JPH039331Y2 - - Google Patents

Description

[Detailed explanation of the invention] <Summary> With the increase in the degree of integration of ICs and LSIs, there has been a strong demand for wire bonding work in recent years to bond thinner wires at higher speeds. On the other hand, if the size is made smaller to meet the requirements, the problem of structural strength will arise. In the present application, the distribution of current density was considered through the shape of the chip part, and both structural strength and thermal time constant were improved.

<Industrial Application Fields> The present invention relates to wire bonding equipment that connects LSIs and printed circuit boards on which LSIs are mounted, and in particular to a heating element structure that achieves both structural strength and improved thermal response. Regarding.

<Prior art> A so-called wire bonder (wire bonding device) is a device that connects wires to required parts by heating and fusing solder or wire rods, and is used for high-density printed circuit boards, LSI frames, etc. Since the heat generating part is connected by wiring, the heat generating part is small, and since the heat generating part is directly energized and heated, a large current is passed at an extremely low voltage. Figure 3 shows a heating element conventionally manufactured for this purpose, in which the pair of conductive parts forming the parallel vertical bars of the U-shape are usually made of electrolytic copper, and the tip part at the bottom of the U-shape is made of molybdenum. It is made of a heat-resistant resistance material that has higher electrical resistance than the materials that make up the conductive part, such as stainless steel and tungsten cemented carbide, has high surface oxidation resistance, and has high mechanical strength at high temperatures, and is U-shaped. It has a wire abutting part (abutting tip) at the tip of the bottom.

Bonding is then performed by contacting this portion with a wire and heating it with electricity.

<Problems> When performing bonding with a heating element of this type, the work involved becomes more complex and the wires become thinner, so requirements that have not been considered until now are related to the finish of the bonding and the problem of dead ends. come.

One is the effect of radiation of heat generated at the tip on neighboring areas, and the other is the effect of heat transfer from the wiring pattern and wires.

Both of these properties can be improved in principle by making the heat generating portion smaller, but if you try to make it smaller, the mechanical strength will become weaker.

<Solution> In the present application, the mechanical strength is reduced by devising the shape of the above-mentioned irrigation chip or the configuration of the heating element including the joint surface where the chip is joined to the conductive part via the joint surface. I will try to solve it without any problems.

As a means of achieving this, in the present invention, the shape of the chip part connected to the conductive part is focused on the distribution of current density inside the chip in the direction of the current path, and the cross-sectional area of the wire contact part that intersects with the current path is reduced. In addition to this, the path resistance for the current flowing from the conductive part to the conductive part near the concave side of the U should be made smaller than that at the part that joins with the conductive part, and preferably in consideration of the current density distribution within the cross-sectional area. Similarly, in order to equalize as much as possible the path resistance and non-uniformity of the current flowing near the convex side of the U (wire contact side), the link of the joint surface that joins with the conductive part of the chip part is made of a part of a rectangle or This is solved by making the path length uniform so that it becomes part of a circle.

<Function> With this configuration, the amount of heat generated at the joint can be suppressed. The heat generation rate is highest around the cross section of the wire contact portion where the cross sectional area is narrowed.
Around the cross section, the heat generation rate is also high on the side closer to the wire contact portion. Because the heat is transferred to the wire abutting part through a much shorter path than the extremely small heat generating part, the efficiency of using the generated heat is increased.
As the heat transfer path described above becomes shorter and only the necessary portion generates heat compared to the structural volume of the chip, the equivalent heat capacity becomes smaller, resulting in a faster response time constant. Since there is no need to make it compact, structural strength can also be ensured.

Furthermore, the temperature of the joint surface is lowered, making it easier to maintain the strength of the joint surface.

<Example> Fig. 1 is an explanatory diagram of one embodiment that also serves as a principle diagram of the present invention, Fig. 2 is an explanatory diagram of another embodiment, Fig. 3 is an explanatory diagram of a conventional example, and Fig. 4 a, b. , c are explanatory diagrams of energization conditions and temperature response of the wire contact portion comparing the conventional example and the embodiment.

In the figure, 10, 20, 30 are chips as resistors, 10a, 20a, 30a are wire contact parts, 1
0b, 20b, 30b and 10c, 20c, 30c
11, 21, 31 and 12,
Reference numerals 22 and 32 designate conductive parts, 4 represents a wire, 5 represents one of the solder-plated printed circuit board patterns, and 6 represents a printed circuit board.

As is clear from the figure, the conventional example and the embodiment differ only in the shape of the chip part, but have a chip part joined to the conductor part. For example, the wire 4 is brought into contact with the solder-plated pattern 5. They are also common in that bonding is performed by holding the parts in place and heating them with electricity.

However, the major difference is the distribution of the current flowing inside the chip, that is, the density distribution seen in the direction of the current path and the density distribution seen in the cross section that intersects the current path, and the resulting temperature distribution and the maximum amount of heat generated per hour. This is the distribution of the area with a large amount of heat generation (referred to as the heat generation rate) (which is roughly the same as the area where the temperature rises to the highest temperature as a result), and the distance from the area with the high heat generation rate to the wire abutting part.
What governs the above difference is the distribution of the cross-sectional area of the chip along the current path and the distribution of the length of the current path flowing inside the chip as seen in the cross section that intersects with the current path. What is important is the shape of the tip portion 10 or 20.

In the chip part shown in Figure 1, the joint surface link with the conductor part forms part of a rectangle, and in order to manufacture a heating element, for example, a rectangular chip part is placed on a copper plate, which is the material of the conductor part. A rectangular hole is made into which the material fits, the element is inserted and silver soldered, and the unnecessary parts are removed to form the shape shown in the figure.The tip of the heat generating element is U-shaped overall. That is, U
Not only is the wire contacting part 10b side (referred to as the lower side) at the bottom part of the tip part 10 recessed to catch the wire, but also the opposite side with negative curvature (referred to as the upper side or recessed side) Also, the bonding surfaces 10b and 10c, which are in contact with the bonding surfaces of the chip portion 10 and the conductor portions 20 and 30, form part of a rectangular link, and a pair of parallel opposing surfaces are formed outside the upper end surface. They are joined at their end faces.

As a result, when viewed along the current path, the cross section through which the current passes is constricted so that the cross section near the wire contact area is the smallest, and the cross section in the chip member from the bonding surface of the opposing conductor to the bonding surface is constricted. It is constructed so that the length of the current path is approximately the same on both the upper and lower sides (even in the middle) when viewed in the cross section intersecting the current path.

Figure 2 is an example in which the joint surface of the chip member with the conductor part is a part of a circular arc, but the distribution of cross-sectional area and the distribution of the current path are the same, and therefore the cutting on the upper side to achieve this is also the same. Although the shape is decided based on the idea, it is somewhat easy to make, but it is somewhat inconvenient to manipulate the current distribution within the cross section than the example shown in Figure 1.

Note that since it is originally extremely small, it is difficult to make it into a complicated shape, but if the current path is shortened below the chip, the current concentration further below can be improved.

There are two aspects to note regarding the effect. One is that the temperature at the highest temperature point of the chip part, which is heated to melt the solder with a melting point of about 200°C at the wire contact part, is lowered. In the example shown in Figure 3 and the example shown in Figure 1, the temperature is about 600°C at the neck sections on both sides and the upper side of the chip part 30 in Figure 3, whereas in the example shown in Figure 1, the temperature is around 600°C near the center of the central neck cross section. and 400℃,
It becomes considerably lower, making it easier to ensure heat-resistant life and strength.

Another aspect is the responsiveness as shown in Figure 4 a, b, and c. Although the size of the chip itself is not much different, both the time constant and time lag are smaller, and the energizing waveform is smaller. By changing the temperature, it is possible to rapidly and precisely control the temperature of the area near the wire contact area within the heating time for bonding from 100 ms to several hundred ms to a temperature that is not very high. Summer.

Furthermore, as a result of the above two factors, it has become possible to prevent thermal effects due to heat transfer on the wire or pattern, such as damage to the polyurethane coating of the wire, and damage to the coating of adjacent wires due to radiant heat to a considerable extent.

In this case, I'm not really concerned about anything other than the impact on the surroundings, but I think that the utilization rate of thermal energy is also increasing.

<Effects> As explained above, according to the present invention, by selecting the shape of the tip part, the main heat generating part can be limited and the main heat generating part can be formed very close to the part to be heated. Normal bonding can be performed without raising the temperature too much, and heat transfer to the heated part is quick and smooth, making it extremely easy to manage bonding conditions and allowing detailed work to be done, but the structure is particularly small. Therefore, it has the effect of ensuring strength and extending the service life.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of one embodiment which also serves as a principle diagram of the present invention, Fig. 2 is an explanatory diagram of another embodiment of the present invention, Fig. 3 is an explanatory diagram of a conventional example, and Figs. 4 a, b, c shows an explanatory diagram of the operation of the present invention.

Claims (1)

[Claims for Utility Model Registration] In a heating element that forms a U-shaped current path as a whole and has a pair of conductive parts that serve both as conduction and retention, and a heat-generating chip part that is joined at the bottom of the U-shape. , the cross-sectional area of the portion of the tip portion that holds the wire intersecting with the current path is made smaller than the cross-sectional area of the portion that joins with the conductive portion, and the length of the tip portion as seen in the current line direction is made equal to the U-shaped length. The link of the chip part that constitutes the chip part side of the joint part that is joined to both conductive parts is formed so as to form part of a quadrilateral or part of a circle so that the upper and lower sides of the bottom part do not change much. A heat generating chip for wire bonding.