JPH0970659A - Tool for thermo compression bonding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of soldering by uniformizing the temp. distribution of a press surface of a tool, in the case of simultaneously soldering many lead wires by instantaneous heating. SOLUTION: At the time of supplying electric current to electric supplying terminals 12a, 12b of the tool 10 for theremo compression bonding constituted of a tungsten steel by a pulse electric heating method, the press surface 16 and connecting sides 18a, 18b generate the heat. The length of the press surface 16 for pressing a material to be bonded and the length of two connecting sides 18a, 18b are made almost equal and cross sectional areas of the respective sides are made almost equal and each part except the electric supplying terminals 12a, 12b is coated with no soldering material. At the time of detecting a fixed temp. with a thermocouple 20, the conduction ratio of the current is changed to reduced the average current amt., the press surface 16 is pressed with the material to be bonded to execute the bonding during keeping the fixed temp. and thereafter, the current is cut off. Then, since the tool 10 has small heat capacity, this temp. is quickly lowered and the tool 10 is separated from the bond material to complete the bonding operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat for soldering a large number of lead wires of an integrated circuit or the like at a time to a large number of connecting portions of a printed wiring board or the like which is pre-coated with solder by plating or the like by instantaneous heating. The present invention relates to a crimping tool.

[0002]

2. Description of the Related Art A thermocompression bonding tool for soldering a large number of leads such as an integrated circuit at a time is known. This thermocompression bonding tool is a molybdenum material that is generally a high resistance material and has good solder wettability, and has a long pressing surface that is heated by the Joule heat generated by passing a pulse current through it. This pressing surface is evenly pressed against a number of soldering parts to instantly melt the solder by heat conduction and simultaneously solder the lead wires by the pressing force of the tool. It is desirable to maintain a uniform temperature over as wide a range as possible.

However, since both ends of the side forming the pressing surface (pressing side) are connected to the power supply terminals, the heat of the pressing surface escapes to these power supply terminals, and the temperature near the center of the pressing surface becomes high and near both ends. The temperature becomes low and the non-uniformity of temperature becomes strong. Therefore, the length (soaking length) that falls within a certain allowable temperature range becomes short, and there arises a problem that the soldering state of each portion to be soldered at one time becomes uneven.

To increase the soaking length, a tool as shown in FIG. 4 has been conventionally proposed. (Actual exploitation 57-536
No. 38). In FIG. 4, both sides of the side (pressing side) 2 forming the pressing surface 1 are connected to the pair of power supply terminals 4 (4a, 4b) by the pair of connecting sides 3 (3a, 3b). The plate material is formed into a substantially rectangular frame shape. Here, the upper surface of the pressing side 2, that is, the surface opposite to the pressing surface 1 is raised upward in the vicinity of the center, and the raised portion 5 enhances heat dissipation in the vicinity of the center to lengthen the soaking length.

That is, in order to make both ends of the pressing side 2 cool by heat transfer to the power supply terminal 4, the central area is cooled by heat radiation to make the temperature distribution as a whole uniform. In FIG. 5, the horizontal axis x represents the position of the pressing side in the lengthwise direction, and the vertical axis represents the temperature t. Δt indicates an allowable temperature range, a curve A indicates the case without the raised portion 5, and a curve B indicates the characteristic with the raised portion 5 as shown in FIG.
As described above, according to the tool of FIG. 4, the conventional characteristic A has a narrow soaking length a, but by providing the ridge 5, the soaking length a can be expanded to a soaking length b.

[0006]

However, in these prior arts, in order to increase the soaking length, it is necessary to increase the size of the raised portion 5 to increase the amount of heat radiation and also increase the amount of current to increase the amount of heat generation. . For this reason, there arises a problem that the heat capacity of the whole increases and the response of heating / cooling deteriorates. Further, since the amount of heat transferred to the power supply terminal 4 in the vicinity of both ends of the pressing side 2 does not decrease, the temperature drop in the vicinity of these both ends becomes large, and there is a limit to the expansion of the soaking length. Further, in the case where the raised portion 5 is provided, a bending force is generated due to the temperature change of the pressing side 2, the pressing surface 1 is bent, and it becomes impossible to solder a large number of soldering portions with a uniform pressure.
There is a problem that thermal or mechanical stress is repeatedly applied to the power supply terminal 4 and the connecting side 3, and the rigidity and wear resistance of the conventional molybdenum material causes a decrease in strength due to fatigue and damage.

The present invention has been made in view of the above circumstances, and has good responsiveness of heating and cooling, a soaking length can be greatly increased, and the pressing surface does not bend due to temperature change, and each part It is an object of the present invention to provide a thermocompression bonding tool in which the strength is less likely to decrease due to fatigue.

[0008]

According to the present invention, such a problem arises that the plate material is formed into a substantially rectangular frame shape, and one side of the frame is cut out at the center to form a pair of power supply terminals. In the thermocompression bonding tool whose side facing the power supply terminals is a pressing side for pressing the material to be bonded, the thermocompression bonding tool is made of tungsten steel, and two ends connecting the pressing side and each of the power supply terminals are connected. The heat is characterized in that the length of each side is made substantially equal to the length of the pressing side, the cross-sectional areas of these sides are made substantially equal, and each part except the power supply terminal is covered with a non-solder adherend. Achieved by a crimping tool.

[0009]

1 is a front view showing an embodiment of the present invention, and FIG. 2 is a bottom view thereof. Reference numeral 10 denotes a thermocompression bonding tool formed by processing a plate material made of tungsten steel, preferably tungsten carbide steel, into a substantially rectangular frame shape by wire cutting or the like. The frame-shaped one side (upper side) is notched at the center, and the pair of power supply terminals 12 (1
2a, 12b) are formed. The lower side facing these power supply terminals 12 has a pressing side 14 having a rectangular cross section.
The lower surface of the pressing side 14 serves as a pressing surface 16 for pressing a bonded material, for example, a large number of lead wires of an integrated circuit.

A pair of sides (connecting sides) 18 (18a, 18b) connecting both ends of the pressing side 14 and the power supply terminal 12 have a length equal to the length of the pressing surface 16, and the cross section of the connecting side 18 is pressed. The side 14 has substantially the same shape and the same area. Since tungsten steel is superior in rigidity and wear resistance to molybdenum, the connecting side 18 can be lengthened. However, since tungsten is a cobalt composition in its composition, solder is likely to be deposited, and using a thermocompression bonding tool coated with solder may cause a short circuit due to a solder bridge between lead wires. Absent. Therefore, the connecting side 18 and the pressing side 14 except for the power feeding portion 12 are covered with a non-solder adhered material made of metal, non-metal or the like, preferably titanium nitride which is easy to apply. Titanium nitride is deposited by vapor deposition. Reference numeral 20 is a thermocouple for detecting the temperature near the center of the pressing side 14.

The thermocompression bonding tool 10 thus configured.
When a current is supplied to the power supply terminals 12a and 12b by the pulse energization heating method, the pressing side 16 and the connecting side 18 generate heat. When the thermocouple 20 detects a constant temperature, the current conduction rate changes, the average current decreases, and the temperature is kept constant.
In this way, while the temperature is kept constant, the pressing surface 16 is pressed by the material to be bonded (not shown) to perform bonding, and then the current is cut off. Then, since the tool 10 has a small heat capacity, the temperature thereof is rapidly lowered, and the tool 10
The bonding operation is completed by raising and separating from the material to be bonded.

Since the connecting side 18 extends above the left and right ends of the pressing side 14, the heat generated at the connecting side 18 is transferred to the power supply terminal 12 above the connecting side 18.
Below the connecting side 18, the left and right ends of the pressing side 14 are heated. For this reason, the decrease in the temperature near the left and right ends of the pressing side 16 is reduced, and the temperature drop due to the heat escaping from this vicinity to the power supply terminal 12 is compensated. As a result, the temperature in the vicinity of both ends of the pressing side 14 rises, eventually resulting in a temperature distribution like the characteristic C shown in FIG. 5, and the soaking length c becomes longer. The pressing side 14
4 does not have the raised portion 5 unlike the conventional one shown in FIG. 4, the heat capacity becomes small and the temperature can be rapidly raised or lowered.

Further, since the pressing side 14 has an equal cross-sectional area, no bending occurs due to its temperature change, the pressing surface 16 has a good flatness, and a large number of bonding portions can be pressed uniformly to enable uniform soldering. Become. Therefore, the thermal and mechanical stress applied to the tool 10 is reduced, and the tool 10 is less likely to be damaged by fatigue.

FIG. 3 shows experimental results showing the usefulness of the thermocompression bonding tool 10 according to the present invention. In the figure, the horizontal axis represents the length H (FIG. 1) of the connecting side 18 of the thermocompression bonding tool 10,
The vertical axis represents the temperature difference Δt between the central portion and the end portion of the pressing side 14 at the end of energization. The curve in the figure shows that the length of the pressing side is constant at 36 mm and the length H of the connecting piece 18 is 3, 9, 17
And 4 types of thermocompression bonding tools with 27mm
The temperature difference Δt when heated to 400, 300 and 200 ° C. (the temperature of the central portion of the pressing side 14) is plotted. As is clear from FIG. 3, when the length H of the connecting side 18 is 3 mm, the temperature difference is 40 to 100 ° C.
On the other hand, when the length H of the connecting side 18 is 27 mm, the temperature is 10 to 15 ° C.
It can be seen that the temperature difference between the central part and the end part of is reduced.

Therefore, if the connecting side 18 is made longer than the pressing side 14, it is possible to equalize the temperature over the entire length of the pressing side 14 without any practical problem. However, the thermocompression bonding tool 1
Since 0 is repeatedly subjected to thermal and mechanical stress as described above, the connecting side 18 is preferably short in terms of rigidity. Therefore, the thermocompression-bonding tool 10 of the present invention can obtain a temperature difference which is practically acceptable. The length, that is, the length of the connecting side 18 is selected to be substantially equal to the length of the pressing side 14.

[0016]

As described above, according to the present invention, the rigidity of the connecting side connecting the power supply terminal and the pressing side is increased by using tungsten steel as the material of the tool, and the length of the connecting side corresponds to the length of the pressing side. Since it is formed to be almost equal and the cross section of the pressing side and the connecting side is almost uniform, the temperature drop due to the heat around the left and right sides of the pressing side, which is heated by the heat generated at the bottom of the connecting side, escapes to the power supply terminal is reduced. In addition, the heat dissipation around the right and left sides of the pressing side can be supplemented by the heating by the lower part of the connecting side, and the soaking length of the pressing side can be greatly expanded.

Further, since the pressing side does not have a raised portion or the like, its heat capacity becomes small, rapid heating and cooling are possible, and the working speed can be increased. Moreover, since the cross section of the pressing side is constant, no bending occurs due to temperature change, it is possible to press evenly on many bonding parts, uniform soldering is possible, and thermal deformation can be absorbed. It is possible to prevent the tool from being damaged by fatigue due to mechanical stress.

Furthermore, since the surface of the tool made of tungsten steel used for increasing the rigidity is covered with the non-solder adherent, solder is not adhered to the tool and a short circuit occurs due to the solder bridge between the lead wires. Nothing.

[Brief description of drawings]

FIG. 1 is a front view of one embodiment of the present invention.

FIG. 2 is a bottom view thereof.

FIG. 3 is a diagram showing a temperature difference between a center portion and an end portion of a pressing side measured by changing a length of a connecting side.

FIG. 4 is a perspective view of a conventional thermocompression bonding tool.

FIG. 5 is a temperature distribution diagram of a pressing surface.

[Explanation of symbols]

 10 ... Thermocompression bonding tool 12 ... Power supply terminal 14 ... Pressing side 16 ... Pressing surface 18 ... Connecting side

Claims (1)

[Claims] 1. A plate member is formed in a substantially rectangular frame shape, and one side of this frame is cut out at the center to form a pair of power supply terminals, and a side opposite to these power supply terminals presses a bonded material. In the thermocompression bonding tool described above, the thermocompression bonding tool is made of tungsten steel, and each length of two sides connecting the both ends of the pressing side and each of the power supply terminals is substantially equal to the length of the pressing side. A thermocompression bonding tool, characterized in that the cross-sectional areas of these respective sides are formed to be substantially equal, and each part except the power supply terminal is covered with a non-solder adherend.