KR100790695B1 - Method of manufacturing the ceramics board for electronic element package - Google Patents

Abstract

According to an aspect of the present invention, there is provided a method of forming a laminate by stacking a plurality of green sheets on which conductive patterns and conductive via holes are formed, and firing the laminate to form a low temperature co-fired ceramic (LTCC) substrate body. Printing a conductive paste of a predetermined pattern on one surface, baking the conductive paste to form an external electrode terminal, and heat treating the substrate body on which the external electrode is formed to relieve internal stress of the external electrode terminal and the substrate body. It provides a method of manufacturing a ceramic substrate for an electronic component package comprising the step.

Low Temperature Simultaneous Plasticity (LTCC), Electrode, Heat Treatment

Description

METHODS OF MANUFACTURING THE CERAMICS BOARD FOR ELECTRONIC ELEMENT PACKAGE

1A and 1B are cross-sectional views showing a ceramic substrate manufacturing method of the prior art for enhancing the bonding strength between the ceramic substrate and the electrode.

2A through 2E are process flow diagrams illustrating a method of manufacturing a ceramic substrate according to an embodiment of the present invention.

3A to 3C are process flowcharts of a method of manufacturing a ceramic substrate by a non-shrink process.

4 is a graph showing an experimental value of measuring the bonding strength between the ceramic substrate and the electrode before and after heat treatment in accordance with an embodiment of the present invention.

FIG. 5 is a graph showing experimental values obtained by measuring adhesion strength between a ceramic substrate and an electrode according to a heat treatment environment in an embodiment of the present invention. FIG.

<Description of the symbols for the main parts of the drawings>

21: ceramic substrate layer 22: external electrode

25 conductive via hole 26 internal electrode

33: glue 37: sheet for high temperature firing

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic laminated substrate, and more particularly, to a method of improving the bonding strength of a ceramic laminated substrate and a terminal electrode formed on the substrate.

On the surface of a substrate made of plastics or ceramics, semiconductor elements such as FETs and diodes, electronic components such as resistors, capacitance elements, inductance elements, etc. are mounted. High frequency electronics such as high frequency switches, VCOs, amplifiers and the like are known. Such substrates require protection from mechanical stress of semiconductor devices and electronic components, improvement of electrical characteristics, and thermal protection.

Recently, in the field of mobile communication such as mobile phones, there is a strong demand for miniaturization of component circuit components, and capacitance elements, inductance elements, and the like are manufactured using LTCC (low temperature co-fired ceramics) technology. The technology built in is introduced.

In a high frequency electronic component using such a ceramic laminated substrate, a terminal electrode having various functions on the surface of the ceramic laminated substrate-for example, a circuit board such as a printed board, a terminal electrode for supplying a driving voltage to a semiconductor element, and a high frequency signal Terminal electrodes to be input or output, ground electrodes, etc.-are formed by screen printing or electrode transfer.

As miniaturization and high performance of mobile communication devices are required, miniaturization of high-frequency electronic components is also strongly demanded. Therefore, various terminal electrodes having a size limited to ceramic laminated substrates must be disposed, and as a result, the formation area of the terminal electrodes must not be reduced. Can't.

In a cellular phone, sometimes the user can generate an impact such as a drop, so that the terminal electrode of the high frequency electronic component is also required to have excellent internal and external impact resistance. Moreover, after mounting a high frequency electronic component on a circuit board, the external force which can add curvature and a torsion to the said circuit board may be added, and a stress may act on a terminal electrode. In such a case, since the formation area of a terminal electrode becomes small and the adhesive strength of the said terminal electrode and a ceramic laminated board becomes easy to become inadequate, a terminal electrode may peel from the mounting surface with a circuit board.

In addition, the thermal expansion coefficient of the ceramic material used for the ceramic laminated substrate is 20 to 500 ° C, 5.0 to 10 × 10 ^-6 / ° C, and the thermal expansion coefficient of the terminal electrode is 18 to 21 × 10 ^-6 / ° C, and the ceramic material and the epoxy Thermal expansion coefficient (12 to 75 × 10 ^-6 / ° C) of a circuit board made of (epoxy) resin, glass-epoxy-based composite material, etc., and thermal expansion coefficient of solder (24 × 10 ^-6 / ° C) Are significantly different from each other. For this reason, the result which a stress exists in the interface of a ceramic laminated substrate and a terminal electrode arises. When the bonding strength between the ceramic laminated substrate and the terminal electrode is inferior, the ceramic laminated substrate, the circuit board and the solders to be bonded to each other due to heat generation during operation of the semiconductor element mounted on the ceramic laminated substrate or thermal expansion due to a change in environmental temperature are applied. The stress may act on the terminal electrode to peel off from the ceramic laminated substrate. In such a case, there arises a problem that the high frequency electronic component cannot exhibit the required function.

In particular, in the case of the non-shrink constrained firing method, the external electrode pattern formed after the lapping process to remove and planarize the restraint layer is formed on the fired substrate, and only the outer electrode material is fired after the firing process. The adhesion strength between terminal electrodes is weaker.

As a method for reinforcing the bonding strength between the ceramic laminated substrate and the terminal electrode, a glass frit is added or overglazed between the ceramic laminated substrate and the terminal electrode.

1A and 1B show a prior art for increasing the bonding strength between a ceramic laminate and a terminal electrode.

Referring to FIG. 1A, a glass frit 13 is added between the ceramic laminated substrate 11 and the terminal electrode 12. When glass is added to the electrode, it is very difficult to control according to the wettability and chemical affinity with LTCC, and due to the added glass frit, the surface of the terminal electrode metal is reduced and plating becomes difficult. This will adversely affect the packaging characteristics.

Referring to FIG. 1B, a pattern serving as a protective role with an overglaze 14 is fired at the corner portion of the terminal electrode 12 on the ceramic laminated substrate 11. In this method, the edge part of the terminal electrode 12 can be prevented from being peeled off. However, the printing process must be added again to the outer edge of the formed electrode pattern. have.

SUMMARY OF THE INVENTION An object of the present invention is to reduce the pad size by maintaining the packaging characteristics without forming an additional material at the interface between the multilayer ceramic substrate and the terminal electrode to solve the above problems, and by not forming an additional structure outside the electrode pattern. The present invention provides a method of manufacturing a ceramic substrate for a component package.

The present invention comprises the steps of: forming a laminate by stacking at least one green sheet having a conductive pattern and a conductive via hole; firing the laminate to form a low temperature co-fired ceramic (LTCC) substrate body, the low temperature cofire Forming an electrode pattern by printing a conductive paste on one surface of a ceramic (LTCC) substrate main body, forming an external electrode terminal by firing the conductive paste, and the external electrode terminal and the low temperature co-fired ceramic (LTCC) substrate main body It provides a method of manufacturing a ceramic substrate for an electronic component package comprising the step of heat-treating the low-temperature co-fired ceramic (LTCC) substrate body on which the external electrode terminal is formed so that the internal stress of the.

The forming of the low temperature co-fired ceramic (LTCC) substrate body may include stacking a high temperature firing sheet capable of firing at a higher temperature than the firing temperature of the green sheet on the upper and lower layers of the laminate and firing at a firing temperature of the green sheet. And forming a fired body and peeling the high temperature firing sheet and lapping the surface of the fired body. That is, a ceramic substrate can be formed by a non-shrinkage process.

The heat treatment may be a heat treatment temperature of 150 ℃ to 600 ℃.

In order to prevent oxidation of the surface of the metallic external electrode terminal in the heat treatment step, the heat treatment environment is preferably reduced.

In the heat treatment step, the heat treatment holding time may be 30 minutes or more.

Hereinafter, the invention will be described in detail with reference to the accompanying drawings.

2A to 2E are manufacturing process diagrams of a ceramic laminated substrate and an electrode terminal according to the embodiment of the present invention.

Referring to FIG. 2A, a plurality of green sheets 21a, 21b, and 21c having conductive patterns 26 and conductive via holes 25 are stacked on the surface and the inside thereof.

The green sheet may be coated with a ceramic rally on a resin film such as PET and dried to obtain a ceramic green sheet having a thickness of about 10 to 200 microns. As ceramic powder contained in the ceramics rally, for example, BaO, SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , or a mixture of CaO and the like can be used.

A conductive paste in which a through hole (via hole) having a diameter of about 0.1 mm is drilled through a mold, a laser, and the like, and the metal sheet, which is composed of silver (Ag) or copper (Cu), is mixed with a metal powder, a resin, and an organic solvent. Is filled into a via hole and dried. This becomes the conductive via hole 25.

Referring to FIG. 2B, the laminated green sheet is fired to make a ceramic substrate.

As for the temperature which bakes a ceramic substrate, 800-1000 degreeC is preferable.

The present invention takes a step of printing an electrode on the ceramic substrate after firing the ceramic substrate. This decreases the bonding strength between the ceramic substrate and the electrode, compared to the case of printing the electrode on the green sheet and firing the green sheet and the electrode at the same time, but eliminates problems that may occur due to the difference in shrinkage between the electrode and the ceramic substrate. Can be.

Preferably, the ceramic substrate may be manufactured by a non-shrink process, which will be described separately in FIG. 3.

Referring to FIG. 2C, an external electrode terminal 22a and a circuit pattern are printed using a conductive paste on the fired ceramic substrate.

The width of the external electrode terminal 22a formed at this time is indicated by W ₁ .

The conductive paste for forming the external electrode terminal may be made of gold, silver, copper noble metal or a mixture thereof, or may contain the noble metal and inorganic glass.

Referring to FIG. 2D, the conductive paste printed in FIG. 2C is fired.

In this step, firing is performed at a temperature lower than the firing temperature of the ceramic substrate 21 (800 ° C. or lower). The ceramic substrate 21 which has already been fired by such low temperature firing is not affected by shrinkage or the like, and only the conductive paste is shrunk and fired. Printing the conductive paste on the already baked ceramic substrate and baking only the printed conductive paste at a low temperature is called a post-firing process.

According to the commonly used co-firing process, before firing the ceramic substrate, that is, in the state in which the green sheets are laminated, the electrode and the circuit are printed with the conductive paste on the surface of the green sheet, and then simultaneously fired at the firing temperature of the green sheet. do. In this case, the green sheet layer and the conductive paste layer are fired together and shrink at the same time. Therefore, although the bonding strength between the ceramic layer and the electrode layer after firing is stronger than that by the post-firing process, the problems caused by mismatch phenomenon due to the difference in shrinkage rate during firing of the green sheet layer and the conductive paste layer are more serious. That is, there is a problem that warpage or cracking of the substrate occurs.

In the present invention, the post-firing process is followed to solve the above problems of co-firing.

In the post-firing process, the external electrode terminal 22 shrinks. In the figure, the width of the contracted electrode is denoted by W ₂ . Here, the width W ₂ of the external electrode terminal after firing is narrower than the width W ₁ of the external electrode terminal before firing. The densification occurs at the interface between the ceramic substrate 21 and the external electrode terminal 22 by the contraction of the external electrode terminal 22 during firing, and the bonding strength thereof is determined by the glass of the ceramic substrate or the glass frit in the electrode. Interlocking is created by the flow of glass frit. At this time, different densities of materials are caused by different densities at different temperatures and shrinkage rates, thereby causing plastic stress (sintering stress), densification after firing, and then ceramic substrate 21 and external electrode terminal 22 during cooling. Thermal stresses occur in the liver. The stress causes a weakening of the bonding strength of the ceramic-metal interface.

Referring to FIG. 2E, heat treatment is performed to remove internal stress generated at the interface between the ceramic substrate and the external electrode terminal in the step of FIG. 2D.

The heat treatment may be performed in air, but in order to prevent the metallic electrode from being oxidized during the heat treatment, N ₂ Or N ₂ / H ₂ It is preferably carried out in a reducing atmosphere such as.

As for the temperature of the said heat processing, about 150 degreeC-about 600 degreeC is preferable. In order to give an effect of heat treatment to the external electrode terminal, heat of at least 150 ° C. is required, and since the firing temperature of the external electrode terminal is about 600 ° C., when the temperature exceeds 600 ° C., the physical change of the external electrode terminal is changed. Because there is a fear of causing.

The duration of the heat treatment is preferably maintained at about 30 minutes or more. This is because some heat treatment time is required to remove internal stress generated at the interface. However, the heat treatment effect does not increase in proportion to the heat treatment duration.

Through such a heat treatment step, internal stresses generated at the interface between the ceramic substrate and the external electrode terminal may be alleviated, thereby increasing the adhesion strength of the external electrode terminal to the ceramic substrate.

3A to 3C are flowcharts of a process of making a ceramic substrate by a non-shrinkage process.

Referring to FIG. 3A, a temperature higher than the firing temperature of the green sheet 31 (for example, 1500 ° C. or higher) in the upper layer and the lower layer of the stack 31 before firing the stack 31 of the green sheet. The high temperature baking sheet 37 baked at is laminated | stacked. Generally, green tapes containing metal oxides such as Al ₂ O ₃ , ZrO, SiC, AlN, and Mullite are used as sheets for high temperature baking.

A glue 33, which is an adhesive layer, is applied between the laminate 31 and the high temperature baking sheet 37. The glue 33 is made of an organic binder and a high temperature volatile solvent to strengthen the adhesive force between the green sheet 31 and the high temperature calcining sheet 37, so that the green sheet 31 and the high temperature calcining sheet 37 during firing. ) To prevent separation.

Compressing the laminated laminate under a constant temperature and a predetermined pressure may be included. The pressing may include pressing using a second isostatic press after the first pressing step.

The process using the isotropic pressure means applying the laminated laminate to water in all directions in water or oil.

Referring to FIG. 3B, the laminate laminated in FIG. 3A is co-fired at the firing temperature of the green sheet. That is, the baking process is performed at a low temperature of about 800 ℃ to 1000 ℃. When the low temperature baking process is performed, the green sheet layer 31 shrinks, but the high temperature baking sheet 37 positioned at the uppermost layer and the lowermost layer does not cause plastic shrinkage. Therefore, shrinkage is suppressed in the horizontal direction (x-axis and y-axis) and the shrinkage occurs only in the vertical direction (z-axis), that is, in the thickness direction.

In this way, in order to prevent the green sheet layer from shrinking in the horizontal direction during firing, laminating a high temperature baking sheet on the upper layer and the lower layer of the green sheet layer is called a non-shrinkage process.

In general, there are limitations in implementing composite components and composite modules using only a single type of substrate material. For example, a substrate material having low dielectric constant should be used for high-speed wiring, and a substrate material having low dielectric constant and low dielectric loss should be used for a high frequency inductor and a low capacitance capacitor. In addition, a substrate material having high permeability should be used for a high capacity inductor, and a substrate material having high dielectric constant and low dielectric loss should be used for a high capacity capacitor and a small planer filter.

When the green sheets stacked in this way are used with different material substrates, the plastic shrinkage amounts are different because the composition and type of the metal oxide and the glass component constituting the substrate are different. In the case of simultaneously firing the dissimilar materials, warpage or cracking of the substrate occurs due to mismatch due to the difference in the amount of shrinkage of the plastic. A method for overcoming this phenomenon is a shrinkage process.

Referring to FIG. 3C, after the co-firing, the high temperature baking sheet 37 is peeled off to form a ceramic substrate 31.

At this time, the high temperature baking sheet 37 may be removed through a process such as water washing. The ceramic substrate 31 thus formed becomes a circuit package having a plurality of circuit layers.

The external electrode may be formed on the ceramic substrate 31 formed through such a process through a lapping process, an electrode printing process, and a low temperature baking process.

In order to increase the friction between the conductive paste to be printed and the ceramic substrate, it is preferable to add a step of lapping the surface of the ceramic substrate 21 before printing the conductive paste.

The lapping process forms a surface having a certain roughness on the surface of the ceramic substrate 21, thereby maximizing the contact area with the conductive paste printed on the surface to enhance the adhesion strength of the electrode during low temperature baking.

Here, the roughness Ra of the ceramic substrate 31 after lapping is preferably 0.3 to 1 μm.

Figure 4 shows the experimental value for the bonding strength of the ceramic substrate and the external electrode terminal when the heat treatment.

4 is a graph of an experiment in which silver (Ag) paste is printed and fired on a ceramic substrate, and then subjected to heat treatment for 1 hour or more at a temperature of 300 ° C for the ceramic substrate and the external electrode terminal.

The adhesion strength measured in FIG. 4 is measured by a peel test that pulls the electrode after Ni plating the surface of the external electrode terminal after the heat treatment.

In the case of having the same roughness Ra, first, the fixation strength of about 0.7 N / mm 2 before the heat treatment at Ra = 0.3 μm increased to 1.2 N / mm 2 after the heat treatment. You can see that.

Even before the heat treatment, when the roughness was changed, that is, the bonding strength at Ra = 0.6 µm was about 1.2 N / mm 2, and the bonding strength was greater than that at the Ra = 0.3 µm.

When the roughness is set to Ra = 0.6 mu m and the heat treatment is performed, it has a fixing strength of about 1.8 N / mm 2, and it can be seen that the fixing strength is significantly increased.

As such, the adhesion strength between the ceramic substrate and the external electrode can be increased by removing the stress Ra from the interface formed by the roughness Ra and the heat treatment formed at the interface between the ceramic substrate and the external electrode.

5 is a graph showing a change in the fixing strength according to the heat treatment environment in the embodiment of the present invention.

In the graph of FIG. 5, the silver (Ag) paste is printed on a ceramic substrate and then fired, and the heat treatment environment is changed to measure a change in the bonding strength between the external electrode terminal and the ceramic substrate. In this experiment, the heat treatment holding time was 1 hour.

Referring to Fig. 5, when the heat treatment environment is set to a reducing atmosphere, that is, when the heat treatment space is filled with N ₂ , the fixing temperature of 0.5 N / mm ₂ at a standard room temperature without heat treatment is 200 ° C. In the case of furnace heat treatment, it has a fixing strength of 2.1 N / mm 2, and it can be seen that the fixing strength is increased about four times. On the other hand, when the heat treatment temperature is set to 300 ℃ and 400 ℃ it can be seen that the fixing strength is 2.2 N / mm 2 and 2.1 N / mm 2, respectively, not significantly different from the case of 200 ℃.

Similarly, when the heat treatment environment is set to air, those having a fixing strength of 0.45 N / mm 2 at a room temperature without heat treatment are 2.2 N at 200 ° C, 300 ° C, and 400 ° C, respectively. It can be seen that it has a fixing strength of / mm 2, 2.1 N / mm 2 and 2.0 N / mm 2.

The saturation heat treatment temperature may vary depending on the components of the conductive material and the content of the metal conductive material contained in the conductive paste. However, since the heat treatment temperature has a constant saturation temperature, heat treatment at a saturation temperature is preferable.

As described above, the heat treatment environment is used to reduce the oxidation of the metallic external electrode terminal to facilitate plating on the surface of the external electrode terminal that is performed after the heat treatment step.

As such, the present invention is not limited by the above-described embodiment and the accompanying drawings. That is, the time and temperature for heat treatment may be variously implemented. It is intended that the scope of the invention be defined by the appended claims, and that various forms of substitution, modification, and alteration are possible without departing from the spirit of the invention as set forth in the claims. Will be self-explanatory.

According to the present invention, the internal stress applied between the ceramic substrate and the external electrode is removed to obtain a ceramic substrate having increased adhesion strength, thereby improving the plating property, package yield and reliability of the ceramic substrate external electrode.

Claims (5)

Stacking at least one green sheet having conductive patterns and conductive via holes to form a laminate; Firing the laminate to form a low temperature co-fired ceramic (LTCC) substrate body; Forming an electrode pattern by printing a conductive paste on one surface of the low temperature co-fired ceramic (LTCC) substrate body; Baking the conductive paste to form external electrode terminals; And And heat-treating the low temperature co-fired ceramic (LTCC) substrate body on which the external electrode terminals are formed such that internal stresses of the external electrode terminal and the low-temperature co-fired ceramic (LTCC) substrate body are alleviated. Manufacturing method. The method of claim 1, Forming the low temperature co-fired ceramic (LTCC) substrate body, Stacking high-temperature baking sheets capable of firing at a higher temperature than the firing temperature of the green sheet on upper and lower layers of the laminate, and firing at a firing temperature of the green sheet to form a fired body; And Peeling the high-temperature baking sheet and lapping the surface of the fired body, characterized in that it comprises a step of manufacturing a ceramic substrate for an electronic component package. The method of claim 1, The heat treatment step, A method for producing a ceramic substrate for an electronic component package, characterized in that the heat treatment temperature is 150 ° C to 600 ° C. The method of claim 1, The heat treatment step, A method of manufacturing a ceramic substrate for an electronic component package, characterized in that the heat treatment environment is reduced. The method of claim 1, The heat treatment step, A method for producing a ceramic substrate for an electronic component package, characterized in that the heat treatment holding time is 30 minutes or more.

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