JPH04353472A - Manufacture of thermal head - Google Patents

Abstract

PURPOSE:To simplify the constitution of a thermal head and to markedly enhance the mass productivity and manufacturing yield thereof. CONSTITUTION:The pattern of circuit wiring 38 is formed on the insulating substrate 23 constituting a head substrate 33 using nickel and a pattern is formed in the connection region 41 on the circuit wiring 38 by the electroless plating of a metal 42 to constitute a connection terminal 43. A drive circuit element 25 is connected to the connection terminal 43 through a solder bump 40.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thermal head used as a printing output device such as a facsimile machine or a word processor.

0002

2. Description of the Related Art Conventionally, thermal printers have been widely used as print output devices for word processors and the like. The thermal head installed in a thermal printer has a pattern of electrodes corresponding to a plurality of heat generating resistors on a ceramic substrate, and solder bumps are formed on the drive circuit element that drives the heat generating resistors to generate heat. Connected to circuit wiring by face-to-face bonding. Here, in order to easily achieve mass production and high density, a flip chip is used for the drive circuit element as a technique for mounting the drive circuit element on a ceramic substrate, and the electrodes of the flip chip are connected via solder bumps. The points to be connected on the ceramic substrate and the wiring pattern in the thermal head are formed from an aluminum thin film with a specific resistance of 2.65 x 10-6 Ωcm (20°C), and among the wiring patterns,
At least the part where the flip chip is wirelessly bonded is coated with nickel, as an example of Japanese Patent Laid-Open No. 6
0-12853 or Japanese Patent Laid-Open No. 61-244567.

FIG. 6 is an enlarged sectional view of such a conventional thermal head 1. As shown in FIG. The thermal head 1 includes an insulating substrate 2 made of alumina ceramic or the like, on which circuit wiring 3 made of aluminum is patterned. A nickel layer 4 is patterned on the connection portion 8 of the circuit wiring 3, and a gold layer 5 is further patterned on the nickel layer 4 to form a connection terminal 9. Drive circuit elements 6 configured as integrated circuit elements are connected to connection portions 8 where connection terminals 9 of circuit wiring 3 are formed, with solder bumps 7 facing each other and in contact with each other. The reason why the nickel layer 4 is provided on the circuit wiring 3 is to improve the bonding property of the melt with the solder bump 7, and the gold layer 5 is provided to prevent a decrease in solder leakage due to oxidation of the nickel layer 4. provided.

FIG. 7 is a process diagram illustrating the manufacturing process of such a connecting terminal 9. In step c1, the circuit wiring 3 is patterned using an aluminum thin film on the insulating substrate 2. In step c2, a nickel layer 4 is patterned on the connection portion 8 of the circuit wiring 3, and in step c3, a gold layer 5 is patterned on the nickel layer 4. Such steps c1-c
3 are realized using a photo process using a photoresist, which is known as a thin film forming technique.

[0005]

[Problem to be solved by the invention] Such a conventional example is
When forming the connection terminals 9 to be connected to the solder bumps 7 of the drive circuit element 6, at least three manufacturing steps shown in FIG. 7 are required, which complicates the steps and reduces mass productivity and manufacturing yield. There is a problem with this.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a thermal head that solves the above-mentioned technical problems, simplifies the structure, and significantly improves mass productivity and manufacturing yield.

[0007]

[Means for Solving the Problems] The present invention provides a circuit wiring pattern for energizing a heating resistor layer provided on an insulating substrate, the circuit wiring pattern comprising the following (A) and (
This is a method for manufacturing a thermal head, characterized in that it is formed by the step B).

(A) A step of patterning a conductor made of a first metal material that has a relatively low ionization tendency and is harder than aluminum on an insulating substrate. (B) A step of forming a coating layer made of a second metal material having a smaller ionization tendency than the first metal material at a predetermined connection site on the circuit wiring by electroless plating.

[0009]

[Operation] The method for manufacturing a thermal head according to the present invention is as follows:
A circuit wiring made of a first metal material having a relatively low ionization tendency and higher hardness than aluminum is provided on the insulating substrate, and a circuit wiring made of a first metal material having a relatively low ionization tendency and a higher hardness than aluminum is provided at a predetermined connection site on the circuit wiring. A small covering layer of a second metal material is formed by a well-known photo process. When manufacturing such a wiring board, the circuit wiring is patterned on an insulating substrate, and an electroless plating method is used to form a coating layer made of a second metal at the connection portion on the circuit wiring. Form.

[0010] This greatly simplifies the structure compared to, for example, a structure in which circuit wiring made of aluminum is formed on an insulating substrate and a nickel layer and a gold layer are laminated at the connection portion. Further, the circuit wiring made of aluminum is omitted, and the circuit wiring is made of the first metal material. This simplifies the manufacturing process, improves mass productivity, and improves manufacturing yield.

[0011]

[Embodiment] FIG. 1 is a sectional view of a head substrate 33 as a thermal head according to an embodiment of the present invention, FIG. 2 is a sectional view of a thermal head 21 in which the head substrate 33 is used, and FIG. 21 is a plan view of FIG. The thermal head 21 includes a heat dissipation plate 22 made of a metal material such as aluminum, and a heat dissipation plate 22 made of a metal material such as aluminum.
An insulating substrate 23 made of l2O3 ceramic or the like is fixed with an adhesive layer 30. A heat storage layer 35 is formed on the insulating substrate 23 by using a thick film technique such as screen printing to have a thickness of 80 μm using silicate glass, for example.
Further, a thick film common electrode layer 27 is formed along the outer periphery of the insulating substrate 23.

For example, tantalum nitride T is provided on the heat storage layer 35.
A resistor layer 34 obtained by forming a3N4 to a thickness of several hundred angstroms, a common electrode 36, and a plurality of individual electrodes 37 are formed to constitute a plurality of linearly arranged heat generating resistors 24. Each heating resistor 24 is covered with a protective layer 39 made of, for example, silicon nitride, Si3N4, and formed by a thin film technique such as sputtering, thereby forming a head substrate 33. The head substrate 33 performs thermal printing on the thermal paper 32 between the head substrate 33 and the platen roller 31 via the protective layer 39 .

A predetermined number of individual electrodes 37 are connected to a drive circuit element 25, and a signal line 29 is connected to the drive circuit element 25 to which data for printing operation and various control signals are input from the outside. . These drive circuit elements 25 are covered with a protective layer 26 made of synthetic resin material. The heating resistor 24 is a drive circuit element 2 realized as an integrated circuit element.
5. A protective layer 39 is provided on the drive circuit element 25.
The individual electrode 37 coated with is connected.

The drive circuit element 25 includes solder bumps 4
0, and is connected to the head substrate 33 by face-down bonding. A signal line 29 is provided on the insulating substrate 23 of the head substrate 33.
, circuit wiring 38 such as a common electrode 36 and individual electrodes 37
is patterned from a thin nickel film as shown in FIG.
A gold layer 42 is patterned at a connection site 41 to which 0 is connected.

FIG. 4 is a process diagram illustrating a manufacturing process for manufacturing the head substrate 33 shown in FIG. 1. In step a1 of FIG. 4, a nickel thin film is formed on the entire surface of the resistor layer 34 on the insulating substrate 23, and the circuit wiring 38 is patterned by a photo process using a normal photoresist. Gold layer 4 was formed using the same photo process as above.
2 is patterned.

FIG. 5 is a process diagram illustrating the details of step a2. After the circuit wiring 38 is patterned on the resistor layer 34 on the insulating substrate 23, in step b1, a photoresist is coated over the entire surface of the insulating substrate 23 to cover the circuit wiring 38, and the connection portion 41 is coated with photoresist. The photoresist is exposed to light in such a way that it is removed, developed, and a window opening process is performed. In step b2, a predetermined amount of etching is performed using hydrofluoric nitric acid or the like through the through hole formed at the location corresponding to the connection portion 41 of the photoresist, and the surface of the nickel exposed from the through hole is pretreated. . In step b3, the surface of such an insulating substrate 23 is immersed in a solution containing gold, and a gold layer 42 is formed by a substitution reaction between nickel constituting the circuit wiring 38 and gold. That is, electroless gold plating is performed. In step b4, the remaining photoresist is peeled off,
In this way, the gold layer 42 shown in FIG. 1 is patterned.

At this time, the gold layer 42 is used to prevent oxidation of the surface of the connection portion 41 of the circuit wiring 38 made of nickel, and the film thickness is, for example, 0.01 to 0.10.
μm may be selected. That is, although nickel (Ni) generally has relatively low wettability to solder, the oxidized surface has extremely low solder wettability.

Furthermore, by forming the gold layer 42 on the connection portion 41 in this manner, when the solder bump 40 is heated and melted to make a connection with the connection portion 41, the surface of the molten solder is oxidized. The area other than the connection part 41 of the circuit wiring 38 is repelled, and it only rides on the gold layer 42.
Solder bumps 40 can be used efficiently for connection.

As described above, the circuit wiring 38 made of nickel
can be firmly connected to the solder bumps 40 via the gold layer 42, and even when nickel is used for the circuit wiring 38, the drive circuit element 25 and the like can be connected by solder.

Furthermore, in this embodiment, when forming the connection terminal 43 on the insulating substrate 23, the number of laminated metal layers can be reduced by one, which simplifies the manufacturing process, compared to the conventional example. This makes it possible to significantly improve mass productivity and manufacturing yield. Further, since nickel has a higher hardness than aluminum, when the thermal head 21 is actually used, the mechanical strength of the thermal head 21 is improved, reliability can be improved, and the service life can be extended.

The circuit wiring 38 is not limited to nickel, but may also be made of a nickel alloy (for example, Ni- Cr, Ni-T
Examples using other metals and alloys are also included in the present invention.

Note that in this embodiment, the resistor layer 13
Although the case where a nickel thin film was formed on the insulating substrate 23 was shown, similar effects could be obtained even if the nickel thin film was immediately formed on the insulating substrate 23 by sputtering or vapor deposition.

[0023]

[Effects of the Invention] As described above, according to the method of manufacturing a thermal head of the present invention, circuit wiring made of a first metal material that has a relatively low ionization tendency and is harder than aluminum is provided on an insulating substrate. A coating layer made of a second metal material having a smaller ionization tendency than the first metal material is formed at a predetermined connection site on the circuit wiring. When manufacturing such a wiring board, the circuit wiring is patterned on an insulating substrate, and an electroless plating method is used to form a coating layer made of a second metal at the connection portion on the circuit wiring. Form.

[0024] This greatly simplifies the structure compared to, for example, a structure in which circuit wiring made of aluminum is formed on an insulating substrate and a nickel layer and a gold layer are laminated at the connection portion. Further, the circuit wiring made of aluminum is omitted, and the circuit wiring is made of the first metal material. This simplifies the manufacturing process, improves mass productivity, and improves manufacturing yield.

[Brief explanation of drawings]

FIG. 1 is an enlarged sectional view of a head substrate 33 according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the thermal head 21. FIG.

FIG. 3 is a plan view of the thermal head 21. FIG.

FIG. 4 is a process diagram illustrating the manufacturing process of the connection terminal 43.

FIG. 5 is a process diagram illustrating the manufacturing process of the gold layer 42.

FIG. 6 is an enlarged sectional view of a conventional thermal head 1.

FIG. 7 is a process diagram illustrating a manufacturing process of a conventional connection terminal 9.

[Explanation of symbols]

21 Thermal head 23 Insulating substrate 25 Drive circuit element 29 Signal line 33 Head board 36 Common electrode 37 Individual electrode 38 Circuit wiring 40 Solder bump 41 Connection part 42 Gold layer 43 Connection terminal

Claims (1)

[Claims] 1. A circuit wiring pattern for energizing a heating resistor layer provided on an insulating substrate, characterized in that the circuit wiring pattern is formed by the following steps (A) and (B). A method for manufacturing a thermal head. (A) A process of forming a pattern on an insulating substrate of a conductor made of a first metal material that has a relatively low ionization tendency and is harder than aluminum. (B) A step of forming a coating layer made of a second metal material having a smaller ionization tendency than the first metal material at a predetermined connection site on the circuit wiring by electroless plating.