TW201301456A - Buffer sheet and COF bonding method applying the buffer sheet - Google Patents

Abstract

A buffer sheet is adapted to bonding process of a chip-on-film (COF) and a substrate. The buffer sheet includes a first film layer, a thermal resistant layer and a second film layer stacked in order. The thermal expansion modulus of the thermal resistant layer is smaller than those of the first and the second film layer. Accordingly, when a heat header does not press against the COF, the most of heat from the header can be isolated by the buffer sheet. The heat of the header can be transferred to the conductive glue sandwiched between the COF and the substrate when the header presses the buffer sheet against the COF. Therefore, the temperature and thermal expansion of the COF can be accurately controlled.

Description

Buffer element and flip chip bonding method using the same

The present disclosure relates to a cushioning member, and more particularly to a cushioning member for use in flip chip bonding and a bonding method thereof.

In general, a method of bonding a chip on film to a liquid crystal panel is generally performed by a hot pressing process. In the hot pressing process, the flip chip is first stacked on the liquid crystal panel, and then pressed by a hot head. The film is covered by the soft film. Therefore, the glue between the crystal film and the liquid crystal panel will bond the crystal film and the liquid crystal panel. Further, in the aforementioned pressing process, the thermal head is usually pressed against the flip chip by the buffer material.

In the above hot pressing process, the wiring of the liquid crystal panel and the outer lead of the flip chip are required to be electrically connected, and the wiring and the outer lead are usually parallel electrical wiring (like a gold finger), due to the outer lead The thermal expansion coefficient of the flip chip is higher than the thermal expansion coefficient of the liquid crystal panel where the trace is located. Therefore, before hot pressing (such as normal temperature), the spacing between the outer leads is usually smaller than the spacing between the traces, when the thermal head When the flip chip is pressed against the soft film, since the amount of thermal expansion of the flip chip is larger than the amount of thermal expansion of the liquid crystal panel (glass), the outer lead and the trace can be electrically connected correspondingly at the thermal bonding temperature.

Although the hot pressing process of the above-mentioned flip chip soft film can achieve the purpose of corresponding electrical connection, in practice, the temperature of the flip chip soft film is not easy to control, and when the temperature does not fall within a predetermined range, the thermal expansion amount of the flip chip soft film Will be insufficient or too large, poorly connected or wrong. In addition, in the actual process, the buffer material is disposed between the thermal head and the flip chip, and the temperature of the crystal film is more difficult to control, and it is easier to form a poor electrical connection.

In view of the above, the present disclosure proposes a buffer element and a flip chip bonding method using the buffer element, which is suitable for bonding a flip chip to a substrate.

According to an embodiment, the buffer element comprises a first film layer, a thermal resistance layer and a second film layer which are sequentially stacked. The thermal resistance layer has a thermal conductivity of less than 0.13 W/m-k. The first film has a heat transfer coefficient of 0.4 W/m-k. The thermal conductivity of the second film layer is greater than the thermal conductivity of the first film layer.

According to an embodiment, the second film layer comprises a thermally conductive powder and has a heat transfer coefficient of 0.3 W/m-k. The thickness of the aforementioned thermal resistance layer is between 0.06 mm and 0.1 mm. The first film layer has a thickness of 0.05 mm and the second film layer has a thickness of 0.1 mm. The thermal conductivity of the thermal resistance layer is smaller than the thermal conductivity of the second coating.

According to an embodiment, a flip chip bonding method using a buffer element includes pressing a buffer element with a thermal head on a substrate on which a flip chip is laminated, and a conductive adhesive material is interposed between the flip chip and the substrate, and the thermal head is The temperature is 380 ° C; and after the substrate is continuously pressed for a predetermined time, the thermal head is returned.

By the structure of the above buffer element, the buffer element can isolate the heat of the thermal head without pressing the thermal head (or the buffer element is not contacted), without preheating the flip chip, when the hot head is pressed When the buffer element is on the flip chip, the heat can be quickly transferred to the conductive paste, and after the hot head is retracted, the heat is also separated by the buffer element around the hot head without continuously heating the flip chip. It can more effectively control the bonding temperature of the flip chip and improve the yield of electrical connection.

The above description of the disclosure is intended to be illustrative of the spirit and principles of the disclosure, and to provide further explanation of the scope of the disclosure. The features, implementations, and effects of the present disclosure are described in detail below with reference to the preferred embodiments.

The detailed features and advantages of the present disclosure are described in detail in the following detailed description of the embodiments of the present disclosure, which are The objects and advantages associated with the present disclosure can be readily understood by those skilled in the art.

First, please refer to "FIG. 1", which is a schematic structural diagram of a buffer element according to an embodiment of the present disclosure. The Buffer Sheet 10 is suitable for a chip on film process. Please read it with "Figure 2A". It can be seen from "Fig. 2A" that the cushioning member 10 is wound around the rollers 52a, 52b in the flip chip process, and the rollers 52a, 52b are respectively disposed on the sides of the heat head 30 (Buffer Sheet Cassette). ) 50a, 50b. This thermal head 30 can also be referred to as the present pressure head.

The flip chip 22 is disposed on a substrate 20, which may be a liquid crystal panel or other substrate to be bonded to the flip chip 22. The flip chip 22 has a wafer 24 on the between the flip chip 22 and the substrate, and has a conductive adhesive. The conductive adhesive can be, but not limited to, an anisotropic conductive adhesive (ACF) and various heat curing types. Glue. After the flip chip 22 is bonded to the substrate 20, the outer leads of the wafer 24 are electrically connected to the traces on the substrate 20, and the bonding process will be described in detail later.

The buffer element 10 includes a first film layer 12, a thermal resistance layer 14, and a second film layer 16. The thermal resistance layer 14 includes a first surface 140 and a second surface 142. The thermal resistance layer 14 has a thermal conductivity of less than or equal to 0.13 W/m-k. The thermal resistance layer 14 may be a glass fiber layer. The material of the thermal resistance layer 14 may be, but not limited to, a fiberglass cloth and any material having high thermal resistance. The high thermal resistance material herein may be any material having a thermal conductivity of less than 0.13 W/mk. The fiberglass cloth has a heat transfer coefficient of about 0.13 W/mk. The thickness of the thermal resistance layer 14 may range from 0.06 millimeters (mm) to 0.1 millimeters.

The first film layer 12 is disposed on the first surface 140, and the first film layer 12 has a heat transfer coefficient of 0.4 W/m-k. The first film layer 12 can be a coffin layer. The first film layer 12 may be a tantalum film of an undoped thermally conductive powder having a heat transfer coefficient of about 0.4 W/m-k. The thickness of the first film layer 12 can be between 0.01 mm and 0.05 mm.

The second film layer 16 is disposed on the second surface 142, and the heat transfer coefficient of the second film layer 16 is greater than the heat transfer coefficient of the first film layer 12. The second film layer 16 can be a coffin layer. The second film layer 16 may be, but not limited to, a ruthenium film, and the ruthenium film may also be added with a heat conductive powder. The tantalum film to which the thermal conductive powder is added has a heat transfer coefficient of about 0.3 W/m-k. The thermal conductive powder may be bonded to the ruthenium film by mixing, doping or coating. The thickness of the second film layer 16 can be between 0.06 mm and 0.1 mm. The thermal conductivity of the thermal resistance layer 14 is smaller than the thermal conductivity of the second film layer 16.

The second film layer 16 has a release structure with respect to the other surface 160 of the second surface (the surface facing the flip chip 22). The release structure may be a bump or a pit of a multi-point pattern, or have a release material on the surface 160 to facilitate the separation of the buffer element 10 from the flip chip 22 (isotropic conductive paste) during the process. .

Next, please read it with "2A", "2B" and "2C". It is a schematic diagram of a flip chip bonding process using a buffer element according to an embodiment of the present disclosure.

In the "Fig. 2A", the flip chip 22 is pre-pressed on the substrate 20 in the previous process (pre-pressing process) before moving to the "Fig. 2A" process (also referred to as the press process). As can be seen from the figure, the two ends of the cushioning member 10 are wound around the rollers 52a, 52b and span between the thermal head 30 and the flip chip 22, wherein the first film layer 12 of the cushioning member 10 is oriented toward hot pressing. Head 30. In this state, since the thermal conductivity of the thermal resistance layer 14 and the first film layer 12 are both smaller than the thermal conductivity of the second film layer 16, the heat of the thermal head 30 will be relatively separated from the buffer element 10 ( That is, the thermal head 30 is located so that the heat is not thermally or thermally convected to the flip chip 22, and the flip chip 22, the conductive paste and the substrate 20 are maintained at a predetermined temperature, which is lower than the conductive paste. The welding temperature.

Next, in "Fig. 2B", the thermal head 30 has moved toward the flip chip 22 and the cushioning member 10 is pressed against the flip chip 22, at which time, since the thermal head 30 has pressed against the cushioning member 10 And the flip chip 22, therefore, the heat of the thermal head 30 is thermally transferred to the flip chip 22, the conductive paste and the substrate 20, so the conductive paste will reach the fusion temperature within a predetermined time and the flip chip 22 and The substrate 20 is joined. This predetermined time may vary depending on the structure of the buffer element 10. For example, when the thickness of the thermal resistance layer 14 is thicker, the thermal conductivity of the thermal resistance layer 14 is lower, or the thermal conductivity of the first film layer 12 is lower, the predetermined time is The longer, that is, the predetermined time varies depending on the design of the buffer element 10.

Next, after the conductive adhesive material reaches the fusion temperature, the thermal head 30 can move away from the flip chip 22 (ie, move upwards to the "Fig. 2B"), and after moving, the image is formed as "2C". As shown, in this figure, the bonding of the flip chip 22 to the substrate 20 is completed, after which the bonded substrate 20 can be removed, moved into a new one of the substrates 20, and the flip chip 22 is further processed. Bonding process.

In addition, regarding the influence of the predetermined temperature at the time of joining and the predetermined time on the bonding effect, please refer to "3A", "3B", "3C" and "3D", which are flip chips. Schematic diagram of the results of the soft film bonding. These figures are the bottom view of "Phase 2A", which is a schematic diagram drawn from the perspective of "2A" below.

In the state of "FIG. 2A", the relative positions of the outer leads (also referred to as outer leads) 23a, 23b of the wafer 24 and the traces 21a, 21b of the substrate 20 are as shown in the figure, wherein the outer leads are It may be a conductive wiring on the flip chip 22 for guiding the pins of the wafer 24. When the substrate 20 is a liquid crystal panel, the traces 21a and 21b of the substrate 20 may be an indium tin oxide (ITO). In the "Fig. 2A", the conductive adhesive between the outer leads 23a, 23b and the traces 21a, 21b is not yet soldered, so that the outer leads 23a, 23b and the traces 21a, 21b are not yet joined. And the pitch of the adjacent outer leads 23a, 23b is smaller than the pitch of the traces 21a, 21b.

When the predetermined temperature or the predetermined time is not appropriate, the joint between the outer leads 23a, 23b and the traces 21a, 21b may be inappropriate, that is, if the predetermined temperature is too low or the predetermined time is too short, the outer leads 23a, 23b The flip chip 20 may be insufficiently heated, and the expansion amount of the flip chip 20 is not as expected, so that the distance between the outer leads 23a, 23b is still smaller than the distance between the traces 21a, 21b, but the conductive paste has been joined. Therefore, the joined state as shown in "Fig. 3B" is generated. As can be seen from "Fig. 3B", the outer leads 23a, 23b are located just above the gaps of the traces 21a, 21b, so that the outer leads 23a, 23b electrically connect the adjacent traces 21a, 21b and are short-circuited.

Next, if the predetermined temperature and the predetermined time are appropriate, the outer leads 23a, 23b are electrically connected to the traces 21a, 21b in a one-to-one correspondence, as shown in "3C", the pins of the wafer 24 are completed. The purpose of electrically connecting to the substrate 20.

Furthermore, when the predetermined temperature is too high or the predetermined time is too long, the amount of expansion of the flip chip 20 is more than expected, and the pitch of the outer leads 23a, 23b is larger than the pitch of the traces 21a, 21b, that is, "3D" As shown, at this time, the bonding between the outer leads 23a, 23b and the traces 21a, 21b may be inappropriate. Although the bonding in the "3D" is still in a one-to-one correspondence, the gap after the bonding is changed. Small, in addition to increasing the possibility of short circuit, the joint area between the two is relatively small, and the electrical connection effect is also poor.

Regarding the effect of the buffer element 10 applied to the bonding of the flip chip 22, several experiments are carried out. The first film in the experiment is made of ytterbium (undoped thermal powder) with a thickness of 0.05 mm; the second layer The material is 矽 and doped with thermal conductive powder, the thickness is 0..1 mm; the conductive adhesive between the flip chip 22 and the substrate 20 (the liquid crystal panel used in this experiment) adopts an anisotropic conductive adhesive, and the thermal resistance layer is adopted. The fiberglass cloth has thicknesses of 0.06, 0.08, and 0.1 mm, respectively. In the same process, when the bonding is completed, the amount of expansion of the flip chip is as shown in Fig. 4, which is 22, 15, and 10 μm, respectively. The aforementioned expansion amount refers to the amount of expansion of the flip chip 22 on the horizontal surface when the conductive paste is cured (or at the fusion temperature), and the horizontal plane refers to a surface substantially parallel to the second surface of the cushioning member. It can be seen from "Fig. 4" that the amount of expansion is between 10 and 22 microns. The expansion ratio is between 0.3% and 0.8%. For example, when the width between the outermost two outer leads 23a, 23b is 4.2 millimeters (mm), the amount of expansion in the plane is between 12.6 and 33.6 microns. Of course, the aforementioned amount of expansion may vary depending on the design.

Finally, please refer to FIG. 5 , which is a schematic flow chart of a flip chip bonding method using a buffer element according to an embodiment of the present disclosure. It can be seen from the figure that the method of bonding a chip on film using the buffer element 10 includes: step S90: pressing the buffer element 10 with the thermal head 30 on the substrate 20 on which the flip chip 22 is laminated, and flipping the crystal The flexible film 22 and the substrate 20 have a conductive adhesive material, and the temperature of the thermal head is 380 ° C; and step S92: after pressing the substrate for a predetermined time, the thermal head is returned.

The temperature of the thermal head in step S90 may be higher than the welding temperature of the conductive rubber or the predetermined temperature, or may be the curing temperature of the conductive rubber. Step S90 may mean that the thermal head 30 first contacts the cushioning member 10 at a predetermined speed, and then presses the cushioning member 10 against the substrate 20. This predetermined speed can be a first speed and has a speed value of about 1 to 10 mm/s.

The predetermined time in step S92 may be the time when the thermal head 30 presses the buffer member 10 on the substrate 20 until the conductive adhesive reaches the fusion temperature, or the thermal head 30 is pressed against the buffer member 10 on the substrate 20. The time when the conductive adhesive is cured. The retraction of the thermal head 30 means that the thermal head 30 moves away from the flip chip 22 .

In summary, the cushioning element 10 can isolate the heat of the thermal head 30 from above the cushioning element 10 when the thermal head 30 has not been depressed (ie, as shown in FIG. 2A or is not in contact with the cushioning member). Without preheating the flip chip 22, when the thermal head 30 abuts the resistive element 10 on the flip chip 22, heat can be quickly transferred to the conductive paste, and after the thermal head 30 is retracted, the heat is also buffered. The element 10 is isolated around the thermal head 30 without continuously heating the flip chip 22, thereby more effectively controlling the bonding temperature of the flip chip 22 and improving the yield of the electrical connection.

Regarding the design of the cushioning material, the implementer can select a suitable material as the thermal resistance layer 14 according to the temperature of the thermal head 30 and the falling speed of the thermal head 30, that is, appropriately selecting a material having a high heat transfer coefficient to satisfy the pressure of the hot head 30. The temperature blocking effect in the time before the flip chip 22 is formed, and the temperature blocking effect can also be designed according to the amount of expansion of the flip chip 22 .

The present disclosure is disclosed in the foregoing preferred embodiments. However, it is not intended to limit the disclosure, and the skilled person can make some changes and refinements without departing from the spirit and scope of the disclosure. The scope of patent protection shall be subject to the definition of the scope of the patent application attached to this specification.

10. . . Cushioning element

12. . . First film

14. . . Thermal resistance layer

140. . . First surface

142. . . Second surface

16. . . Second film

160. . . The other side, the surface

20. . . Substrate

21a, 21b. . . Traces

twenty two. . . Cladding film

23a, 23b. . . Outer lead

twenty four. . . Wafer

30. . . Hot head

50a, 50b. . . Card

52a, 52b. . . roller

FIG. 1 is a schematic structural view of a cushioning member according to an embodiment of the present disclosure.

2A, 2B, and 2C are schematic views of a flip chip bonding operation using a buffer element according to an embodiment of the present invention.

3A, 3B, 3C, and 3D are structural schematic views of the results of the flip-chip soft film bonding.

Figure 4 is a comparison of the amount of expansion of the flip chip film.

FIG. 5 is a schematic flow chart of a flip chip bonding method using a buffer element according to an embodiment of the present disclosure.

10. . . Cushioning element

12. . . First film

14. . . Thermal resistance layer

140. . . First surface

142. . . Second surface

16. . . Second film

160. . . The other side, the surface

Claims (15)

A buffer element is suitable for a flip chip process, the buffer element comprises: a thermal resistance layer having a first surface and a second surface, the thermal resistance layer having a thermal conductivity of less than or equal to 0.13 W/mk; a film layer disposed on the first surface, the first film layer having a heat transfer coefficient of 0.4 W/mk; and a second film layer disposed on the second surface, the second film layer having a heat transfer coefficient greater than the first layer The thermal conductivity of a film layer. The cushioning member of claim 1, wherein the second film layer comprises a thermally conductive powder. The buffer element of claim 1, wherein the second film layer has a heat transfer coefficient of 0.3 W/m-k. The cushioning member of claim 1, wherein the thermal resistance layer has a thickness of between 0.06 mm (mm) and 0.1 mm. The cushioning member of claim 4, wherein the second film layer has a thickness of 0.1 mm. The cushioning member of claim 5, wherein the first film layer has a thickness of 0.05 mm. The snubber element of claim 6, wherein the thermal resistance layer has a thermal conductivity smaller than a thermal conductivity of the second film layer. The cushioning member of claim 1, wherein the second film layer has an off-structure with respect to the other side of the second surface. The cushioning component of claim 1, wherein the material of the thermal resistance layer is a fiberglass cloth, the material of the first film layer is a ruthenium film, and the material of the second film layer is a ruthenium film. A chip-on-film bonding method comprises: pressing a buffer element with a thermal head on a substrate on which a flip chip is laminated, and the flip chip has a conductive adhesive material between the film and the substrate, The temperature of the thermal head was 380 ° C; and after the substrate was continuously pressed for a predetermined time, the hot head was returned. The flip chip bonding method according to claim 10, wherein the crystalline soft film has a swelling ratio between 0.3% and 0.8% at the time of curing of the conductive rubber. A flip chip bonding method according to claim 10, wherein the flip chip is expanded in a horizontal plane between 10 micrometers (um) and 22 micrometers when the conductive paste is cured. The flip chip bonding method according to claim 10, wherein the step of pressing the buffer member with the thermal head is such that the thermal head contacts the buffer member at a predetermined speed and then presses the buffer member against the substrate. . The flip chip bonding method of claim 13, wherein the predetermined speed is a first speed. The flip chip bonding method of claim 13, wherein the speed is 1 to 10 mm/s.