Patent Application
20070045871
The present invention relates to a pad open structure, mainly aims to the Chip on Glass package, that makes the gold bump on a driving IC used for electric connection have an extra flat surface.
Compared liquid crystal displays (LCDs) with traditional CRTs, LCDs have characteristics of low-driving voltage, micro-power consumption, large-display capacity, low radiation and light, thin in size, so they are widely used in various audio-video equipments and communication equipments. Packages for the driving IC of a LCD are developed from the Chip on Board (COB) and the Tape Carrier Bounding (TAB) at early days to the Chip on Glass (COG) and Chip on Film (COF) at these days.
The bonding method for the COG structure is firstly to provide the glass substrate 13 which has plural electrodes 131 that are formed by the conductive film; to bond the ACF 12 to the glass substrate 13; and to put the driving IC 11 on the ACF 12. There are plural gold bumps 111 on the driving IC 11. The number of gold bumps 111 is corresponding to the number of electrodes 131 on the glass substrate 13 respectively. Then, do the operations of pre-bonding and main bonding to the abovementioned structure under the condition of fixed temperature, velocity, and pressure so as to actualize the electric connection between the gold bumps 111 of the driving IC 11 and the electrodes 131 on the glass substrate 13 through the conductive particles 122 of the ACF 12, and bind the driving IC 11 to the glass substrate 13 by the binder 121 (as shown in
The main characteristic of the ACF 12 is that it has electric conduction in the direction of z-axis whereas it is not conductive in the horizontal direction. Hence, when the conductive particles 122 are small enough or insulated among each other adequately, the fine pitch binding effect among the gold bumps 111 can be achieved.
Because LCDs are required for higher resolution, pins of the driving IC 11 become more and more. In other words, not only the integration extent is higher and higher but also the number of the gold bumps 111 is more and more.
Accordingly, for the purpose of reducing the space occupied by the pitches among the gold bumps 111, except the layout consideration for those electric connection wires, reducing the pitches among the gold bumps 111 is another way for designers to work on. Because if the pitches among the gold bumps 111 cannot be reduced effectively, the goal for reducing the chip dimension is limited.
However, the range for the diameter of common conductive particles 122 is 3˜15 μm. Too large conductive particles 122 reduce the number of contacting particles of each electrode, and the shorted situation 14 (as shown in
However, the schematic diagram for the electric pad of the driving IC 11 as shown in
In the bond between the common standard gold bumps 111 and the electrode 131 of the glass substrate 13, more than five conductive particles 122 will be broken. The reason is that the gold bump 111 is formed at the surface of the pad open 114 and the surrounding insulation layer 113, so the surface 1141 of the gold bump 111 will form a surface configuration that hollows approximately 2 μm due to the thickness of the insulation layer 113 when the surface area of the common gold bump 111 is approximate 2000 m2. During electroplating, a ±1 μm plating difference occurs on the same surface due to the manufacturing process.
To sum up, the drop height between the highest and the lowest surface 1141 of the gold bump 111 will be 4 μm. Therefore, because of the drop height of the surface 1141 that will not break conductive particles 122 enough, the contacting area between the small-diameter conductive particles 122 with 3˜4 μm in diameter and the gold bump 111 is not enough such that the electric connection effect is not good.
Consequently, the main purpose of the current invention is to solve the flattening problem for the surfaces of the gold bumps on the driving IC. By flattening the surfaces of the gold bumps, the small-diameter conductive particles are bonded but not broken enough so that the problems of insufficient contact area won't occur. During the bonding process of the COG, the electric connection effects among the connecting electrodes are good.
Another purpose of the current invention is that for any driving IC used in the COG package can adopt the ACF with small-diameter conductive particles to achieve the goal of reducing fine pitches among gold bumps without changing manufacturing process. By way of this, the integration extent of the circuit on the driving IC can be increased. This invention is a pad open structure, which is used as the connecting pad to the outside. After the insulation layer is installed at the surface of the pad, the insulation layer forms plural pad opens by lithography. The pad opens small area surfaces of the pad are exposed by pad opens. The gold bump forms the upper part of the insulation layer, which forms an electric connection through the pad opens to the pad.
The present invention changes the original structure of large area pad opens to plural pad opens. By adjusting the ratio between areas of the pad opens and the unopened region with the insulation layer and under the consideration of electric connection, when the gold bump is formed at the surface of the pad open and the surrounding insulation layer, because the single area of the pad opens is not large so as to reduce the affection produced by a well-known single large area pad open that hollows the surface of the gold bump seriously such that the gold bump of this invention has an extra flat surface.
The detailed descriptions for content and technology of this invention associated with figures are as follows.
This invention is mainly a pad open structure, which aims to improve the electric pad structure of the driving IC 21. The situation for the conductive particles 222 which is bonded but not broken enough won't occur during the bonding process of the COG.
The contact areas between the gold bumps 211 and the electrodes 231 on the glass substrate 23 are sufficient and the electric connection effect is good.
The gold bump 211 forms on the top of the insulation layer 213 and an electric connection through the pad opens 214 and the pad 212. The material of the gold bump 211 can be copper, nickel, gold, or a Sn—Pb alloy, which is formed by electroplating with thickness between 15˜18 μm.
The characteristic of present invention is that this invention changes the well-known original structure of large-area pad opens 114 (as shown in
This invention improves the well-known hollowing phenomenon by substituting plural pad opens 214 for the well-known single pad open 114. However, the upper surface of the unopened insulation layer 213 is still a plane configuration. Under the principle of that there is industry-standard electric connection between the gold bump 211 and the electrode 231 and by adjusting the ratio between areas of the total opens (the area of the plural pad opens 214) and unopened region with the insulation layer 213, both the electric connection between the gold bump 211 and the electrode 231 and improving the flattening for the surface 2141 of the gold bump 211 can be achieved.
Regarding the common industry standard, more than five conductive particles 222 are broken between the gold bump 211 and the electrode 231 of the glass substrate 23 can be counted as a good effect of electric connection with sufficient contacting area. Consequently, for the electric pad formed in the driving IC 21 of this invention, the surface 2141 of the gold bump 211 becomes extra flat due to the plural small-area pad opens 214. As a result, when the conductive particles 222 are small-diameter with diameter 3˜4 μm, the well-known problem that small-diameter conductive particles 222 are bonded but not broken enough so that the problems of insufficient contact area won't occur. During the bonding process of the COG, the electric connection effects among the connecting electrodes are good.
Because the aforementioned breaking problem for the small-diameter conductive particles 222 is solved through the electric pad structure of this invention, the pitch between each gold bump 211 should be greater than three times of the diameter of the conductive particle 222 according to the industry standard. In other words, this invention can adopt the ACF 22 with small-diameter conductive particles 222. Take the conductive particle 222 with diameter 3 μm as an example; the pitch between each gold bump 211 can be reduced to 10 μm, i.e. the goal of fine pitch is achieved. The integration extent of the circuit on the driving IC can be increased at the same time.
However, the above description is only a better practice example for the current invention, which is not used to limit the practice scope of the invention. All equivalent changes and modifications based on the claimed items of this invention are in the scope of the present invention.
