JP3743716B2 - Flexible wiring board and semiconductor element mounting method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flexible wiring board having a multilayer structure and a method for mounting a semiconductor element.
[0002]
[Prior art]
A flexible wiring board has a multilayer structure in which a metal wiring pattern is formed on the surface or front and back surfaces of a flexible film substrate and is appropriately protected by a resin or the like, and is mainly disposed between electronic components and devices. Often used as a connection circuit board. There are also devices on which semiconductor elements such as IC and LSI, electronic components, and the like are mounted. Due to the flexibility of the flexible wiring board, it can absorb minute positional shifts and vibrations between electronic components and devices, and can be used by being bent. , Are used a lot.
[0003]
The structure of a conventional flexible wiring board is shown in FIG. The flexible wiring board FC has metal wirings 2A and 2B made of copper or the like formed in a predetermined shape on the front and back surfaces of the film substrate 1 made of a resin film such as polyimide, and the through hole 5 and the through hole plating. The wirings 2A and 2B on the front and back surfaces are appropriately conducted by 5a. In the mounting area 3 on the film substrate 1, an electrode terminal P is formed by wiring 2A, and a semiconductor element 4 such as an LSI is mounted. Further, a protective agent (a cover film made of urethane solder resist, polyimide, or the like) 6 is disposed to protect the wirings 2A and 2B. As shown in FIG. 3, the cross-sectional shape of the flexible wiring board FC is such that the film substrate 1, the wirings 2A and 2B, and the protective agent 6 overlap each other, and the flexible wiring board FC having such a shape is a flexible wiring having a multilayer structure. Also called a substrate.
[0004]
The semiconductor element 4 is mounted by thermocompression bonding using an anisotropic conductive resin film (ACF) 7 that is a paste or film adhesive. ACF7 is obtained by dispersing conductive particles in a thermoplastic or thermosetting resin film. As shown in FIG. 4, the mounting method is such that the flexible wiring board FC is fixed to the transfer stage S, ACF 7 is applied to the mounting area 3, the semiconductor element 4 is aligned, and the heating tool 8 moves up and down from above. It is performed by heating and pressing. As a result, the conductive particles of the ACF 7 are in close contact between the connection terminal 4a of the semiconductor element 4 and the electrode terminal P, and the connection terminal 4a and the electrode terminal P are conducted.
[0005]
[Problems to be solved by the invention]
When the wirings 2A and 2B and the protective agent 6 are formed on both surfaces of the flexible wiring board FC, the wiring 2B and the protective agent 6 are also formed on the back surface side of the mounting region 3 on which the semiconductor element 4 is mounted. The pressure during thermocompression bonding was absorbed in each layer. That is, when the semiconductor element 4 is mounted, between the semiconductor element 4 to be heated and pressurized and the transfer stage S, in addition to the ACF 7, the electrode terminal P by the wiring 2A, the film substrate 1, the wiring 2B, and the protective agent 6 are arranged in this order. When the semiconductor element 4 is mounted on the flexible wiring board FC having a multilayer structure via the ACF 7 through the four layers, the pressure by the heating tool 8 is deprived by each layer, the adhesion of the conductive particles of the ACF 7 is reduced, and the conduction is reduced. There was a problem that stability could not be obtained. Further, when the pattern shape of the wiring 2B on the back surface side is not uniform in the mounting region 3, the pressure by the heating tool 8 is not constant, and thus there is a problem that the adhesion of the conductive particles of the ACF 7 is biased. . In addition, a continuity test by energization is performed after mounting. However, depending on the degree of unevenness of adhesion, even if continuity is recognized during the continuity test, the continuity test may not be performed thereafter due to vibration or aging degradation. In addition, a power source, a measuring instrument, and the like are necessary for the continuity test, and the labor and cost are problematic when conducting a complete test especially in the case of mass-produced products.
[0006]
Accordingly, an object of the present invention is to uniformly adhere a paste-like or film-like adhesive with sufficient pressure when a semiconductor element is thermocompression bonded to a flexible wiring board having a multilayer structure using a paste-like or film-like adhesive. Accordingly, it is an object to provide a flexible wiring board with high reliability and a method for mounting a semiconductor element on the board.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the flexible wiring board according to claim 1 of the present invention has at least a wiring layer having electrode terminals on both the front and back surfaces of the film substrate, and a semiconductor element is mounted on the mounting region on the film substrate. In a flexible wiring board having a multilayer structure in which the connection terminal of the semiconductor element is electrically connected to the wiring layer by being heat-pressed using a paste-like or film-like adhesive, mounting in the mounting area of the film substrate. A region on the back surface side of the semiconductor element formed is formed with a region where the wiring layer is not disposed with an area equal to or larger than the bottom area of the semiconductor element.
[0008]
According to the present invention, on the back surface side of the mounting area where the semiconductor element is mounted, the area where the wiring layer is not disposed is formed in an area equal to or larger than the bottom area of the semiconductor element. When mounting by thermocompression bonding, pressure is not absorbed by the wiring layer on the back surface side, and the connection reliability of mounting of the semiconductor element can be improved.
[0009]
Moreover, the flexible wiring board according to claim 2 of the present invention is based on the invention according to claim 1, and the film substrate is positioned at a position of a semiconductor element to be mounted or a position of a connection terminal of the semiconductor element to be mounted. However, it is transparent so that it can confirm from the area | region where the said wiring layer is not distribute | arranged. Here, when the paste-like or film-like adhesive is an anisotropic conductive film (ACF), the film substrate is transparent so that the conductive particles in the adhesive can be confirmed from the region where the wiring layer is not disposed. It is also good.
[0010]
According to this invention, after mounting the semiconductor element, the position of the semiconductor element, the position of the connection terminal of the semiconductor element from the back side of the film substrate, or the conductive particles of the adhesive in the case of the anisotropic conductive film (ACF) Can be confirmed. Therefore, the connection part can be confirmed by a simple appearance inspection before conducting a conduction test by energization.
[0011]
According to a third aspect of the present invention, there is provided a method for mounting a semiconductor element on a flexible wiring board. When the semiconductor element is mounted on the flexible wiring board according to the first or second aspect by thermocompression bonding, A fixing plate having the same area and the same or larger thickness as that of the region is fitted into a region that is not disposed, and after applying heat and pressure, the fixing plate is removed.
[0012]
According to the present invention, since the fixing plate is fitted into the area where the wiring layer is not disposed and heat and pressure are applied, the pressure applied to the semiconductor element can be reliably received by the fixing plate without any gaps. Therefore, when the flexible wiring board according to claim 1 or 2 is mounted and heated and pressurized while being fixed to a transfer stage having the same shape as the conventional one, the thickness of the wiring layer etc. on the back side is reduced. Compared with the case where a gap is formed between the semiconductor element and the transfer stage, the method of the present invention can more effectively apply pressure to the semiconductor element.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional structure diagram of the flexible wiring board of the present embodiment, and FIG. 2 is a diagram showing a structure in which a semiconductor element is mounted on the flexible wiring board of the present embodiment. In the flexible wiring board FC of the present embodiment, metal wirings 2A and 2B made of copper or the like are formed in a predetermined shape on the front and back surfaces of the film substrate 1 formed of a resin film such as polyimide, and through holes. 5 and through-hole plating 5a, the wirings 2A and 2B on the front and back surfaces are appropriately conducted. The film substrate 1 is translucent, and the wiring 2A on the front side can be confirmed from the back side. The film substrate 1 does not need to be completely colorless and transparent, and may be transparent to the extent that desired matters can be confirmed with the naked eye or a microscope from the back side. The desired matter is the position of the semiconductor element to be mounted, the position of the connection terminal of the semiconductor element to be mounted, or the paste-like or film-like adhesive is an anisotropic conductive film (ACF). In the case of the semiconductor element 4 with protruding electrodes (bumps), which will be described later, the protruding particles are conductive particles in the adhesive. In addition, in order to make it easy to confirm these desired matters, it is possible to color the object. The film substrate 1 can be made nearly transparent by reducing the thickness of the film substrate 1 (for example, about 25 μm). In the mounting area 3 on the film substrate 1, an electrode terminal P is formed by wiring 2A, and a semiconductor element 4 such as an IC or LSI is mounted. Further, a protective agent (a cover film made of urethane solder resist, polyimide, or the like) 6 is disposed to protect the wirings 2A and 2B.
[0014]
Then, on the back side of the mounting region 3 where the semiconductor element 4 is mounted, a window 9 from which the wiring 2B on the back side and the protective agent 6 are removed is formed so as to be a rectangle having a slightly larger area than the semiconductor element 4. ing. The window 9 is a region where a wiring layer, a protective layer, or the like on the back surface of the film substrate 1 is not disposed, and is formed in a rectangular shape. In the present embodiment, the length of one side of the rectangular window 9 is about 1.5 to 2 times the length of one side of the semiconductor element 4 mounted on the back side of the window 9. 4 is formed so that a gap is formed between the side of the window 9 and the side of the semiconductor element 4, but on the back surface of the window 9, the inside of the window 9 (enclosed by the side of the window 9). As long as the semiconductor element 4 can be fitted in the portion, the size may be the same, and the shape does not matter. In the case of the semiconductor element 4 with bump electrodes (bumps), it is possible to form the window 9 only on the bumps to be connected.
[0015]
The semiconductor element 4 is mounted by thermocompression bonding using an anisotropic conductive film (ACF) 7 which is a paste-like or film-like adhesive. ACF7 is obtained by dispersing conductive particles in a thermoplastic or thermosetting resin film. Specifically, the conductive particles are dispersed in an insulating adhesive, and are conductive in the thickness direction (connection direction) and insulative in the surface direction (lateral direction), and are composed of conductive particles and an adhesive. Is done. The connection is basically thermocompression bonding, in which the conductive particles are in charge of the electrical connection function and the adhesive is in charge of the function of maintaining the pressure contact state. An insulating film is applied to the surface of the conductive particles, and when the pressure is applied in a specific direction, the insulating film is partially destroyed. As the material of the insulating film, a lot of resin is used. In addition, there is also one that heat-presses so as to crush the conductive particles. In the case of ACF7, the paste-like or film-like adhesive used in the present invention does not limit the configuration of the conductive particles and the adhesive, and any general-purpose adhesive can be used as long as it is used by thermocompression bonding. ACF may be sufficient, and in cases other than ACF, a conductive adhesive (conductive paste) or cream solder may be used.
[0016]
When the semiconductor element 4 is mounted, the flexible wiring board FC is fixed to the transfer stage S as shown in FIG. A fixed plate 10 having the same shape as the window 9 and a size that can be fitted into the window 9 is attached to the transfer stage S in advance, and the flexible wiring board FC is fixed so that the fixed plate 10 is fitted into the window 9. Next, ACF 7 is applied to the mounting region 3, the semiconductor element 4 is aligned, and heated and pressed by the heating tool 8 from above (the back side of the mounting surface of the semiconductor element 4). Thereby, the conductive particles of the ACF 7 are in close contact between the connection terminal 4a of the semiconductor element 4 and the electrode terminal P, and the connection terminal 4a and the electrode terminal P are electrically connected. Specifically, when the semiconductor element 4 is mounted, only the electrode terminal P and the film substrate 1 by the wiring 2 </ b> A are interposed between the fixing plate 10 and the semiconductor element 4 in addition to the ACF 7. For this reason, the pressure by the heating tool 8 is not absorbed by the wiring 2B and the protective agent 6 on the back surface side, and the pressure is applied to the semiconductor element 4 without deviation. As a result, pressure is applied to the conductive particles without being biased, and the insulating film of the conductive particles is evenly broken, or the elasticity (restorability) of the conductive particles is effectively exhibited. Therefore, the conductive particles of the ACF 7 are in close contact with the connection terminal 4a and the electrode terminal P of the semiconductor element 4 without being biased, and stable conduction is obtained.
[0017]
In order to effectively obtain pressure by the heating tool 8, the thickness of the fixing plate 10 needs to be at least larger (thick) than the depth of the window 9. Although the fixing plate 10 of the present embodiment is made of stainless steel, it can sufficiently withstand the heat and pressure generated by the heating tool 8 and has sufficient hardness so as not to absorb the pressure generated by the heating tool 8. Any other metal, ceramic, or resin may be used. In addition, since the fixing plate 10 is manufactured in accordance with the shape of the window 9, it is preferable that the fixing plate 10 be attached to and detached from the conventional transfer stage S (preferably to be detachable). Note that it is possible to form the fixed plate 10 as a transfer stage S integrated with the transfer stage, depending on the implementation.
[0018]
As described above, in the present embodiment, the case where the semiconductor element 4 is mounted on the flexible wiring board FC has been described as an example. However, the present invention can also be applied to the case where other electronic elements such as capacitors and electronic components are mounted.
[0019]
【The invention's effect】
In the flexible wiring board having a multilayer structure of the present invention, a region where a wiring layer or the like is not disposed is formed on the back surface side of the mounting region where the semiconductor element is mounted, in the same area as or larger than the bottom area of the semiconductor element. Therefore, when mounting a semiconductor element by thermocompression bonding via a paste or film adhesive, sufficient pressure can be applied without absorbing the pressure on the wiring layer on the back side, and connection reliability Can be increased. Further, by bringing the film substrate closer to transparency, the position of the semiconductor element, the position of the connection terminal of the semiconductor element, and the like can be confirmed from the back side of the film substrate after the semiconductor element is mounted. Therefore, before conducting a continuity test by energization, it is possible to select a part with a good mounting state by checking the connection part by a simple visual inspection, and only those with a high probability of a good mounting state. Can be subjected to a continuity test.
[0020]
Further, according to the method for mounting a semiconductor element of the present invention, the pressure applied to the semiconductor element does not go through a gap by inserting a fixing plate in a region where the wiring layer and the protective layer are not arranged and applying heat and pressure. It can be reliably received by a fixed plate. Therefore, when mounting the flexible wiring board according to claim 1 or 2 and fixing it to the transfer stage having the same shape as that of the prior art and applying heat and pressure, the thickness of the wiring layer etc. on the back side can be reduced. As compared with the case where there is a gap between the transfer stage and the transfer stage, the semiconductor element mounting method of the present invention can more effectively apply pressure to the semiconductor element, and a highly reliable flexible wiring board can be obtained. .
[0021]
[Brief description of the drawings]
FIG. 1 is a cross-sectional structure diagram of a flexible wiring board in an embodiment of the present invention. FIG. 2 is a diagram showing a mounting structure of a semiconductor element in an embodiment of the present invention. FIG. 4 is a diagram showing a mounting structure of a semiconductor element in a conventional form.
DESCRIPTION OF SYMBOLS 1 Film substrate 2A, 2B Wiring 3 Mounting area | region 4 Semiconductor element 4a Connection terminal 5 Through-hole 5a Through-hole plating 6 Protective agent 7 ACF
8 Heating tool 9 Window (area where wiring layer and protective layer are not arranged)
10 Fixed plate FC Flexible wiring board P Electrode terminal S Transfer stage

Claims (3)

At least wiring layers having electrode terminals are provided on both the front and back surfaces of the film substrate, and the semiconductor element is thermally bonded to the mounting region on the film substrate using a paste-like or film-like adhesive. In a flexible wiring board having a multilayer structure in which the connection terminal is electrically connected to the wiring layer,
In the mounting region on the film substrate, a portion on the back surface side of the semiconductor element mounted is formed with a region where the wiring layer is not disposed in the same area as or larger than the bottom area of the semiconductor element. Flexible wiring board. 2. The film substrate is transparent so that a position of a semiconductor element to be mounted or a position of a connection terminal of the semiconductor element to be mounted can be confirmed from a region where the wiring layer is not disposed. The flexible wiring board as described. When the semiconductor element is mounted on the flexible wiring board according to claim 1 by thermocompression bonding, a fixing plate having the same area and the same or larger thickness as that of the area is fitted in the area where the wiring layer is not disposed. A method for mounting a semiconductor element, wherein the fixing plate is removed after applying heat and pressure.

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