JP3973068B2 - Soldering method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of soldering an electronic element such as a thyristor or a diode, and more particularly, to a soldering method suitable for simultaneously soldering a plurality of connection objects to the electronic element using heating reflow.
[0002]
[Prior art]
FIG. 5 is a block diagram showing the configuration of the vehicle regulated rectifier. In order to rectify and supply the alternating current output from the alternating current generator 51 to the load 52 and the battery 53, diodes D1 to D6, It comprises thyristors S1 to S3, a voltage detection circuit 54, and the like.
[0003]
As a method for electrically and mechanically connecting the electronic elements such as the diode D and the thyristor S to the substrate, a solder paste is applied to a predetermined region of the circuit board surface by screen printing or a dispenser method, or A method is known in which a solder sheet described in Japanese Patent Application Laid-Open No. 62-118597 is used, and an electronic element is mounted thereon and passed through a heating reflow furnace.
[0004]
Further, when an electronic element to be soldered generates a large amount of heat like a power transistor or a thyristor, it is necessary to dissipate the heat to the outside so that the element does not reach an allowable temperature or more. In such a case, a heat sink is fixed on a circuit board, and an electronic element is soldered on this heat sink.
[0005]
[Problems to be solved by the invention]
FIGS. 6 to 9 are diagrams for explaining technical problems when soldering a thyristor to a heat sink and an electrode according to a conventional technique.
[0006]
In FIG. 6, preliminary solders 2c, 2g, and 2a are previously applied to the cathode and gate exposed on the upper surface of the thyristor 1 and the anode exposed on the lower surface, respectively. The thyristor 1 is placed on the upper surface of the heat sink 3 via solder pellets 4. On the upper surface of the thyristor 1, one end of the cathode electrode 5 and the gate electrode 6 is placed on each of the cathode and gate preliminary solders 2c and 2g.
[0007]
When this is passed through the heating reflow path, the mass of the heat sink 3 is larger than that of the respective electrodes 5 and 6, and the heat capacity of each of the electrodes 5 and 6 is smaller than the heat capacity of the heat sink 3, as shown in FIG. In addition, the preliminary solder 2c and 2g for the cathode and the gate melt faster than the preliminary solder 2a and the solder pellet 4 for the anode. Therefore, the cathode electrode element 5 and the gate electrode element 6 are first held to the thyristor 1 by the surface tension of the preliminary solders 2c and 2g and substantially semi-fixed.
[0008]
Thereafter, when the temperature of the heat sink 3 rises and the anode preliminary solder 2a and the solder pellet 4 begin to melt, the posture of the heat sink 3 is temporarily collapsed as shown in FIG. At this time, since the cathode electrode 5 and the gate electrode 6 and the thyristor 1 are in a semi-fixed state, if the posture of the heat sink 3 collapses, the posture of the electrodes 5 and 6 also collapses and the solder floats. There is a case. Alternatively, as shown in FIG. 9, the thyristor 1 may be pulled upward by the surface tension of the preliminary solder 2c and 2g previously melted, and the connection between the thyristor 1 and the heat sink 3 may be broken.
[0009]
The object of the present invention is to solve the above-described problems of the prior art, and when soldering an electronic device to a plurality of connection objects simultaneously, each connection object is soldered to the electronic device in a desired posture. There is to be done.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is characterized in that the following measures are taken.
[0011]
(1) In a soldering method in which an electronic element is soldered on a first connection object by heating reflow, and at the same time a second connection object is soldered to the electronic element, the electronic element is connected to the first connection object. The first solder to be connected to is melted earlier than the second solder to connect the electronic element to the second connection object.
[0012]
(2) In a soldering method of simultaneously soldering an electronic element to a plurality of connection objects by heating reflow, among the plurality of connection objects, the electronic element is a first connection object having a large mass. The first solder to be connected is melted faster than the second solder to be connected to the second connection object having a small mass.
[0013]
According to each of the above-described features, the first solder is melted first, the second solder is melted after the electronic element is stably semi-fixed to the first connection object in a normal posture, and the second solder is melted. The two objects to be connected are attracted to the electronic element side by the surface tension of the second solder, and both are semi-fixed at a predetermined relative position. At this time, the first solder is already melted, and the relative position between the electronic element and the first connection object is not further displaced, so the relative position between the second connection object and the electronic element is displaced. I don't have to.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a thyristor portion of a regulated rectifier manufactured by a soldering method to which the present invention is applied. The same reference numerals as those described above represent the same or equivalent portions.
[0015]
Copper foil soldering pads 8 (8a, 8b, 8c) are formed on the surface of the aluminum substrate 10 via an insulating film 9, and each pad 8 is a wiring pattern ( (Not shown). The heat sink 3 is fixed to the surface of the pad 8b by soldering. An anode exposed on the lower surface of the thyristor 1 is soldered to the upper surface of the heat sink 3. One end of the cathode electrode 5 and the gate electrode 6 is soldered to the cathode and gate exposed on the upper surface of the thyristor 1, and the other end is soldered to the solder pads 8a and 8c on the surface of the aluminum substrate. ing. The aluminum substrate 10 is accommodated in an outer case 11 and an insulating resin 12 is filled in the outer case.
[0016]
FIG. 2 is a diagram showing a soldering procedure of the thyristor 1. The cream solder 13 is applied on the soldering pad 8 b of the aluminum substrate 10, and the heat sink 3 is placed thereon. Preliminary solders 2a, 2c and 2g are preliminarily applied to the anode, cathode and gate of the thyristor 1, respectively. The thyristor 1 is mounted on the heat sink 3 via solder pellets 4.
[0017]
A high concentration flux 7 c is applied to the contact surface between the solder pellet 4 and the heat sink 3, and a low concentration flux 7 b is applied to the contact surface between the anode preliminary solder 2 a and the solder pellet 4. The cathode electrode 5 and the gate electrode 6 are arranged so that one end thereof covers the preliminary solders 2c and 2g, respectively. A low-concentration flux 7 a is applied to the contact surface between the preliminary solders 2 c and 2 g and the electrodes 5 and 6.
[0018]
Each of the fluxes is applied to the solder surface in advance or sprayed in the form of a mist so as to adhere to the solder surface in order to remove the oxide film on the solder surface or change the solder activity to control the melting point. The An activator such as a chlorine compound is added to each flux, and the dilution of the activator is low in the high concentration flux 7c and high in the low concentration fluxes 7b and 7a.
[0019]
FIG. 10 is a diagram showing the relationship between the dilution and concentration of the flux and the activity of the solder. The lower the dilution of the flux, in other words, the higher the flux concentration, the activity of the solder to which this is applied. The degree increases and the melting point decreases.
[0020]
When the heat sink 3 mounted with the thyristor 1 is introduced into the heating reflow furnace and heated as described above, the solder pellet 4 on the side of the heat sink 3 that has been coated with the high-concentration flux 7c and has become highly active melts. Due to the surface tension, the preliminary solder 2a of the thyristor 1 is drawn toward the heat sink 3 side. Furthermore, since the thyristor 1 is attracted to the solder “pond” of the molten solder pellet 4 and the spare solder 2a, the thyristor 1 is semi-fixed to the heat sink 3 with high viscosity as shown in FIG.
[0021]
Further, when the fluxes of the preliminary solders 2c and 2g formed on the upper surface of the thyristor 1 are activated with a lapse of time with a lapse of time, as shown in FIG. 4, the cathode electrode 5 and the gate electrode 6 Is soldered to the thyristor 1. At this time, in the present embodiment, the thyristor 1 is already semi-fixed in a normal posture with respect to the heat sink 3, and the relative position between the thyristor 1 and the heat sink 3 does not change. Therefore, the postures of the cathode electrode 5 and the gate electrode 6 with respect to the thyristor 1 are not relatively displaced, and both are soldered in a normal posture.
[0022]
In the above-described embodiment, it has been described that the substantial melting points of the preliminary solders 2c, 2a, and 2g are made different by controlling the dilution degree of the flux applied to each preliminary solder 2 of the thyristor. However, the present invention is not limited to this, and a difference in melting point may be provided by making the composition and material of each preliminary solder different.
[0023]
【The invention's effect】
According to the present invention, the first connection object (heat sink) on which the electronic element is placed and the first solder for fixing the electronic element are melted first and both are semi-fixed, and then the electronic The second solder for fixing the element and the second connection object (electrode) is melted and both are semi-fixed. When the second solder starts to melt, the first solder is already melted, and the relative position between the electronic element and the first connection object is not further displaced, so the second connection object and the electronic element The relative position with respect to is not displaced. Therefore, the soldering of the electronic element to the first connection object and the soldering of the second connection object to the electronic element can be reliably performed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a thyristor portion of a regulated rectifier manufactured by a soldering method to which the present invention is applied.
FIG. 2 is a view showing a soldering procedure of a thyristor to which the present invention is applied.
FIG. 3 is a diagram showing a soldering process (part 1) according to the present invention.
FIG. 4 is a diagram showing a soldering process (No. 2) according to the present invention.
FIG. 5 is a block diagram of a main part of a regulated rectifier.
FIG. 6 is a diagram showing a thyristor soldering method according to the prior art.
FIG. 7 is a diagram showing a thyristor soldering method according to the prior art.
FIG. 8 is a diagram for explaining a problem of the prior art.
FIG. 9 is a diagram for explaining a problem of the prior art.
FIG. 10 is a graph showing the relationship between flux dilution and concentration and solder activity.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Thyristor, 2 ... Preliminary solder, 3 ... Heat sink, 4 ... Solder pellet, 5 ... Cathode electrode, 6 ... Gate electrode, 8 ... Pad for soldering, 9 ... Insulating film, 10 ... Aluminum substrate, 11 ... External Case, 12 ... Insulating resin, 13 ... Cream solder

Claims (3)

In the soldering method of soldering the second connection object to the electronic element at the same time as soldering the electronic element on the first connection object by heating reflow,
The first and second solders are connected so that the first solder that connects the electronic element to the first connection object melts faster than the second solder that connects the electronic element to the second connection object. Apply active material to the surface,
The dilution of the active material applied to the first solder is made lower than the dilution of the active material applied to the second solder, and the activity of the first solder is made higher than the activity of the second solder. A soldering method characterized by the above. In the soldering method in which the electronic element is simultaneously soldered to a plurality of connection objects by heating reflow,
Of the plurality of connection objects, a first solder that connects the electronic element to a first connection object having a large mass is more than a second solder that connects the electronic element to a second connection object having a small mass. An active material is applied to the surfaces of the first and second solder so as to melt as soon as possible;
The dilution of the active material applied to the first solder is made lower than the dilution of the active material applied to the second solder, and the activity of the first solder is made higher than the activity of the second solder. A soldering method characterized by the above.   The soldering method according to claim 1 or 2, wherein the first connection object is a heat sink, and the second connection object is an electrode.

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