JPH06140460A - Lead bonding method - Google Patents

Abstract

PURPOSE:To provide a lead bonding method by which a plurality of leads can be bonded under a uniform-pressure and uniform-temperature condition. CONSTITUTION:In this method in which one ends of a plurality of leads 14 for leading out are soldered to lead terminals 11 on a circuit board 9 by heating the one ends of the leads 14 while they are press-contacted with the terminals 11, a hot bar 1 is press-contacted with the leads 14 in such a state that spacers 8 are put between both end sections of the press-contacting surface of the bar 1 and the circuit board 9.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for joining leads. More specifically, connection of a lead used for joining a circuit board of a hybrid IC to an external lead or joining an external lead of an electronic component or an assembly of electronic components having an external lead to a circuit board. Regarding legality.

[0002]

2. Description of the Related Art Conventionally, in an electronic component or an assembly of electronic components, a metal lead-out lead is electrically connected to a peripheral portion of a circuit board by soldering or a conductive adhesive. As the soldering method, conventionally, a soldering iron bonding method, a light or heat ray bonding method, a hot bar bonding method, or the like is known. However, the method (3) is apt to cause a solder bridge, which causes a short circuit defect. In addition, in the method of (3), a solder ball is likely to be generated and the solder is likely to be scattered. Because of this, or the method of (1) cannot cope with the narrowing of the lead pitch. Therefore, when the leads of an electronic component having a plurality of leads with a narrow pitch are joined, the joining with a hot bar is mainly performed.

As shown in FIG. 4, in the joining by the hot bar, first, a solder paste 33 is applied to the surface of a lead terminal 32 provided as an electrode on the peripheral portion of the surface of the circuit board 31, and then, from above. The ends of the leads 34 for external extraction are brought into contact with each other. Then, while the back surface of the circuit board 31 is supported by the pedestal 35, the hot bar 36 simultaneously heats the plurality of external lead-out leads 34 while pressing them against the surface of the lead terminals 32. After the solder paste 33 has melted, the heating is stopped and the solder paste 33 solidifies, and then the hot bar 36
Joining is completed by separating the lead 34 from the external lead 34.

[0004]

However, when joining with the above-mentioned hot bar, pressure is applied at a pressure of about 20 kgf / cm ² to stabilize a plurality of external leads, and the thickness of the hot bar is 2 mm. Since the temperature has risen to about 300 ° C., the hot bar 36 is bent. For example, in the case of a 26-pin hybrid IC, the length L of the pressure contact surface of the hot bar 36 is about 30 mm, and the maximum deflection amount δ at this time is about
Reach 0.1 mm.

Due to this deflection, the lead 34 for external drawing
The pressure is locally applied to the end A of the row, while the pressure is reduced at the central portion B of the row of the external lead 34. Therefore, it is impossible to press all the external lead-out leads 34 with a uniform pressure. If the pressure becomes non-uniform, there will be a difference in heat conduction from the hot bar 36 to the external lead 34. That is, since the heat is excessively conducted at the end portion A, the temperature rises, while the temperature at the central portion B conversely decreases. Therefore, if the heating temperature is adjusted according to the central portion B, the temperature at the end portion A becomes too high, and the copper foil of the lead terminal 32 may be peeled off. On the contrary, if the heating temperature is adjusted according to the end portion A, insufficient heating of the central portion B may cause defective bonding.

The present invention solves this problem and provides a lead joining method in which all external leads are joined under uniform pressure and temperature conditions so that the lead terminals are not partially burdened. To aim.

[0007]

The lead joining method of the present invention is a lead joining method in which a lead terminal on a circuit board and one end of an external lead are joined by pressure welding using a hot bar and heating. Then, the spacers are interposed between the portions without external leads and the circuit board at both ends of the pressure-contact surface of the hot bar, and pressure-contact is performed.

[0008]

According to the present invention, since the spacer is interposed between both ends of the pressure contact surface of the hot bar and the circuit board, the hot bar is not bent and is applied to the end side of the row of external leads. Concentration of pressure is relieved. As a result, a substantially uniform pressure can be applied to all the leads for external extraction, a uniform temperature distribution can be obtained, and the leads can be joined under good conditions.

[0009]

The present invention will be described below with reference to the drawings. 1 is a cross-sectional explanatory view showing an embodiment of the lead joining method of the present invention, FIG. 2 is a perspective view showing an embodiment of the lead joining method of the present invention, and FIG. 6 is a graph showing the peel strength of the lead for external pulling out of the obtained hybrid IC.

The hot bar used in the lead joining method of the present invention is constructed as shown in FIG. In the hot bar 1, for example, an arm 3 is formed by bending both ends of a horizontally extending main body 2 made of a molybdenum bar or the like having a rectangular cross section, and the heat radiating block 4 is formed at the upper end of the arm 3. A power source 5 and a switch 6 are provided, and are formed by devising their shapes so that the whole body is uniform and has a constant temperature by directly passing a current. The lower surface of the main body 2 is formed as a smooth flat surface as the pressure contact surface 7. Spacers 8 are provided at both ends of the pressure contact surface 7. The spacer 8 is preferably formed so that its thickness is approximately the same as that of the lead for externally drawing out the electronic component. A copper foil 15 for preventing warpage is formed on a portion of the circuit board facing the end of the hot bar 1 so that the height is almost the same as that of the lead terminal 11 and the thickness of the spacer 8 is pulled out to the outside. By making the thickness approximately the same as that of the lead 14 for soldering, the thickness of the lead 14 for external drawing is thinner by a thickness of 12 minutes of solder paste, but this means that the solder paste is compressed and pressure is applied to the lead portion. This is necessary.

The spacer 8 is made of a material such as iron or phosphor bronze. Further, in order to make the temperature distribution of the hot bar 1 uniform without disturbing, it is preferable that the hot bar 1 is formed of a material having the same thermal conductivity as the external lead.

When a hybrid integrated circuit device (hereinafter referred to as a hybrid IC) is manufactured using the above hot bar 1, the following procedure is performed.

As shown in FIGS. 1 and 2, first, a lead terminal portion is mounted on a substrate 9 having a plurality of electronic components (not shown) mounted on the surface of the substrate 9 of the hybrid IC by a reflow method or the like. In this way, it is placed on the pedestal 10 for lead joining, and the solder paste 12 is applied to the lead terminals 11 formed on the surface of the substrate 9. Next, one ends of the plurality of external lead-out leads 14 whose other ends are connected by the frame 13 are brought into contact with the lead terminals 11.

Next, the hot bar 1 is pressed against the external lead 14 and, at the same time, the solder paste 12 is heated and melted. At this time, the spacers 8 provided at the ends of the pressure contact surface 7 of the hot bar 1 come into contact with the surface of the copper foil 15 formed around the substrate, and the leads for external extraction on both ends are formed.
It is possible to alleviate the concentration of pressure on 14 and the lead terminals 11 and apply uniform pressure to all the leads 14 for external extraction. Therefore, it is possible to solder all the external lead-out leads 14 under the optimum pressure and temperature conditions. Even if solder is supplied to the lead terminals 11 by a process such as solder precoating instead of the solder paste 12, no problem occurs in the joining work.

After that, when the heating is stopped, the external lead 14 and the lead terminal 11 are joined.

Next, the substrate 9 and the entire electronic component are completely covered with a resin (not shown), and finally the frame 13 connecting the external lead-out leads 14 to each other is cut off, thereby separating the hybrid IC. Manufacturing is complete.

As a specific example, the external lead 14 is
For example, in the case of a 26-pin hybrid IC, the length is 8
mm, width 0.35 mm, thickness 0.15 mm with leads 0.8 mm pitch
26 will be placed. In addition, a joint having a length of about 1.5 mm and a width of about 0.5 mm is formed at the tip of each lead in order to facilitate soldering, and the lead terminal 11 is formed slightly larger than that. The thickness of the external lead 14 before joining is about 0.3 mm higher than the surface of the copper foil 15 because the thickness of the solder paste 12 is added. In the hot bar 1 corresponding to this, the width of the pressure contact surface 7 for pressing the joint portion of each lead is formed to be about 2 mm, and the both ends of the pressure contact surface 7 are made of iron, phosphor bronze or the like and have a length of 10 mm. , Width 3mm,
A spacer 8 having a thickness of 0.15 mm is provided. Therefore, if the spacer 8 is pressed until it contacts the surface of the copper foil 15, the solder paste 12 is almost completely compressed and the two spacers 8 are pressed.
In the area of the pressure contact surface 7 sandwiched between the hot bar 1 and the hot bar 1, the hot bar 1 hardly bends.

Next, FIG. 3 shows the results of examining the bonding strength of the external lead 14 of the hybrid IC manufactured as described above.

In FIG. 3A, each one of the leads 14 for external extraction of the hybrid IC manufactured according to this embodiment,
The distribution of the peel strength applied to each of the external lead-out leads 14 when one is pulled above the substrate 9 is shown. The peel strength of the hybrid IC obtained by the conventional manufacturing method is the peel strength (see FIG. 3B).
As is clear from comparison with
It can be seen that since the concentration of the pressure at both ends is relaxed, the peel strength at both ends is significantly improved. That is, according to the conventional method, the pressure at the end is strong and the peel strength between the copper foil of the lead terminal 11 and the substrate is almost 0 (lead pins 1, 25,
No. 26) is similar to the peel strength of the pin in the central portion in this embodiment.

Further, the uniformization of the pressure improves the peel strength as a whole in this embodiment. As a result of investigating the temperature of the joining portion in the joining method of the conventional example, there was a difference of about 30 ° C. at the end portion of 350 ° C. and the central portion of 320 ° C.

In the above embodiment, the spacer is adhered to the pressure contact surface of the hot bar. However, the present invention is not limited to this, and the spacer and the hot bar are separately provided on the substrate. The joining may be performed only by placing it.

Further, although the example of soldering is shown in the above-mentioned embodiment, the present invention can be similarly applied not only to soldering but also to joining with a resin or the like which is solidified by heating.

[0023]

According to the present invention, since uniform pressure is applied to all leads and bonding can be performed under uniform temperature conditions, a bonding failure caused by insufficient pressurization and heating can be eliminated, and at the same time all leads can be bonded. The bonding strength can be improved. As a result, a highly reliable electronic component can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing an embodiment of a lead joining method of the present invention.

FIG. 2 is a perspective view showing an embodiment of a lead joining method of the present invention.

FIG. 3 (a) shows the peel strength of external lead for hybrid IC obtained by the bonding method of the present invention,
(B) is a figure which shows the peeling strength by the method of the prior art example.

FIG. 4 is an explanatory cross-sectional view showing a conventional joining method of leads for external extraction.

[Explanation of symbols]

 1 Hot bar 7 Pressure contact surface 8 Spacer 9 Board 11 Lead terminal 12 Solder paste 14 External lead

Claims (1)

[Claims] 1. A method for joining leads, wherein lead terminals on a circuit board and one ends of external leads are joined by pressure contact using a hot bar and heating, wherein both ends of the pressure contact surface of the hot bar are externally connected. A lead joining method characterized in that a spacer is interposed between a portion without leads and a circuit board to perform pressure welding.