the entire region corresponding to the pattern electrode after the connecting metal member is welded. It is possible to avoid an increase in the size.

It is a longitudinal cross-sectional view of the junction structure concerning an embodiment. It is a schematic diagram explaining a joining reinforcement | strengthening part. It is a top view explaining the width | variety of a joining reinforcement | strengthening part. It is a schematic diagram explaining the area | region which can form a joining reinforcement | strengthening part. It is a schematic diagram explaining the distance of an adjacent fusion spot. It is a longitudinal section explaining a manufacturing method of a joined structure concerning an embodiment. FIG. 7A is a micrograph of a cross section in the vicinity of a melting spot, FIG. 7A is an overall image, and FIG. 7B is an enlarged image of a region X in FIG. 7A. It is a figure explaining the distance from the center of a fusion spot. FIG. 3 is a plan view showing a joint structure of Example 1. FIG. 6 is a plan view showing a joint structure of Example 2. It is a schematic diagram which shows the joining structure body of a prior art example, FIG. 11A is a top view, and FIG. 11B is a side view. It is a figure which shows the fracture strength of the joining structure of an Example, and the joining structure of a prior art example. FIG. 13A is a plan view and FIG. 13B is a side view illustrating a temperature sensor to which the bonding structure according to the embodiment is applied. It is a figure explaining the manufacturing process of a temperature sensor, FIG. 14A is a top view, FIG. 14B is AA sectional drawing in FIG. 14A. It is a figure which shows the state following FIG. 14, FIG. 15A is a top view, FIG. 15B is AA sectional drawing in FIG. 15A. FIG. 16A is a plan view of the state following FIG. 15, and FIG. 16B is a cross-sectional view taken along line AA in FIG. 16A. 16A is a partially enlarged view of the BB cross section in FIG. 16A, FIG. 17A is a cross-sectional view of a state where a thick metal film is provided on the surface of the terminal portion, and FIG. 17B is a cross-sectional view illustrating a state of laser welding the lead frame. . It is a figure which shows the state following FIG. 16, FIG. 18A is a top view, FIG. 18B is a side view.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1. Overall Configuration A joining structure 10 shown in FIG. 1 includes a flexible insulating substrate 12, an electrode layer 14 provided on the flexible insulating substrate 12, and a connecting metal member 16 welded to the electrode layer 14. I have. As described later, the electrode layer 14 includes a metal thin film 13 formed on the surface of the flexible insulating substrate 12 and a metal thick film 15 that protects the metal thin film 13. The metal thin film refers to a metal film having a thickness of 1000 nm or less, and the metal thick film refers to a metal film having a thickness of 3 μm or more.

  In the present embodiment, a polyimide resin sheet having a thickness of about 7.5 to 125 μm is used as the flexible insulating substrate 12. The metal thin film 13 is an Au layer having a thickness of about 50 to 1000 nm. The metal thick film 15 is a Ni plating layer having a thickness of about 5 to 15 μm. As the connecting metal member 16, a lead frame made of stainless steel (hereinafter referred to as SUS) is used. The thickness of the SUS lead frame is generally about 50 to 150 μm.

  A melting spot 20 is provided from the surface of the connecting metal member 16 to the surface of the flexible insulating substrate 12. As will be described later, the melting spot 20 is an irradiation mark of laser light. In the present embodiment, the melting spot 20 is constituted by the region 22 in which the connecting metal member 16 has been altered, the region 24 in which the electrode layer 14 has been altered, and the integrated layer 26 between these regions. The integrated layer 26 is made of an alloy containing SUS and Ni. The integrated layer 26 may contain Au.

  The region 24 in which the electrode layer 14 having a smaller volume than the SUS lead frame as the connecting metal member 16 is altered may not exist. The region 22 in which the connecting metal member 16 is altered and the integrated layer 26 may be welded and sputtered. A void is generated in this region. As shown by reference numeral 26 a in FIG. 1, the integrated layer 26 is also formed at the interface between the electrode layer 14 around the molten spot 20 and the connecting metal member 16.

  The interface between the flexible insulating substrate 12 and the electrode layer 14 has a bonding reinforcing portion 18 around the melting spot 20. Immediately below the melting spot 20, there is a region 28 in which the flexible insulating substrate 12 has been altered and partially melted.

  As shown in FIG. 2, at the interface 19 between the flexible insulating substrate 12 and the electrode layer 14 around the melting spot 20, the flexible insulating substrate 12 and the electrode layer 14 are engaged with each other to form a bonding reinforcement portion 18. Has been. The joint strengthening part 18 includes a plurality of convex parts. The height h of the convex portion is about 0.1 to 0.5 μm, and the distance d between the adjacent convex portions is about 0.1 to 1.5 μm. In FIG. 2, the flexible insulating substrate 12 side is viewed as a convex portion. Conversely, when the electrode layer 14 side is viewed as a convex portion, the height h of the convex portion and the adjacent convex portion are also seen. The distance d between the parts is the same.

  For example, when observed on the surface of the flexible insulating substrate 12, the bonding reinforcing portion 18 exists in an annular shape around the melting spot 20 as shown in FIG. 3. The plurality of concave portions described above are included in the annular joint reinforcing portion 18 in the radial direction. Since the melting spot 20 is a laser beam irradiation mark, the shape of the melting spot 20 observed on the surface of the flexible insulating substrate 12 is substantially circular. The width w of the joint strengthening portion 18 formed around the melting spot 20 is about 3 to 30 μm. Similarly, the width w of the joint strengthening portion 18 is about 3 to 30 μm when observed on the surface of the metal thin film 13.

  As described above, the joint strengthening portion 18 is formed around the melting spot 20. Since the fusion spot 20 is a laser beam irradiation trace, the range in which the bonding reinforcement portion 18 is formed is determined by the laser light irradiation conditions. A region where the bonding strengthening portion 18 can be formed is shown as a region 30 in FIG. In the present embodiment, a region from D1 (50 μm) to D2 (200 μm) from the center p of the melting spot is a region 30 in which the joint strengthening portion can be formed.

When two or more melting spots 20 exist, as shown in FIG. 5, the distance D3 between the centers p of adjacent melting spots 20 can be 500 μm or more. The molten spot 20 is preferably provided at a density of 1.25 points or more per 1 mm ^{2 with} respect to the metal thick film 15. The distance D3 between the centers p of the adjacent melting spots 20 can be appropriately determined according to the area of the portion of the thick metal film 15 that contacts the connecting metal member 16 in consideration of the density of the melting spots 20.

2. Manufacturing Method In the bonding structure 10 of the present embodiment, the connecting metal member 16 is disposed on the electrode layer 14 formed on the surface of the flexible insulating substrate 12, and laser light is irradiated from the connecting metal member 16 side. Thus, the electrode layer 14 and the connecting metal member 16 can be melted and joined.

  If the flexible insulating substrate 12 has a thickness of about 7.5 to 125 μm, it is possible to achieve both appropriate strength and flexibility required for the bonded structure 10. The polyimide resin sheet is particularly preferable as the flexible insulating substrate 12 because it has high heat resistance in addition to flexibility.

  On the flexible insulating substrate 12, Au is formed into a predetermined thickness by sputtering to obtain a metal thin film 13. The metal thin film 13 is provided for the purpose of ensuring electrical continuity with a predetermined target such as a thin film thermistor of a temperature sensor, for example. For this reason, it is sufficient that the thickness of the metal thin film 13 is about 1000 nm or less.

  On the metal thin film 13, a Ni plating layer is formed with a predetermined thickness to form a metal thick film 15. The metal thick film 15 protects the metal thin film 13 during laser light irradiation. When the metal thick film 15 is too thin, it is difficult to protect the metal thin film 13. On the other hand, when the metal thick film 15 is too thick, the metal thick film 15 is easily peeled off. Such inconvenience can be avoided if the thickness of the metal thick film 15 is about 3 to 20 μm. The thickness of the metal thick film 15 is more preferably about 5 to 15 μm.

  A lead frame made of SUS as the connecting metal member 16 is disposed on the metal thick film 15 to obtain the laminate 11 as shown in FIG. As shown in FIG. 6, the laminated body 11 is irradiated with laser light L from the connecting metal member 16 side. The beam diameter of the laser light L can be set to about 0.08 to 0.3 mm.

  When the beam diameter is too large, the connecting metal member 16 and the metal thick film 15 are melted in a wide range, so that an area that is damaged by welding increases. Further, when the beam diameter is too large, the laser light L is dispersed.

  If the beam diameter of the laser beam L is 0.3 mm or less, the energy of the laser beam is concentrated. By irradiating such laser light, only the desired regions of the connecting metal member 16 and the metal thick film 15 can be melted and joined.

  When the beam diameter of the laser beam L is 0.3 mm or less, the output required for welding also decreases. As a result, it is possible to shorten a process work time for achieving an even timing of a production process in manufacturing, a so-called tact time.

  In laser welding, large energy can be obtained by converging a laser amplified by a laser oscillator with a focus lens. In general, the beam diameter d at the condensing point is expressed by the following formula (1) using the beam diameter D incident on the lens and the focal length f of the lens.

d = A · λf / D Formula (1)
In the above formula (1), A is a constant, and λ is the wavelength of the laser. In the case of an apparatus that generates laser light having the energy required in this embodiment, the minimum beam diameter of a general laser light is 0.08 mm. The lower limit (0.08 mm) of the laser beam diameter is based on this.

  When irradiating the laser beam L with a beam diameter of about 0.08 to 0.3 mm, the output can be about 0.2 to 0.4 kW, and the irradiation time can be about 0.5 to 1.5 ms. If the irradiation time is within 1.5 ms, heat dissipation can be avoided.

  By irradiating the laser beam L under the above-described conditions, in the region irradiated with the laser beam L, the connecting metal member 16 and the electrode layer 14 are altered as shown in FIG. The formation layer 26 is produced. By forming the integrated layer 26, the connecting metal member 16 is welded to the electrode layer 14. The region 22 in which the connecting metal member 16 has been altered, the region 24 in which the electrode layer 14 has been altered, and the integrated layer 26 correspond to irradiation marks of the laser light L. The regions 22 and 24 and the integrated layer 26 constitute the molten spot 20.

  Immediately below the melting spot 20, the flexible insulating substrate 12 is altered and partly melted to form a region 28. Around the melting spot 20, the energy of the laser beam L causes unevenness at the interface 19 between the flexible insulating substrate 12 and the electrode layer 14, and the flexible insulating substrate 12 and the electrode layer 14 are engaged.

  As described above, the bonding reinforcing portion 18 is formed at the interface between the flexible insulating substrate 12 and the electrode layer 14 in the periphery of the melting spot 20 by the engagement of the flexible insulating substrate 12 and the electrode layer 14. It is formed.

  The width w (see FIG. 3) of the joint strengthening portion 18 can be appropriately set according to the irradiation condition of the laser light L. Similarly, the region 30 (see FIG. 4) where the bonding strengthening portion 18 is formed can be appropriately set according to the irradiation condition of the laser light L.

  In the case where a plurality of melting spots 20 are formed, it is preferable that the joint strengthening portions 18 around the adjacent melting spots 20 do not interfere with each other. As described with reference to FIG. 5, it is desirable to irradiate the laser beam L such that the distance D3 between the centers p of the adjacent melt spots 20 is 500 μm or more.

Moreover, when forming the several fusion | melting spot 20, it is preferable to irradiate the laser beam L so that it may become a density of 1.25 or more per mm < ² > about the metal thick film 15. FIG. For example, when the area of the metal thick film 15 is 4.8 mm ² , the laser beam is irradiated so that the melting spot 20 becomes 6 points or more. The presence of the melting spot 20 at a density of 1.25 points or more per 1 mm ² can further increase the bonding strength between the flexible insulating substrate 12 and the electrode layer 14.

3. Action and Effect In the bonded structure 10 according to the present embodiment, a melting spot 20 that penetrates the electrode layer 14 from the surface of the connecting metal member 16 and reaches the surface of the flexible insulating substrate 12 is formed. The melting spot 20 is a laser beam irradiation mark. A part of the flexible insulating substrate 12 around the melting spot 20 is melted by heat generated by the irradiation of the laser beam, and the flexible insulating substrate 12 and the electrode layer 14 are engaged with each other to form the bonding reinforcing portion 18.

  The interface between the flexible insulating substrate 12 and the electrode layer 14 is originally bonded by chemical bonding. Due to the presence of the bonding reinforcing portion 18 as described above, a so-called anchor structure is formed at the interface between the flexible insulating substrate 12 and the electrode layer 14. The anchor structure provides a mechanical joining effect and increases the resistance in the sliding direction. As a result, the bonding strength between the flexible insulating substrate 12 and the electrode layer 14 was increased. Since bonding is performed by laser light irradiation, the bonded structure 10 can be manufactured more easily than when a metal material is embedded.

  In addition, the electrode layer 14 in the bonded structure 10 includes a thick metal film 15 that protects the metal thin film 13. When the metal thick film 15 and the connecting metal member 16 are integrated by the laser light irradiation, the connecting metal member 16 and the electrode layer 14 are more firmly bonded. When the connecting metal member 16 is made of a metal having a melting point higher than that of the metal thick film 15, the metal thick film 15 is sufficiently melted by the irradiation of the laser beam, so that the connecting metal member 16 and the electrode layer 14 are joined together. Become more certain.

  In addition to the fact that the connecting metal member 16 and the electrode layer 14 are firmly bonded, the bonding structure 10 has a high bonding strength between the flexible insulating substrate 12 and the electrode layer 14. Improved.

  Since the joining structure 10 is joined by irradiating laser light, the area required for joining can be reduced unlike joining by resistance welding. The electrode layer 14 between the melting spots and the flexible insulating substrate 12 are not damaged. Furthermore, even if the joining structure 10 is used in a high temperature environment, no problem occurs in joining the electrode layer 14 and the connecting metal member 16.

4). The present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope of the gist of the present invention.

  In the above embodiment, a polyimide resin sheet is used as the flexible insulating substrate 12, but a polyethylene terephthalate (PET) resin, a polyethylene naphthalate (PEN) resin, or the like can be used in addition to the polyimide resin sheet.

  The thickness of the metal thin film 13 constituting the electrode layer 14 and the metal to be used can be appropriately changed. The thickness of the Au layer can be appropriately selected within the range of 50 to 1000 nm. You may provide a 5-100 nm Cr layer or a NiCr layer in the lower layer of Au layer. If the metal thin film 13 having a predetermined thickness is obtained, the metal thin film 13 can be formed on the surface of the flexible insulating substrate 12 by a method other than the sputtering method.

  The thick metal film 15 that protects the metal thin film 13 may use Cr, Au, Pt, or the like in addition to Ni. If the metal thick film 15 exists on the metal thin film 13, the metal thin film 13 can be protected. The thickness of the metal thick film 15 can be appropriately selected according to the thickness of the connecting metal member 16 and the like. If the thick metal film 15 having a predetermined thickness is obtained, the thick metal film 15 may be formed by a method other than plating.

  In the above-described embodiment, the lead frame is used as the connecting metal member 16, but the connecting metal member 16 such as a conductive wire can be used in addition to the lead frame. Further, although SUS is used as a metal for forming the connecting metal member 16, any metal that can absorb and melt the irradiated laser light L to form the metal thick film 15 and the integrated layer 26 is used. be able to. Examples of the material of the connecting metal member 16 that can be used other than SUS include Cu and Ni.

  For the connecting metal member 16 and the metal thick film 15, it is desirable to select a combination of metals so that the melting point of the connecting metal member 16 is higher than the melting point of the metal thick film 15.

  It is not always essential that the melting spot 20 is provided by completely filling the connecting metal member 16 and the electrode layer 14. By irradiation with the laser light L, a part of the connecting metal member 16 and the electrode layer 14 may be evaporated, and a gap may be formed in a part of the melting spot 20. At the interface between the connecting metal member 16 and the electrode layer 14, a part 26a of the integrated layer exists around the melting spot 20 (see FIG. 1). Thus, even if a gap is generated in a part of the melting spot 20, a part 26 a of the integrated layer exists at the interface between the connecting metal member 16 and the electrode layer 14 around the melting spot 20. By doing so, the connecting metal member 16 and the electrode layer 14 are joined.

5. Example First, the connecting metal member was welded to the electrode layer on the flexible insulating substrate, and the joint strengthening portion between the flexible insulating substrate and the electrode layer was observed.

  A polyimide resin sheet with a thickness of 50 μm was used as the flexible insulating substrate. On this polyimide resin sheet, an Au layer was formed to a thickness of 200 nm by sputtering to form a metal thin film. On the metal thin film, a Ni plating layer was formed to a thickness of 10 μm to form a metal thick film. An electrode layer is constituted by the metal thin film and the metal thick film.

  On the electrode layer, a lead frame made of SUS (thickness: 80 μm) as a metal member for connection was placed, and a laser beam with a beam diameter of 0.2 mm and an output of 0.3 kW was irradiated for an irradiation time of 1 ms. As a result, the connecting metal member and the metal thick film were joined to produce a joined structure.

  FIG. 7A shows a cross-sectional photomicrograph in the vicinity of the melting spot of the obtained bonded structure. An electrode layer 14 is formed on the flexible insulating substrate 12, and a connecting metal member 16 is provided on the electrode layer 14. In the melting spot 20, the connecting metal member 16 and the electrode layer 14 are both melted and partly evaporated to form voids.

  FIG. 7B shows an enlarged image of the interface (region X) between the flexible insulating substrate 12 and the electrode layer 14 around the molten spot 20. The electrode layer 14 includes a metal thin film 13 and a metal thick film 15 on the metal thin film 13. At the interface 19 between the flexible insulating substrate 12 and the electrode layer 14, a bonding reinforcing portion 18 in which the flexible insulating substrate 12 and the electrode layer 14 are engaged is confirmed.

  FIG. 8 shows the center of the melting spot 20 and the beam diameter BD in the bonded structure produced here. The beam diameter BD is 0.2 mm. In FIG. 8, the position of D1 (50 μm) from the center of the melting spot 20 is A, and the position of D2 (200 μm) is B. 7A and FIG. 8 together, it can be seen that the bonding strengthening portion 18 exists in the region of D1 or more and D2 or less.

  Next, a sample of a bonded structure was prepared by changing the number of melting spots, and the bonding strength between the flexible insulating substrate and the electrode layer was examined.

Example 1
In Example 1, a sample 40A as shown in FIG. 9 was produced.

In producing the sample 40A, first, an Au layer (thickness: 200 nm) as the metal thin film 13 is formed by sputtering on two places on the polyimide resin sheet (thickness: 50 μm) as the flexible insulating substrate 12. did. On each metal thin film 13, a Ni plating layer (thickness 10 μm) as a metal thick film 15 was formed with an area of 4.5 mm ² .

  An SUS lead frame (thickness: 80 μm) as a connecting metal member 16 is arranged so as to overlap with the metal thick film 15, and the metal thick film 15 and the connecting metal member 16 are joined by irradiating laser light. Sample 40A was obtained.

The laser light irradiation conditions were a beam diameter of 0.2 mm, an output of 0.3 kW, and an irradiation time of 1 ms. The number of melting spots 20 was 12 for each connecting metal member 16. In this case, the density of the melting spot 20 is 2.67 points / mm ² .

  As shown in FIG. 9, the sample 40A of Example 1 was provided with 24 melting spots 20 in total. At the interface between the flexible insulating substrate 12 and the metal thin film 13, a bonding strengthening portion (not shown) was confirmed around the melting spot 20.

  Furthermore, the sample of Example 2 and the prior art example was produced by the same method as Example 1 except having changed the following points.

(Example 2)
A sample of Example 2 was produced in the same manner as in Example 1 except that the number of melting spots 20 formed on each connecting metal member 16 was changed to 15. A plan view of the sample of Example 2 is shown in FIG. As shown in FIG. 10, the sample 40B of Example 2 was provided with 30 melting spots 20 in total. In this case, the density of the melt spot 20 is 3.33 points / mm ² .

  As in the case of the sample 40A of the first embodiment, also in the sample 40B of the second embodiment, a bonding strengthening portion (not shown) is provided around the melting spot 20 at the interface between the flexible insulating substrate 12 and the metal thin film 13. confirmed.

(Conventional example)
A sample of a conventional example was produced in the same manner as in Example 1 except that the connecting metal member 16 and the metal thick film 15 were joined by resistance welding. A plan view of a sample of a conventional example is shown in FIG. 11A, and a side view is shown in FIG. 11B. As shown in FIGS. 11A and 11B, in the sample 140 of the conventional example, two melting spots 120 are formed at the interface between the connecting metal member 16 and the metal thick film 15. The diameter of the melting spot 120 was about 150 μm. In the sample 140 of the conventional example, there is no bonding reinforcement portion at the interface between the flexible insulating substrate 12 and the metal thin film 13.

<Measurement of physical properties>
The samples of Examples 1 and 2 and the conventional example were peeled in the direction in which the flexible insulating substrate 12 was peeled from the connecting metal member 16, and the breaking strength was measured. A digital force gauge ZTA-5N manufactured by Imada Co., Ltd. was used for the measurement of the breaking strength. The samples of the examples and comparative examples are shown in FIG. 12 with the maximum strength until peeling at the interface between the flexible insulating substrate 12 and the metal thin film 13 as the breaking strength.

Since resistance welding in the conventional example is one-side spot welding, the number of welding spots cannot be changed substantially. As for the form of the welded portion, Examples 1 and 2 (laser welding) are metal compound formation, whereas in the conventional example (resistance welding), joining by solid phase diffusion is used. In each of Examples 1 and 2 and the conventional example, the fracture occurs between the flexible insulating substrate 12 and the electrode layer 14, but there is a possibility that the fracture occurs at other portions. From these points, the samples of Examples 1 and 2 and the conventional example were compared by breaking strength. In either case, the electrode area is 4.5 mm ² .

  The sample of Example 1 has a breaking strength exceeding the conventional example in which the connecting metal member 16 is joined to the metal thick film 15 by resistance welding. As shown in the results of Example 2, when the number of melting spots 20 is increased, higher breaking strength can be obtained.

  Generally, the joint strength of the joint surface by welding is proportional to the number of welding spots. For example, when the intensity per spot is 300 mN, if the number of spots is three, the bonding strength of the bonding surface is 900 mN. Actually, when the strength between the electrode layer 14 and the connecting metal member 16 is improved, the strength between the flexible insulating substrate 12 and the electrode layer 14 is increased. Below the strength between. For this reason, the breaking strength matches the interface strength between the flexible insulating substrate 12 and the electrode layer 14.

  When the sample of the conventional example is broken for strength measurement, it breaks at the interface between the flexible insulating substrate 12 and the electrode layer 14. In this case, the strength remains at 600 mN. What can be improved by conventional resistance welding is the strength of the joint surface by welding, that is, the strength between the electrode layer 14 and the connecting metal member 16. Resistance welding cannot improve the breaking strength of the sample.

  On the other hand, the breaking strengths of the samples of Examples 1 and 2 are 850 mN and 1000 mN, respectively. In the sample of the example, the strength of the interface between the original flexible insulating substrate 12 and the electrode layer 14 was higher than 600 mN, and the interface strength between the flexible insulating substrate 12 and the electrode layer 14 was increased. I understand.

  In the sample of the example, the part that changes at the interface between the flexible insulating substrate 12 and the electrode layer 14 before and after welding is only the joint strengthening part. The breaking strength is improved in proportion to the number of welding spots. From these facts, it can be seen that the joint strengthening portion improved the interfacial strength between the flexible insulating substrate 12 and the electrode layer 14 and improved the breaking strength of the entire sample.

6). Application to Temperature Sensor The bonding structure according to the present embodiment can be applied to bonding of a pattern electrode and a lead frame in a temperature sensor as shown in FIGS. 13A and 13B.

  The illustrated temperature sensor 50 includes a pair of lead frames 16A, a sensor unit 53 connected to the pair of lead frames 16A, and an insulating holding unit that is fixed to the pair of lead frames 16A and holds the pair of lead frames 16A. 54. The holding part 54 has an opening 54a for attachment. The pair of lead frames 16A corresponds to the connecting metal member 16 in the joint structure 10 shown in FIG.

  The pair of lead frames 16A is formed of an alloy such as a copper-based alloy, an iron-based alloy, or stainless steel, and is supported by a resin-made holding portion 54 at a constant interval. The pair of lead frames 16 </ b> A is connected to the pair of lead wires 55 within the holding portion 54.

  The sensor unit 53 is a film type thermistor sensor provided with an insulating film 12A. As the insulating film 12A, a polyimide resin sheet having a thickness of 7.5 to 125 μm is used. The insulating film 12 </ b> A corresponds to the flexible insulating substrate 12 in the bonded structure 10.

  A thin film thermistor portion 57 patterned with a thermistor material is provided on the surface of the insulating film 12A. A pair of patterned comb electrodes 58 are formed on the thin film thermistor portion 57. A pair of pattern electrodes 13A is formed on the surface of the insulating film 12A so as to be connected to the pair of comb-shaped electrodes 58. The thin film thermistor portion 57 and the comb-shaped electrode 58 are covered with an insulating protective film 60.

  The thermistor material forming the thin film thermistor portion 57 is a metal nitride represented by the general formula: TixAlyNz (0.70 ≦ y / (x + y) ≦ 0.95, 0.4 ≦ z ≦ 0.5, x + y + z = 1) It is. The metal nitride has a hexagonal wurtzite single-phase crystal structure. The thickness of the thin film thermistor portion 57 is generally about 10 to 1000 nm.

  The pair of comb-shaped electrodes 58 is formed in a comb-shaped pattern in which comb portions (not shown) are alternately arranged on the thin film thermistor portion 57 so as to face each other. The comb-shaped electrode 58 has a laminated structure of a base layer made of Cr or NiCr with a thickness of 5 to 100 nm and an Au layer with a thickness of 50 to 1000 nm.

  The pair of pattern electrodes 13 </ b> A has tips connected to the comb-shaped electrodes 58. The base ends of the pair of pattern electrodes 13A serve as terminal portions joined to the lead frame 16A. Similar to the comb-shaped electrode 58, the pattern electrode 13A has a laminated structure of an underlayer made of Cr or NiCr with a thickness of 5 to 100 nm and an Au layer with a thickness of 50 to 1000 nm. The pattern electrode 13 </ b> A corresponds to the metal thin film 13 in the bonded structure 10.

  A lead frame 16A is joined to each terminal portion of the pair of pattern electrodes 13A via a Ni plating layer (not shown) having a thickness of 5 to 15 μm. The Ni plating layer interposed between the terminal portion of the pattern electrode 13 </ b> A and the lead frame 16 </ b> A corresponds to the metal thick film 15 in the bonded structure 10.

  The pair of lead frames 16A joined to the terminal portion of the pattern electrode 13A extends on the surface of the insulating film 12A with the thin film thermistor portion 57 interposed therebetween, and is bonded to the insulating film 12A. The surface of the insulating film 12A provided with the thin film thermistor portion 57, the pattern electrode 13A, and the lead frame 16A is entirely covered with an insulating protective sheet 61.

  In the temperature sensor 50, the pattern electrode 13A and the like are formed on the insulating film 12A to obtain the sensor portion 53, and the lead frame 16A is joined to the terminal portion of the pattern electrode 13A via a metal thick film (not shown). Can be manufactured. Below, the manufacturing method of the temperature sensor 50 is demonstrated concretely. As the insulating film 12A in the sensor unit 53, a polyimide resin sheet having a thickness of 50 μm is used.

  In producing the sensor portion 53, first, a thin film thermistor portion 57 as shown in FIGS. 14A and 14B is formed on the insulating film 12A. The thin film thermistor portion 57 forms a TixAlyNz (x = 0.09, y = 0.43, z = 0.48) alloy film on the entire surface of the insulating film 12A, and patterns the formed TixAlyNz alloy film. Can be obtained.

The TixAlyNz alloy film can be formed by reactive sputtering using a Ti—Al alloy sputtering target. Sputtering is performed at an ultimate vacuum of 5 × 10 ⁻⁶ Pa, a sputtering gas pressure of 0.4 Pa, a target input power (output) of 200 W, and in a mixed gas atmosphere of Ar gas + nitrogen gas with a nitrogen gas fraction of 20%. Thus, a TixAlyNz alloy film having a thickness of 200 nm is formed.

  A resist solution is applied onto the formed TixAlyNz alloy film with a bar coater and pre-baked at 110 ° C. for 90 seconds to form a resist film. A predetermined region of the resist film is exposed, and unnecessary portions of the resist film are removed with a developer. Further, a resist pattern is obtained by post-baking at 150 ° C. for 5 minutes.

  Using the resist pattern as a mask, wet etching is performed with a commercially available Ti etchant to remove unnecessary portions of the TixAlyNz alloy film. By stripping the resist pattern, a thin film thermistor portion 57 having a predetermined shape is obtained at a predetermined position of the insulating film 12A (FIGS. 14A and 14B).

  As shown in FIG. 15A, a conductive film such as a pair of comb-shaped electrodes 58 and a pattern electrode 13A is formed on the insulating film 12A on which the thin film thermistor portion 57 is provided. As shown in FIG. 15B, the pair of comb electrodes 58 are provided so as to be connected to the thin film thermistor portion 57 and cover the thin film thermistor portion 57. In order to form a conductive film, first, a Cr layer (thickness 20 nm) and an Au layer (thickness 200 nm) are sequentially formed by sputtering to obtain a metal laminated film.

  A resist solution is applied onto the metal laminated film with a bar coater and pre-baked at 110 ° C. for 90 seconds to form a resist film. A predetermined region of the resist film is exposed, and unnecessary portions of the resist film are removed with a developer. Further, post-baking is performed at 150 ° C. for 5 minutes to obtain a resist pattern.

  Using the resist pattern as a mask, wet etching is sequentially performed with a commercially available Au etchant and Cr etchant to remove unnecessary portions of the metal laminated film. The resist pattern is peeled off, and a pair of comb electrodes 58 having a plurality of comb portions 58a and a pattern electrode 13A connected to each comb electrode 58 are obtained. The pair of comb-shaped electrodes 58 are formed to face each other so that the comb portions 58a are staggered. The base end of the pattern electrode 13A serves as a terminal portion 13B connected to a lead frame (not shown).

  The pair of comb electrodes 58 and the pattern electrode 13 </ b> A can also be provided between the insulating film 12 </ b> A and the thin film thermistor portion 57. In this case, the metal laminate film as described above may be formed on the insulating film 12A before the thin film thermistor portion 57 is formed, and wet etching may be performed.

  An insulating protective film 60 is formed so as to cover the comb electrode 58 connected to the thin film thermistor portion 57 as shown in FIGS. 16A and 16B. As the insulating protective film 60, for example, a polyimide film having a thickness of 20 μm can be used. The polyimide film is obtained by applying polyimide varnish by a printing method and curing at 250 ° C. for 30 minutes. In this way, the sensor unit 53 in which the thin film thermistor unit 57, the comb electrode 58, and the pattern electrode 13A are provided on the insulating film 12A is manufactured.

  On the terminal portion 13B of the pattern electrode 13A on the sensor portion 53, as shown in FIG. 17A, a thick metal film made of a Ni plating layer 15A is formed to a thickness of 10 μm. As shown in FIG. 17A, an electrode layer 14A is constituted by a laminated structure of a terminal portion 13B of a patterned electrode 13A (metal thin film) provided on the surface of the insulating film 12A and a Ni plating layer 15A (metal thick film). The

  A lead frame 16A (thickness 80 μm) is disposed on the Ni plating layer 15A as shown in FIG. 17B, and the laser beam L is irradiated from the lead frame 16A side. As shown in FIGS. 18A and 18B, the pair of lead frames 16A held by the holding portion 54 is provided on the insulating film 12A and connected to the sensor portion 53 by the laser light irradiation. 16 A of lead frames are joined to the electrode layer (not shown) in the sensor part 53 by welding.

  At the joint between the lead frame 16A and the pattern electrode 13A, a melting spot (not shown) is formed from the surface of the lead frame 16A to the surface of the insulating film 12A. As described with reference to FIG. 1, the interface between the insulating film 12 </ b> A and the pattern electrode 13 </ b> A is a joint strengthening portion (not shown) in which the insulating film 12 </ b> A and the pattern electrode 13 </ b> A mesh with each other around the melting spot. Have

  In the sensor part 53, the protective sheet 61 is affixed on the surface of the insulating film 12A provided with a pair of lead frames 16A. As the protective sheet 61, a polyimide film with an adhesive can be used. Thus, the temperature sensor 50 shown in FIGS. 13A and 13B is obtained.

  As described above, in the temperature sensor 50, the lead frame 16A is joined to the terminal portions 13B of the pair of pattern electrodes 13A (metal thin film) by laser welding via the Ni plating layer 15A (metal thick film). By interposing the Ni plating layer 15A, the strength of the joint can be further increased, and it can be used well even in a high temperature environment.

  The Ni plating layer 15A as the metal thick film is not provided on the entire surface of the pattern electrode 13A but partially on the terminal portion 13B with a thickness of 5 to 15 μm. Therefore, the thickness of the entire pattern electrode 13A increases. Heat capacity does not increase. Therefore, the problem that the responsiveness of the sensor part 53 falls can be avoided.

  In addition to the temperature sensor, in a humidity sensor using a thermistor, a lead frame as a connecting metal member and a pattern electrode as a metal thin film are joined by laser welding via a metal thick film. A similar effect can be obtained.

DESCRIPTION OF SYMBOLS 10 Joining structure 12 Flexible insulating substrate 14 Electrode layer 16 Metal member for connection 18 Bonding reinforcement part 20 Melting spot

Claims (11)

A flexible insulating substrate, an electrode layer formed on the flexible insulating substrate, and a connection metal member welded to the electrode layer, the flexible insulation from the surface of the connection metal member A bonded structure provided with a melting spot reaching the surface of the substrate,
An interface between the flexible insulating substrate and the electrode layer has a bonding strengthening portion in which the flexible insulating substrate and the electrode layer are engaged with each other around the melting spot.   The bonded structure according to claim 1, wherein the flexible insulating substrate is a polyimide resin sheet.   The bonded structure according to claim 1, wherein the electrode layer includes a metal thin film formed on a surface of the flexible insulating substrate, and a metal thick film that protects the metal thin film.   4. The joining structure according to claim 3, wherein the connecting metal member is made of a metal having a melting point higher than that of the metal thick film.   The joint strengthening portion includes a plurality of convex portions, the height of the convex portions is 0.1 to 0.5 μm, and the distance between adjacent convex portions is 0.1 to 1.5 μm. The bonded structure according to any one of claims 1 to 4.   The bonded structure according to any one of claims 1 to 5, wherein the bonding strengthening portion exists around the melting spot with a width of 3 to 30 µm.   The joining structure according to any one of claims 1 to 6, wherein the joining strengthening portion is provided in a range of 50 µm or more and 200 µm or less from a center of the melting spot.   The joining structure according to any one of claims 1 to 7, wherein a plurality of the melting spots are provided and the distance between the centers is adjacent to each other with a distance of 500 µm or more. 9. The joined structure according to claim 8, wherein the melting spots are provided at a density of 1.25 points or more per 1 mm ² .   The bonded structure according to claim 3, wherein the metal thin film is a pattern electrode provided in contact with a thin film thermistor of a temperature sensor. The junction structure according to claim 3, wherein the thick metal film is partially provided on a surface of the metal thin film.

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