**4. Different material patterning process**

The different material patterning process can form some material patterns in one ceramic sheet without bump structure. The ceramic material is often used for the module circuit [11]. When the different ceramic materials are used, the module circuit with some electronic characteristics is realized. When the ceramic material and the conductive material are used, the conductive circuit pattern with high-aspect-ratio pattern and the flat surface pattern. **Figure 7** shows the patterning

**Figure 7.** Schematic illustration of photoresist process for different material pattern.

**Figure 5.** Schematic illustration of mechanism of residual pattern.

adjusting the gap between the blade and the resist surface.

**Figure 4.** Formed fine conductive pattern.

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These images were observed by the confocal microscope. The filling process was metal blade method. A pore and a crack were not shown on the surface of the conductive pattern, and the paste was filled completely. The width and height of the pattern were 10.3 and 1.85°μm, respectively. The fine and high-aspect-ratio pattern was achieved. However, a thin-film conductor around the line pattern was observed. It is a residual conductive paste that was coated on the resist pattern. When the conductive paste was filled, the gap between the metal blade and the resist pattern was occurred. And then, the dried paste on the resist remained with the side of the pattern. The schematic illustration of the mechanism of the residual pattern is shown in **Figure 5**. 3D measuring result of the conductive pattern using same fabrication process is shown in **Figure 6**. The side of the conductor formed the thin pattern. It is solved by process of the different material pattern. The first material sheet is formed by the base photoresist process. The ceramic sheet with the through-pattern is achieved. Another photoresist is prepared for covering the patterned ceramic sheet. In this time, the film type photoresist is used. The reversal pattern is exposed on the film type photoresist film, and then, the developed film is used for the mask film. The formed mask photoresist is laminated on the ceramic sheet with an alignment pattern. The different ceramic material slurry is filled in the only through-pattern because the first ceramic sheet is covered. After drying the sheet and removing the mask photoresist, the ceramic sheet with the patterned different material is achieved.

In the conventional patterning process for the different material, the pattern forms on the ceramic base sheet. **Figure 8** shows the schematic illustration of the conventional different pattern processing. Each material sheet is stacked, and it is difficult to form the different ceramic material pattern in the same ceramic sheet.

The proposed process for the different material pattern will be applied to a multilayer ferrite inductor. In the conventional multilayer ferrite inductor, the minor magnetic loop causes the degradation of the inductance and the Q factor because the ferrite magnetic ceramic covered around the internal conductor. When the nonmagnetic ceramic is inserted between the conductors of each layer, it is possible to suppress the minor magnetic loop. The mechanism of the minor loop and suppressing pattern is shown in **Figure 9**. The image of the minor loop suppressing multilayer inductor is shown in **Figure 10**.

ceramic (LTCC) is mixed powder of a glass and an alumina ceramic, and it was used for the nonmagnetic pattern. The composite weight ratio of the glass powder and the alumina powder in the glass alumina composite material was 63 and 37. The glass powder was composed of

and LTCC was the mixture of the organic solvents and some additives. The composite material

The microscope image of the fabricated LTCC pattern is shown in **Figure 12**. The complex

To achieve the suppressing inductor, the conductive pattern was formed by the photoresist process on the LTCC as the nonmagnetic material pattern. The fabrication process is shown

and composite weight ratio of each ceramic are shown in **Table 1**.

**Figure 10.** Image of minor loop suppressing multilayer ceramic inductor.

**Figure 9.** Mechanism of minor loop and suppressing pattern.

pattern was shaped, and the different material slurry filled completely.

. The particle diameter of LTCC powder 1 μm. The ceramic slurry of ferrite

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SrO-B<sup>2</sup> O3 -Al<sup>2</sup> O3 -SiO2

Examples of the designed different material pattern with the photoresist process are shown in **Figure 11**. This design includes the different ceramic material pattern. The base material was the magnetic material and the patterned material was nonmagnetic material. The film type photoresist was used to form a thick pattern. The thickness of the photoresist film for the through-pattern was 90 μm and the mask film was 35 μm, respectively. The photoresist films were attached to the poly ethylene terephthalate (PET) carrier film.

The co-fired NiCuZn ferrite was used for the magnetic material. The start materials of the ferrite powder were NiO, ZnO, CuO, and Fe<sup>2</sup> O3 and the molecular ratio was 8.8–32–10–49.2, respectively. The particle diameter of ferrite powder was about 300 nm. low-temperature co-fired

**Figure 8.** Conventional process to introduce a different ceramic material.

**Figure 9.** Mechanism of minor loop and suppressing pattern.

ceramic (LTCC) is mixed powder of a glass and an alumina ceramic, and it was used for the nonmagnetic pattern. The composite weight ratio of the glass powder and the alumina powder in the glass alumina composite material was 63 and 37. The glass powder was composed of SrO-B<sup>2</sup> O3 -Al<sup>2</sup> O3 -SiO2 . The particle diameter of LTCC powder 1 μm. The ceramic slurry of ferrite and LTCC was the mixture of the organic solvents and some additives. The composite material and composite weight ratio of each ceramic are shown in **Table 1**.

The microscope image of the fabricated LTCC pattern is shown in **Figure 12**. The complex pattern was shaped, and the different material slurry filled completely.

To achieve the suppressing inductor, the conductive pattern was formed by the photoresist process on the LTCC as the nonmagnetic material pattern. The fabrication process is shown

**Figure 10.** Image of minor loop suppressing multilayer ceramic inductor.

**Figure 8.** Conventional process to introduce a different ceramic material.

process of the different material pattern. The first material sheet is formed by the base photoresist process. The ceramic sheet with the through-pattern is achieved. Another photoresist is prepared for covering the patterned ceramic sheet. In this time, the film type photoresist is used. The reversal pattern is exposed on the film type photoresist film, and then, the developed film is used for the mask film. The formed mask photoresist is laminated on the ceramic sheet with an alignment pattern. The different ceramic material slurry is filled in the only through-pattern because the first ceramic sheet is covered. After drying the sheet and removing the mask photo-

In the conventional patterning process for the different material, the pattern forms on the ceramic base sheet. **Figure 8** shows the schematic illustration of the conventional different pattern processing. Each material sheet is stacked, and it is difficult to form the different

The proposed process for the different material pattern will be applied to a multilayer ferrite inductor. In the conventional multilayer ferrite inductor, the minor magnetic loop causes the degradation of the inductance and the Q factor because the ferrite magnetic ceramic covered around the internal conductor. When the nonmagnetic ceramic is inserted between the conductors of each layer, it is possible to suppress the minor magnetic loop. The mechanism of the minor loop and suppressing pattern is shown in **Figure 9**. The image of the minor loop

Examples of the designed different material pattern with the photoresist process are shown in **Figure 11**. This design includes the different ceramic material pattern. The base material was the magnetic material and the patterned material was nonmagnetic material. The film type photoresist was used to form a thick pattern. The thickness of the photoresist film for the through-pattern was 90 μm and the mask film was 35 μm, respectively. The photoresist films

The co-fired NiCuZn ferrite was used for the magnetic material. The start materials of the ferrite

tively. The particle diameter of ferrite powder was about 300 nm. low-temperature co-fired

and the molecular ratio was 8.8–32–10–49.2, respec-

O3

resist, the ceramic sheet with the patterned different material is achieved.

ceramic material pattern in the same ceramic sheet.

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suppressing multilayer inductor is shown in **Figure 10**.

powder were NiO, ZnO, CuO, and Fe<sup>2</sup>

were attached to the poly ethylene terephthalate (PET) carrier film.

in **Figure 13**. In this process, the through-hole to connect the circuit pattern on each layer was formed mechanically. The microscope image of the formed ceramic sheet is shown in **Figure 14**. The conductive pattern was formed on the LTCC pattern, and the through-hole was achieved by filling the conductive paste. By this result, the two different material patterns were formed on the ferrite sheet. However, the LTCC pattern is observed around the conductive pattern.

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For the different material patterning process, the viscosity of the material slurry and the shrinking process are an important factor. **Figure 15** shows the cross-sectional image of the ferrite sheet by the microscope, and the round bump is observed around the edge of through-pattern. It is because of the surface tensions of the slurry. The proposed process requires the drying process the filled slurry was shrunk during the drying and peeling off the photoresist film. In this time, the edge part formed the round bump shape. It is easy to peel the resist pattern, but the thickness of the dried sheet or patterns become a nonflat pattern. By this reason, the LTCC pattern between the conductor and the ferrite pattern was formed. It is required that the viscosity is adjusted for

form a clear pattern. **Figure 16** shows a schematic illustration of the shrinking process.

**Figure 13.** Fabrication process of filling conductive paste.

Moreover, the thickness of the mask photoresist influences the surface of the fabricated pattern. In this case, a thin film resist was 15μm, and a thick film resist was 35μm. The cross-sectional image of the fabricated patterns by the scanning electron microscope is shown in **Figure 17(a)** and **(b)**.

#### **Figure 11.** Designed different material patterns.


**Table 1.** Composition weight ratio of ceramic slurry.

**Figure 12.** Microscope image of fabricated LTCC patterns on ferrite ceramic sheet.

in **Figure 13**. In this process, the through-hole to connect the circuit pattern on each layer was formed mechanically. The microscope image of the formed ceramic sheet is shown in **Figure 14**. The conductive pattern was formed on the LTCC pattern, and the through-hole was achieved by filling the conductive paste. By this result, the two different material patterns were formed on the ferrite sheet. However, the LTCC pattern is observed around the conductive pattern.

For the different material patterning process, the viscosity of the material slurry and the shrinking process are an important factor. **Figure 15** shows the cross-sectional image of the ferrite sheet by the microscope, and the round bump is observed around the edge of through-pattern. It is because of the surface tensions of the slurry. The proposed process requires the drying process the filled slurry was shrunk during the drying and peeling off the photoresist film. In this time, the edge part formed the round bump shape. It is easy to peel the resist pattern, but the thickness of the dried sheet or patterns become a nonflat pattern. By this reason, the LTCC pattern between the conductor and the ferrite pattern was formed. It is required that the viscosity is adjusted for form a clear pattern. **Figure 16** shows a schematic illustration of the shrinking process.

Moreover, the thickness of the mask photoresist influences the surface of the fabricated pattern. In this case, a thin film resist was 15μm, and a thick film resist was 35μm. The cross-sectional image of the fabricated patterns by the scanning electron microscope is shown in **Figure 17(a)** and **(b)**.

**Figure 13.** Fabrication process of filling conductive paste.

**Material Ferrite LTCC** Ceramic powder 100 100 Binder 7 5 Dispersing agent 5 2.9 Plasticizer 1 1.3 Toluene 23 23 Xylene 23 23 Isopropyl alcohol 23 23

**Figure 12.** Microscope image of fabricated LTCC patterns on ferrite ceramic sheet.

**Table 1.** Composition weight ratio of ceramic slurry.

**Figure 11.** Designed different material patterns.

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**Figure 14.** Microscope image of formed ferrite sheet with conductive pattern and LTCC pattern.

**Figure 15.** Cross-sectional image of fabricated ferrite sheet with through-pattern by microscope.

The result of using the thin mask resist showed the distance between the LTCC pattern surface and the ferrite pattern surface, and it was 20 μm. On the other hand, the flat surface of the different materials pattern was achieved by using the thick mask resist. The formed pattern showed the shrinking, the higher thickness than the base layer is required to hold the large volume of the filler material. The mechanism of the different thickness is shown in **Figure 18**.

**Figure 18.** Schematic illustration of mechanism of the different thickness.

**Figure 17.** Cross-sectional image using each thickness mask photoresist film (a) 15 μm mask film, (b) 35 μm mask film.

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In this chapter, the photoresist process was proposed. The proposed process is combined with the photolithography process and the printing process. The fine pattern for the conductor was formed by the photolithography process, because it is usually used for the production process of the IC. The printing process was used for the filling process as the conductive paste and the

**5. Conclusions**

different material pattern.

**Figure 16.** Schematic illustration of the shrinking process.

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**Figure 17.** Cross-sectional image using each thickness mask photoresist film (a) 15 μm mask film, (b) 35 μm mask film.

**Figure 18.** Schematic illustration of mechanism of the different thickness.

The result of using the thin mask resist showed the distance between the LTCC pattern surface and the ferrite pattern surface, and it was 20 μm. On the other hand, the flat surface of the different materials pattern was achieved by using the thick mask resist. The formed pattern showed the shrinking, the higher thickness than the base layer is required to hold the large volume of the filler material. The mechanism of the different thickness is shown in **Figure 18**.
