TWI711506B - Welding joining method and welding joining device - Google Patents

Abstract

We provide welding and joining technology that has a short joining time and can easily ensure joining accuracy. In electromagnetic induction heating, only metal heats up when alternating current flows through the coil wire. Since power output control is easy, complex control such as stage control can be performed easily and with high accuracy. For example, heating control is performed. For solder paste containing thermosetting resin and solder pellets, the thermosetting resin is softened before the solder pellets are melted, while for solder paste containing solder pellets, solvent and flux, the solder paste is evaporated before the solder pellets are melted. Solvent, liquefied flux.

Description

Welding joining method and welding joining device

The present invention relates to welding and joining technology of electrical products.

In electrical products, the wiring terminal and the wiring terminal are welded together. Soldering is also used when packaging semiconductors to circuit boards. Solder joining is performed by placing solder between the joining objects and then heating the solder to melt it. When heating, a reflow furnace (heating furnace) is generally used.

Nowadays, resin is used in most electrical products. If the resin product is heated in a reflow furnace (heating furnace), the resin part may be thermally damaged. For this reason, a resin with high heat resistance is also used with a relatively low melting point solder (low temperature solder).

In addition, low-temperature solder is also used for the packaging of components with weak heat resistance such as image sensors.

Nevertheless, the strength and toughness of low-temperature solder (for example, SnBi-based solder) are insufficient. In response to this, a technique of reinforcing with thermosetting resin has been proposed (for example, Patent Document 1).

On the other hand, by using laser irradiation welding and joining-related technology, spot welding can be performed. By heating the joint only momentarily, the thermal damage to the surrounding resin part is reduced. Therefore, solder with a relatively high melting point (high temperature solder) can be used to ensure sufficient strength and toughness.

【Prior Technical Literature】

【Patent Literature】

Patent Document 1: JP 2010-232388 A

The use of thermosetting resin reinforcement technology can solve the problems related to low-temperature solder, but due to the use of a reflow furnace, the joining time becomes longer and productivity deteriorates. Generally, the time required for a series of joining operations is about 5 minutes. In addition, it is difficult to control the temperature of the reflow furnace. The consequence is that it is difficult to maintain the joining accuracy. In addition, the reflow furnace makes the device larger.

On the other hand, by using the technology related to welding and joining by laser irradiation, although one joining is completed in an instant, since multiple places are joined continuously, the joining time becomes longer and productivity deteriorates. In addition, in recent years, joining objects tend to be extremely miniaturized, and it is difficult to irradiate more accurately. The consequence is that it is difficult to maintain the joining accuracy. In addition, there are also problems related to scattering of flux or scattering of solder particles.

The present invention is to solve the above-mentioned problems, and its object is to provide a technique that can easily ensure accuracy with a short joining time.

The bonding method of the present invention to solve the above-mentioned problems includes: a process of disposing a solder paste between a first to-be-bonded element and a second to-be-bonded element; and a process of melting the solder contained in the solder paste by electromagnetic induction heating. In this electromagnetic induction heating, the heating temperature and heating time are controlled.

In the above-mentioned invention, it is preferable to control the power output and output time of the electromagnetic induction heating device in multiple stages in the electromagnetic induction heating.

The output control is easy in electromagnetic induction heating. Therefore, complicated heating control can be easily performed.

In the above invention, it is preferable that the solder paste contains solder pellets and thermosetting resin; in the electromagnetic induction heating process, the thermosetting resin is heated so as not to exceed the melting temperature of the solder to soften the thermosetting resin, and then heated to a temperature above the melting temperature of the solder to melt Solder pellets.

In the above invention, preferably: the solder paste contains solder particles, solvent and flux; in the electromagnetic induction heating process, heating is used to evaporate the solvent, maintain the temperature to liquefy the flux, remove the oxide film, and heat to melt the solder grain.

The bonding device of the present invention, which solves the above problems, uses electromagnetic induction heating to melt the solder paste disposed between the first to-be-joined element and the second to-be-joined element to join the first to-be-joined element and the second to-be-joined element, And can control the power output and output time of the electromagnetic induction heating.

According to the joining technique of the present invention, the joining time can be shortened and the joining accuracy can be easily ensured.

2, 5‧‧‧Connecting terminal

3‧‧‧Formed body

4‧‧‧Flexible sheet

8‧‧‧Thin Film Substrate

9‧‧‧LED chip

Figure 1 shows the basic principles of electromagnetic induction.

Figure 2 is an explanatory diagram of terminal bonding at the FPC (first embodiment).

Figure 3 is a schematic explanatory diagram of the joining procedure (first embodiment).

Figure 4 is a conceptual diagram of heating control (first embodiment).

Figure 5 is an example of empirical experiment control.

Fig. 6 is an explanatory diagram of the chip package on the film substrate (the second embodiment).

Figure 7 is a conceptual diagram of heating control (the second embodiment).

<Device and Principle>

Explain the basic principle of electromagnetic induction heating based on Figure 1. The electromagnetic induction heating device is composed of a coil wire and a power source.

When alternating current flows through the coil wire, magnetic lines of force with varying intensity are produced. When a conductive substance (usually a metal, more specifically a joining object) is placed near it, eddy current flows through the metal under the influence of the changing magnetic field lines. Since metals usually have electrical resistance, when current flows through the metal, Joule heat will be generated, causing the metal to heat itself. This phenomenon is called induction heating.

The calorific value Q caused by electromagnetic induction is expressed by the following formula.

Q=(V ² /R)×t[V=applied voltage; R=impedance; t=time]

In electromagnetic induction heating, since only metal generates heat, thermal damage to the surrounding resin part is reduced.

In electromagnetic induction heating, since only metal generates heat, it can be joined in a short time with less energy. The time required for one connection is several to ten seconds.

In electromagnetic induction heating, if it is in a uniform magnetic field, since a predetermined Joule heat is obtained, the bonding accuracy is high. In addition, if it is in a uniform magnetic field, multiple bonding can be performed at a time.

In electromagnetic induction heating, it is easy to control the power output and output time by the control device. Therefore, the heating temperature and heating time can also be easily controlled. Thereby, it is possible to easily perform a complicated operation (step cure) as described below. The control device can also pre-store the heating profile.

<First implementation type>

Take terminal bonding on non-heat-resistant FPC (flexible printed circuit board) as an example. For example, as shown in FIG. 2, the connecting terminal 2 of a transparent resin plate and the connecting terminal 5 of a flexible plate (FPC) 4 formed by forming electrodes and wires of a predetermined pattern on the surface and the back. The transparent resin sheet material is formed into, for example, a shell-shaped molded body 3 by thermoforming. In addition, the electrodes and wiring formed on the transparent resin plate are not shown because they are extremely thin and cannot be visually observed.

Figure 3 is a schematic explanatory diagram of the joining procedure. The upper side of the figure is a cross-sectional view, and the lower side of the figure is a plan view.

The connection terminal 2 and the connection terminal 5 are arranged to face each other, and a solder paste is applied between the connection terminal 2 and the connection terminal 5. At this time, solder paste can also be placed between the connection terminals 2 and 2. For example, the connection terminal 5 is arranged after solid printing of the solder paste at the corresponding position of the connection terminal 2.

In addition, a load is applied through a nozzle, and the connection terminal 2 and the connection terminal 5 are brought into close contact with each other. In order to prevent the FPC from bending under the nozzle load at this time, be careful not to crush the solder particles contained in the solder paste.

The solder paste contains solder pellets and thermosetting resin. It may also contain suitable flux. Although the solder particles may be high-temperature solder, a low-temperature solder (for example, SnBi solder) is described here. The melting point of SnBi solder is about 138°C. The thermosetting resin is not particularly limited, and an epoxy resin is used for description here.

In this state, the melting of the solder is controlled by heating, and solder bonding is realized. Figure 4 is a conceptual diagram of heating control.

First, it is heated to close to the melting point of the solder in about 1 second, and then the temperature is maintained for about 1 second (A zone in the figure). Thermosetting resin will not be cured immediately by heating, but will soften and fluidize first. The thermosetting resin between the connection terminal 2 and the connection terminal 5 flows between the connection terminals 2 and 2 (between patterns). Since the melting point of the solder has not been reached at this time, the solder particles have not changed.

Then, it is heated to a predetermined temperature exceeding the melting point of the solder (for example, 220° C.) in about 2 seconds, and the predetermined temperature range is maintained for about 1 second (in the figure B area). The solder pellets between the connection terminal 2 and the connection terminal 5 melt to form a solder mass. A part of this heat energy is conducted to the solder pellets between the connecting terminals 2 and 2, and the solder pellets between the connecting terminals 2 and 2 flow through the softened cured resin and are located at the solder bumps between the connecting terminal 2 and the connecting terminal 5. Cohesion. This means that there are no solder particles between the connection terminals 2 and 2.

Next, heating is performed for about 3 seconds while suppressing output. The temperature of the joint gradually drops to close to the melting point of the solder (C area in the figure). The thermosetting resin is gelling and semi-cured.

The temperature of the joint drops rapidly by ending the heating (Figure D area). The thermosetting resin is completely cured so as to cover the periphery of the joint. In this way, the joint is reinforced.

There is no thermosetting resin between the connection terminal 2 and the connection terminal 5, and the solder joint can reliably conduct electricity.

There are no solder particles between the connection terminals 2 and 2, and it is reinforced by thermosetting resin while ensuring insulation.

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

In addition, the heating control shown in Fig. 4 is an example, and the numerical values are examples to assist understanding. The appropriate temperature profile can be set corresponding to the melting characteristics of the solder and the curing characteristics of the resin.

The inventor conducted the following empirical experiments. Figure 5 shows a control example in a demonstration experiment with nozzles. Perform simpler control for empirical experiments. In the figure, "15%" and "35%" are indicators of power output. The larger the value, the greater the degree of heating.

After continuing to output "15%" for about 3 seconds and make the temperature of the joint 140°C (the "15%-3s" interval shown in Figure 5), continue to output "35%" for about 2 seconds and make the joint When the temperature is 230°C (the "35%-2s" interval shown in Figure 5), then the output ends. The temperature of the joint is reduced by natural cooling. Record the temperature history within 10 seconds.

The inventor confirmed the results of the empirical experiment through enlarged photos (not shown). Before heating, by applying solder paste, solder particles are evenly arranged on the connection terminals and between the patterns.

Then confirm the state of the pattern room after heating. After welding and joining, the joint was peeled off for observation. The solder bumps on the connection terminals are reliably spread and the resin between the patterns is solidified. In addition, observe in detail between enlarged patterns. Although there are some solder particles remaining in the resin between the patterns, in the state of covering the resin, the particles are kept independent of each other without melting. Thereby, even if solder particles remain in the resin between the patterns, the insulating state between the patterns is maintained.

Then evaluate the reliability. First, evaluate the reliability of the connection impedance value. High temperature/low temperature cycle test environment is carried out under multiple conditions. Under any conditions, there is no deterioration over time. Next, the reliability of the peel adhesion strength was evaluated. High temperature/low temperature cycle test environment is carried out under multiple conditions. Under any conditions, there is no deterioration over time. In addition, the above-mentioned reliability evaluation results are comparable to the prior art.

In addition, since it does not contain solvents, there will be no problems related to flux scattering.

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

As described above, with simple heating control, it is confirmed that a highly accurate welding joint is feasible in a short time.

In addition, the solder paste containing the high-temperature solder of the second embodiment can also be used for the connection of the terminals. Print solder paste on the joints.

<Second Implementation Type>

As shown in Fig. 6, the soldering joining of packaging LED chips to PET or other film substrates will be described as an example.

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

Solder paste contains solder pellets, solvent and flux. Although low temperature solder can be used for the solder pellets, since only the metal generates heat under electromagnetic induction heating, the surrounding thermal damage is reduced, so high temperature solder (for example, SnAgCu-based solder) can be used. The melting point of SnAgCu solder is about 220°C.

In this state, the melting of the solder is controlled by heating, and solder bonding is realized. Figure 7 is a conceptual diagram of heating control.

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

Next, heat for about 3 seconds to maintain the temperature of the joint at 150°C (zone B in the figure). This liquefies the flux and removes the oxide film at the joint.

In addition, heating is performed for about 2 seconds so that the peak temperature (for example, 240° C.) exceeds the melting point of the solder (zone C in the figure). This melts the solder particles.

The temperature of the joint drops rapidly by ending the heating (Figure D area).

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

In addition, since the wafer side is far away from the magnetic field, it is difficult to generate heat and the wafer will not be thermally damaged.

In addition, the solder paste containing low-temperature solder of the first embodiment can also be used in the packaging of the chip. Print solder paste on the joints.

<Summary>

Electromagnetic induction heating has few restrictions on materials, etc., and has a wide range of applications.

Electromagnetic induction heating has the advantage of energy saving compared with heating using reflow furnace and laser heating.

Electromagnetic induction heating, compared with heating by reflow furnace and laser heating, has extremely short joining time and high productivity.

Electromagnetic induction heating is very easy to control heating compared to heating using reflow furnace and laser heating, so the joining accuracy is high.

<Applications other than welding connection>

Although the present invention is related to welding and joining, it can also be applied to other than welding joining. For example, in the curing of thermosetting adhesives, the electromagnetic induction heating and heating control of the present invention can be applied.

Specifically, for a molded product in which a plastic shell and a metal element are integrated, the metal element is coated with a thermosetting adhesive, and the metal element is heated by electromagnetic induction heating, so that the thermosetting adhesive reacts.

In addition, in IC (Integrated Circuit) and other component packages that use aluminum wiring for antenna circuits, the aluminum pad of the connection pad is heated by electromagnetic induction heating, making conductive material/anisotropic conductive film (ACF)/anisotropic conductive Polymer adhesives such as paste (ACP) react.

Therefore, it is easy to achieve energy saving, short time, high productivity, and high precision adhesion.

Claims (2)

A soldering method for joining a first element to be joined with a second element to be joined by solder paste, characterized in that the first element to be joined is formed on a non-heat-resistant element and is adjacent to each other in an insulated state A plurality of metal terminals; the solder paste contains solder particles and thermosetting resin, and does not contain foaming materials; between the metal terminals of the first element to be joined and between the first element to be joined and the second element to be joined A procedure for disposing solder paste; and a procedure for melting the solder contained in the solder paste by directly heating at least the first joined element by electromagnetic induction, wherein in the electromagnetic induction heating procedure, the first joined element and the Under the condition that the solder paste between the second components to be joined is applied with a load, the thermosetting resin is heated so as not to exceed the melting temperature of the solder to soften the thermosetting resin, and the thermosetting between the first component to be joined and the second component to be joined After the resin flows between the metal terminals of the first element to be joined, it is heated to a temperature above the melting temperature of the solder to melt the solder pellets between the first element to be joined and the second element to be joined. As the solder mass is formed With the softening of the thermosetting resin, the solder particles between the metal terminals of the first to-be-joined element in a fluid state agglomerate at the solder mass, so that the first to-be-joined element and the second to-be-joined element are energized At the same time, the insulation between the metal terminals of the first joined element is maintained, and the power output and output time of the electromagnetic induction heating device are controlled to control the heating temperature and heating time in multiple stages. A welding and joining device using the welding and joining method described in item 1 of the scope of patent application is characterized in that the power output and output time of the electromagnetic induction heating can be controlled.

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