JP6481085B2 - Solder joining method and solder joining apparatus - Google Patents

Description

  The present invention relates to a solder joint technology for electrical products.

  In the electrical product, the wiring terminal and the wiring terminal are joined by soldering. Soldering is also performed when a semiconductor is mounted on a circuit board. Solder bonding is performed by placing solder between bonding objects and then heating and melting the solder. In general, a reflow furnace (heating furnace) is used for heating.

  By the way, resin is used for most electric products. When a resin product is put into a reflow furnace (heating furnace) and heated, the resin part may be damaged by heat. For this reason, a resin having high heat resistance is used, and a solder having a relatively low melting point (low temperature solder) is used.

  Low-temperature solder is also used to mount components with low heat resistance such as image sensors.

  However, low-temperature solder (for example, SnBi solder) has insufficient strength and toughness. On the other hand, the technique (for example, patent document 1) reinforced with a thermosetting resin is proposed.

  On the other hand, by using a technique related to laser irradiation solder bonding, spot solder bonding can be performed. By heating only the joining portion instantaneously, the peripheral resin portion is less likely to be damaged by heat. Therefore, solder having a relatively high melting point (high temperature solder) can be used, and sufficient strength and toughness are ensured.

JP 2010-232388 A

  The use of a technology that reinforces with a thermosetting resin can solve the problems associated with low-temperature soldering, but since a reflow furnace is used, the joining time becomes longer and the productivity becomes worse. Generally, the time required for a series of joining operations is around 5 minutes. Moreover, it is difficult to control the temperature of the reflow furnace. As a result, it is difficult to maintain the joining accuracy. Furthermore, the reflow furnace increases the size of the apparatus.

  On the other hand, by using the technology related to laser irradiation soldering, one joining is completed instantly, but since many places are joined successively, the total joining time becomes longer, resulting in poor productivity. . In recent years, the objects to be joined have a tendency to be extremely small, and it is difficult to irradiate with high accuracy. As a result, it is difficult to maintain the joining accuracy. Furthermore, there are also problems related to flux scattering and solder particle scattering.

  The present invention solves the above-described problems, and an object of the present invention is to provide a technique capable of ensuring accuracy with a short joining time.

  The joining method of the present invention that solves the above problems includes a step of arranging a solder paste between a first member to be joined and a second member to be joined, and a step of melting solder contained in the solder paste by electromagnetic induction heating. . In the electromagnetic induction heating, the heating temperature and the heating time are controlled.

  In the above invention, preferably, in the electromagnetic induction heating, a power output amount and an output time of the electromagnetic induction heating device are controlled in multiple stages.

  Output control is easy with electromagnetic induction heating. Therefore, complicated heating control can be facilitated.

  Preferably, in the above invention, the solder paste includes solder grains and a thermosetting resin, and in the electromagnetic induction heating step, the thermosetting resin is softened by heating so as not to exceed a solder melting temperature. Then, the solder grains are melted by heating above the solder melting temperature.

  Preferably, in the above invention, the solder paste contains solder particles, a solvent, and a flux. In the electromagnetic induction heating step, the solvent is evaporated by heating, the temperature is maintained, and the flux is liquefied. The oxide film is removed and further heated to melt the solder grains.

  The solder bonding apparatus of the present invention that solves the above problems melts the solder paste disposed between the first member to be bonded and the second member to be bonded by electromagnetic induction heating, and the first and second members to be bonded. The member to be joined is joined, and the power output amount and output time of the electromagnetic induction heating can be controlled.

  According to the joining technique of the present invention, the joining time is short and the joining accuracy can be easily secured.

Basic principles of electromagnetic induction Explanatory diagram related to terminal bonding in FPC (first embodiment) Schematic explanatory diagram relating to the joining process (first embodiment) Conceptual diagram related to heating control (first embodiment) Demonstration experiment control example Explanatory drawing concerning chip mounting on a film substrate (second embodiment) Conceptual diagram related to heating control (second embodiment)

  <Apparatus and principle>

  Based on FIG. 1, the basic principle of electromagnetic induction heating will be described. The electromagnetic induction heating device includes a coil conductor and a power source.

  When an alternating current is passed through the coil conductor, magnetic field lines with varying strength are generated. When a substance that conducts electricity (usually a metal, more specifically, an object to be joined) is placed near it, an eddy current flows in the metal under the influence of the changing magnetic field lines. Since metal usually has electrical resistance, when current flows through the metal, Joule heat is generated and the metal self-heats. This phenomenon is called induction heating.

The calorific value Q due to electromagnetic induction is expressed by the following equation. Q = (V ² / R) × t [V = applied voltage: R = resistance: t = time]

  In electromagnetic induction heating, only the metal generates heat, so there is little risk of thermal damage to the surrounding resin part.

  In the electromagnetic induction heating, only the metal generates heat, so that it can be joined with less energy and in a short time. The time required for one bonding is several to several tens of seconds.

  In the electromagnetic induction heating, a predetermined Joule heat can be obtained within a uniform magnetic field, so that the joining accuracy is high. Moreover, if it exists in a uniform magnetic field, several joining can be performed at once.

  In the electromagnetic induction heating, it is easy to control the power output amount and the output time by the control device. As a result, it is easy to control the heating temperature and the heating time. Thereby, the following complicated operation (step cure) can be facilitated. The control device may store the heating profile in advance.

<First Embodiment>
An example of terminal bonding with a non-heat resistant FPC (flexible printed circuit board) will be described. For example, as shown in FIG. 2, the connection terminal 2 of the transparent resin sheet and the connection terminal 5 of the flexible sheet (FPC) 4 in which electrodes and wirings of a predetermined pattern are formed on the front and back surfaces are joined. The transparent resin sheet is formed into, for example, a case-shaped molded body 3 by thermoforming. In addition, since the electrode and wiring which were formed in the transparent resin sheet are so thin that it cannot be visually observed, illustration is abbreviate | omitted.

  FIG. 3 is a schematic explanatory diagram relating to the joining process. The upper side in the figure is a sectional view, and the lower side in the figure is a plan view.

  The connection terminal 2 and the connection terminal 5 are disposed so as to face each other, and a solder paste is applied between the connection terminal 2 and the connection terminal 5. At this time, a solder paste may be disposed between the connection terminals 2 and 2. For example, the connection terminal 5 is arranged after the solder paste is solid-printed at the position corresponding to the connection terminal 2.

  Further, a load is applied by the nozzle, and the connection terminal 2 and the connection terminal 5 are brought into contact with each other. At this time, care must be taken not to crush the solder grains contained in the solder paste so that the FPC does not warp the nozzle load.

  The solder paste contains solder grains and a thermosetting resin. A flux may be included as appropriate. The solder grains may be high-temperature solder, but will be described as low-temperature solder (for example, SnBi solder). The melting point of SnBi solder is about 138 ° C. The thermosetting resin is not particularly limited, but will be described as an epoxy resin.

  In this state, the solder is melted by heating control to perform solder joining. FIG. 4 is a conceptual diagram related to heating control.

  First, it is heated to near the solder melting point for about 1 second, and further maintained for about 1 second (A zone in the figure). The thermosetting resin does not cure immediately upon heating, but once becomes soft and fluidizes. The thermosetting resin between the connection terminal 2 and the connection terminal 5 flows between the connection terminals 2 and 2 (between patterns). At this time, since it is less than the solder melting point, there is no change in the solder grains.

  Next, it is heated to a predetermined temperature (for example, 220 ° C.) exceeding the solder melting point for about 2 seconds, and the predetermined temperature range is maintained for about 1 second (B zone in the figure). Solder grains between the connection terminal 2 and the connection terminal 5 melt and form a solder lump. Part of this heat is transmitted to the solder grains between the connection terminals 2 and 2, and the solder grains between the connection terminals 2 and 2 flow due to the softened cured resin, and the solder mass between the connection terminals 2 and 5. Aggregate. That is, there are no solder grains between the connection terminals 2 and 2.

  Furthermore, it heats for about 3 seconds, suppressing an output. The temperature at the joining point gradually decreases to near the solder melting point (C zone in the figure). The thermosetting resin is gelled and semi-cured.

  When the heating is completed, the temperature at the joining point rapidly decreases (D zone shown in the figure). The thermosetting resin is completely cured so as to cover the periphery of the joint. Thereby, a joining location is reinforced.

  There is no thermosetting resin between the connection terminal 2 and the connection terminal 5, and the current can be reliably supplied by soldering.

  There are no solder grains between the connection terminals 2 and 2 and they are reinforced by a thermosetting resin and reliably insulated.

  A series of joining operations are completed in about 10 seconds.

  Note that the heating control shown in FIG. 4 is an example, and the numerical value is an example for supplementing the understanding. What is necessary is just to set a temperature profile suitably according to the fusion | melting characteristic of a solder, and the hardening characteristic of resin.

  The inventor conducted the following demonstration experiment. FIG. 5 is an example of control in the demonstration experiment. Simpler control is used for demonstration experiments. In the figure, “15%” and “35%” are indices for setting the power output, and the larger the value, the more the heating is performed.

  After the output “15%” was continued for about 3 seconds and the temperature of the joint portion was about 140 ° C., the output “35%” was continued for about 2 seconds and the temperature of the joint portion was about 230 ° C., and the output was terminated. The temperature at the joint was lowered by natural cooling. A temperature history of about 10 seconds was recorded.

  The inventor confirmed the result of the demonstration experiment with an enlarged photograph (not shown). Prior to heating, solder particles were evenly disposed on the connection terminals and between the patterns by applying solder paste.

  Next, the state between the heated patterns was confirmed. After soldering, the joint was peeled off and observed. The solder lump surely spread on the connection terminals, and the resin was surely cured between the patterns. Furthermore, the pattern space was enlarged and observed in detail. Although a few solder grains remained in the resin between the patterns, the resin was covered with the resin and was not melted and kept independent while maintaining the grain shape. Thereby, even if a small amount of solder particles remain in the resin between the patterns, the insulation state between the patterns is maintained.

  Furthermore, reliability was evaluated. First, the reliability related to the connection resistance value was evaluated. High-temperature and low-temperature cycle test environments were conducted under multiple conditions. Under any conditions, deterioration with time did not occur. Furthermore, the reliability related to peel adhesion strength was evaluated. High-temperature and low-temperature cycle test environments were conducted under multiple conditions. Under any conditions, deterioration with time did not occur. The reliability evaluation result was the same as that of the prior art.

  Moreover, since the solvent is not included, a problem related to flux scattering does not occur.

  In addition, since the solder particles are indirectly heated, there is no problem relating to the scattering of the solder particles.

  As described above, it was confirmed that accurate soldering can be performed in a short time by simple heating control.

  In addition, you may use the solder paste containing the high temperature solder of 2nd Embodiment for joining of a terminal. Solder paste is printed on the joints.

Second Embodiment
As shown in FIG. 6, an example of solder joint in which an LED chip or the like is mounted on a film substrate such as PET will be described.

  A solder paste is printed at a predetermined position on the film substrate 8, and the LED chip 9 is mounted.

  The solder paste contains solder grains, a solvent, and a flux. Low-temperature solder may be used as the solder grains, but only metal is heated in electromagnetic induction heating, so that there is little thermal damage in the surroundings, and high-temperature solder (for example, SnAgCu solder) can be used. The melting point of SnAgCu solder is about 220 ° C.

  In this state, the solder is melted by heating control to perform solder joining. FIG. 7 is a conceptual diagram related to heating control.

  First, it is heated to 150 ° C. for about 4 seconds at a substantially constant heating rate (A zone in the figure). This evaporates the solvent. Moreover, the flux is not scattered.

  Subsequently, it heats for about 3 seconds so that the temperature of a junction location may be maintained at about 150 degreeC (B zone shown in figure). As a result, the flux is liquefied and the oxide film at the joint portion is removed.

  Further, heating is performed for about 2 seconds so that the peak temperature (for example, 240 ° C.) exceeds the solder melting point (C zone shown in the figure). As a result, the solder grains are melted.

  When the heating is completed, the temperature at the joining point rapidly decreases (D zone shown in the figure).

  A series of joining operations are completed in about 10 to several seconds. By using high-temperature solder, there are no problems related to strength and toughness.

  Further, since the chip side is away from the magnetic field, it is difficult to generate heat and the chip is not thermally damaged.

  In addition, you may use the solder paste containing the low temperature solder of 1st Embodiment for mounting of a chip | tip. Solder paste is printed on the joints.

<Summary>
Electromagnetic induction heating has few restrictions on materials, etc., and has a wide application range.

  Electromagnetic induction heating is superior in terms of energy saving compared to heating that uses a reflow furnace or laser heating.

  Electromagnetic induction heating has a very short bonding time and good productivity as compared with heating using a reflow furnace or laser heating.

  The electromagnetic induction heating is extremely easy to control the heating compared to the heating using the reflow furnace or the laser heating, and as a result, the bonding accuracy is high.

<Applications other than solder joints>
The present invention relates to solder bonding, but can be applied to other than solder bonding. For example, the present electromagnetic induction heating and heating control can be applied to thermosetting adhesive curing.

  Specifically, for a molded product in which a plastic housing and a metal part are integrated, a thermosetting adhesive is applied to the metal part, and the metal part is heated by electromagnetic induction heating. Allow the adhesive to react.

  Also, when mounting antenna circuit components using aluminum wiring such as IC (Integrated Circuit), the aluminum pad, which is a connection pad, is heated by electromagnetic induction heating to produce conductive material, anisotropic conductive film (ACF), anisotropic A polymer adhesive such as conductive paste (ACP) is reacted.

  As a result, energy-saving, easy productivity in a short time with high accuracy can be facilitated.

2 Connection terminal 3 Molded body 4 Flexible sheet 5 Connection terminal 8 Film substrate 9 Chip

Claims (2)

A solder joining method for joining a first joined member and a second joined member with a solder paste,
The first member to be joined is formed on a non-heat-resistant member, and is a plurality of adjacent metal terminals in an insulated state,
The solder paste contains solder grains and a thermosetting resin, does not contain a bubble generating material,
Disposing a solder paste between the metal terminals of the first bonded member and between the first bonded member and the second bonded member;
Melting the solder contained in the solder paste by directly heating at least the first member to be joined by electromagnetic induction;
With
In the electromagnetic induction heating step,
In a state where a load is applied to the solder paste between the first member to be joined and the second member to be joined, the thermosetting resin is softened by heating so as not to exceed the solder melting temperature. After allowing the thermosetting resin between the member and the second bonded member to flow between the metal terminals of the first bonded member,
Heating to a temperature equal to or higher than the solder melting temperature melts the solder grains between the first member to be joined and the second member to be joined to form a solder lump, and the fluidized first state as the thermosetting resin softens. Solder particles between metal terminals of one member to be joined are aggregated into the solder lump, energized between the first member to be joined and the second member to be joined, and between the metal terminals of the first member to be joined In order to maintain insulation, control the power output amount and output time of the electromagnetic induction heating device,
A soldering method characterized by controlling the heating temperature and the heating time in multiple stages. An apparatus used in the soldering method according to claim 1,
A power supply output amount and output time of the electromagnetic induction heating can be controlled.

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