Circuit board

Abstract

Provided is a circuit board comprising a substrate and a plurality of adjacent circuit patterns arranged on a main surface of the substrate. The substrate has a surface region including the main surface, and a base region other than the surface region. The surface region includes a modified portion having a higher oxygen atom content than the base region, and a non-modified portion that is the portion other than the modified portion. Each of the plurality of circuit patterns is arranged on the modified portion. The non-modified portion is present between the adjacent circuit patterns in plan view from the main surface side.

Description

Circuit board

[0001] The present disclosure relates to a circuit board.

[0002] A circuit board having a desired circuit pattern formed on an insulating base material such as resin is known. Such a circuit board can be manufactured, for example, by a subtractive method (Patent Document 1) in which a copper foil is formed on the base material and then copper in non-circuit portions is removed by an etching process, or by a semi-additive method (Patent Document 2) in which a circuit pattern is formed by masking non-circuit portions and then applying copper plating.

[0003] Japanese Patent No. 5005883, Japanese Patent No. 4430990, Japanese Unexamined Patent Application Publication No. 11-314310

[0004] When plating copper on a resin base material, it is known to roughen the surface of the resin base material in order to improve the adhesion of the copper plating. On the other hand, roughening of the resin base material can be a cause of transmission loss of signals flowing through the circuit pattern. Therefore, there is a demand for a circuit board provided with a wiring pattern formed without roughening the surface of the base material.

[0005] As a method to replace the roughening treatment, a method (Patent Document 3) is known in which the entire surface of the base material is hydrophilized by subjecting the surface of the resin base material to plasma treatment to improve the adhesion of the plating.

[0006] Regarding such a method, the present inventor has newly found that by hydrophilizing the surface of the base material, migration in the wiring pattern can be more likely to occur.

[0007] The present disclosure has been made in view of the above problems. That is, the main object of the present disclosure is to provide a wiring board in which the occurrence of migration is suppressed.

[0008] The present inventor has arrived at an invention of a circuit board in which the above main object is achieved.

[0009] A circuit board according to one embodiment of the present disclosure comprises a substrate and a plurality of adjacent circuit patterns arranged on the main surface of the substrate, wherein the substrate has a surface region including the main surface and a substrate region other than the surface region, the surface region includes a modified portion having a higher oxygen atom content than the substrate region and an unmodified portion which is the portion other than the modified portion, each of the plurality of circuit patterns is arranged on the modified portion, and in a plan view from the main surface side, the unmodified portion is located between the adjacent circuit patterns.

[0010] According to a circuit board according to one embodiment of the present disclosure, the occurrence of migration is suppressed.

[0011] Figure 1 is a schematic cross-sectional view showing a circuit board according to one embodiment of the present disclosure. Figure 2 is a schematic cross-sectional view showing a circuit board according to another embodiment of the present disclosure. Figure 3 is a schematic cross-sectional view showing a circuit board according to another embodiment of the present disclosure. Figure 4 is a schematic enlarged cross-sectional view showing portion A of the circuit board shown in Figure 3. Figure 5 is a graph showing the content distribution of a predetermined element in a circuit board according to one embodiment of the present disclosure.

[0012] The embodiments of this disclosure will be described in detail below. It should be noted that the applicant provides the following descriptions and examples to enable those skilled in the art to fully understand this disclosure, and is not intended to limit the subject matter described in the claims. In other words, this disclosure is not particularly limited to the preferred embodiments described below, and can be modified and implemented as appropriate within the scope of its purpose. For convenience, embodiments and examples may be presented separately to facilitate explanation or understanding of key points, but partial substitution and / or combination of configurations shown in different embodiments is possible. In descriptions of such embodiments, redundant explanations of substantially identical matters may be omitted, and only differences may be described. In particular, similar effects and benefits from similar configurations may not be mentioned sequentially in each embodiment.

[0013] Furthermore, in this specification, "above" an element includes not only cases where it is in contact with the upper surface of the element, but also cases where it is not in contact with the upper surface of the element. In other words, "above" an element includes not only positions above the element at a distance, i.e., positions above the element via other objects, or positions above it at a distance, but also positions directly above the element in contact with it. Moreover, "above" does not necessarily mean the upper side in the vertical direction. "Above" merely indicates the relative positional relationship of an element.

[0014] The various numerical ranges referred to herein are intended to include the lower and upper limits themselves, unless otherwise specified. The term "approximately" means that a variation or difference of a few percent, for example, ±10%, may be included.

[0015] In this specification, "cross-sectional view" refers to the form viewed from a direction approximately perpendicular to the thickness direction Y of the substrate (simply put, the form when the substrate is cut by a plane parallel to the thickness direction Y of the substrate). Furthermore, in this specification, "plan view" refers to a sketch of the object viewed from the main surface side of the substrate, along the thickness direction Y of the substrate.

[0016] [Circuit Board] (First Embodiment) Figure 1 is a schematic cross-sectional view showing a circuit board 1 according to one embodiment of the present disclosure. The circuit board 1 mainly comprises a base material 10 and a circuit pattern 20 arranged on the main surface 10A of the base material 10. The base material 10 may be an insulating resin material. The base material 10 comprises a surface region 11 including the main surface 10A and a base region 13 which is a region other than the surface region 11. In other words, the base material 10 comprises two regions: the surface region 11 and the base region 13 other than the surface region 11. The surface region 11 includes the main surface 10A on which the circuit pattern 20 is provided and is a region having a constant thickness from the main surface 10A toward the interior side of the base material 10. The base region 13 is a region other than the surface region 11 including the main surface 10A, and the surface region 11 and the base region 13 can also be understood as regions stacked in the thickness direction Y of the base material 10. For example, if the main surface 10A is considered as the top surface, the base region 13 corresponds to the area below the surface region 11. In other words, the surface region 11 corresponds to the area above the base region 13 of the base material 10. The surface region 11 and the base region 13 may be adjacent in the vertical direction Y of the base material 10 when the main surface 10A of the base material is considered as the top surface.

[0017] The surface region 11 is a region that includes the modified portion 15, which will be described later. For example, the surface region 11 may be a region with a thickness of 0.1 μm extending from the main surface 10A into the interior of the substrate 10. That is, in the substrate 10, the surface region 11 may be the region from the main surface 10A to a depth of 0.1 μm along the thickness direction Y. In other words, if the main surface 10A is considered as the top surface, the lower layer region deeper than 0.1 μm along the thickness direction from the main surface 10A corresponds to the substrate region 13. For example, the surface region 11 may also be called the "surface zone," "surface layer region," or "main surface containing layer." On the other hand, the substrate region 13 may also be called the "bulk region," "main region," or "lower layer region." Alternatively, the "surface region" and the "substrate region" may simply be called the "first region" and the "second region," respectively.

[0018] The surface region 11 and the substrate region 13 are contained within a single substrate 10. That is, the substrate 10 may be an integrated material comprising the surface region 11 and the substrate region 13. In such a structure, the substrate 10 comprising the surface region 11 and the substrate region 13 is distinguished from a multilayer substrate comprising multiple layers. On the other hand, the circuit board 1 may have a multilayer structure comprising multiple substrates 10.

[0019] The surface region 11 has a portion with a higher oxygen atom content. Specifically, as shown in Figure 1, the surface region 11 has a modified portion 15 with a higher oxygen atom content than the substrate region 13, and an unmodified portion 17 which is the portion other than the modified portion 15. The surface region 11 is a region that includes the main surface 10A, and it can also be understood that the main surface 10A has the modified portion 15 and the unmodified portion 17.

[0020] The modified portion 15 has a higher oxygen atom content than the unmodified portion 17. The unmodified portion 17 may have an oxygen atom content equivalent to that of the substrate region 13. In other words, the substrate 10 has a modified portion 15 with a partially higher oxygen atom content, and this modified portion 15 may be located in the surface region 11. Due to this structure, the modified portion 15 can also be referred to as the "oxygen-enriched portion," "high-oxygen portion," or "oxygen-concentrated portion."

[0021] The modified portion 15 may contain more oxygen-containing groups than the base region 13. Because the modified portion 15 contains more oxygen-containing groups, it may have a higher oxygen atom content. For example, the polymer constituting the base material 10 contains oxygen-containing groups, and these oxygen-containing groups may be distributed in greater numbers in the modified portion 15. Examples of oxygen-containing groups include at least one group selected from the group consisting of oxo groups, hydroxyl groups, alkoxy groups, carboxyl groups, and alkoxycarbonyl groups. Alternatively, the modified portion 15 may contain more crosslinked oxygen atoms in the polymer structure compared to the base region 13. As a result, the modified portion 15 may have a higher oxygen atom content than the base region 13.

[0022] As described above, the oxygen-containing groups or cross-linked oxygen atoms in the base material 10 may be present in greater quantities in the modified portion 15 than in the base region 13. For example, in the base material 10, the C:O elemental concentration ratio in the modified portion 15 may be greater than the C:O elemental concentration ratio in the base region 13. This means that the oxygen atom content in the modified portion 15 is greater than the oxygen atom content in the base region 13. Also, the C:O elemental concentration ratio in the unmodified portion 17 may be smaller than the C:O elemental concentration ratio in the modified portion 15. Furthermore, the C:O elemental concentration ratio in the unmodified portion 17 may be about the same as the elemental concentration ratio in the base region 13.

[0023] The circuit pattern 20 may be formed from a conductive material mainly composed of metal. For example, the circuit pattern 20 may have one or more layers of plating. The plating may be an electroless plating film or an electrolytic plating film. The metal contained in the plating film may be at least one selected from the group consisting of, for example, copper, silver, gold, tin, nickel, and palladium. Such a circuit pattern may also be called, for example, a metal pattern, a conductor pattern, or a wiring pattern.

[0024] The planar shape of the circuit pattern is not particularly limited and may have any shape. For example, the circuit pattern can be linear, curved, polylinear, polygonal, circular, elliptical, or irregular in shape.

[0025] The circuit board 1 comprises a plurality of adjacent circuit patterns 20 on a base material 10. In this specification, "a plurality of adjacent circuit patterns" means that at least a portion of the circuit patterns arranged on the base material 10 are arranged adjacent to each other. Therefore, the plurality of adjacent circuit patterns do not necessarily have to be separate circuit patterns and may be connected at any point. In a plan view, there is space between adjacent circuit patterns. For example, "a plurality of adjacent circuit patterns" includes a structure in which one continuous circuit pattern is arranged in a curved manner (for example, in a roughly U-shape) so that one end of the circuit pattern and the other end are partially adjacent. Alternatively, separate circuit patterns may be arranged adjacent to each other. The adjacent circuit patterns may extend parallel to each other or in different directions.

[0026] In the circuit board 1 of this disclosure, the circuit pattern 20 is arranged so as to overlap with the modified portion 15 in a plan view from the main surface 10A side of the base material 10 (hereinafter simply referred to as "plan view"). In other words, in a plan view, the modified portion 15 is located below the circuit pattern 20. The base material 10 has the modified portion 15 at a position that overlaps with the circuit pattern 20 in a plan view. The modified portion 15 and the circuit pattern 20 may be in direct contact without the use of a separate component such as a bonding agent.

[0027] The oxygen contained in the modified portion 15 can combine (for example, through coordination bonds) with the metal components contained in the circuit pattern 20, thereby contributing to improved adhesion of the circuit pattern 20 on the main surface 10A. Furthermore, the inclusion of oxygen-containing groups in the modified portion 15 improves its hydrophilicity. As a result, when forming the circuit pattern 20 by plating, the plating solution can more easily reach the modified portion 15, allowing for the formation of the circuit pattern 20 favorably on the modified portion 15. Therefore, the modified portion 15 allows the circuit pattern 20 formed by plating to adhere favorably to the modified portion 15.

[0028] The modified portion 15 overlaps with each of the adjacent circuit patterns 20 in a plan view. Similar to the circuit patterns 20, the modified portions 15 may be spaced apart from each other in a plan view. Each of the adjacent circuit patterns 20 may be positioned on each of the spaced-apart modified portions 15. Unmodified portions 17 exist between the adjacent modified portions 15. In other words, the modified portions 15 may face each other in a cross-sectional view via the unmodified portions 17. In a plan view, the unmodified portions 17 exist between the adjacent circuit patterns 20. In other words, the adjacent circuit patterns 20 may be spaced apart from each other in a plan view such that unmodified portions 17 exist between the circuit patterns 20.

[0029] Multiple modified portions 15 that overlap with each of multiple adjacent circuit patterns 20 may be separated by unmodified portions 17 that exist between the circuit patterns 20. As described above, the modified portions 15 have a high oxygen atom content and may therefore have higher hydrophilicity than the unmodified portions 17. For this reason, the surface region 11 of the substrate 10 can be understood to consist of modified portions 15 with excellent hydrophilicity and unmodified portions 17 with poor hydrophilicity. In other words, the substrate 10 has modified portions 15 with excellent hydrophilicity at positions that overlap with each of multiple adjacent circuit patterns 20, while having unmodified portions 17 with poor hydrophilicity between adjacent circuit patterns 20. The inventors have newly discovered that migration between circuit patterns 20 in the circuit board 1 can be suppressed by providing such a structure.

[0030] The inventors have newly discovered that the continuous presence of the modified portion 15 between circuit patterns 20 can be involved in the occurrence of migration between the circuit patterns 20. Specifically, the modified portion 15 has a high oxygen atom content, which improves the adhesion between the circuit pattern 20 and the substrate 10, while its excellent hydrophilicity makes it easy to form a water film on the modified portion 15. Therefore, when the modified portion 15 is continuously present between adjacent circuit patterns 20, the water film formed on the modified portion 15 makes it easier for the metal contained in the circuit pattern 20 to dissolve between the circuit patterns 20. Migration can occur as metal ions dissolved on the modified portion 15 extending between the circuit patterns 20 move.

[0031] On the other hand, in the circuit board 1 of this disclosure, there are unmodified portions 17 with poor hydrophilicity between the circuit patterns 20. Due to their poor hydrophilicity, a water film is less likely to form on the unmodified portions 17. Furthermore, because they have a lower oxygen atom content compared to the modified portions 15, even if metal ions leach from the circuit patterns 20, the leached metal ions are less likely to move across the unmodified portions 17. Therefore, the circuit board 1 of this disclosure can suppress the movement of metal ions leached from one of several adjacent circuit patterns 20 across the unmodified portions 17 to the other circuit pattern 20. This can suppress the occurrence of migration between adjacent circuit patterns 20.

[0032] Furthermore, the circuit board of this disclosure may also be advantageous in terms of dielectric properties. Generally, in order to adhere the circuit pattern 20 to the substrate 10, methods such as roughening the main surface 10A by etching or applying a bonding agent to the main surface 10A may be used. However, roughening the main surface 10A and the bonding agent placed between the main surface 10A and the circuit pattern 20 can increase the dielectric constant of the substrate 10 and worsen the dielectric properties of the circuit board 1. For this reason, especially in circuit boards for transmitting high-frequency signals, it is desirable to avoid roughening the main surface 10A and using bonding agents.

[0033] According to this disclosure, by having a modified portion 15 on the surface region 11 of the substrate 10, a circuit pattern with excellent adhesion can be provided on the substrate 10 having the modified portion 15 without roughening the substrate surface by etching or using an adhesive. In other words, according to this disclosure, the main surface 10A of the substrate 10 having the circuit pattern 20 can be a smooth surface instead of a rough surface. Furthermore, no adhesive is required between the circuit pattern 20 and the main surface 10A. As a result, it is possible to form the circuit pattern 20 without excessively increasing the dielectric constant of the substrate 10, compared to the case where the circuit pattern is formed by roughening the main surface or using an adhesive. Therefore, according to this disclosure, a circuit board with excellent dielectric properties can be obtained while suppressing the occurrence of migration.

[0034] The shape of the substrate 10 is not particularly limited and can be of various shapes. For example, the substrate 10 can be in the form of a film or a sheet. Examples of materials for the substrate 10 include at least one selected from the group consisting of polyester polymers, silicone polymers, acrylic polymers, polyolefin polymers, and copolymers thereof.

[0035] More specifically, the materials for the base material 10 include polyimide (PI), liquid crystal polymer (LCP), epoxy resin (EP), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyether sulfone (PES), polycarbonate (PC), triacetylcellulose (TAC), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polysilane, polysiloxane, polysilazane, polycarbosilane, polyacrylate, polymethacrylate, Examples include polymethyl acrylate, polyethyl acrylate, polyethyl methacrylate, polymethyl methacrylate (PMMA), cycloolefin copolymer (COC), cycloolefin polymer (COP), polyethylene (PE), polypropylene (PP), polyacetal (POM), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroalkyl polymer (PFA), polystyrene (PS), and styrene acrylonitrile copolymer (SAN). These materials can be used individually or in combination of two or more.

[0036] The oxygen atom content of the substrate 10 can be measured by performing EDX analysis on a cross-sectional TEM image of the circuit board 1. Specifically, it can be measured by the following procedure.

[0037] First, a cross-section parallel to the thickness direction Y of the substrate 10 is cut out to obtain a measurement sample in which the cross-section of the circuit board 1 is exposed. Next, the cross-section of the measurement sample is photographed with a transmission electron microscope (TEM), and line analysis is performed on the obtained TEM image along the thickness direction Y using energy-dispersive X-ray (EDX) analysis. Figure 5 is an exemplary graph showing a part of the measurement results obtained by performing line analysis on a line segment passing from the circuit pattern 20 side to the substrate region 13. When the modified portion 15 is included on the line segment on which the line analysis was performed, it can be seen that the oxygen atom content is increased on the main surface 10A side of the substrate 10 (region from M1 to M2) compared to the average value of the oxygen atom content in the substrate region 13. The average value of the oxygen atom content in the substrate region 13 is shown as the dashed line Ave in the graph of Figure 5. This average value is the average value of the oxygen atom content obtained by line analysis in the region with a depth of 0.11 μm to 0.2 μm from the main surface 10A of the substrate 10. The modified portion 15 can be a region (the region from M1 to M2) having an oxygen atom content of 101% or more of the average value. If there are multiple regions having an oxygen atom content of 101% or more of the average value, the region located closest to the main surface 10A can be considered the modified portion. The distance from M1 to M2 corresponds to the thickness of the modified portion 15.

[0038] The oxygen atom content of the modified portion 15 can be, for example, 101% or more, preferably 105% or more, more preferably 110% or more, and even more preferably 120% or more, of the average value of the oxygen atom content of the substrate region 13. When the oxygen atom content of the modified portion 15 is within the above range relative to the average value of the oxygen atom content of the substrate region 13, a circuit board 1 with excellent adhesion to the circuit pattern 20 can be provided.

[0039] There is no particular upper limit to the oxygen atom content of the modified portion 15 relative to the average value of the oxygen atom content of the substrate region 13. On the other hand, if the difference in oxygen atom content between the substrate region 13 and the modified portion 15 is excessively large, the overall strength of the base material 10 may decrease. If the strength of the base material 10 is important, the oxygen atom content of the modified portion 15 can be, for example, 500% or less, preferably 200% or less, of the average value of the oxygen atom content of the substrate region 13.

[0040] In the modified portion 15, the oxygen atom content may gradually decrease from the main surface 10A side to the substrate region 13 side. Furthermore, the oxygen atom content of the base material 10 may gradually increase from the interior side of the base material 10 toward the main surface 10A side containing the modified portion 15. This suppresses abrupt fluctuations in the oxygen atom content within the base material 10. This means that the structure of the base material 10 between the modified portion 15 and the substrate region 13 changes gradually. This allows the base material 10, including the modified portion 15 and the substrate region 13, to have a more integrated structure. For example, if the oxygen atom content between the modified portion 15 and the substrate region 13 changes abruptly, the mechanical properties of the base material 10 (e.g., hardness) may also change abruptly due to the structural change at the point of change. Stress tends to concentrate at such points of abrupt change. On the other hand, a gradual change in oxygen atom content reduces stress concentration, and damage to the base material 10 caused by such stress concentration can be suppressed.

[0041] The thickness T2 of the modified portion 15, measured along a line segment passing through the center of the width direction of the circuit pattern 20 and along the thickness direction Y of the substrate 10, may be smaller than the thickness T1 of the circuit pattern 20 along the same line segment (see Figure 1). The modified portion 15 may slightly increase the dielectric constant of the substrate 10. On the other hand, by making the thickness T2 of the modified portion 15 smaller than the thickness T1 of the circuit pattern 20, the increase in the dielectric constant of the substrate 10 due to the presence of the modified portion 15 can be suppressed.

[0042] The thickness T2 of the modified portion 15, measured along a line segment passing through the center of the width direction of the circuit pattern 20 and along the thickness direction Y of the substrate 10, may be 5% or less, 3% or less, or 1% or less of the thickness T1 of the circuit pattern 20 on the same line segment. Note that the thickness T2 of the modified portion 15 is a dimension obtained by calculating the distance from M1 to M2 obtained in the line analysis described above. On the other hand, the thickness T1 of the circuit pattern 20 is the thickness of the circuit pattern 20 on the line segment on which the line analysis was performed, as measured from the TEM image. For example, when the modified portion 15 is formed by a method including light irradiation, as described later, the molecular main chain and / or side chains of the resin material in the modified portion 15 may be cut during the formation of the modified portion 15. Therefore, if the thickness T2 of the modified portion 15 is excessively large, the area in which the molecular main chain and / or side chains of the resin material are cut will be large, and the strength of the modified portion 15 may decrease. In some cases, such a decrease in strength may cause the circuit pattern 20 placed on the modified portion 15 to peel off from the substrate 10 together with the modified portion 15. On the other hand, if the thickness T2 of the modified portion 15 is less than or equal to the above value, the decrease in strength of the modified portion 15 is suppressed, and the circuit pattern 20 can be suitably held on the substrate 10.

[0043] On the other hand, if emphasis is placed on improving the adhesion of the circuit pattern 20 by the modified portion 15, the lower limit of the thickness T2 of the modified portion 15 may be, for example, 10 nm or more, or 15 nm or more. Alternatively, the lower limit of the thickness T2 of the modified portion 15 may be 0.05% or more, or 0.1% or more, of the thickness T1 of the circuit pattern 20.

[0044] As shown in FIG. 1, in a plan view, the modified portion 15 may extend from a region overlapping the circuit pattern 20 to a region not overlapping the circuit pattern 20. In a plan view, the modified portion 15 may extend from a region inside the edge 21 of the circuit pattern 20 to a region outside the edge 21 of the circuit pattern 20. The edge 151 of the modified portion 15 may be located outside the edge 21 of the circuit pattern 20. The modified portion 15 includes a first modified region 153 overlapping the circuit pattern 20 in a plan view, and a second modified region 155 continuous from the first modified region 153 and extending outside the edge 21 of the circuit pattern 20. The unmodified portion 17 may be adjacent to the second modified region 155 between adjacent circuit patterns 20. That is, in a plan view, between adjacent circuit patterns 20, the second modified region 155 and the unmodified portion 17 may exist. Even in such a structure, the presence of the unmodified portion 17 between the circuit patterns 20 can suppress the occurrence of migration between the circuit patterns 20.

[0045] The width W1 of the unmodified portion 17 located between adjacent circuit patterns 20 may be 10 μm or more, and preferably 15 μm or more. For example, the width W1 of the unmodified portion 17 may be 30% or more, or 60% or more of the distance D between adjacent circuit patterns 20. When the width W1 of the unmodified portion 17 is not less than the above value, the occurrence of migration between adjacent circuit patterns 20 can be preferably suppressed.

[0046] The distance D between the circuit patterns 20 can be measured as the distance from the edge 21 of one circuit pattern 20 to the edge 21 of the other circuit pattern 20 in a cross-sectional TEM image including the cross-sections of two adjacent circuit patterns 20. The width W1 of the unmodified portion 17 can be measured as the distance from the edge 151 of the modified portion 15 overlapping one circuit pattern 20 to the edge 151 of the modified portion 15 overlapping the other circuit pattern 20. Specifically, it can be measured by the following procedure.

[0047] First, a cross-section parallel to the thickness direction Y of the base material 10 is cut out to obtain a measurement sample in which the cross-section of the circuit board 1 is exposed. For example, the cross-section may be a surface cut so that the cross-sections of two adjacent circuit patterns approaching each other are exposed. Next, the cross-section of the measurement sample is photographed with a transmission electron microscope (TEM) to obtain a cross-section TEM image. By observing the obtained cross-section TEM image, the distance D between the circuit patterns 20 can be measured. Further, in the same manner as the measurement of the oxygen atom content of the base material 10 described above, EDX analysis is performed using the cross-section TEM image, and line analysis is performed along the thickness direction Y. Specifically, similar line analysis is performed at a plurality of locations across between adjacent circuit patterns 20, and by confirming the presence of the modified portion 15 in the surface region 11 of the base material 10, the position of the edge 151 of the modified portion 15 can be determined. For example, line analysis is performed at intervals of 1 μm in width from the edge 21 of the circuit pattern 20 in plan view toward the other adjacent circuit pattern 20 side, and the point where the result that the thickness T2 of the modified portion 15 becomes 1 nm or less is obtained can be set as the edge 151 of the modified portion 15. Similarly, the position of the edge 151 of the other adjacent modified portion 15 is specified through the non-modified portion 17. Thereby, the distance between the edges 151 of the adjacent modified portions 15 can be calculated as the width W1 of the non-modified portion 17.

[0048] (Second Embodiment) FIG. 2 is a cross-sectional view schematically showing a circuit board 1A according to the second embodiment of the present disclosure. As shown in the figure, in plan view, the edge 151 of the modified portion 15 and the edge 21 of the circuit pattern 20 may overlap. For example, in plan view, the outer contour of the modified portion 15 and the outer contour of the circuit pattern 20 may coincide. Note that the edge 151 of the modified portion 15 and the edge 21 of the circuit pattern 20 do not necessarily coincide over the entire circumference of the outer contour of the modified portion 15, and may have a portion where they do not coincide. In cross-sectional view, the width of the modified portion 15 and the width of the circuit pattern 20 may be the same. In such an embodiment, the modified portion 15 may have a first modified region 153 that overlaps the circuit pattern 20 in plan view, while not having a second modified region 155 that does not overlap the circuit pattern 20.

[0049] In this configuration, in a plan view, an unmodified portion 17 exists between adjacent circuit patterns 20, while a modified portion 15 does not necessarily exist. For example, in a plan view, the unmodified portion 17 may extend over the entire region between adjacent circuit patterns 20. With such a structure, in a plan view, the region between adjacent circuit patterns 20 can be made a region with poor hydrophilicity. This suppresses the leaching of metal from the circuit patterns 20. Therefore, the occurrence of migration between circuit patterns 20 can be more effectively suppressed.

[0050] (Third Embodiment) Figure 3 is a schematic cross-sectional view showing a circuit board 1B according to the third embodiment of the present disclosure. In a plan view, the circuit pattern 20 may partially overlap with the unmodified portion 17. For example, in a plan view, the unmodified portion 17 may extend from a region outside the edge 21 of the circuit pattern 20 to a region inside the edge 21. The edge 151 of the modified portion 15 may be located in a region inside the edge 21 of the circuit pattern 20. In other words, the edge 21 of the circuit pattern 20 may be located in a region outside the edge 151 of the modified portion 15. The unmodified portion 17 adjacent to the modified portion 15 may have a region 27 that overlaps with the circuit pattern 20. In a plan view, the circuit pattern 20 may include a first circuit pattern region 25 that overlaps with the modified portion 15 and a second circuit pattern region 27 that overlaps with the unmodified portion. The second circuit pattern region 27 may extend in a strip-like manner along the edge 21 of the circuit pattern 20. The second circuit pattern region 27 may extend continuously along the edge 21 of the circuit pattern 20, or it may exist intermittently.

[0051] With this structure, the modified portion 15 is located in the region inside the edge 21 of the circuit pattern 20, and there is no modified portion 15 that extends outside the edge 21 of the circuit pattern 20 on the substrate 10. In other words, there is no modified portion 15 with excellent hydrophilicity around the circuit pattern 20, and the unmodified portion 17 extends from the region inside the edge 21 of the circuit pattern 20 to the region between adjacent circuit patterns 20. In a plan view, there is an unmodified portion 17 with poor hydrophilicity in the region that overlaps with the edge 21 of the circuit pattern 20. As a result, the leaching of metal from the edge 21 of the circuit pattern 20 is suppressed, and the occurrence of migration between adjacent circuit patterns 20 can be suppressed even more effectively.

[0052] As shown in Figure 3, in a cross-sectional view, the second circuit pattern region 27 that overlaps with the unmodified portion 17 may be located on both edges of the circuit pattern 20. In other words, in a cross-sectional view, one circuit pattern 20 may have two second circuit pattern regions 27. The second circuit pattern region 27 may be located on both sides of the first circuit pattern region 25. With this structure, the leaching of metal from both edges of the circuit pattern 20 can be suppressed, and the deterioration of the circuit pattern 20 can be suppressed.

[0053] In the circuit pattern 20, the width W2 of the first circuit pattern region 25 that overlaps with the modified portion 15 may be larger than the width W3 of the second circuit pattern region 27 that overlaps with the unmodified portion 17. Here, the width W3 of the second circuit pattern region 27 is the width W3 of one second circuit pattern region 27 in the circuit pattern 20. As shown in Figure 4, the width W3 of the second circuit pattern region 27 can also be understood as the distance from the edge 151 of the modified portion 15 to the edge 21 of the circuit pattern 20. Because the width W2 of the first circuit pattern region 25 that overlaps with the modified portion 15 is larger than the width W3 of one second circuit pattern region 27 that overlaps with the unmodified portion 17, the modified portion 15 and the circuit pattern 20 can overlap over a wide area. With such a modified portion 15, a circuit board 1 can be obtained in which the circuit pattern 20 has excellent adhesion to the substrate 10.

[0054] The width W2 of the first circuit pattern region 25 and the width W3 of the second circuit pattern region 27 can be measured by acquiring a cross-sectional TEM image of the circuit board 1 and performing EDX analysis on the cross-sectional TEM image. In short, the width W2 of the first circuit pattern region 25 and the width W3 of the second circuit pattern region 27 can be measured by determining the edge 21 of the circuit pattern 20 from the cross-sectional TEM image and determining the edge 151 of the modified portion 15 by EDX analysis of the cross-sectional TEM image. Specifically, the measurement can be performed by the following procedure.

[0055] First, a cross section parallel to the thickness direction Y of the substrate 10 is cut out to obtain a measurement sample in which the cross section of the circuit board 1 is exposed. For example, the cross section may be a plane cut so as to expose the cross sections of two adjacent circuit patterns that are close to each other. Next, the cross section of the measurement sample is photographed with a transmission electron microscope (TEM) to obtain a cross-sectional TEM image. The position of the edge 21 of the circuit pattern 20 (see Figure 4) is determined by observing the obtained cross-sectional TEM image. Furthermore, in the same manner as the measurement of the oxygen atom content of the substrate 10 described above, EDX analysis is performed using the cross-sectional TEM image to perform line analysis along the thickness direction Y. For example, the line analysis may be performed along a direction that is parallel to the thickness direction Y and perpendicular to the direction of extension of the circuit pattern on the plane cut so as to expose the cross sections of two adjacent circuit patterns that are close to each other. Specifically, by performing similar line analysis at multiple locations in the region where the substrate 10 and the circuit pattern 20 overlap in a plan view, and investigating the presence of the modified portion 15 on the surface region 11 of the substrate 10, the position of the edge 151 of the modified portion 15 can be determined. For example, the edge 151 of the modified portion 15 can be determined by performing line analysis at 1 μm intervals from the point containing the modified portion 15 that overlaps with the circuit pattern 20 in a plan view toward the edge 21 of the circuit pattern 20, and obtaining a result where the thickness T2 (see Figure 1) of the modified portion 15 is 1 nm or less. W2 of the first circuit pattern region 25 can be calculated as the distance from one edge 151 of the modified portion 15 to the other edge 151. Similarly, W3 of the second circuit pattern region 27 can be calculated as the distance from the edge 151 of the modified portion 15 to the edge 21 of the circuit pattern 20.

[0056] Figure 4 is a schematic enlarged cross-sectional view showing portion A of the circuit board 1B shown in Figure 3. In plan view, the circuit pattern 20 may overlap with the unmodified portion 17 by a predetermined width W3. The width W3 of the region of the circuit pattern 20 that overlaps with the unmodified portion 17 (second circuit pattern region 27) may be greater than the thickness T3 of the circuit pattern 20 at the boundary between the first circuit pattern region 25 and the second circuit pattern region 27. The thickness T3 of the circuit pattern 20 may be a value measured from a TEM image. The circuit pattern 20 may extend outward from the edge 151 of the modified portion 15 by a width W3 greater than the thickness T3 of the circuit pattern 20 on the edge 151 of the modified portion 15. By having the second circuit pattern region 27 with such a width W3, the modified portion 15 is sufficiently covered by the circuit pattern 20. This effectively suppresses the leaching of metal from the circuit pattern 20 and the occurrence of migration caused by such leaching.

[0057] For example, the width W3 of the second circuit pattern region 27 may be 105% or more, 130% or more, or 150% or more of the thickness T3 of the circuit pattern 20 at the boundary between the first circuit pattern region 25 and the second circuit pattern region 27. If the width W3 of the second circuit pattern region 27 is greater than or equal to the above values, migration may be suitably suppressed. Furthermore, if emphasis is placed on improving the adhesion between the circuit pattern 20 and the substrate 10 due to the modified portion 15, the width W3 of the second circuit pattern region 27 may be 300% or less, or 200% or less, of the thickness T3 of the circuit pattern 20 at the boundary between the first circuit pattern region 25 and the second circuit pattern region 27.

[0058] [Method for Manufacturing a Circuit Board] An exemplary method for manufacturing a circuit board according to the present disclosure will be described below. The method may include a surface treatment step of forming a modified portion 15 on a substrate 10, which includes a main surface 10A on which a circuit pattern 20 is formed, and a plating step of forming a circuit pattern on the main surface 10A.

[0059] The surface treatment step includes irradiating a predetermined area of ​​the main surface 10A with light to increase the oxygen atom content in the predetermined area, thereby forming a modified portion 15 with a higher oxygen atom content than the substrate region 13.

[0060] The surface treatment step includes irradiating the substrate 10 with light from the main surface 10A side, where the circuit pattern 20 will be formed in the subsequent plating step. In other words, the main surface 10A may be irradiated with light in the surface treatment step. When irradiating with light, the irradiation area may be patterned so that only a predetermined area is irradiated with light. The patterning method is not particularly limited, and known methods can be used. For example, the irradiation area on the main surface 10A of the substrate may be patterned by irradiating with light through a known exposure mask, such as a quartz plate on which a thin chromium film is formed. Alternatively, the irradiation area may be patterned on the main surface 10A by masking a predetermined area before light irradiation.

[0061] Light irradiation is carried out in an oxygen-containing atmosphere. The oxygen-containing atmosphere may be, for example, air or an inert atmosphere containing oxygen. Examples of inert atmospheres include nitrogen and argon. When light is irradiated onto a predetermined area of ​​the substrate 10 under an oxygen-containing atmosphere, the molecular main chain and / or side chains of the resin on the surface area 11 of the substrate 10 are cleaved in the irradiated area, and hydrogen atoms are separated. Subsequently, functional groups such as oxo groups, hydroxyl groups, alkoxy groups, carboxyl groups, and / or alkoxycarbonyl groups are generated by the surrounding oxygen atoms. The generation of such functional groups can increase the oxygen atom content of the irradiated area. As a result, a modified portion 15 with a relatively high oxygen atom content is formed in the irradiated area. The presence of such a modified portion 15 allows for the formation of a circuit pattern 20 on the substrate 10 without the need to roughen the main surface 10A or use a bonding agent.

[0062] The surface treatment step may further include heating the substrate 10. In addition to light irradiation treatment of the main surface 10A, the surface treatment step may further include heat treatment of the substrate 10. Heating may be performed simultaneously with and / or after light irradiation. Preferably, heating is performed simultaneously with light irradiation. By performing heating in conjunction with light irradiation, a dehydration condensation reaction occurs of the molecules having oxygen-containing groups generated by light irradiation. The substrate 10 obtained through the generation of oxygen-containing groups by light irradiation and the subsequent dehydration condensation reaction by heat treatment can greatly contribute to improving the adhesion of the circuit pattern 20. Although not limited to a specific theory, it is presumed that such a dehydration condensation reaction causes the molecules of the modified portion 15 that were cleaved by light irradiation to recombine via bridging oxygen atoms, thereby increasing the oxygen atom content of the modified portion 15. Furthermore, the modified portion 15 may contain bridging oxygen atoms in the polymer structure. The bridging oxygen atoms contained in the modified portion 15 contribute to improving the adhesion of the circuit pattern 20 on the main surface 10A. Thus, by further including a heat treatment in the surface treatment step, it becomes possible to suitably obtain the effect of improving the adhesion strength of the circuit pattern 20 in the modified portion 15.

[0063] The light irradiated onto the substrate 10 can be, for example, far-ultraviolet rays, ultraviolet rays, near-ultraviolet rays, infrared rays, electromagnetic waves such as X-rays and gamma rays, as well as electron beams, proton beams, neutron beams, plasma streams, etc. Considering the efficiency of cutting the molecular chains of the resin material constituting the substrate 10 and / or forming functional groups, and the availability of the irradiation device, the irradiated light is more preferably ultraviolet rays or electron beams.

[0064] Masking may be carried out using known materials capable of protecting the substrate from the irradiated light. For example, the substrate 10 may be masked using various materials such as polycarbonate film, polyester film, acrylic film, carbon black film, epoxy resin film, and metal plate.

[0065] After the surface treatment step, the obtained substrate 10 is then subjected to a plating step. In the plating step, a metal plating film may be formed on the main surface 10A of the substrate 10 as a circuit pattern by a known plating method.

[0066] For example, the substrate 10 obtained in the surface treatment step may be subjected to electroless plating. For example, the type of metal is not particularly limited, and various electroless plating treatments can be performed, such as electroless nickel plating, electroless copper plating, or electroless silver plating. Furthermore, the electroless plating treatment may be carried out using known plating methods.

[0067] Furthermore, electroless plating may be performed on the metal plating film formed by electroless plating. Alternatively, electroplating may be continuously performed on the metal plating film formed by electroless plating. This makes it possible to form a circuit pattern 20 having multiple metal plating layers on the substrate 10.

[0068] The embodiments of this disclosure have been described above, but these are merely typical examples. Those skilled in the art will readily understand that this disclosure is not limited thereto, and various embodiments are conceivable without altering the essence of this disclosure.

[0069] Furthermore, the above-described embodiment of the present disclosure includes the following preferred embodiments: <1> A circuit board comprising a substrate and a plurality of adjacent circuit patterns arranged on the main surface of the substrate, wherein the substrate has a surface region including the main surface and a substrate region other than the surface region, the surface region includes a modified portion having a higher oxygen atom content than the substrate region and an unmodified portion which is the portion other than the modified portion, each of the plurality of circuit patterns is arranged on the modified portion, and in a plan view from the main surface side, the unmodified portion is located between the adjacent circuit patterns. <2> The circuit board according to <1>, wherein in a plan view, the modified portion includes a first modified region overlapping with the circuit pattern and a second modified region extending outward from the first modified region beyond the edge of the circuit pattern. <3> The circuit board according to <1>, wherein in a plan view, the edge of the modified portion overlaps with the edge of the circuit pattern. <4> The circuit board according to <1>, wherein in the plan view, the unmodified portion extends to a region inside the edge of the circuit pattern. <5> The circuit board according to <4>, wherein in the plan view, the circuit pattern comprises a first circuit pattern region overlapping with the modified portion and a second circuit pattern region overlapping with the unmodified portion, and the width of the second circuit pattern region is greater than the thickness of the circuit pattern at the boundary between the first circuit pattern region and the second circuit pattern region. <6> The circuit board according to claim <4> or <5>, wherein, viewed from the thickness direction of the circuit pattern, the circuit pattern comprises a first circuit pattern region overlapping with the modified portion and a second circuit pattern region overlapping with the unmodified portion, and the width of the second circuit pattern region is smaller than the width of the first circuit pattern region. <7> The circuit board according to any one of <1> to <6>, wherein in a cross-sectional view, the thickness of the modified portion is smaller than the thickness of the circuit pattern. <8> The circuit board according to any one of <1> to <7>, wherein, in a cross-sectional view, the thickness of the modified portion is 1% or less of the thickness of the circuit pattern.

[0070] A demonstration test was conducted in accordance with this disclosure.

[0071] (Example 1) A sheet material of epoxy resin (manufactured by Panasonic Industries, Ltd., R1661) measuring 100 mm x 100 mm x 0.1 mm was used as the substrate. UV irradiation was performed only on two separated irradiation areas on the main surface of the substrate via an exposure mask (manufactured by Toyo Precision Industries Co., Ltd.). The distance between the two irradiation areas was 50 μm. UV irradiation was performed in air at a temperature of 25°C using a UV irradiation device (manufactured by Koto Electric Co., Ltd., KOL4-200). The UV irradiance was 8.5 mW / cm and the irradiation time was 2 minutes. As a result, modified areas were formed only on the main surface of the substrate in two adjacent, separated irradiation areas, and a substrate with an unmodified area between the modified areas was obtained.

[0072] After UV irradiation, a plating process was performed to form a circuit pattern on the substrate surface. Specifically, the substrate was degreased for 2 minutes using an alkaline degreasing solution, then immersed in a Pd-based catalyst solution for 2 minutes to impart a Pd catalyst to the substrate, and finally immersed in a DMAB-based accelerator solution for 2 minutes to activate the substrate. Subsequently, electroless copper plating was performed on the substrate surface using a Rochelle salt-based electroless Cu plating solution. The plating formed a circuit pattern with a width of 50 μm and a thickness of approximately 10 μm on the modified portion formed by UV irradiation. After that, heat treatment was performed at 200°C for 60 minutes using a constant temperature oven (ESPEC, SPHH-102). As a result, a circuit board was obtained in which the modified portion included adjacent modified portions separated by an unmodified portion, and the circuit pattern was formed on the modified portion. The distance between adjacent circuit patterns separated by an unmodified portion was 50 μm.

[0073] (Example 2) A circuit board was fabricated in the same manner as in Example 1, except that a 100 mm x 100 mm x 0.1 mm sheet material of cycloolefin polymer (COP) (manufactured by Zeon Corporation, Zeonor® ZF-16) was used as the base material.

[0074] (Comparative Example 1) As a comparative example, a circuit board was fabricated in which a modified portion was formed over the entire main surface of the substrate by UV irradiation of the entire main surface of the substrate. Specifically, using the same sheet material as in Example 1, UV irradiation was performed on the entire main surface of the substrate in air at a temperature of 25°C using a UV irradiation device (KOL4-200, manufactured by Koto Electric Co., Ltd.). The UV irradiance was 8.5 mW / cm and the irradiation time was 2 minutes. As a result, a substrate in which a modified portion was formed over the entire main surface of the substrate was obtained.

[0075] After UV irradiation, the substrate was degreased for 2 minutes using an alkaline degreasing solution, then immersed in a Pd-based catalyst solution for 2 minutes to impart a Pd catalyst to the substrate, and finally immersed in a DMAB-based accelerator solution for 2 minutes to activate the substrate. Subsequently, electroless copper plating was performed on the entire surface of the substrate using a Rochelle salt-based electroless Cu plating solution. After that, heat treatment was performed at 200°C for 60 minutes using a constant temperature oven (ESPEC, SPHH-102). After heat treatment, the circuit pattern on the substrate was masked, and the copper plating in areas other than the circuit pattern was removed with dilute sulfuric acid. After that, the masking material was removed, and copper sulfate plating was performed to form a circuit pattern with a width of 50 μm and a thickness of approximately 10 μm. As a result, a circuit board was obtained in which the modified portion was included over the entire main surface of the substrate, and the circuit patterns were adjacent to each other at a distance from each other on the main surface. The distance between adjacent circuit patterns was 50 μm.

[0076] (Comparative Example 2) A circuit board was fabricated in the same manner as in Comparative Example 1, except that the same sheet material as in Example 2 was used as the base material.

[0077] (TEM-EDX analysis) TEM-EDX analysis was performed on the circuit boards of the examples and comparative examples to confirm the presence or absence of modified areas. First, a cross section parallel to the thickness direction Y of the substrate was cut out to obtain a measurement sample in which the cross section of the circuit pattern was exposed. Next, a cross-section of the measurement sample was photographed using a field emission transmission electron microscope (FE-TEM) (FE-TEM / EDX (JEOL JEM-F200 / Noran system 7)). Line analysis was then performed on the obtained TEM image using energy-dispersive X-ray (EDX) analysis along a line segment passing through the center of the circuit pattern in the width direction and parallel to the thickness direction Y. From the results of the line analysis, it was confirmed that in both the example and comparative example circuit boards, an increase in oxygen atom content was observed in the surface region including the main surface of the substrate, confirming the formation of a modified area. Similarly, line analysis was also performed along a line segment parallel to the thickness direction Y at the midpoint between adjacent circuit patterns. In the circuit boards of Comparative Example 1 and Comparative Example 2, a modified area was confirmed between adjacent circuit patterns. On the other hand, in the circuit boards of Example 1 and Example 2, no increase in oxygen atom content was observed between adjacent circuit patterns, confirming that no modified area was formed.

[0078] (Migration Test) Five circuit boards each of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were prepared, and a migration test was performed on each circuit board. The test was performed using an insulation reliability measurement system SIR (manufactured by Kusumoto Chemical Co., Ltd.). Specifically, under conditions of a temperature of 85°C and a humidity of 85%, 15V was applied to the circuit pattern, and the decrease in resistance was monitored. The time until the resistance value became 10% of the initial resistance value at the start of voltage application was recorded. The migration test results obtained for each circuit board of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are shown in Table 1. Note that the test results (time) shown in Table 1 are the average values ​​of the test results obtained for each of the five circuit boards.

[0079]

[0080] As is clear from the results shown in Table 1, the circuit boards of Example 1 and Example 2 showed suppressed resistance reduction compared to Comparative Example 1 or Comparative Example 2, respectively, which used the same base material. This means that the circuit boards of the examples can maintain their insulation for a longer period of time compared to the circuit boards of the comparative examples. In other words, the above results confirm that migration is suppressed in the circuit boards of the present disclosure compared to the circuit boards of the comparative examples. Therefore, compared to the circuit boards of the comparative examples, in which modified portions are formed even between circuit patterns, the circuit boards of the present disclosure are able to suppress migration in the circuit patterns by providing unmodified portions between circuit patterns.

[0081] Furthermore, the effects described above are merely examples. Therefore, this disclosure is not limited to the matters described above, and there may be additional effects.

[0082] 1, 1A, 1B: Circuit board 10: Substrate 10A: Main surface 11: Surface area 13: Substrate area 15: Modified portion 151: Edge of modified portion 153: First modified area 155: Second modified area 17: Unmodified portion 20: Circuit pattern 21: Edge of circuit pattern 25: First circuit pattern area 27: Second circuit pattern area

Claims

1. A circuit board comprising a substrate and a plurality of adjacent circuit patterns arranged on the main surface of the substrate, wherein the substrate has a surface region including the main surface and a substrate region other than the surface region, the surface region includes a modified portion having a higher oxygen atom content than the substrate region and an unmodified portion which is the portion other than the modified portion, each of the plurality of circuit patterns is arranged on the modified portion, and in a plan view from the main surface side, the unmodified portion is located between the adjacent circuit patterns.

2. The circuit board according to claim 1, wherein, in a plan view, the modified portion includes a first modified region that overlaps with the circuit pattern and a second modified region that extends from the first modified region outward beyond the edge of the circuit pattern.

3. The circuit board according to claim 1, wherein, in the plan view, the edge of the modified portion overlaps with the edge of the circuit pattern.

4. The circuit board according to claim 1, wherein, in the plan view, the unmodified portion extends to a region inward from the edge of the circuit pattern.

5. The circuit board according to claim 4, wherein, in a plan view, the circuit pattern comprises a first circuit pattern region overlapping with the modified portion and a second circuit pattern region overlapping with the unmodified portion, and the width of the second circuit pattern region is greater than the thickness of the circuit pattern at the boundary between the first circuit pattern region and the second circuit pattern region.

6. The circuit board according to claim 4 or 5, wherein, viewed from the thickness direction of the circuit pattern, the circuit pattern comprises a first circuit pattern region overlapping with the modified portion and a second circuit pattern region overlapping with the unmodified portion, and the width of the second circuit pattern region is smaller than the width of the first circuit pattern region.

7. The circuit board according to any one of claims 1 to 6, wherein, in a cross-sectional view, the thickness of the modified portion is smaller than the thickness of the circuit pattern.

8. The circuit board according to any one of claims 1 to 7, wherein, in a cross-sectional view, the thickness of the modified portion is 1% or less of the thickness of the circuit pattern.

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