JP7790938B2 - Method for manufacturing a connection structure and a connection structure - Google Patents

Description

This technology relates to a method for manufacturing a connection structure for mounting a connector, and to the connection structure itself.

When mounting surface mount devices (SMD) on rigid or flexible boards, solder paste is generally printed on the board, the surface mount components are then mounted on top using a mounter, and then the components are mounted using a reflow process.

General solder pastes have limitations when used with fine-pitch connections because the absolute amount of solder itself is high, which can lead to solder bridging. Therefore, to accommodate fine pitch connections, anisotropic conductive adhesives containing solder have been proposed that reduce the amount of solder remaining between the wiring and utilize the self-cohesion properties of solder (see, for example, Patent Documents 1 and 2).

When mounting connector components to a circuit board using conventional reflow soldering, the tension and wettability of the binder in the anisotropic conductive adhesive causes the binder resin to creep up to the outside of the connector. This is particularly true for vertical mating connectors, which require male and female mating, and can prevent the connector from functioning properly.

8 is a cross-sectional view showing a typical example of mounting a plug of a conventional vertical mating connector on a circuit board. When pins 111A and 111B of plug 101 are joined to board terminals 152A and 152B of board 105 with solder 142A and 142B, the binder of anisotropic conductive adhesive 103 gathers on plug 101 due to its tension, and the binder's wettability causes the binder to creep up to the periphery of plug 101. If the binder creep-up height _T0 is large, the surfaces of pins 112A and 112B are covered with the insulating binder, resulting in a loss of electrical continuity between the male and female connectors when they are mated.

JP 2017-041442 A JP 2016-219808 A

This technology was proposed in light of these existing circumstances, and provides a connection structure and a manufacturing method for such a structure that can reduce electrical continuity problems caused by mating connectors.

The method for manufacturing a connection structure according to the present technology includes the steps of: placing an anisotropic conductive adhesive containing solder particles on a wiring board; and placing a plug of a vertical mating connector and a surface-mounted component on the anisotropic conductive adhesive; and joining the plug and surface-mounted component to the wiring board using a reflow furnace set at a temperature equal to or higher than the melting point of the solder particles. When the plug and receptacle are mated, the height from the plug terminal surface on the side to the receptacle pin is 70 μm or more and 150 μm or less, and the distance between the side of the plug and the side of the surface-mounted component is 0.2 mm or more and 3.0 mm or less.

The connection structure according to this technology comprises a wiring board, a plug for a vertical mating connector, a surface-mounted component, and an adhesive layer that bonds the plug and the surface-mounted component to the wiring board. When the plug and receptacle are mated, the height from the plug terminal surface on the side to the receptacle pin is 70 μm or more and 150 μm or less, and the distance between the side of the plug and the side of the surface-mounted component is 0.2 mm or more and 3.0 mm or less.

This technology prevents binder from creeping up the sides of the plug of a vertical mating connector by keeping the distance between the sides of the surface-mounted component within a specified range, thereby reducing poor electrical continuity when the connectors are mated.

FIG. 1 is a cross-sectional view schematically showing an example of a plug of a vertical mating connector in the short side direction. FIG. 2 is a cross-sectional view schematically illustrating an example of a receptacle of a vertical mating connector in the short side direction. 3 is a cross-sectional view schematically showing a state in the lateral direction in which the plug shown in FIG. 1 and the receptacle shown in FIG. 2 are mated. FIG. 4 is a cross-sectional view schematically showing an example of an arrangement process to which the present technology is applied. FIG. 5 is a cross-sectional view schematically showing an example of a connection structure to which the present technology is applied. FIG. 6 is a plan view schematically showing another example of a connection structure to which the present technology is applied. FIG. 7 is a plan view for explaining a test for evaluating the distance between peripheral components when a plurality of peripheral components are mounted in the longitudinal direction of the plug. FIG. 8 is a cross-sectional view showing a typical example of mounting a plug of a vertical mating connector on a conventional board.

Hereinafter, embodiments of the present technology will be described in detail in the following order with reference to the drawings.
1. Method for manufacturing a connection structure 2. Connection structure 3. Thermosetting connection material 4. Examples

<1. Method for manufacturing connection structure>
The method for manufacturing a connection structure according to this embodiment includes a placement step of placing an anisotropic conductive adhesive containing solder particles on a wiring board and placing a plug of a vertical mating connector and a surface-mounted component on the anisotropic conductive adhesive, and a joining step of joining the plug and surface-mounted component to the wiring board using a reflow furnace set at a temperature equal to or higher than the melting point of the solder particles. When the plug and receptacle are mated, the height from the plug terminal surface to the receptacle pin on the side is 70 μm to 150 μm, and the distance between the side of the plug and the side of the surface-mounted component is 0.2 mm to 3.0 mm. This prevents the binder from creeping up the side of the plug and reduces poor electrical continuity due to mating of the connectors. Here, a connection structure refers to two materials or components electrically connected together. Furthermore, joining refers to joining two materials or components together.

Figure 1 is a cross-sectional view showing an example of a short-side view of a plug of a vertical mating connector, Figure 2 is a cross-sectional view showing an example of a short-side view of a receptacle of a vertical mating connector, and Figure 3 is a cross-sectional view showing an example of a short-side view of the plug shown in Figure 1 mated with the receptacle shown in Figure 2.

As shown in FIG. 1, the vertical mating connector plug 1 comprises a first male pin 11A, a second male pin 11B, a first plug terminal 12A extending from the first male pin 11A to the bottom surface and then extending outward in the short direction, a second plug terminal 12B extending from the second male pin 11B to the bottom surface and then extending outward in the short direction, and insulating resin that secures these together. The insulating resin is made of, for example, polyamide or LCP (Liquid Crystal Polymer), and the pins 11A, 11B and plug terminals 12A, 12B are secured longitudinally at a predetermined pitch by, for example, resin molding. Furthermore, leads are formed on the ends of each of the plug terminals 12A, 12B, and the plug terminals 12A, 12B form a surface-mounted lead array.

As shown in Figure 2, the receptacle 2 of the vertical mating connector includes a first female pin 21A, a second female pin 21B, a receptacle terminal row 22A extending from the first female pin 21A to the bottom surface and extending outward in the short direction, second receptacle terminals 22B extending from the second female pin 21B to the bottom surface and extending outward in the short direction, and insulating resin that secures the pins 21A, 21B and receptacle terminals 22A, 22B at a predetermined pitch in the longitudinal direction. The insulating resin is made of, for example, polyamide or LCP, and secures the pins 21A, 21B and receptacle terminals 22A, 22B at a predetermined pitch in the longitudinal direction, for example, by resin molding. Furthermore, leads are formed on the ends of each of the receptacle terminals 22A, 22B, and the receptacle terminals 22A, 22B form a surface-mounted lead array.

As shown in Figure 3, when male pins 11A, 11B are mated with female pins 21A, 21B, the height _T1 from the bottom surface of plug terminals 12A, 12B at the side to pins 21A, 21B of receptacle 2 is 70 μm or more and 150 μm or less, preferably 70 μm or more and 140 μm or less, and more preferably 70 μm or more and 130 μm or less. If this height _T1 is too high, the vertical mating connector will become too tall, which is undesirable from the perspective of miniaturizing the connection structure. Note that female pins 21A, 21B of receptacle 2 have a concave shape, and height _T1 is measured from the side of concave pins 21A, 21B of receptacle 2, i.e., the receptacle terminals 22A, 22B side.

If the height of the binder creeping up on the side of plug 1 is greater than height _T1 from the bottom surfaces of plug terminals 12A, 12B at the side when plug 1 and receptacle 2 are mated to pins 21A, 21B of receptacle 2, insufficient mating between plug 1 and receptacle 2 occurs, resulting in poor conductivity. In this embodiment, surface-mounted components are mounted around the plug of the vertical mating connector, and the distance between the side of the plug and the side of the surface-mounted component is set within a predetermined range, thereby preventing the binder from creeping up on the side of the plug.

With reference to Figures 4 and 5, the following describes the placement process in which an anisotropic conductive film containing solder particles is placed on a wiring board, and the plug of a vertical mating connector and a surface-mounted component are placed on the anisotropic conductive film, and the joining process in which the plug and surface-mounted component are joined to the wiring board using a reflow furnace set at a temperature above the melting point of the solder particles.

[Placement process]
FIG. 4 is a cross-sectional view schematically illustrating a placement process using the present technology. In the placement process, an anisotropic conductive adhesive 4 containing solder particles 41 is placed on a wiring board 5, and then a plug 1 of a vertical mating connector and a surface-mounted component 3 are placed on the anisotropic conductive adhesive 4. For example, a tool is used to align the plug terminals 12A and 12B of the plug 1 with the board terminals 52A and 52B of the wiring board 5, and also to align the surface-mounting terminals of the surface-mounted component 3 with the terminals 53 of the wiring board 5, and then the plug 1 and the surface-mounted component 3 are mounted on the anisotropic conductive adhesive 4. The tool is typically a mounter tool, but it is preferable that it has a suction mechanism for adsorbing the plug 1 and the surface-mounted component 3, and it may also be a heated pickup tool. The anisotropic conductive adhesive may be in a paste or film form. A paste-like adhesive may be transformed into a form similar to a film when mounting the surface-mounted component.

In the placement process, the plug 1 and the surface-mounted component 3 are placed such that, when the plug 1 and the receptacle 2 are mated, the height _T1 from the plug terminal surface at the side to the pin of the receptacle 2 is 70 μm to 150 μm, and the distance W between the side of the plug 1 and the side of the surface-mounted component 3 is 0.2 mm to 3.0 mm. A preferred placement condition is a distance W of 0.2 mm to 2.0 mm for the height _T1 in the above range, and a more preferred placement condition is a distance W of 0.2 mm to _1.5 mm for the height T1 in the above range. If the distance W is 0.2 mm, interference will occur with the leads at the ends of the plug terminals 12A and 12B, and if the distance W exceeds 2.0 mm, it will be difficult to prevent the binder of the anisotropic conductive adhesive 4 from creeping up to the side of the plug 1.

In the placement process, it is preferable to place one surface-mounted component 3 along the length of the plug 1. Furthermore, multiple surface-mounted components 3 are preferably placed along the length of the plug 1 at intervals of 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.5 mm or less. By placing the surface-mounted components 3 along the length of the plug 1 in this manner, it is possible to prevent the binder of the anisotropic conductive adhesive 4 from creeping up along the sides of the plug 1 along the length of the aligned pins 11A and 11B. Furthermore, considering the relationship between the distance W between the side of the plug 1 and the side of the surface-mounted component 3 and the distance Ws between the surface-mounted components 3, it is preferable to place the surface-mounted components 3 so that the distance W between the side of the plug 1 and the side of the surface-mounted component 3 is 0.2 mm to 1.5 mm, while the distance Ws between the surface-mounted components 3 is 1.5 mm to 0.2 mm. This allows the creep-up height to be 120 μm or less.

The placement process may also involve temporary pressure bonding, in which a tool is used to press the plug 1 and surface-mounted component 3 from the side. The temporary pressure conditions are preferably 2.0 MPa or less, more preferably 1.5 MPa or less, and even more preferably 1.0 MPa or less.

When the plug 1 and surface-mounted component 3 are pressed together, the upper limit of the ratio of the thickness of the anisotropic conductive adhesive 4 to the average particle size of the solder particles 41 is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less. By pressing the anisotropic conductive adhesive 4 until the distance between the terminal rows of the plug 1 and surface-mounted component 3 and the terminal rows of the wiring board 5 is close to the diameter of the solder particles, residual air bubbles between the board and the component can be reduced, improving adhesion.

[Joining process]
In the bonding process, a reflow furnace set at a temperature above the melting point of the solder particles 41 is used to bond the plug 1 and the surface-mounted component 3 to the wiring board 5, and the plug 1 and the surface-mounted component 3 are mounted on the wiring board 5 all at once.

Reflow furnaces include atmospheric reflow, vacuum reflow, atmospheric ovens, and autoclaves (pressure ovens). Of these, vacuum reflow and autoclaves are preferred, as they can eliminate air bubbles trapped in the joint. Reflow furnaces can heat and bond the components without applying mechanical pressure or load, thereby minimizing damage to the plug 1, surface-mounted component 3, and wiring board 5.

The lower limit of the peak temperature (maximum temperature reached) in the reflow furnace should be equal to or higher than the temperature at which the solder particles 41 melt and the temperature at which the anisotropic conductive adhesive 4 begins to harden, and is preferably 150°C or higher, more preferably 180°C or higher, and even more preferably 200°C or higher. The upper limit of the peak temperature in the reflow furnace is 300°C or lower, more preferably 290°C or lower, and even more preferably 280°C or lower.

In the reflow furnace, the anisotropic conductive adhesive 4 melts due to heating, and this heating, which is above the solder melting point, causes the solder particles 41 between the electrodes to move, aggregate, and melt due to binder flow, etc. The solder spreads over the electrodes, and upon cooling, the plug terminals 12A, 12B of the plug 1 are solder-joined to the board terminals 52A, 52B of the wiring board 5, and the terminals of the surface-mounted component 3 are solder-joined to the terminals of the wiring board 5.

In addition to the temperature-raising and temperature-lowering steps, reflow may also include a step of maintaining a constant temperature (a "keep" step). There may be a peak step where the temperature reaches its highest point, or a peak step may be included during the temperature increase or decrease. The temperature-raising step may be divided into two stages: a step of melting the binder (e.g., up to 120°C) and a step of melting and spreading the solder particles (e.g., 120-175°C). Therefore, the temperature-raising rate may be, for example, 10-120°C/min or 20-100°C/min. The maintenance time of the "keep" step (e.g., 175-180°C) also serves as a binder hardening process. This temperature is, for example, 160-230°C, and may vary by 5-10°C, or may be the same as the peak temperature. This time can be selected appropriately, for example, 0.5 min or more or 0.75 min or more. Since a longer time reduces manufacturing efficiency, it is, for example, 5 min or less or 3 min or less.

For example, if the binder of the anisotropic conductive adhesive 4 is thermosetting, by matching the temperature increase, maintenance, and decrease in the reflow process with the thermosetting behavior of the binder, it is possible to optimize the resin melting during the reflow process, the sandwiching of solder particles between the terminals, and the solder melting and resin hardening. The thermosetting behavior of the binder can be determined by DSC measurement or viscosity measurement using a rheometer.

Figure 5 is a cross-sectional view showing a schematic example of a connection structure to which this technology is applied. The connection structure is configured by joining plug terminals 12A, 12B of plug 1 to board terminals 52A, 52B of wiring board 5 with solder 42A, 42B, and by joining terminals of surface-mounted component 3 to terminals of wiring board 5 with solder 42C. Furthermore, the connection structure is mounted such that plug 1 and surface-mounted component 3 are mounted at a distance that remains consistent with the placement conditions in the placement process.

According to the method for manufacturing a connection structure of this embodiment, by setting the distance between the side of the plug and the side of the surface-mounted component to a predetermined condition, relative to the height _T1 from the plug terminal surface on the side to the receptacle pin when the plug and receptacle are mated, the height _T2 from the plug terminal surface to which the binder creeps up on the side of the plug can be reduced, and poor conductivity due to mating of connectors can be suppressed.

<2. Connection structure>
The connection structure according to this embodiment includes a wiring board, a plug for a vertical mating connector, a surface-mounted component, and an adhesive layer that bonds the plug and the surface-mounted component to the wiring board, and when the plug and receptacle are mated, the height from the plug terminal surface to the receptacle pin at the side is 70 μm to 150 μm, and the distance between the side of the plug and the side of the surface-mounted component is 0.2 mm to 3.0 mm. This prevents binder from creeping up the side of the plug, thereby preventing poor conductivity when the connectors are mated.

As shown in Figures 4 and 5, the connection structure includes a plug 1 having plug terminals 12A and 12B, a wiring board 3 having board terminals 52A and 52B corresponding to the plug terminals 12A and 12B, and an adhesive layer that joins the plug terminals 12A and 12B to the board terminals 52A and 52B with solder 42A and 42B, and also joins the terminal of the surface-mounted component 3 to the terminal 53 of the wiring board 5 with solder 42C.

The plug 1 comprises a first male pin 11A, a second male pin 11B, a first plug terminal 12A extending from the first male pin 11A to the bottom surface and outward in the short direction, a second plug terminal 12B extending from the second male pin 11B to the bottom surface and outward in the short direction, and insulating resin that secures these in place.

The upper limit of the minimum distance between adjacent terminals (space distance) on the plug terminals 12A, 12B and board terminals 52A, 52B is preferably 0.8 mm or less, more preferably 0.3 mm or less, and even more preferably 0.2 mm or less. Furthermore, the lower limit of the minimum distance between adjacent terminals on the plug terminals 12A, 12B and board terminals 52A, 52B is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. If the distance is less than this, the risk of short circuits increases. Furthermore, the surfaces of the plug terminals 12A, 12B are preferably gold-plated.

The surface-mounted components 3 are not particularly limited as long as they can be joined by solder reflow, and examples include connectors, IC (Integrated Circuit) and LSI (Large Scale Integration) packages, LEDs (Light Emitting Diodes), switches, etc.

The wiring board 5 has board terminals 52A and 52B on a base material 51 that correspond to the plug terminals 12A and 12B. The wiring board 5 may be anything that can be broadly defined as a printed wiring board (PWB), and may be either a rigid board or a flexible board (FPC: Flexible Printed Circuits). Examples of substrates based on the type of base material 51 include glass boards, ceramic boards, and plastic boards.

From an economical standpoint, it is preferable that adjacent board terminals 52A, 52B not have short-circuit prevention processing (such as walls or grooves) formed between them, as is the case with solder resist. For example, the upper limit of the height of the space between adjacent board terminals 52A, 52B is preferably 100 μm or less, more preferably 35 μm or less, and even more preferably 12 μm or less than the height of board terminals 52A, 52B. The lower limit of the height between adjacent board terminals 52A, 52B from the terminals may be the same as the height of board terminals 52A, 52B (i.e., the space between the terminals is horizontal and flush with the board surface, there are no protrusions on the terminals, and the connection surface of the board is flat). Alternatively, board terminals 52A, 52B mounted on the board may protrude from the board plane. The surfaces of board terminals 52A, 52B are preferably gold-plated.

The adhesive layer includes solder 42A, 42B that joins the plug terminals 12A, 12B and the board terminals 52A, 52B. The adhesive layer is made of a cured anisotropic conductive adhesive, described below. The solder 42A, 42B joins the plug terminals 12A, 12B and the board terminals 52A, 52B, respectively, and the solder 42C joins the terminals of the surface-mounted component 3 and the terminals of the wiring board 5. Multiple solder joints may exist within each board terminal 52A, 52B, and binder-bonded areas may exist outside of the multiple solder joints. The electrodes of the plug terminals 12A, 12B and the board terminals 52A, 52B may be in direct contact with each other, and the binder may hold this in place. Alternatively, nearby solder particles connecting the electrodes may act to support this connection. Solder particles may be sandwiched between the electrodes, and after the electrodes are directly connected, surrounding solder particles may melt and contribute to the bond.

Furthermore, the connection structure is mounted under the following conditions: when the plug 1 and the receptacle 2 are mated, the height _T1 from the plug terminal surface at the side to the pin of the receptacle 2 is 70 μm to 150 μm, and the distance W between the side of the plug 1 and the side of the surface-mounted component 3 is 0.2 mm to 3.0 mm. A preferred mounting condition is a distance W of 0.2 mm to 2.0 mm for the height _T1 in the above range, and a more preferred mounting condition is a distance W of 0.2 mm to 1.5 mm for the height _T1 in the above range. A distance W of 0.2 mm may interfere with the leads at the ends of the plug terminals 12A and 12B, or may make mating with the receptacle difficult. Furthermore, a distance W of more than 2.0 mm makes it difficult to reduce the height _T2 from the plug terminal surface at the side of the plug 1, at which the binder creeps up.

Figure 6 is a plan view schematically illustrating another example of a connection structure to which the present technology is applied. The connection structure preferably has one surface-mounted component 3 mounted on one side of the plug 1 along the longitudinal direction. Also, as shown in Figure 6, the connection structure preferably has multiple surface-mounted components 3 mounted on one side of the plug 1 at a predetermined distance Ws along the longitudinal direction.

The connection structure shown in Figure 6 comprises a plug 1 and multiple or multiple types of surface-mounted components 3. The multiple surface-mounted components 3 are mounted so that a predetermined distance W is between the side of the plug 1 and the side of the surface-mounted components 3, and are mounted on the side of the first pin 11A and the side of the second pin 12A of the plug 1 so that they are spaced a predetermined distance Ws apart in the longitudinal direction. Note that the A-A cross section of the plug 1 shown in Figure 6 is a cross section in the short direction of the plug 1 shown in Figures 4 and 5.

The multiple surface-mounted components 3 are mounted in the longitudinal direction of the plug 1, preferably at a distance Ws of 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.5 mm or less. By mounting the surface-mounted components 3 in the longitudinal direction of the plug 1 in this manner, it is possible to prevent the binder of the anisotropic conductive adhesive 4 from creeping up along the sides of the plug 1 in the longitudinal direction of the aligned pins 11A and 11B.

Furthermore, in terms of the relationship between the distance W between the side of the plug 1 and the side of the surface-mounted component 3 and the distance Ws between the surface-mounted components 3, it is preferable to mount the components so that the distance W between the side of the plug 1 and the side of the surface-mounted component 3 is 0.2 mm to 1.5 mm, while the distance Ws between the surface-mounted components 3 is 1.5 mm or less. This allows the creep-up height _T2 to be 120 μm or less.

The connection structure of this embodiment allows for a predetermined distance between the side of the plug and the side of the surface-mounted component relative to the height from the plug terminal surface on the side to the receptacle pin when the plug and receptacle are mated. This prevents binder from creeping up the side of the plug, thereby reducing poor electrical continuity when the connectors are mated. Furthermore, the connection structure of this embodiment is connected using solder particles that are widely used in BGAs (ball grid arrays) and other devices, and has high connection reliability, making it suitable for a wide range of applications, including sensor equipment, automotive equipment, and IoT (Internet of Things) devices.

<3. Anisotropic conductive adhesive>
The anisotropic conductive adhesive according to this embodiment contains solder particles and has a minimum melt viscosity of 150 Pa·s or less, preferably 100 Pa·s or less, more preferably 80 Pa·s or less, and even more preferably 50 Pa·s or less. Increasing the minimum melt viscosity can prevent the binder from creeping up to the sides of the plug during reflow, but this can impair the flow of the solder particles under no load, preventing them from coagulating and melting, which may interfere with the solder connection between the terminals. Furthermore, when the minimum melt viscosity of the anisotropic conductive adhesive is 150 Pa·s or less, the height of the binder creeping up to the sides of the plug is a constant value of approximately 155 μm. However, by setting the distance between the sides of the plug and the sides of the surface-mounted component to a predetermined condition, the height _T2 from the plug terminal surface to which the binder creeps up on the sides of the plug can be set to 150 μm or less.

Furthermore, the minimum melt viscosity temperature of the anisotropic conductive adhesive is preferably ±50°C above the melting point of the solder particles, more preferably ±40°C above the melting point of the solder particles, and even more preferably ±30°C above the melting point of the solder particles. This allows the resin to melt by reaching the minimum melt viscosity before the solder melts, and then the solder particles melt after the resin melts, and the resin can then harden, resulting in a good solder joint. Here, the minimum melt viscosity temperature of the anisotropic conductive adhesive refers to the temperature at which the viscosity reaches its minimum value (minimum melt viscosity) when measured using, for example, a rotational rheometer (manufactured by TA Instrument) under the following conditions: measurement pressure 5 g, temperature range 30-200°C, heating rate 10°C/min, measurement frequency 10 Hz, measurement plate diameter 8 mm, and load fluctuation on the measurement plate 5 g.

The anisotropic conductive adhesive may be in either film or paste form. Furthermore, the paste may be in film form when connected, or may be made into a film-like form by mounting components. In the case of a paste, it is sufficient to apply a predetermined amount evenly onto the board; for example, application methods such as dispensing, stamping, and screen printing can be used, and the adhesive may be dried as needed. In the case of a film, not only can the amount of bonding material (e.g., anisotropic conductive bonding material) be made uniform depending on the film thickness, but it is also easy to handle, improving work efficiency.

When the anisotropic conductive adhesive is in film form, the lower limit of the ratio of the thickness of the anisotropic conductive adhesive to the average particle size of the solder particles is preferably 0.6 or more, more preferably 0.8 or more, and even more preferably 0.9 or more. If the ratio of the thickness of the anisotropic conductive adhesive to the average particle size of the solder particles is large, it will be easier to sandwich the solder particles between the electrodes in the aforementioned placement process, but there is a risk that the adhesive will be difficult to handle when made into a film.

Furthermore, the upper limit of the ratio of the thickness of the anisotropic conductive adhesive to the average particle size of the solder particles is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

Film thickness can be measured using a known micrometer or digital thickness gauge (e.g., Mitutoyo Corporation's MDE-25M, minimum display 0.0001 mm) capable of measuring 1 μm or less, preferably 0.1 μm or less. Film thickness can be determined by averaging measurements taken at 10 or more locations. However, if the film thickness is thinner than the particle diameter, a contact-type thickness gauge is not suitable, and it is therefore preferable to use a laser displacement meter (e.g., Keyence Corporation's spectral interference displacement type SI-T series). Here, film thickness refers to the thickness of the binder resin layer only, excluding the particle diameter.

The binder for the anisotropic conductive adhesive may be thermosetting or thermoplastic, but it is preferable that it be thermosetting, which can be melted and hardened by temperature control in the reflow process. Below, we will explain thermosetting binders (insulating binders).

[Thermosetting binder]
The thermosetting binder preferably has a peak exothermic temperature higher than the melting point of the solder particles, and preferably has a melting temperature lower than the melting point of the solder particles. Here, the peak exothermic temperature can be measured using a rotational rheometer (manufactured by Thermo Fisher Scientific) under the following conditions: measurement pressure 1 N, temperature range 30 to 200°C, heating rate 10°C/min, measurement frequency 1 Hz, and measurement plate diameter 8 mm. This melts the thermosetting binder upon heating, and the solder melts while the solder particles are sandwiched between the terminals, allowing electronic components with fine-pitch electrodes to be joined.

Examples of thermosetting binders include thermal radical polymerization resin compositions containing a (meth)acrylate compound and a thermal radical polymerization initiator, thermal cationic polymerization resin compositions containing an epoxy compound and a thermal cationic polymerization initiator, and thermal anionic polymerization resin compositions containing an epoxy compound and a thermal anionic polymerization initiator. Known pressure-sensitive adhesive compositions may also be used. Note that the term "(meth)acrylic monomer" refers to both acrylic and methacrylic monomers.

The following describes a specific example of a thermal anionic polymerization resin composition containing a solid epoxy resin, a liquid epoxy resin, and an epoxy resin curing agent.

The solid epoxy resin is not particularly limited as long as it is solid at room temperature and has one or more epoxy groups in its molecule. For example, it may be bisphenol A epoxy resin, biphenyl epoxy resin, etc. This allows the film shape to be maintained. Note that room temperature is the range of 20°C ± 15°C (5°C to 35°C) as specified in JIS Z 8703.

There are no particular limitations on the liquid epoxy resin, as long as it is liquid at room temperature. For example, it may be bisphenol A epoxy resin, bisphenol F epoxy resin, or a urethane-modified epoxy resin.

The amount of liquid epoxy resin blended is preferably 160 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of solid epoxy resin. If the amount of liquid epoxy resin blended is too high, it becomes difficult to maintain the film shape. Furthermore, if the amount of liquid epoxy resin blended is too high, the cured physical properties after thermal curing generally become high elasticity due to a high crosslink density, reducing the stress relaxation ability.

The epoxy resin curing agent is not particularly limited as long as it is a heat-curing agent that initiates curing when heated. Examples include anionic curing agents such as amines and imidazoles, and cationic curing agents such as sulfonium salts. The curing agent may also be microencapsulated to provide resistance to the solvents used in forming the film.

[Solder particles]
The solder particles can be appropriately selected from, for example, Sn-Pb, Pb-Sn-Sb, Sn-Sb, Sn-Pb-Bi, Bi-Sn, Sn-Cu, Sn-Pb-Cu, Sn-In, Sn-Ag, Sn-Pb-Ag, Pb-Ag, etc., as specified in JIS Z 3282-1999, depending on the electrode material, connection conditions, etc. Bi-based solder is an alloy with low toughness, and there are concerns about cracking at the solder's metal joints. However, by applying this technology, stress can be alleviated, cracking at the solder's metal joints can be suppressed, and an increase in connection resistance can be suppressed.

The lower limit of the melting point of the solder particles is preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 130°C or higher. The upper limit of the melting point of the solder particles may be 200°C or lower, preferably 180°C or lower, more preferably 160°C or lower, and even more preferably 150°C or lower. Furthermore, a flux compound may be directly bonded to the surface of the solder particles for the purpose of activating the surface. Activating the surface can promote metallic bonding with the electrode portion.

The average particle size of the solder particles is preferably 0.5 times or less, more preferably 0.3 times or less, and even more preferably 0.2 times or less, the minimum inter-terminal distance (space distance) between the first terminal row of the surface-mounted component and the second terminal row of the wiring board. This relationship between the space distance and the average particle size of the solder particles makes it possible to join the first terminal row of the surface-mounted component and the second terminal row of the wiring board using a reflow oven. If the average particle size of the solder particles is greater than 0.5 times the minimum inter-terminal distance between the first terminal row of the surface-mounted component and the second terminal row of the wiring board, there is a higher possibility of a short circuit occurring.

The lower limit of the average particle size of the solder particles is preferably 0.5 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. This allows for a consistent coating thickness of the film. If the average particle size of the solder particles is less than 0.5 μm, a good solder bond with the electrode cannot be achieved, and reliability tends to deteriorate. The upper limit of the average particle size of the solder particles may be 50 μm or less, and is 30 μm or less, preferably 20 μm or less, and even more preferably 10 μm or less.

The average particle size is the average major axis diameter of particles measured, for example, with N=20 or more, preferably N=50 or more, and more preferably N=200 or more, in observation images using a metallurgical microscope, optical microscope, or electron microscope such as a scanning electron microscope (SEM). In the case of spherical particles, it is the average diameter of the particles. It may also be measured using known image analysis software (such as "WinROOF" from Mitani Corporation or "Azokun (registered trademark)" from Asahi Kasei Engineering Corporation) or using an image-based particle size analyzer (e.g., FPIA-3000 from Malvern Instruments) (N=1000 or more). The average particle size determined from observation images or an image-based particle size analyzer can be the average maximum length of the particles. When preparing an anisotropic conductive adhesive, manufacturer values such as the particle size (D50) at which the cumulative frequency in the particle size distribution determined by laser diffraction/scattering method reaches 50% or the arithmetic mean diameter (preferably by volume) can be used.

The maximum diameter of the solder particles can be 200% or less of the average particle size, preferably 150% or less of the average particle size, and more preferably 120% or less of the average particle size. By having the maximum diameter of the solder particles within this range, the solder particles can be sandwiched between electrodes, and the electrodes can be joined by melting the solder particles.

Furthermore, in the case of an aggregate formed by the aggregation of multiple solder particles, the size of the aggregate may be the same as the average particle size or maximum diameter of the solder particles described above, or the average particle size or maximum diameter of the solder particles may be smaller than the above-mentioned values. The size of individual solder particles can be determined by image observation as described above.

The solder particles are preferably dispersed in a binder, and may be arranged randomly or according to a certain pattern. The solder particles may also be in the form of aggregates of multiple particles.

The lower limit of the mass ratio range of the solder particle content is preferably 30 wt% or more, more preferably 40 wt% or more, and even more preferably 50 wt% or more. The lower limit of the volume ratio range of the solder particle content is preferably 5 vol% or more, more preferably 8 vol% or more, and even more preferably 12 vol% or more. By ensuring that the solder particle content satisfies the aforementioned mass ratio or volume ratio range, excellent conductivity, heat dissipation, and adhesion can be achieved. When the solder particles are present in a binder, the volume ratio may be used. When an anisotropic conductive bonding material is produced (before the solder particles are present in the binder), the mass ratio may also be used. The mass ratio can be converted to a volume ratio based on the specific gravity and compounding ratio of the compound. If the solder particle content is too low, excellent conductivity, heat dissipation, and adhesion cannot be achieved. If the content is too high, the anisotropy is easily impaired, making it difficult to achieve excellent conductivity reliability.

[Other additives]
In addition to the binder and solder particles described above, the anisotropic conductive adhesive can contain various additives that have been conventionally used in adhesives, provided that the effects of the present invention are not impaired. The particle size of the additive is preferably smaller than the average particle size of the solder particles, but is not particularly limited as long as it does not impede inter-electrode bonding.

The anisotropic conductive adhesive can be obtained, for example, by mixing an insulating binder and solder particles in a solvent, applying the mixture to a predetermined thickness on a release-treated film using a bar coater, and then drying to volatilize the solvent. Alternatively, the mixture can be applied to a release-treated film using a bar coater and then pressurized to a predetermined thickness. To improve the dispersibility of the solder particles, it is preferable to apply a high shear force while the solvent is still present. For example, a known batch-type planetary mixing device can be used. The residual solvent content of the anisotropic conductive adhesive is preferably 2% or less, and more preferably 1% or less.

4. Examples
In this example, a connector component and peripheral components were mounted on a rigid substrate at a predetermined distance using an anisotropic conductive film containing solder particles. Then, insulation evaluation and connection resistance evaluation of the mounted body were performed. However, this example is not limited to these.

[Preparation of anisotropic conductive film]
A 35 μm thick anisotropic conductive film was prepared using 80 parts by weight of solid epoxy resin (bisphenol F epoxy resin, Mitsubishi Chemical Corporation, JER4007P), 20 parts by weight of liquid epoxy resin (dicyclopentadiene backbone epoxy resin, ADEKA Corporation, EP4088L), 5 parts by weight of epoxy resin curing agent (imidazole-based curing agent, Shikoku Chemical Industry Co., Ltd., Curesol 2P4MHZ-PW), 3 parts by weight of flux compound (glutaric acid (1,3-propanedicarboxylic acid), Tokyo Chemical Industry Co., Ltd.), and 200 parts by weight of solder particles (MCP-137, 5NPlus Inc., Sn-58Bi alloy, solidus temperature 138°C) with an average particle size of 20 μm. The minimum melt viscosity of the anisotropic conductive adhesive was approximately 100 Pa·s.

[Connector implementation]
The following connector components, peripheral components, and substrate were prepared, an anisotropic conductive film was placed on the substrate, and the connector components and peripheral components were mounted at a predetermined distance in accordance with the wiring of the substrate. The connector components and peripheral components were then mounted through a reflow process under the following reflow conditions.
Connector part: 10-pin (20-pin) 0.35mm pitch plug connector, Hirose Electric Co., Ltd., BM23FR0.6-20DP-0.35V (895)
Peripheral parts: 10-pin (20-pin) 0.35mm pitch receptacle connector, Hirose Electric Co., Ltd., BM23FR0.6-20DS-0.35V (895)
Substrate: Rigid substrate compatible with the above plug connector (Dexerials evaluation glass epoxy substrate, Ni-Au plated)
Mating connector: 10 pins on one side (20 pins on both sides), 0.35 mm pitch receptacle connector, Hirose Electric Co., Ltd., BM23FR0.6-20DS-0.35V (895), height from the plug terminal surface (mounting surface) on the side to the receptacle pin when the plug and receptacle are mated: 120 μm
Reflow conditions: 150°C to 260°C for 100 seconds, peak temperature 260°C

[Evaluation of the package]
In the cross-sectional view shown in Figure 5, for a package in which the distance W between the side of the plug connector and the side of the peripheral component is a predetermined value, the height _T2 from the plug terminal surface to which the binder of the anisotropic conductive film creeps up on the side of the plug connector was measured. A mating receptacle connector was also mated to the package in which the plug connector was mounted, and the resistance value was measured when a current of 1 mA was passed through each pin, and the median value was calculated. Packages with one or more pins whose median resistance value exceeded 0.1 Ω were evaluated as "NG," and all other packages were evaluated as "OK."

Table 1 shows the measurement results of the binder creep height and the evaluation results of the conductivity test.

In Comparative Example 1, no peripheral components were mounted on the side of the plug connector, so the creep-up height _T2 was 156 μm, and the continuity evaluation after mating was NG. In Comparative Examples 2 and 3, peripheral components were mounted on the side of the plug connector, but the distance W between the side of the plug connector and the side of the peripheral component was 2.0 mm or more, so the creep-up height _T2 was greater than the height _T1 from the plug terminal surface to the receptacle pin ( _T1 < _T2 ), and the continuity evaluation after mating was NG.

In Examples 1 to 4, the distance W between the side of the plug connector and the side of the peripheral component was 0.2 mm or more and 1.5 mm or less, so the creep-up height _T2 was suppressed and the creep-up height _T2 was equal to or less than the height _T1 from the plug terminal surface to the receptacle pin ( _T1 > _T2 ). In Examples 3 and 4, the distance W between the side of the plug connector and the side of the peripheral component was small, so the receptacle connector could not be mated, but mating became possible by using a receptacle connector with a narrow side width. Note that it is difficult to make the distance W between the side of the plug connector and the side of the peripheral component less than 0.2 mm due to the lead terminals of the plug connector and the mating of the receptacle connector.

Furthermore, by mounting peripheral components on the side of the plug connector, the creep-up height _T2 can be kept within the range of 70 μm to 150 μm, and therefore, it was found that the effects of this technology can be obtained in a vertical mating connector in which the height from the plug terminal surface on the side to the receptacle pin when the plug and receptacle are mated is 70 μm to 150 μm. Furthermore, it was found that by setting the distance between the side of the plug connector and the side of the peripheral components to 0.2 mm to 3.0 mm and mounting them all at once in the reflow process, it is possible to prevent the binder from creeping up the side of the connector.

[Evaluation of a mounting assembly with multiple peripheral components]
Figure 7 is a plan view illustrating a test for evaluating the distance between peripheral components when multiple peripheral components are mounted in the longitudinal direction of a plug. In the plan view shown in Figure 7, the distance W between the side of the plug 1 and the side of the peripheral surface-mounted component 3 was set to 0.2 mm, and two surface-mounted components 3 were mounted with the distance Ws between the surface-mounted components 3 set to a predetermined value. The height _T2 from the plug terminal surface at which the binder creeps up was measured at the midpoint of the distance Ws between the surface-mounted components 3.

Table 2 shows the measurement results of binder creep-up height versus the distance between adjacent parts.

In Comparative Examples 4 and 5, the distance Ws between the peripheral components was 1.8 mm or more, so the creeping height _T2 was greater than the height _T1 from the plug terminal surface to the receptacle pin ( _T1 < _T2 ). In Examples 4 to 8, the distance Ws between the peripheral components was 0.2 mm or more and 1.5 mm or less, so the binder was also drawn into the side surfaces of the peripheral components, suppressing the creeping height _T2 and making it possible to make the creeping height _T2 equal to or less than the height _T1 from the plug terminal surface to the receptacle pin (T1 > T2).

Furthermore, from the relationship between the distance W between the side of the plug connector and the side of the peripheral component and the distance Ws between the peripheral components, it was found that the creep-up height _T2 can be made 120 μm or less by making the distance W between the side of the plug connector and the side of the peripheral component 0.2 mm to 1.5 mm and the distance Ws between the peripheral components 1.5 mm to 0.2 mm.

REFERENCE SIGNS LIST 1 plug, 2 receptacle, 3 surface-mounted component, 4 anisotropic conductive adhesive, 5 wiring board, 11A, 11B pin, 12A, 12B plug terminal, 21A, 21B pin, 22A, 22B receptacle terminal, 41 solder particle, 51 substrate, 52A, 52B substrate terminal, 53 terminal, 101 plug, 103 anisotropic conductive adhesive, 105 substrate, 111A, 111B pin, 152A, 152B substrate terminal, 142A, 142B solder

Claims (9)

a placement step of placing an anisotropic conductive adhesive containing solder particles on a wiring board, and placing a plug of a vertical mating connector and a surface mount component on the anisotropic conductive adhesive;
a bonding step of bonding the plug and the surface mount component to the wiring board using a reflow furnace set at a temperature equal to or higher than the melting point of the solder particles,
When the plug and receptacle are mated, the height from the plug terminal surface at the side to the receptacle pin is 70 μm or more and 150 μm or less, and the distance between the side of the plug and the side of the surface mount component is 0.2 mm or more and 1.5 mm or less ,
A method for manufacturing a connection structure , wherein the height of the binder of the anisotropic conductive adhesive creeping up to the side of the plug is smaller than the height from the plug terminal surface to the pin of a receptacle . A method for manufacturing a connection structure according to claim 1, wherein the placement step places one surface-mounted component along the longitudinal direction of the plug. 2. The method for manufacturing a connection structure according to claim 1, wherein in the arranging step, a plurality of surface mount components are arranged in the longitudinal direction of the plug so that the distance between the surface mount components is 1.5 mm or less, while the distance between the side of the plug and the side of the surface mount components is 0.2 mm to 1.5 mm. A method for manufacturing a connection structure according to any one of claims 1 to 3, wherein the minimum melt viscosity of the anisotropic conductive adhesive is 150 Pa·s or less. a wiring board, a plug of a vertical mating connector, a surface mount component, and an adhesive layer that bonds the plug and the surface mount component to the wiring board;
When the plug and receptacle are mated, the height from the plug terminal surface at the side to the receptacle pin is 70 μm or more and 150 μm or less, and the distance between the side of the plug and the side of the surface mount component is 0.2 mm or more and 1.5 mm or less ,
A connection structure in which the height of the binder of the adhesive layer creeping up to the side of the plug is smaller than the height from the plug terminal surface to the pin of a receptacle . The connection structure of claim 5, wherein one surface-mounted component is mounted along the entire length of the plug. 6. The connection structure according to claim 5, wherein a plurality of surface-mounted components are mounted in the longitudinal direction of the plug so that the distance between the side of the plug and the side of the surface-mounted components is 0.2 mm to 1.5 mm, and the distance between the surface-mounted components is 1.5 mm or less. 8. The connection structure according to claim 5, wherein the binder of the adhesive layer creeps up to a side of the plug to a height of less than 150 [mu]m. 8. The connection structure according to claim 5, wherein the binder of the adhesive layer creeps up to a side of the plug to a height of 120 [mu]m or less.