JPS61159289A - Electric resistance welding method - Google Patents

Abstract

PURPOSE:To join securely a high-conductivity material and low-conductivity material by resistance welding while preventing the temp. elevation and welding of the contact surface between electrodes and an insert material owing to the smaller tendency of the insert material to heat generation by interposing the high-conductivity material between the low conductivity material and the electrode in the resistance welding stage of the high-conductivity material and low-conductivity material. CONSTITUTION:The high-conductivity material 1 and the low-conductivity material 2 are superposed in the electric resistance welding stage of the two materials. The high-conductivity material 5 is then pressed to the bottom surface of the material 2 to form a 3-layered construction and thereafter the materials are sandwiched by the electrodes 3, 4 from above and below and welding current is passed between the electrode 3 and the electrode 4 while the materials are pressed. Then mainly the material 2 generates heat and the contact surface 6 between the material 2 and the material 1 as well as the contact surface 7 between the material 6 as well as the material 5 are respectively fused to each other. Since the materials 1 and 5 generate heat to the smaller extent, the welding of said materials to the contact surface 8 with the electrode 3 or 4 and the contact surface 9 does not arise.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a highly electrically conductive material to be welded (hereinafter referred to as a "highly conductive material").
This article relates to a method of electrical resistance welding a material to be welded with a low electrical conductivity (hereinafter referred to as a "low electrical conductive material"), and specifically relates to a method of electrical resistance welding the low electrical conductive material and the electrode while preventing welding of both electrically conductive materials. .

[Conventional technology]

Semiconductor devices such as ICs are rapidly developing, and the demand for lead frames that support IC packages is also increasing significantly. Important properties required of such lead frames include moldability, adhesion of bonding plating, and thermal properties. That is, in large-sized computers, the amount of heat generated by the computer is large, and if the temperature of the computer with a large amount of heat storage increases excessively, the computer function may be impaired. Therefore, for the lead frame forming material, a material with a small calorific value and good heat dissipation, that is, a material with high electrical conductivity and thermal conductivity, is desired, and the conventional Fe-N1 alloy has been switched to a Cu alloy. There are nine.

On the other hand, for some parts, emphasis is placed on both thermal properties (heat generation and heat dissipation) as well as mechanical properties, and the lead frames of such parts are made of materials with high strength but low electrical conductivity. ing.

Therefore, when forming a computer by combining ICs and the like, a situation may be encountered in which a highly conductive lead frame and a low conductive lead frame are joined.

By the way, electric resistance welding has traditionally been used to join lead frames together, but pFe-Nl alloy (
In the case of low-conductivity materials, good bonding was achieved without any particular problem. That is, when electrical resistance welding is performed between low-conductivity lead frames, for example, as shown in FIG. A welding current is passed between them, and since the electrical resistance of the lead frame is much larger than that of the electrode, heat is generated mainly in the lead frame portion, and the contact surfaces 6 of the lead frames 2 can be fused together.

Incidentally, since current flows through the electrode, it is generally made of a Cu alloy having high electrical conductivity to prevent the electrode from generating heat, and the stain electrode itself is also usually water-cooled. However, since temperature rise cannot be completely prevented, high mechanical properties are also required in order to prevent deformation under the temperature rise. However, since electrical conductivity and mechanical properties are contradictory physical properties, it is necessary to sacrifice electrical conductivity to some extent in order to satisfy mechanical properties. Cu
The alloy has an electrical conductivity of approximately 90 Chi AC3.

However, when electrical resistance welding is performed between a highly conductive lead frame 1 and a low conductive lead frame 2 as shown in FIG. 6, the distribution of heat generation becomes significantly unbalanced due to the high electrical resistance of the low conductive lead frame 2. However, as shown in the stippled area in FIG. 6, only the portion 2a of the low conductivity lead frame 2 near the electrodes rises in temperature, and a good bonding state cannot be obtained. Therefore, if the welding current value is increased in the direction of sufficiently welding the high conductive lead frame 1 and the low conductive lead frame 2, the contact surface 9a of the low conductive lead frame 2 and the electrode 4 will be welded together, and the welding will end. After that, it becomes difficult to peel off the electrode 4 from the low conductivity lead frame 2. In addition, the damage to the electrode surface after peeling cannot be regenerated by simple dressing (cleaning) means, which impedes productivity.

[Problem that the invention seeks to solve]

The present inventors focused on these circumstances and
・Research has been conducted to provide an electric resistance welding method that can join conductive materials and low conductive materials without welding the welding material.

That is, although the main reason for welding of the low conductive lead frame and the electrode is that the low conductive lead frame generates a large amount of heat, it is thought that the heat generated by the electrode itself also has a large effect.

This is supported by the fact that the welding becomes more intense as the number of electrode strikes increases. In other words, considering the contact surface between the low-conductivity lead frame and the electrode, here are ■ the amount of heat transferred from the low-conductivity lead frame, ■ the amount of heat transferred from the electrode, and ◎ the amount of heat generated based on the contact resistance of the contact surface. In addition, these factors are considered to be added together to cause the temperature of the contact surface to rise excessively, causing the above-mentioned welding.

Therefore, it is considered that if any one of the above three heating factors can be reduced, welding can be alleviated. However, the material of the electrode according to (2) cannot be changed due to the above-mentioned circumstances, and it is difficult to reduce the amount of heat generated. In addition, the contact resistance of O is a value that depends on the uneven surface shape of the low conductive lead frame and electrode, oxide film, contact area, pressure contact force, etc., and is almost determined by the type of low conductive lead frame and electrode and the selection of welding conditions. It is difficult to reduce the amount of oxidation that occurs over time, and if one were to attempt to reduce it, complicated treatment operations such as polishing and pickling would be required. Therefore, it is difficult to make substantial improvements in these aspects, and it is considered almost impossible, especially when the object to be welded is a lead frame. Under these circumstances, it may be necessary to reduce the amount of heat transferred from the low-conductivity lead frame, but of course it is not possible to change the type (material) of the low-conductivity lead frame that is the material to be welded. Therefore, as a result of further studies, the present inventors found that by interposing a spacer between the low-conductivity lead frame and the electrode, the contact surface (electrode surface in the state where the spacer is interposed)
(2) We came up with the idea of reducing the amount of heat transfer from the low conductivity lead frame.

[Means for solving problems]

The present invention was completed as a result of further consideration of the above idea, and its gist is to perform electrical resistance welding between a high conductive material and a low conductive material, and to weld a highly conductive material between a low conductive material and an electrode. It exists in that it is interposed.

[Effect]

The material interposed between the low conductive material and the electrode needs to be a highly conductive material. That is, the intervening material must ensure electrical connection between the low conductive material and the electrode, and in that sense, it only needs to be an apparently conductive material.

However, if the intervening material is a low conductive material similar to the above-mentioned low conductive materials, the intervening material generates heat during electrical resistance welding, and this heat is applied to the contact surface with the electrode, causing the contact surface to rise in temperature. The electrode and intervening material are welded together. Therefore, the intervening material must be a highly conductive material with low calorific value.

The above-mentioned highly conductive material is not particularly limited as long as it has an electrical conductivity equal to or higher than that of the highly conductive material, but examples thereof include Cu, Cu alloy, A g
Examples include r A g alloy.

〔Example〕

FIG. 1 is a schematic diagram showing an embodiment of the present invention. When electrical resistance welding a high conductive lead frame 1 (80 to 110 inches IACS) and a low conductive lead frame 2 (50% IACS), both After overlapping and further abutting a Cu alloy plate (,80~!, 10% IAC5) 5 on the open surface (bottom surface of the figure) of the low conductive lead frame 2 to form a three-layer structure, electrodes 3 and 4 are stacked. Welding current is applied between electrodes 3 and 4 while holding and pressing them from above and below. As a result, the low conductivity lead frame 2 mainly generates heat, and the contact surface 6 between the low conductivity lead frame 2 and the high conductivity lead frame 1 and the contact surface 7 with the Cu alloy plate 5 fuse together. At this time, since the heat generation of the highly conductive lead frame 1 and the Cu alloy plate 5 is small, the contact surfaces 8 and 9 with the electrodes 3 or 4 do not fuse together.

FIG. 2 is a schematic diagram showing another embodiment of the present invention. Instead of using the Cu alloy plate 5 as described above, the tip of the highly conductive lead frame 1 is bent and the bent end 1a is made of a low conductive material. It is in contact with the bottom surface of the lead frame 2. Then, the electrode 3 is brought into contact with the upper surface of the highly conductive lead frame 1, and the electrode 4 is brought into contact with the lower surface of the bent end 1a and pressed.
By flowing a welding current between the electrode 3 and the electrode 40, the same effect as described above can be obtained. In this embodiment, since a reactive current B is generated in addition to the welding current A, it is desirable to make the bending length of the highly conductive lead frame 2 as long as possible.

In addition, in forming the above-mentioned folded portion, each end of the high conductive lead frame 1 and the low conductive lead frame 2 is pressed in advance as shown in Fig. 3 (Fig. 3).
It is sufficient if they are overlapped as shown in b).

Examples The materials to be welded shown in Table 1 were subjected to electric resistance welding under the welding conditions shown in Table 1 and below. The joint strength of the welded portion was as shown in Table 1.

Welding conditions Electrode: Cr-Cu alloy 8mmφ Pressure force: 100kg As shown in Table 1, for Nnl+3+5, the electrode and low conductivity material are in direct contact with each other and electrical resistance welding is performed as before. Regardless of the material combination, the welding between the electrode and the low-4 electric material was so severe that in most cases the electrode could not be removed. For these rh2.4.6 (
In Example), button breakage was observed, but the high-conductivity material and the low-conductivity material could be sufficiently joined, and no welding between the electrode and the intervening material was observed.

〔Effect of the invention〕

The present invention is constructed as described above, and since a highly electrically conductive material is interposed between a low electrically conductive material and an electrode, heat generation due to the specific resistance of the intervening material can be reduced, and the electrode and intervening material It is possible to suppress the temperature rise of the contact surface to a low level. Therefore, when performing electric resistance welding of a high conductivity material and a low conductivity material, it is possible to firmly weld the high conductivity material and the low conductivity material while preventing welding to the electrode surface.

[Brief explanation of drawings]

Figures 1 and 2 are schematic diagrams showing embodiments of the present invention;
Figures 0) and (b) are perspective views showing how the lead frames are assembled, Figure 4 is a perspective view showing the state of button breakage, and Figure 5.
FIG. 6 is a schematic diagram showing a conventional electric welding mode.

Claims (1)

[Claims] Electric resistance welding of a high electrical conductivity welding material and a low electrical conductivity welding material, characterized by interposing a high electrical conductivity material between the low electrical conductivity welding material and the electrode. Welding method.