JP7565766B2 - Component mounting method and device - Google Patents

Description

This specification relates to a component mounting method and a component mounting device that joins electrodes of a component to joints of a circuit pattern when mounting the component on a board.

In recent years, three-dimensional printers (three-dimensional modeling machines) that apply inkjet technology have been put to practical use, and three-dimensional structures designed using CAD are being layer-by-layer manufactured. Furthermore, it is now possible to form a board using a resin ink that hardens when exposed to ultraviolet light and a conductive ink that hardens when baked in the inkjet modeling section of a three-dimensional printer, and then mount components on the board to manufacture the desired electronic device (board product). Here, boards on which the resin ink has hardened have lower heat resistance than conventional boards made of glass epoxy resin, etc. Therefore, when mounting components, it is difficult to solder electrodes due to temperature restrictions, so a method of joining electrodes is used. One example of a technique for this type of component mounting method is disclosed in Patent Document 1.

Patent Document 1 discloses a multi-chip mounting method in which adhesive is interposed between the electrode formation surface on the substrate and the chip electrode surface (bottom surface), and the electrodes (joints) of the substrate and the electrodes of the chip (component) facing them are aligned, with a buffer layer interposed on the back surface (top surface) of the chip, and then heat and pressure are applied. This is said to provide an effective mounting method when chips have different heights or are mounted on both sides of the substrate.

Japanese Patent Application Publication No. 10-256311

In the multi-chip mounting method of Patent Document 1, the electrodes are aligned when mounting the components, and then the components are bonded using an adhesive. Then, by applying pressure to the components while heating and curing the adhesive, it is possible to increase to a certain degree the reliability of the joints where the electrodes of the board and the electrodes (joints) of the components are joined. This mounting method does not use soldering, and is a technology that can be applied to boards on which the aforementioned resin ink has been cured.

Here, the substrate, components, electrodes, adhesive, and other components are thermally deformed due to temperature changes during use, and stress is generated at the joints according to differences in thermal expansion coefficients. The adhesive between the electrode formation surface and the chip electrode surface (bottom surface) in Patent Document 1 hardens and acts as a reinforcing material, but it cannot be said to be sufficient to relieve the above-mentioned stress. This makes the joints less reliable, and there are concerns about problems such as peeling. In order to relieve the stress generated at the joints and ensure the reliability of the joints, it is preferable to form a reinforcing material that covers not only the bottom surface of the component, but also the side and top surfaces of the component.

However, in the multi-chip mounting method of Patent Document 1, even if an attempt is made to apply a large amount of adhesive and heat cure it, the adhesive is pushed out before it cures due to pressure from the buffer layer. This makes it difficult to form a reinforcing material that covers the side and top surfaces of the components. Furthermore, there is a risk that the pushed-out adhesive will cover other electrodes that should be exposed, which can be counterproductive.

Therefore, the problem to be solved in this specification is to provide a component mounting method and a component mounting device that can improve the reliability of the joint between the electrode of a component and the joint of the circuit pattern on the board side compared to conventional methods.

This specification discloses a component mounting method that includes a joining process in which an electrode provided on the bottom surface of a component is joined to a joint provided on a circuit pattern formed on a resin layer of a substrate, and a bottom space is formed between the bottom surface of the component and the resin layer of the substrate; a bottom reinforcement process in which an underfill is injected into the bottom space, and the underfill is heat-cured while applying downward pressure to the component through a buffer layer to form a bottom reinforcement material; and an outer reinforcement process in which an outer reinforcement material is formed to cover at least a portion of the side and top surfaces of the component.

This specification also discloses a component mounting device that includes a joining process execution unit that joins an electrode provided on the bottom surface of a component to a joint provided on a circuit pattern formed on a resin layer of a substrate and forms a bottom space between the bottom surface of the component and the resin layer of the substrate, a bottom reinforcement process execution unit that injects underfill into the bottom space and applies downward pressure to the component while heat-curing the underfill to form a bottom reinforcement material, and an outer reinforcement process execution unit that forms an outer reinforcement material that covers at least a portion of the side and top surfaces of the component.

In the component mounting method and component mounting device disclosed in this specification, the bottom reinforcement material and the outer reinforcement material are formed in separate processes. As a result, it is possible to improve the adhesion between each reinforcement material and the component and the board, and further to improve the shape precision of each reinforcement material, thereby mechanically reinforcing the joint between the electrode and the joint. In this way, the bottom reinforcement material and the outer reinforcement material act synergistically to relieve stress that occurs at the joint due to temperature changes during use, etc. Therefore, it is possible to improve the reliability of the joint compared to the conventional method.

FIG. 2 is a block diagram showing a functional configuration of the component mounting device according to the embodiment, and also serves as a block diagram of a three-dimensional modeling machine. 1 is a process diagram for explaining the steps of a component mounting method according to an embodiment, and also serves as a production process diagram for a board product. FIG. 11 is a partial front cross-sectional view illustrating a state in which a joining step is carried out. FIG. 11 is a partial cross-sectional side view illustrating a state in which a joining step is carried out. 11 is a partial front cross-sectional view illustrating the state in which underfill is injected in a bottom reinforcing process. FIG. 1 is a partial front cross-sectional view illustrating a bottom reinforcement process in which the underfill is heated and cured while applying downward pressure to the component through the buffer layer to form a bottom reinforcement material. FIG. FIG. 11 is a partial front cross-sectional view illustrating the implementation status of the outer reinforcement process. FIG. 11 is a partial front cross-sectional view illustrating another implementation state of the outer reinforcement process.

1. Configuration of the three-dimensional modeling machine 10 and the component mounting device 1 First, the configuration of the component mounting device 1 of the embodiment will be described with reference to Figs. 1, 3, 5, 7, etc. As shown in Fig. 1, the component mounting device 1 is incorporated into the three-dimensional modeling machine 10. The three-dimensional modeling machine 10 produces a three-dimensional structure using an additive manufacturing method in which unit layers are stacked. The shape of the three-dimensional structure is defined by modeling data representing the shape of each of the multiple unit layers. When producing a board product, the three-dimensional modeling machine 10 first forms a board 9, and then mounts components 8 on the board 9 to produce the board product. The three-dimensional modeling machine 10 is composed of a conveying unit 21, a resin layer forming unit 22, a circuit forming unit 23, a component supply unit 24, a first head 25, a heating unit 26, a second head 27, a pressurizing and heating unit 28, a third head 29, and the like.

The conveying unit 21 carries pallets 31 (see Figures 3 and 7) into the machine, transports them within the machine, and carries them out of the machine. The pallets 31 are formed into a rectangular plate using a material with excellent heat resistance, such as an iron plate or a heat-resistant hard resin. The circuit board products are placed on the pallets 31 during production and are transported together with the pallets 31 by the conveying unit 21.

The resin layer forming unit 22 forms a resin layer 91 on the substrate 9. The resin layer forming unit 22 is composed of, for example, a modeling nozzle, a modeling head, a head drive unit, and an ultraviolet ray irradiation unit. The modeling nozzle ejects modeling ink that hardens when irradiated with ultraviolet rays. The modeling head is driven in two horizontal directions by the head drive unit while holding the modeling nozzle. As a result, the modeling nozzle models a thin unit resin layer on the pallet 31, on the top of the already formed resin layer 91, or on the top of the already formed circuit pattern 94, based on the modeling data.

Next, the pallet 31 is transferred to the ultraviolet irradiation section, and the liquid unit resin layer is irradiated with ultraviolet light. The liquid unit resin layer is then cured and becomes part of the solid resin layer 91. The resin layer forming section 22 may use a modeling ink that is cured by a method other than ultraviolet light irradiation.

The circuit forming unit 23 forms the circuit pattern 94 on the substrate 9. The circuit forming unit 23 is composed of, for example, a drawing nozzle, a drawing head, a head drive unit, and a baking unit. The drawing nozzle ejects conductive ink that solidifies when baked. An example of conductive ink is an ink in which fine metallic particles are mixed into a base. The drawing head is driven in two horizontal directions by the head drive unit while holding the drawing nozzle. As a result, the drawing nozzle draws a thin unit circuit layer on the pallet 31, on the top side of the already formed resin layer 91, or on the top side of the already formed circuit pattern 94 based on the modeling data.

Next, the pallet 31 is transferred to the baking section, where the liquid unit circuit layer is baked. The liquid unit circuit layer then solidifies as the base evaporates, becoming part of the solid circuit pattern 94. The resin layer forming section 22 and the circuit forming section 23 repeat the operations multiple times based on the modeling data, forming the substrate 9 shown in FIG. 3.

The resin layer 91 of the illustrated board 9 has a flat bottom surface, a lower top surface of the central portion 92 where the component 8 is mounted, and a higher top surface of the peripheral portion 93. The circuit pattern 94 of the board 9 is formed in a continuous manner from the bottom surface of the resin layer 91 to the top surface of the central portion 92. One component 8 is mounted on the illustrated board 9, but multiple components are mounted on an actual board. The shape of the board 9 and the type of component 8 mounted can be modified in various ways.

The component supply unit 24 supplies a plurality of components 8. The component supply unit 24 has a configuration similar to that of a tray-type component supply device equipped in a known component mounting machine, for example. The component supply unit 24 includes a component handling unit that picks up, moves, and places the components 8. The component 8 illustrated in Figures 3 and 4 has six electrodes 81 on its bottom surface 82.

The first head 25 has a first nozzle and is driven in two horizontal directions by the first head drive unit. The first nozzle ejects a conductive paste that solidifies when heated. An example of the conductive paste is a paste material in which silver particles are added to a base. The conductive paste has a higher viscosity than the conductive ink used in the circuit formation unit 23. The heating unit 26 heats the conductive paste to solidify it. The heating temperature at this time is lower than the soldering temperature and is acceptable for the substrate 9 made of a resin layer 91. An example of the heating unit 26 is a thermostatic bath that keeps the inside of the bath at a set temperature.

The second head 27 has a second nozzle and is driven in two horizontal directions by the second head drive unit. The second nozzle ejects underfill UF (see FIG. 5). A resin material that is insulating, liquid at room temperature, and thermosetting is used as the underfill UF. The inclination angle of the tip of the second nozzle is adjustable so that the underfill UF can be injected into narrow areas. The pressurizing and heating unit 28 heats and hardens the underfill UF while applying downward pressure to the component 8 through the buffer layer 41 (see FIG. 6). The configuration and function of the pressurizing and heating unit 28 will be described in detail later.

The third head 29 has a third nozzle and is driven in two horizontal directions by the third head drive unit. The third nozzle ejects a liquid or paste-like reinforcing material that hardens when heated. An example of a liquid or paste-like reinforcing material is thermosetting epoxy resin, which is a type of thermosetting resin, but is not limited to this. This reinforcing material may be the same material as the modeling ink that is the raw material for the resin layer 91, or the underfill UF. When this reinforcing material is heated by the heating unit 26 described above, it hardens and solidifies. The heating temperature at this time is acceptable for the substrate 9 made of the resin layer 91.

The component mounting device 1 is responsible for mounting the components 8. The component mounting device 1 is composed of a joining process execution section 51 shown by a solid line in FIG. 1, a bottom reinforcement process execution section 52 shown by a dashed line, and an outer reinforcement process execution section 53 shown by a broken line. The joining process execution section 51 is composed of the aforementioned conveying section 21, component supply section 24, first head 25, and heating section 26. The bottom reinforcement process execution section 52 is composed of the conveying section 21, second head 27, and pressurizing and heating section 28. The outer reinforcement process execution section 53 is composed of the conveying section 21, third head 29, and heating section 26.

2. Operation of the component mounting device 1 (component mounting method according to the embodiment)
Next, the operation of the component mounting device 1 will be described with reference to the process diagram in Fig. 2 and the situation explanatory diagrams in Fig. 3 to Fig. 8. The content of the operation of the component mounting device 1 includes the component mounting method of the embodiment. In the board formation process P1 in Fig. 2, the board 9 is formed by multiple operations of the resin layer formation unit 22 and the circuit formation unit 23 described above.

In the next joint formation process P2, the first head 25 applies conductive paste to a predetermined component mounting position of the circuit pattern 94 visible from above the board 9. This conductive paste is solidified by the heating unit 26 to become a joint 95 where the electrode 81 of the component 8 is joined (see FIG. 3). The joint 95 can also be referred to as the electrode on the board 9 side. It is also possible to omit the board formation process P1 and the joint formation process P2 and place a separately formed board 9 on a pallet 31 and carry it in from outside the machine by the transport unit 21.

3 and 4, the joint 95 on the circuit pattern 94 protrudes upward from the central portion 92 of the resin layer 91. On the other hand, the lower surface of the electrode 81 of the component 8 is generally at the same level as the bottom surface 82. Therefore, assuming a situation in which the electrode 81 is joined to the joint 95, a bottom space 96 is formed between the bottom surface 82 and the resin layer 91. Conversely, the bottom space 96 is also formed in a configuration in which the joint 95 is generally at the same level as the central portion 92 of the resin layer 91 and the electrode 81 protrudes downward from the bottom surface 82. Furthermore, the bottom space 96 is naturally formed in a configuration in which the joint 95 protrudes upward from the central portion 92 of the resin layer 91 and the electrode 81 protrudes downward from the bottom surface 82.

In the next joining process P3, the joining process execution unit 51 operates. More specifically, the first head 25 applies the conductive paste CP to an area of the assumed bottom space 96 that is separated from the electrode 81 and the joint 95. For example, the center of the component 8 is selected as the area to be applied, as shown in FIG. 4. The surface to be applied may be either the bottom surface 82 of the component 8 or the top surface of the resin layer 91, but the top surface of the resin layer 91 is selected, as this is where there is no risk of the conductive paste CP dripping. The application thickness is set to be slightly greater than the height of the bottom space 96.

Next, the component supply unit 24 picks up the component 8 and moves it so that the electrode 81 is placed on the joint 95. This actually forms the bottom space 96. At this time, the component supply unit 24 applies a downward load to the component 8, pressing the electrode 81 against the joint 95 and causing the conductive paste CP to spread somewhat horizontally. While maintaining this state, the substrate 9 and the component 8 are transported to the heating unit 26 by the transport unit 21.

In the heating section 26, the conductive paste CP located in the center of the component 8 is heated and solidified. As a result, the bottom surface 82 of the component 8 is bonded to the resin layer 91, and the electrode 81 is bonded to the joint 95, and the component 8 is attached to the substrate 9.

Here, the conductive paste CP located in the center of the component 8 is not used as a conductive material, but as a substitute for adhesive. Therefore, it is possible to use a dedicated adhesive instead of the conductive paste CP. Nevertheless, by using the conductive paste CP as a substitute for adhesive, the number of work heads, nozzles, and head drive units is reduced, simplifying the configuration of the component mounting device 1 and the three-dimensional modeling machine 10 and promoting cost reduction.

In the next bottom reinforcement process P4, the bottom reinforcement process implementation unit 52 operates. More specifically, the second head 27 injects underfill UF into the bottom space 96 as shown in FIG. 5. In practice, the second head 27 applies the tip of the second nozzle to the opening on the side of the bottom space 96 and ejects the underfill UF. The underfill UF then automatically flows into the bottom space 96 due to the action of capillary action, and is prevented from flowing out due to the action of surface tension. The amount of underfill UF injected is limited to an amount that does not overflow from the component 8. This injection amount is appropriately determined based on the size of the component 8, the height of the bottom space 96, the size and number of the electrodes 81 and the joints 95, and the amount of conductive paste CP used, etc.

While maintaining this state, the substrate 9 and the component 8 are transferred to the pressurizing and heating section 28 by the conveying section 21. As shown in FIG. 6, the pressurizing and heating section 28 is composed of a buffer layer 41, a pressurizing and heating plate 44, and a pressurizing device and a heating device (not shown). The buffer layer 41 is formed using a material that easily elastically deforms, such as a rubber sheet. The buffer layer 41 has a flat upper surface, a thin central portion 42, and a thick peripheral portion 43. The buffer layer 41 is placed on the upper side of the substrate 9 and the component 8. The central portion 42 of the buffer layer 41 contacts the upper surface 84 of the component 8. The peripheral portion 43 of the buffer layer 41 contacts the peripheral portion 93 of the resin layer 91 or is positioned with a small distance therebetween.

The pressure heating plate 44 is made of a sturdy metal plate, for example, an iron plate. The pressure heating plate 44 is placed on the upper side of the buffer layer 41. The pressure device is composed of a hydraulic mechanism or a pneumatic mechanism, and applies a downward load F to the pressure heating plate 44. The heating device is composed of an electric heater, and heats the pressure heating plate 44.

The pressurizing and heating unit 28 applies downward pressure to the component 8 through the buffer layer 41 while heating and hardening the underfill UF. The downward load F applied by the pressurizing device is distributed by the pressurizing and heating plate 44 and the buffer layer 41, and is converted into a pressure that acts generally evenly over the entire top surface 84 of the component 8. In addition, compression of the central portion 42 of the buffer layer 41 increases the pressure shared by the peripheral portion 43, or the separation distance disappears and pressure is shared by the peripheral portion 43. This makes it easier to maintain the appropriate amount of pressure acting on the top surface 84 of the component 8. If the peripheral portion 43 did not exist, it would be difficult to equalize the pressure acting on the top surface 84 of the component 8, and the amount of pressure would be prone to fluctuation.

The heat applied to the pressure heating plate 44 is transferred from the component 8 to the underfill UF via the buffer layer 41. As a result, the underfill UF hardens and becomes the bottom reinforcement material 71. The heating temperature at this time is acceptable for the substrate 9 and the component 8, which are made of the resin layer 91.

The action of the pressure and heating unit 28 described above allows pressure to be applied to the joint where the electrode 81 and the joint 95 are joined while hardening the underfill UF around the joint. This improves the reliability of the joint to a certain extent. In addition, the bottom reinforcement 71 has the effect of mitigating stress, particularly shear force, that occurs at the joint due to temperature changes during use of the board product, thereby improving the reliability of the joint.

The pressurizing and heating unit 28 may be configured differently from that described above, for example, by including a buffer layer 41, a pressure plate, a pressure device, and a thermostatic bath. In this configuration, the thermostatic bath increases the temperature inside the bath while housing the substrate 9 and components 8 inside the bath, thereby thermally hardening the underfill UF. Meanwhile, the buffer layer 41, the pressure plate, and the pressure device exert the effect of applying downward pressure to the components 8 inside the thermostatic bath.

In the next outer reinforcement process P5, the outer reinforcement process implementation unit 53 operates. More specifically, the third head 29 ejects a liquid or paste-like reinforcing material (corresponding to the reference symbol 72) so as to cover the entire side surface 83 and top surface 84 of the part 8, as shown in FIG. 7. The reinforcing material thickly covers the part 8 above the central portion 92 of the resin layer 91, while extending to the sides of the peripheral portion 93. In order to thickly cover the part 8 as shown in the figure and form a mountain shape, it is preferable that the reinforcing material has a certain degree of viscosity, specifically a viscosity of about 1 (Pa·s) or more.

While maintaining this state, the substrate 9 and the component 8 are transported to the heating section 26 by the transport section 21. The liquid or paste-like reinforcing material is heated and hardened in the heating section 26 to become the outer reinforcing material 72. The outer reinforcing material 72 has the effect of mitigating stresses that occur at the joint due to temperature changes during use of the substrate product, particularly the force in the direction in which the electrode 81 moves away from the joint 95. As shown in FIG. 8, the outer reinforcing material 73 may be shaped to cover the entire side surface 83 and the peripheral portion of the top surface 84 of the component 8, but not to cover the center of the top surface 84.

Furthermore, in the embodiment, outer reinforcement materials (72, 73) are formed with a thermal expansion coefficient lower than that of the resin layer 91. Therefore, when the resin layer 91 expands with an increase in temperature during use, the degree of expansion of the outer reinforcement materials (72, 73) is relatively small, and adhesion to the component 8 is maintained. Therefore, the outer reinforcement materials (72, 73) have a remarkable effect of alleviating stress generated at the joint. Furthermore, the outer reinforcement materials (72, 73) and the bottom reinforcement material 71 act synergistically to alleviate stress in various directions generated at the joint, further enhancing the reliability of the joint.

In the component mounting method and component mounting device 1 of the embodiment, the bottom reinforcement 71 and the outer reinforcement (72, 73) are formed in separate processes. As a result, the adhesion between each reinforcement (71, 72, 73) and the component 8 and the substrate 9 can be improved, and the shape precision of each reinforcement (71, 72, 73) can be improved to reinforce the joint between the electrode 81 and the joint 95. As a result, the bottom reinforcement 71 and the outer reinforcement (72, 73) act synergistically to relieve stress generated at the joint due to temperature changes during use, etc. Therefore, the reliability of the joint can be improved compared to the conventional method.

3. Applications and Modifications of the Embodiments In addition to the conveying unit 21 and the pallet 31, some components of the component mounting device 1 and the three-dimensional modeling machine 10 can be made common or used for both purposes. For example, the baking unit of the circuit forming unit 23 and the heating unit 26 can be made common. Also, a part of the pressurizing and heating unit 28 can be used for both purposes. On the other hand, the three-dimensional modeling machine 10 that forms the substrate 9 and the component mounting device 1 that mounts the components 8 on the substrate 9 can be configured separately. In addition, the embodiments can be applied and modified in various ways.

1: Component mounting device 21: Conveyor 22: Resin layer forming section 23: Circuit forming section 24: Component supply section 25: First head 26: Heating section 27: Second head 28: Pressurizing and heating section 29: Third head 31: Pallet 41: Buffer layer 44: Pressurizing and heating plate 51: Joining process execution section 52: Bottom reinforcement process execution section 53: Outer reinforcement process execution section 71: Bottom reinforcement material 72, 73: Outer reinforcement material 8: Component 81: Electrode 82: Bottom surface 83: Side surface 84: Top surface 9: Substrate 91: Resin layer 94: Circuit pattern 95: Joint 96: Bottom space 10: Three-dimensional modeling machine P1: Substrate formation process P2: Joint formation process P3: Joint process P4: Bottom reinforcement process P5: Outer reinforcement process CP: Conductive paste UF: Underfill

Claims (9)

a bonding process for bonding an electrode provided on a bottom surface of a component to a bonding portion provided on a circuit pattern formed on a resin layer of a substrate, and forming a bottom space between the bottom surface of the component and the resin layer of the substrate;
a bottom reinforcing step of injecting an underfill into the bottom space after the bonding step is completed, and applying downward pressure to the component through a buffer layer while heat-curing the underfill to form a bottom reinforcing material;
an outer reinforcement step of forming an outer reinforcement member covering at least a part of a side surface and a top surface of the part after the bottom reinforcement step is completed ;
A component mounting method comprising: The component mounting method according to claim 1, which satisfies at least one of the conditions that the electrode protrudes below the bottom surface and that the joint protrudes above the resin layer. The component mounting method according to claim 1 or 2, wherein the outer reinforcement step forms the outer reinforcement material to cover the entire side and top surfaces of the component. The component mounting method according to any one of claims 1 to 3, wherein in the outer reinforcement process, the outer reinforcement material is formed to have a lower thermal expansion coefficient than the resin layer. The component mounting method according to any one of claims 1 to 4, wherein in the outer reinforcement process, the outer reinforcement material is formed by applying a thermosetting resin and then heating and curing it. The component mounting method according to any one of claims 1 to 5, wherein the amount of underfill injected during the bottom reinforcement process is limited to an amount that does not overflow from the component. The component mounting method according to any one of claims 1 to 6, wherein in the joining step, a conductive paste is applied to an area of the bottom space separated from the electrode and the joint, and the paste is heated and cured to join the electrode and the joint. The component mounting method according to any one of claims 1 to 7, further comprising a joint forming step of applying a conductive paste to the circuit pattern and heating and hardening the paste to form the joint. a bonding process execution unit that bonds an electrode provided on a bottom surface of a component to a bonding portion provided on a circuit pattern formed on a resin layer of a substrate, and forms a bottom space between the bottom surface of the component and the resin layer of the substrate;
a bottom reinforcing process performing unit that, after the operation of the bonding process performing unit is completed, injects an underfill into the bottom space and heat-cures the underfill while applying a downward pressure to the component to form a bottom reinforcing material;
an outer reinforcement process performing unit that forms an outer reinforcement material covering at least a part of a side surface and an upper surface of the component after the operation of the bottom reinforcement process performing unit is completed ;
A component mounting device comprising:

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