JP6763008B2 - Wiring board manufacturing method and thermal head manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a wiring board and a method for manufacturing a thermal head .

In recent years, there has been a strong demand for smaller and lighter wiring boards. In order to reduce the size and weight of the wiring board, it is important to realize high-density wiring, but there is a problem of migration in the wiring electrode. In addition, migration (electrochemical migration) is a phenomenon in which when an electric field is applied between electrodes at narrow intervals, metal ions are deposited on the cathode side and extend to the anode side in a branch shape to short-circuit between the conductor circuits. To say.

Conventionally, a technique has been proposed which can suppress the migration of wiring electrodes and prevent defects in the substrate due to a short circuit of the wiring electrode pattern (see Patent Document 1). In Patent Document 1, a gold (Au) paste-like composition is printed on a substrate in a predetermined pattern, and silver (Ag) powder is conducted on a thick film of the formed paste-like composition. A method for manufacturing a high-density wiring board in which a paste-like composition contained as a material is printed in a size smaller than the above-mentioned predetermined pattern size is described.

Japanese Unexamined Patent Publication No. 10-209611

However, in the high-density wiring board described in Patent Document 1, a predetermined pattern of Au paste-like composition is formed by printing, and then a size smaller than the above-mentioned predetermined pattern size is formed by Ag paste-like composition. Since the pattern is formed by printing, it is not suitable for forming a fine pattern, and there is room for improvement.

According to the first aspect, the method for manufacturing a wiring substrate includes an insulating substrate, at least a pair of electrodes extending in parallel with each other and having electrode terminals at ends, and a portion other than the electrode terminals. It is a method of manufacturing a wiring substrate provided with an insulating protective film that covers the surface of the substrate, wherein the electrode terminal has a second conductive layer arranged on the insulating substrate and is on the second conductive layer. A first conductive layer having a larger ionization tendency than the second conductive layer is laminated and arranged, and the first conductive layer and the second conductive layer are subjected to a single etching process to obtain the first conductive layer. The second conductive layer is separated from the second conductive layer, and the second conductive layer is formed so as to project laterally from the first conductive layer.
According to the second aspect, in the method of manufacturing a thermal head, at least a pair of the electrodes are formed on the glaze layer of a substrate provided with a glaze layer by using the method of manufacturing a wiring board according to the first aspect. On the glaze layer of the substrate, a band-shaped common electrode having one end side provided between the pair of the electrodes is formed, and a heat generating resistance straddling the electrode and the one end of the common electrode. Form the body.

According to the present invention, it is possible to provide a highly reliable wiring board in which migration is suppressed and a higher density wiring board.

The cross-sectional schematic diagram which shows the structure of a thermal head. The schematic diagram which shows the main part of the conventional thermal head. The schematic diagram which shows the wire bonding part of FIG. 2 enlarged. The schematic diagram which shows the main part of the thermal head which concerns on 1st Embodiment. (A) is a schematic plan view of the wiring board before the etching process, and (b) is a schematic side sectional view of the wiring board before the etching process. (A) is a schematic plan view of the wiring board after the etching process, and (b) is a schematic side sectional view of the wiring board after the etching process. (A) is a partially enlarged view showing the VII part of FIG. 6 (a), and FIG. 7 (b) is a schematic cross-sectional view taken along the line Viib-viib of FIG. 7 (a). The graph which shows the experimental result about the migration resistance of a wiring board. A table showing the experimental results on the migration resistance of the wiring board. A table showing the experimental results on the sulfurization resistance of the wiring board. The schematic diagram which shows the main part of the thermal head which concerns on 2nd Embodiment. (A) is a schematic plan view of the wiring board before the etching process, and (b) is a schematic side sectional view of the wiring board before the etching process. (A) is a schematic plan view of the wiring board after the etching process, and (b) is a schematic side sectional view of the wiring board after the etching process. (A) is a partially enlarged view showing the XIV portion of FIG. 13 (a), and (b) is a schematic cross-sectional view taken along the line xivb-xivb of FIG. 14 (a). The schematic diagram which shows the main part of the thermal head which concerns on 3rd Embodiment.

− First Embodiment −
FIG. 1 is a schematic cross-sectional view showing the configuration of the thermal head 100. FIG. 2 is a schematic view showing a main part of the conventional thermal head 100. FIG. 2A is a schematic plan view of a main part of the thermal head 100, and FIG. 2B is a schematic cross-sectional view of a main part of the thermal head 100. In the schematic plan view of FIG. 2A, hatching showing a cross section of each configuration is added in FIG. 2B for convenience of explanation. FIG. 3 is a schematic view showing an enlarged view of the wire bonding portion of FIG. As shown in FIG. 1, the thermal head 100 includes a wiring board 50 and a printed wiring board 30 fixed on a support plate 32. On the printed wiring board 30, a driver IC 11 and a connector 31 for connecting the thermal head 100 to an external device that controls printing or the like are provided.

The wiring board 50 will be described in detail. The wiring board 50 has wirings and electrodes formed on the insulating substrate 12. The insulating substrate 12 is formed of an electrically insulating ceramic or the like. A glaze layer 13 made of glass or the like is formed on the entire upper surface of the insulating substrate 12. The glaze layer 13 plays a role as a heat storage layer that shortens the time required to raise the temperature of the heat generation resistor 6 described later and enhances the thermal response characteristics of the thermal head 100.

A common electrode 5 and a plurality of individual electrodes 8 are formed on the upper surface of the glaze layer 13. As shown in FIG. 2A, the common electrode 5 has a rectangular electrode surface 5a in a plan view and a transport direction of thermal paper (not shown) from the electrode surface 5a (x direction shown in FIG. 2A). It has a comb-like shape with a plurality of strip-shaped electrodes 5b extending along the above. Each of the plurality of individual electrodes 8 has a strip shape extending along the transport direction x. The plurality of strip-shaped electrodes 5b and the plurality of individual electrodes 8 are alternately arranged in the y direction orthogonal to the transport direction x.

A linear heat generating resistor 6 is formed on the common electrode 5 and the plurality of individual electrodes 8 by thick film printing or the like. The heat generation resistor 6 extends along the y direction so as to straddle the plurality of strip-shaped electrodes 5b and the plurality of individual electrodes 8. The heat generation resistor 6 is made of, for example, ruthenium oxide (RuO2) or the like.

As shown in FIG. 1, one end of each individual electrode 8 is connected to the driver IC 11 via a gold wire 10. The gold wire 10 and the driver IC 11 are molded with a sealing resin 16 made of an epoxy resin material. In the driver circuit (not shown) of the driver IC 22, a current flows from the common electrode 5 to each individual electrode 8 via the heat generating resistor 6. As shown in FIG. 2A, when a current flows through the heat generating resistor 6 between the band-shaped electrode 5b and the individual electrode 8 in the common electrode 5, that portion generates heat. When this heat is transferred to the thermal paper (not shown), the thermal paper develops color and a predetermined printed image is formed on the thermal paper.

As shown in FIG. 2, the thermal head 100 is formed with an insulating protective film 7 on the entire surface of the insulating substrate 12 so as to cover the individual electrodes 8, the common electrode 5, and the heat generating resistor 6. The insulating protective film 7 is made of, for example, a PbO-SiO2-ZrO2-based glass material having electrical insulating properties. Since the heat generating resistor 6 is covered with the insulating protective film 7, the heat of the heat generating resistor 6 is transferred to the thermal paper (not shown) through the insulating protective film 7.

As shown in FIGS. 2 and 3, conventionally, a low-purity gold-containing paste is used to form a low-purity gold layer 14 on an insulating substrate 12, and a high-purity gold-containing paste is used on an upper layer of the low-purity gold layer 14. By laminating the formed high-purity gold layers 15, the wire bonding portion 9 which is the electrode terminal of the individual electrode 8 was formed.

Gold (Au) is a metal that is less likely to migrate than silver (Ag), but it is very expensive and increases the manufacturing cost. Therefore, instead of gold, it is conceivable to use a material such as silver, which is cheaper than gold, but there is a problem that migration is more likely to occur than gold.

FIG. 4 is a diagram similar to FIG. 3, and is a schematic diagram showing a main part of the thermal head 100A according to the first embodiment. FIG. 4A is a schematic plan view of a main part of the thermal head 100A, and FIG. 4B is a schematic cross-sectional view of a main part of the thermal head 100A.

In the present embodiment, in order to reduce the amount of expensive gold used, gold is used for a part of the wire bonding portion 18 of the individual electrode 8 and silver is used for the other part. Further, in each of the plurality of wire bonding portions 18 adjacent to each other in the y direction, the size of the second conductive layer made of gold is made larger than the size of the first conductive layer made of silver. It was decided to suppress migration by making the outermost peripheral portion a second conductive layer made of gold. Further, by utilizing the characteristic that the etching rates of the two types of conductive layers are different, the second conductive layer is projected to the side of the first conductive layer by one etching treatment for the two types of conductive layers. The stepped portion 23 or the alloy layer (alloyed portion) 24 is formed on the outer peripheral portion of the wire bonding portion 18. Since a fine pattern can be formed by the etching process, high-density wiring can be realized. The details will be described below.

The configuration of the individual electrode 17 of the thermal head 100A according to the present embodiment is different from that of the conventional individual electrode 17 of the thermal head 100, but other configurations are the same, and thus the description thereof will be omitted. The individual electrode 17 of the thermal head 100A according to the first embodiment is composed of a silver layer (first conductive layer) 20 whose wiring portion extending in the x direction is made of silver. A wire bonding portion 18 for wire bonding is provided as an electrode terminal at the end of the individual electrode 17 in the x direction.

In the present specification, the electrode terminal which is an exposed portion of the individual electrode 17 not covered with the insulating protective film 7 is referred to as a wire bonding portion 18. The wire bonding portion 18 has a laminated structure composed of a gold layer (second conductive layer) 19 made of gold provided on the insulating substrate 12 via the glaze layer 13 and a silver layer 20 provided on the gold layer 19. Has been done. The gold layer 19 has a size that is one size larger on the xy plane than the silver layer 20, and a step portion 23 or an alloy layer 24 is formed on the outer peripheral portion of the boundary between the gold layer 19 and the silver layer 20.

Since the wire bonding portion 18 is not covered with the insulating protective film 7, it is necessary to suppress the occurrence of migration between the adjacent wire bonding portions 18. In the present embodiment, in order to prevent the occurrence of migration, as described above, in the wire bonding portion 18, the outer peripheral size of the gold layer 19 is made to be one size larger than the outer peripheral size of the silver layer 20. A method of forming such a wire bonding portion 18 will be described with reference to FIGS. 5 to 7. In addition, in FIGS. 5 to 7, in order to make the explanation easy to understand, it will be described in a simple shape. In FIGS. 5 to 7, the glaze layer is omitted.

(Gold layer and silver layer forming process)
5 (a) is a schematic plan view of the wiring board before the etching process, FIG. 5 (b) is a schematic side sectional view of the wiring board before the etching process, and FIG. 5 (a) cuts the vb-vb line. The cross section is shown. As shown in FIG. 5, a gold paste-like composition (for example, the gold content is 15 to 100% by weight) is spread parallel to the short side of the insulating substrate 1 on the rectangular flat plate-shaped insulating substrate 1. Print with the existing rectangular pattern. Then, the silver paste-like composition (for example, the silver content is 15 to 100% by weight) is covered with a rectangular pattern having a size one size smaller than that of the insulating substrate 1 so as to cover the pattern of the gold paste-like composition. Print with. After that, the insulating substrate 1 is fired (for example, about 800 ° C.) to form the gold layer 2 and the silver layer 3. By firing, a gold-silver alloy layer 4 is formed at the boundary between the gold layer 2 and the silver layer 3 (not shown in FIG. 5, see FIG. 7). That is, the gold layer 2 and the silver layer 3 are laminated and arranged on the insulating substrate 1 by printing and firing. In this embodiment, since the above-mentioned step portion 23 is not formed by printing, high accuracy is not required in this step.

(Photolithography / etching process)
A substantially H-shaped pattern as shown by the alternate long and short dash line in FIG. 5 is formed by photolithography. After that, by performing a wet etching process once, that is, by immersing the wiring board in the etching solution, the portion other than the portion surrounded by the alternate long and short dash line (substantially H-shaped pattern) shown in FIG. 5A is dissolved and removed. To do.

Here, the gold constituting the gold layer 2 is a material having a lower ionization tendency than the silver constituting the silver layer 3. Therefore, the dissolution rate (etching rate) of the gold layer 2 is slower than the dissolution rate (etching rate) of the silver layer 3. In this embodiment, a potassium iodide solution in which the mixing ratio of iodine, potassium iodide, and water was 1: 2:10 (wt ratio) was used as the etching solution. In this case, there is a difference of about 3 times between the gold layer 2 and the silver layer 3 in the rate at which dissolution proceeds toward the side (side etching rate).

FIG. 6A is a schematic plan view of the wiring board after the etching treatment, FIG. 6B is a schematic side sectional view of the wiring board after the etching treatment, and the vib-vib line cutting of FIG. 6A is shown. The cross section is shown. 7 (a) is a partially enlarged view showing the VII portion of FIG. 6 (a), and FIG. 7 (b) is a schematic cross-sectional view taken along the line Viib-viib of FIG. 7 (a). As shown in FIGS. 6 and 7, in the etching treatment, the etching proceeds from the outer surface, so that the upper part of the silver layer 3 is most dissolved and the amount of dissolution decreases downward. Therefore, as shown in FIG. 7, the dimension between the opposite side surfaces in the groove 26 between the pair of substantially H-shaped patterns becomes shorter from the upper part to the lower part. Also in the gold layer 2, the upper part is most dissolved, and the dissolved amount decreases toward the lower part. Therefore, the dimension between the opposite side surfaces in the groove 27 between the pair of substantially H-shaped patterns becomes shorter from the upper part to the lower part.

As described above, in the gold layer 2 and the silver layer 3, the dissolution rate of the silver layer 3 is faster than the dissolution rate of the gold layer 2. Therefore, the distance between the grooves 26 is larger than the distance between the grooves 27.

The side surface of the groove 26 is an inclined surface that spreads laterally (outwardly) from the upper part of the silver layer 3 toward the lower side. Similarly, the side surface of the groove 27 is an inclined surface that spreads laterally (outwardly) from the upper part of the gold layer 2 toward the lower side. Since the gold layer 2 has a slower dissolution rate than the silver layer 3, a step portion 23 is formed at the outer peripheral portion of the boundary between the silver layer 3 and the gold layer 2. The gold layer 2 is formed so as to project laterally by about 1 μm as compared with the silver layer 3. Further, the alloy layer 4 formed by firing is exposed by the etching process. That is, the gold-silver alloy layer 4 is formed on the outer peripheral portion of the boundary between the gold layer 2 and the silver layer 3 by the etching process. By arranging the gold layer 2 on the outer peripheral side of the laminated structure portion and forming the gold-silver alloy layer 4, the effect of suppressing migration is improved, and the effect of suppressing sulfurization is also improved. To do.

The migration suppressing effect and the sulfurization suppressing effect will be described with reference to FIGS. 8 to 10. 8 and 9 are graphs and tables showing the experimental results of the migration resistance of the wiring board. On the wiring board used in the experiment, a pattern was formed in which the electrode length was 30 mm and the distance between the electrodes was 100 μm. After the silver layer 3 was laminated on the gold layer 2, the gold layer 2 and the silver layer 3 were subjected to photolithography etching treatment once (simultaneously). The environmental conditions were 85 ° C. and 85% RH. In this environment, a voltage of 32 V DC was applied and the voltage was continuously energized, and the time until the insulation resistance value became 10 MΩ or less, which is the determination reference value, was measured.

As a comparative example with the present embodiment, a wiring board in which the electrode is composed of only the gold layer 2 having a film thickness of 0.66 μm is used in Comparative Example 1, and the electrode is composed of only the silver layer 3 having a film thickness of 3.3 μm. Let the substrate be Comparative Example 2. Two types of wiring boards of this embodiment were prepared and experiments were conducted for each. In the first wiring board of the present embodiment, the film thickness of the gold layer 2 is 0.25 μm, and the film thickness of the silver layer 3 is 0.80 μm. That is, in the first wiring board, the film thickness of the gold layer 2 is about 1/3 of the film thickness of the silver layer 3. In the second wiring board of the present embodiment, the film thickness of the gold layer 2 is 1.00 μm and the film thickness of the silver layer 3 is 1.57 μm. That is, in the second wiring board, the film thickness of the gold layer 2 is about ⅔ of the film thickness of the silver layer 3.

As shown in FIGS. 8 and 9, in Comparative Example 1, even if the continuous energization time exceeded 2000 hours, the insulation resistance value hardly decreased, and a high migration resistance result was obtained. In Comparative Example 2, the insulation resistance value became 10 MΩ (judgment reference value) or less before the continuous energization time was less than 50 hours. As described above, there is a large difference in migration resistance between the gold layer 2 and the silver layer 3. However, in Comparative Example 1, since the electrode is composed of only the gold layer 2, the cost is increased.

As shown in FIGS. 8 and 9, in the first wiring board of the present embodiment, a result that a high insulation resistance value can be maintained up to a continuous energization time of 200 hours was obtained. It was confirmed that the migration resistance of the first wiring board was significantly improved as compared with Comparative Example 2. It was found that in the second wiring board of the present embodiment, even if the continuous energization time exceeds 2000 hours, the insulation resistance value hardly decreases, and high migration resistance can be obtained. From this experimental result, it was found that the migration resistance can be improved by increasing the ratio of the film thickness of the gold layer 2. That is, by changing the ratio of the film thicknesses of the gold layer 19 and the silver layer 20, the degree of suppression of migration can be adjusted as necessary.

FIG. 10 is a table showing the experimental results on the sulfurization resistance of the wiring board. As a comparative example of this embodiment, a wiring board in which an electrode is composed only of a gold layer 2 having a film thickness of 0.65 μm is a wiring board in which an electrode is composed of only a silver layer 3 having a film thickness of 3.3 μm. Is referred to as Comparative Example 4. Two types of wiring boards of this embodiment were prepared and experiments were conducted for each. In the third wiring board of the present embodiment, the film thickness of the gold layer 2 is 0.3 μm, and the film thickness of the silver layer 3 is 3.3 μm. That is, in the third wiring board, the film thickness of the gold layer 2 is about 1/10 of the film thickness of the silver layer 3. In the fourth wiring board of the present embodiment, the film thickness of the gold layer 2 is 3.3 μm, and the film thickness of the silver layer 3 is 0.3 μm. That is, in the fourth wiring board, the film thickness of the gold layer 2 is about 10 times the film thickness of the silver layer 3. The fourth wiring board has a configuration in which the gold layer 2 is arranged in the upper layer and the silver layer 3 is arranged in the lower layer, which corresponds to the second embodiment described later.

In the experiment, each wiring board was left for a predetermined period, and the resistance value fluctuation of less than + 1% was regarded as very good ◎, and the resistance value fluctuation of + 1% or more and less than + 20% was regarded as good ○. The value of + 20% or more and less than + 100% was judged as defective Δ, and the resistance value fluctuation of + 100% or more was judged as poor ×.

As shown in FIG. 10, in Comparative Example 3, there was almost no change in the resistance value even when left for 36 months, and it was judged to be very good. In Comparative Example 4, it was determined to be defective in about 1 month and inferior in about 3 months.

In the third wiring board of the present embodiment, there was almost no fluctuation in the resistance value even if it was left for 12 months, and it was judged to be very good. The third wiring board was judged to be good even if left for 36 months, and a high sulfurization resistance result was obtained. In the fourth wiring board, there was almost no change in the resistance value even if it was left for 36 months, and it was judged to be very good. Based on the results of this experiment, high sulfurization resistance can be obtained by forming the gold layer 2 and the silver layer 3 in a laminated structure regardless of whether the gold layer 2 or the silver layer 3 is arranged on the lower layer side. I understood. Further, from the results of this experiment, it was found that the sulfurization resistance can be improved by increasing the ratio of the film thickness of the gold layer 2. That is, by changing the ratio of the film thicknesses of the gold layer 19 and the silver layer 20, the degree of suppression of sulfurization can be adjusted as necessary.

According to the above-described embodiment, the following effects can be obtained.
(1) The wiring board according to the present embodiment includes an insulating substrate 1 and a silver layer 3 and a gold layer 2 laminated on the insulating substrate 1. The gold layer 2 has a lower ionization tendency than the silver layer 3. By performing a single etching treatment on the silver layer 3 and the gold layer 2, a step portion 23 in which the gold layer 2 projects laterally from the silver layer 3 is provided on the outer peripheral portion of the boundary between the silver layer 3 and the gold layer 2. Migration resistance can be improved by providing the stepped portion 23 or the alloy layer 24 in which the gold layer 2 projects laterally from the silver layer 3. Furthermore, sulfurization resistance can be improved.

(2) Since the stepped portion 23 in which the gold layer 2 is projected laterally from the silver layer 3 can be formed by one etching process, it is possible to prevent the gold layer 2 and the silver layer 3 from being misaligned. .. According to this embodiment, the positional accuracy between the gold layer 2 and the silver layer 3 (that is, the maximum value of the relative displacement between the gold layer 2 and the silver layer 3) can be set to 10 μm or less. Further, the laminated structure composed of the gold layer 2 and the silver layer 3 can form a fine pattern having a width dimension of 5 μm or less. Further, the distance between the laminated structures composed of the gold layer 2 and the silver layer 3 can be set to 10 μm or less. Therefore, it is possible to provide a wiring board having a higher density than the invention described in Patent Document 1.

(3) Since it is not necessary to perform the etching process in a plurality of times, the manufacturing man-hours can be reduced.

-Second embodiment-
The thermal head 100B according to the second embodiment will be described with reference to FIGS. 11 to 14. In the figure, the same or corresponding parts as those in the first embodiment are designated by the same reference numerals, and the differences will be mainly described. FIG. 11 is a diagram similar to FIG. 4, and is a schematic diagram showing a main part of the thermal head 100B according to the second embodiment.

In the first embodiment, an example in which the silver layer 20 is provided on the gold layer 19 in the wire bonding portion 18 has been described (see FIG. 4). On the other hand, in the second embodiment, in the wire bonding portion 18B, the gold layer 19B is provided on the silver layer 20B, and wire bonding is performed on the upper surface of the gold layer 19.

In the wire bonding portion 18B, the gold layer 19B projects laterally from the silver layer 20B, and a step portion 23B or an alloy layer 24B is formed on the outer peripheral portion of the boundary between the silver layer 20B and the gold layer 19B. A method of forming such a wire bonding portion 18B will be described with reference to FIGS. 12 to 14. In addition, in FIGS. 12 to 14, in order to make the explanation easy to understand, it will be described in a simple shape. In FIGS. 12 to 14, the glaze layer is omitted.

(Gold layer and silver layer forming process)
FIG. 12 (a) is a schematic plan view of the wiring board before the etching process, FIG. 12 (b) is a schematic side sectional view of the wiring board before the etching process, and FIG. 12 (a) shows the xiib-xiib line cutting. The cross section is shown. As shown in FIG. 12, a silver paste-like composition is printed on a rectangular flat plate-shaped insulating substrate 1 in a rectangular pattern having a size one size smaller than that of the insulating substrate 1. Then, the gold paste-like composition is printed on the upper surface of the central portion of the pattern of the silver paste-like composition in a rectangular pattern extending parallel to the lateral direction of the insulating substrate 1. After that, the insulating substrate 1 is fired (for example, about 800 ° C.) to form the gold layer 2 and the silver layer 3. By firing, a gold-silver alloy layer 4 is formed at the boundary between the gold layer 2 and the silver layer 3 (not shown in FIG. 12, see FIG. 14).

(Photolithography / etching process)
A substantially H-shaped pattern as shown by the alternate long and short dash line in FIG. 12 is formed by photolithography. After that, by performing a wet etching process once, that is, by immersing the wiring board in the etching solution, the portion other than the portion surrounded by the alternate long and short dash line (substantially H-shaped pattern) shown in FIG. 12A is dissolved and removed. To do.

13 (a) is a schematic plan view of the wiring board after the etching process, FIG. 13 (b) is a schematic side sectional view of the wiring board after the etching process, and FIG. 13 (a) cuts the xiib-xiib line. The cross section is shown. 14 (a) is a partially enlarged view showing the XIV portion of FIG. 13 (a), and FIG. 14 (b) is a schematic cross-sectional view taken along the line xivb-xivb of FIG. 14 (a). As shown in FIGS. 13 and 14, in the etching process, the etching proceeds from the outer surface, so that the upper part of the gold layer 2 is most dissolved and the amount of dissolution decreases downward. Therefore, as shown in FIG. 14, the dimension between the opposite side surfaces in the groove 27 between the pair of substantially H-shaped patterns becomes shorter from the upper part to the lower part. Also in the silver layer 3, the upper part is most dissolved, and the dissolved amount decreases toward the lower part. Therefore, the dimension between the opposite side surfaces in the groove 26 between the pair of substantially H-shaped patterns becomes shorter from the upper part to the lower part.

As described above, in the gold layer 2 and the silver layer 3, the dissolution rate of the silver layer 3 is faster than the dissolution rate of the gold layer 2. Therefore, the distance between the grooves 26 is larger than the distance between the grooves 27.

The side surface of the groove 26 is an inclined surface that spreads laterally (outwardly) from the upper part of the silver layer 3 toward the lower side. Similarly, the side surface of the groove 27 is an inclined surface that spreads laterally (outwardly) from the upper part of the gold layer 2 toward the lower side. Since the gold layer 2 has a slower dissolution rate than the silver layer 3, a step portion 23 is formed at the outer peripheral portion of the boundary between the silver layer 3 and the gold layer 2. The gold layer 2 is formed so as to project laterally with respect to the silver layer 3. Further, the alloy layer 4 formed by firing is exposed by the etching process. That is, the gold-silver alloy layer 4 is formed on the outer peripheral portion of the boundary between the gold layer 2 and the silver layer 3 by the etching process. By arranging the gold layer 2 on the outer peripheral side of the laminated structure portion and forming the gold-silver alloy layer 4, the effect of suppressing migration is improved, and the effect of suppressing sulfurization is also improved. To do.

According to the second embodiment as described above, the same action and effect as those of the first embodiment are obtained.

-Third embodiment-
The thermal head 100C according to the third embodiment will be described with reference to FIG. In the figure, the same or corresponding parts as those in the first embodiment are designated by the same reference numerals, and the differences will be mainly described. FIG. 15 is a diagram similar to FIG. 4, and is a schematic diagram showing a main part of the thermal head 100C according to the third embodiment.

The wiring board according to the third embodiment includes an insulating substrate 12, a silver layer 20C provided on the insulating substrate 12, and a silver layer 20C provided on the insulating substrate 12 on the same plane as the silver layer 20C. It is provided with a gold layer 19C having a lower ionization tendency than that of the gold layer 19C. The gold layer 19C has an overlapping portion 19a that overlaps the edge portion of the silver layer 20C and a non-overlapping portion 19b that does not overlap the silver layer 20C, and the non-overlapping portion 19b is configured as a wire bonding portion (electrode terminal) 18C. Has been done. In the present embodiment, the non-overlapping portions 19b of the silver layer 20C and the gold layer 19 are respectively arranged on the insulating substrate 12 via the glaze layer 13.

In the third embodiment, the gold-silver alloy layer 24C can be formed by firing by forming the overlapping portion 19a of the gold layer 19C and the silver layer 20C into a laminated structure. Further, since the wire bonding portion 18C is composed of only the gold layer 19C, it has high migration resistance and sulfurization resistance.

According to such a third embodiment, it is possible to provide a wiring board having high migration resistance and sulfurization resistance, as in the first embodiment.

The following modifications are also within the scope of the present invention, and one or more of the modifications can be combined with the above-described embodiment.
(Modification example 1)
In the above-described embodiment, an example in which the first conductive layer having a high ionization tendency is a silver layer 20, 20B, 20C and the second conductive layer having a low ionization tendency is a gold layer 19, 19B, 19C has been described. Is not limited to this. A copper layer made of copper or an aluminum layer made of aluminum may be used as the first conductive layer, and a platinum layer made of platinum or a palladium layer made of palladium may be used as the second conductive layer. At least the second conductive layer has a lower ionization tendency than the first conductive layer, and the second conductive layer is projected laterally from the first conductive layer to form the stepped portion 23 or the alloy layers 24, 24B, 24C. The present invention can be applied to the wiring board of the above.

(Modification 2)
In the first and second embodiments, examples of forming the gold layers 19 and 19B and the silver layers 20 and 20B by printing and firing, respectively, have been described, but the present invention is not limited thereto. The gold layers 19, 19B and the silver layers 20, 20B are formed by vapor deposition or sputtering, respectively, and then the stepped portion 23 is subjected to a single etching process on the laminated structure portion of the gold layers 19, 19B and the silver layers 20, 20B. May be formed. When the gold layers 19, 19B and the silver layers 20, 20B are formed by vapor deposition or sputtering, the alloy layers 24, 24B described above are not formed. That is, the case where only the step portion 23 is formed and the alloy layers 24 and 24B are not formed is also within the scope of the present invention. Further, the case where only the alloy layers 24 and 24B are formed and the step portion 23 is not formed is also within the scope of the present invention. Migration resistance and sulfurization resistance can be improved even when only the alloy layers 24 and 24B are formed. It is preferable to form both the step portion 23 and the alloy layer 24 because the migration resistance and the sulfurization resistance can be greatly improved by forming the alloy layer 24 as well as the step portion 23.

(Modification 3)
In the above-described embodiment, an example in which the step portion 23 is formed on the wire bonding portion 18 of the individual electrode 17 has been described, but the present invention is not limited thereto. The step portion 23 or the alloy layer 24 may be formed in the wiring portion not covered with the insulating protective film 7 to suppress the occurrence of migration.

(Modification example 4)
In the above-described embodiment, the thermal head 100 provided with the glaze layer 13 has been described as an example, but the present invention may be applied to the thermal head not provided with the glaze layer 13.

(Modification 5)
In the above-described embodiment, an example of applying the present invention to the wiring board of the thermal head has been described, but the present invention is not limited thereto. The present invention can be applied to substrates of various electronic devices. For example, the present invention can be applied to a catalyst substrate in a steam reformer that produces hydrogen by catalytic reforming from a raw material gas and steam.

Although various embodiments and modifications have been described above, the present invention is not limited to these contents. Other aspects considered within the scope of the technical idea of the present invention are also included within the scope of the present invention.

1 Insulated substrate, 2 Gold layer, 3 Silver layer, 4 Alloy layer, 5 Common electrode, 5a electrode surface, 5b Band-shaped electrode, 6 Heat-generating resistor, 7 Insulating protective film, 8 Individual electrode, 9 Wire bonding part, 10 Gold Wire, 11 Driver IC, 12 Insulated Substrate, 13 Glaze Layer, 14 Low Purity Gold Layer, 15 High Purity Gold Layer, 16 Encapsulating Resin, 17 Individual Electrodes, 18 Wire Bonding Part, 19 Gold Layer, 20 Silver Layer, 23 Steps Parts, 24, alloy layer, 26 grooves, 27 grooves, 30 printed wiring boards, 31 connectors, 32 support plates, 50 wiring boards, 100 thermal heads

Claims (5)

An insulating substrate, at least a pair of electrodes extending in parallel with each other and having electrode terminals at the ends, and an insulating protective film covering the surface of the substrate including a portion other than the electrode terminals. It is a manufacturing method of the wiring board provided.
The electrode terminal is
A second conductive layer is arranged on an insulating substrate, and a first conductive layer having a higher ionization tendency than the second conductive layer is laminated and arranged on the second conductive layer.
The first conductive layer and the second conductive layer are separated from each other by a single etching process, and the second conductive layer is separated from the first conductive layer. A method for manufacturing a wiring board, which is formed so as to project laterally from a layer. In the method for manufacturing a wiring board according to claim 1 , further
An alloy layer of the first conductive layer and the second conductive layer is formed at the boundary between the first conductive layer and the second conductive layer.
By the etching treatment, a stepped portion of the alloy layer is formed on the outer peripheral portion of the boundary between the first conductive layer and the second conductive layer, and the second conductive layer is projected laterally from the alloy layer. A method of manufacturing a wiring board. In the method for manufacturing a wiring board according to claim 1 or 2 .
A method for manufacturing a wiring board, in which a metal that is less likely to migrate than the first conductive layer is used as the second conductive layer. The method of manufacturing a wiring board according to any one of claims 1 to 3,
Further, a method for manufacturing a wiring board, which forms a sealing resin that covers the electrode terminals. At least a pair of the electrodes are formed on the glaze layer of the substrate provided with the glaze layer by using the method for manufacturing a wiring board according to any one of claims 1 to 4.
On the glaze layer of the substrate, a band-shaped common electrode having one end side provided between the pair of the electrodes is formed.
A heat-generating resistor that straddles the electrode and one end of the common electrode is formed.
Manufacturing method of thermal head.

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