JP5673064B2 - Method for manufacturing a coil-embedded substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a coil built-in substrate, and more particularly, to a method for manufacturing a coil built-in substrate having a coil element between laminated ceramic base layers.

  Conventionally, various ceramic multilayer substrates manufactured by firing unfired laminates obtained by laminating and press-bonding unfired ceramic base layers have been proposed.

  For example, Patent Document 1 discloses that a sintered ceramic base layer is produced by simultaneously firing an unfired laminate in which an unfired ceramic base layer is sandwiched between unfired ceramic auxiliary layers to produce a ceramic multilayer substrate. Sintered ceramic multilayer substrate by setting the difference α1-α2 between the linear expansion coefficient α1 of the material layer and the linear expansion coefficient α2 of the sintered ceramic auxiliary layer to be 0.2 to 5 ppm / ° C. It is disclosed that the mechanical strength of the is increased.

  In Patent Document 2, in a ceramic multilayer substrate having internal electrodes between laminated ceramic base layers, an unfired laminated body provided with a shrinkage-suppressing green layer in contact with a conductive paste serving as an internal electrode is fired. By suppressing the shrinkage in the surface direction of the conductive paste during firing by the green layer for shrinkage suppression, by making the shrinkage in the thickness direction of the conductive paste larger than the shrinkage degree in the thickness direction of the surrounding ceramic green sheet, It is disclosed to reduce the waviness of the substrate surface.

  Patent Document 3 discloses that when firing an unfired laminated body for a ferrite substrate, the furnace temperature is raised stepwise and the firing process is performed after the binder removal process.

International Publication No. 2007/145189 JP 2001-257473 A JP 2010-245088 A

  The coil-embedded substrate provided with the coil elements between the ceramic base layers is arranged so that the coil elements overlap each other when seen through from the stacking direction. When manufacturing such a coil-embedded substrate, when the ceramic green sheets on which the unfired coil elements are formed are laminated, the portion where the unfired coil elements overlap is raised more than the other portions. In this state, the ceramic green sheet is pressed to form an unfired laminate with a flat surface, and when fired, undulation occurs on the surface of the fired laminate, that is, the coil-embedded substrate.

  A terminal electrode for mounting the coil built-in substrate on another circuit board such as a mother board is formed on the coil built-in substrate. Further, when an electronic component is mounted on the coil built-in substrate itself, land electrodes are formed on the coil built-in substrate. If the surface of the coil built-in substrate is wavy, inconvenience occurs when the coil built-in substrate is mounted on another circuit board or when an electronic component is mounted on the coil built-in substrate.

  In view of such circumstances, the present invention intends to provide a method for manufacturing a coil-embedded substrate that can suppress the undulation of the surface of the coil-embedded substrate.

  In order to solve the above problems, the present invention provides a method for manufacturing a coil-embedded substrate configured as follows.

The method for manufacturing a coil-embedded substrate includes first to third steps. In the first step, between (a) a plurality of unfired ceramic substrate layers laminated together, and (b) a different set of the unfired ceramic substrate layers adjacent to each other, A plurality of unfired coil elements formed around an imaginary central axis extending in the laminating direction in which the unfired ceramic base material layers are laminated and overlapping each other when seen through from the laminating direction; and (c) the unfired ceramic substrate An unsintered interlayer connecting conductor that connects the unsintered coil elements through a material layer; and (d) the unsintered ceramic between the unsintered ceramic base layer and at least one unsintered coil element. An unsintered laminated body including at least one disappearing layer formed using a void forming material that disappears at a sintering temperature at which the base material layer is sintered is formed. In the second step, the unfired laminate is fired to sinter the unfired ceramic base layer, the unfired coil element, and the unfired interlayer connection conductor, and the voids in the vanishing layer The gap forming material is formed by eliminating the part forming material. In the third step, the sintered laminated body formed by firing the unfired laminated body is divided, and one or more coil-embedded substrates are taken out. In the second step, the material for forming voids of the disappearing layer is heat-treated at a first temperature at which the unfired ceramic base material layer does not start shrinking, whereby the unfired ceramic base material layer shrinks. A portion of the green ceramic base layer is left to shrink , and then the green ceramic base layer is subjected to heat treatment at a second temperature at which the green ceramic base layer starts to shrink, thereby reducing the portion of the green ceramic base layer to shrink. Along with this, the gap is formed by gradually disappearing.

  According to the above method, by firing the unsintered laminated body in which the void portion is formed in the portion where the coil elements overlap in the laminating direction, the undulation of the surface of the sintered laminated body is suppressed, and from the sintered laminated body, Swelling of the surface of the formed coil-embedded substrate can be suppressed. Moreover, the residual stress of the coil element after sintering is suppressed by the gap, and the inductance value of the coil is increased and the efficiency is improved.

  Preferably, in the green laminate, the vanishing layer is formed between one main surface of the green coil element and the green ceramic base layer, and the other main surface of the green coil element is It is in contact with the other unfired ceramic substrate layer.

  In this case, a gap is formed only on one side of the coil element. Compared with the case where gaps are formed on both sides of the coil element, it is possible to suppress a decrease in the substrate strength, and when the sintered laminate is divided, the substrate is unlikely to crack.

  Preferably, the gap portion has a thickness in the stacking direction of 25 μm or less.

  In this case, the waviness of the substrate can be suppressed while ensuring the strength of the substrate.

  Preferably, the thickness in the laminating direction after sintering of the green coil element is not less than 1 μm and not more than 25 μm.

  In this case, it is possible to suppress the undulation of the substrate while ensuring the characteristics of the coil.

  According to the present invention, the undulation of the surface of the coil-embedded substrate can be suppressed.

It is sectional drawing of a coil built-in board | substrate. Example 1 It is sectional drawing of a coil built-in board | substrate. (Example 2) It is sectional drawing of a coil built-in board | substrate. (Example 3) It is sectional drawing of a coil built-in board | substrate. Example 4 It is sectional drawing of a coil built-in board | substrate. (Example 5) It is sectional drawing of a coil built-in board | substrate. (Example 6) It is a graph which shows the baking shrinkage of a ceramic green sheet. Example 1 It is a graph which shows the TG curve and DTA curve of a carbon paste. Example 1 It is sectional drawing of a coil built-in board | substrate. (Example)

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  <Example 1> A coil-embedded substrate of Example 1 will be described with reference to FIGS. 1, 6, and 7. FIG.

  FIG. 1 is a cross-sectional view schematically showing only main components of the coil-embedded substrate 10. As shown in FIG. 1, the coil-embedded substrate 10, as indicated by a chain line 11, is a piece obtained by dividing and dividing a collective substrate including a plurality of substrate main body 12 portions along the break grooves 12 x and 12 y. It is.

  The substrate body 12 includes a first non-magnetic ferrite layer 16a, a first magnetic ferrite layer 14a, an intermediate non-magnetic ferrite layer 16c, a second magnetic ferrite layer 14b, The non-magnetic ferrite layer 16b is laminated. The first and second magnetic ferrite layers 14a and 14b include a magnetic ceramic material, for example, a magnetic ferrite mainly composed of iron oxide, zinc oxide, nickel oxide, and copper oxide, and a ceramic material. The first and second non-magnetic ferrite layers 16a and 16b and the intermediate non-magnetic ferrite layer 16c include, for example, non-magnetic ferrite and ceramic materials mainly composed of iron oxide, zinc oxide, and copper oxide. Each layer 14a, 14b, 16a, 16b, 16c of the substrate body 12 is made of a ceramic base layer including one layer or two or more layers of laminated ceramic materials.

  Although not shown, terminal electrodes for mounting the coil built-in substrate 10 on another circuit board such as a mother board are formed on the lower surface 12t of the substrate body 12. Land electrodes for mounting electronic components on the coil-embedded substrate 10 may be formed on the upper surface 12 s of the substrate body 12.

  Inside the substrate body 12, a coil 30, an interlayer connection conductor and an in-plane connection conductor (not shown) are formed. The interlayer connection conductor is a conductor that penetrates the ceramic base layer. The in-plane connection conductor is a conductor formed between adjacent ceramic base layers. The interlayer connection conductor and the in-plane connection conductor connect the coil 30 to terminal electrodes and land electrodes formed on the surfaces 12 s and 12 t of the substrate body 12, and circuit elements such as resistors and capacitors inside the substrate body 12. Or form.

  The coil 30 includes a coil element 32 formed inside the first and second magnetic ferrite layers 14a and 14b and the intermediate nonmagnetic ferrite layer 16c. The coil element 32 is formed between different ceramic substrate layers of adjacent ceramic substrate layers. The coil element 32 has a virtual central axis 31 extending in the stacking direction when seen through the substrate body 12 from the stacking direction (vertical direction in FIG. 1) in which the layers 14a, 14b, 16a, 16b, and 16c of the substrate body 12 are stacked. Are formed in a substantially C shape around each other and overlap each other in an annular region. The chain line 32s indicates the position of the inner periphery of the region where the coil elements 32 overlap each other when seen through from the stacking direction. The chain line 32t indicates the position of the outer periphery of the region where the coil elements 32 overlap each other when seen through from the stacking direction.

  In the coil 30, the ends of the coil elements 32 adjacent to each other in the stacking direction are connected to each other via an interlayer connection conductor (not shown).

  A gap 40 is formed in the substrate body 12 in contact with one coil element 32x. The upper surface 32y of the coil element 32x is exposed in the gap 40, and the lower surface 32z of the coil element 32x is in contact with the ceramic base layer. When seen through from the stacking direction, the gap 40 is formed so as to overlap the annular region where the coil elements 32 overlap each other, and is formed so as not to protrude from the annular region where the coil elements 32 overlap each other. For example, when viewed from the stacking direction, the gap 40 is formed in an annular shape and overlaps with the coil element 32x.

  Since the magnetic flux passes through the inner periphery of the annular region where the coil elements 32 overlap with each other and the outer periphery of the outer periphery, the magnetic flux passing therethrough decreases and the L value of the inductor decreases. Further, if a gap is formed outside the outer periphery of the annular region where the coil elements 32 overlap with each other, the gap between the break grooves 12x and 12y and the gap is narrowed, and the substrate body 12 is divided from the collective substrate. When cracking, cracks starting from the voids are likely to occur. In order to prevent these disadvantages, the gap 40 is formed so as not to protrude from the annular region where the coil elements 32 overlap each other when seen through from the stacking direction. In other words, the void 40 is not formed inside or outside the outer periphery of the annular region where the coil elements 32 overlap each other as seen through from the stacking direction.

  Since the gap 40 is formed only on one side of the coil element 32x, compared to the case where the gap is formed on both sides of the coil element 32x, a decrease in strength of the substrate body 12 can be suppressed, and sintering is performed. Cracks are unlikely to occur in the substrate body 12 when the used laminate is divided.

  When the gap 40 is formed, the residual stress of the coil element 32 after sintering is suppressed, and the inductance value of the coil 30 is increased and the efficiency is improved.

  The void portion 40 is formed by disappearance of a void portion forming material such as a carbon paste disposed inside the unfired laminate for forming the substrate body 12 during firing.

  If the gap 40 is too thick in the stacking direction, the strength of the substrate body 12 decreases. Therefore, it is preferable that the thickness of the gap portion 40 in the stacking direction is 25 μm or less to suppress the undulation of the substrate while ensuring the strength of the substrate body 12.

  The thickness of the coil element 32 in the stacking direction is selected in the range of 1 μm or more and 25 μm or less depending on the thickness and the number of layers of the coil element 32 in the stacking direction and the thickness and the number of layers of the gap 40 in the stacking direction. It is preferable to suppress the undulation of the substrate while ensuring the characteristics of the coil.

  Next, a manufacturing process when the coil-embedded substrate 10 is manufactured in a collective substrate state will be described.

  (1) First, in order to form each layer of the substrate body 12, an unsintered ceramic green sheet containing a ceramic material powder and formed into a sheet shape is prepared.

  For the ceramic green sheets for forming the first and second magnetic ferrite layers 14a and 14b, for example, magnetic ferrite mainly composed of iron oxide, zinc oxide, nickel oxide and copper oxide is used. The ceramic green sheet for forming the first and second non-magnetic ferrite layers 16a and 16b and the intermediate non-magnetic ferrite layer 16c is, for example, non-magnetic mainly composed of iron oxide, zinc oxide and copper oxide. Body ferrite is used.

The graph of FIG. 7 is a graph which shows the shrinkage | contraction behavior at the time of baking of a ceramic green sheet. The ceramic green sheet was fired at a constant speed, the shrinkage (L ₀ -L ₁ ) / L ₀ obtained from the dimensions L ₀ and L ₁ before and after firing was shown on the vertical axis, and the temperature (° C. on the horizontal axis. ). A solid line indicates a ceramic green sheet for forming the first and second magnetic ferrite layers 14a and 14b. A broken line indicates a ceramic green sheet for forming the first and second nonmagnetic ferrite layers 16a and 16b and the intermediate nonmagnetic ferrite layer 16c. From FIG. 7, it can be seen that the temperature at which the ceramic green sheet starts to shrink is about 600 ° C.

  An unfired interlayer connection conductor is formed by processing a through hole at an appropriate position of the ceramic green sheet by laser processing, punching processing or the like, and embedding a conductor paste in the through hole by printing or the like.

  Further, a conductor paste is printed on one main surface of the ceramic green sheet by a screen printing method, a gravure printing method, or the like to form a conductor pattern of coil elements, in-plane wiring conductors, land electrodes, and terminal electrodes.

  Furthermore, for the ceramic green sheet on which the coil element 32x is formed, a carbon paste in which carbon particles are mixed in a solvent is applied to the unfired coil element 32x as a gap forming material. The D50 of carbon in the carbon paste is 0.1 to 5.0 μm. D50 is a cumulative 50 volume% diameter in the particle size distribution measured by the laser diffraction scattering method.

  The graph of FIG. 8 shows a TG curve and a DTA curve of the carbon paste applied to the coil element 32x. The TG curve is a record of the change in weight of the sample with increasing ambient temperature versus temperature. The DTA curve is obtained by detecting the temperature difference between the reference and the sample by the electromotive force of the thermocouple provided in the sample holder. It can be seen from the TG curve in FIG. 8 that the carbon paste gradually disappears as the temperature rises.

  (2) Next, an unsintered ceramic green sheet for forming each layer of the substrate body 12 is laminated to form an unfired laminate. At this time, when the ceramic green sheet is overlaid on the base plate, the overlapping part of the coil elements is raised from the other part, but by pressing down on the plane and crimping the ceramic green sheet, the unfired laminate with a flat surface Form.

  (3) Next, the green laminate is fired.

First, the temperature of the firing furnace is raised from room temperature to a temperature that does not exceed the temperature at which the ceramic green sheet starts to shrink, for example, 400 ° C. (heat treatment is performed at the first temperature) . The oxygen concentration in the firing furnace is 5 to 25%. At this time, the solvent contained in the ceramic green sheet or the carbon paste of the vanishing layer is vaporized with heating, or the organic material is thermally decomposed and vaporized, and disappears from the unsintered laminated body. The carbon in the carbon paste remains.

Next, the temperature of the firing furnace is increased to a temperature at which the ceramic green sheet and the conductive paste are sintered, for example, to about 900 ° C. (heat treatment is performed at the second temperature) . The oxygen concentration in the firing furnace is 0.1 to 10.0%. As the temperature rises, the ceramic green sheet shrinks and sinters. The carbon in the carbon paste remaining in the disappearing layer can be gradually disappeared when the ceramic green sheet contracts. Thereby, the space | gap part 40 can be formed in the inside of a sintered laminated body, suppressing the wave | undulation of a board | substrate. The disappearance rate of carbon can be reduced when the particle size of carbon is increased, and can be increased when it is decreased.

  (4) Next, after cooling to room temperature, the break grooves 12x and 12y are formed on the sintered laminate, that is, the collective substrate of the coil-embedded substrate 10 by laser processing or dicing. If necessary, the land electrodes formed on the upper surface 12s of the substrate body 12 and the terminal electrodes formed on the lower surface 12t are plated, and electronic components such as surface mount components and IC chips are mounted on the land electrodes.

  (5) The collective substrate of the coil built-in substrate 10 completed by the above steps is cut along the break grooves 12x and 12y, and divided into individual pieces of the coil built-in substrate 10.

  The void formation material (for example, the particle size of carbon in the carbon paste) and the firing conditions (for example, oxygen concentration, temperature profile) are adjusted, and the disappearance rate of the void formation material and the shrinkage of the laminate during firing By controlling the speed, the undulation of the substrate, that is, the undulations of the surfaces 12s and 12t of the substrate body 12 can be suppressed.

  Example 2 A coil built-in substrate 10a of Example 2 will be described with reference to FIG.

  FIG. 2 is a cross-sectional view schematically showing only main components of the coil-embedded substrate 10a. As shown in FIG. 2, the coil built-in substrate 10a is configured in substantially the same manner as the coil built-in substrate 10 of the first embodiment. In the following, the same reference numerals are used for the same components as in the first embodiment, and differences from the first embodiment will be mainly described.

  As shown in FIG. 2, a coil 30a including a coil element 32a is formed inside the substrate body 12 of the coil built-in substrate 10a. As in the first embodiment, the swell of the surfaces 12s and 12t of the substrate body 12 is suppressed by forming the gap 40a in contact with the coil element 32a.

  Each coil element 32a is formed in a substantially C shape around the virtual central axis 31 as in the first embodiment, but is thicker and has a larger number of layers than the coil element 32 in the first embodiment. The gap 40a is formed for all the coil elements 32a. The thicker the coil element and the greater the number of coil element layers, the greater the amount of bulging of the coil part where the coil elements overlap in the stacking direction. Is increasing.

  However, if the number of voids is too large relative to the thickness and number of layers of the coil element, the coil part will sink when sintered, so depending on the thickness of each layer of the substrate body and the thickness of the coil element It is necessary to form a gap with a sufficient number of layers.

  <Example 3> The coil built-in substrate 10b of Example 3 will be described with reference to FIG.

  FIG. 3 is a cross-sectional view schematically showing only main components of the coil-embedded substrate 10b. As shown in FIG. 3, the coil 30b formed inside the substrate body 12 includes a first coil element 32b and a second coil element 34b.

  When the substrate body 12 is seen through from the stacking direction, the first coil elements 32b are formed in a substantially C shape around the virtual central axis 31 and overlap each other.

  When the substrate body 12 is seen through from the stacking direction, the second coil elements 34b are formed in a substantially C shape around the imaginary central axis 31, and inside the region where the first coil elements 32b overlap each other, They are overlapping.

  A first coil element 32b and a second coil element 34b adjacent in the stacking direction are connected in series via an interlayer connection conductor to constitute a coil 30b.

  The gap 40b is formed so as to be in contact with the first coil element 32b, and the upper surface of the first coil element 32b is exposed in the gap 40b, and the lower surface of the coil element 32b is formed on the ceramic base layer. It touches. The void portion 40 is formed in an annular shape so as to overlap only the annular region where the first coil elements 32b overlap when seen through from the stacking direction, and inside the inner periphery of the annular region where the first coil elements 32b overlap. Is not formed outside the outer periphery.

  Example 4 A coil built-in substrate 10c of Example 4 will be described with reference to FIG.

  FIG. 4 is a cross-sectional view schematically showing only main components of the coil-embedded substrate 10c. As shown in FIG. 4, the coil 30c formed inside the substrate body 12 includes a first coil element 32b and a second coil element 34b, as in the third embodiment.

  Unlike Example 3, a gap 40c in contact with the second coil element 34b is formed, and the upper surface of the coil element 34b is exposed in the gap 40c, and the lower surface of the coil element 34b is formed on the ceramic base layer. It touches. The void portion 40c is formed in an annular shape so as to overlap only the annular region where the second coil element 34b overlaps when seen through from the stacking direction, and is located inside the inner periphery of the annular region where the second coil element 34b overlaps. Is not formed outside the outer periphery.

  Example 5 A coil built-in substrate 10d of Example 5 will be described with reference to FIG.

  FIG. 5 is a cross-sectional view schematically showing only main components of the coil-embedded substrate 10d. As shown in FIG. 5, the coil 30 d formed inside the substrate body 12 includes a first coil element 32 b and a second coil element 34 b as in the third and fourth embodiments.

  Unlike Example 3 and Example 4, both the gap 40b in contact with the first coil element 32b and the gap 40c in contact with the second coil element 34b are formed.

  When the coil elements 30b to 30d include the first and second coil elements 32b and 34b as in the third to fifth embodiments described above, the gap 40b and the second coil in contact with the first coil element 32b are used. If at least one of the gaps 40c in contact with the element 34b is formed, the undulation of the surfaces 12s and 12t of the substrate body 12 can be suppressed.

  <Example 6> The coil built-in substrate 10e of Example 6 will be described with reference to FIG.

  FIG. 6 is a cross-sectional view schematically showing only main components of the coil-embedded substrate 10e. As shown in FIG. 6, a coil 30e including nine layers of coil elements 32e is formed inside the substrate body 12 of the coil-embedded substrate 10e. The coil element 30 e is formed around the virtual center axis 31.

  A gap 40e is formed in contact with three layers of the nine layers of coil elements 30e. The inner circumference 40q of the gap 40e is in contact with the inner circumference of the region where the coil elements 30e overlap when the substrate body 12 is seen through from the stacking direction.

  On the other hand, the outer periphery 40p of the gap 40e extends inward from the outer periphery with a space between the outer periphery of the region where the coil elements 30e overlap. As a result, the gap between the break grooves 12x and 12y and the gap 40e is widened, so that when the substrate body 12 is divided from the aggregate substrate, cracks starting from the gap 40e are less likely to occur.

  By providing the gap 40e, the undulation of the substrate can be suppressed. For example, in a prototype in which the thickness of the coil element 32e is 10 to 12 μm, the coil element 32e is 9 layers, and the thickness of the substrate body 12 is 0.600 mm, The waviness amount (difference between the maximum value and the minimum value) of the surfaces 12s and 12t was 50 μm, but by forming three gap portions 40e as in Example 6, the surfaces 12s and 12t of the substrate body 12 were formed. The amount of waviness could be reduced to 15 μm.

  <Summary> When the gap portion in contact with the coil element is formed by the manufacturing method described above, undulation of the surface of the coil-embedded substrate can be suppressed.

  That is, as schematically shown in the cross-sectional view of FIG. 9A, in the case where no gap is formed inside the substrate body 2x, the region 4x where the coil elements 4 overlap in the stacking direction is raised by firing, Waviness occurs on the surface 2s. As schematically shown in the cross-sectional view of FIG. 9B, when the gap 6 in contact with the coil element 4 is formed inside the substrate body 2, the bulge due to firing can be suppressed and the undulation of the surface 2t can be suppressed.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications.

2,2x Substrate body 2s, 2t Surface 4 Coil element 6 Air gap 10, 10a to 10e Coil built-in substrate 12 Substrate body 12s Upper surface (surface)
12t bottom surface (surface)
12x, 12y Break groove 14a First magnetic ferrite layer 14b Second magnetic ferrite layer 16a First nonmagnetic ferrite layer 16b Second nonmagnetic ferrite layer 16c Intermediate nonmagnetic ferrite layer 30, 30a 30e coil 31 virtual central axis 32 coil element 32b first coil element 32e, 32x coil element 34b second coil element 40, 40a to 40c, 40e gap

Claims (4)

A plurality of unfired ceramic substrate layers laminated together;
The green ceramic base layers between different sets of the green ceramic base layers adjacent to each other are formed around a virtual central axis extending in the stacking direction in which the green ceramic base layers are stacked, A plurality of unfired coil elements that overlap each other when seen through from the stacking direction;
An unfired interlayer connection conductor that connects the unfired coil elements through the unfired ceramic substrate layer;
At least formed between the green ceramic base layer and at least one green coil element using a void forming material that disappears at a sintering temperature at which the green ceramic base layer is sintered. One vanishing layer,
A first step of forming an unfired laminate comprising:
The unfired laminate is fired to sinter the unfired ceramic base layer, the unfired coil element, and the unfired interlayer connection conductor, and to eliminate the void forming material of the disappearing layer. A second step of forming a void portion;
A third step of dividing the sintered laminate formed by firing the unfired laminate and taking out one or more coil-embedded substrates;
With
In the second step, the material for forming voids of the disappearing layer is heat-treated at a first temperature at which the unfired ceramic base material layer does not start shrinking, whereby the unfired ceramic base material layer shrinks. A portion of the green ceramic base layer is left to shrink, and then the green ceramic base layer is subjected to heat treatment at a second temperature at which the green ceramic base layer starts to shrink, thereby reducing the portion of the green ceramic base layer to shrink. A method for manufacturing a coil-embedded substrate, wherein the gap is formed by gradually disappearing. The green laminate is
The vanishing layer is formed between one main surface of the unfired coil element and the unfired ceramic base layer, and the other main surface of the unfired coil element is the other unfired ceramic base layer. The method for manufacturing a coil-embedded substrate according to claim 1, wherein the substrate is in contact.   3. The method for manufacturing a coil-embedded substrate according to claim 1, wherein the gap portion has a thickness in the stacking direction of 25 μm or less.   The method for manufacturing a coil-embedded substrate according to any one of claims 1 to 3, wherein a thickness of the green coil element after sintering is not less than 1 µm and not more than 25 µm.

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