JP4413543B2 - Electronic component adhesive and electronic component mounting method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an adhesive for electronic components used for bonding electronic components to a substrate and an electronic component mounting method using the adhesive material for electronic components.
[0002]
[Prior art]
As a method for mounting electronic components on a substrate, a solder bonding method is widely used. When the mounted electronic component is a fine-pitch component, etc., when the amount of solder bonding is small and the bonding strength is insufficient, the electronic component is fixed to the board with an adhesive to reinforce the solder bonding portion. Is called. In this mounting method, a so-called “resin pre-coating” is adopted in which a thermosetting resin adhesive is applied in advance to the mounting position of the substrate prior to mounting the electronic component, and the electronic component is mounted on the adhesive. There is a case. According to this method, there is an advantage that the effect of the thermosetting resin can be performed in the same process as the solder joining in the reflow process.
[0003]
As a resin adhesive used in such “resin pre-coating” applications, self-alignment characteristics in the reflow process, that is, when the solder melted by heating spreads on the electrodes of the substrate, the surface tension of the molten solder There is known an adhesive having a characteristic that terminals and bumps of an electronic component follow the position of the electrode. As such a self-alignment type adhesive, conventionally, a thermoplastic resin powder is dissolved and dispersed in a solvent such as alcohol at a predetermined ratio (for example, see Patent Document 1), or a thermosetting resin. The adhesive that does not lose its fluidity at the solder melting temperature by adjusting the type and composition of the added curing agent (see, for example, Patent Documents 2, 3, 4, and 5) is used. .
[0004]
[Patent Document 1]
Japanese Patent No. 2573929 [Patent Document 2]
Japanese Patent No. 2682366 [Patent Document 3]
Japanese Patent No. 2639293 [Patent Document 4]
Japanese Patent No. 3147116 [Patent Document 5]
Japanese Patent No. 3146888 [0005]
[Problems to be solved by the invention]
However, the above self-alignment type adhesive has the following drawbacks. First, in the adhesive of the type that imparts fluidity with a solvent as shown in Patent Document 1, voids are easily generated inside the resin reinforcing portion due to gas evaporated by heating during reflow, and a sufficient reinforcing effect is obtained. It may not be possible.
[0006]
Moreover, in the adhesive of the type which ensures the fluidity | liquidity at the time of solder joining by the hardening | curing agent in a thermosetting resin as shown to patent document 2,3,4,5, the lead-free solder which the use range has expanded in recent years is used. When applied to the mounting method used, there is a problem that it is difficult to achieve both sufficient bonding strength and self-alignment.
[0007]
That is, since the Ag-Sn lead-free solder has a higher melting temperature than the conventionally used Pb-Sn eutectic solder, the width between the solder melting temperature and the allowable maximum heating temperature in the reflow process is narrowed. For this reason, when the composition of the curing agent is set so that the heat curing temperature is increased, only the heating at the time of reflow results in that the adhesive is not completely cured and the adhesive strength is not ensured. On the other hand, if the composition of the curing agent is set so that the thermal curing temperature is lowered so that the thermal curing is completed by heating during reflow, the fluidity of the adhesive is lost when the solder melts and self-alignment is hindered. Is done.
[0008]
Therefore, the present invention provides an adhesive for electronic components that can solve the above-described problems and ensure sufficient adhesive strength and self-alignment property, and an electronic component mounting method using the adhesive for electronic components. Objective.
[0009]
[Means for Solving the Problems]
The electronic component adhesive according to claim 1 is used for bonding an electronic component mounted on a substrate by solder bonding to the substrate, and does not hinder the self-alignment phenomenon of the electronic component in the solder bonding. A thermosetting resin containing a main agent containing one of epoxy and acrylic and a curing agent for thermosetting the main agent, and has the property of being solid at room temperature and changing to a liquid state upon heating. And terpene resin, phenol resin, xylene resin, urea resin, melanin resin, amorphous rosin, imide resin, olefin resin, acrylic resin, amide resin, and polyester resin are selected as having compatibility with the above main ingredients. at least one solid resin is a composition which contains at a content of 5 to 75 wt%, viscosity at room temperature is 200 Pa · s was c is less than or equal to.
[0010]
The adhesive for electronic components according to claim 2 is the adhesive for electronic components according to claim 1 , and includes an activator that removes an oxide film of solder .
[0011]
The adhesive for electronic components according to claim 3 is the adhesive for electronic components according to claim 1 or 2 , wherein the solid resin content is 10 to 40% by weight .
[0013]
The electronic component mounting method according to claim 4 is an electronic component mounting method in which the connection electrode formed on the electronic component is solder-bonded to a plurality of electrodes formed on the substrate, and is either epoxy-based or acrylic-based. One have a varying nature in the liquid by heating is solid at room temperature in a thermosetting resin containing a main agent and a base resin a curing agent for thermosetting including, terpene resins, phenol resins, xylene resins, urea resins, melamine A content of 5 to 75% by weight of at least one solid resin selected from resin, amorphous rosin, imide resin, olefin resin, acrylic resin, amide resin, and polyester resin as having compatibility with the main agent. An adhesive for electronic components having a composition at a normal temperature and a viscosity at room temperature of 200 Pa · sec or less is provided between the electrode forming surface of the substrate and the electronic component. In the state of being interposed, the mounting step of aligning the connection electrode with the electrode and mounting the electronic component on the substrate, heating the substrate to melt the solder, and curing reaction of the thermosetting resin A heating step of changing the solid resin into a liquid state while promoting, and a solidification step of solidifying the solid resin and solder by returning the substrate to room temperature.
[0014]
According to the present invention, an adhesive for electronic components having a composition in which a solid resin having a property of being solid at room temperature and changing to a liquid state upon heating is contained in a thermosetting resin at a content of 5 to 75% by weight is used. As a result, both strength in the normal temperature region and fluidity in the high temperature region can be achieved, and sufficient adhesive strength after mounting and self-alignment property in the solder joining process can be ensured.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 and FIG. 2 are process explanatory views of an electronic component mounting method according to an embodiment of the present invention, and FIG. 3 is a graph showing the solid resin content and the shear strength in an electronic component adhesive according to an embodiment of the present invention. FIG. 5, FIG. 6, FIG. 7 are diagrams illustrating the process of the electronic component mounting method according to the embodiment of the present invention, and FIG. 8 is a diagram illustrating a heating profile during soldering in a reflow furnace.
[0016]
First, an electronic component mounting method will be described with reference to FIGS. In this electronic component mounting method, connection electrodes formed on an electronic component are soldered to a plurality of electrodes formed on a substrate.
[0017]
In FIG. 1A, a substrate 1 is formed with a plurality of different types of electrodes 2a, 2b, 2c. Connection electrodes for different types of electronic components are connected to the electrodes 2a, 2b, and 2c by solder bonding. Prior to mounting the electronic components, first, as shown in FIG. 1 (b), cream solder 3 is applied to the upper surfaces of the electrodes 2b and 2c, and then both outer sides of the electrode 2a as shown in FIG. 1 (c). In the middle of the electrodes 2b and 2c, an electronic component adhesive 4 (hereinafter simply referred to as "adhesive" 4) is applied. The adhesive 4 temporarily functions to fix the electronic component to the substrate 1 until the reflow process, and has a function as a reinforcing resin that solidifies after reflowing and fixes the electronic component to the substrate 1.
[0018]
Here, the adhesive 4 is required to have fluidity that does not hinder the self-alignment phenomenon caused by the melted solder at the time of solder bonding. In the solidified state after the solder bonding, the adhesive 4 is reinforced to fix the electronic component to the substrate. Adhesive strength as a resin for use is required. As a sufficient adhesive strength as a reinforcing resin, a shear strength measured by a method described later is required to be 10 N or more at room temperature (25 ° C.). The fluidity is determined by whether or not the self-alignment phenomenon is hindered by actual soldering.
[0019]
Here, the composition of the adhesive 4 having such characteristics will be described. The adhesive 4 contains solid resin and inorganic filler particles that are solid at room temperature and change into a liquid state upon heating in a thermosetting resin so that the viscosity at room temperature is 200 Pa · sec or less. . As will be described later, the solid resin content is set in the range of 5 to 75% by weight, and the inorganic filler content is set in the range of 30% by weight or less.
[0020]
Here, the thermosetting resin has a composition including a main agent containing one of epoxy and acrylic, a curing agent for thermosetting the main agent, and an activator for removing the oxide film of the solder. ing. As the solid resin, at least one selected from terpene resin, phenol resin, xylene resin, urea resin, melanin resin, amorphous rosin, imide resin, olefin resin, acrylic resin, amide resin, and polyester resin is thermosetting. It is mixed in the resin. When selecting these solid resins, solid resins that are compatible with the main agent are selected in relation to the components of the main agent. Thereby, when mixing solid resin in a main ingredient, it is possible to implement | achieve the liquid resin provided with fluidity | liquidity, without using the solvent containing a vaporizable gas component.
[0021]
FIG. 3 shows the relationship between the solid resin content (% by weight) in the adhesive 4 and the aforementioned shear strength at room temperature. For comparison, the same shear strength was measured for a conventional product not containing a solid resin. This shear strength is measured by first immersing a 1608 size rectangular chip in an adhesive applied to a flat surface with a thickness of 0.1 mm and pulling it up to transfer the adhesive to the lower surface of the rectangular chip, and To be installed. This aluminum plate was heat-treated in a reflow furnace according to the heating profile during actual soldering (FIG. 8), cooled to room temperature, and then the shear strength was measured. The shear strength was measured using a shear tester jig 50 mm / min. On the long side of a rectangular chip 0.1 to 0.2 mm high from the upper surface of the aluminum plate. The force when pressed and peeled at a speed of was measured.
[0022]
As shown in the graph of FIG. 3, the shear strength rapidly increases as the solid resin content increases, and reaches a shear strength of 10 N at a content of 5%. And the highest share strength is shown at a content rate of 20%, and the share strength gradually decreases with an increase in the content rate, and when it exceeds 75%, the share strength becomes less than 10N. Further, the conventional product (thermosetting resin) that does not contain a solid resin cannot be sufficiently cured because the amount of heat necessary for thermosetting is insufficient in the heating profile of FIG. 8, and the adhesive strength is extremely weak. Therefore, it can be seen that the range of the solid resin content in the adhesive 6a that satisfies the strength condition of the resin portion 6 described above is the range A (5 to 75%) shown in FIG. As can be seen from the graph, a more desirable result can be obtained by selecting the range B (10 to 40%).
[0023]
As shown in FIG. 2A, three types of electronic components 5, 6, and 7 are mounted on the substrate 1 on which the adhesive 4 is applied for temporarily fixing the electronic components. The electronic component 5 is a bumped component having solder bumps 5a as connection electrodes formed on the lower surface, and flux (not shown) is transferred to the bump 5a in advance (see FIG. 4). The electronic component 6 is a rectangular chip having terminals 6a as connection electrodes on both sides, and the electronic component 7 is a lead component having leads 7a as connection electrodes on both sides.
[0024]
These electronic components 5, 6 and 7 have bumps 5a, terminals 6a and leads 7a as connection electrodes in a state where adhesive 4 is interposed between the electrode forming surface of substrate 1 and the electronic components. The substrate 1 is mounted on the substrate 1 in alignment with the electrodes 2a, 2b and 2c (mounting process). Thereby, as shown in FIG.2 (b), the electronic components 5, 6, and 7 are temporarily fixed by the adhesive agent 4 to the board | substrate 1, and are sent to a reflow apparatus in this state. Then, the substrate 1 is heated to melt the bumps 5a on the electrodes 2a and the cream solder 3 on the electrodes 2b and 2c, and at the same time, the thermosetting resin is accelerated while promoting the curing reaction of the thermosetting resin in the adhesive 4. The solid resin contained in the resin is changed to a liquid state (heating step).
[0025]
Thereafter, the substrate 1 is taken out from the reflow apparatus and the substrate 1 is returned to room temperature, so that the solid resin, the bumps 5a, and the molten solder (cream solder 3) in the adhesive 4 are solidified (solidification step). As a result, in the electronic component 5, a solder joint portion 5 c is formed in which the molten solder is solidified in a state of being joined to the electrode 2 a, and in the electronic component 6, a solder fillet in which the molten solder connects the electrode 2 a and the terminal 6 a is formed. In the electronic component 7, the lead 7a is encased in the solder s and soldered to the upper surface of the electrode 2c. The electronic components 5, 6, and 7 are fixed to the substrate 1 by the solidified adhesive 4.
[0026]
Next, the behavior of the electronic component 5 in the above-described solder joining process will be described with reference to FIGS. In the mounting operation of the electronic component 5 shown in FIG. 2, the electronic component 3 is not always correctly aligned with the substrate 1, and as shown in FIG. 4A, the bump 5a is formed on the electrode 2a. On the other hand, there is a case where the electronic component 5 is temporarily fixed by the adhesive 4 in a state where the electronic component 5 is landed at a position deviated by a deviation amount d in the horizontal direction. Even in such a case, when the substrate 1 is heated and solder bonding is performed in the reflow process, as shown in FIG. 4B, the misalignment state is eliminated by the self-alignment action of the solder, and the electrode Solder joint 5c is formed at the correct position on 2a.
[0027]
This solder bonding process will be described with reference to FIG. FIG. 5 shows a process of solder bonding between the outer electrode 2a * and the bump 5a * located closest to the adhesive 4 in the combination of the bump 5a and the electrode 2a to be solder-bonded. In general, an oxide film is generated on the surface of the solder by exposure to the atmosphere. When the electronic component 5 is mounted on the substrate 1, as shown in FIG. 5A, the bump 5a covered with the oxide film 5b is formed. * Lands on the electrode 2a * via the flux 8.
[0028]
At this time, the adhesive 4 applied to the outside tends to flow inward on the substrate 1, and the adhesive 4 enters the contact interface between the surface of the bump 5 a * and the attached flux 8 by this flow. (See arrow a). The flow of the adhesive 4 is further promoted with a temporary decrease in viscosity in the process in which the thermosetting reaction of the adhesive 4 proceeds by heating. As shown in FIG. 5a * is separated from the oxide film 5b on the surface.
[0029]
In general, when the flux 7 is separated from the surface of the bump 4, the oxide film 4a remains in the solder bonding process and inhibits the solder bonding. However, in this embodiment, such a state occurs. Even in this case, good solder joint results can be obtained as described below. That is, since the adhesive 4 contains an activator having an oxide film removing ability, the oxide film 5b is removed by this active action. Further, the bump 5a * is melted by further heating, and is favorably soldered to the surface of the electrode 2a * covered with the flux 8.
[0030]
At this time, the melted bump 5a * is attracted to the upper surface of the electrode 2a * by the self-alignment effect derived from the surface tension of the molten solder, and the misalignment state before reflow is eliminated, and the positions of the electrode 2a * and the bump 5a * are eliminated. Almost coincide with each other (see FIG. 4B). Further, the bump height variation in the height direction is also absorbed by the sinking of the solder, and the bondability is improved. As the molten solder is cooled and solidified, as shown in FIG. 5D, the electronic component 5 is mounted on the substrate 1 with the solder joint portion 5c * positioned at the correct position on the electrode 2a *. (See FIG. 4 (b)).
[0031]
When the solder is melted, the solid resin in the thermosetting resin that is a component of the adhesive 4 changes to a liquid state, so that the adhesive 4 does not lose its fluidity even when heated to the solder melting temperature. The alignment phenomenon is not hindered. Then, after this soldering process is completed, the adhesive 4 is completely fixed by solidifying the solid resin once liquefied by heating together with curing by completing the thermosetting of the thermosetting resin. The outer edge portion of the electronic component 5 is fixed to the substrate 1 and functions as a resin reinforcing portion that reinforces the solder joint portion 5c on the upper surface of the electrode 2a.
[0032]
Next, the behavior of the electronic component 6 in the above-described solder joining process will be described with reference to FIG. When the electronic component 6 is mounted on the substrate 1, the rectangular electronic component 6 is not necessarily mounted with the direction in the horizontal plane correctly aligned, as shown in FIG. There are cases where the terminals 6a at both ends are mounted with their positions shifted from the electrodes 2b to which the cream solder 3 is supplied.
[0033]
Even in such a case, when the terminal 6a contacts the molten solder in which the cream solder 3 on the electrode 2b is melted in the solder joining process, the terminal 6a is sucked toward the center of the electrode 2b by the self-alignment action of the molten solder. The misalignment state before reflow is eliminated, and the center lines of the electrode 2c and the terminal 6a substantially coincide. At this time, the adhesive 4 applied between the electrodes 2c does not lose fluidity and does not hinder the self-alignment phenomenon even when heated to the solder melting temperature as in the case described above.
[0034]
Next, the behavior of the electronic component 7 in the above-described solder joining process will be described with reference to FIG. When the electronic component 7 is mounted on the substrate 1, the lead 7a extending from the side surface of the electronic component 7 is not always in contact with the cream solder 3 on the electrode 2c, as shown in FIG. As described above, the lead 7 a may be lifted away from the cream solder 7 while the lower surface is temporarily fixed by the adhesive 4.
[0035]
Even in such a case, the adhesive 4 is heated in the soldering process to increase the fluidity, so that the height position of the electronic component 7 is lowered and the lead 7a contacts the cream solder 3 on the electrode 2c. It becomes like this. When the lead 7a comes into contact with the molten solder in which the cream solder 3 is melted, the lead 7a is wrapped by the molten solder due to the self-alignment action of the molten solder, and the lifted state before reflow is eliminated, and the upper surface of the electrode 2c is in good condition. Soldered. At this time, the adhesive 4 applied between the electrodes 2c does not lose fluidity even in a state where it is heated to the solder melting temperature as in the case described above, and does not hinder the self-alignment phenomenon.
[0036]
As described above, the electronic component adhesive shown in the present embodiment is a solid resin having a property of being solid at room temperature and changing to a liquid state upon heating, and a content of 5 to 75% by weight in the thermosetting resin. It is the composition made to contain. Thereby, the adhesive strength in the normal temperature region and the fluidity in the high temperature region can be made compatible, and sufficient adhesive strength after mounting and self-alignment property in the solder joining process can be ensured.
[0037]
As a result, there is no problem in using a type of adhesive that imparts fluidity with a solvent, i.e., a problem that a void is generated inside the resin reinforced part due to the gas evaporated by heating during reflow. It is possible to obtain a sufficient reinforcing effect by forming a resin reinforced portion without a gap.
[0038]
In addition, the adhesive that secures the fluidity at the time of soldering by adjusting the blending ratio of the curing agent in the thermosetting resin, when applied to a mounting method using lead-free solder, which has been used in recent years However, it is difficult to achieve both sufficient bonding strength and self-alignment properties. However, in the adhesive 4 shown in the present embodiment, by blending a solid resin component that becomes liquid by heating, the solder can be melted. There is an advantage that the fluidity of the adhesive can be secured.
[0039]
In addition, since the solid resin solidifies by cooling to room temperature and contributes to adhesive strength, even if the thermosetting resin is not completely cured for some reason, such as fluctuations in heating conditions, It is possible to ensure sufficient adhesive strength.
[0040]
【The invention's effect】
According to the present invention, an adhesive for electronic parts having a composition in which a solid resin having a property of being solid at room temperature and changing to a liquid state upon heating is contained in a thermosetting resin at a content of 5 to 75% by weight is used. Therefore, the strength in the normal temperature region and the fluidity in the high temperature region can both be achieved, and sufficient adhesive strength after mounting and self-alignment property in the solder joining process can be ensured.
[Brief description of the drawings]
FIG. 1 is a process explanatory diagram of an electronic component mounting method according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a process of an electronic component mounting method according to an embodiment of the present invention. FIG. 4 is a process explanatory diagram of an electronic component mounting method according to an embodiment of the present invention. FIG. 5 is a process explanatory diagram of the electronic component mounting method according to the embodiment of the present invention. FIG. 6 is a process explanatory diagram of an electronic component mounting method according to an embodiment of the present invention. FIG. 7 is a process explanatory diagram of an electronic component mounting method according to an embodiment of the present invention. Explanatory drawing [Fig. 8] Diagram showing the heating profile during soldering in a reflow furnace [Explanation of symbols]
1 Substrate 2a, 2b, 2c Electrode 3 Cream solder 4 Adhesive 5, 6, 7 Electronic component 5a Bump 5b Oxide film 5c Solder joint 6a Terminal 7a Lead

Claims (4)

An adhesive for electronic components that is used to adhere an electronic component mounted on a substrate by solder bonding to the substrate, and does not hinder the self-alignment phenomenon of the electronic component in the solder bonding , either epoxy-based or acrylic-based or a main agent and a base resin comprising one of in a thermosetting resin containing a curing agent for thermosetting, have a property of changing into a liquid by heating is solid at ordinary temperature, terpene resins, phenol resins, xylene resins, urea 5 to 75% by weight of at least one solid resin selected from a resin, a melanin resin, an amorphous rosin, an imide resin, an olefin resin, an acrylic resin, an amide resin, and a polyester resin as having compatibility with the main agent. An electron having a composition that is contained at a content ratio of 200 Pa · sec or less at room temperature. Adhesive for goods. The adhesive for electronic parts according to claim 1 , further comprising an activator for removing an oxide film of the solder . The adhesive for electronic parts according to claim 1 or 2, wherein the solid resin content is 10 to 40% by weight . An electronic component mounting method in which connecting electrodes formed on an electronic component are solder-bonded to a plurality of electrodes formed on a substrate, wherein the main agent containing one of epoxy and acrylic and a curing agent that thermally cures the main agent have a varying nature in the liquid by heating is solid at room temperature in a thermosetting resin containing an agent, terpene resins, phenol resins, xylene resins, urea resins, melamine resins, amorphous rosin, imide resins, olefin A composition containing at least one solid resin selected from a resin, an acrylic resin, an amide resin, and a polyester resin as having compatibility with the main agent at a content of 5 to 75% by weight and having a viscosity at room temperature. In the state where the adhesive for electronic parts of 200 Pa · sec or less is interposed between the electrode forming surface of the substrate and the electronic parts, And mounting the electronic component on the substrate by aligning with the electrode, melting the solder by heating the substrate, and changing the solid resin into a liquid state while promoting the curing reaction of the thermosetting resin An electronic component mounting method comprising: a heating step; and a solidifying step of solidifying the solid resin and solder by returning the substrate to room temperature.

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