Method for manufacturing insulating sheets and multilayer substrates

Abstract

To provide an insulation sheet capable of achieving both suppressed shrinkage strain and ensured interlayer adhesion, and a method of manufacturing a multilayer substrate.SOLUTION: An insulation sheet 22 contains 25 vol% or more and 50 vol% or less of dielectric fillers 63. By adding a predetermined amount of the dielectric fillers 63 into a liquid crystal polymer 61 in this way, the shrinkage strain of the insulation sheet 22 can be suppressed. Herein, the grain size distribution of the dielectric fillers 63 has two or more maximum points and also has a first maximum point PA1 on a small particle size side in the range of 0.1 μm or more and 0.8 μm or less. By adding the small particle size dielectric fillers 63 with an amount that forms a maximum point on a small particle size side in this way, the shrinkage strain can be suppressed with a small additive amount. By reducing the additive amount of the dielectric fillers 63 in this way, the interlayer adhesion of the insulation sheet 22 can be improved.SELECTED DRAWING: Figure 2

Description

Technical Field

[0005]

[0001] The present invention relates to an insulating sheet and a method for manufacturing a multilayer substrate.

Background Art

[0002] Conventionally, a multilayer substrate in which a plurality of base material sheets are laminated is known. For example, Patent Document 1 below discloses a structure in which a base material sheet includes an insulating sheet containing a thermoplastic resin. Further, Patent Document 1 discloses that the insulating sheet contains a liquid crystal polymer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the insulating sheet according to the above-described conventional technology, the molecular orientation of the liquid crystal polymer is locally biased, so that a thermal expansion difference occurs in the sheet plane, and shrinkage distortion may occur. On the other hand, when shrinkage distortion is suppressed by controlling the molecular orientation of the liquid crystal polymer by adding an inorganic filler to the insulating material, the interlayer adhesion of the multilayer substrate using the insulating sheet may become a problem. Therefore, there has been a demand for an insulating sheet that can achieve both suppression of shrinkage distortion and ensuring of interlayer adhesion.

[0005] An object of the present invention is to provide an insulating sheet and a method for manufacturing a multilayer substrate that can achieve both suppression of shrinkage distortion and ensuring of interlayer adhesion.

Means for Solving the Problems

[0006] An insulating sheet according to one embodiment of the present invention is an insulating sheet comprising a thermoplastic resin containing a liquid crystal polymer and an inorganic filler, wherein the inorganic filler is present in the insulating sheet at a concentration of 25 vol% to 50 vol%, and the particle size distribution of the inorganic filler has two or more maximum points and a first maximum point on the small particle size side in the range of 0.1 μm to 0.8 μm, and when the first maximum point is in the range of 0.1 μm to less than 0.3 μm, the particle size distribution ratio on the small particle side is 5 vol% to 35 vol% of the total volume of the inorganic filler, and when the first maximum point is in the range of 0.3 μm to 0.8 μm, the particle size distribution ratio on the small particle side may be 10 vol% to 35 vol% of the total volume of the inorganic filler.

[0007] In the insulating sheet, the inorganic filler is contained in an amount of 25 vol% to 50 vol%. By adding a predetermined amount of inorganic filler to the liquid crystal polymer in this way, shrinkage strain of the insulating sheet can be suppressed. Here, the particle size distribution of the inorganic filler has two or more maximum points, and a first maximum point on the small particle size side in the range of 0.1 μm to 0.8 μm. By adding an amount of small-particle inorganic filler that forms a maximum point on the small particle size side in this way, shrinkage strain can be suppressed with a small amount of additive. In this way, by reducing the amount of inorganic filler added, the interlayer adhesion of the insulating sheet can be improved. Furthermore, when the first maximum point is in the range of 0.1 μm or more and less than 0.3 μm, the particle size distribution ratio on the smaller particle side is 5 vol% or more and 35 vol% or less of the total volume of the inorganic filler. When the first maximum point is in the range of 0.3 μm or more and 0.8 μm or less, the particle size distribution ratio on the smaller particle side is 10 vol% or more and 35 vol% or less of the total volume of the inorganic filler. Thus, when the first maximum point is in the range of 0.3 μm or more and 0.8 μm or less, the lower limit of the particle size distribution ratio on the smaller particle side is higher than when the first maximum point is in the range of 0.1 μm or more and less than 0.3 μm. As a result, even in particle size distributions where the first maximum point on the smaller particle side and the second maximum point on the larger particle side are close together, the amount of inorganic filler added on the smaller particle side can be secured, and interlayer adhesion can be improved with a small amount of additive. Therefore, it is possible to achieve both suppression of shrinkage strain and securing interlayer adhesion.

[0008] The particle size distribution of the inorganic filler may have a second maximum point on the larger particle size side in the range of 1 μm or more and 3 μm or less. In this case, the molecular orientation of the liquid crystal polymer can be suitably controlled with the large-particle inorganic filler.

[0009] The aspect ratio of the inorganic filler may be between 0.7 and 1.0. In this case, the molecular orientation of the liquid crystal polymer can be suitably controlled by the inorganic filler.

[0010] A method for manufacturing a multilayer substrate according to one embodiment of the present invention comprises the steps of: forming wiring on a conductive film; forming interlayer connecting posts on the wiring; supplying insulating material on the wiring; forming the insulating sheet described above by heat pressing the insulating material; and stacking a group of base sheets, each containing at least one insulating sheet, and heat pressing them to form a multilayer substrate.

[0011] According to this method of manufacturing a multilayer substrate, the same functions and effects as those of the insulating sheet described above can be obtained.

[0012] The insulating material may contain powdered liquid crystal polymer and powdered inorganic filler. In this case, the particle size distribution of the inorganic filler within the insulating sheet can be easily controlled. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an insulating sheet that can suppress shrinkage strain and ensure interlayer adhesion, and a method for manufacturing a multilayer substrate. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic cross-sectional view showing a multilayer substrate according to one embodiment of the present invention. [Figure 2] Figure 1 is a schematic cross-sectional view showing the base sheet. [Figure 3] Figure 1 shows the steps involved in the manufacturing process of the multilayer substrate. [Figure 4] Figure 1 shows the steps involved in the manufacturing process of the multilayer substrate. [Figure 5] This is a conceptual diagram showing the insulating material used in the process of supplying insulating material onto wiring during the manufacturing of insulating sheets. [Figure 6] This graph shows the particle size distribution of dielectric fillers. [Figure 7] This graph shows another example of the particle size distribution of dielectric fillers. [Figure 8] This graph shows the effect of the insulating sheet. [Figure 9]This is a table showing experimental conditions and experimental results. [Figure 10] This is a table showing the evaluation of experimental results. [Figure 11] This is a graph showing the particle size distribution of the insulating sheet related to the experiment. [Figure 12] This is a graph showing the particle size distribution of the insulating sheet related to the experiment.

Modes for Carrying Out the Invention

[0015] Hereinafter, various embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0016] As shown in FIG. 1, a multilayer substrate 1 according to an embodiment has a structure in which a plurality of base material sheets 20 are laminated. In this embodiment, a multilayer substrate 1 including three base material sheets 20 will be described.

[0017] As shown in FIGS. 1 and 2, the base material sheet 20 has a thin film-like outer shape with a substantially uniform thickness. The base material sheet 20 includes an insulating sheet 22, and via posts 30 and wirings 40 embedded in the insulating sheet 22 for interlayer connection.

[0018] The insulating sheet 22 is a thin film-like member having an upper surface 20a and a lower surface 20b. The insulating sheet 22 includes a thermoplastic resin containing a liquid crystal polymer (LCP) and an inorganic filler. The detailed configuration of the insulating sheet 22 will be described later.

[0019] The via post 30 for interlayer connection is made of a conductive material, and in this embodiment, it is made of Cu. The via post 30 for interlayer connection extends along the thickness direction of the base material sheet 20 and penetrates the base material sheet 20, and includes a wiring portion 32 and a main body portion 34 configured separately. The height of the via post 30 for interlayer connection (the length in the thickness direction of the base material sheet 20) is about 30 to 100 μm, and is 50 μm as an example.

[0020] The wiring portion 32 is a flat, thin section extending parallel to the lower surface 20b of the insulating sheet 22. The wiring portion 32 has a nearly uniform thickness. For example, the thickness of the wiring portion 32 is 10 μm. The lower surface of the wiring portion 32 constitutes the lower surface 30b of the interlayer connection post 30, and the lower surface 30b of the interlayer connection post 30 is parallel and flush with the lower surface 20b of the base sheet 20. The upper surface of the wiring portion 32 extends parallel to the lower surface 30b of the interlayer connection post 30 and the lower surface 20b of the base sheet 20.

[0021] The main body portion 34 is a columnar portion that extends upward from the wiring portion 32 to the upper surface 20a. In this embodiment, the main body portion 34 has a circular cross-sectional shape perpendicular to its extending direction (i.e., the thickness direction of the base sheet 20). The diameter of the main body portion 34 is designed to be uniform in the extending direction of the main body portion 34. The upper surface of the main body portion 34 constitutes the upper surface 30a of the interlayer connecting post 30. The upper surface 30a of the interlayer connecting post 30 is parallel and flush with the upper surface 20a of the base sheet 20.

[0022] The wiring 40 is made of the same conductive material as the interlayer connection post 30, and in this embodiment, it is made of Cu. The wiring 40 has a substantially rectangular cross-section. The wiring 40 is formed on the lower surface 20b side of the base sheet 20, and not on the upper surface 20a side. The wiring 40 extends parallel to the lower surface 20b of the insulating sheet 22 and is exposed on the lower surface 20b. The lower surface of the wiring 40 is parallel to and flush with the lower surface 20b of the base sheet 20. The upper surface of the wiring 40 extends parallel to the lower surface of the wiring 40 and the lower surface 20b of the base sheet 20. The wiring 40 has a substantially uniform thickness. The thickness of the wiring 40 is the same as the thickness of the wiring portion 32 of the interlayer connection post 30, and is 10 μm as an example. On the lower surface 20b side, the wiring 40 forms part of the circuit of the base sheet 20.

[0023] Next, the manufacturing method of the multilayer substrate 1 described above will be explained with reference to Figures 3 and 4.

[0024] To manufacture the multilayer substrate 1, it is necessary to manufacture a base sheet 20. When manufacturing the base sheet 20, first, a support plate 50 is prepared, with a conductive film 51 provided on one main surface 50a, as shown in Figure 3(a). The support plate 50 is flat and can be made of, for example, glass epoxy, glass, or silicon. The conductive film 51 is a film that functions as a plating seed and can be made of, for example, a metal such as Cu. The conductive film 51 may be a metal film formed by sputtering or the like, or it may be a metal foil such as Cu foil. Alternatively, an ultra-thin copper foil with a carrier may be used, with part of the support plate 50 serving as both the conductive film 51 and the conductive film 51. Then, the interlayer connecting posts 30 and wiring 40 described above are formed on the main surface 50a of the support plate 50. Specifically, the interlayer connecting posts 30 and wiring 40 are plated onto the main surface 50a of the support plate 50 according to the process shown in Figures 3(a) to 3(d).

[0025] In the process shown in Figure 3(a), a resist 52 is patterned on the main surface 50a of the support plate 50. The resist 52 has openings in the areas of the wiring portion 32 and the wiring 40 of the interlayer connecting post 30 described above.

[0026] In the process shown in Figure 3(b), a first plating layer 53 is formed by electroplating Cu using a resist 52 and a conductive film 51 as a seed. Subsequently, the resist 52 is removed in the process shown in Figure 3(c). The first plating layer 53 becomes the wiring portion 32 and wiring 40 of the interlayer connecting post 30.

[0027] In the process shown in Figure 3(d), a second plating layer 54 is formed by electroplating Cu using the same process as shown in Figures 3(a) to 3(c) (i.e., resist patterning, electroplating, and resist removal). In this embodiment, the procedure for removing the resist 52 is shown after the formation of the first plating layer 53 but before the formation of the second plating layer 54. However, the resist 52 may be removed at the same time as the resist used when forming the second plating layer 54. The second plating layer 54 is selectively formed only on the first plating layer 53, which becomes the wiring portion 32 of the interlayer connecting post 30. The second plating layer 54 becomes the main body portion 34 of the interlayer connecting post 30. After forming the second plating layer 54, a layer to prevent oxidation of Cu (Cr layer, Ti layer, Sn layer, SnAg layer, etc.) can be formed on the surfaces of the first plating layer 53 and the second plating layer 54, particularly on the top surface 54a of the second plating layer 54.

[0028] Next, an insulating sheet 22 is formed to integrally cover the interlayer connecting posts 30 and wiring 40 provided on the main surface 50a of the support plate 50. Specifically, the insulating sheet 22 is formed according to the process shown in Figures 4(a) to 4(c).

[0029] In the process shown in Figure 4(a), prior to the formation of the insulating sheet 22, a frame 55 (frame body) is provided on the main surface 50a of the support plate 50, surrounding the area in which the insulating sheet 22 will be formed. The frame 55 is provided so as to integrally surround the interlayer connecting posts 30 and wiring 40 when viewed from the thickness direction of the support plate 50. In this embodiment, the frame 55 has the same height as the interlayer connecting posts 30. For example, in the process of forming the first plating layer 53 and the second plating layer 54, a frame 55 made of plating can be formed on the main surface 50a of the support plate 50 by patterning a resist having openings corresponding to the shape of the frame 55. Alternatively, a separately prepared member may be placed on the main surface 50a of the support plate 50 as the frame 55. The frame 55 is useful for controlling the thickness of the insulating sheet 22 because, in the process of forming the insulating sheet 22, it can suppress the outflow of the insulating material of the insulating sheet 22 from the area and prevent excessive pressing that could lead to the sheet becoming thinner than the desired thickness. When the frame 55 is formed by plating using the procedure described above, the height position of the upper surface of the second plating layer 54 and the height position of the upper surface of the frame 55 tend to coincide, which is therefore even more useful for controlling the thickness of the insulating sheet 22.

[0030] In the process shown in Figure 4(b), insulating material 60, which will become the insulating sheet 22, is supplied into the frame 55 on the main surface 50a of the support plate 50, and the area enclosed by the frame 55 is covered with insulating material 60. At this time, the first plating layer 53 and the second plating layer 54 formed on the main surface 50a are also covered with insulating material 60. Then, the support plate 50 is heat-pressed from the main surface 50a side using a heat plate 62, and then cooled.

[0031] As a result, as shown in Figure 4(c), the main surface 50a of the support plate 50 is covered by the insulating sheet 22 within the frame 55. At this time, the top surface 54a of the second plating layer 54 is exposed from the insulating sheet 22. If a resin film is formed on the top surface 54a of the second plating layer 54 after hot pressing, polishing treatments such as CMP, grinding, or fly cutting may be performed to expose the top surface 54a of the second plating layer 54 from the insulating sheet 22.

[0032] Finally, the conductive film 51 and the support plate 50 are removed from the insulating sheet 22 to obtain the base sheet 20 shown in Figure 2. Any method can be used to remove the conductive film 51 and the support plate 50, such as a method using a thermal release adhesive, laser peeling, known etching techniques, or polishing treatments such as grinding with a grinding wheel.

[0033] The base sheet 20 may be configured without the frame 55 used when forming the insulating sheet 22, or it may be configured with the frame 55. If the base sheet 20 includes the frame 55, the frame 55 can surround the insulating sheet 22 when viewed from the thickness direction of the insulating sheet 22 and have the same height as the interlayer connecting post 30.

[0034] The multiple base sheets 20 prepared as described above can be stacked together by heat pressing to obtain the multilayer substrate 1 described above. When stacking the base sheets 20, a conductive layer for connection, made of Au, Sn, Ag, solder, etc., may be formed on one or both of the upper surface 30a and lower surface 30b of the interlayer connecting post 30.

[0035] Next, the structure of the insulating sheet 22 will be described in more detail with reference to Figures 5 and 6. Figure 5 is a conceptual diagram showing the insulating material 60 in the step of supplying the insulating material 60 onto the wiring 40 (step 4(b)) during the manufacturing process of the insulating sheet 22. Figure 6 is a graph showing the particle size distribution of the dielectric filler 63 as an inorganic filler. As shown in Figure 5, the insulating material 60 includes powdered liquid crystal polymer 61 and powdered dielectric filler 63.

[0036] The structure of the liquid crystal polymer 61 is not particularly limited; for example, a polycondensate structure of phenol and phthalic acid with p-hydroxybenzoic acid may be adopted. Alternatively, the liquid crystal polymer 61 may be a polycondensate structure of ethylene terephthalate with p-hydroxybenzoic acid, or a polycondensate structure of 2,6-hydroxynaphthoic acid with p-hydroxybenzoic acid. The particle size of the liquid crystal polymer 61 in powder form may be in the range of 3 μm to 30 μm (average particle size 10 μm). This particle size is the particle size of the liquid crystal polymer 61 before hot pressing.

[0037] As the dielectric filler 63, for example, silica, strontium titanate, magnesium titanate, calcium titanate, titanium oxide, alumina, etc. may be used. The dielectric filler 63 may be contained in the insulating sheet 22 in an amount of 25 vol% or more. Alternatively, the dielectric filler 63 may be contained in the insulating sheet 22 in an amount of 50 vol% or less. The volume portion of the insulating sheet 22 other than the dielectric filler 63 is liquid crystal polymer 61. The aspect ratio of the dielectric filler 63 may be 0.7 or more. The aspect ratio of the dielectric filler 63 may be 1.0 or less. In this embodiment, the dielectric filler 63 is an example of an inorganic filler with a high dielectric constant, but is not limited to this. For example, as the inorganic filler, an insulating material with a low dielectric constant and low dielectric loss tangent that has excellent high-frequency characteristics may be used, such as hollow silica or boron nitride.

[0038] Next, the particle size distribution of the dielectric filler 63 will be described. First, an example of a method for measuring the particle size distribution of the dielectric filler 63 in the multilayer substrate 1 will be described. One method involves removing the resin components of the multilayer substrate 1 by firing in an oxygen atmosphere, followed by the aggregation and decomposition of the inherent dielectric filler 63, and then measuring the particle size distribution using a general particle size analyzer.

[0039] Specifically, the multilayer substrate 1 is placed in a ceramic crucible such as alumina (with treatment to prevent scattering of fine powder during heating), and heat treatment is performed at a temperature higher than the decomposition temperature of the liquid crystal polymer 61, but at a temperature in which the dielectric filler 63 and copper do not melt. In order to oxidize and remove the carbonized resin, the heat treatment must be carried out in an atmospheric environment (example of heat treatment conditions: 600°C for 1 hour or more).

[0040] Next, in order to remove the metal from the circuit from the obtained ash, the dielectric filler 63 and the metal are separated using a sieve with a sufficiently large mesh size relative to the particle size of the dielectric filler 63. If possible, it is better to select only the parts without circuit metal beforehand and calcine them, and the recovery method can be either using a sieve or removing the copper by hand.

[0041] Next, the aggregated dielectric filler 63 resulting from the firing process is broken up. The best method for breaking it up is ultrasonic treatment in a solvent so as not to destroy the dielectric filler 63 itself, but depending on the degree of aggregation, a ball mill method using media within a range of conditions that do not destroy the dielectric filler 63 may also be used.

[0042] The following procedure can be used to measure the particle size distribution of the dielectric filler 63 obtained by the method described above. For example, the dielectric filler 63 is added to MEK solvent along with a dispersant as needed, and secondary aggregation of the dielectric filler 63 is broken up using an ultrasonic disperser. Next, the particle size distribution of the obtained dispersion is measured using a particle size distribution analyzer (such as the ZETA SIZER Nano-ZS from Malvern Panalytical).

[0043] The particle size distribution of the dielectric filler 63 shown in Figure 6 can be obtained by the measurement method described above. As shown in Figure 6, the particle size distribution of the dielectric filler 63 has two or more (two in Figure 6) maximum points PA1 and PA2. The particle size distribution also has a minimum point PB1 between the first maximum point PA1 and the second maximum point PA2. The maximum points PA1 and PA2 are the points where the slope of the tangent to the particle size distribution curve switches from positive to negative. The minimum point PB1 is the point where the slope of the tangent to the particle size distribution curve switches from negative to positive. A boundary line L1 is set at the position of the particle size at the minimum point PB1. In this case, the particle size distribution on the negative side of the boundary line L1 is sometimes called the "small particle size distribution," and the particle size distribution on the positive side of the boundary line L1 is sometimes called the "large particle size distribution." Furthermore, the first maximum point PA1 corresponds to the maximum point on the small particle size side, and the second maximum point PA2 corresponds to the maximum point on the large particle size side.

[0044] The ratio of the particle size distribution in the region negative to the boundary line L1 to the total volume of the dielectric filler 63 is called the ratio of the particle size distribution on the small particle side. The ratio of the particle size distribution in the region positive to the boundary line L1 to the total volume of the dielectric filler is called the ratio of the particle size distribution on the small particle side. In Figure 6, the entire area of ​​the particle size distribution graph, i.e., the area from the peak start PS to the peak end PE, corresponds to the total volume of the dielectric filler. The area from the peak start PS to the minimum point PB1 relative to the area of ​​the entire particle size distribution corresponds to the ratio of the particle size distribution on the small particle side. The area from the minimum point PB1 to the peak end PE relative to the area of ​​the entire particle size distribution corresponds to the ratio of the particle size distribution on the large particle side.

[0045] Furthermore, when viewing the measured particle size distribution graph under magnification, there may be numerous maximum and minimum points due to minute vibrations caused by measurement errors and variability. In this case, by applying a known smoothing process to the particle size distribution, the maximum points PA1, PA2 and minimum point PB1 may be set for the particle size distribution after smoothing out the minute vibrations.

[0046] Furthermore, the particle size distribution may have three or more maximal points. For example, as shown in Figure 7(a), the particle size distribution may have three maximal points PA1, PA2, and PA3. In this case, the smallest first maximal point PA1 becomes the maximal point on the small particle size side, and the other maximal points PA2 and PA3 become the second maximal points on the large particle size side. Furthermore, as shown in Figures 7(b) and (c), the particle size distribution may have gentle peaks that do not form maximal points. In these peaks, the sign of the tangent slope does not change, but they are the parts that protrude upward in the particle size distribution. In the particle size distribution of Figure 7(b), peak PK1 is located positive to PA2, the second maximal point on the large particle size side. In the particle size distribution of Figure 7(c), peak PK2 is located between the minimum point PB1 and PA2, the second maximal point on the large particle size side. In the particle size distribution shown in Figure 7, the particle size distribution ratio is determined based on the boundary line L1.

[0047] The particle size distribution of the dielectric filler 63 may have a first maximum point PA1 on the small particle size side in the range of 0.1 μm or more. Alternatively, the particle size distribution may have a first maximum point PA1 on the small particle size side in the range of 0.8 μm or less. The particle size distribution may have a second maximum point PA2 on the large particle size side in the range of 1 μm or more. The particle size distribution may have a second maximum point PA2 on the large particle size side in the range of 3 μm or less, and the second maximum point PA3 may be in a similar range.

[0048] Furthermore, if the first maximum point PA1 is in the range of 0.1 μm or more and less than 0.3 μm, the particle size distribution ratio on the smaller particle size side may be 5 vol% or more and 35 vol% or less with respect to the total volume of the dielectric filler 63. If the first maximum point PA1 is in the range of 0.3 μm or more and 0.8 μm or less, the particle size distribution ratio on the smaller particle size side may be 10 vol% or more and 35 vol% or less with respect to the total volume of the dielectric filler 63.

[0049] Next, the operation and effects of the insulating sheet 22 and the multilayer substrate 1 according to this embodiment will be described.

[0050] In the insulating sheet 22, the dielectric filler 63 (inorganic filler) is contained in an amount of 25 vol% to 50 vol%. By adding a predetermined amount of dielectric filler 63 to the liquid crystal polymer 61 in this way, shrinkage strain of the insulating sheet 22 can be suppressed. Here, the particle size distribution of the dielectric filler 63 has two or more maximum points, and a first maximum point PA1 on the small particle size side in the range of 0.1 μm to 0.8 μm. In this way, by adding a small amount of dielectric filler 63 that forms a maximum point on the small particle size side, shrinkage strain can be suppressed with a small amount of additive. In this way, by reducing the amount of dielectric filler 63 added, the interlayer adhesion of the insulating sheet 22 can be improved. Furthermore, when the first maximum point PA1 is in the range of 0.1 μm or more and less than 0.3 μm, the particle size distribution ratio on the small particle size side is 5 vol% or more and 35 vol% or less of the total volume of the dielectric filler 63. When the first maximum point PA1 is in the range of 0.3 μm or more and 0.8 μm or less, the particle size distribution ratio on the small particle size side is 10 vol% or more and 35 vol% or less of the total volume of the dielectric filler 63. Thus, when the first maximum point PA1 is in the range of 0.3 μm or more and 0.8 μm or less, the lower limit of the particle size distribution ratio on the small particle size side is higher than when the first maximum point PA1 is in the range of 0.1 μm or more and less than 0.3 μm. As a result, even in the case of a particle size distribution where the first maximum point PA1 on the small particle size side and the second maximum point PA2 on the large particle size side are close together, the amount of dielectric filler 63 added on the small particle size side can be secured, and interlayer adhesion can be improved with a small amount of additive. Therefore, it is possible to achieve both suppression of shrinkage strain and ensuring interlayer adhesion.

[0051] For example, Figure 8 shows the measurement results for the performance of Comparative Example 1, in which the particle size distribution of the dielectric filler 63 has only one maximum point, and Example 1, in which it has two maximum points. Figure 8(a) is a graph of the measurement results showing the relationship between the amount of dielectric filler 63 added and shrinkage strain. Figure 8(b) is a graph of the measurement results showing the relationship between the amount of dielectric filler 63 added and the sheet adhesion force of the insulating sheet 22. Here, the adhesion force between the surface of the insulating sheet 22 and the copper foil was measured. As shown in Figure 8(a), Example 1 is able to reduce shrinkage strain even though the amount of dielectric filler 63 added is the same as that of Comparative Example 1. Example 1 in Figure 8(a) is able to reduce shrinkage strain to the same extent as Comparative Example 1 with an addition amount of 40 vol%. As shown in Figure 8(b), Example 1 is able to improve the sheet adhesion force compared to Comparative Example 1 with an addition amount of 40 vol%, which has equivalent shrinkage strain reduction performance. Thus, Example 1 is able to achieve both suppression of shrinkage strain and securing interlayer adhesion better than Comparative Example 1.

[0052] The particle size distribution of the dielectric filler 63 may have second maximum points PA2 and PA3 on the larger particle size side in the range of 1 μm or more and 3 μm or less. In this case, the molecular orientation of the liquid crystal polymer 61 can be suitably controlled by the large particle size dielectric filler 63.

[0053] The aspect ratio of the dielectric filler 63 may be 0.7 or greater and 1.0 or less. In this case, the molecular orientation of the liquid crystal polymer 61 can be suitably controlled by the dielectric filler 63.

[0054] The manufacturing method of the multilayer substrate 1 according to this embodiment comprises the steps of: forming wiring 40 on a conductive film 51; forming interlayer connecting posts 30 on the wiring 40; supplying insulating material 60 on the wiring 40; forming the insulating sheet 22 by heat pressing the insulating material 60; and stacking a group of base sheets, each containing at least one insulating sheet 22, and heat pressing them to form the multilayer substrate 1.

[0055] According to the manufacturing method of this multilayer substrate 1, the same effects and functions as those of the insulating sheet 22 described above can be obtained.

[0056] The insulating material 60 may include powdered liquid crystal polymer and powdered dielectric filler 63. In this case, the particle size distribution of the dielectric filler 63 in the insulating sheet 22 can be easily controlled.

[0057] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. For example, the number of base sheets constituting the multilayer substrate is not limited to three layers, but can be increased or decreased as appropriate. Also, the constituent materials of the wiring portion and the main body portion of the interlayer connecting posts may be the same material or different materials.

[0058] Examples are shown below, but the present invention is not limited to these examples.

[0059] [Examples] As a large-particle dielectric filler, silica with a particle size of 2 μm (referred to as "Silica 1") was prepared, and as a small-particle dielectric filler, silica with a particle size of 0.6 μm (referred to as "Silica 2") was prepared. Comparative Example 1 was an insulating sheet made using an insulating material in which only "Silica 1" was added to a liquid crystal polymer. Dielectric fillers "Composition 1" to "Composition 8" were prepared by combining the mixing ratios of "Silica 1" and "Silica 2" as shown in Figure 9, and insulating sheets were made using insulating materials in which these dielectric fillers were added to a liquid crystal polymer. Insulating sheets with compositions 1 and 5 were designated as Comparative Examples 2 and 3. Insulating sheets with compositions 2 to 4 and 6 to 8 were designated as Examples 1 to 6. In Comparative Examples 1 to 3 and Examples 1 to 6, the dielectric filler was contained in the insulating sheet at a concentration of 30 vol%.

[0060] The particle size distribution of the dielectric fillers in Examples 1-6 and Comparative Examples 1-3 was measured. Figure 11(a) shows the particle size distribution of Comparative Example 1, Figure 11(b) shows the particle size distribution of Comparative Example 2, Figure 11(c) shows the particle size distribution of Example 1, and Figure 11(d) shows the particle size distribution of Example 2. Figure 12(a) shows the particle size distribution of Example 3, Figure 12(b) shows the particle size distribution of Comparative Example 3, Figure 12(c) shows the particle size distribution of Example 4, Figure 12(d) shows the particle size distribution of Example 5, and Figure 12(e) shows the particle size distribution of Example 6. The minimum and maximum points of the particle size distribution corresponding to Comparative Examples 1-3 and Examples 1-6 were detected, and the particle size distribution ratio on the small particle size side and the particle size distribution ratio on the large particle size side were also detected. These detection results are shown in the "Particle Size Distribution" section of Figure 9. For Comparative Examples 1 and 2, the particle size distribution ratio on the large particle size side was assumed to be 100%. Comparative Example 3 had a particle size distribution ratio of 55 vol% on the small particle size side, which was greater than 35 vol%. Examples 1 to 6 all had two or more maximum values. When the first maximum point was in the range of 0.1 μm or more and less than 0.3 μm, the particle size distribution ratio on the small particle size side was 5 vol% or more and 35 vol% or less relative to the total volume of the dielectric filler. When the first maximum point was in the range of 0.3 μm or more and 0.8 μm or less, the particle size distribution ratio on the small particle size side was 10 vol% or more and 35 vol% or less relative to the total volume of the dielectric filler.

[0061] For the insulating sheets of Comparative Examples 1-3 and Examples 1-6, CTE variation, shrinkage strain, and inter-sheet adhesion were measured. CTE variation was measured by thermomechanical analysis (TMA). In this measurement method, the CTE was measured at four locations (the center and two locations from each end) on a single insulating sheet, and the difference between the maximum and minimum CTE values ​​was defined as "CTE variation." Adhesion was measured using a push-pull gauge to determine the peel strength when copper wiring was vertically peeled from the liquid crystal polymer. The measurement results are shown in Figure 9. Furthermore, in Figure 10(a), the measurement results of Comparative Examples 1-3 and Examples 1-6 were evaluated using the evaluation criteria shown in Figure 10(b). Comparative Examples 1 and 2 failed in both CTE variation and shrinkage strain. Comparative Example 3 passed in both CTE variation and shrinkage strain, but failed in inter-sheet adhesion. On the other hand, Examples 1-6 passed in all aspects: CTE variation, shrinkage strain, and inter-sheet adhesion.

[0062] [Form 1] An insulating sheet comprising a thermoplastic resin containing a liquid crystal polymer and an inorganic filler, The inorganic filler is contained in the insulating sheet in an amount of 25 vol% or more and 50 vol% or less. The particle size distribution of the inorganic filler has two or more maximum points, and a first maximum point on the smaller particle size side in the range of 0.1 μm or more and 0.8 μm or less. When the first maximum point is in the range of 0.1 μm or more and less than 0.3 μm, the particle size distribution ratio on the small particle size side is 5 vol% or more and 35 vol% or less with respect to the total volume of the inorganic filler. An insulating sheet in which, when the first maximum point is in the range of 0.3 μm or more and 0.8 μm or less, the particle size distribution ratio on the small particle size side is 10 vol% or more and 35 vol% or less with respect to the total volume of the inorganic filler. [Form 2] The insulating sheet according to Embodiment 1, wherein the particle size distribution of the inorganic filler has a second maximum point on the larger particle size side in the range of 1 μm or more and 3 μm or less. [Form 3] The insulating sheet according to Embodiment 1 or 2, wherein the aspect ratio of the inorganic filler is 0.7 or more and 1.0 or less. [Form 4] The process of forming wiring on a conductive film, The process of forming interlayer connection posts on the aforementioned wiring, A step of supplying insulating material onto the wiring, A step of forming an insulating sheet according to any one of the embodiments 1 to 3 by heat pressing the insulating material, A method for manufacturing a multilayer substrate, comprising the steps of stacking a group of base sheet sheets, each containing at least one insulating sheet, and heat-pressing them to form a multilayer substrate. [Form 5] The method for manufacturing a multilayer substrate according to Embodiment 4, wherein the insulating material comprises a powdered liquid crystal polymer and a powdered inorganic filler. [Explanation of symbols]

[0063] 1…Multilayer substrate, 20…Base sheet, 22…Insulating sheet, 30…Posts for interlayer connection, 40…Wiring, 61…Liquid crystal polymer, 62…Dielectric filler (inorganic filler), PA1…First maximum point, PA2, PA3…Second maximum points.

Claims

1. An insulating sheet comprising a thermoplastic resin containing a liquid crystal polymer and an inorganic filler, The inorganic filler is contained in the insulating sheet in an amount of 25 vol% or more and 50 vol% or less. The particle size distribution of the inorganic filler has two maximum points, with a first maximum point on the small particle size side in the range of 0.1 μm to 0.8 μm, and a second maximum point on the large particle size side in the range of 1 μm to 3 μm. When the first maximum point is in the range of 0.1 μm or more and less than 0.3 μm, the particle size distribution ratio on the small particle size side is 5 vol% or more and 35 vol% or less with respect to the total volume of the inorganic filler. An insulating sheet in which, when the first maximum point is in the range of 0.3 μm or more and 0.8 μm or less, the particle size distribution ratio on the small particle size side is 6 vol% or more and 35 vol% or less with respect to the total volume of the inorganic filler.

2. The insulating sheet according to claim 1, wherein the aspect ratio of the inorganic filler is 0.7 or more and 1.0 or less.

3. The process of forming wiring on a conductive film, The process of forming interlayer connection posts on the aforementioned wiring, A step of supplying insulating material onto the wiring, A step of forming an insulating sheet according to claim 1 by heat pressing the insulating material, A method for manufacturing a multilayer substrate, comprising the step of stacking a group of base sheet sheets, each containing at least one layer of the aforementioned insulating sheet, and heat-pressing them to form a multilayer substrate.

4. The method for manufacturing a multilayer substrate according to claim 3, wherein the insulating material comprises a powdered liquid crystal polymer and a powdered inorganic filler.

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