TW583756B - Manufacturing method of glass micro fluid chip - Google Patents

Abstract

This invention utilizes micro electro-mechanical manufacturing technique to provide a manufacturing method of glass micro fluid chip, which comprises using a photoresist as a glass etching mask to quickly define etching pattern by a standard lithographic process, providing a special baking process to reduce residual stress between the photoresist layer and the glass substrate, and finally using a hot melt bonding method to encapsulate the glass chip, which does not require complicated temperature ramping up and down process and can completely bond the glass chip with material of the same property. This invented process technique can be applied to manufacture various types of micro fluid chips using glass as the substrate.

Description

583756 _Case No. 91123979_ Modification of the Year and Month_ V. Description of the Invention (1) [Technical Field of the Invention] The present invention provides a method for manufacturing a glass wafer, which is used to fabricate various microfluidic wafers in a glass substrate. Most of them, the first: development of photoresist as an etching mask for glass wet etching; the second: development of glass etching technology and the third: development of glass bonding technology, which can be applied to various types of biochips, integrated types Microfluidic wafers, miniature chemical reaction wafers, etc. [Background of the Invention] In recent years, the miniaturized analysis device has been widely studied in the fields of biomedical and chemical analysis due to its advantages such as lightness, shortness, short response time, and few samples consumed. The analysis device manufacturing process also tends to be more diversified, and various materials have been included in the research scope, such as glass, quartz, silicon, PDMS, and polymer materials. Among them, glass-based microfluidic wafers Has development potential. The glass material has been widely used in the manufacture of a variety of experimental containers and equipment since many years ago, so everyone is familiar with the various chemical and physical properties of glass. If you want to transform the research platform to the scale of microfluidics The difficulties encountered will be minimized compared to other materials. Moreover, the properties of glass against mechanical stress, chemical resistance, electrical insulation, and optical transmission wavelength range are much higher than other materials. Although the glass-based detection device has many of the above advantages, it often encounters some difficulties in the manufacturing process, which limits the use of glass substrates. The current methods for making micro-channels on glass substrates by wet etching are mostly made of quartz or boron glass as substrates. Although these two materials have good optical and chemical properties, they are more expensive and have an etching rate. slow

583756 _ Case No. 91123979_ Year Month Revision _ V. Description of the invention (2) Slow, it must be etched for a long time to reach the required pipe depth. Therefore, using quartz or boron glass as the base material of the glass wafer, it is necessary to make a #etching mask (e t c h m a sk) that can bear the #etch liquid invasion for a long time. Traditionally, a thin film deposition technique must be used to coat the glass surface with a thin metal film as an etch mask. Therefore, a vacuum coating process must be used, which is an expensive and time-consuming process, and is not suitable for mass production that is fast and low cost.

In view of this, many people have proposed the idea of using a thin film of a high-molecular polymer as a cover glass. According to the literature published by Mathies, the positive photoresist of the model Shipley 1 400 0-3 1 is coated on a glass substrate as an etching mask, which can be used in buffered ο X ideetchant (B 0 E). After 15 minutes of I insect engraving, you can #engraved a depth of about 8 // m. In addition, in the report submitted by Stjernstrom, S h i p 1 e y 1 8 1 3 positive photoresist was used as the #etching mask, and the glass was etched in a buffer solution of hydrofluoric acid. In order to prevent the etching mask from peeling off prematurely in the etching solution, both of these studies have extended the soft baking time after photoresist coating. The baking process is more than 80 minutes, but the etching mask can only be used in the etching solution. Medium resists for more than ten minutes, so deeper micro-pipe structures cannot be obtained.

For microfluidic wafers, the roughness of the surface and the geometry after etching will greatly affect the performance of the wafer. In the literature of Delahaye et al., It is pointed out that for glass with a more complex composition (such as soda glass) after etching in an acidic etchant, the surface will be very rough, and white precipitates will adhere to the surface. The precipitate is generated during the etching process and adheres to the surface of the glass, which seriously affects the quality of the etching and causes the surface of the glass to be rough after being etched.

Page 558756 _Case No. 91123979_ Years and Months Revision_ V. Description of the Invention (3) In wafer bonding technology, low-temperature bonding methods have been widely used in glass bonding applications, such as hydrogen-acid bonding or adhesion Layer bonding method ... etc. Glass bonding using hydrofluoric acid bonding method will inevitably have an adverse effect on the roughness of the surface of the micro-pipe, and will change the width of the pipe after etching, and its bonding strength is not high, and it cannot bear too much external pressure, making it suitable for applications. The scope is limited. Furthermore, glass bonding using hydrofluoric acid requires a strict cleaning procedure for the glass substrate. If any small particles adhere to the glass substrate, the bonding will fail. Therefore, the combined power of this method is not high. If glass bonding is performed using an adhesive layer, there is also a problem that the bonding strength is not high. What's more serious is that the use of adhesive layer bonding often causes blockage of micro-channels, so the failure rate is extremely high. The traditional high-temperature fusion bonding method provides extremely high bonding strength and no residue of bonding materials. Therefore, a high-temperature fusion bonding method is widely used for bonding glass substrates. Generally speaking, the temperature of fusion-bonding of boron-containing glass is about 6 0 ° C ~ 80 0 ° C, and the holding time is about 6 hours to 8 hours, while quartz must be as high as 1 3 0 0 Above ° C, it does not include heating and cooling time. In other words, fusion bonding is a time-consuming process. [Summary of the Invention] In view of the shortcomings and disadvantages of the conventional glass wafer process, the present invention provides a method for manufacturing a glass microfluidic wafer, which at least includes the following procedures: Provide a glass substrate as the lower plate of the wafer; Bottom wafer; baking process; exposure process; photoresist development; glass etching process; stripping photoresist process; providing another glass substrate as the wafer upper plate; drilling holes on the wafer upper plate; and thermal melting Way to join the upper and lower wafers

583756 _ Case No. 91123979_ Year Month Amendment _ V. Description of the invention (4) Board. The aforementioned manufacturing method further includes a procedure for cleaning the glass substrate, which is performed before the procedure for bonding the upper plate and the lower plate of the wafer. The glass substrate may be various glass materials such as soda glass, boro glass, lead glass, P Y R E X glass, or quartz. Among them, sodium glass is preferred. The aforementioned baking process includes a soft baking process (preferably at 90-100 ° C), which is a process implemented after coating a photoresist on a wafer, and a hard baking process (preferably at 1 0 0-1 50 ° C), which is the procedure after photoresist development. The aforementioned photoresist may be a positive or negative photoresist, and among them, a photoresist of A Z 4 6 2 0 is preferred, and the aforementioned photoresist may be defined by an etching pattern using a standard photolithography process. The aforementioned use of photoresist as a glass etching mask can eliminate expensive and complicated metal coating procedures and obtain good etching results. The aforementioned glass etching technology uses chemical methods to remove the precipitates generated during the etching process, and can obtain an etching structure with good surface flatness, and increase the etching rate to one micron per minute, which is dozens of times faster than the etching rate of quartz and boron glass. Times. The aforementioned glass bonding technology can further use a substrate as a spacer during bonding to provide good bonding flatness. This joining technology cooperates with the control of the heating and cooling rate and temperature holding time, so that the glass can be joined within six hours and obtain excellent joint strength. The aforementioned substrate material may be, for example, a ceramic substrate, a stainless steel plate, a silicon carbide plate, a tungsten carbide plate, an alumina plate, a zirconia plate, etc., and any heat-resistant material may be used. Among them, a ceramic substrate is preferred.

583756 _ Case No. 91123979_ Year and month amendment_ V. Description of the invention (5) The present invention provides a process technology with low production cost, short production time, and can be applied to glass substrates without losing reliability. To make a variety of microfluidic wafers. [Comparison of the main component symbols] 1 — Lower plate of the wafer 2 — Photoresist layer 3 --- Photomask 4---Micropipe 5 --- Upper plate of the wafer 6 --- 孑 L hole 7 --- Water film 8 ——Photoresist etching mask 9 --- Glass substrate 1 0 --- Microfluidic wafer 1 1 --- Cross-shaped capillary electrophoresis wafer 1 2 --- Microfluidic cell counting wafer 13 --- Optical fiber structure 1 4 --- Continuous injection electrophoresis wafer 1 5 --- Substrate [Detailed description of the invention] As shown in FIG. 1, the manufacturing method of the glass microfluidic wafer provided by the present invention mainly includes the following procedures: First, as shown in FIG. 1 ( As shown in FIG. 1), a glass substrate is provided as the lower plate 1 of the wafer, and a photoresist layer 2 is coated thereon for soft baking; as shown in FIG. 1 (B), a designed photomask 3 is used for Exposure; after that, as shown in FIG.

583756 _Case No. 91123979_ Modification of the month of the year _ V. Description of the invention (6) The lower plate 1 of the wafer is hard baked to increase the time that the photoresist can resist the erosion of the etching solution in the etching buffer; As shown in FIG. 1 (D), a glass etching process is performed to make a predetermined microchannel 4. Then, as shown in FIG. 1 (E), the remaining photoresist layer 2 is stripped to complete the process of manufacturing the lower plate 1 of the wafer. Next, as shown in FIG. 1 (F), another glass substrate is provided as the wafer upper plate 5 and drilled at a predetermined position to form a hole 6; after that, as shown in FIG. 1 (G), the wafer is first plated 5 and the lower plate 1 of the wafer chemically clean the precipitates and impurities on the glass surface, and then align the upper plate 5 and the lower plate 1 of the wafer, and then drip a little deionized water between the two wafers to form a water film 7 so that The two wafers are temporarily bonded, and finally, as shown in FIG. 1 (i), the upper and lower plates 5 and 1 of the wafer are joined by thermal fusion to complete the process of the microfluidic wafer 10. In the procedure of FIG. 1 (i), the two substrates 15 can be used as spacers for bonding, that is, the upper wafer plate 5 and the lower wafer plate 1 are fixed between the two substrates 15 as shown in FIG. It can provide a flat surface and the small pressing force required for thermal fusion bonding. The material of the aforementioned substrate 15 is, for example, a ceramic substrate, a stainless steel plate, a silicon carbide plate, a tungsten carbide plate, an alumina plate, a zirconia plate, etc. Any heat-resistant material can be used. Among them, the ceramic substrate can withstand high temperature and does not deform. Glass gaskets are best for high temperature bonding. Of course, the procedure in Fig. 1 (Η) can also be used without using any substrate as a gasket, and the joining process can be completed by only placing the upper and lower glass plates in a high-temperature furnace. The manufacturing method of the present invention develops a fast and reliable photoresist process, which appropriately utilizes an adhesive layer to improve the photoresist adhesion, and utilizes an improved baking process to make it stay on the glass substrate.

583756 _Case No. 91123979_Year Month Revision_ V. Description of the Invention (7) The residual stress between the etching mask and the mask can be reduced, and the resist time of the photoresist in the etching solution can be extended. According to experimental data, the photoresist of AZ 4 6 2 0 used in the present invention can withstand ultrasonic vibration in the etching buffer for more than 70 minutes after the baking process developed by this process. Time, and can achieve an etching depth of more than 60 microns. In addition, the present invention provides a brand-new etching method. Using ultrasonic vibration and original sediment removal technology, the etching rate can be greatly increased, and the problem of rough chain degree on the surface after touching can be effectively improved to obtain a smooth surface. Carved surface.

In addition, in the process developed by the present invention, a new step of fusion bonding is proposed, which can not only complete the heating and cooling procedure of the bonding within six hours, shorten the time spent for bonding, and obtain a fast, reliable and Excellent bonding results. The advantages and processes of a method for manufacturing a glass microfluidic wafer according to the present invention will be further described through the following examples. [Embodiment 1] Materials · Generally commercially available microscope slides or various surface polished soda glasses were used as the glass substrate of the present invention. The glass substrate must be subjected to an annealing process at a high temperature of 400 ° C for 4 hours before use to remove the stress remaining in the glass substrate.

Cleaning: All glass substrates must be boiled in a boiling Piranha solution (H2S04 (° / 〇): H2 02 (° / 〇) = 3: 1) before use for 10 minutes, then removed and deionized DI water is rinsed and blown with dry air, and then the blown glass substrate is baked on a 100 t hot plate for 3 minutes in order to completely remove water molecules on the glass surface.

Page 10 583756 _Case No. 91123979_ Year Month Amendment _ V. Description of Invention (8)

Etching pattern lithography: After the glass substrate is cooled, place it in a closed container, and drop a few drops of Η M D S (h x x a me t h y 1 d i s i 1 a z a n e) solution into the container, and leave it for about 5 minutes after sealing. After 5 minutes, the glass substrate was taken out and placed on a hot plate at 100 ° C for 3 minutes. After the glass substrate was cooled to room temperature, the AZ 4 6 2 0 positive photoresist was uniformly applied on a spin coater. It was coated on the surface of the glass substrate and then baked at 100 t for 3 minutes. The thickness of the photoresist after soft baking is about 3 // m, and then the exposure and development procedures are performed. The developed glass substrate was blow-dried with dry nitrogen and then hard-baked. On the hard baking of the photoresist, two steps of gradually increasing the temperature are used to increase the time that the photoresist can resist in the etching buffer. The steps are as follows: first, the electric heating plate is heated to 100 t, and the dried The glass substrate was placed on it, then the temperature was set to 150 t, and heating was started. When the temperature rose to 150 ° C, it started to count for 10 minutes, and the hard baking process was completed. Etching: After hard baking, wait for the glass substrate to cool, and immerse it in the etching buffer (B 0 E 6: 1) to perform micro-channel etching, and the entire etching environment is placed in an ultrasonic vibration tank. During the etching process, precipitates will be attached to the surface of the micropipes. At this time, 1M hydrochloric acid is used to remove the precipitates on the surface of the micropipes to avoid affecting the etching quality. Therefore, every 5 minutes, the glass substrate is removed from the etching solution, rinsed with deionized water, and then immersed in a hydrochloric acid solution, and the stirring time is slightly shaken for about 10 to 15 seconds. After completion, soak it with deionized water, and then put it back into the remaining solution for the remaining time. This process is repeated until the set etching depth is completed, and the glass microfluidic wafer lower plate manufacturing process is completed. Fusion bonding: the previously etched wafer lower plate and the drilled upper plate (the wafer upper plate is drilled at another location by another glass substrate)

583756 _Case No. 91123979_ Modification of the Year of the Year_ 5) (Invention (9) and made), placed in boiling Piranha solution for 10 minutes to clean the glass surface, and then aligned the upper and lower plates of the wafer, Then, a little deionized water was dropped between the two glass plates, and the two glass plates were bonded together using atmospheric pressure, and then the two glass substrates were used as gaskets to sandwich the upper and lower glass plates. After fixing, it is placed in a sintering furnace. The glass is heated to a slightly molten state by a high temperature, and the upper and lower plates of the wafer are bonded to each other. The aforementioned temperature increasing rate is 5 t / min, and the temperature is maintained at 580 ° C for 10 minutes, and then the temperature is decreased to complete the microfluidic wafer. FIG. 3 is an electron microscope image of the photoresist mask 8 after etching. The photoresist etching mask 8 is still intactly attached to the glass substrate 9 after being etched by the hydrofluoric acid buffer solution for a period of time, and is not eroded at all. It shows that the photoresist etching mask 8 produced by this process , Has the ability to resist glass etching solution erosion for a long time. Figure 4 shows the top view of the glass wafer after the etching is completed and the photoresist is removed. By using a photoresist film coated on a glass substrate as an etching mask for glass, the glass can get a good geometric definition after etching. Even with the extremely sharp angles shown in the dotted line in Figure 4, a good Etching results. Fig. 5 is a sectional view of a glass microfluidic wafer after the upper and lower plates of the wafer are thermally fusion-bonded. After the glass is bonded at 580 ° C, the upper and lower plates of the wafer are combined into one, and the middle interface disappears after bonding, showing that the bonding effect is extremely good. This bonding technology not only provides a micro-pipe surface with uniform material properties, and there is no interface between the upper and lower plates of the wafer, which can prevent the gap generated during bonding from affecting the performance of the microfluidic wafer analysis. Figure 6 shows the surface pattern of the etched glass surface scanned with an atomic force microscope. As can be seen from the figure, the surface flatness after etching is good.

Page 12 583756 ______ Case No. 91123979_ Year Month Day Amendment _ V. Description of the Invention (10) Actual measurement of the surface of the glass after etching (area 7 X 7 // m2), the average surface roughness (Ra) is 18.5 · 95 Angstroms, which is no different from the roughness before the glass etching, shows that the glass etching using the process of the present invention can provide high-quality and reliable engraving results. The present invention is a development of a technology platform that can be used to make various microfluidic wafers. Various microfluidic wafers made by the manufacturing method of the present invention and their subsequent applications will be further explained through different embodiments. [Embodiment 2] FIG. 7 shows a cross-shaped capillary electrophoresis wafer 11 ′ manufactured using the present invention. The microchannel 4 has a depth of 40 μm and a width of 100 μm. A plurality of holes 6 are provided on the wafer 11. For liquid in and out. The operation sample in this example is a mixed solution of 10-4 M Rhodamine B and 6. 5x10_3 M Cy3 dye. The injection voltage during operation is 1.2 kV and the separation voltage is 2.0 kV. Figure 8 shows the cross-linked capillary electrophoresis wafer 1 1 using the present invention to separate the dye mixture map, the results show that the wafer can smoothly separate two dyes' and three hydrolysates of C y 3 dyes can be successfully separated This shows that the cross-type capillary electrophoresis wafer 11 has a good separation efficiency. In addition, after three consecutive injections of the same sample, FIG. 8 shows that the wafer 1 1 also has good reproducibility. In order to prove that the wafer produced by this process can be used for the detection of biological samples, this embodiment uses the polypeptide (P ο 1 y p e p t i d e) calibrated by F I T C dye as a sample for electrophoretic analysis. The amino acid sequence of the peptide is AEEEIYGVLFAKKKK (purity 70%, molecular weight 2111.39, Sigma, USA). The sample solution used was to dissolve 250 ppm of the peptide in 1 mM sodium phosphate solution. Its note

Page 13 583756 _Case No. 91123979_ Year Month Amendment _ V. Description of the invention (11) The emission and separation voltages are 1.2 k V and 2.0 k V, respectively. Fig. 9 shows the separation pattern of peptides using the cross-shaped capillary electrophoresis wafer 11 made by the present invention. The results show that the wafer 11 can not only inject a stable electroosmotic flow into the separation pipeline, but also can be used in the separation pipeline. The biological sample was successfully separated. In addition, after four consecutive injections of the same sample, Figure 9 shows that the wafer 11 also has good reproducibility. [Embodiment 3] Figure 10 shows a microfluid cell counting wafer 12 made by the method of the present invention, which contains microchannels 4 and holes 6, which can be used for counting, detecting, and classifying cell samples. Integrate fiber structure 1 3 for real-time inspection within the chip. [Embodiment 4] Figure 11 is a continuous-injection electrophoresis wafer 14 produced by this process. The widest part of the microchannel 4 is 3 mm. After the upper and lower plates of the wafer are joined, there is no collapse or adhesion. Shows the bonding technology of this process, which can bond glass wafers of large pipes. The wafer 14 can be used for continuous injection of biological samples for long-term dynamic measurement. [Effects of the invention] The present invention provides a process technology for glass microfluidic wafers, which is used to make various microfluidic wafers in glass substrates. Compared with the conventional technology, its advantages are as follows: 1. The process technology of the present invention It can be applied to various glass substrates, and its price is only one tenth to one tenth of that of traditional quartz or boron glass process technology. 2. The present invention uses a simple positive photoresist as a glass etching mask, and the etching pattern is defined by a standard photolithographic development procedure, eliminating the complicated, expensive and time-consuming processes such as metal plating or chemical vapor deposition.

Page 14 583756 _ Case No. 91123979_ Year Month Amendment _ V. Description of the invention (12), so it can reduce costs and shorten the process time. 3. This process develops a photoresist baking process. Not only does it have no complicated temperature rise and fall process, but the entire baking process only takes about fifteen minutes. The photoselective layer of the etching solution for more than 70 minutes. 4. This process proposes a unique glass etching procedure, which is performed under ultrasonic vibration, and can be used to remove sediments with special chemical methods to obtain a very flat etching surface, and its etching rate can reach one micron per minute. Therefore, the required etching depth can be quickly achieved, and the process time can be shortened. 5. This process proposes a rapid thermal fusion bonding method for glass bonding, which not only does not require complicated and strict cleaning procedures, and does not require a lengthy temperature rise and fall process, it only needs to continue for 10 minutes at 580 ° C to obtain Microfluidic wafer with excellent bonding strength and uniform surface properties of microchannels. 6. The process developed by the present invention is extremely short. It can complete all steps including wafer bonding within ten hours. Compared with the traditional process technology, it must take more than ten hours in the bonding process. This process is an existing document disclosed. The technology with the shortest process time in the report. 7. This process is a process technology platform, which can produce various types of glass microfluidic wafers, has a wide range of applications, and its fast and reliable process characteristics are very suitable for commercial needs.

Page 15 583756 _Case No. 91123979_ Year Month Revision _ Brief Description of Drawings Figures 1 (A) to 1 (一) are process flow diagrams showing the glass microfluidic wafer of the present invention. Fig. 2 is a schematic diagram showing the use of a substrate to fix the upper and lower plates of the wafer in Fig. 1 (i). Figure 3 is an electron microscope image of a photoresist mask after etching. Figure 4 is an electron micrograph of a glass wafer after the etching is completed and the photoresist is removed. Fig. 5 is a sectional view showing the upper and lower plates of a glass wafer after thermal fusion bonding. Figure 6 shows the surface pattern of the etched glass surface scanned with an atomic force microscope. Fig. 7 shows a cross-shaped capillary electrophoresis wafer manufactured by the method of the present invention. Figure 8 shows the separation of the dye mixture using the cross-shaped capillary electrophoresis wafer of Figure 7. Figure 9 shows the separation of dopeptide biological samples using the cross-shaped capillary electrophoresis wafer of Figure 7. Fig. 10 shows a microfluidic cell counting wafer made by the method of the present invention. Figure 11 shows the continuous injection electrophoresis produced by the method of the present invention

Claims (1)

583756 _Case No. 91123979_ Modification of Year of the Year_ 6. Application for Patent Scope 1. A method for manufacturing a glass microfluidic wafer, including at least the following procedures: Provide a glass substrate as the lower plate of the wafer; A baking process for the lower wafer board; an exposure process for the lower wafer board; a photoresist development process for the lower wafer board; a glass etching process for the lower wafer board; a stripping light for the lower wafer board Resistance procedure; providing another glass substrate as a wafer upper plate; drilling holes in the wafer upper plate; and The wafer upper plate and the lower plate are joined by a thermal fusion method. 2. The method for manufacturing a glass microfluidic wafer as described in item 1 of the scope of the patent application, further comprising a procedure for cleaning the glass substrate, which is performed before the procedure for bonding the upper plate and the lower plate of the wafer. 3. The method for manufacturing a glass microfluidic wafer according to item 1 of the scope of the patent application, wherein the aforementioned glass substrate may be soda glass, boro glass, lead glass, PYREX glass, or quartz. 4. The method for manufacturing a glass microfluidic wafer as described in item 1 of the scope of patent application, wherein the aforementioned glass substrate is preferably soda glass. 5. The method for manufacturing a glass microfluidic wafer as described in item 1 of the scope of the patent application, wherein the foregoing baking process includes: a soft baking process, which is a process implemented after coating a photoresist on a wafer; and a hard baking process. , Is implemented after the photoresist development process. 6. The manufacturing method of glass microfluidic wafer as described in item 5 of the scope of patent application Page 17 583756 Case No. 91123979 Amendment VI. Patent Application Law, in which the aforementioned soft roasting temperature is preferably 90 °-100 ° C. 7. The method for manufacturing a glass microfluidic wafer as described in item 5 of the scope of the patent application, wherein the temperature of the aforementioned hard roasting is preferably 100-150 ° C, and the temperature is gradually increased in two stages. . 8. The method for manufacturing a glass microfluidic wafer as described in item 1 of the scope of patent application, wherein the aforementioned photoresist can be a positive or negative photoresist. 9. The method of manufacturing a glass microfluidic wafer as described in item 8 of the scope of the patent application, wherein the aforementioned photoresist is preferably a photoresist of AZ 4 6 2 0. 10. The method for manufacturing a glass microfluidic wafer as described in item 1 of the scope of the patent application, further comprising fixing the wafer upper plate and the wafer lower plate between the two substrates to facilitate thermal fusion bonding. 1 1. The method for manufacturing a glass microfluidic wafer as described in item 10 of the scope of the patent application, wherein the aforementioned substrate may be any of a ceramic substrate, a stainless steel plate, a silicon carbide plate, a tungsten carbide plate, an alumina plate, and a hafnium oxide plate. Any heat-resistant material is acceptable. 1 2. The method for manufacturing a glass microfluidic wafer as described in item 11 of the scope of patent application, wherein the aforementioned substrate is preferably a ceramic substrate. Page 18