Circuit board

Abstract

To provide a circuit board that makes it difficult for electronic components to detach from the circuit board. [Solution] The circuit board is a circuit board having at least one pair of second terminals, wherein a bonding material is placed on the second terminals, and the second terminals and the bonding material are placed in a recess formed in a resin layer, surrounded by the resin layer, and when the sum of the thicknesses of the second terminals and the bonding material is dimension h2, dimension h2 is 1 μm or more and 10 μm or less, and when the width of the recess in the resin layer is dimension d2, dimension d2 is 2 μm or more and 30 μm or less, metal wiring made of a sintered body of metal particles is removed from the second terminals, and the inner surface of the recess has a tapered shape.

Description

Technical Field

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

Background Art

[0002] Electronic components are often mounted on a circuit board via solder. When an electronic component is mounted on a circuit board using solder, solder balls may be formed in the reflow process, and there has been a problem that the pair of terminals of the electronic component may be short-circuited by the solder balls. In order to solve such a problem, a technique of forming protrusions between a pair of terminals has been disclosed (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, with the miniaturization of electronic devices, the miniaturization of electronic components used in electronic devices has also progressed. For example, there is also a demand for a mounting substrate in which electronic components of about 20 μm, such as micro LEDs, are mounted on a circuit board. However, the smaller the electronic component, the smaller the solder needs to be, but it is difficult to control the amount of solder, and there may be variations in the amount of solder to be joined. Therefore, variations appear in the solder size, the balance of the force for holding the electronic component is lost, and stress is often applied to the solder after joining, resulting in insufficient strength. As a result, there has been a problem that when a physical impact is applied, the electronic component is likely to be peeled off from the circuit board.

[0005] An object of the present disclosure is to provide a circuit board capable of making it difficult for an electronic component to be peeled off from the circuit board.

Means for Solving the Problems

[0006] The circuit board according to this disclosure is a circuit board having at least one pair of second terminals, wherein a bonding material is placed on the second terminals, and the second terminals and the bonding material are placed in a recess formed in a resin layer, surrounded by the resin layer, and when the sum of the thicknesses of the second terminals and the bonding material is dimension h2, dimension h2 is 1 μm or more and 10 μm or less, and when the width of the recess in the resin layer is dimension d2, dimension d2 is 2 μm or more and 30 μm or less, metal wiring made of a sintered body of metal particles is removed from the second terminals, and the inner surface of the recess has a tapered shape.

[0007] The dimension h2 can be larger than the thickness of the resin layer.

[0008] The inner surface of the recess may be wider as it moves away from the substrate.

[0009] The bonding material may contain Sn.

[0010] The resin layer may contain epoxy resin or acrylic resin. [Effects of the Invention]

[0011] According to this disclosure, it is possible to provide a mounting substrate and a circuit board that can prevent electronic components from peeling off the circuit board. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic cross-sectional view showing a mounting substrate according to an embodiment of this disclosure. [Figure 2] This is a schematic plan view showing the positional relationship between the recess and the terminal when the mounting board is viewed from above. [Figure 3] This is a schematic cross-sectional view showing a circuit board according to an embodiment of the present disclosure. [Figure 4] This is a schematic cross-sectional view showing a modified mounting substrate. [Figure 5] This is a schematic cross-sectional view showing a modified mounting substrate. [Figure 6] This is a schematic cross-sectional view showing a modified mounting substrate. [Figure 7] This is a schematic cross-sectional view showing a modified mounting substrate. [Figure 8] This table shows the conditions and test results for the examples and comparative examples. [Modes for carrying out the invention]

[0013] The mounting substrate 1 according to an embodiment of the present disclosure will be described with reference to Figure 1. Figure 1 is a schematic cross-sectional view showing the mounting substrate 1 according to an embodiment of the present disclosure. As shown in Figure 1, the mounting substrate 1 comprises electronic components 2 and a circuit board 3. The mounting substrate 1 is constructed by mounting the electronic components 2 on the circuit board 3 via a bonding material 4.

[0014] The electronic component 2 comprises a main body 6 and a pair of terminals 7 (first terminals). The main body 6 is the component that performs the function of the electronic component 2. The terminals 7 are metal parts formed on the main surface of the main body 6. As the material for the terminals 7, Cu, Ti, Au, Ni, Sn, Bi, P, B, In, Ag, Zn, Pd, Mo, Pt, Cr, or alloys selected from at least two of these materials are used. The electronic component 2 is composed of, for example, a micro-LED. The micro-LED is a component that emits light in response to input from the circuit board 3.

[0015] The circuit board 3 comprises a base material 8, a resin layer 9, and a pair of terminals 10 (second terminals). The base material 8 is the flat main body of the circuit board 3. The resin layer 9 is a resin layer formed on the upper surface of the base material 8. Examples of materials used for the resin layer 9 include epoxy resin, acrylic resin, phenolic resin, melamine resin, urea resin, and alkyd resin. Particularly preferred are epoxy resin and acrylic resin. The terminals 10 are metal parts formed on the main surface of the base material 8. Examples of materials used for the terminals 10 include Ni, Cu, Ti, Cr, Al, Mo, Pt, Au, and alloys selected from at least two of these.

[0016] The bonding material 4 is a member that bonds the terminal 7 of the electronic component 2 and the terminal 10 of the circuit board 3. The bonding material 4 may contain Sn or may be composed of an alloy containing Sn. However, the bonding material 4 is not necessarily limited to those containing Sn. The bonding material 4 may be composed of an alloy containing an element that lowers the melting point of Sn in addition to Sn. Examples of the element that lowers the melting point of Sn include Bi. The bonding material 4 functions as solder. As a result, between the base material 8 and the main body 6, the terminal 10, the bonding material 4, and the terminal 7 are laminated in order from the upper surface of the base material 8. Note that, at this location, soldering is performed after the terminal 10, the bonding material 4, and the terminal 7 are laminated. Therefore, a structure in which the metals of the terminal 10, the bonding material 4, and the terminal 7 are melted and diffused is formed. Such a structure after soldering may be a structure including brittle intermetallic compounds (IMCs). When there are brittle intermetallic compounds, the reliability is likely to decrease. Therefore, the effect of the structure in which the structure of the soldering joint is surrounded by the resin layer 9 becomes more prominent.

[0017] A pair of recesses 11 are formed in the resin layer 9. The recess 11 is constituted by a through hole penetrating the resin layer 9. As a result, the upper surface of the base material 8 is exposed on the bottom side of the recess 11. The recess 11 is rectangular when viewed from the thickness direction of the circuit board 3 (see FIG. 2). The terminal 7, the terminal 10, and the bonding material 4 are arranged in the recess 11 formed in the resin layer 9 and are surrounded by the resin layer 9 on all sides. A slight gap is formed between the terminal 7, the terminal 10, and the bonding material 4 and the inner side surfaces 11a on the four sides of the recess 11.

[0018] Among the resin layer 9, the portion existing between the pair of terminals 7 is referred to as the first portion 9A, and the portion surrounding the electronic component 2 is referred to as the second portion 9B. In the present embodiment, the heights of the first portion 9A and the second portion 9B from the base material 8 are the same. Further, the first portion 9A of the resin layer 9 existing between the pair of terminals 7 contacts the main body 6 of the electronic component 2. Specifically, the upper surface of the first portion 9A of the resin layer 9 contacts the lower surface of the main body 6 of the electronic component.

[0019] Next, referring to FIGS. 1 and 2, the dimensional relationships of each element of the mounting substrate 1 will be described. FIG. 2 is a schematic plan view showing the positional relationship between the recess 11 and the terminal 7 when the mounting substrate 1 is viewed from above. In FIG. 2, the resin layer 9 and the components other than the terminal 7 of the electronic component 2 are omitted.

[0020] The sum of the thicknesses of the terminal 7, the terminal 10, and the bonding material 4 will be described as the dimension h1. At this time, the dimension h1 is preferably 1 μm or more, more preferably 4 μm or more. Also, the dimension h1 is preferably 20 μm or less, more preferably 15 μm or less, and still more preferably 10 μm or less. In one mounting substrate 1, a plurality of combinations of "terminal 7, terminal 10, bonding material 4" are provided, but the dimension h1 related to each combination may be different from each other. In this case, it is preferable that the dimension h1 related to the combination with the highest height measurement result satisfies the above conditions. However, it is sufficient that at least one dimension h1 that satisfies the above conditions exists in the mounting substrate 1. The dimension h1 can be measured by vertically cutting the mounting substrate 1 and observing the cross section by SEM or the like.

[0021] When the width of the terminal 7 is defined as the dimension d1 and the width of the recess 11 of the resin layer 9 is defined as the dimension d2, (dimension d2 - dimension d1) is preferably 10 μm or less, preferably 6 μm or less, and still more preferably 2 μm or less. The lower limit value of (dimension d2 - dimension d1) is not particularly limited, and may be 0 μm as the lower limit value if it does not affect the manufacturing.

[0022] Dimension d1 is preferably 2 μm or more, and more preferably 5 μm or more. Dimension d1 is preferably 20 μm or less, and more preferably 10 μm or less. Dimension d2 is preferably 2 μm or more, and more preferably 7 μm or more. Dimension d2 is preferably 30 μm or less, and more preferably 15 μm or less. The distance between one recess 11 and the other recess 11 is preferably 4 μm or more, and 20 μm or less. Dimensions d1 and d2 can be measured by cutting the mounting substrate 1 parallel to the top surface and observing it with an SEM.

[0023] A single mounting board 1 contains multiple combinations of "terminal 7, recess 11," but the (dimension d2 - dimension d1) for each combination may be different from one another. In this case, it is sufficient that there is at least one (dimension d2 - dimension d1) in the mounting board 1 that satisfies the above conditions. Corner radii may be formed at the corners of the recess 11 in the resin layer 9 and at the corners of the terminals 7 and 10. The corner radii may be set to, for example, 1 μm, 5 μm, or 10 μm.

[0024] As shown in Figure 2, if terminal 7 is a square, the dimension of one of its sides corresponds to dimension d1. If terminal 7 is a rectangle, the dimension of the shorter side corresponds to dimension d1. If terminal 7 is circular, the diameter corresponds to dimension d1. If terminal 7 is elliptical, the minor axis corresponds to dimension d1. If terminal 7 is a polygon with five or more sides, the distance between each vertex and the side opposite that vertex is measured, and the shortest distance is taken as dimension d1. The method for determining dimension d2 according to the shape of the recess 11 is the same as for dimension d1.

[0025] As shown in Figure 1, the height of the first portion 9A of the resin layer 9 located between the pair of terminals 7 is defined as dimension R1, and the height of the second portion 9B of the resin layer 9 surrounding the electronic component 2 is defined as dimension R2. In this case, dimension R1 is preferably 2 μm or more, and more preferably 4 μm or more. Dimension R1 is preferably 20 μm or less, and more preferably 10 μm or less. Dimension R2 is preferably 3 μm or more, and more preferably 4 μm or more. Dimension R2 is preferably 30 μm or less, and more preferably 10 μm or less.

[0026] In the example shown in Figure 1, dimensions R1 and R2 are set to the same value. In this case, the resin layer 9 can be easily formed. However, dimensions R1 and R2 may be set to different values. As shown in Figure 6, dimension R1 may be set to a smaller value than dimension R2. In this case, the upper surface of the second portion 9B may be positioned higher than the lower surface of the main body portion 6 of the electronic component 2.

[0027] Next, the manufacturing method of the mounting board 1 and the configuration of the circuit board 3 during the manufacturing process will be described.

[0028] First, a circuit board 3 is prepared as shown in Figure 3. In this state, the bonding material 4 is placed on the terminals 10. Since this bonding material 4 is in a state prior to being bonded to the electronic components 2, it is at least thicker than the bonding material 4 in the mounted substrate 1 state shown in Figure 1. This bonding material 4 may be a metal containing Sn that becomes a low-temperature solder, and any microstructure is acceptable as long as its overall composition has a low melting point. For example, at the stage of flowing the circuit board 3, the bonding material 4 may have a laminated structure having a layer of Sn and a layer of another metal such as Bi. Alternatively, it may be preheated so that Sn and the other metal are alloyed, and the circuit board 3 is then flowed.

[0029] In this state, the terminal 10 and the bonding material 4 are placed in the recess 11 formed in the resin layer 9, and are surrounded by the resin layer 9. If the sum of the thicknesses of the terminal 10 and the bonding material 4 is the dimension h2, then the dimension h2 is preferably 1 μm or more, and more preferably 3 μm or more. The dimension h2 is preferably 20 μm or less, and more preferably 10 μm or less.

[0030] The electronic component 2 is placed on the circuit board 3. At this time, the pair of terminals 7 of the electronic component 2 are placed on the pair of bonding materials 4. Soldering is performed by heating the circuit board 3 and the electronic component 2 in this state. The heating method can be any of the following: reflow soldering, which is heated in a furnace; thermocompression soldering, which is heated while pressing the electronic component 2; or photothermal soldering, which is heated by applying light. A combination of these methods may also be used. As a result, the electronic component 2 is mounted on the circuit board 3, and the mounted board 1 is completed.

[0031] The operation and effects of the mounting board 1 and circuit board 3 according to this embodiment will be described below.

[0032] In the mounting substrate 1, terminals 7, terminals 10, and bonding material 4 are placed within recesses 11 formed in the resin layer 9, and are surrounded by the resin layer 9. This provides an impact-absorbing structure around the joint portion using the resin layer 9. Furthermore, by setting the sum of the thicknesses of terminals 7, terminals 10, and bonding material 4, dimension h1, to 1 μm or more and 20 μm or less, the joint portion can be made less prone to breakage. In addition, by setting the value of (dimension d2 - dimension d1) to 10 μm or less, the electronic component 2 can be made less likely to peel off the circuit board 3 when the mounting substrate 1 is subjected to physical impact.

[0033] The first portion 9A of the resin layer 9 located between the pair of terminals 7 may be in contact with the main body 6 of the electronic component 2. In this case, the lower surface of the main body 6 of the electronic component 2 is in contact with and supported by the first portion 9A of the resin layer 9, so that even if the mounting substrate 1 is subjected to physical impact, less force is applied to the bonding material 4, making it less likely for the electronic component 2 to peel off the circuit board 3.

[0034] If the height of the first portion 9A of the resin layer 9 between the pair of terminals 7 is defined as dimension R1, and the height of the second portion 9B of the resin layer 9 surrounding the electronic component 2 is defined as dimension R2, then dimension R1 may be smaller than dimension R2. In this case, the main body 6 of the electronic component 2 is supported by being surrounded by the second portion 9B of the surrounding resin layer 9, so even if the mounting board 1 is subjected to physical impact, less force is applied to the bonding material 4, making it less likely for the electronic component 2 to peel off the circuit board 3.

[0035] The circuit board 3 is a circuit board 3 having at least one pair of terminals 10, wherein a bonding material 4 is placed on the terminals 10, and the terminals 10 and the bonding material 4 are placed in a recess 11 formed in the resin layer 9, and are surrounded by the resin layer 9. When the sum of the thicknesses of the terminals 10 and the bonding material 4 is taken as dimension h2, dimension h2 is 1 μm or more and 20 μm or less, and when the width of the recess 11 in the resin layer 9 is taken as dimension d2, dimension d2 is 2 μm or more and 30 μm or less.

[0036] According to the circuit board 3 of this embodiment, when electronic components 2 are mounted, a mounting board 1 can be obtained that exhibits the same functions and effects as described above.

[0037] This disclosure is not limited to the embodiments described above.

[0038] For example, as shown in Figure 4, a component 20 may be placed between the bonding material 4 and the resin layer 9. This further prevents the electronic component 2 from peeling off the circuit board 3 by providing support with the component 20.

[0039] Furthermore, as shown in Figure 5, a component 20 may be placed between the first portion 9A of the resin layer 9 located between the pair of terminals 7 and the main body 6 of the electronic component 2. This allows the main body 6 of the electronic component 2 to be held by the component 20, thereby improving its strength.

[0040] Furthermore, as shown in Figure 5, the component 20 may be in contact with the main body 6. In this case, the lower surface of the main body 6 of the electronic component 2 can be fixed with the component 20. Therefore, even if the mounting substrate 1 is subjected to physical impact, less force is applied to the bonding material 4, making it less likely for the electronic component 2 to detach from the circuit board 3.

[0041] Furthermore, as shown in Figure 7, the inner surface 11a of the recess 11 may have a tapered shape such that it is wider on the side of the electronic component 2. When thermal shock is applied due to the difference in thermal expansion coefficients between the resin layer 9 and the base material 8, force is applied to the bonding material 4 from the resin layer 9. However, by having a tapered shape on the inner surface 11a of the recess 11, force is less likely to be applied to the bonding material 4 from the resin layer on the electronic component 2 side, making it less likely for the electronic component 2 to detach from the circuit board 3 during thermal shock testing. When defining the width dimension d2 of the recess 11, the width dimension at the upper end of the recess 11 (i.e., the position of the upper surface of the resin layer 9) is defined as dimension d2. In other words, dimension d2 is determined at the point in the recess 11 where the width dimension is largest.

[0042] Furthermore, the height dimension h2 of the bonding material 4 on the circuit board 3 may be greater than the height dimension R2 of the resin layer 9 (see, for example, Figure 3). When the electronic component 2 is mounted, the terminals 7 can be pressed into the bonding material 4 and made to adhere tightly, thus reducing the void between the bonding material 4 and the terminals 7 after bonding. As a result, the bonding material 4 is less likely to break even if the mounted circuit board 1 is subjected to impact, thus improving its strength.

[0043] [Examples] Examples of the mounting substrates relating to this disclosure will be described below. Note that this disclosure is not limited to the following examples.

[0044] First, the mounting substrates for Examples 1 to 11 and Comparative Examples 1 and 2 were fabricated using the following manufacturing method. First, a substrate 8 on which terminals 10 were formed was prepared. A glass epoxy substrate was used as the substrate 8. Cu terminals coated with a Ni film were used as the terminals 10. 100 pairs of terminals 10 were formed on the substrate 8. Next, paired Bi / Sn laminated pads were formed on the terminals 10 as bonding material 4 to the desired thickness. 100 pairs of bonding material 4 were formed on the substrate 8.

[0045] Next, a resin layer 9 was formed on the substrate 8 so as to surround the terminals 10 and the bonding material 4. Epoxy resin was used for this resin layer 9. This resulted in a circuit board 3 as shown in Figure 3. Next, LED chips were placed on the circuit board 3 as electronic components 2. 100 LED chips were mounted on the circuit board 3. Each LED chip had an Au terminal as terminal 7. Next, the mounted substrate 1 in this state was reflowed at 150°C to 190°C. This bonded the circuit board 3 and the electronic components 2. The dimensions and the presence or absence of constituent materials for Examples 1 to 11 and Comparative Examples 1 and 2 are shown in the table in Figure 8.

[0046] The following tests were performed on the mounting substrates of Examples 1 to 11 and Comparative Examples 1 and 2 described above. The obtained mounting substrates were dropped 10 times from a height of 30 cm. Next, the ratio of the number of LED chips remaining after the test to the total number of LED chips on the mounting substrate before the test was determined as the "LED survival rate". The ratio of LED chips that emitted light among the remaining LED chips was determined as the "luminous efficiency of the remaining LEDs". A luminous efficiency of 50% or more was considered acceptable for the remaining LEDs. In addition, the ratio of LED chips that emitted light to the total number of LED chips before the test was determined as the "OK rate after the test". The test results are shown in the table in Figure 8.

[0047] First, in Comparative Example 1, it was confirmed that the dimension h1 was too long, making the joint prone to breaking under impact, resulting in a large number of non-emitting LED chips. In Comparative Example 2, it was confirmed that (dimension d2-dimension d1) was too wide, failing to protect the LED chips from the impact of the test, making the LED chips prone to detaching from the circuit board. In contrast, it was confirmed that Examples 1-11 had a large number of remaining LED chips, and that a high percentage of the remaining LED chips were able to emit light.

[0048] From Example 1, it can be seen that because dimension h1 is low, the variation in the amount of solder applied to the formed joint becomes large, resulting in variations in joint strength, and a slight decrease in luminous efficiency because some solder joints cannot withstand the test. From Examples 2 and 3, it can be seen that when dimension h1 is at an appropriate height, (dimension d2 - dimension d1) becomes smaller, the joint can be protected, and the percentage of OK after testing can be increased. From Example 4, it can be seen that because dimension h1 is higher than in Examples 2 and 3, the joint becomes slightly thinner, and the number of LED chips that can withstand the test decreases slightly. From Example 5, it can be seen that because dimension h1 is higher than in Example 4, the joint becomes slightly thinner, and the number of LED chips that can withstand the test decreases slightly.

[0049] From Example 6, it can be seen that reducing (dimension d2 - dimension d1) protects the joint and increases the percentage of OK after testing. From Examples 7, 8, and 9, (dimension d2 - dimension d1) is larger than in Example 6, but there are many joints in contact with the wall of the recess, and the impact they receive during testing is suppressed by the wall of the recess, so it can be seen that the decrease in luminescence is slightly suppressed. From Example 10, (dimension d2 - dimension d1) is the same as in Example 9, but because dimension h1 is high, the joint becomes elongated and more prone to breaking under impact, so it can be seen that the percentage of OK after testing is slightly lower. From Example 11, it can be seen that good results are obtained in all items. [Explanation of Symbols]

[0050] 1... Mounting board, 2... Electronic component, 3... Circuit board, 4... Bonding material, 6... Main body, 7... Terminal (first terminal), 9... Resin layer, 10... Terminal (second terminal), 11... Recess.

Claims

1. A circuit board having at least one pair of second terminals, The bonding material is placed on the second terminal, The second terminal and the bonding material are arranged in a recess formed in the resin layer, and are surrounded by the resin layer. When the sum of the thicknesses of the second terminal and the bonding material is denoted as dimension h2, dimension h2 is 1 μm or more and 10 μm or less. When the width of the recess in the resin layer is denoted as dimension d2, dimension d2 is 2 μm or more and 30 μm or less. From the second terminal, the metal wiring made of a sintered body of metal particles is removed. The inner surface of the recess has a tapered shape, and is a circuit board.

2. The circuit board according to claim 1, wherein the dimension h2 is greater than the thickness of the resin layer.

3. The circuit board according to claim 1 or 2, wherein the inner surface of the recess widens as it moves away from the substrate.

4. The circuit board according to any one of claims 1 to 3, wherein the bonding material contains Sn.

5. The circuit board according to any one of claims 1 to 4, wherein the resin layer comprises an epoxy resin or an acrylic resin.

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