JPH0527252B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a wire bonding method, and particularly relates to a wire bonding method, in which wire bonding methods are used to bond devices such as thermal printing heads used in high-speed cameras and contact type image sensors used in financial instruments, etc. This invention relates to a wire bonding method that reduces contact between wires when wiring between connected terminals that have been connected to each other, makes it easy to repair contacts, and enables highly reliable wiring between connecting terminals that have differences in level. It is. [Technical Background of the Invention and Problems Therewith] A thermal printing head used, for example, in a facsimile machine will be explained with reference to FIGS. 1 and 2. That is, a plurality of heating resistors 1 are arranged in a line with high density using thin film technology or thick film technology on an insulating substrate such as ceramic, and an integrated circuit for driving the heating resistors consisting of a shift register, a transistor drive, and a selector. (hereinafter referred to as an integrated circuit) 2 and a common electrode 3 to which one end 10 of each heating resistor 1 is commonly connected;
Mainly composed of an input signal group 4 for selectively energizing each heating resistor 1 to generate heat via an integrated circuit 2,
A first group of connection terminals 11 from each heating resistor 1 is provided to correspond to a second group of connection terminals 21 from the integrated circuit 2 that is selectively output, and wire bonding is used between each connection terminal. connected by. Regarding the number of connection terminals in the second connection terminal group 21, it is generally said that 32 connection terminals per 21 convergence circuits is economically advantageous. Therefore, the heating resistors 1 are connected to the second connection terminal group 21 from the integrated circuit 2 in units of 32. In the figure, 5 is an output signal terminal of the integrated circuit 2, and 6 is a power supply to the integrated circuit 2. To record a facsimile using a thermal printing head with such a structure, a predetermined heat generating resistor 1 is selectively energized to generate heat, a thermal transfer film is brought into contact with the heat generating resistor 1, and the facsimile is printed onto plain paper through the thermal transfer film. It is beginning to be transcribed. To explain this state with reference to FIG. 2, there is a resistance substrate 40 made of ceramic or the like in which heating resistors 1 are arranged in a row at a high density in a direction perpendicular to the plane of the paper, a drive substrate 41 ₁ on which a focusing circuit 2 is arranged, and a common electrode 3. The common electrode substrate 41 ₂ on which the common electrode substrate 41 2 is made of metal such as aluminum is placed and fixed on a heat sink 42 . On this heating resistor 1, a thermal transfer film 43 coated with heat-softening ink and plain paper 44 are inserted between the heating resistor 1 and a platen roller 45 that slides into pressure contact with this heating resistor 1. As the platen roller 45 rotates in the direction of arrow ₄₅₁ , both the thermal transfer film 43 and the plain paper 44 move in the direction of arrow 50. In the figure, 46 ₁ ,
46 ₂ is an auxiliary roller that supports the movement of the thermal transfer film 43. Also, the connection of the thermal printing head is
A wire 47 that also connects the first connection terminal group 11 from the heat generating resistor 1 and the second connection terminal group 21 from the output of the integrated circuit 2, and a wire that connects one end 10 of the heat generating resistor 1 and the common electrode 3. 48, the first wire 49 connecting the integrated circuit 2 and the input signal group 4
The circuit will be configured as shown in the figure. With this structure, if "sag" or "wrinkle" occurs in the thermal transfer film 43 between the auxiliary rollers 46 ₁ and 46 ₂ , the recording position from the heating resistor 1 to the plain paper 44 via the thermal transfer film 43 may shift, or heat generation may occur. It is desirable that the distance l between the auxiliary rollers 46 ₁ and 46 ₂ be as small as possible because the heat of the resistor 1 is not conducted uniformly, which not only deteriorates the resolution of the recorded image but also prevents delicate recording. . Therefore, as shown in the figure, there is a step h between the resistance board 40, the drive board 41 ₁ , and the common electrode board 41 ₂ .
The technology for reducing the distance l by providing
This is shown in Publication No. 139558. According to this publication, if the height difference h is about 0.3 mm, it is possible to connect the height difference h using the normal wire bonding method, but if the height difference h is about 0.3 mm, the distance l between the auxiliary rollers 46 ₁ and 46 ₂ is possible. There is little hope of reducing the effect. That is, typically integrated circuit 2
This is because the thickness is 0.3 to 0.5 mm. From this, the height difference h needs to be 0.5 to 1.5 mm. Next, the main parts of FIGS. 1 and 2 will be explained with reference to FIG. 3. That is, a first connection terminal group 11 in which connection terminals 11 ₁ and 11 ₂ are arranged in a staggered manner at the end of a lead wire from a heat generating resistor on a resistance board 40;
A second connection terminal group 21 in which output connection terminals 21 ₁ , 21 ₂ are arranged in a staggered manner on the resistor substrate 1 side of the integrated circuit 2 on the integrated circuit 1 is arranged opposite to the second connection terminal group 21 through a step h. , those close to the step h between the first connection terminal group 11 and the second connection terminal group 21 11 ₁ and 2
1 ₁ , distant comrades 11 ₂ and 21 ₂ are connected by wires 47 ₁ and 47 ₂ , respectively, using conventional techniques. In this case, the resistor board 40 and the drive board 41 are on the same plane, or have a step corresponding to the thickness of the integrated circuit 2, and wire bonding is performed from the higher side to the lower side. 11 and the second connection terminal group 21, close distance comrades of the first connection terminal group 11 and second connection terminal group 21, namely 11 ₁ and 21 ₂ , and long distance comrades, ie 11
Connect ₂ and 21 ₂ and connect the short distance comrade wire 47 ₁
A wire bonding method in which the height of the wire 47 is lower than the height of the long-distance wire ₄₇₂ was disclosed in Japanese Patent Application Laid-Open No. 57-
This is shown in Publication No. 165272. However, this wire bonding method
Fully automatic bonder with 30μm gold wire {Shinkawa Co., Ltd.
According to experiments conducted by the proposers using the model name SWB-FA-UTC-7}, the size of the step is equal to the thickness of the integrated circuit 2, that is, in the range of 0.3 to 0.5 mm, and the wire length is 2 mm or less. Even if it is useful, if the height difference is 0.5 mm or more and the wire length is 2 mm or more, the wire 47 ₁ of the short distance and the wire 47 ₂ of the long distance have a height of 20 μm in the high step part, as shown in FIG.
In extreme cases where the wires were close to each other by 30 μm from m, there were cases where the wires 47 ₁ and 47 ₂ came into contact as shown in FIG. 3a. Also, as shown in Fig. 3a, wires 4 of close distance
Some of the 7 ₁ 's had curves down to the bottom. In particular, wires 47 ₁ and 47 ₂ do not come in contact with each other, but wire 47 ₁ and wire 4
7 Occurs between ₂ . This is because fully automatic bonders use gold wire with a high elongation rate (7 to 10% at room temperature) to prevent wire breakage during bonding, so the wire is stretched at high speed and then shrinks, resulting in a wire loop. The only degree of freedom to maintain stability is in the direction perpendicular to the stretched wire, and it is thought that the wire will fall and sag. Further, during the experiment, the wire collapse was unidirectional within one integrated circuit, and the contact position between the wires 47 ₁ and 47 ₂ was approximately at the center of the wires. Furthermore, as shown in FIG. 3b, after bonding the wires 47 ₁ that are close together, when the capillary 51 is lowered to bond the wire 47 ₂ that is long distance comrades, the tip and side ends of the capillary 51 become wires. 47 ₁ , a wire stepping phenomenon by the capillary 51 is observed, and the wire 47 ₁ may be deformed as 47 ₁ ′. This is because when bonding where the step is 0.5 mm or more, the wire tension (which usually uses a friction method that pinches the wire) that determines the wire loop shape is loosened.
₁ deforms in the direction of the arrow because it becomes longer during bonding to the connection terminal 21 ₁ which is the first connection point, and then to the connection terminal 47 ₂ which is the next connection point,
The capillary 5 when bonding the wire 47 1 to the capillary 21 ₂ when bonding the wire 47 ₁ to the connection terminal 21 ₂ which is the first connection point is deformed outward from the connection terminal 21 ₁ which is the first connection point.
1 appears when the wire 47 ₁ is stepped on.
This phenomenon is caused by the connection terminals 11 ₁ , 21 ₁
The ratio between the distance ISL between the bonding positions of the long-distance terminals and the distance OSL between the bonding positions of the long-distance connecting terminals 11 ₂ and 21 ₂ is inappropriate, and this tendency may be particularly noticeable when the h/ISL ratio is large. Confirmed experimentally. [Object of the Invention] The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a wire bonding method between electrode groups having steps that can reduce contact accidents between wires and increase density. The purpose is [Summary of the Invention] That is, the present invention connects corresponding pairs of connecting terminals of a first connecting terminal group and a second connecting terminal group that are provided so as to face each other with a difference in level by wire honing. In the wire bonding method, h/SL=between the step h between the first connecting terminal group and the second connecting terminal group and the distance SL between the bonding positions of the corresponding pair of connecting terminals. This is a wire bonding method characterized by having a relationship of 0.4 to 0.6, in which the first connection terminal group and the second connection terminal group are arranged in a staggered manner, and the connection between close and long distances is possible. When the terminal pairs are made to correspond to each other, and the distance between the bonding positions of the close-distance pair of connecting terminals is ISL, and the distance between the bonding positions of the long-distance pair of connecting terminals is OLS, h/ISL = 0.40 to 0.45. ,
having a relationship of h/OSL=0.50 to 0.60;
The embodiment is such that the height difference h is in the range of 0.5 to 1.5 mm, and the wire bonding is performed on the side with the lower height difference first and the side with the higher height difference later. [Embodiments of the Invention] In a thermal printing head, the number of heating resistors is extremely large, approximately several thousand as described above, and therefore, the drive circuit is integrated to reduce the number of external peripheral circuits. In this case, the problem is how to efficiently connect the several thousand heat-generating resistors to the output of the integrated circuit, the heat-generating resistors, and the common electrode with high reliability, and how to prevent wires from falling during bonding. The point is how easily it can be repaired. Regarding this point, the inventors further proposed a wire bonding method in which pairs of corresponding connection terminals of a first connection terminal group and a second connection terminal group, which are provided to face each other with a step in between, are connected by wire bonding. As a result of various experiments and studies on this method, we found that as the height difference increases, the wire becomes longer, so in order to prevent wire breakage, the tension of the wire must be smaller than when the wire is short. It has been found that by optimizing the ratio between bonding positions, wire slack can also be eliminated. In this case, if the size of the step is 0.5 mm or less, the conventional wire bonding method is possible, but if the step is 0.5 mm or more, the above-mentioned problem will occur, and if the step is 1.5 mm or more, the wire will become longer. During bonding, a tensile force acts on the bonding position of the first bonded wire and the connecting electrode, increasing the risk of peeling, and at the same time, the inherent bending of the wire (usually called a curl phenomenon) occurs, causing the adjacent This increases the number of contacts with wires, making it unsuitable for high-density wiring, such as one having nine connection terminals per millimeter. Therefore, the range of the step in the wire bonding method of the present invention is 0.5 mm.
1.5mm is optimal. Also, if you bond the wire to the side with a higher level difference first, when bonding the side with a lower level difference, especially if gold or aluminum wire is used, a tensile force will be applied to the neck of the wire immediately above the bonding area, resulting in extreme In this case, there is a risk of peeling off at the bonding position, and also because of the constraint of reducing the distance between the auxiliary rollers of the product to which bonding is applied, it is preferable to bond the side with the lower level difference first. Next, an embodiment of the wire bonding method of the present invention will be described with reference to FIG. However, the same reference numerals as in FIG. 3 indicate the same parts. That is, the resistance board 40 has lead wires connected to a plurality of pairs of heating resistors (not shown) disposed at their tips as a first connection terminal group 11 consisting of connection terminals 11 ₁ and 11 ₂ in a staggered manner. Alignment marks (not shown) on the heat sink 42 and the resistor board 4
It is placed by aligning with the heat generating resistor pair on 0 and mounting it. Further, the drive board 41 ₁ on which the integrated circuit 2 is adhesively mounted has connection terminals 11 ₁ and 11 ₂ of the resistor board 40,
A second connection terminal group 21 consisting of staggered connection terminals 21 ₁ , 21 ₂ of the integrated circuit 2 on the drive board 41
Keeping an appropriate distance from the terminal, use a microscope etc. to connect the connection terminals 11 ₁ and 21 ₁ and 11 of the close and long distance comrades.
₂ and 21 ₂ are positioned, and the heat sink 4
2. In this case, the difference between the height of the resistor board 40 and the height on the surface of the integrated circuit 2, that is, the step h, is 1 mm, assuming that the platen roller diameter is 40 mm and the auxiliary roller diameter is 10 mm, as shown in FIG.
Since the front and back sides are desirable, in this example it is set to 1 mm.
At this time, the staggered first connection terminal group 11 on the resistance board 40 side and the staggered second connection terminal group 21 on the integrated circuit 2 side are long-distance comrades, ie, 11 ₁ and 21 ₁ , and short-distance comrades, ie. 11 ₂ and 21 ₂ are arranged facing each other, and the thermal printing head is completed by bonding them with wire. Here, the ratio of the step h between the bonding positions to the short-distance distance OSL and the long-distance distance ISL of the distance between the bonding positions, that is, the bonding step ratio is expressed as bonding step ratio=h/ISL=h/OSL. Also, including ISL and OSL, SL becomes subh/SL. Next, the table below shows the bonding results with the bonding step ratio varied from 0.25 to 0.80, including those using the conventional method. However, bonding was performed on the lower side first.

【table】

〔Effect of the invention〕

By using the wire bonding method of the present invention, not only is contact between connected wires extremely reduced, but even if contact occurs, it can be easily repaired. Furthermore, the yield of the product is improved and the number of repair parts is reduced, which improves the work efficiency of wire bonding. Furthermore, since the wires are less bent, the encapsulant that protects the wires can pass more easily between the wires, thereby preventing the wires from coming into contact during the encapping process. Furthermore, by providing such a step difference, the distance between the auxiliary rollers can be reduced, preventing the thermal transfer film from sagging or wrinkling, and making fine transfer onto plain paper possible.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a thermal printing head, Figure 2 is an explanatory cross-sectional view showing how the thermal printing head is used to record on plain paper via a thermal transfer film, and Figure 3 is an explanatory diagram of a conventional wire bonding method. 3A is a plan view for explanation, FIG. 3B is a cross-sectional view for explanation, and FIG. 4 is a diagram showing step bonding according to an embodiment of the wire bonding method of the present invention. , FIG. 4a is an explanatory plan view, and FIG. 4b is an explanatory cross-sectional view. DESCRIPTION OF SYMBOLS 1... Heating resistor, 2... Integrated circuit, 3... Common electrode, 4... Input signal group, 11, 21... Connection terminal group, 11 ₁ , 11 ₂ , 21 ₁ , 21 ₂ ... Connection terminal , 40...Resistance board, 41...Drive board,
41 ₂ ...Common electrode substrate, 42...Heat sink,
43...Thermal transfer film, 44...Plain paper, 45
...Platen roller, 46 ₁ , 46 ₂ ... Auxiliary roller, 47, 47 ₁ , 47 ₂ , 47 ₁ ', 48, 49...
...Wire, 51...Capillary.

Claims (1)

[Scope of Claims] 1. First parts provided opposite to each other with a difference in level.
In the wire bonding method, the first connection terminal group and the second connection terminal group are connected by wire bonding between corresponding connection terminal pairs of the connection terminal group and the second connection terminal group, respectively.
A wire bonding method characterized in that a relationship h/SL=0.4 to 0.6 is established between the height difference h between the connecting terminal group and the distance SL between the bonding positions of the corresponding pair of connecting terminals. 2. The first connection terminal group and the second connection terminal group are arranged in a staggered manner, and the short-distance connection terminal pairs and the long-distance connection terminal pairs are made to correspond to each other, respectively, and bonding of the short-distance connection terminal pairs is performed. When the distance between the positions is ISL and the distance between the bonding positions of the long-distance pair of connection terminals is OSL, h/ISL
=0.40 to 0.45, and h/OSL=0.50 to 0.60.
Wire bonding method described in section. 3. The wire bonding method according to claim 1 or 2, wherein the step h is in the range of 0.5 to 1.5 mm. 4. The wire bonding method according to any one of claims 1 to 3, characterized in that the wire is bonded on the side with a lower level difference first and the side with a higher level difference last.