Wiring board

Abstract

This wiring board has an insulating substrate composed of a plurality of insulating layers. The insulating substrate is made of glass ceramics and serves as a structure of the wiring board. Among the plurality of insulating layers, the insulating layer constituting the outermost layer of the insulating substrate has a plurality of alumina particles. The coefficient of thermal expansion of the insulating layer is greater than the coefficient of thermal expansion of the alumina particles. When one of the two surfaces based on the structural shape of the insulating substrate is defined as a first surface and the side opposite to the first surface is defined as a second surface, the area of a conductor in contact with the first surface is smaller than the area of a conductor in contact with the second surface. When an insulating layer having the first surface is defined as a first insulating layer and an insulating layer having the second surface is defined as a second insulating layer, the first insulating layer has a higher proportion of the alumina particles than the second insulating layer.

Description

Wiring substrate

[0001] The disclosed embodiment relates to a wiring substrate.

[0002] In recent years, a highly stacked type wiring substrate has been proposed, which is multilayered by using a plurality of ceramic base materials, and wirings are arranged between the layers thereof.

[0003] International Publication No. WO 2005 / 067359

[0004] A wiring substrate according to one aspect of the embodiment includes an insulating base formed of a plurality of insulating layers. The insulating base is made of glass-ceramic and serves as the skeleton of the wiring substrate. Among the plurality of insulating layers, the insulating layer constituting the outermost layer of the insulating base contains a plurality of alumina particles. The coefficient of thermal expansion of the insulating layer is larger than that of the alumina particles. When one of two surfaces based on the skeleton shape of the insulating base is defined as a first surface and the opposite side of the first surface is defined as a second surface, the area of a conductor in contact with the first surface is smaller than the area of a conductor in contact with the second surface. When the insulating layer including the first surface is defined as a first insulating layer and the insulating layer including the second surface is defined as a second insulating layer, the first insulating layer has a higher proportion of alumina particles than the second insulating layer.

[0005] FIG. 1 is a cross-sectional view illustrating an example of the wiring substrate according to the first embodiment. FIG. 2 is a plan view illustrating an example of the wiring substrate according to the second embodiment. FIG. 3 is a view illustrating an example of the A-A cross-section of FIG. 2. FIG. 4 is a cross-sectional view illustrating another example of the wiring substrate according to the second embodiment. FIG. 5 is a plan view illustrating an example of the wiring substrate according to the third embodiment. FIG. 6 is a cross-sectional view illustrating an example of the wiring substrate according to the fourth embodiment. FIG. 7 is a perspective view schematically illustrating an example of a method for manufacturing the wiring substrate according to the embodiment. FIG. 8 is a perspective view schematically illustrating another example of a method for manufacturing the wiring substrate according to the embodiment.

[0006] According to one aspect of this disclosure, the mounting reliability of a multilayer wiring board can be improved. Hereinafter, embodiments for implementing the wiring board according to this disclosure (hereinafter referred to as "embodiments") will be described in detail with reference to the drawings. Note that the wiring board according to this disclosure is not limited by these embodiments. Furthermore, each embodiment can be combined as appropriate, provided that the processing content is not inconsistent. In the following, identical or similar components are denoted by the same reference numerals, and detailed descriptions are omitted.

[0007] (First Embodiment) Figure 1 is a cross-sectional view showing an example of a wiring board according to the first embodiment. As shown in Figure 1, the wiring board 100 according to this embodiment has an insulating substrate 10.

[0008] The insulating substrate 10 is made of glass ceramics 2 and forms the framework of the wiring board 100. Here, the framework refers to the connected skeletal structure that maintains the shape of the wiring board 100. In the wiring board 100, the insulating substrate 10 refers to the portion occupied by insulating material, excluding the conductive portion described later. In the wiring board 100, the insulating substrate 10 preferably occupies 80% or more of the volume.

[0009] The insulating substrate 10 has two main surfaces based on its skeletal shape at both ends in the thickness direction (Z-axis direction). Of the two main surfaces of the insulating substrate 10, one is designated as the first surface 101, and the one opposite the first surface 101 is designated as the second surface 102. In this case, the area of ​​the conductor 21 in contact with the first surface 101 is smaller than the area of ​​the conductor 22 in contact with the second surface 102.

[0010] The insulating substrate 10 is composed of multiple insulating layers 1. The insulating substrate 10 is a laminate of multiple insulating layers 1. The insulating substrate 10 is made up of multiple insulating layers 1 that are laminated and integrated. Figure 1 shows an example in which the insulating substrate 10 has seven insulating layers 1, but the number of insulating layers 1 that the insulating substrate 10 has is not limited to this.

[0011] Of the multiple insulating layers 1, the insulating layers 1A and 1B that constitute the outermost layers of the insulating substrate 10 have multiple alumina particles 3. Insulating layer 1A is a first insulating layer having a first surface 101. Insulating layer 1B is a second insulating layer having a second surface 102. It is preferable that the alumina particles 3 are present only in insulating layers 1A and 1B of the multiple insulating layers 1.

[0012] The insulating layer 1A has a higher proportion of alumina particles 3 than the insulating layer 1B. The proportion of alumina particles 3 refers to the area ratio of alumina particles 3 on the first surface 101 or the second surface 102. Specifically, the proportion of the area of ​​the first surface 101 or the second surface 102 that is occupied by the area where the first surface 101 or the second surface 102 is in contact with the alumina particles 3 is called the area ratio of alumina particles 3 on the first surface 101 or the second surface 102, i.e., the proportion of alumina particles 3.

[0013] In this disclosure, if there is a difference in the area ratio of alumina particles 3 between the first surface 101 and the second surface 102, it means that the difference in the area ratio of alumina particles 3 between the first surface 101 and the second surface 102 is 0.2% or more.

[0014] As shown in the specific example described later, the area ratio of alumina particles 3 on the first surface 101 is, for example, 1% to 2%. Also, the area ratio of alumina particles 3 on the second surface 102 is, for example, 0.2% to 0.8%.

[0015] The area ratio of alumina particles 3 can be determined, for example, by observation and photography using a scanning electron microscope, and by using an analyzer attached to the scanning electron microscope (electron probe microanalyzer (EPMA) or energy dispersive X-ray spectroscopy (EDS)).

[0016] The glass ceramic 2 constituting the insulating layer 1 may be in any of the following forms: a composite of a glass phase and ceramic particles, a composite of a glass phase and a crystalline phase formed by the crystallization of a part of the glass phase, a form in which ceramic particles exist within the glass phase, or a form in which the glass phase exists at the grain boundaries between ceramic particles. Silica may be used as the ceramic particles. The ceramic particles may also exist as fillers in the glass ceramic 2.

[0017] The insulating layer 1 is preferably a porcelain composition that can be fired together with copper, as will be described later.

[0018] The thermal expansion coefficient of the insulating layer 1 is greater than that of the alumina particles 3. In particular, it is desirable that the thermal expansion coefficient of the inner insulating layer 1C, excluding the outermost insulating layers 1A and 1B containing the alumina particles 3, be greater than that of the alumina particles 3.

[0019] The thermal expansion coefficient of insulating layer 1 is 8 × 10⁻⁶. －６ / K or more 13×10 －６ It is preferable that it be less than or equal to / K.

[0020] The thermal expansion coefficient of alumina particle 3 is 7.5 × 10⁻⁶. －６ It is preferable that the temperature is below / K. For this reason, the alumina particles 3 should contain 90% by mass or more of alumina (aluminum oxide).

[0021] The fact that the insulating layer 1 is glass ceramic 2 and that it contains alumina particles 3 can be identified using analyzers such as scanning electron microscopes, X-ray diffraction, and X-ray fluorescence.

[0022] Furthermore, if the alumina particles 3 can be identified as alumina (for example, corundum) by X-ray diffraction of the wiring substrate 100, the thermal expansion coefficient of alumina (in this case, corundum) listed in the science almanac will be used. The thermal expansion coefficient of the insulating layer 1 will be measured by cutting out the insulating substrate 10 and using a thermal expansion coefficient measuring device.

[0023] The wiring board 100 according to this embodiment can improve mounting reliability. Specifically, semiconductor elements such as silicon are mounted on the first surface 101. The second surface 102 is connected to a motherboard, for example. Normally, the thermal expansion coefficient of semiconductor elements such as silicon is smaller than that of the motherboard. Under these conditions, if the insulating layer 1A on the first surface 101 side contains more alumina particles 3 than the insulating layer 1B on the second surface 102 side, the thermal expansion coefficient of the insulating layer 1A becomes smaller than that of the insulating layer 1B. As a result, the thermal expansion coefficient of the insulating layer 1A becomes closer to that of the semiconductor elements such as silicon, thus improving the mounting reliability of the first surface 101 side. On the second surface 102 side, the decrease in thermal expansion coefficient is small, so mounting reliability to the motherboard can also be maintained in a good state.

[0024] Furthermore, as shown in Figure 1, the alumina particles 3 contained in the insulating layer 1A, which is the first insulating layer, may be present in an exposed state on the first surface 101. The alumina particles 3 contained in the insulating layer 1B, which is the second insulating layer, may be present in an exposed state on the second surface 102.

[0025] If the alumina particles 3 are present on the outermost surface of the insulating layers 1A and 1B, which are the outermost layers of the insulating substrate 10, the influence of the change in the coefficient of thermal expansion from the outermost insulating layers 1A and 1B to the inner insulating layer 1C, which is not the outermost layer, due to the inclusion of the alumina particles 3 in the insulating layers 1A and 1B can be reduced.

[0026] As a result, even if the content of alumina particles 3 differs between the two outermost insulating layers 1A and 1B, which are both the outermost layers, the difference in stress caused by the two outermost insulating layers 1A and 1B can be reduced. Even if strain occurs in the wiring board 100 due to changes in ambient temperature, the strain will be nearly uniform on both sides, and malfunctions caused by stress differences in semiconductor elements mounted on the wiring board 100, motherboards connected to the wiring board 100, etc. can be reduced.

[0027] Furthermore, among the multiple alumina particles 3, there may be alumina particles 3A that contain glass and protrude from the surface of the glass ceramic 2 of the outermost insulating layers 1A and 1B. It is preferable that the height of the alumina particles 3A protruding from the surface of the glass ceramic 2 is 2 μm or more.

[0028] With this configuration, even if alumina particles 3 are fixed to the surface of the outermost insulating layers 1A and 1B, most of the alumina particles 3 protrude from the surface of the glass ceramics 2, so there is little portion of the alumina particles 3 that are solid-solved and bonded to the glass ceramics 2. Therefore, the effect of the change in the coefficient of thermal expansion from the outermost insulating layers 1A and 1B to the inner insulating layer 1C, other than the outermost layer, due to the inclusion of alumina particles 3 in the insulating layers 1A and 1B can be reduced.

[0029] In the wiring board 100 of this disclosure, it is preferable that the alumina particles 3 are present only on the surface of the insulating layers 1A and 1B of the surface layer.

[0030] When alumina particles 3 are included inside the surface insulating layers 1A and 1B, their dielectric properties will differ from those of the other inner insulating layers 1C by the amount of the alumina particles 3.

[0031] For example, if the material constituting the insulating layer 1 is a glass ceramic 2 containing silica particles, the alumina particles 3 have a higher dielectric constant compared to the silica particles.

[0032] The insulating layers 1A and 1B on the surface have a higher relative permittivity than the insulating layer 1C located in the inner layers below them, resulting in a difference in relative permittivity between the inner insulating layer 1C and the insulating layers 1A and 1B on the surface. Consequently, insulating layers 1 with different relative permittivity are arranged in the stacking direction (Z-axis direction) of the wiring board 100.

[0033] Due to differences in the relative permittivity in the stacking direction (Z-axis direction), the wiring board 100 exhibits different impedances for currents flowing through its internal wiring and via conductors.

[0034] If the alumina particles 3 are present only on the surface of the insulating layers 1A and 1B, it becomes possible to reduce the likelihood of such defects occurring.

[0035] (Second Embodiment) Figure 2 is a plan view showing an example of a wiring board according to the second embodiment. Figure 3 is a diagram showing an example of the A-A cross section of Figure 2. Figure 4 is a cross-sectional view showing another example of a wiring board according to the second embodiment.

[0036] The insulating substrate 10 may be a hexahedral plate having a first surface 101 and a second surface 102, and a third surface 103, a fourth surface 104, a fifth surface 105, and a sixth surface 106 that are in contact with the first surface 101 and the second surface 102. The third surface 103 and the fourth surface 104 are located at both ends in the X-axis direction, respectively. The fifth surface 105 and the sixth surface 106 are located at both ends in the Y-axis direction, respectively.

[0037] The third surface 103, the fourth surface 104, the fifth surface 105, and the sixth surface 106 each form a ridge between the first surface 101 and the second surface 102. Specifically, the insulating substrate 10 has ridges r1 to r4 located between the third surface 103, the fourth surface 104, the fifth surface 105, and the sixth surface 106 and the first surface 101. In addition, the insulating substrate 10 has ridges r5 to r6 located between the third surface 103, the fourth surface 104, the fifth surface 105, and the sixth surface 106 and the second surface 102.

[0038] As shown in Figure 3, among the multiple alumina particles 3, there may be alumina particles 3B located on the ridge r1 which is the ridge portion of the insulating substrate 10.

[0039] With this configuration, the alumina particles 3 are fixed to the edges of the surface of the outermost insulating layers 1A and 1B. Therefore, the effect of reducing the coefficient of thermal expansion caused by the adhesion of the alumina particles 3 to the glass ceramics 2 can be generated up to the edges of the insulating layers 1A and 1B.

[0040] Furthermore, as shown in Figure 4, among the alumina particles 3 located on the ridge r1 which is the ridge portion, there may be alumina particles 3C that have the same orientation as the third surface 103 which is the side surface of the insulating substrate 10 and have a cross-section 3a that is along that side surface.

[0041] Even in such a case, since the alumina particles 3 are fixed to the edges of the surfaces of the outermost insulating layers 1A and 1B, the effect of reducing the coefficient of thermal expansion caused by the fixation of the alumina particles 3 to the glass ceramics 2 can be exerted over the entire edge surfaces of the outermost insulating layers 1A and 1B. In this case, since the unevenness on the side surfaces of the insulating base 10 is reduced, the positioning accuracy of the wiring substrate 100 can be improved.

[0042] The alumina particles 3B shown in FIG. 3 and / or the alumina particles 3C shown in FIG. 4 may be present on any one or more of the ridge lines r1 to r8, or may be present on all the ridge line portions.

[0043] (Third Embodiment) FIG. 5 is a plan view showing an example of a wiring substrate according to the third embodiment. As shown in FIG. 5, among the plurality of alumina particles 3, there may be alumina particles 3D positioned so as to circumferentially surround the peripheral edge portion 101A of the insulating base 10.

[0044] According to this configuration, since the alumina particles 3 are circumferentially disposed along the ridge line portion of the insulating base 10, the effect of reducing the coefficient of thermal expansion caused by the fixation of the alumina particles 3 to the glass ceramics 2 can be exerted over the entire surface of the outermost insulating layer 1A. Although FIG. 5 illustrates the alumina particles 3D positioned on the first surface 101, the alumina particles 3D may be positioned on the second surface 102. Further, the alumina particles 3D may be positioned on both the first surface 101 and the second surface 102, respectively.

[0045] Further, the alumina particles 3D may include alumina particles 3C having a cross section along the side surface of the insulating base 10, and most of the alumina particles 3D may be alumina particles 3C having such a cross section.

[0046] (Fourth Embodiment) FIG. 6 is a cross-sectional view showing an example of a wiring substrate according to the fourth embodiment.

[0047] The wiring substrate 100 includes conductors 20. The conductors 20 may be made of copper. The conductors 20 may be disposed in each insulating layer 1 in at least one form of wiring and via conductors. The conductors 20 may include conductors 21 and 22.

[0048] The thermal expansion coefficients of copper, glass ceramics 2, and alumina particles 3 are in the order of copper > glass ceramics > alumina particles.

[0049] When the wiring board 100 is divided into two equal parts in the thickness direction (Z-axis direction), with the first surface 101 side designated as the first wiring section 111 and the second surface 102 side as the second wiring section 112, the second wiring section 112 has a larger volume ratio of conductors 20 than the first wiring section 111. When the volume ratio of conductors 20 located in the first wiring section 111 is V1 (%) and the volume ratio of conductors 20 located in the second wiring section 112 is V2 (%), it is desirable that the relationship V2 - V1 < 5 holds.

[0050] Because this wiring board 100 has a high concentration of alumina particles 3 on the first surface 101 side of the first wiring section 111, the thermal expansion coefficient of the first surface 101 side is smaller than that of the second surface 102 side located on the second wiring section 112 side.

[0051] Even if the proportion of conductor 20 containing copper, which has a higher coefficient of thermal expansion than the glass ceramics 2 and alumina particles, is higher on the second wiring section 112, which is on the second surface 102 side, as long as the difference in the ratio of conductor 20 is within the above limits, the state in which the coefficient of thermal expansion on the first surface 101 side is smaller than the coefficient of thermal expansion on the second surface 102 side can be maintained.

[0052] The conductors 20 may be located between the layers of the laminated insulating layer 1. The conductors 20 may be located on the first surface 101 and / or the second surface 102, which are the surfaces of the insulating substrate 10. For example, the conductor 20 can be made from a conductive paste containing copper powder that has been fired. The conductor 20 is preferably a metallized copper film.

[0053] In the wiring board 100, the conductor 20 should ideally account for 20% or less of the total volume. Here, the volume ratio of the conductor 20 can be measured and calculated as follows. Specifically, it can be calculated based on the volume of the conductor 20, which is the sum of the volumes of each conductor calculated based on the pattern area of ​​each conductor viewed from the first surface 101 and the thickness of each conductor obtained from the cross-section of the wiring board 100, and the volume of the wiring board 100. Note that the pattern area of ​​each conductor may be calculated, for example, using data from the plate-making specifications.

[0054] Furthermore, based on the embodiments described later, the thickness of the insulating layer 1 on the wiring board 100 is preferably 2 mm or more and 4 mm or less. Also, the area of ​​the first surface 101 and the second surface 102 of the wiring board 100 in plan view is preferably 50 mm × 50 mm or more and 150 mm × 150 mm or less.

[0055] (Manufacturing Method for Wiring Boards) Figure 7 is a schematic perspective view showing an example of a manufacturing method for wiring boards according to the embodiment. Figure 8 is a schematic perspective view showing another example of a manufacturing method for wiring boards according to the embodiment.

[0056] The manufacturing method for the wiring board 100 of this disclosure may include, for example, the steps of: (1) forming a pattern sheet having at least one of via conductors and conductor patterns on a green sheet; (2) preparing a plurality of pattern sheets to form a first laminate; (3) forming a second laminate by laminating a restraining sheet containing alumina, which has a higher sintering start temperature and is less prone to shrinkage than the green sheet, on the upper and lower surfaces in the lamination direction of the first laminate; (4) firing the second laminate at a predetermined temperature (for example, 850°C to 1000°C) lower than the sintering start temperature of the restraining sheet; and (5) removing the restraining sheet from the second laminate after firing.

[0057] Furthermore, in the above process, an interlayer film pattern may be formed between the layers of the first laminate, having a shrinkage start temperature lower than that of the green sheet and a shrinkage end temperature that is the same as or lower than the shrinkage start temperature of the green sheet, and this interlayer film pattern may be interposed between two adjacent green sheets in the lamination direction at the periphery of the first laminate to form the first laminate.

[0058] Furthermore, in the above process, if there is excess material around the second laminate 100A after the firing step of the second laminate (see (4) above) or after the removal of the restraining sheet (see (5) above) (see Figure 7), or if the second laminate that will become the wiring board 100 is made of multiple base laminates 100B formed in a raw state before firing (see Figure 8), a method of cutting these into individual pieces along the cutting line CL may be adopted. By such a method, for example, a wiring board 100 having alumina particles 3C as shown in Figure 4 can be obtained.

[0059] For cutting the sintered body after firing (in the state where the wiring board 100 is formed), dicing or laser cutting is preferable.

[0060] The wiring board 100 according to each embodiment is not limited to one manufactured using the method described above, but may be a wiring board 100 manufactured by any method.

[0061] (Sample Preparation) First, a green sheet (150 mm x 150 mm x 200 μm thick) containing glass ceramic raw material powder was prepared. The glass ceramic raw material powder was a mixed powder of borosilicate glass and silica particles. Specifically, a mixed powder was used in which 50 parts by mass of silica particles were added to 100 parts by mass of borosilicate glass. In addition, a butyral-based organic resin was used as the organic vehicle for the green sheet.

[0062] For the conductive paste, a mixture of copper powder and borosilicate glass powder was used. A cellulose-based organic resin was used as the organic vehicle. The solid content was a composition of 30 parts by mass of borosilicate glass powder added to 100 parts by mass of copper powder.

[0063] Next, a pattern sheet was prepared as follows: Through holes were made in the green sheet as needed, and conductive paste was embedded in these through holes using a printing method to form raw via conductors. Then, conductive paste was printed onto the surface of the green sheet on which the raw via conductors were formed to form a conductive pattern.

[0064] On the surface of the green sheet, which is placed on the outermost layer on the first surface 101 side that will become the insulating layer 1A, 50 x 50 pads with a diameter of 0.5 mm are formed in a grid pattern at a pitch of 1 mm (the area of ​​the region where the pads are arranged is approximately 50 mm x 50 mm).

[0065] On the surface of the green sheet, which is placed on the outermost layer of the second surface 102 that will become the insulating layer 1B, 40 x 40 pads with a diameter of 1 mm are formed in a grid pattern at a pitch of 2 mm (the area of ​​the region where the pads are arranged is approximately 80 mm x 80 mm).

[0066] The other green sheets also had predetermined conductor patterns and via conductors formed on them.

[0067] A laminate (first laminate) was created by stacking multiple layers of pattern sheets. The number of layers was 30.

[0068] Next, a restraining sheet containing alumina particles was placed on both sides of the first laminated structure, and the second laminated structure was fabricated by sandwiching the first laminated structure between them. The second laminated structure was made as a single-piece laminated structure, as shown in Figure 7.

[0069] The alumina particles used in the restraint sheet had an average particle size of approximately 1 μm. When the particle size distribution was measured and viewed with respect to the average particle size, the alumina particles used showed a distribution where the smaller particle size side had a high frequency region (0.5 μm to 0.8 μm), unlike the larger particle size side.

[0070] Generally, smaller particles have a larger specific surface area and are therefore more reactive.

[0071] Next, the second laminate was fired. The firing was performed under the conditions of degreasing in a humid nitrogen atmosphere, followed by firing in a dry nitrogen atmosphere at a maximum temperature of 860°C for 2 hours.

[0072] The restraining sheet was removed from the sintered body of the second laminate after firing to obtain a precursor for the wiring board. The precursor for the wiring board is the state in which the restraining sheet has been removed from the sintered body of the second laminate.

[0073] As shown in Figure 7, the precursor of the wiring board has a portion at its periphery that will be removed by cutting, as it is still in the pre-cut state.

[0074] In this embodiment, as shown in Figure 7, a laminate having one wiring board was used, and a portion to be removed was provided around the wiring board.

[0075] After firing, the surface area of ​​the circuit board was 90 mm x 90 mm, and the thickness was approximately 3 mm. The shrinkage rate was 50% in the Z direction and 0-1% in the X-Y directions.

[0076] Next, as shown in Figure 7, the precursor of the wiring board was cut along the cutting line using dicing to obtain one wiring board from the precursor (number of samples: 1).

[0077] After firing, a plating film (electroless Au+Sn) was formed on the pads of the wiring board. The resulting wiring board has an insulating layer made of glass ceramics containing silica particles as fillers, as described above. Alumina particles originating from the covering sheet were fixed to the surface of the insulating layer (outermost layer) on both sides of the wiring board.

[0078] In this case, the alumina particles were scattered around the periphery of the first surface 101, which forms the insulating layer 1A. On the first surface 101 side, the alumina particles were scattered around the wiring board. On the other hand, on the second surface 102, which forms the insulating layer 1B, the alumina particles were scattered around each pad.

[0079] As a comparative example, the laminate prepared as the second laminate was fired at different temperatures and evaluated in the same manner. The firing temperatures were 850°C and 900°C.

[0080] No alumina particle adhesion was observed in the sample (wiring board) fired at 850°C. The sample prepared at 850°C was used as a comparative example to evaluate the thermal stress of the wiring board.

[0081] In the sample (wiring board) fired at 900°C, many areas had the covering sheet attached, making it unsuitable for subsequent silicon substrate mounting and thermal stress evaluation.

[0082] In the sample of this embodiment, the area ratio of alumina particles on the first surface 101 was 1.3%, and the area ratio of alumina particles on the second surface 102 was 0.6%.

[0083] The area ratio of alumina particles was determined using an EDS attached to a scanning electron microscope.

[0084] Next, the effect of fixing alumina particles to the surface of the wiring board was evaluated using the following method. Hereinafter, the wiring board of this embodiment, fired at 860°C, will be referred to as Sample 1, and the wiring board of the comparative example, fired at 850°C, will be referred to as Sample 2.

[0085] A silicon substrate with an area of ​​50 mm x 50 mm and a thickness of 0.3 mm was mounted on the first surface 101 side of the wiring boards of both Sample 1 and Sample 2.

[0086] The silicon substrate has a pad-shaped Au vapor-deposited film at a position corresponding to the pad on the first surface 101 of the wiring board.

[0087] A silicon substrate was mounted onto the wiring board. A reflow oven set to a temperature of 280°C was used for mounting the silicon substrate.

[0088] A micro-Raman analyzer was used to measure the thermal stress of the wiring board. The measurement involved shining light onto a measurement point on the silicon substrate and capturing the light reflected from that spot. A method was used to determine the stress based on the difference in the color of the light.

[0089] The measurement itself is simple, involving merely irradiating and analyzing light to measure the spectral distribution. However, to increase the resolution, the spot was narrowed and reduced in size. Therefore, the measurement device used was equipped with a microscope that uses a laser as the light source to narrow the spot.

[0090] Raman analysis was performed on four locations (a total of four locations) centered around the corners of the silicon substrate on the wiring board with the silicon substrate mounted on it. The measured values ​​were used to check the color state at four locations for both this example (Sample 1) and the comparative example (Sample 2).

[0091] As mentioned above, this Raman analysis used a method to determine intensity from differences in the color of reflected light, so absolute values ​​of stress were not obtained. However, the intensity of the light was visually confirmed, and the differences in color were used to identify differences in thermal stress as arbitrarily controlled units.

[0092] The thermal stress of sample 1 was lower than that of sample 2, as indicated by the color. This disclosure makes it possible to improve the mounting reliability of multilayer wiring boards.

[0093] Although the present disclosure has been described in detail above, this disclosure is not limited to the embodiments described above, and various modifications and improvements are possible without departing from the gist of this disclosure.

[0094] In one embodiment, (1) the wiring board has an insulating substrate composed of a plurality of insulating layers, the insulating substrate is made of glass ceramics and forms the framework of the wiring board, the insulating layer constituting the outermost layer of the insulating substrate has a plurality of alumina particles, the thermal expansion coefficient of the insulating layer is greater than the thermal expansion coefficient of the alumina particles, when one of the two surfaces based on the skeletal shape of the insulating substrate is designated as the first surface and the opposite side of the first surface as the second surface, the area of ​​the conductor in contact with the first surface is smaller than the area of ​​the conductor in contact with the second surface, when the insulating layer having the first surface is designated as the first insulating layer and the insulating layer having the second surface is designated as the second insulating layer, the proportion of alumina particles in the first insulating layer is higher than that of the second insulating layer.

[0095] (2) In the wiring board described in (1) above, the alumina particles contained in the first insulating layer are present exposed on the first surface, and the alumina particles contained in the second insulating layer may be present exposed on the second surface.

[0096] (3) In the wiring board of (1) or (2) above, among the plurality of alumina particles, there may be alumina particles that contain glass and protrude from the surface of the glass ceramic of the insulating layer located in the outermost layer.

[0097] (4) In any one of the wiring boards described in (1) to (3) above, the insulating substrate is a hexahedron plate having the first surface and the second surface and the third surface, fourth surface, fifth surface and sixth surface located in contact with the first surface and the second surface, the third surface, fourth surface, fifth surface and sixth surface each form a ridge between the first surface and the second surface, and among the plurality of alumina particles, there may be alumina particles located on the ridge of the insulating substrate.

[0098] (5) In the wiring board described in (4) above, among the alumina particles located on the ridge line, there may be alumina particles that are oriented in the same direction as the side surface of the insulating substrate and have a cross section along that side surface.

[0099] (6) In any one of the wiring boards described in (1) to (5) above, there may be alumina particles among the plurality of alumina particles that are positioned to surround the peripheral edge of the insulating substrate in a circumferential manner.

[0100] (7) In any one of the wiring boards described in (1) to (6) above, a copper conductor is provided, the conductor is arranged in each insulating layer in at least one form of wiring and via conductor, the coefficients of thermal expansion of copper, glass ceramics and alumina particles are in the order of copper > glass ceramics > alumina particles, and when the wiring board is divided into two equal parts in the thickness direction, with the first surface side being the first wiring section and the second surface side being the second wiring section, the second wiring section has a larger volume ratio of conductors than the first wiring section, and when the volume ratio of conductors located in the first wiring section is V1 (%) and the volume ratio of conductors located in the second wiring section is V2 (%), the relationship V2 - V1 < 5 may be met.

[0101] Further effects and other embodiments can be readily derived by those skilled in the art. Therefore, broader embodiments of this disclosure are not limited to the specific details and representative embodiments expressed and described above. Accordingly, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents.

[0102] 1. 1A-1C Insulating layer 2. Glass ceramics 3. 3A-3D Alumina particles 10. Insulating substrate 20. Conductor 100. Wiring board

Claims

1. A wiring board having an insulating substrate composed of a plurality of insulating layers, wherein the insulating substrate is made of glass ceramics and forms the framework of the wiring board, the insulating layer constituting the outermost layer of the insulating substrate has a plurality of alumina particles, the thermal expansion coefficient of the insulating layer is greater than the thermal expansion coefficient of the alumina particles, when one of the two surfaces based on the skeletal shape of the insulating substrate is designated as the first surface and the opposite side of the first surface as the second surface, the area of ​​the conductor in contact with the first surface is smaller than the area of ​​the conductor in contact with the second surface, and when the insulating layer having the first surface is designated as the first insulating layer and the insulating layer having the second surface is designated as the second insulating layer, the wiring board having a higher proportion of alumina particles in the first insulating layer than in the second insulating layer.

2. The wiring substrate according to claim 1, wherein the alumina particles contained in the first insulating layer are exposed on the first surface, and the alumina particles contained in the second insulating layer are exposed on the second surface.

3. The wiring substrate according to claim 1 or 2, wherein among the plurality of alumina particles, there are alumina particles that include glass and protrude from the surface of the glass ceramic of the insulating layer located in the outermost layer.

4. The wiring board according to any one of claims 1 to 3, wherein the insulating substrate is a hexahedron plate having a first surface and a second surface, and a third surface, a fourth surface, a fifth surface and a sixth surface located in contact with the first surface and the second surface, the third surface, the fourth surface, the fifth surface and the sixth surface each form a ridge between them and the first surface and the second surface, and among the plurality of alumina particles, there are alumina particles located on the ridge of the insulating substrate.

5. The wiring substrate according to claim 4, wherein among the alumina particles located on the ridge portion, there are alumina particles that are oriented in the same direction as the side surface of the insulating substrate and have a cross-section along that side surface.

6. The wiring board according to any one of claims 1 to 5, wherein among the plurality of alumina particles, there are alumina particles positioned so as to surround the peripheral edge of the insulating substrate.

7. A wiring board according to any one of claims 1 to 6, having copper conductors, wherein the conductors are arranged in each insulating layer in at least one form of wiring and via conductors, the coefficients of thermal expansion of copper, glass ceramics and alumina particles are in the order of copper > glass ceramics > alumina particles, and when the wiring board is divided into two equal parts in the thickness direction, with the first surface side being the first wiring section and the second surface side being the second wiring section, the second wiring section has a larger volume ratio of conductors than the first wiring section, and when the volume ratio of conductors located in the first wiring section is V1 (%) and the volume ratio of conductors located in the second wiring section is V2 (%), the relationship V2 - V1 < 5 is met.

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