Patent Application
20050205291
The present invention relates to a flexible substrate, and a process for producing the same. In particular, the present invention relates to a flexible substrate and a multilayer flexible substrate in which a part of a front-sided wiring pattern and a part of a rear-sided wiring pattern are jointed to each other in such a manner that they penetrate through a film, and also relates to a process for producing the same.
Recently, not only is electronics device becoming smaller, lighter and thinner, but also the electronic circuit is becoming high-speed processing. Therefore, it has been considerably required to achieve a miniaturization and a high frequency-wave performance of the electronic components. For example, as to a portable electronics device such as a cellular phone, it is one of the most important challenges to achieve a smaller, lighter and thinner device (see Japanese Patent Kokai Publication No. 2003-163422, for example). Accordingly, it is needed that a miniaturization and a high frequency-wave performance are achieved by mounting various types of the mounted-components with a short length of the wiring at a high density.
In these circumstances, a flexible substrate which leads to achievement of a high-density mounting is getting so much attention (see Japanese Patent Kokai Publication No. 2001-111189, for example). Hereinafter, a process for producing a conventional flexible substrate will be described with respect to
First, as shown in
In the next place, with respect to
First, as shown in
As described above, an etching technique (i.e. a wet process) is employed for the purpose of forming the wire pattern in the case of the conventional production process. Therefore, an influence of an etchant on an insulating sheet is of concern. In this case, it was troublesome to carry out the washing and drying steps as a post-treatment. Furthermore, the conventional wiring patterns formed by the etching technique are exposed to their surroundings on the surfaces of a flexible substrate. This will cause a microcrack of the wiring patterns when the flexible substrate is folded, which will be far from satisfying in terms of a flexing life.
Considering that the conventional process comprises the step for forming through-holes and thereafter filling the through-holes with a conductive paste, such conventional production process is fundamentally the same as a process for producing a rigid substrate (i.e. typical print circuit). The above-mentioned step is cumbersome (because of taking about 3 hours), so it is desired to simplify or abbreviate it. However, it has been considered that such step is essential for producing the flexible substrate as well as the multilayer flexible substrate, and that it is therefore basically difficult to abbreviate it. Also, due to an essential step, such step has been regarded as a matter of no concern. Therefore, there is no process for producing a flexible substrate and a multilayer flexible substrate with careful regard to the issues as described above.
Therefore, an object of the present invention is to provide a process for producing a flexible substrate and a multilayer flexible layer wherein a formation of through-holes and a filling of a conductive paste are abbreviated. Also, a further object of the present invention is to provide a flexible substrate and a multilayer flexible substrate as obtained by such process.
In order to achieve the object, the present invention provides a process (referred to also as “production process (I)” for producing a flexible substrate comprising of a film, an insulating resin layer and a wiring pattern, said process comprising the steps of:
Also, the present invention provides a process (referred to also as “production process (II)”) for producing a flexible substrate comprising of a sheet member and a substrate, said process comprising the steps of;
Furthermore, the present invention provides a process for producing a multilayer flexible substrate wherein the step of the production process (I) and/or production process (II) as well as the step of for stacking further another flexible substrates is included. In addition, the present invention provides a multilayer flexible substrate obtained by such process.
The “junction (i.e. junction section)”, which is formed due to the joint or dent, serves to electrically connect the front-sided wiring pattern and the rear-sided wiring pattern to each other. Therefore, the term “junction” is herein referred to also as “interlaminar junction”.
As to a connection of the wiring patterns, the production processes (I) and (II) does not require a formation of through-holes and a filling of a conductive paste. According to the present invention, wiring patterns may be connected to each other by means of a needle-like member or a roll member with protrusions, for example. In the case where the roll member with a plurality of protrusions is used as a pair of roll members, a plurality of interlaminar junctions can be formed when a sheet member passes through a pair of roll members. Therefore, it is possible for production processes (I) and (II) to employ a roll-to-roll process, which in turn leads to a improved producibility and a mass production. This roll-to-roll process has an advantage of holding a sheet member easily while producing a flexible substrate.
Unlike in the case of filling with a conductive paste, an interlaminar junction prevents a discordance of an impedance between wiring patterns and vias (corresponding to the interlaminar junctions of the present invention) because the interlaminar junction consists of the same material as the wiring patterns in a seamless state. Also, due to the same material as the wiring patterns, there is no difference between a thermal expansion coefficient of each of the interlaminar junctions and that of the wiring patterns, which will lead to a better reliability in connection.
Furthermore, a sheet members used in production processes (I) and (II) can be obtained by transferring a wiring pattern which is preliminarily formed on a carrier sheet to each insulating resin layer formed on the film. Thus, not by means of a wet etching process but by means of a dry process, the sheet members can be prepared. In addition, a dry process can be carried out for the purpose of obtaining the interlaminar junction by using of a needle-like member or a roll member. Therefore, as a whole, the production processes (I) and (II) can be carried out by means of the dry process, which in turn leads to a simple production process that is easy to handle.
FIGS. 1(a) to (f) show cross-sectional views illustrating the steps in a process for producing a conventional flexible substrate.
FIGS. 2(a) to (c) show cross-sectional views illustrating the steps in a process for producing a conventional flexible substrate.
FIGS. 6(a) and (c) show cross-sectional views illustrating the steps in a process for preparing a sheet member 10.
FIGS. 11(a) and (b) show cross-sectional views of embodiments wherein concave portions formed in a surface of a wiring pattern is filled with conductive members 27.
FIGS. 35(a) and (b) show cross-sectional views illustrating the steps in a process for producing a multilayer flexible substrate 250 wherein convex portions 26 are formed on a wiring pattern 17.
FIGS. 44(a) and (b) show cross-sectional views illustrating the step for disposing passive components 85a,85b within a flexible device.
Hereinafter, the processes for producing a flexible substrate and a multilayer flexible substrate will be concretely described. In conjunction with that, the flexible substrate and the multilayer flexible substrate obtained by such processes will be also described concretely.
First of all, the production process (I) of the present invention will be described. In FIG. (3), a cross-sectional view of a construction of a sheet member 10 used in the step (a) is shown. Also, in FIGS. (4) and (5), cross-sectional and perspective views of a construction of the obtained flexible substrate 100 are respectively shown.
As for the step (a), a sheet member 10 is prepared. As shown in
It is preferred that the film 11 is thinner than the insulating resin layer 12. For example, a ratio of insulating resin layer (12) thickness/film (11) thickness is preferably 1.1 to 8, more preferably 1.2 to 6. As used in this specification and claims that follows, the phrase “insulating resin layer thickness” means a thickness of the insulating resin layer formed on one face of the film. Concretely, the thickness Ti of the insulating resin layer 12 is for example 3 to 80 μm, and the thickness Tf of the film 11 is 2 to 16 μm. In this way, due to a thin film 11 of the sheet member 10, the interlaminar junctions are easy to form. In addition, because the wiring patterns 20 (20a,20b) are buried in the insulating resin layers, the spacing between the front-sided wiring pattern 20a and the rear-sided wiring pattern 20b is small. Thus, the front-sided wiring pattern 20a and the rear-sided wiring pattern 20b are easy to joint to each other upon being pressed. For example, the spacing between the front-sided wiring pattern 20a and the rear-sided wiring pattern 20b is preferably 2 to 15 μm, more preferably 2 to 9 μm. Furthermore, in the case where the insulating resin layer 12 is thicker than the film 11, a sliding flexibility or a flexing life of the obtained flexible substrate is improved. The reason for this is that, when the flexible substrate is folded, the stress applied on the film and the buried wiring patterns is alleviated by the insulating resin layer having a low modulus of elasticity.
The film 11 is generally a resin film having an insulating characteristic, preferably a heat-resisting film. For example, the film 11 is a resin film made of an aramid or a polyimide. It is further preferred that an aramid film is used as the film 11. The reason for this is that the aramid film is better in terms of a surface flatness, a low absorptivity and a dimensional stability. Further reason for this is that, even in the case where the aramid film is thinner than a polyimide film, a given strength is easy to achieve, and that the aramid film is cheaper than the polyimide film. In addition to that, the aramid has a high elasticity-strength so that it is suitable for forming a thin film. For example, about 4 μm of the aramid film thickness corresponds to about 12.5 μm of the polyimide film thickness.
The insulating resin layers 12 formed on both surfaces of the film 11 serve to house the wiring patterns 20. In order to improve an adhesion strength between the insulating resin layers 12 and the wiring patterns 20, or to improve an adhesion strength between the multi layered substrates, it is preferred that the insulating resin layers 12 have an adhesive property. Therefore, the insulating resin layer is preferably made of at least one resin material selected from the group consisting of an epoxy resin, a polyimide resin, and an acrylic resin and a modified resin thereof.
The sheet member 10 used in the production process of the present invention is characterized in that the wiring patterns 20 are embedded in the insulating resin layers 12. For the purpose of obtaining these wiring patterns 20, first, a substrate 80 in which insulating resin layers 12 are formed on the front surface and rear surfaces of a film 11 is prepared as shown in
The wiring patterns 20 may be made of any materials if they have an electrically conductive properties. For example, it is preferred that the wiring patterns 20 are made of metal materials selected from the group consisting of a copper, a nickel, a gold and a silver. It is also preferred that the carrier sheet used in the transferring technique is made of organic films such as a PET, or an metal foil such as a copper foil, and that it is therefore something like a sheet-like member which is about 25 to 200 μm in thickness.
Next, the step (b) will be hereinafter described. In the step (b), a part of at least one of the front-sided and rear-sided wiring patterns is pressed into the inside of the sheet member in order to crash through the insulating resin layer(s) and film, and thereby a part of the front-sided wiring pattern and a part of the rear-sided wiring pattern are jointed to each other. This causes a part of the front-sided wiring pattern and a part of the rear-sided wiring pattern to be pressure-jointed to each other. Therefore, the step (b) is herein referred to also as “pressure-joint step”. However, it should be noted that if the front-sided wiring pattern and the rear-sided pattern are electrically connected to each other, it is no longer required to be pressed more, and therefore the term “joint” does not necessarily mean the phrase “pressure joint” herein. It is preferred that a pressing direction is approximately perpendicular to a plane of the sheet member. In
As a pressing tool, a needle-like member, or a roll member 33 with protrusions 35 (see
In the case where both of a portion of the front-sided wiring pattern and a portion of the rear-sided wiring pattern are pressed, a cross-sectional view of a wiring section composed of those portions is approximately “X” in shape. In contrast, in the case where one of a portion of the front-sided wiring pattern and a portion of the rear-sided wiring pattern is pressed, a cross-sectional view of a wiring section composed of the pressed portion is approximately “U” in shape.
In the case where both of a portion of the front-sided wiring pattern and a portion of the rear-sided wiring pattern are pressed, it could lead to an embodiment wherein a portion of the front-sided wiring pattern and a portion of the rear-sided wiring pattern are jointed to each other within the interior of the film. In some cases, it could lead to an embodiment wherein a portion of the front-sided wiring pattern and a portion of the rear-sided wiring pattern are jointed to each other within the interior of the insulating resin layer in such a manner that one of them penetrates through the film. In the meanwhile, in the case where one of a portion of the front-sided wiring pattern and a portion of the rear-sided wiring pattern is pressed, it could lead to an embodiment wherein a portion of the front-sided wiring pattern and a portion of the rear-sided wiring pattern are jointed to each other in such a manner that the pressed portion of the wiring pattern only penetrates through the film.
A pressing operation of the step (b) can be carried out at normal temperature (e.g. 20 to 80° C.). A pressing force applied for each interlaminar junction is preferably 100 to 1200 gf, more preferably 500 to 1000 gf.
In the step (b), in the case where the pressing operation is carried out by means of the roll member with protrusions while the sheet member is moving unidirectionally, it is possible to form the interlaminar junctions continuously. Thus, it is possible to employ a roll-to-roll process in the production process (I), which in turn leads to a mass production of the flexible substrate.
In a preferred embodiment, as shown in
In such an embodiment that the conductive projecting members 27 are disposed, the concave portions (i.e. depressed portions) in the surface of the wiring pattern, which portions are formed due to the pressing, are supposed to be filled with the conductive members 27 so that the surface of each wiring pattern is flat, as shown in FIGS. 11(a) or 11(b). As a result, the surface of the flexible substrate 100 becomes flat, which in turn leads to a construction suitable for a multilayering process. In such flexible substrate 100, due to the filled conductive member 27, the resistance of each interlaminar junction becomes low, which in turn allows a large electric current to pass therethrough if necessary.
In the case where a part of the front-sided wiring pattern or a part of the rear-sided wiring pattern is pressed through the intermediary of the conductive projecting member, a needle-like member or a roll member may be used.
It is preferred that the conductive projecting member 27 is mainly made of a metal, for example an alloy. It is preferred that such alloy mainly consists of a metal selected from the group consisting of a copper, a nickel, an aluminum, a gold, a silver and a combination thereof. Also, as a material of the conductive projecting member 27, a conductive paste which contains carbon powder or the above-mentioned metal in powder may be used.
In order to form the conductive projecting member 27, a paste printing technique, a bump forming technique, a ball mounting technique, or an electrophotography technique may be employed. That is, in the case of employing the paste printing technique, a projecting conductive member is formed by paste-printing a conductive material and thereafter drying it. In the case of employing the bump forming technique or the ball mounting technique, the conductive projecting members are formed by forming bumps on a metal layer, or mounting metal balls on a metal layer. As to the electrophotography technique, an embodiment thereof is shown in
In the case where the conductive projecting member is disposed on one of the front-sided wiring pattern and the rear-sided wiring pattern, not on both of them, the cross-sectional view of a portion of the wiring section composed of the pressed part of one of the front-sided wiring pattern and the rear-sided wiring pattern becomes approximately “U” in shape after the pressing step (b) is carried out with the roll member 34. Incidentally, not before the pressing step (b) but after that, the conductive projecting member may be formed. That is, in order to achieve the flat surface of the wiring pattern as well as a low resistance of the interlaminar junction, the concave portion on the surface of the wiring pattern, which portion is formed due to the pressing step (b), may be filled with the conductive material.
In a preferred embodiment of the step (b), a part of the front-sided wiring pattern and a part of the rear-sided wiring pattern may be jointed to each other through the intermediary of the solder. For example, as shown in
As shown in
In a preferred embodiment, a heat treatment of the joint-surface of the junction may be carried out so as to improve the connecting condition of the junction. For example, as shown in
In particular, as shown in
Not only an embodiment wherein the ultrasonic wave is applied after the formation of the interlaminar junctions is possible, but also an embodiment wherein the ultrasonic wave is applied during the formation of the interlaminar junctions is possible. In the case where the ultrasonic wave is applied during the formation of the interlaminar junctions, it is preferred that the needle-like member or the roll member having protrusions is used. In other words, the pressing step (b) is carried out by means of the needle-like member or roll member, both of which are respectively provided with a function of applying an ultrasonic wave. For example, as to the needle-like member, it is preferred that the tip of the needle-like member is provided with such function.
In a further embodiment, it is preferred that the interlaminar junctions are heated before or after being treated by an ultrasonic wave. This will cause the region adjacent the interlaminar junctions to soften and thereby such region becomes easy to transform. As a result, a desirable ultrasonic bonding can be obtained due to a lager connecting area. The sheet member or the flexible substrate may be placed on the heated roll member or conveyor because a heating of the sheet member itself results in a heating of the interlaminar junctions. In this case, the sheet member or flexible substrate may be heated to for example 50 to 400° C., preferably 100 to 300° C.
It is preferred that the application of the ultrasonic wave is carried out while measuring a physical characteristic of a part of the wiring patterns. For example, the measured physical characteristic is a resistance of a part of each wiring pattern, or a degree of the dent or depression of each wiring pattern. In the case where the application of the ultrasonic wave as well as the measurement of the physical characteristic (e.g. resistance) are concurrently carried out, a strength characteristic of the interlaminar junction can be obtained in real time, which in turn allows the ultrasonic wave to be applied to such a degree that a desired strength characteristic is obtained. It is only necessary to carry out the measurement of the physical characteristic at first one time or a few times. That is to say, according to the result of such measurement, it is afterward possible to adjust the amount of the energy of the ultrasonic wave (e.g. an applying time or an amount of the ultrasonic wave).
In the case where the ultrasonic wave is applied, the conductive members 15 may be disposed on the inner side of the wiring patterns 20 in the sheet member 94 as shown in
According to the embodiment as shown in
Hereinabove, the production process (I) has been described. As shown in
By using of this flexible substrate 100, it is possible to produce a multilayer flexible substrate 150 as shown in
Hereinafter, the steps for producing a flexible substrate 100 of the present invention as well as a transferring step will be described with respect to
First, as shown in
Before such transferring step, it is required that the wiring patterns 20 are disposed on carrier sheets 32. Due to a rotating of the roll members 31, the carrier sheets 32 are conveyed toward the direction indicated by the arrow 42. Thus, due to a nip pressure of the roll members 31 will cause the wiring patterns 20 (i.e. 20a and 20b) to be pressed toward the insulating resin layers 12 of the substrate 80, which will embed the wiring patterns 20 into the insulating resin layers 12.
After the wiring patterns 20 (i.e. 20a and 20b) are embedded, a sheet member 90 moving in the direction indicated by the arrow 41 passes through a pair of roll members 33. As shown in
The embodiment wherein a part of each wiring pattern is pressed through the intermediary of the conductive projecting member is shown in
In a preferred embodiment, as shown in
Turning now to
The embodiment wherein a multilayer flexible substrate 150 is produced by means of the roll-to-roll process using a flexible substrate 100 is shown in
In a preferred embodiment, a roll member 33 may be employed as shown in
Hereinabove, the production process (I) of the present invention and the flexible substrate obtained thereby have been described. In the second place, the production process (II) of the present invention and the flexible substrate obtained thereby will be hereinafter described. The production process (II) comprises the steps of;
In the embodiment shown in
As to the flexible substrate 200 obtained by the production process (II), a part 22 of the wiring pattern 20 of the sheet member 210 and a part 17a of the wiring pattern 17 of the substrate 215 are jointed to each other with pressure, as shown in
It should be noted that the sheet member 210 prepared in the production process (II) is different from the sheet member 10 prepared in the production process (I) in that the wiring pattern is formed only on one face of the film in the sheet member 210 of the production process (II) whereas the two wiring patterns are formed on both faces of the film in the sheet member 10 of the production process (I). Incidentally, the sheet member 210 may be referred to also as “flexible wiring layer” because it could be understood that the sheet member 210 is flexible layer having the wiring patterns.
As for the sheet member 210, it is preferred that the film 11 is thinner than the insulating resin layer 12. For example, a ratio of insulating resin layer (12) thickness/film (11) thickness is preferably 1.1 to 8, more preferably 1.2 to 6. As with the production process (I), the phrase “insulating resin layer thickness” means a thickness of an insulating resin layer formed on one face of the film 11. Concretely, the thickness Ti of the insulating resin layer 12 is 3 to 80 μm, and the thickness Tf of the thickness of the film 11 is 2 to 16 μm, for example. In this case, due to a thin film 11, the interlaminar junctions are easy to form therethrough. In addition, because the wiring pattern 20 is buried in the insulating resin layer 12, the spacing between the wiring pattern 20 of the sheet member 210 and the wiring pattern 17 of the substrate 215 is small. Thus, the wiring pattern 20 of the sheet member 210 and the wiring pattern 17 of the substrate 215 are easy to joint to each other upon being pressed. For example, the spacing between the wiring pattern 20 of the sheet member 210 and the wiring pattern 17 of the substrate 215 is preferably 2 to 15 μm, more preferably 2 to 9 μm. As with the production process (I), in the case where the wiring pattern is embedded in the insulating resin layer 12 that is thicker than the film 11, a sliding flexibility or a flexing life of the obtained flexible substrate 200 is improved.
The film 11 is generally a resin film having an insulating characteristic, preferably a heat-resisting film. For example, the film 11 is a resin film made of an aramid or a polyimide. As with the production process (I), it is preferred that an aramid film is used as the film 11.
The insulating resin layer 12 serves to house the wiring pattern 20 as well as enhance an adhesion strength between the multilayered substrates. Thus, it is preferred that the insulating resin layer has an adhesive property. Therefore, it is preferred that the insulating resin layer is made of at least one resin material selected from the group consisting of an epoxy resin, a polyimide resin, and an acrylic resin and a modified resin thereof, for example.
As to the sheet member 210 used in the production process (II) of the present invention, the wiring pattern is buried in the front-sided insulating resin layer 12. As with the production process (I), it is preferred that the transferring technique are employed to obtain the wiring pattern 20. Also, it is preferred that the wiring pattern 20 is made of the material as described with respect to the production process (I).
The “substrate 215 having a wiring pattern 17 formed on a front face thereof” prepared in the step (a2) has a flexibility. The substrate 215 is not limited if it has a flexibility. Thus, a typical flexible substrate 500 as shown in FIG. (f) may be used as the substrate 215. Although only on one face of the substrate 215 shown in
Next, the step (b) of the production process (II) will be hereinafter described. In the step (b), a part 22 of the wiring pattern 20 of the sheet member 210 is pressed toward the substrate 215 so that such part 22 penetrates through the insulating resin layers 12 and film 11. As a result, a part 22 of the wiring pattern 20 of the sheet member 210 and a part 17a of the wiring pattern 17 of the substrate 215 are jointed to each other. Prior to a pressing step, the sheet member 210 is stacked on the substrate 215 in such a manner that the rear-sided insulating resin layer 12 of the sheet member 210 is contacted with a front face of the substrate 215. In this case, the adjustment of the position is carried out in such a manner that the wiring pattern 20 of the sheet 210 is opposed to the wiring pattern 17 of the substrate 215.
As with the production process (I), a needle-like member or a roll member 33 with protrusions 35 (see
After a portion of the wiring pattern is pressed in the step (b), the cross-sectional view of the pressed portion is approximately “U” in shape as shown in
Although the sheet member 210 is disposed only on one face of the substrate 215 in the examples shown in
As shown in
Next, the production process (II) of the present invention will be hereinafter described with respect to the
First, a sheet member 210 in which wiring pattern is buried in an insulating resin layer 12 formed on a film 11 is prepared, and a substrate 215 having a flexibility is also prepared. As to the substrate 215, wiring patterns 17 are formed on both surfaces thereof, and the front-sided wiring pattern 17 and the rear-sided wiring pattern 17 are electrically connected to each other through a via 18 (e.g. conductive paste portion). In the shown embodiment, a thermosetting adhesive layer 12′ is disposed on an organic film 11′ made of a polyimide, and the wiring patterns 17 made of a copper are formed on the thermosetting adhesive layer 12′. From a roll 30a, the substrate 215 is conveyed in the direction indicated by the arrow 40. In contrast, the sheet member 210 superposed on a carrier sheet 32 is conveyed from a roll 30b. As shown in
As shown in
Subsequently, the conductive members 27 are disposed on the obtained stacked substrate 90 in such a manner that they project from the surface of the substrate 90. That is to say, the substrate 90 is provided with the conductive projecting members 27. Incidentally, the conductive projecting members 27 are formed on the wiring pattern 20 in such a position that they align with the pattern of the interlaminar junctions (so-called “via”). As with the production process (I), the conductive projecting member 27 may be formed by means of a paste printing technique, a bump forming technique, a ball mounting technique or an electrophotography technique.
Subsequently, the stacked substrate 90 on which the conductive projecting members 27 are formed passes through a pair of roll members 34. This causes the conductive projecting members 27 to be pressed into the inside of the stacked substrate 90. As a result of that, the interlaminar junctions are formed, and conductive members 27 is supposed to be located in the concave portions (formed due to the pressing) in the surface of the wiring pattern. Concretely, when the roll members 34 are contacted with the conductive projecting member 27, the conductive projecting member 27 is pressed toward the interior of the stacked substrate 90, and consequently a part 22 of the wiring pattern 20 of the sheet member 210 is pressed toward the interior of the stacked substrate 90. As a result, a part 22 of the wiring pattern 20 and a part 17a of the wiring pattern 17 of the substrate 215 are jointed to each other. Incidentally, due to the conductive projecting member 27 located in the concave portion in the surface of the wiring pattern, a surface flatness of the multilayer flexible substrate 220 can be achieved. Subsequently, the obtained multilayer flexible substrate 220 having the interlaminar junctions is conveyed in the direction indicated by the arrow 40, and then is supposed to be wound around a roll 30d, and finally cut into a predetermined size. In the case where further multilayering process is carried out, the obtained multilayer flexible substrate 220 may be subjected to a further superposing step.
As for the embodiment shown in
Also, as for the embodiment shown in
Furthermore, as shown in
In the production process (II), the flexible substrate 100 as obtained by the production process (I) may be used as the substrate 215 having a flexibility. The embodiment of this case is shown in
By suitably using of the flexible substrate obtained by the production process (II), it is possible to construct a three-dimensional coil (i.e. inductor) as shown in
According to the production process (II), as with the production process (I), it is possible to form the interlaminar junctions easily without making the through holes and filling the conductive paste. This will lead to achievement of a simple production process of the flexible substrate. Also, as with the production process (I), a so-called roll process (i.e. roll-to-roll process) can be employed in the production process (II) because all the processes carried out in the production process (II) are dry processes. Therefore, it is possible to produce the multilayer flexible substrates continuously, which in turn leads to achievement of a mass production.
Also, as with the production process (I), the aramid film, which has a higher elastic strength than the polyimide film and therefore is suitable for forming a thin film, may be used in the production process (II). This will lead to achievement of an extremely thin flexible substrate.
Furthermore, as with the production process (I), the transferring technique may be employed in the production process (II). Therefore, it is possible to embed the wiring pattern 20 into the insulating resin layer 12 in such a manner that the surface of the wiring pattern 20 is on the same level (or approximately the same) level as a surface of the sheet member 210. That is to say, it is preferred that the surface of the wiring pattern 20 is flush with the surface of the sheet member 210. This will lead to achievement of a better flatness of the flexible substrate 200, and thereby the superposing process can be carried out easily.
Hereinabove, the production processes (I) and (II) as well as the flexible substrates 100 and 200 obtained thereby have been described.
In the next place, a process for producing a multilayer flexible substrate will be hereinafter described. Such process is characterized in that the multilayer flexible substrate is produced by using of the flexible substrates 100 and 200 obtained by the production processes (I) and (II) of the present invention.
In order to achieve a thin multilayer flexible substrate 180 (i.e. small thickness Ti), it is preferred that the flexible substrates 100, 200 that are respectively 10 to 25 μm in thickness. In stead of using the flexible substrates 100,200, the typical flexible substrate (e.g. flexible substrate shown in
As shown in
In the case where the thickness T2 of the semiconductor chip 81 is for example 50 to 130 μm, and the thickness T1 of the six-layer flexible substrate (i.e. multilayer flexible substrate 180) is for example 75 to 150 μm, the flexible device 300 is as small as 125 to 280 μm in thickness (=T2+T1). Such extremely thin flexible device 300 (i.e. less than and equal to 300 μm in thickness) serves many uses.
As shown in
Incidentally, a flexible device 300 having the wiring patterns (not shown) formed on the surface thereof can be obtained by transferring the composite sheet 84 having the wiring patterns formed on the surface thereof to the multilayer flexible substrate 180. As to the flexible device 300, a preferable surface flatness is achieved, so that further electronic components can be mounted to the flat surface of the flexible device 300.
As shown in
In order to make full use of the characteristics of the flexible substrates 100,200, the multilayer 180, or flexible devices 300, it is preferred that they are mounted to a thin compact electronics device or a compact electronics device wherein a mounting area is extremely limited. For example, as shown in
In the thin cellular phone 400 shown in
Within the housing 499 of the cellular phone 400, a display unit 491 (e.g. LCD panel), key unit 496 (in which antenna 492, battery 493, and buttons 496a are mounted), camera unit 497 (e.g. CCD or CMOS image sensor) are mounted. In spite of a limited mounting region within the housing 499, it is possible to effectively use the flexible substrates 100, 200 having a better flexing life. The flexible substrate 100 serving as a circuit board can be relatively easily provided with curved sections (or flexural portions) 100a or clinched portions 100b, which in turn leads to achievement of a high-density mounting.
Hereinabove, although the present invention has been explained as above with reference to preferred embodiments, it will be understood by those skilled in the art that the present invention is not limited to such embodiments and can be modified in various ways. For example, in order to lower the cost of the production processes (I) or (II) of the present invention, it is possible to use a commercially available laminate with metal layer in stead of the sheet member, and preferably a copper-clad laminate is used.
As an additional remark, Japanese Patent Kokai Publication No. 3-201498, Japanese Patent Kokai Publication No. 49-27866, Japanese Patent Kokai Publication No. 55-102291, Japanese Patent Kokai Publication No. 9-283881, and Japanese Patent Kokai Publication No. 52-71677 will be hereinafter described, although the inventions disclosed in those publications are fundamentally different from the present invention in terms of their technical meanings.
Japanese Patent Kokai Publication No. 3-201498 and Japanese Patent Kokai Publication No. 49-27866 disclose the technology wherein a part of the wiring pattern is crashed through the insulative layer and then connected to the metal substrate (e.g. aluminum substrate) without a screw tool for the purpose of ensuring an electrical connection between the wiring pattern and the metal substrate. As to such disclosed technology, a connecting tool is used to connect a part of the wiring pattern to the metal substrate. By means of this connecting tool, the relatively soft surface of the aluminum substrate is deeply caved. Thus, the disclosed technology can not be employed for forming the vias of double-sided flexible substrate. Beyond that, no wiring pattern is formed in the metal plate (aluminum plate) serving as a radiator plate. Basically, what are disclosed in those publications are alternative technologies for the connection with the screw, and therefore are fundamentally different from the present invention.
Japanese Patent Kokai Publication No. 55-102291 discloses a structure of the through-hole conductor of the flexible circuit board. The technology disclosed in this publication is an alternative technology for a process for making a conventional through hole, and therefore is fundamentally different from the present invention. Further, the structure of the through-hole conductor disclosed in this publication has a possibility of less reliable connection from a structural standpoint. That is to say, as to the disclosed technology, the concern remains about the reliability in connection. The reason for this is that the circuit wiring patterns formed on one surface and the other surface are connected to each other at a so-called “shoulder position” of the through hole, and therefore a point-contact in a cross-sectional view and plane-contact in an overall view are conceivable. In contrast, as to the interlaminar junction of the present invention, a stable line-contact in a cross-sectional view and plane-contact in an overall view are conceivable. Therefore, in that respect, the technology disclosed in the publication is greatly different from the present invention. Incidentally, in the case of the plated through-hole, the disconnection of the wiring tends to take place at the “shoulder position”, and therefore it is required to take measures against such disconnection. In the meanwhile, as to the flexible substrate of the present invention, the stress occurred at the position corresponding to the above “shoulder position” is low. In such a light, they are also different from each other.
Japanese Patent Kokai Publication No. 9-283881 discloses a circuit board including pressure-welding vias. In this circuit board, the pressure-welding via is formed within the board by butting a part of the wiring disposed in the front surface of the board. During a formation of the pressure-welding via, a softening technique is carried out with heat. For example, the pressure-welding via is formed by means of a pressure-plate that is heated with a heating medium (see
According to examples (1) to (3), the experiments about the flexible substrate and the process for producing the same were performed.
First, according to examples (1) and (2), the experiments concerning a flexing life of the flexible substrate of the present invention were performed.
(Film Material)
A film (organic film) used in this example is shown in Table 1.
(Preparation of the Substrate Used for Measuring Flexing Life)
By applying an epoxy-base thermosetting resin layer to both surfaces of the film with a roll coater process, the insulating resin layers were formed. Subsequently, the wiring patterns were embedded into the insulating resin layers.
Prior to embedding of the wiring patterns, a thin peel-apart layer (consisting of a nickel-phosphorus alloy) was prepared on both surfaces of the electrolytic copper foil having a thickness of 70 μm (which foil served as a supporting member of the wiring pattern), and then another copper foil (12 μm in thickness) was formed on the peel-apart layer by means of an electroplating technique. After that, a wiring pattern was formed by superposing a dry film resist on the formed copper foil, followed by carrying out a light exposure, a development, an etching, and a removing of the resist in series.
Subsequently, the supporting member having the wiring pattern was superposed on the insulating resin layers formed on the front face and the rear face of the film with adjustment of the position, and therefore the wiring pattern of the supporting member was embedded into the insulating resin layer by heating to a temperature of 60° C. as well as pressing at the pressure of 3 MPa for 5 minutes. Subsequently, after cooling, the only supporting member was peeled off, followed by carrying out a real curing of the insulating resin layer by heating it for an hour under the condition of 140° C. and 5 MPa. In this way, a substrate (i.e. sample substrate), which is regarded as a base member for the flexible substrate, was obtained. The specification of the obtained substrate is shown in the following Table 2.
(Measurement of Flexing Life)
Based on the technique of IPC-240C and JIS-C5016, the flexing life for various types of the sample substrates was measured.
Prior to the measurement, the sample substrate was fixed between two flat plates that were respectively opposed at a certain distance in such a manner that the sample substrate was folded at 180 degree so as to achieve a constant curvature. Subsequently, the two flat plates were moved to each other in parallel at a predetermined speed and stroke. That is to say, the sample substrate was repeatedly slid and moved to each other so that a reciprocating motion thereof was carried out. During that, the direct current resistance of the wiring patterns located at the curved inner surface of the sample substrate was monitored. The flexing life was regarded as a cycle number of the reciprocating motion wherein the resistance was increased by 80% compared with the initial resistance. By way of comparison, the flexing life of the copper foil used for the wiring pattern (i.e. copper foil having a thickness of 12 μm, and which was formed by electroplating technique) was also measured with a similar method to the above example.
(Result)
The result of the example is shown in
(Preparation of the Substrate Used for Measuring Flexing Life)
In this example, by using of the method similar to the above example (1), various types of the sample substrates were prepared in such a manner that a ratio of insulating resin layer thickness/film, thickness is diversely changed. The specification of the prepared substrate is shown in the following Table 3.
(Test Condition)
All of the films used in this example were aramid film (“MICTRON” manufactured by TORAY Co., Ltd.) The sample substrates 2a to 2e were approximately same in thickness thereof, and the sample substrates 2c, 2f, and 2g were same in thickness of the film. The flexing life of such sample substrates were measured by using of the method similar to the above example (1). As another test condition, the speed (i.e. frequency) was 25 Hz, the stroke was 25 mm, and the curvature radius was 2 mm, 4 mm and 8 mm.
(Result)
The results of the example (2) are shown in the
In this example, the effect of the pressure-joint carried out in the production process of the present invention was confirmed. And also, the effect of the application of the ultrasonic wave to the interlaminar junctions was confirmed.
(Preparation of the Substrate Used for the Example (3))
As with the example (1), the film on both surfaces of which the insulating resin layers were formed was prepared, and also the two carrier sheets (i.e. copper foils that were respectively 70 μm in thickness) in which the wiring patterns were formed were prepared. The film used in the example (3) was aramid film (“MICTRON” manufactured by TORAY Co., Ltd.) having 4 μm in thickness. Each of insulating resin layers formed on both surfaces of the film was 10 μm in thickness. Each of the wiring patterns on the carrier sheets was formed by means of the electroplating technique in such a manner that the thickness of the wiring pattern was 9 μm. Subsequently, Each of carrier sheets on which the wiring patterns were preliminarily formed was superposed on the front-sided and rear-sided insulating resin layers of the film with adjustment of the position, and thereafter each of wiring patterns was embedded into each of the insulating resin layers by heating to a temperature of 60° C. as well as pressing at the pressure of 3 MPa for 5 minutes. After cooling, only carrier sheets were peeled off. In this way, the pre-cured sheet member in which the front-sided and rear-sided wiring patterns were formed was obtained. Here, each of the wiring patterns used was something like that providing a so-called “chain-via” in which the electrodes formed on the both surfaces of the substrate were connected and jointed to each other within the substrate. In that regard, the diameter of the electrode for forming the interlaminar junctions was 600 μm.
(The Formation of the Interlaminar Junctions)
Subsequently, by pressing the electrode formed on one surface of the pre-cured sheet member toward the interior thereof, the opposed electrodes were jointed to each other within the substrate. Consequently, the interlaminar junctions were formed in such a manner that 100 interlaminar junctions were coupled to each other. In that regard, a need-like cylindrical member (the tip thereof was hemispherical in shape) was used as a pressing tool, which member was made of stainless material and 100 μm in thickness. After pressing, the real curing was carried out by heating for an hour under the condition of a temperature of 140° C. as well as a pressure of 5 MPa. In this way, the flexible substrate in which the chain-vias (i.e. interlaminar junctions) was formed wad obtained.
(Preparation of the Flexible Substrate Treated by an Ultrasonic Wave)
By means of an ultrasonic applying tool (ULTRASONIC ENGINEERING Co., Ltd., type: USW-610Z20S), the ultrasonic vibration was applied to the interlaminar junctions (i.e. chain-via) via electrodes thereof. As a result of that, the flexible substrate treated by an ultrasonic wave was obtained. In that regard, the ultrasonic vibration was 28 kHz, and the generating power was 200 W.
(Measurement of the Resistance)
First, the resistances of the chain-vias of the above two types of flexible substrates (i.e. one is the ultrasonic-wave treated flexible substrate and the other is the ultrasonic-wave non-treated flexible substrate) were measured by means of a four-terminal measurement. Next, subsequent to measuring the resistance of the wiring, such resistance of the wiring was subtracted from the resistance of the chain-vias in order to obtain the resistance of each interlaminar junction. In that regard, the resistance of each interlaminar junction was obtained as an average value of ten samples for each flexible substrate prepared. As to the measurement of the wiring resistance, the wiring patterns were formed in such a manner that they had the same wiring length and wiring width as the wiring regions where no interlaminar junction existed, and thereafter the resistance of such wiring patterns was measured by means of the four-terminal measurement.
(Result)
(Liquid Bath Type Thermal Shock Test)
Subsequently, the liquid bath type thermal shock test was carried out as to the sample substrates prepared with a constant pressing load of 750 gf. Ten samples for each of two types substrates were employed. Regarding a 5-minute exposure of the sample substrate to two liquid baths respectively having −55° C. and 125° C. as 1 cycle, such cycles up to 2000 were carried out for each sample substrate. After the above exposure, the resistance of the interlaminar junction was measured. In that regard, the sample substrate in which a resistance change of more than and equal to 10% come out was regarded as “defective”. The result was as follows: a percent defectives for the ultrasonic-wave non-treated flexible substrate exposed at 1000 cycles was 0%; a percent defectives for the ultrasonic-wave non-treated flexible substrate exposed at 2000 cycles was 20%; a percent defectives for the ultrasonic-wave treated flexible substrate exposed at 1000 cycles was 0%; a percent defectives for the ultrasonic-wave treated flexible substrate exposed at 2000 cycles was 0%. Hereinabove, a beneficial effect of the flexible substrate of the present invention was confirmed.
(General Overview)
The following matters were derived from the example (3) (however, those matters may be altered to suit the design condition the flexible substrate):
It is preferred that the frequency of the ultrasonic vibration is approximately in the range of between 15 kHz and 150 kHz. The reason for this is that the ultrasonic vibration above such range will cause too large generating power, which in turn leads to an unfavorable condition concerning a high-precision processing, whereas the ultrasonic vibration below such range will cause too small generating power, which in turn leads to an insufficient melting.
It is preferred that the generating power is approximately in the range between 10 W and a few thousand W. The reason for this is also that the generating power above such range will lead to an unfavorable condition concerning a high-precision processing, whereas the generating power below such range will lead to an insufficient melting.
It is preferred that the applying time is in the range between 0.1 second and 10 second (typically about 1 second), which corresponds to the applying energy of 1 kJ to a few KJ.
The flexible substrate, multilayer flexible substrate, flexible device, all of which are obtained by the production process of the present invention, can be used as a circuit board of a cellular phone. However, not applying to the cellular phone, they can be used for a PDA or a notebook computer. Furthermore, they can be used for a digital still camera or a wall-hung thin-shaped television (i.e. flat-panel display). As the use of the flexible substrate in more various fields progresses, it is conceivable that a technical value of the flexible substrate (in particular the multilayer flexible substrate) of the present invention will increase more than ever.
The present application claims the right of priority of Japanese Application No. 2004-079848 (filed Mar. 19, 2004, the title of the invention: “FLEXIBLE SUBSTRATE, MULTILAYER FLEXIBLE SUBSTRATE, FLEXIBLE DEVICE, ELECTRONICS DEVICE, AND PROCESS FOR PRODUCING THE SAME”), Japanese Application No. 2004-088853 (filed Mar. 25, 2004, the title of the invention: “FLEXIBLE SUBSTRATE, MULTILAYER FLEXIBLE SUBSTRATE, FLEXIBLE DEVICE, AND PROCESS FOR PRODUCING FLEXIBLE SUBSTRATE”), Japanese Application No. 2004-088854 (filed Mar. 25, 2004, the title of the invention: “FLEXIBLE SUBSTRATE, FLEXIBLE DEVICE, AND PROCESS FOR PRODUCING FLEXIBLE SUBSTRATE”), Japanese Application No. 2004-318887 (filed Nov. 2, 2004, the title of the invention: “PROCESS FOR PRODUCING FLEXIBLE SUBSTRATE, FLEXIBLE SUBSTRATE, FLEXIBLE DEVICE, AND CIRCUIT BOARD MODULE”), Japanese Application No. 2004-318888 (filed Nov. 2, 2004, the title of the invention: “PROCESS FOR PRODUCING FLEXIBLE SUBSTRATE, AND FLEXIBLE SUBSTRATE, FLEXIBLE DEVICE”), the disclosures of which are all incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2004-079848 | Mar 2004 | JP | national |
| P2004-088853 | Mar 2004 | JP | national |
| P2004-088854 | Mar 2004 | JP | national |
| P2004-318887 | Nov 2004 | JP | national |
| P2004-318888 | Nov 2004 | JP | national |
