CN201149866Y - Ceramic/Metal Composite Structure - Google Patents

Abstract

A ceramic/metal composite structure comprising a lower metal layer; a lower metal interface layer, which is covered on the lower metal layer; the ceramic substrate is positioned on the lower metal interface layer; an upper metal interface layer coated on the ceramic substrate; and an upper metal layer located on the upper metal interface layer.

Description

Ceramic/Metal Composite Structure

technical field

The utility model relates to a ceramic/metal composite structure, in particular to a composite structure formed by combining an aluminum oxide layer and a copper layer.

Background technique

When electrons flow in electronic parts, heat will be generated, and the heat generation will increase the resistance, hinder the flow of electrons, and then greatly affect the function of electronic parts. Under the current situation that the manufacturing technology of electronic parts is greatly improved, the line width in electronic parts is getting smaller and smaller, but the circuit density is getting higher and higher, so the heat generated by electronic parts is also increasing rapidly. Taking the computer's central processing unit (Central Processing Unit, CPU) as an example, the earliest version of Intel's Pentium only needs to be packaged with a heat dissipation power of 16W. However, the heat generation of the central processing unit produced in 2004 has reached 84W, and the heat generation of the central processing unit produced in 2006 has reached 98W. If the heat cannot be taken away quickly, the temperature of the central processing unit of the computer will Will increase rapidly, so that the computer's central processing unit can not function properly. Therefore, whether the substrate in contact with the central processing unit of the computer has a rapid heat dissipation capability is really a key factor that determines whether the computer can operate normally.

General power components, such as solid state relays, are also similar to the central processing unit of a computer, and generate high heat during operation. Therefore, the power components also need to use the substrate in contact with them to dissipate heat quickly in order to operate normally.

Taking light emitting diodes (Light Emitting Diode, LED) as an example, light emitting diodes of various colors have been developed successively in recent years, among which the successful development of white light emitting diodes is the most important. This is because white light-emitting diodes can be used as light sources for lighting fixtures. The power consumption of street lights of this light source is 75% less than that of mercury lamps and 49% less than that of high-pressure sodium lamps. Therefore, it has the advantage of low energy consumption and is an important development for energy conservation. . However, if we take the headlights of daily life and vehicles as an example, these applications must use white light emitting diodes with a power greater than 3W. Such high-power white light emitting diodes will also emit high heat, but the biggest problem with LED lighting is that LEDs are not resistant to High heat, generally speaking, the temperature cannot exceed 90°C. If it exceeds this temperature, the brightness will drop rapidly. Therefore, the rapid heat dissipation capability of the heat dissipation mechanism in contact with the LED is the biggest challenge for the light-emitting diode to become a lighting source. This also shows that the heat dissipation The development of the substrate plays an important role in the application of light-emitting diodes in lighting.

In order to take into account the thin and light design requirements of today's 3C electronic products, the substrates that are in contact with the central processing units, power components or light-emitting diode components of these computers must meet the following four basic requirements at the same time:

1. Requirements for heat dissipation: This material must have a high thermal conductivity to meet the requirements of rapid heat dissipation.

2. Insulation requirements: In order to avoid short circuit of high-power electronic parts, this material must have high resistivity.

3. Thin layer requirements: After meeting the above two basic requirements, the thickness of the substrate should be as thin as possible.

4. Reliability of long-term use: This is because after the high-power electronic parts are packaged, the high-power electronic parts will perform tens of thousands of on-off cycles, and the substrate in contact with the high-power electronic parts It will heat up and down tens of thousands of times instantly. The reliability of electronic parts after long-term use is an extremely important requirement, and this has an absolute relationship with the bonding strength of ceramics and metals.

At present, in terms of heat dissipation mechanisms of electronic components, a large number of mechanisms such as heat dissipation fins and heat pipes are used, supplemented by fans, in order to quickly take away the heat generated by high-power electronic components. However, the thickness of these heat dissipation mechanisms is relatively large, thus hindering the design requirements of 3C electronic products to be light, thin and short.

After a comprehensive material search and evaluation, the best choice to meet the above first heat dissipation requirement and cost considerations is the metal material. Taking copper as an example, the thermal conductivity of copper can reach 380W/mK. There are many materials that can meet the second insulation requirement above, and most of the organic materials or ceramic materials can meet this requirement. In order to take into account the requirement of heat dissipation and the requirement of long-term reliability, ceramic material is a better choice. Ceramic materials that can provide high thermal conductivity and insulation include alumina and aluminum nitride. The thermal conductivity of alumina can reach 20-38W/mK, while the thermal conductivity of aluminum nitride can reach 40-200W/mK. The reason why the thermal conductivity of ceramics has a large range is that the thermal conductivity of ceramics is greatly affected by the purity of ceramics and sintering additives. Furthermore, the resistivity of alumina and aluminum nitride is as high as 10 ¹⁰ Ωm or more, so both ceramics have excellent electrical insulation. In addition, aluminum oxide and aluminum nitride also have the advantages of low dielectric constant (Dielectric constant) and high dielectric strength (Dielectric strength), so they are commonly used in substrates.

In order to solve the heat dissipation of the substrate, there are researches in the prior art to combine ceramics and copper sheets to form a substrate with a composite structure. The ceramic layer is sandwiched between the two copper sheets and is in direct contact with the copper sheet.

However, because alumina is a high-melting solid (melting point > 2000°C) with covalent bonds and ionic bonds coexisting, and copper atoms are combined with metal bonds, the melting point is only 1083°C. Bonding alumina and copper together is a very Challenging field. In the prior art, there are two methods for bonding alumina and copper together, one is solid state bonding, and the other is liquid phase bonding. . The processing temperature of these two methods is above 1000°C.

After a long period of research, we found that the substrate bonded together by aluminum oxide and copper, the interface strength between aluminum oxide and copper must be very high to have application value. This is because the bonding between alumina and copper is different, and the coefficient of thermal expansion of copper (17×10 ⁻⁶ K ⁻¹ ) is twice that of alumina (8×10 ⁻⁶ K ⁻¹ ). According to the formula derived by Selsing (Selsing, J., J. Am. Ceram. Soc., 44, 419, 1961), it is as follows:

$\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;\&alpha;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;<figure-callout\; id="1"\; label="T"\; filenames="Y20072019463700181.png"\; state="\{\{state\}\}">T</figure-callout></span>}}{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; al</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; al</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; Cu</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; Cu</span>}}}}$

In the above formula, Δα is the difference in thermal expansion coefficient between alumina and copper, ΔT is the difference between the manufacturing process or the temperature used and room temperature, v is Poisson’s ratio, and E is the elastic constant. Since the bonding temperature of the alumina sheet and the copper sheet is above 1000°C, the thermal stress caused by the difference in thermal expansion coefficient between the alumina sheet and the copper sheet after high-temperature joining (Joining) can be estimated to reach several More than 100 MPa. This thermal stress is very large, which has a great influence on the bonding strength of the aluminum oxide sheet and the copper sheet, and after being packaged with electronic parts that generate heat, after tens of thousands of on-off cycles of the electronic parts, if the aluminum oxide sheet And the bonding strength of the copper sheet is not high enough, there will be delamination between the aluminum oxide sheet and the copper sheet, and the heat dispersion ability will be greatly reduced, which will have an irreparable impact on the long-term use reliability of high-power electronic components.

Therefore, how to provide a ceramic/metal composite structure with high bonding strength is an urgent problem to be solved.

Contents of the invention

In order to solve the above technical problems, the purpose of this utility model is to provide a ceramic/metal composite structure, through the strong bond formed between the ceramic and the metal material, it can be used as an electronic component under thinning and long-term reliability. The purpose of providing good heat dissipation and insulation functions.

In order to achieve the above object, the utility model provides a ceramic/metal composite structure, which includes: a lower metal layer; a lower metal interface layer, covered on the lower metal layer; a ceramic substrate, located on the lower metal interface layer; The upper metal interface layer is coated on the ceramic substrate; and an upper metal layer is located on the upper metal interface layer.

According to a specific solution of the present utility model, the ceramic substrate may be made of one or a combination of materials including alumina, silicon oxide, aluminum nitride, silicon nitride, silicon carbide, glass, and glass ceramics. finished substrate.

The lower metal layer and the upper metal layer may be copper sheet layers.

The coating includes coating the lower metal interface layer and the upper metal interface layer on the lower metal layer and the ceramic substrate respectively by using a conventional electroless plating method. The electroless plating method can be, for example, deposition or coating. ) etc.

According to a specific solution of the present invention, at least one line or contact is arranged on the upper metal layer, so as to facilitate the integration and packaging of the composite structure and high-power electronic components, and achieve good electrical connection and heat dissipation functions.

The composite structure provided by the utility model may have at least one notch, and the notch extends along the upper metal layer to at least the upper metal interface layer.

The ceramic/metal composite structure described in the present invention can also include an electronic component, which is located in the aforementioned gap. In order to achieve a better heat dissipation effect, thermal conductive glue can be provided. According to the specific solution of the present utility model, when the gap extends to the ceramic substrate along the upper metal layer, the ceramic substrate in the gap is provided with a heat-conducting glue, and the electronic components are arranged on the heat-conducting glue, or, when the When the notch extends along the upper metal layer to the upper metal interface layer, the upper metal interface layer in the notch is provided with heat-conducting glue, and the electronic components are arranged on the heat-conducting glue.

A plurality of wires may also be arranged in the ceramic/metal composite structure, which connect the electronic components to the above-mentioned upper metal layer. Moreover, the upper metal layer at the periphery of the notch can form a slope or a curved surface. When the electronic component is an LED, the slope or curved surface can reflect the non-main light of the electronic component upwards, so as to increase the luminous efficiency of the electronic component.

In addition, in the ceramic/metal composite structure provided by the present invention, multiple sets of electronic components can be arranged on the ceramic substrate in any arrangement, for example arranged in an array above the ceramic substrate.

The manufacturing method of the ceramic/metal composite structure provided by the utility model may comprise the following steps:

First, a ceramic substrate is provided;

Then, coat the upper metal interface layer and the lower metal interface layer on both sides of the ceramic substrate respectively. For example, the two metal interface layers can be coated on the ceramic substrate by electroless plating;

Next, the upper metal layer is placed on the upper metal interface layer, and the lower metal layer is placed on the lower metal interface layer. It is worth noting that before the metal layer is placed on the metal interface layer, multi-stage pre-oxidation treatment can be performed first, and the multi-stage pre-oxidation treatment is carried out at a temperature of 50 to 700 ° C;

Then, the ceramic substrate, the upper metal interface layer, the lower metal interface layer, the upper metal layer and the lower metal layer are heated, so that each metal interface layer is bonded with the ceramic substrate and each metal layer simultaneously to form a strong bond. For example, the ceramic substrate, the upper metal interface layer, the lower metal interface layer, the upper metal layer and the lower metal layer can be heated to above 1000° C. to form a strong bond to make the ceramic/metal composite structure of the present invention.

To sum up, the utility model discloses a composite structure combining copper and alumina, and the carrier board provides the basic requirements of heat dissipation and insulation at the same time. And because the resistivity of copper is extremely low, only 10 ^-4 Ω·m, various lines or contacts can be made on the copper part by etching. Through the lines or contacts, the composite structure can be integrated and packaged with high-power electronic components to achieve good electrical connection and heat dissipation functions. In addition, using the composite structure of the present utility model to make the substrate, because the interface strength of the composite structure is high, it will also increase the life of high-power electronic components that will undergo tens of thousands of on-off cycles in the future. has been of great help.

Description of drawings

FIG. 1 shows a schematic top view of a ceramic/metal composite structure according to Embodiment 1 of the present invention.

FIG. 2 shows a schematic cross-sectional view of the ceramic/metal composite structure according to Embodiment 1 of the present invention.

FIG. 3 shows a schematic top view of a ceramic/metal composite structure according to Embodiment 2 of the present invention.

FIG. 4 shows a schematic cross-sectional view of a ceramic/metal composite structure according to Embodiment 2 of the present invention.

FIG. 5 shows a schematic cross-sectional view of a ceramic/metal composite structure according to Embodiment 3 of the present invention.

FIG. 6 shows a schematic top view of a ceramic/metal composite structure according to Embodiment 3 of the present invention.

FIG. 7 shows a schematic cross-sectional view of a ceramic/metal composite structure according to Embodiment 4 of the present invention.

FIG. 8 shows a schematic cross-sectional view of a ceramic/metal composite structure according to Embodiment 5 of the present invention.

FIG. 9 shows a schematic top view of a ceramic/metal composite structure according to Embodiment 6 of the present invention.

Fig. 10 shows a graph of test results of the ceramic/metal composite structure according to the present invention.

Description of main component symbols:

11: Lower metal layer 12: Lower metal interface layer

13: Ceramic substrate 14: Upper metal interface layer 15: Upper metal layer/copper sheet

16: Notch 17: Bevel 18: Curved surface

19: Electronic components 20: Thermally conductive adhesive 21: Wire

22: Encapsulation material

Detailed ways

In order to make the above content of the present invention more obvious and understandable, the preferred embodiments will be described in detail below together with the accompanying drawings.

Example 1

According to Embodiment 1 of the present utility model in conjunction with Fig. 1 and Fig. 2, the ceramic/metal composite structure provided by the present utility model comprises a lower metal layer 11, a lower metal interface layer 12, a ceramic substrate 13, and an upper metal interface layer 14 and an upper metal layer 15 . Wherein, the lower metal layer 11 may be a copper sheet layer, the thickness of the lower metal layer 11 may be between 0.1 mm and 2 mm, and the lower metal interface layer 12 is located on the lower metal layer 11 .

The ceramic substrate 13 is located on the lower metal interface layer 12 . The thickness of the ceramic substrate 13 is between 0.1 mm and 3 mm. The ceramic substrate 13 may be a substrate made of one or a combination of materials including alumina, silicon oxide, aluminum nitride, silicon nitride, silicon carbide, glass, and glass ceramics.

The upper metal interface layer 14 is located on the ceramic substrate 13 . The upper metal interface layer 14 or the lower metal interface layer 12 can be made of one or more materials including gold, beryllium, bismuth, cobalt, copper, iron, nickel, palladium, platinum, titanium, yttrium and alloys thereof. Combine the fabricated metal interface layer. Alternatively, the upper metal interface layer 14 or the lower metal interface layer 12 may preferably be a metal interface layer made of one or more combinations of nickel, nickel alloy, copper and copper alloy. The thickness of the upper metal interface layer 14 or the lower metal interface layer 12 is between 0.1 micron and 10 microns, more preferably between 1 micron and 5 microns.

The upper metal layer 15 is located on the upper metal interface layer 14 . The upper metal layer 15 may be a copper sheet layer with one or more lines or one or more contacts thereon. The thickness of the upper metal layer 15 is between 0.1 mm and 2 mm.

Example 2

According to Embodiment 2 of the present utility model and in combination with FIG. 3 and FIG. 4 , FIG. 4 is a sectional view along the A-A direction of FIG. 3 . Embodiment 2 is similar to Embodiment 1, except that the upper metal layer 15 has at least one gap 16, or the ceramic substrate 13 in the gap 16 may also be formed with an upper metal interface layer 14 (not shown).

Example 3

According to Embodiment 3 of the present utility model in conjunction with FIG. 5 and FIG. 6 (for clarity, FIG. 6 does not show the encapsulation material 22 ), FIG. 5 is a cross-sectional view along the B-B direction of FIG. 6 . The ceramic/metal composite structure of Embodiment 3 may further include an electronic component 19 located in the gap 16 of the composite structure and disposed on the ceramic substrate 13 . The electronic component 19 can be a central processing unit, a power component (such as a power transistor) or a light emitting diode component. It should be noted that, in the fourth embodiment, the present invention can regard the electronic component 19 as a part of the ceramic/metal composite structure.

In order to achieve a better heat conduction effect, a heat conduction adhesive 20 may be provided in the ceramic/metal composite structure.

When the notch 16 extends to the ceramic substrate 13 along the upper metal layer 15, the ceramic substrate 13 in the notch 16 is provided with a thermally conductive glue 20, and the electronic component 19 is arranged on the thermally conductive glue 20, or, when the notch 16 extends along the upper metal layer 15 to the upper metal interface layer 14 (not shown in the figure), the upper metal interface layer 14 in the gap 16 is provided with a thermally conductive adhesive 20, and the electronic component 19 is arranged on the thermally conductive adhesive 20 superior. The thermally conductive adhesive 20 may be formed by mixing organic polymer materials and metal or ceramic filling materials. The metal or ceramic filling material may include one or a combination of silver particles, copper particles, aluminum particles, aluminum oxide particles, aluminum nitride particles, boron nitride particles, and titanium boride particles. The thermal conductivity of the thermally conductive adhesive 20 can generally reach above 3W/mK.

In order to control the operation of the electronic component 19 , the ceramic/metal composite structure of this embodiment may further include a plurality of wires 21 for connecting the electronic component 19 to the upper metal layer 15 . The packaging material 22 encapsulates the electronic components 19 and the wires 21 . Most of the heat emitted by the electronic components 19 is conducted and dissipated in the direction indicated by the arrow in FIG. 7 .

Example 4

FIG. 7 shows a schematic cross-sectional view of a ceramic/metal composite structure according to Embodiment 4 of the present invention. As shown in FIG. 7 , an inclined surface 17 is formed on the upper metal layer 15 at the periphery of the notch 16 in the composite structure of this embodiment. When the electronic component 19 is an LED, the slope 17 can reflect the non-main light of the electronic component 19 upwards, so as to increase the luminous efficiency of the electronic component 19 .

Example 5

FIG. 8 shows a schematic cross-sectional view of a ceramic/metal composite structure according to Embodiment 5 of the present invention. As shown in FIG. 8 , a curved surface 18 is formed on the upper metal layer 15 around the notch 16 of the composite structure in this embodiment. When the electronic component 19 is an LED, the curved surface 18 can also reflect the non-main light of the electronic component 19 upwards, so as to increase the luminous efficiency of the electronic component 19 .

Example 6

FIG. 9 shows a schematic top view of a ceramic/metal composite structure according to Embodiment 6 of the present invention. As shown in FIG. 9 , multiple sets of electronic components 19 can be arranged in an array (or array form) and disposed above the ceramic substrate 13 .

In order to enhance the interface strength and improve the reliability of the ceramic/metal composite structure, the composite structure of the present invention can be manufactured through a multi-stage pre-oxidation manufacturing process. After this multi-stage pre-oxidation treatment, the surface of the metal layer can be properly oxidized material, so that the metal layer and the ceramic substrate can be successfully bonded under the generally well-known eutectic temperature, and the resulting ceramic/metal bond is very strong, which effectively improves the interface strength between the ceramic substrate and the metal layer , and then improve the reliability of the ceramic/metal composite structure when it is used repeatedly in temperature rise and fall. And the temperature of this multi-stage pre-oxidation is low (the ratio of the absolute temperature value of the maximum temperature of multi-stage pre-oxidation and the absolute temperature value of the melting point of copper is below 0.75), so it will contribute to cost reduction, and more importantly With this relatively low temperature pre-oxidation condition, a thermal dispersion substrate with high interface strength can be produced. Moreover, the multi-stage pre-oxidized and rejoined ceramic/metal composite structure has excellent heat dissipation capability, and can simultaneously provide rapid heat dissipation capability and insulation requirements. The ceramic-metal substrates produced according to this spirit can be regarded as the extension of the present invention.

Test case

An alumina substrate with a size of 32×23×0.5mm (the purity of alumina is 96%) is first coated with a metal copper layer on the alumina substrate by electroless plating. The thickness of the metal copper layer is 2-4 microns, and then with a two-stage pre-oxidized copper sheet with a thickness of 0.3 mm and two different temperatures and oxygen partial pressures between 100 ° C and 600 ° C, in a tube furnace that has been subjected to temperature correction, in 1056°C and high-temperature bonding treatment under flowing nitrogen. During high-temperature bonding, this metal alloy thin layer can be bonded to aluminum oxide sheet and copper sheet at the same time, and form a strong bond. The bonded aluminum oxide/copper composite structure was tested with a universal testing machine (Universal Testing Machine, MTS-810, MTS, USA) and a three-point bending method (3-point bending method) to test the strain behavior of the aluminum oxide substrate under stress. The width of the two stress-bearing points is 22.5 mm, and the stress application rate is 0.002 mm/sec. The resulting stress-strain curve is shown in FIG. 10 . After the aluminum oxide/copper composite structure bears a stress of 190 Newton (Newton), the stress drops to 90 Newton, and then continues to test, it can still withstand a higher stress to 160 Newton, then drops, then rises and falls, and the displacement is 0.8 mm (mm) to stop the test and observe. At this time, the composite structure is not broken, and the integrity of the sample is still maintained. Observation of the composite structure after the observation test shows that the aluminum oxide substrate in this composite structure has a small crack, but the interface with the copper sheet is not completely separated, and the copper sheet can still hold the aluminum oxide sheet tightly, and still The integrity of the composite structure can be maintained.

The above examples prove that coating a thin layer of copper metal on the surface of alumina or copper can improve the strength of the composite structure. Due to the existence of the metal copper layer, the wetting angle of the copper sheet to the alumina can indeed be observed to decrease. , the interface strength is thus enhanced. This intermediate metal coating is not only beneficial to the improvement of the interface strength, but also greatly helps to increase the life of high-power electronic components that will undergo tens of thousands of on-off cycles in the future.

The specific embodiments proposed in the detailed description of the preferred embodiments are only convenient to illustrate the technical content of the present utility model, rather than restricting the utility model to the above-mentioned embodiments in a narrow sense, without exceeding the spirit of the utility model and the following rights In the case of claiming the scope of protection, the implementation of various changes all belong to the scope of the present utility model.

Claims (9)

1, a kind of ceramic/metal composite structure is characterized in that, this ceramic/metal composite structure comprises:

One lower metal layer;

Once metallic interfacial layer is coated on the described lower metal layer;

One ceramic substrate is positioned on the described metallic interfacial layer down;

Metallic interfacial layer on one is coated on the described ceramic substrate;

Metal level on one is positioned at described going up on the metallic interfacial layer.

2, ceramic/metal composite structure as claimed in claim 1 is characterized in that, described lower metal layer and described upward metal level are the copper sheet layer.

3, ceramic/metal composite structure as claimed in claim 1 is characterized in that, described going up on the metal level has at least one circuit or contact.

4, ceramic/metal composite structure as claimed in claim 1 is characterized in that, this composite construction has at least one breach, and this breach extends on the metallic interfacial layer at least along last metal level.

5, ceramic/metal composite structure as claimed in claim 4 is characterized in that, this composite construction also comprises:

Electronic component, it is arranged in described breach.

6, ceramic/metal composite structure as claimed in claim 5 is characterized in that, described breach extends on the ceramic substrate along last metal level, and the ceramic substrate in this breach is provided with heat-conducting glue, and described electronic component is located on this heat-conducting glue.

7, ceramic/metal composite structure as claimed in claim 5 is characterized in that, described breach extends on the metallic interfacial layer along last metal level, and the last metallic interfacial layer in this breach is provided with heat-conducting glue, and described electronic component is located on this heat-conducting glue.

8, ceramic/metal composite structure as claimed in claim 5 is characterized in that, this composite construction also comprises:

Many leads, it connects described electronic component to the described metal level of going up.

9, ceramic/metal composite structure as claimed in claim 4 is characterized in that, the last metal level at breach periphery place forms inclined-plane or curved surface.

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