JPH01178378A - Joining method for dissimilar metal for conductive piece of electronic parts - Google Patents

Abstract

PURPOSE:To form a reliable conductive piece for electronic parts by making one part of electrode chips a high m.p. material and forming the tip pressurizing part at a fixed curvature as well after executing solder plating in advance on one part of the dissimilar metal for the conductive piece of an electronic part. CONSTITUTION:The tip pressurizing part of an upper part electrode chip 1 is formed by a fixed curvature and the pressurizing part of lower part electrode chip 2 is formed in plane shape. The material of the upper part electrode chip 1 is taken as the high m.p. material of tungsten, silver tungsten, etc., and that of the lower part electrode chip 2 as a chrome copper alloy. A large current is passed by pressurizing both metal blanks 11, 12 by the upper part electrode chip 1 and a copper blank 11 by the lower part electrode chip 2 by interposing a 42 nickel alloy blank 12 respectively. A plating layer 13 is removed by melting it by the local temp. rise due to the resistance heating on the intermediate plating layer 13, the copper blank 11 and 42 nickel alloy blank 12 are locally melted and joined by forming the nugget of the casting structure of both metals.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a joining method for joining dissimilar metals for conductive pieces of electronic components by spot welding.

"Prior art and its problems" Soldering is generally used to join conductive pieces that electrically connect electronic components such as transistors and IC parts, and conductive pieces that electrically connect electronic components and circuits on boards. It is being Therefore, the quality of the joints made by soldering or the like is one of the factors that directly affects the quality and reliability of the product itself incorporating the electronic component. In addition, as the size of electronic components has become extremely small, the conductive pieces have also become smaller, causing a reduction in the joint strength and deterioration of joints such as soldering due to stress caused by mechanical vibrations or repeated thermal stress during cooling and heating cycles. This has become a problem. Particularly, when electronic components having significantly different coefficients of linear expansion are joined by soldering, the joint strength may be significantly deteriorated if the electronic components are subjected to a thermal cycle of -30°C to 110°C.

For this reason, as a countermeasure against deterioration of joints of dissimilar metals, there is a method of ensuring a strong joint using silver brazing, but the brazing temperature is high at approximately 700°C, and the heating may affect electronic components, etc.
This is difficult to implement easily considering productivity and other factors.

Next, from the viewpoint of productivity and bonding strength, spot welding may be adopted as a method for joining electronic components made of dissimilar metals. Conditions for performing spot welding favorably include the duration of one welding current application, the pressing force, and the material and shape of the electrode. In addition to the above conditions, the joining of dissimilar metals is affected by the material.In particular, it is necessary to spot-weld a conductive piece with low electrical resistance or a plated conductive piece directly to a circuit on a board, etc. It is not easy to find optimal conditions for reliability depending on the material of the circuit or the like.

The reason why the joint strength of joints such as soldered joints deteriorates under the above-mentioned cooling and heating cycles is due to joining of dissimilar metals having significantly different coefficients of linear expansion. Therefore, in the parts to be joined by soldering etc., a member with a linear expansion coefficient relatively close to that of the members to be joined is interposed and soldered, and the member and the conductive piece are strengthened by spot welding. By firmly joining them, it is possible to solve the problem of deterioration of joints such as soldering under thermal cycles. However, as mentioned above, conductive pieces for electronic components are to be joined to circuits, etc. on a board by soldering, etc., so in order to form a plating layer necessary for soldering etc. on the surface of the conductive material, If tin or solder plating is applied after spot welding, the plating process will deform and the accuracy of dimensions and shapes cannot be maintained, and the plating solution that has seeped into the gaps between the welds will not be removed by washing, resulting in poor plating quality. The occurrence of inconveniences such as inhibiting the

In order to solve the above-mentioned problems, the present invention provides an electronic component in which solder plating or the like is applied at the raw material stage, followed by spot welding to join and then molding. The purpose of this method is to provide a method for joining Class 51 metals for electrically conductive pieces of electronic components, and the specific method thereof is to apply tin or solder plating to at least one of the dissimilar metals for conductive pieces of electronic components, and then to connect one of the electrodes. Using a spot welding machine, the tip is made of a high melting point material such as tungsten or silver tungsten, and the tip pressure part is formed with a constant curvature, and the other electrode tip is made of chrome steel and the pressure part is formed into a flat shape. spot weld,
The present invention is characterized in that the plating layer for bonding to a circuit board, etc., remains without damage on the pressurized side of the metal that is pressurized to the planar electrode chip.

"Function" As clarified in the description of the above-mentioned specific means, the present invention provides tin or solder plating to at least one of the dissimilar metals to be joined in advance, and a plating layer is interposed between the contacting dissimilar metals. , the 'X-pole tip has a high electrical resistance value compared to conductive materials for electronic components that have high electrical conductivity, and the tip pressure part is made of a high melting point material such as tungsten with a constant curvature, and a copper chromium alloy is used for pressure application. When pressure is applied using a planar electrode tip and a large current is applied, a local temperature rise due to resistance heat generation in the intermediate plating layer melts and removes the plating layer. The 481 metal is locally melted to form a cast structure, ie, a nugget, of both metals and then joined together. On the other hand, the plating layer on the pressure side of the metal material that is pressed against the planar electrode has a large pressure area and the heat generated at the electrode is conducted to the electrode tip, so it remains without any mechanical or thermal damage.

"Example" An embodiment of the present invention will be described based on the accompanying drawings.

FIG. 1 shows an outline of a capacitor type spot welding machine that implements the method of the present invention, in which the tip pressurizing part of the upper electrode tip 1 is formed with a constant curvature (1.5 to 2.5 mmR), and the lower electrode tip The pressure section 2 is formed into a flat shape. The material of the upper electrode chip 71 is tungsten, but a material with high thermal conductivity, high electrical conductivity, and high melting point, such as tungsten or molybdenum, can be used. Further, the material of the lower electrode tip 2 is a chromium-copper alloy. The upper and lower electrode tips 1.2 are connected to a power source 4 via a welding transformer 3. 5 is a capacitor connected in parallel to the power supply circuit, 6
is a timer that controls the energization time.

Fig. 2 shows metal materials for conductive pieces of electronic components to be joined by the method of the present invention, 11 is a copper material with a plate thickness of 0°151++*, and 12 is a 42 nickel alloy with a plate J't [0.25 mm]. These materials are each subjected to solder plating to form a plating layer 13 of solder (90% Sn). Solder plating may be replaced with solder plating.

When these two metal materials 11 and 12 are pressed by sandwiching the steel material 11 with the upper electrode tip 1 and the 42 nickel alloy material 12 with the lower electrode tip 2 of a capacitor type spot welding machine and applying a large current, the intermediate plating 71
Due to the local temperature rise due to resistance heating at 13, the plating layer 13 is melted and removed, and the fR materials 11 and 42
The Nigel alloy material is locally melted to form a nugget, which is a cast structure of both metals, and then joined.

FIG. 3 is an enlarged sectional view of a joint welded by the method of the present invention, and as described above, the joint 14 has a cast structure of copper and 42 nickel alloy, and the solder plating 1114 is molten. The solder plating 113 on the pressure surface side of the 42 nickel alloy material 12, which is pressurized by the scraping tip 2 on the flat lower part of the zero length to be removed, has a large pressure rM product of the electrode tip 2, and has a high thermal conductivity. Due to its large size, it remains undamaged mechanically and thermally. On the other hand, copper material 12
Since the pressurizing surface side of is locally pressurized by the upper electrode tip 1 whose tip pressurizing surface is formed with a constant curvature, an indentation 15 is formed in which the solder plating layer 13 is destroyed.

In this example, dissimilar metal materials for conductive pieces of electronic components, ie, copper material 11 and 42 nickel alloy material 12, which are solder-plated as described above, are joined by spot welding. Ensure welding strength, 42
A solder plating layer 13 is provided on the pressure side of the nickel alloy material 12.
The welding conditions, plating thickness, etc. that will allow the metal to remain without any damage will be confirmed through various experiments and their data as described below.

Here, the welding strength is determined by peeling off the joint spot welded by the method of the present invention by pulling a picture material formed into a ring shape at a speed of 30-min/min as shown in Fig. 4. Measure and find the force.

Further, the weld joint strength is determined by measuring the diameter of the copper nugget remaining in the 42 nickel alloy material 12 after peeling.

The radius of the copper nugget is determined by direct measurement as shown in FIG. 5(a), or by measuring the short axis and long axis and calculating the average thereof as shown in FIG. 5(b).

The welding strength of spot welding in the above example is
Measurement was performed using the measurement method described above, with a pressing force of 10 kg and varying the thickness of each solder plating and the curvature of the pressurized portion at the tip of the upper electrode tip 1 as shown in the table below.

(Table) As a result, the current value to obtain a welding strength of approximately 5 kg is:
In the case of a and b in the previous table when the plating thickness is 2t1, approximately 2.
Although there is no difference from 5KA, it was found that when the plating thickness is 8 pm, the current value increases as the curvature increases, such as approximately 3.2KA for C and approximately 3.8KA for d.

In addition, when the pressing force was 10 kg and the solder plating thickness and the curvature of the tip pressurized part of the upper Q4 pole chip 1 were the same as in the previous table, the diameter of the remaining copper nugget was measured, and the result was about D-1 m. The current value is approximately equal to the current value at which the welding strength is 5 kg, and the welding strength is correlated with the diameter of the remaining copper nugget.

Figure 6 shows the possible welding range based on the relationship between the pressurizing force (kg) and the current value (KA). If the strength is less than 5 kr, the strength will be insufficient, and if the applied force is less than 20 kg and the current value is about 4.5 KA or more, the flash will be activated, and if the applied force is more than 20 kg and the current value is about 4.5 KA or more, the flash will be activated.
The solder plating layer on the non-bonding surface of the No. 2 nickel alloy may melt, resulting in a non-bonding area.

The copper and 42 nickel alloy materials to be joined by the method of the present invention are joined by spot welding and then formed into a conductive piece by press forming, etc., and the welding strength and residual steel nugget diameter are approximately 5 kg and 5 kg, respectively. The approximate value is ls+s, and it is possible to determine the optimum conditions for spot welding, such as the welding current value, 1 energization time for pressing force, electrode shape, etc., based on the above-mentioned experimental results.

Further, in this embodiment, solder plating was performed on the partner of dissimilar metals, but depending on the type of metals to be joined, solder plating may be performed on only one of the metals.

"Effects" In the method of the present invention, at least one of dissimilar metals for a conductive piece of an electronic component is previously plated with tin or solder, and then one electrode tip is plated with tungsten.

The tip is made of a high melting point material such as silver tungsten, and the pressure part at the tip is formed with a constant curvature, and the material of the other electrode tip is chromium copper, and the pressure part is spot welded using a spot welding machine. is characterized in that the plating layer for bonding to a circuit board, etc. remains without damage on the pressurized side of the metal that is pressurized to the planar electrode chip, and after bonding. When forming a conductive piece for an electronic component that is to be joined to another electronic component or circuit board by soldering, etc., the remaining metal with the plating layer undamaged must be solder-plated again. Since there is no need to form a plating layer such as solder, soldering etc. can be carried out immediately without disrupting the shape or dimensional accuracy during the plating process.

In addition, if the linear expansion coefficients of the bonded metal and other electronic components or circuit boards, etc. to be bonded by soldering etc. are similar values, the bonding strength of the solder joint will be Since there is no reduction or deterioration in the electrical conductivity, it has excellent effects such as being able to provide a method for joining dissimilar metals necessary for forming reliable conductive pieces for electronic components.

[Brief explanation of the drawing]

The attached drawings illustrate embodiments of the present invention, and FIG. 1 is a schematic diagram of a capacitor spot welder, FIG. 2 is a schematic sectional view illustrating dissimilar metals to be joined, and FIG. 3 is an enlarged sectional view of a welded joint. Figure 4 is an explanatory diagram showing how to measure welding strength, Figure 5 is an explanatory diagram showing how to determine the diameter of residual copper nuggets, and Figure 6 is an explanatory diagram showing how to measure the welding strength.
The figure shows the weldable range based on the relationship between pressing force and current value. 131. Upper electrode tip, 211. lower electrode tip,
11., Copper material, 12.. 42 Nickel alloy material, 13... plating layer. Patent applicant: Aichi Steel Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 5 (a) (b) Welding section＼

Claims (1)

[Claims] After at least one of the dissimilar metals for the conductive piece of an electronic component is plated with tin or solder in advance, one electrode tip is made of a high melting point material such as tungsten or silver tungsten, and the tip pressurizing part is formed with a constant curvature. Then, the other electrode tip is made of chromium copper and its pressurizing part is spot welded using a spot welding machine, and a circuit board is attached to the pressurized side of the metal that is pressurized by the planar electrode tip. A method for joining dissimilar metals for a conductive piece of an electronic component, characterized in that the plating layer of the plating for joining with the like remains without being damaged.