JPH0779188B2 - Method for manufacturing double-sided wiring board - Google Patents

Description

The present invention relates to a method for manufacturing a double-sided wiring board.

[Prior Art] In recent years, in a thermal print head, there is a demand for finer pitches of a heating resistor and an electrode wiring in accordance with miniaturization and higher density. In such a thermal print head, a large number of heat generating resistors are arranged on a substrate at equal intervals, and a select electrode and a common electrode are opposed to each other with each heat generating resistor sandwiched therebetween and connected to each heat generating resistor. The structure is such that the drive transistor of the IC chip is connected.

In this thermal print head, if a heating resistor and an IC chip are provided on the same surface of the board, the overall size of the device will increase, so a heating resistor will be provided on the front side of the board and on the back side.
The miniaturization by mounting an IC chip is being considered.

[Problems to be Solved by the Invention] However, in the above-mentioned thermal print head, in order to mount the IC chip on the back surface side of the substrate and connect each driving transistor of this IC chip to each selection electrode on the front surface of the substrate. Is
It is necessary to form through holes on the front and back surfaces of the substrate on each selection electrode, but since the through holes are conventionally formed by machining such as drilling or punching,
It is difficult to form fine holes. Therefore, there is a problem that the selection electrode cannot be formed with a width smaller than the hole diameter of the through hole, high-density wiring is difficult, the entire substrate becomes large, and miniaturization cannot be achieved. Even if the select electrode is formed with a fine width, the above-mentioned problem occurs because the portion where the through hole is formed must be formed with a width wider than the hole diameter of the through hole.

An object of the present invention is to provide a method for manufacturing a double-sided wiring board, which can form a through hole with a fine hole diameter, can achieve miniaturization of electrodes such as selection electrodes, and can achieve high-density wiring and miniaturization of the board. Is.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a method for manufacturing a double-sided wiring board in which electrodes provided on both surfaces of the board are electrically connected by through holes. The electrode is formed by a conductive layer composed of an underlayer made of a metal other than gold on one surface and a gold layer provided on the upper surface of the underlayer and the other surface of the substrate, and the reaction is performed using the gold layer as a mask. A through hole is formed by penetrating the underlying layer and the substrate at a location corresponding to the electrode by the reactive ion etching.

[Operation] The operation of the present invention is as follows.

Since the through hole penetrating the substrate is formed at a position corresponding to the electrode by the reactive ion etching, the through hole can be formed with a fine hole diameter. Therefore, the electrodes can be formed on both surfaces of the substrate with a fine width and a fine pitch, and the high-density wiring and the substrate can be downsized. In particular, since the uppermost part of the conductive layer is formed of a gold layer, this gold layer can be used as a mask,
The manufacturing process can be simplified, and fine through holes can be accurately formed during reactive ion etching.

[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 part of the thermal print head. In these figures, 1 is a film substrate. The film substrate 1 is made of synthetic resin such as polyimide.
A large number of selection electrodes 2 and common electrodes 3 are arranged facing each other over the entire area in the width direction so as to face each other. A connection electrode 4 corresponding to the selection electrode 2, a ground electrode 5 corresponding to the common electrode, and an input electrode 6 are arranged on the lower surface. The selection electrode 2 and the connection electrode 4 are electrically connected to each other through a through hole 7, and the common electrode 3 and the ground electrode 5 are connected to a predetermined portion through a through hole 8. Each of these electrodes 2 to 6 has a structure in which an Au layer is plated directly on the surface of a metal layer such as Cu or Al or via a Ni layer or the like, and the film thickness is formed to be relatively thick, about 10 μm. As a result, as will be described later, the width is 30 to 70 μm.
Even if it is small, it is possible to conduct a large current.

In this case, the selection electrodes 2 are each formed in a thin strip shape as shown in FIG. 2, and these are equally spaced, for example, 16 dots.
If it is / mm, it is arranged in parallel at intervals of about 62.5 μm. Along with this, the connection electrodes 4 on the lower surface side are the selection electrodes 2
The portions corresponding to are arranged at the same intervals, but the portions extending to the IC chip 15 side described later are arranged at a narrower interval. Therefore, the through hole 7 connecting the selection electrode 2 and the connection electrode 4 is formed by a reactive ion etching (RIE) described later with a hole diameter (for example, about 10 to 20 μm) smaller than the width of each electrode 2, 4. Moreover, the common electrode 3 is formed in a comb shape. That is, one end on the side of the selection electrode 2 is formed in the same shape as the selection electrode 2, and is arranged in a so-called zigzag pattern in which the one end is separated from each end of the selection electrode 2 by a predetermined distance and the positions are alternately displaced in the arrangement direction. And
The other end 6 is formed in a wide band shape along the arrangement direction of the above-mentioned one end, and each one end is connected. The ground electrode 5 on the lower surface side is provided corresponding to the wide portion of the common electrode 3. 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. The input electrode 6 is formed similarly to the above-mentioned electrode.

On the other hand, on the film substrate 1, as shown in FIG. 1, a fiber 9 is adhered between the selection electrode 2 and the common electrode 3 with an adhesive 10. The fiber 9 is a linear fiber made of glass, quartz, resin, or the like, and may or may not be transparent. The fiber 9 has a thickness of about 50 μm and is provided so as to project above the upper surfaces of the electrodes 2 and 3. The adhesive 10 is preferably a polyimide-based adhesive that has high reliability against heat stress, but is not limited to this. The thin-film heat generation resistance layer 11 is provided on the fiber 9 with the electrodes 2, 3
Are provided in a strip shape along the arrangement direction. That is,
The thin-film heat generation resistance layer 11 is formed in a band shape having a width wider than that between the electrodes 2 and 3 facing each other, passes over the fiber 9, and both side ends thereof extend to and are connected to respective facing end portions of the selection electrode 2 and the common electrode 3. Has been done. The thin-film heat generation resistance layer 11 is made of tantalum nitride,
It is made of ruthenium oxide, ion-doped polysilicon, etc. and has a thin film thickness of about 1000Å. A protective layer 12 is provided on the upper surface of these. This protective layer has a two-layer structure of a moisture-resistant protective film 13 such as SiO ₂ and a wear-resistant protective film 14 such as Ta ₂ O ₅ , but it may have a single-layer structure.

The IC chip 15 is connected to the connection electrode 4 and the input electrode 6 on the lower surface of the film substrate 1. This IC chip 15
Includes a drive transistor that selectively supplies a print current to each selection electrode 2 through the connection electrode 4, a control element that controls the drive transistor, and the like. The array is formed. Each bump 16 of the IC chip 15 is joined to the connection electrode 4 and the input electrode 6 by a face-down method such as a flip-chip method, and the joining portion is resin-sealed with a sealing resin 17. Further, an insulating film 19 is adhered to the lower surface of the film substrate 1 with an adhesive 18, and a metal plate 20 for heat dissipation is adhered to the lower surface of the insulating film 19 with an adhesive 21. In this case, the IC chip 15
Has an opening 22 through which the IC
A storage recess 23 for storing the chip 15 is formed.

Next, the case where the electrodes 2 to 6 are formed on the film substrate 1 of the above-mentioned thermal print head will be described.

In this case, first, Cr is deposited on both upper and lower surfaces of the film substrate 1 by a vacuum deposition method or a sputtering method, a Cu layer is laminated thereon by electrolytic plating, and a direct or Ni plating layer is further formed thereon. The Au layer is laminated by electrolytic plating.
In this case, the Cu layer and the Ni layer each have a thickness of about 5 μm, and the Au layer has a thin thickness of about 0.5 μm. As a result, a metal layer having an Au layer deposited on the top is formed with a film thickness of about 10 μm. Then, a resist is patterned on this metal layer by photolithography, and only the Au layer of the metal layer is etched using this resist as a mask,
The Au layer corresponding to the through holes 7 and 8 is removed.
In this case, the portion corresponding to the through hole 7 is formed to have a small diameter, and the portion of the through hole 8 is formed to have a larger diameter. As a result, the Au layer is patterned. Then, reactive ion etching is performed using the Au layer as a mask. At this time, O ₂ gas is used as a reaction gas. Therefore, the Au layer does not react with the reaction gas,
Only the place where the Au layer is removed is etched. As a result, a through hole 7 penetrating the film substrate 1 through the metal layer is formed at a small diameter portion of the Au layer, and
A through hole 8 penetrating the film substrate 1 through a metal layer is formed at a portion having a large diameter. In this case, since the reactive ion etching can perform fine processing, it is possible to form the small-sized through hole 7 with a hole diameter of about 10 to 20 μm. Therefore, even if the width of the selection electrode 2 and the connection electrode 4 is as narrow as about 30 to 70 μm, the through hole 7 can be reliably formed within the width. After that, a resist is patterned again on the upper surface of the metal layer by photolithography, and the resist is used as a mask for the metal layer (Au
(Including layers) to remove unwanted portions of the metal layer. As a result, the selection electrode 2, the common electrode 3, the connection electrode 4, the ground electrode 5, and the input electrode 6 are patterned on the upper and lower surfaces of the film substrate 1. After that, a resist is applied to the portions other than the through holes 7 and 8, and then a conductive layer is deposited on the inner surfaces of the through holes 7 and 8 by electroless plating or sputtering. As a result, the selection electrode 2 and the connection electrode 4 are connected by the through hole 7, and the common electrode 3 and the ground electrode 5 are connected by the through hole 8.

As described above, according to the above-described thermal print head, the through hole 7 that connects the selection electrode 2 and the connection electrode 4 can be formed with a fine hole diameter, so that the width and interval of each electrode 2, 4 can be made fine. Can be formed, and high-density wiring and high-density mounting are possible, and by extension the film substrate 1
The entire size can be reduced. Therefore, in this thermal print head, the thin film heat generation resistance layer 11 can be provided on the upper surface side of the film substrate 1 and the IC chip 15 can be mounted on the lower surface side, so that even if the size is reduced, the heat generating portion is pressed against the platen or the like. When the thermal printing is performed on the recording paper by the IC chip 15, the IC chip 15 does not interfere with the platen, and the thermal printing can be favorably performed.

The present invention is not limited to the above embodiment. For example, the substrate need not be the film substrate 1, but may be a glass substrate, a quartz substrate, a ceramic substrate, or the like. The selection electrodes 2 and the common electrodes 3 do not necessarily have to be arranged in a zigzag pattern, and the ends of the electrodes 2 and 3 may be arranged so as to face each other with a space therebetween. Furthermore, the present invention is not limited to substrates for thermal print heads, but can be widely applied to general methods for manufacturing double-sided substrates.

[Effects of the Invention] As described in detail above, according to the present invention, a through hole penetrating the substrate is formed at a position corresponding to the electrode by reactive ion etching, so that the through hole is formed with a fine hole diameter. be able to. Therefore, electrodes can be formed on both surfaces of the substrate with a fine width and a fine pitch, and high-density wiring and miniaturization of the entire substrate can be achieved. In particular, since the uppermost part of the conductive layer is formed of a gold layer, the gold layer can be used as a mask, the manufacturing process can be simplified, and fine through holes can be formed during reactive ion etching. Can be accurately formed.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention.
FIG. 1 is an enlarged cross-sectional view of the main part of the thermal print head, and FIG. 2 is a plan view of the main part before a protective layer is provided. 1 ... film substrate, 2 ... selection electrode, 4 ... connection electrode, 7 ... through hole.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-58-70594 (JP, A) JP-A-60-138992 (JP, A) JP-A-63-302591 (JP, A)

Claims (1)

[Claims] 1. A method for manufacturing a double-sided wiring board in which electrodes provided on both sides of a substrate are electrically connected by through holes, wherein an underlayer made of a metal other than gold is provided on at least one side of the substrate, and the underlayer. Forming an electrode with a conductive layer consisting of a gold layer provided on the upper surface of the substrate and the other surface of the substrate, and using the gold layer as a mask, the underlying layer and the portion of the base layer corresponding to the electrode by reactive ion etching. A method for manufacturing a double-sided wiring board, which comprises forming a through hole penetrating the board.