JPH0434989A - Manufacture of double-sided wiring board - Google Patents

Abstract

PURPOSE:To contrive the miniaturization of electrodes, such as a selective electrode and the like, and to contrive a high-density wiring and a reduction in the size of a substrate by a method wherein conductive layers, whose uppermost parts consist of a gold layer, are respectively formed on both surfaces of the substrate and a through hole which penetrates the substrate is formed at places, where respectively correspond to the electrode on the upper surface of the substrate and the electrode on the lower surface of the substrate, by performing a reactive ion etching using the metal layers of the uppermost parts as masks. CONSTITUTION:A through hole 7, through which a selective electrode 2 is connected with a connection electrode 4, can be formed at a fine hole diameter. As a result, the widths of the electrodes 2 and 4 and the interval between the electrodes 2 and 4 can be formed fine, a high-density wiring and a high-density mounting become possible and in its turn a reduction in the size of the whole film substrate 1 becomes possible. Accordingly, in this thermal printing head, a thin film heating resistance layer 11 is provided on the side of the upper surface of the substrate 1 and an IC chip 15 can be mounted on the side of the lower surface of the substrate. Thereby, even if the size of the whole substrate 1 is reduced, the chip 15 does not obstruct a platen when a heat generating part is pushed against the platen or the like and a heat-sensitive printing is performed on a recording paper and the heat-sensitive printing can favorably be conducted.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a double-sided wiring board.

[Prior Art] In recent years, with the miniaturization and higher density of thermal print heads, there has been a demand for finer pitches for heating resistors and electrode wiring. Such a thermal print head has a large number of heating resistors arranged at equal intervals on a substrate, a selection electrode and a common electrode facing each other across each heating resistor, and connected to each heating resistor. It has a structure in which drive transistors of IC chips are connected.

In this thermal print head, installing a heating resistor and an IC chip on the same side of the board would increase the size of the entire device, so the heating resistor is installed on the front side of the board and the IC chip is mounted on the back side. Aiming for miniaturization is being considered.

[Problems to be Solved by the Invention] However, in the thermal print head described above, an IC chip is mounted on the back side of the substrate, and in order to connect each drive transistor of this IC chip to each selection electrode on the front surface of the substrate, However, since through holes are conventionally formed by mechanical processing such as drilling or punching, it is difficult to form micro holes in each selection electrode. Have difficulty. Therefore,
The selection electrode cannot be formed with a width finer than the diameter of the through hole, making high-density wiring difficult, making the entire substrate large, and making it impossible to achieve miniaturization. Even if the selection electrode is formed with a minute width, the area where the through hole is formed must be formed with a width wider than the diameter of the through hole, which causes the above-mentioned problem.

An object of the present invention is to provide a method for manufacturing a double-sided wiring board, which allows through-holes to be formed with a fine hole diameter, miniaturizes electrodes such as one selection electrode, and enables high-density wiring and miniaturization of the board. It is.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention forms conductive layers on both sides of a substrate, at least the uppermost portion of which is a gold layer, and uses the uppermost gold layer as a mask to conduct a reactive layer. The method involves forming through holes penetrating the substrate at locations corresponding to the electrodes by ion etching.

[Effect] The operation of this invention is as follows.

Since a through hole penetrating the substrate is formed at a location corresponding to the electrode by reactive ion kneading, the through hole can be formed with a fine hole diameter. Therefore,
Electrodes can be formed on both sides of the substrate with fine convergence and fine pitch, allowing for high-density wiring and miniaturization of the substrate.

In particular, since the top of the conductive layer is formed of a gold layer, this gold layer can be used as a mask, simplifying the manufacturing process, and allowing fine etching during reactive ion etching. Through holes can be formed with high precision.

[Embodiment] An embodiment in which the present invention is applied to a thermal print head will be described below with reference to FIGS. 1 and 2.

1 and 2 show the main parts of a thermal print head. In these figures, 1 is a film substrate. This film substrate 1 is made of synthetic resin such as polyimide. On the upper surface thereof, a large number of selection electrodes 2 and common electrodes 3 are arranged facing each other and spaced apart over the entire width direction. On the bottom surface, there are a connection electrode 4 corresponding to the selection electrode 2, and a ground electrode 5 corresponding to the common electrode. and input electrodes 6 are arranged. The selection electrode 2 and the connection electrode 4 are electrically connected to each other by a through hole 7, and the common electrode 3 and the ground electrode 5 are connected to each other at a predetermined point by a through hole 8. These electrodes 2 to 6 each have a structure in which an Au layer is plated on the surface of a metal layer such as C11OAI directly or via a Ni layer, etc., and the film thickness is relatively thick at about 10 pm. As will be described later, even when the width is as small as about 30 to 70 ILm, it is possible to conduct a large current.

In this case, as shown in FIG. 2, the selection electrodes 2 are formed into thin strips, and if they are arranged at equal intervals, for example 16 dots)/mm, they are arranged in parallel at intervals of about 62.57 zm. There is. Accordingly, the portions of the connection electrodes 4 on the lower surface side corresponding to the selection electrodes 2 are arranged at the same spacing, but the portions extending toward the IC chip 15, which will be described later, are arranged at narrower intervals. . Therefore, the through holes 7 connecting the one selection electrode 2 and the connection electrode 4 are formed by reactive ion etching (RIE), which will be described later.
．． It is formed with a hole diameter smaller than the width of No. 4 (for example, about 10 to 207 tm). Further, the common electrode 3 is formed in a comb shape. That is, one end of the first selection electrode 2 side is formed in the same shape as the selection electrode 2, and is spaced apart from each end of the selection electrode 2 by a predetermined interval and arranged in a so-called zigzag pattern in which the positions are alternately shifted in the arrangement direction. The other end 6 is formed in a wide band shape along the arrangement direction of the one end, and the ground electrode 5 on the lower surface side to which each end is connected corresponds to the wide part of the common electrode 3. It is provided. therefore,
The through hole 8 connecting the common electrode 3 and the ground electrode 5 does not need to be formed with a small hole diameter like the through hole 7 described above, but is formed with a relatively large hole diameter. Note that the input electrode 6 is formed similarly to the electrode described above.

On the other hand, on the film substrate l, as shown in Sta, a fiber 9 is connected with an adhesive lO between the selective electrode 2 and the common electrode 3.
It is glued by. The fiber 9 is a linear material made of glass, quartz, resin, etc., and may or may not be transparent. It is provided so as to protrude upwards. The adhesive 10 is desirably made of polyimide, which is highly reliable against thermal stress, but is not limited to this.A thin film heating resistor layer 11 is formed on the fiber 9 along the direction in which the electrodes 2.3 are arranged. It is arranged in a strip shape. That is, the thin film heat generating resistance layer 11 is formed in a band shape with a width wider than the width between the opposing electrodes 2.3, and extends over the fiber 9.
Both ends thereof extend over and are connected to opposing ends of the selection electrode 2 and the common electrode 3, respectively. This thin film heating resistance layer 11 is made of tantalum nitride, ruthenium oxide, polysilicon doped with ions, etc., and is formed to have a thin film thickness of about 1000λ. Note that a protective layer 12 is provided on these upper surfaces. This protective layer is a moisture-resistant H-retaining film 1 such as 5i02.
Although it has a two-layer structure consisting of a wear-resistant protective film 14 such as No. 3 and No. 205, it may have a single-layer structure.

Further, on the lower surface of the film substrate 1, an IC chip 15 is connected to the connection electrode 4 and the input electrode 6. This IC chip 15 incorporates a drive transistor that selectively supplies printing current to each selection electrode 2 via the connection electrode 4, a control element for controlling this drive transistor, etc., and has bumps on its upper surface. 16 are arranged in a protruding manner. Each bump 16 of the IC chip 15 is bonded to the connection electrode 4 and the input electrode 6 by a face-down method such as a flip-chip method, and the bonded portion is resin-sealed with a sealing resin 17. Further, an insulating film 19 is bonded to the lower surface of the film substrate 1 with an adhesive 18, and a metal plate 2o for heat dissipation is bonded to the lower surface of this insulating film 19 with an adhesive 21. in this case,
An opening 22 through which the IC chip 15 is inserted is formed in the insulating film 19, and an IC chip 15 is inserted into the metal plate 2o.
A storage recess 23 is formed to store the storage device 5.

Next, the film substrate l for the thermal printing described above is
The case where each electrode 2 to 6 is formed will now be described.

In this case, first, Cr is applied to both the upper and lower surfaces of the film substrate l.
is deposited by vacuum evaporation or sputtering, and then C
A U layer is laminated by electrolytic plating, and an Au layer is further laminated thereon directly or via an Xi plating layer by electrolytic plating. In this case, the Cu layer and Xi calendar are each 5.
gm, and the Au layer is about 0.5. It is formed as thin as about m. As a result, a metal layer with an Au layer deposited on top is formed with a film thickness of about 10 JLm. Then, a resist is patterned on this metal layer by photolithography technology, and this resist is used as a mask to form the Au of the metal layer.
Milli-etch the layer and remove the A1 layer at the location corresponding to the through hole 7.8. In this case, the portion corresponding to the through hole 7 is formed with a small diameter, and the portion of the through hole 8 is formed with a larger diameter. This results in
The Au layer is patterned. After that, reactive ion etching is performed using the Au layer as a mask. At this time, 02 gas is used as the reactive gas. Therefore, the Au layer does not react with the reactive gas, and only the areas where the Au layer has been removed are etched. be done. As a result, a through hole 7 that passes through the film substrate 1 through the metal layer is formed at a small diameter portion of the Au layer, and a through hole 8 that passes through the film substrate 1 through the metal layer is formed at a large diameter portion. Ru. In this case, reactive ion etching allows fine processing, so the small diameter through hole 7 can be
It is possible to form the hole with a hole diameter of about θ to 20 gm.

Therefore, the width of the selection electrode 2 and the connection electrode 4 is 30 to 7
Even if the width is as narrow as approximately 0.4 m, the through hole 7 can be reliably formed within that width. Thereafter, a resist is again patterned on the upper surface of the metal layer by photolithography, and using this resist as a mask, the metal layer (including the Ju calendar) is etched to remove unnecessary portions of the metal layer.

As a result, selection electrodes 2, common electrodes 3, connection electrodes 4, ground electrodes 5, and input electrodes 6 are patterned on the upper and lower surfaces of the film substrate l. After that, through hole 7.
After applying a resist to locations other than 8, a conductive layer is applied to the inner surface of each through hole 7.8 by electroless plating or sputtering. As a result, the selection electrode 2 and the connection electrode 4 are connected through the through hole 7, and the common electrode 3 and the ground electrode 5 are connected through the through hole 8.

In this way, according to the above-described thermal print head, the through hole 7 connecting the selection electrode 2 and the connection electrode 4 can be formed with a fine hole diameter, so that the convergence and spacing of each electrode 2.4 can be made fine. This enables high-density wiring and high-density packaging, which in turn enables film substrate l
The overall size can be reduced. Therefore, in this thermal print head, the thin film heat generating resistor layer 11 can be provided on the upper surface side of the film substrate l, and the IC chip 15 can be mounted on the lower surface side, so that even when downsized, the heat generating part can be pressed against the platen etc. Perform thermal printing on recording paper! ij to IC
The chip 15 does not get in the way of the platen, and thermal printing can be performed well.

Note that the present invention is not limited to the embodiments described above. For example, the substrate does not need to be a film substrate, but may be a glass substrate, a quartz substrate, a ceramic substrate, etc. , and the common electrodes 3 do not necessarily have to be arranged in a staggered manner, and may be arranged with the ends of each electrode 2.3 facing each other, separated from each other. The present invention can be widely applied not only to substrates but also to general methods of manufacturing double-sided substrates.

[Effects of the Invention] As explained in detail below, according to the present invention, a through hole is formed through the substrate at a location corresponding to the electrode by reactive ion etching, so the through hole can be formed with a fine hole diameter. can do. Therefore, electrodes can be formed on both sides of the substrate with fine convergence and fine pitch, and high-density wiring and miniaturization of the entire substrate can be achieved. In particular, since the top of the conductive layer is formed with a gold layer, this gold layer can be used as a mask, simplifying the manufacturing process, and making it possible to form fine through holes during reactive ion etching. can be formed with high precision.

1...Film substrate, 2...Selection electrode, 4...Connection electrode, 7...Through hole.

Claims (1)

[Claims] A method for manufacturing a double-sided wiring board in which electrodes provided on both sides of the board are electrically connected by through holes, the electrodes being connected on both sides of the board with conductive layers whose top portions are at least made of gold. A method for manufacturing a double-sided wiring board, comprising: forming a through-hole through the substrate at a location corresponding to the electrode by reactive ion etching using the uppermost gold layer as a mask.