JPH0143474B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a wiring board in which a metal plate such as an Al plate is used as a support substrate for a wiring pattern, and various electronic circuit components such as semiconductor elements, capacitors, and resistors are mounted on this support substrate. It is used by bending a metal plate. Conventionally, rigid insulating boards made of glass, ceramic, glass epoxy, etc. have generally been used as wiring boards for electronic devices. These board materials are usually used in the form of a flat plate in consideration of material strength, bending or drawing workability, etc., and due to space factors such as wiring board storage space in electronic devices, single board materials are used. If the board cannot be used as a flat board, a split connection structure is adopted in which the board is vertically connected to a separately provided flat board using a cable, connector, or the like. Conventional wiring boards are difficult to deform, so multiple flat printed circuit boards must be joined together to form the desired shape.
There is a problem that not only the number of parts increases, but also that it is not possible to sufficiently meet the demands for smaller, lighter, and thinner electronic devices. To solve the above problems, a wiring board has been proposed in which a metal plate such as Al is used as a wiring board and a copper foil pattern is formed as a wiring pattern on an insulating layer interposed thereon (Jikkosho). 46−
No. 21904). However, in this case, there are limits to miniaturization and high density because multilayering is impossible and the copper foil becomes thick, making it difficult to form fine wiring. The present invention was made in view of the above-mentioned problems, and consists of a metal plate, an organic film insulating layer, a polyimide insulating layer with a low recrystallization temperature, and an ionically engineered deposited film of Al, which has strong adhesion and high malleability. Ni or Cu that can be soldered to thin film wiring at least on the surface
A flat substrate with high-density wiring formed by a combination of thin film wiring formed by is machined and deformed by arbitrary bending etc. to form a metal plate,
The three-layer structure of the insulating layer and the Al thin-film wiring is bent, and the current-carrying circuit of the device electrically connected to the Ni or Cu thin-film wiring by soldering is thereby bounded by the bent three-layer structure. A pattern of Al thin film wiring is developed over both main surfaces of the metal plate.
The object of the present invention is to provide a new and useful thin film wiring board that facilitates high-density packaging of fine wiring. An example of the method for manufacturing a wiring board according to the present invention will be described in the first example.
This will be explained with reference to Figures a to g. First, as shown in Figure 1a, the cleaned Al and Cu
A first organic insulating material 2 such as polyimide varnish or polyamide varnish is coated on a metal plate 1 using a roll coater method or the like, and heated {for example, 150°C (30 minutes) + 250°C
(30 minutes)} to evaporate the solvent components.
In this case, a semi-cured organic sheet may be used instead of the above-mentioned varnish, or an adhesive may be applied and a polyimide film or the like may be attached by applying heat and pressure. That is, any flexible insulating layer can be used. The flexibility of the organic insulating layer 2, together with the toughness of the metal plate 1 serving as the base, works effectively when the wiring board is bent as in each of the above embodiments, and even if it is bent, it will not be damaged. Since there is no need to worry about pinholes etc., extremely stable and high insulation properties can be obtained. Next, deposition is performed on the organic insulating layer 2 by ion engineering techniques (vapor deposition, sputtering, ion clustering), and then unnecessary portions are removed by etching to form a lower wiring conductor 3 made of a thin film of Al or the like as shown in FIG. 1b. A desired pattern is formed as shown in FIG. In this case, if necessary, it may be possible to use multiple thin film wiring by overlapping other metal films, but it is possible to use a multi-thin film wiring with good elongation and adhesion to the base during subsequent bending.
Make sure that only the thin film of Al, etc. remains in the areas that require processing. After the lower wiring 3 is formed into a desired pattern, a second organic insulating layer 4 having adhesive properties (for example, a polyimide film coated with an adhesive, polyimide varnish, polyamide-imide varnish) is applied to the upper surface of the lower wiring conductor 3. Arrange as shown in Figure c. here,
The second organic insulating layer 4 is applied with pressure and heat (for example, 250
It is necessary to use a highly insulating material that can be bonded to the first organic insulating layer 2 and the lower wiring 3 at a temperature of about 10.degree. In this example, a polyimide film with adhesive was selected as a material that satisfies this condition, but it is also possible to use semi-cured polyamide-imide film, polyamide-acid film, etc., which have adhesive strength, and thermoplastic films such as FEP. etc. may be used. In addition, various liquid forms such as polyimide varnish and polyamide-imide varnish that can be applied onto the substrate using printing methods, roll coater methods, etc.
A paste-like microwave may also be used. Next, as shown in FIG. 1d, a resist made of organic and inorganic substances is printed on the second organic insulating layer 4, and then, using this as a mask, O ₂ plasma etching is performed to form the through holes 5 and the necessary terminal portions 6. form. The use of a mixed organic and inorganic resist as a mask in this process means that during plasma etching of the second organic insulating layer 4, the organic substance in the resist is also etched at the same time.
This is because a gentle inclination can be obtained in the step, and a stable and good through-hole contact can be obtained later. Wet etching with hydrazine, NaOH, etc. may be performed without using plasma etching, but in this case, it is important to ensure that the lower wiring conductor 3 is not affected by these and that the second organic insulating layer 4 is not etched by these. However, there are restrictions such as the fact that the material is However, in the case of plasma etching, all organic layers are O ₂
There is an advantage that it is possible to use a polyimide film coated with an adhesive, for example, because it can be etched by plasma. (hydrazine,
In the case of etching with NaOH, etching of the adhesive is not possible. ) Furthermore, as shown in FIG. 1e, the deposition is performed again from above using the ion technology method, and the through-hole is electrically connected to the lower wiring conductor 3 via the through-hole hole 5 by the deposited metal film. At the same time as contact is obtained, the upper wiring conductor 7
is formed of an Al thin film or the like in the same manner as the lower wiring conductor 3. This upper wiring conductor 7 can be formed into a multilayer thin film wiring in which conductive films are superimposed as needed, as with the lower wiring conductor 3 described above, but the parts that will be bent later will have problems with elongation and adhesion with the base. Ensure that only a thin film such as Al, which has good properties, remains, or that no wiring remains at all. In this embodiment, a case is shown in which bonding of a device is performed to an upper wiring conductor, and for this purpose, a two-layer wiring in which a Ni film, a Cu film, etc. are superimposed on an Al film is used. That is, the Al film is designed to have good adhesion to the base, and the Ni film or Cu film is designed to enable bonding with solder in a subsequent process. Next, since this embodiment employs soldering using a tape carrier device as a method of connecting the device and the board, solder is formed on the connecting portion by printing or the like. This connection part may be either the upper or lower part, but in this embodiment, the device is connected to the upper wiring conductor 7. Thereafter, the flat multilayer wiring board is machined to bend or draw the metal plate 1 together with the organic insulating layer and the upper and lower wiring conductors at at least one place, so that it is suitable as a wiring board. It is processed and molded into a shape. FIG. 1f shows an example in which the periphery of the substrate is bent. Next, the formed tape carrier semiconductor device 8 is die-bonded with a conductive paste 9, and the outer lead 10 is soldered to the upper wiring conductor 7 of the wiring board to form a current-carrying circuit. This state is shown in Figure 1g.
Shown below. For die bonding of devices such as the semiconductor device 8, as shown in the figure, in addition to being on the second organic insulating layer 4, the organic insulating layer is removed by etching in advance and is directly attached to the Al plate 1 with a conductive paste, or on the first organic insulating layer 4. It may be on the layer 2, on the lower wiring conductor 3, or on the upper wiring conductor 7. Note that die bonding is not required if unnecessary. The device may be a beam lead chip, a wireless chip such as a flip chip, or a wire bond chip, and the same applies even if the number of devices is large. Although the wiring board described above has a multilayer wiring structure of two layers, upper and lower, it is natural that it may have a single layer wiring structure or a multilayer structure of three or more layers. Further, the metal plate may be bent after the device is attached, or the device may be attached after the bending process. Next, the thin film wiring material of the bent portion formed in this manner will be described in detail. At this bent portion, the aluminum plate, the organic insulating layer, and the thin film wiring all elongate. Therefore, in order to eliminate disconnections in the wiring, it is effective to use a material with a low recrystallization temperature, such as Al, as the wiring material. That is, when the material is deposited on the substrate by sputtering, the surface temperature of the substrate is
As the temperature rises to 200℃ to 350℃, in the case of Al, it exceeds the recrystallization temperature (approximately 200℃) and enters an annealing state, and as shown in Figure 2, the stress-elongation curve of the material changes from the l ₁ state to the l ₁ ' state. The wire is in a stable state because its ability to follow elongation increases and the risk of wire breakage decreases. Furthermore, in the case of Al or an Al alloy, the fact that it has good adhesion with the organic insulating layer and has the same coefficient of thermal expansion also works effectively from the viewpoint of reliability. On the other hand, if a wiring material with a high recrystallization temperature, such as Cu or Ni alloy, is used for the bent part, even if an attempt is made to improve elongation by annealing it, the substrate must be heated considerably. Process problems arise, such as deterioration of the organic film on the metal plate. That is, in the case of Cu-Ni, the stress-elongation curve is as shown in l 2 of FIG. ₂ , which hardly follows the elongation and leads to wire breakage. In addition, in the case of multiple thin film interconnections with low and high recrystallization temperatures, such as Al + Cu-Ni alloy, the adhesion between Al and Cu-Ni is strong, and the Cu-Ni
This is not preferable because it is dominated by alloy breakage. As an example to prove these points, Table 1 shows the wire breakage rates before and after bending.

[Table] As shown above, when bending a wiring board consisting of an organic insulating layer and thin film wiring using a metal plate as a base substrate, the wiring material for the bent part should have good adhesion to the organic insulating layer, thermal expansion. A single layer or multiple thin film of Al or Al alloy, which has the same coefficient and which exceeds the recrystallization temperature and enters an annealing state by increasing the temperature during sputtering, is suitable. Next, an embodiment of a liquid crystal TV driver module using the wiring board of the present invention will be shown. Broadly speaking, LCD image display methods can be divided into active matrix methods, in which a silicon substrate on which a liquid crystal drive circuit is formed is placed on the back substrate of the liquid crystal cells that make up the display screen, and time-sharing methods, which are an extension of conventional calculators and watches. There are two methods. To explain the features of these two methods, the basic configuration is that in the active matrix method, one substrate is a glass substrate and the other substrate is a silicon substrate, and each pixel has a pixel selection switching device on the silicon substrate. A set of MOS transistors, auxiliary memory pixel capacitors, and pixel electrodes are arranged in a matrix across the screen, and the gate and source electrodes of each transistor are connected to a drive circuit formed around the panel. . On the other hand, in the time division method, a glass substrate on which scanning electrodes made of striped transparent electrodes are formed and a glass substrate on which signal electrodes are similarly formed are arranged so that the electrodes are perpendicular to each other through a liquid crystal, and each electrode is connected to the periphery. It has a structure in which it is connected to a circuit board formed in . The display area is limited by the size of the silicon substrate in the active matrix method, but can be made relatively large in the time division method. With the active matrix method, the number of electrodes to be taken out from the panel is small because the scanning circuit and signal processing circuit can be built into the silicon substrate.
In the time division method, as the number of pixels increases, the number of electrodes taken out increases significantly (that is, if the multiplicity is n, n times the number of signal electrodes is required). In terms of image quality, the active matrix method has better image quality than the time-sharing method.In terms of production, the active matrix method requires a large number of elements to be formed on a silicon substrate at the same time, leading to lower yields and higher costs, but the time-sharing method Since the cell is constructed from a glass substrate and the completed device is attached to a separate substrate, yields are improved and costs can be reduced. In the above explanation, one of the biggest obstacles to the time division system at present is the need to take out many terminals from the panel at minute pitches. The reason for this is explained as follows. That is, in a matrix television display, the number of pixels practically required is 10,000 or more. Therefore, in the case of a simple matrix structure, approximately 100 or more scanning lines are required. However, when such a large number of scanning lines are driven, the time for selecting one scanning electrode becomes extremely short, making it difficult to display an accurate image. For this reason,
It is necessary to reduce the number of scanning lines in some way. One way to reduce the number of scanning lines is to increase the multiplicity of time-division driving. In general, when the multiplicity is N, the number of scanning electrodes is 1/N compared to a simple matrix, but the number of signal electrodes is N times larger. Therefore, if the multiplicity is increased extremely, there will be problems with multi-terminal processing of signal electrodes, and crosstalk will occur. Problems with talk arise. Currently, a quadruple matrix (120 x 180 pixels, 46.1 mm x 61.4 mm screen) has been announced as a multiplicity that is close to practical. In this case, the number of scanning electrodes is 120/4=
30, the number of signal electrodes is 61.4mm, 180×4÷2=
360 terminals, that is, 5.8 terminals/mm on one side, and even if the electrodes are expanded a little, a multi-terminal processing of about 5 terminals/mm (0.2 mm pitch) is required. Next, FIG. 3 shows an example of a conventional time-division drive type liquid crystal television module. In this method, the liquid crystal panel 11 and the electronic components 14 and wiring 16 of the wiring board 13 are connected using a flexible wiring board 12 having flexible wiring 15. The terminals are soldered. However, this connection method has the following drawbacks. (1) Difficult to replace. (2) It is necessary to form a parent solder metal on the terminal part in advance. (3) During soldering, the joints become hot, but since there is a difference in elongation due to thermal expansion between the flexible film and glass, it is necessary to take this point into consideration. (4) There are two connection points, which increases man-hours. (The flexible wiring board 12 is the liquid crystal panel 1
Connections are required at two locations: 1 and wiring board 13. ) (5) Film wiring boards are expensive. (6) Since the film is bent and mounted, wasted space is created. Of these, (1) to (5) are major factors in increasing costs, and (6) is a major obstacle to making LCD televisions smaller and thinner. Now, connection using conductive rubber can be considered as a means to eliminate all of the above drawbacks (1) to (6). First, a generally considered form is as shown in FIG. In the figure, the same symbols as in FIG. 3 indicate the same contents. In this case, the thickness of the conductive rubber 17 is approximately 3 mm (glass thickness a+clearance b+electronic component thickness c). There is currently no conductive rubber that has such a thickness and can connect multiple terminals at a rate of 5 terminals/mm. next,
As a method for improving this, the configuration shown in FIG. 5 or 6 can be considered. FIG. 5 shows that a general electronic component 4 is attached to a wiring board 3 in order to reduce the thickness of the conductive rubber 17.
It is mounted on the back side of the panel, and the wiring is pulled out to the front side for connection to the panel. However, in this method, it is technically difficult to process through holes (about 5 holes/mm) that penetrate the substrate. Furthermore, if the pitch is increased, the substrate becomes larger, making it unsuitable for miniaturization. Also in FIG. 6, the height of the substrate at the connection portion is increased in order to reduce the thickness of the conductive rubber 7. In this method as well, there are five through holes penetrating from the bottom surface of the board (side A) to the end surface of the board (side B).
It is technically difficult to form at a rate of approximately 1 mm/mm. As described above, it is technically difficult to connect the flat wiring board 3 and the liquid crystal panel 1 using conductive rubber. However, these problems can be solved by using the folded wiring board according to the present invention. One embodiment will be described below based on FIG. 7. The wiring board 18 with bent edges is attached to the liquid crystal panel 11.
The conductive rubber 17 connects the micropitch multi-terminals of the liquid crystal panel 11 and the wiring board 18 at the bent edges. As described above, the bent portion is provided with a thin film wiring having good adhesion to an organic insulating layer such as Al or Al alloy. Further, the electronic component 14 is attached to the bottom surface of the recess of the bent wiring board 18. With such a structure, both the thickness of the conductive rubber and the clearance with parts can be set to any desired length. Therefore, connections of about 5 wires/mm are possible by using the current thin conductive rubber. Also,
Even if the conductive rubber pressing jig 20 is required, it can be attached without particularly increasing the thickness by utilizing the space A created by bending. Compared to conventional structures, LCD TV modules with this structure are more efficient in mounting as they eliminate all wasted space, which greatly promotes miniaturization and thinning. Therefore, all of the conventional drawbacks (1) to (5) mentioned above are eliminated, and a significant cost reduction is achieved. Although the above embodiment describes a driver module for a liquid crystal television, the present invention can also be applied to flat display devices such as EL displays, plasma displays, electrochromic displays, etc. It can also be applied to learning devices and game devices. As described above, according to the present invention, a wiring board is formed using a metal plate on which a wiring conductor is formed through an organic insulating layer, and a bent part is provided on the wiring board to incorporate the wiring conductor into a housing of various electronic devices. The wiring board can be processed into any shape to fit the mounting space without damaging the mounting space, making it easier to design the wiring board and electronic equipment, and enabling high-density mounting of the components that make up the equipment. A wiring board suitable for miniaturization and thinning can be obtained. Therefore, in this way, metal plates, polyimide, and
By effectively combining Al thin films, it is always fixed in a fixed shape with a single bend.
It is possible to function as a highly reliable board with no disconnections, and this bending makes it possible to create a minimum space for mounting electronic components, so when constructing a module using this, it is possible to Enables reliable electrical connection compatible with wiring.

[Brief explanation of drawings]

FIGS. 1a to 1g are process cross-sectional views illustrating the manufacturing process of a wiring board according to the present invention. FIG. 2 is a characteristic diagram showing a stress-elongation curve of a wiring conductor. Third
4, 5, and 6 are configuration diagrams illustrating the configuration of the liquid crystal panel module. FIG. 7 is a configuration diagram showing one embodiment of a liquid crystal panel module using the wiring board of the present invention. DESCRIPTION OF SYMBOLS 1... Metal plate, 2... First organic insulating layer, 3...
... lower wiring conductor, 4 ... second organic insulator layer, 5 ...
... Through hole hole, 6 ... Terminal section, 7 ... Upper wiring conductor, 8 ... Semiconductor device, 9 ... Conductive paste, 10 ... Outer lead, 11 ... Liquid crystal panel, 14 ... Electronic component, 17 ... ...Conductive rubber, 1
8...Wiring board.

Claims (1)

[Scope of Claims] 1. A metal plate 1 on which a lower wiring conductor 3 made of an ionically deposited thin film of Al is patterned on its main surface through an insulating layer 2 mainly made of polyimide, and said lower wiring conductor. 3, and a device 8 electrically connected by soldering to an upper wiring conductor 7 whose surface is made of Ni or Cu at least. The three-layer structure of the metal plate 1, the insulating layer 2, and the lower wiring conductor 3 is provided with a bent part formed by drawing or bending at the end of the three-layer structure, the shape of which is fixed; A wiring board characterized in that it has a current-carrying circuit disposed from a wiring conductor 7 through the lower wiring conductor 3 over a main surface area of the metal plate 1 bordering on the bent portion.