TWI780387B - Solder type acf bonding structure - Google Patents

Abstract

A solder type ACF bonding structure is provided. A solder type ACF is bonded between the upper substrate and the lower substrate. The solder type ACF contains a plurality of metal particles, and the metal particles are gathered on the bonding pads of the upper substrate and the lower substrate during the bonding process to generate eutectic bonds. For the aggregation of metal particles of the solder type ACF, the present invention provides a suitable design of the line width, line spacing and effective area of the bonding pad. Therefore, it is possible to avoid offset during the bonding process to achieve self-alignment. In addition to being effectively applied to flat products, it can also be applied to curved products to solve the problem of offset.

Description

Welded Anisotropic Conductive Film Bonding Structure

The invention relates to an anisotropic conductive film, in particular to a welded anisotropic conductive film joining structure.

Today's displays, touch devices and other products are getting closer and closer to daily life, and their functions are becoming more and more diverse. In order to correspond to finer applications, the number of bond pads needs to be increased, but under the condition that the effective bonding area is limited, the width of the bond pads can only be reduced to increase the number of bond pads; thus , the difficulty of joining has really increased a lot.

With the trend of the times, the appearance design of products is also gradually being valued, and products with complex curved shapes are becoming more and more common, such as wearable products, automotive products, home appliances, etc. Corresponding to this, the bonding requirements of Anisotropic Conductive Film (ACF) that allow application on non-planar surfaces are also discussed.

In addition, in the existing bonding process, the uniformity of temperature and pressure is very important; however, when the pitch is getting smaller and smaller, the alignment accuracy of the process and the conductivity after bonding are also important. An important issue in today's bonding process.

Therefore, there is a need to find an innovative anisotropic conductive film bonding technology to overcome the various problems encountered in the above-mentioned prior art.

The main purpose of the present invention is to provide a welded anisotropic conductive film bonding structure, using the welded anisotropic conductive film to achieve eutectic bonding, and according to the aggregation of metal particles in the welded anisotropic conductive film during the bonding process phenomenon, especially designed for the line width, line spacing and effective area of the bonding pad, so as to effectively exert the self-alignment function of the soldered anisotropic conductive film and reduce the offset of the bonding process.

In order to achieve the above object, the present invention provides a welding type anisotropic conductive film bonding structure, which includes an upper substrate, a lower substrate and a soldered anisotropic conductive film. The lower surface of the upper substrate is provided with a plurality of equidistantly arranged first Bonding pads, the upper surface of the lower substrate is provided with a plurality of second bonding pads arranged equidistantly, and the welding-type anisotropic conductive film is combined between the lower surface of the upper substrate and the upper surface of the lower substrate, and the welding-type anisotropic The conductive film contains a plurality of metal particles, and these metal particles are gathered on the first bonding pad and the second bonding pad to perform eutectic bonding.

In the present invention, the first bonding pad and the second bonding pad must meet the following conditions: L1≦S2, A > 0, B > 0; Wherein, L1 is the line width of one of the first bonding pads; S2 is a pitch of one of the second bonding pads; A is the overlapping width between the first bonding pad and the second bonding pad overlapping it in the vertical projection direction; and B is the distance between the first bonding pad and its non-overlapping second bonding pad in the vertical projection direction.

Further, in the present invention, the first bonding pad and the second bonding pad also satisfy the following conditions: L1/S1>1.5, L2/S2>1.5, A≧1/3 L1; Wherein, S1 is the pitch of the first bonding pad; and L2 is the line width of the second bonding pad.

In the present invention, the line width or line distance of the first bonding pad and the second bonding pad is 5 times of the particle size of the metal particles.

In the present invention, the aforementioned upper substrate is a flexible circuit board.

In the present invention, the aforementioned lower substrate is a display panel or a touch panel.

In the present invention, an intermetallic compound is formed at the eutectic junction between the aforementioned metal particles and the first bonding pad and the second bonding pad.

In the present invention, the material of the first bonding pad and the second bonding pad is selected from gold, silver or copper.

The bonding structure of the welded anisotropic conductive film provided by the present invention avoids excessive alignment offset through the design of the line width, line distance and effective area of the bonding pad, so that the welded anisotropic conductive film can It can effectively exert its self-alignment function, and can be suitable for the bonding process of flat or curved surface products, effectively solving the problem of alignment deviation, and will be very competitive in industrial applications.

In the following, a detailed description will be made through the specific embodiments and the accompanying drawings, so that it will be easier to understand the purpose, technical content, characteristics and effects of the present invention.

Please refer to Figure 1 and Figure 2 in sequence. Figure 1 is a side view of the welding-type anisotropic conductive film bonding structure 100 disclosed in the embodiment of the present invention during the bonding process, and Figure 2 is the welding-type anisotropic conductive film bonding disclosed in the embodiment of the present invention A side view of the structure 100 after bonding.

In this embodiment, the soldered anisotropic conductive film bonding structure 100 includes an upper substrate 10, a lower substrate 20, and a soldered anisotropic conductive film 30 bonded between the upper substrate 10 and the lower substrate 20. The lower substrate of the upper substrate 10 The surface is provided with a plurality of first bonding pads 11 arranged equidistantly, and the upper substrate 10 can be a flexible circuit board, while the upper surface of the lower substrate 20 is provided with a plurality of second bonding pads 21 arranged equidistantly, and the lower substrate 20 It can be a display panel or a touch panel.

In addition, the welding-type anisotropic conductive film 30 is in the form of a thin film, which is distributed with a plurality of metal particles 31 in the electrical insulating gel, and the materials of the first bonding pad 11 and the second bonding pad 21 can be selected from compatible metals. Particles 31 form a eutectic bonded metal, such as gold, silver or copper. As shown in FIG. 1 , the metal particles 31 in the soldered anisotropic conductive film 30 gather on the first bonding pad 11 and the second bonding pad 21 due to the strong physical attraction between the metals after being heated, and melt. The metal particles 31 react with the first bonding pad 11 and the second bonding pad 21 to form a eutectic bond and bond together. As shown in FIG. Generally, the metal particles of the anisotropic conductive film achieve electrical conduction through contact, and the metal conductivity of the anisotropic conductive film is relatively low. In addition, during the melting process of the welding-type anisotropic conductive film 30, there will be no residual metal particles 31 between the first bonding pad 11 and the second bonding pad 21, causing a short circuit, and the eutectic bonding is also It can effectively improve the adhesion of the metal particles 31 between the first bonding pad 11 and the second bonding pad 21 after bonding.

Please also refer to FIG. 1 and FIG. 2 to illustrate the self-alignment process of the soldered anisotropic conductive film bonding structure 100 disclosed in the embodiment of the present invention. When the metal particles 31 of the soldered anisotropic conductive film 30 are heated, the first bonding pads 11 and the second bonding pads 21 can be effectively bonded due to the cohesive force of the first bonding pads 11 and the second bonding pads 21 in liquid state and their affinity with the intermetallic compound. 11 and the second bonding pad 21 are pulled closer, so that if there is a deviation during the alignment process, the alignment deviation between the first bonding pad 11 and the second bonding pad 21 after bonding can be reduced by this ability The amount of displacement is called self-alignment.

According to the current demand for electronic products with higher and higher specifications, the number of bonding pads is increasing. In a limited space, the number can only be increased by shrinking the line pitch. At present, most designs are L≧S, and L is the number of bonding pads. Line width, S is the line spacing of bonding pads to reduce the blank (space) area and increase the number of groups of bonding pads. However, according to the size and aggregation characteristics of the metal particles of the welded anisotropic conductive film, the present invention proposes the design of the applicable L/S and joint effective area for the joint structure of the welded anisotropic conductive film after analysis and induction, so as to avoid bias If the displacement is too large, the metal bonding pad is connected to the next-door electrode in series.

As shown in FIG. 3, the first bonding pad 11 and the second bonding pad 21 must meet the following conditions: L1≦S2, A>0, B>0; where L1 is the line of one of the first bonding pads 11 width; S2 is the line pitch of one of the second bonding pads 21; A is the overlapping width between one of the first bonding pads 11 and its second bonding pad 21 overlapping in the vertical projection direction; and B is one of the The distance between the first bonding pad 11 and its closest second bonding pad 21 that does not overlap in the vertical projection direction.

Here, too, joint effective area (%)=A/L1 is defined.

Further, the first bonding pad 11 and the second bonding pad 21 also satisfy the following conditions: L1/S1<1.5, L2/S2<1.5, A≧1/3 L1; wherein, S1 is the line pitch of one of the first bonding pads 11 ; and L2 is the line width of one of the second bonding pads 21 .

In this embodiment, the particle size of the metal particles 31 of the soldered anisotropic conductive film 30 is between 2 and 10 microns (μm), and the size of the metal particles 31 will affect the bonding between the first bonding pad 11 and the second bonding pad 21. For the design of the line width and line spacing, it is more appropriate to set the line width and line spacing to be 5 times the particle size of the metal particle 31 at present.

Through the above design, the welded anisotropic conductive film can better exert its self-alignment function. In the present invention, the eutectic ability between the metal particles and the metal of the welded anisotropic conductive film is defined as F1, the cohesive force of the metal particles itself is F2, the adhesion between the metal particles and the adhesive is F3, and the cohesive force of the adhesive itself is F4, and During the bonding process, the aggregation of metal particles was observed simultaneously. Experiments have found that after the metal particles are heated and melted, the molten metal particles will first bond with the metal bonding pad, and in the later stage of heating, more heated metal particles will gather towards the bonding pad, and the pulling force generated by the movement of the metal particles will cause displacement , can cause the effect of pulling back between the joint pads, and complete the joint. And this experiment result shows, F1>F2>F3+F4.

The present invention also makes use of different offsets in the joint alignment process to verify the self-alignment ability of the welded anisotropy conductive film, as shown in Table 1, three sets of welded anisotropy with different L/S designs The proportion of offset produced by the conductive film bonding structure, and the degree of offset after bonding are significantly reduced. The SEM images can be obtained from Figures 4A~4C, respectively. Figure 5 shows three groups of bonding with different L/S designs The effective areas (%) have all increased, indicating that the soldered anisotropic conductive film provided by the present invention does have excellent self-alignment ability.

In summary, according to the bonding structure of the soldered anisotropic conductive film provided by the present invention, the two substrates are eutectically bonded by using the soldered anisotropic conductive film, and the metal particles of the soldered anisotropic conductive film Agglomeration phenomenon provides a suitable design for the line width, line distance and effective area of the bonding pad, so that the soldered anisotropic conductive film can exert its self-alignment function. In addition to being effectively applied to planar products, it can also be applied to Surface products to effectively solve the problem of alignment offset.

Furthermore, the present invention is particularly applicable to the bonding process of flexible circuit boards on flat or curved surfaces of bonding pads that can form eutectic bonds with metal particles, which can reduce the offset of the bonding process, thereby improving process yield and product quality.

The above-mentioned embodiments are only to illustrate the technical ideas and characteristics of the present invention, and the purpose is to enable those who are familiar with the art to understand the content of the present invention and implement it accordingly, and should not limit the patent scope of the present invention. , that is, all equivalent changes or modifications made according to the spirit disclosed in the present invention should still be covered by the patent scope of the present invention.

100, 100’, 100”: welded anisotropic conductive film bonding structure

10: Upper substrate

11: First Bonding Pad

20: Lower substrate

21: Second Bonding Pad

30: Welded anisotropic conductive film

31: metal particles

C: Eutectic junction

FIG. 1 is a side view of the welding-type anisotropic conductive film bonding structure disclosed in the embodiment of the present invention during the bonding process. FIG. 2 is a side view of the soldered anisotropic conductive film bonding structure disclosed in the embodiment of the present invention after the bonding is completed. Fig. 3 is a schematic diagram of the size design of the bonding pad of the soldered anisotropic conductive film bonding structure of the present invention. Figures 4A-4C are SEM images of the welding-type anisotropic conductive film bonding structure using different L/S designs of the present invention. Fig. 5 is the change result of the bonding effective area before and after bonding of the welding-type anisotropic conductive film bonding structure using different L/S designs according to the present invention.

100: Welded anisotropic conductive film joint structure

10: Upper substrate

11: First Bonding Pad

20: Lower substrate

21: Second Bonding Pad

30: Welded anisotropic conductive film

31: metal particles

C: Eutectic junction

Claims (7)

A welding-type anisotropic conductive film bonding structure is used to perform a eutectic bonding process. The welding-type anisotropic conductive film bonding structure includes: an upper substrate, and a plurality of equidistant first substrates are arranged on the lower surface of the upper substrate. bonding pads; a lower substrate, the upper surface of the lower substrate is provided with a plurality of second bonding pads arranged equidistantly; Between the surface and the upper surface of the lower substrate, and containing a plurality of metal particles, the materials of the first bonding pads and the second bonding pads are selected from metals that can form eutectic bonds with the metal particles, the The metal particles are gathered and eutectically bonded to the first bonding pads and the second bonding pads during the eutectic bonding process; wherein, the first bonding pads and the second bonding pads satisfy the following conditions: L1 ≦S2, A≧1/3 L1, B>0; wherein, L1 is the line width of one of the first bonding pads; S2 is the line pitch of one of the second bonding pads; A is The overlapping width between the one of the first bonding pads and a second bonding pad that overlaps in a vertical projection direction; and B is the one of the first bonding pads and its non-overlapping and closest other in the vertical projection direction A pitch of the second bonding pad. The soldered anisotropic conductive film bonding structure according to claim 1, wherein the upper substrate is a flexible circuit board. The soldered anisotropic conductive film bonding structure according to claim 1, wherein the lower substrate is a display panel or a touch panel. The welding type anisotropic conductive film bonding structure as described in Claim 1, wherein the first contacts The bonding pad and the second bonding pads also meet the following conditions: L1/S1<1.5, L2/S2<1.5; wherein, S1 is the line distance of one of the first bonding pads; and L2 is one of the second bonding pads The line width of the pad. The soldered anisotropic conductive film bonding structure according to claim 1 or 4, wherein the line width or line pitch of the first bonding pad and the second bonding pad is 5 times the particle size of the metal particles. The bonding structure of soldered anisotropic conductive film as claimed in claim 1, wherein the eutectic bonding between the metal particles and the first bonding pads and the second bonding pads forms an intermetallic compound. The soldered anisotropic conductive film bonding structure according to claim 1, wherein the materials of the first bonding pads and the second bonding pads are selected from gold, silver or copper.

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