TWI228805B - Flip-chip bonding process - Google Patents

Abstract

A flip-chip bonding process is provided to attach a chip on a substrate. By means of stripping off a part of the oxide on the surface of the bumps and a flux film forms around the stripped portion of the oxide, here the outside surface of the bumps. When the chip attaches to the substrate thereby through the bumps which is under reflow process, the flux film is easy to clear the oxide on the surface of the bump because the oxide is destroyed. It facilitates the bonding well between the chip and the substrate and reduces the contact resistance thereof.

Description

1228805 V. Description of the invention (1) [Technical field to which the invention belongs] The present invention relates to a flip-chip bonding process, and more particularly, to a flip-chip bonding process that improves the bonding between a wafer and a substrate. [Prior art]

F 1 ip C hip I nterc ο η nect Technology (FC for short) is a method of using area array to place multiple die pads on the active surface of a die. (Active surface), and bumps are formed on the wafer pad, and then the wafer is flipped (f 1 ip), and then these bumps are used to electrically and mechanically connect the wafer pad of the wafer to the carrier, respectively. ) Contact (c ntact), so that the chip can be electrically connected to the carrier through the bump, and electrically connected to the external electronic device through the internal circuit of the carrier. It is worth noting that, because the flip-chip bonding technology (FC) is applicable to high pin count (High Pin Count) chip packaging structure, and has many advantages such as reducing the chip packaging area and shortening the signal transmission path, so the flip-chip bonding The technology has been widely used in the field of chip packaging. Common chip packaging structures using flip-chip bonding technology include Flip Chip Ball Grid Array (FC / BGA) and Flip Chip Array (Flip Chip). Pin Grid Array (FC / PGA) and other types of chip packaging structures. .

Please refer to Figures 1A to 1D, which sequentially show the flow chart of the conventional flip-chip bonding process. The conventional flip-chip bonding process generally includes steps such as bump fabrication (b u m p i n g), wafer dicing (di e s a w), wafer bonding (bonding), and reflow (reflow). As shown in Figure 1A,

10550twf.ptd Page 5 1228805 V. Description of the invention (2) The bump process refers to forming bumps 120 on the wafer by steaming (eva ρ 〇rati ο η), printing or electroplating. 1 1 0 is on the wafer pad 1 1 1, and the bump 1 2 0 is, for example, a tin-lead bump, and the tin-lead ratio is 9 5: 5 or 6 3: 37. Next, as shown in FIG. 1B, the wafer 110 is diced to form a singulated wafer 1 12. Then, as shown in FIG. 1C, the wafer bonding means that after the wafer 11 2 is turned over, a vacuum nozzle (vacuin c ο 1 1 et) 1 0 is used to adsorb the back of the wafer 1 1 2 to move the wafer 1 1 2 to the substrate 1 3 0, so that the bumps 1 2 0 of the wafer 1 12 respectively contact the bump pads 1 3 2 of the corresponding substrate 1 3 0, and finally, as shown in FIG. 1D, the bumps The wafers 12 and 120 in contact with the block 120 are sent to a reflow oven for reflow, so as to complete the fabrication of the flip-chip package.所示 As shown in Figure 1C, it is worth noting that, in order to improve the bonding between the wafer 1 12 and the substrate 1 30, the conventional technique is to pre-bond the wafer 1 12 to the substrate 1 30 in advance. A soldering film 1 2 2 is formed on the surface of the bump 1 2 0, and the wafer pad 1 1 1 of the wafer 11 2 is accurately disposed on the bump pad 1 3 2 of the substrate 1 3 0. The role of the flux film 1 2 2 can not only temporarily fix the wafer 1 12 to the substrate 130, but also enable the tin-lead bump 120 to remove the tin-lead bump by the flux film 122 during reflow. An oxide layer 124 on the surface of the block 120. Finally, after re-soldering, the soldering flux film 12 2 remaining on the surface of the tin-lead bump 120 is removed by cleaning. However, when the oxide layer 1 2 4 on the surface of the tin-lead bump 1 2 0 is too thick, so that the solder film 1 2 2 cannot completely remove the oxide layer 1 2 4, it will affect the wafer 1 1 2 and the substrate 1 3 0 And the contact resistance between the wafer 1 12 and the substrate 130 is increased. [Summary of the Invention]

10550twf.ptd Page 6 1228805 V. Description of the invention (3) Therefore, the object of the present invention is to provide a flip-chip bonding process to improve the bonding between the wafer and the substrate and reduce the contact between the wafer and the substrate. resistance. In order to achieve the above object, the present invention provides a flip-chip bonding process suitable for bonding a wafer to a substrate, wherein the wafer has an active surface and a plurality of bumps, and the bumps are arranged on the active surface, and these The bumps each have an oxide layer, which respectively covers the surfaces exposed by the bumps, and the substrate further has a substrate surface and a plurality of bonding pads, and these bonding pads are arranged on the substrate surface. This flip-chip bonding process includes at least the following steps: (a) removing portions of the oxide layers on the bumps; (b) forming a soldering film on the outer surface of the bumps, respectively, and the soldering film system + is formed at least on Localized outer surfaces of the bumps from which the oxide layer has been removed; (c) contacting the bumps to one of their corresponding bonding pads and (d) resoldering the bumps so that the bumps are bonded to their respective locations Corresponds to one of the bonding pads, and causes the soldering films to remove one of the corresponding oxidized layers. According to a preferred embodiment of the present invention, the above-mentioned step (a) includes removing the localized oxide layers by grinding. In addition, at the step (b), it includes forming these soldering films by means of adhesion. In addition, the substrate further has a plurality of pre-solder blocks, which are respectively connected to one of the corresponding bonding pads, and at step (c), the bumps are respectively passed through one of the corresponding pre-solder blocks. And indirectly contact one of the corresponding bonding pads, and at the time of step (d), the bumps are respectively bonded to one of the corresponding pre-soldering blocks.

10550twf.ptd Page 7 1228805 V. Description of the invention (4) The flip-chip bonding process of the present invention removes part of the oxide layer on the surface of the bump, so that the flux film can easily remove the oxide layer on the surface of the bump, so It can improve the bonding between the wafer and the substrate, and reduce the contact resistance between the wafer and the substrate. In order to make the above-mentioned objects, features, and advantages of the present invention more comprehensible, a preferred embodiment is given below in conjunction with the accompanying drawings to describe in detail as follows: [Embodiment] 2A ~ 2F 图 依A sequence diagram of a flip-chip bonding process according to a preferred embodiment of the present invention is shown in sequence. Please refer to FIGS. 2A and 2B. First, a bump process is performed on the surface of a wafer 200, and the wafer 200 is cut to form a single wafer 210. The wafer 210 has an active surface 212 and a plurality of bumps 220, wherein the bumps 216 are arranged on the active surface 212 of the wafer 210, and the material of the bumps 2 2 0 is, for example, a tin-lead alloy, and its tin-lead ratio can be 5: 9 5 or 6 3: 37. In addition, the bumps 2 2 0 each have an oxide layer 2 2 2, which respectively covers the surfaces exposed by the bumps 220. Please refer to Figures 2C and 2E at the same time. After turning over the wafer 2 1 0, use the vacuum nozzle 10 to suck the back 2 1 4 of the wafer 2 1 0 to move the wafer 2 1 0 to a substrate 2 3 0. So that the wafer 2 10 is bonded to the substrate 2 3 0 through the bump 2 2 0. Please refer to Figures 2C and 2D at the same time. It is worth noting that in order to improve the bonding between the wafer 2 10 and the substrate 2 3 0, the present invention removes the bumps 2 2 0 by grinding. The local oxide layer 远离 > 2 2 2 farther away from one end of the wafer 2 10 to destroy the local oxide layer on the top of the bump 2 2 0. Next, a flux film 2 24 is formed on the outer surface of the & block 2 2 0 respectively, and the flux film 2 2 4

10550twf.ptd Page 8 1228805 V. Description of the invention (5) It is respectively coated on the corresponding oxide layer 2 2 2. It is important that the flux film 224 is formed at least on the removed oxide layer 222 of the bump 220 The local outer surface of the flux film 2 2 4 is formed by dipping the bump 2 2 0 in the container 20 containing the flux 30 and taking out the bump 2 2 0. Alternatively, the flux film 2 2 4 is formed by sucking the wafer 2 10 with a vacuum nozzle and then placing it on the flux platform to attach the flux. Referring to FIG. 2E, a substrate 2 3 0 is provided. The substrate 2 3 0 has a substrate surface 232 and a plurality of bonding pads 2 34, and the bonding pads 2 34 are disposed on the substrate surface 2 3 2. The wafer 2 10 is electrically and mechanically connected to the substrate 2 3 0 through the bump 2 2 0, and the bump 2 2 0 is in contact with the corresponding bonding pad 2 34 respectively. Next, referring to FIG. 2F, the wafer 210 and the substrate 2 3 0 in contact with the bump 2 2 0 are sent to a reflow furnace for re-soldering, so that the bumps 2 2 0 are respectively bonded to the corresponding bonding pads 2 3 4, and the flux film 2 2 4 is used to remove the corresponding coated oxide layer 2 2 2 respectively. At this time, since the oxide layer 2 2 2 is damaged, the flux film 2 2 4 can easily remove the oxide layer 2 2 2 on the surface of the bump 2 2 0 to promote the wafer 2 1 0 and the substrate 2 3 0. And reduce the contact resistance between the wafer 210 and the substrate 230. In addition, as shown in FIG. 2E, in order to enable the bump 220 to be bonded to the bonding pad 234, the bonding pad 2 3 4 of the substrate 230 has a plurality of pre-soldering blocks 2 3 6 (pre-solder), and the pre-soldering is performed. The material of the block 236 is a tin-alloy, and the tin-alloy ratio is, for example, 6 3: 3 7. In this way, the bumps 2 2 0 can indirectly contact the corresponding bonding pads 234 through their corresponding pre-soldering bumps 2 3 6, and when the bumps 220 are re-soldered, the bumps 220 can be respectively bonded to their respective pads Corresponding pre-soldering block 2 3 6. Finally, after the bump 2 2 0 is re-soldered, the flux film 2 24 remaining on the surface of the bump 2 2 0 is added in a cleaning manner.

l () 550twf.ptd Page 9 1228805 V. Description of the invention (6) To remove. Of course, in the above 2C and 2D drawings, it is also possible to first form a flux film 2 2 4 on the outer surface of the bump 2 2 0 respectively, and the flux film 2 2 4 is respectively coated on the corresponding oxide layer 2 2 2 and then remove the local oxide layer 2 2 2 located at one end of the bump 2 2 0 farther away from the wafer 2 1 0 by grinding, so that the soldering film 2 2 4 can easily remove the bump The oxide layer 2 2 2 on the surface of the block 2 2 0. Please refer to Figs. 3A to 3B, which sequentially show enlarged diagrams of the bumps of Fig. 2C before and after grinding. It is known that the oxide layer 2 2 2 on the surface of the bump 2 2 0 is too thick, so that the solder film 224 cannot completely remove the oxide layer 222, and the present invention uses a grinder to polish a local oxide layer 2 on the surface of the bump 2 2 0. 22, for example, the top of the comprehensively polished bump 2 2 0. Therefore, when the soldering film 2 24 is formed on the surface of the bump 2 2 0, the soldering film 224 can easily remove the oxide layer 2 2 2 on the surface of the bump 2 2 0 to enhance the wafer 2 1 0 and the substrate 2 3 0, and reduce the contact resistance between the wafer 210 and the substrate 230. It can be known from the above description that the flip-chip bonding process disclosed in the present invention removes a local oxide layer on the surface of the bump, and then forms a soldering film on the outer surface of the bump, respectively. The soldering film can be coated Oxide layer. Therefore, when the wafer contacts the substrate through the bump and re-solders the bump, the oxide layer is easily removed because of the oxide layer being damaged, so as to improve the bonding between the wafer and the substrate And reduce the contact resistance between the wafer and the substrate. Although the present invention has been disclosed above with a preferred embodiment, it is not intended to limit the present invention. Anyone skilled in the art will not depart from the essence of the present invention. 11

III IH 10550twf.ptd Page 10 1228805 V. Description of the invention (7) Within the scope of God and God, there should be some changes and retouching. For example, the method of removing the local oxide layer is not limited to the grinding method, nor is it limited to removing the oxide layer on the top of the bump. Removing the oxide layer on any part of the bump can achieve the effect of the present invention. Therefore, the present invention The scope of protection shall be determined by the scope of the attached patent application.

10550twf.ptd Page 11 1228805 Brief Description of Drawings Figures 1 A to 1 D sequentially show the flow chart of the conventional flip-chip bonding process. Figures 2A to 2F sequentially illustrate a flow chart of a flip-chip bonding process according to a preferred embodiment of the present invention. Figures 3A to 3B show the bump enlargement of the wafer before and after polishing in order. [Description of Graphical Symbols] 10: Vacuum Nozzle 20 ·· Container 30: Flux 110 wafer 111 wafer 塾 112 wafer 120 bump 122 flux film 124 oxide layer 130 substrate 132 substrate surface 210 wafer 2 12 active surface 214 back 220 bump 222 oxide layer 224 flux film

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Claims (1)

1228805 VI. Scope of patent application 1. A flip-chip bonding process suitable for bonding a wafer to a substrate, wherein the wafer has an active surface and a plurality of bumps, and the bumps are arranged on the active surface, and The bumps each have an oxide layer, which respectively covers the surfaces exposed by the bumps, and the substrate further has a substrate surface and a plurality of bonding pads, and the bonding pads are disposed on the substrate surface. The flip-chip bonding process includes at least the following steps: (a) removing portions of the oxide layers of the bumps; (b) forming a soldering film on the outer surfaces of the bumps, respectively, and the soldering film is Formed on at least a portion of the outer surface of the bump from which the oxide layer has been removed; (c) contacting the bumps to one of the corresponding bonding pads $ respectively; and (d) resoldering the bumps , So that the bumps are respectively bonded to one of the bonding pads corresponding to the bumps, and the soldering flux films are respectively used to remove one of the oxide layers corresponding to the coatings. 2. According to the flip-chip bonding process described in item 1 of the scope of patent application, at step (a), the partially removed oxide layers are located at the ends of the bumps away from the wafer. 3. The flip-chip bonding process described in item 1 of the scope of the patent application, wherein the material of the bumps is a tin-lead alloy. 4. The flip-chip bonding process described in item 3 of the scope of patent application, wherein the tin-lead ratio of the bumps is one of 5: 9 5 and 6 3: 3 7.逦, 5. According to the flip-chip bonding process described in item 1 of the scope of patent application, at step (a), it includes grinding to remove the local oxidation. 10550twf.ptd Page 14 1228805 Sixth, the scope of patent application. 6. The flip-chip bonding process described in item 1 of the scope of patent application, in step (b), includes forming the flux films by attaching a flux. 7. The flip-chip bonding process as described in item 1 of the scope of the patent application, wherein the substrate further has a plurality of pre-soldering blocks, which are respectively connected to one of the corresponding bonding pads, and in step (c) The bumps are indirectly in contact with one of the corresponding bonding pads through one of the corresponding pre-soldering blocks respectively, and at the time of step (d), the bumps are They are respectively joined to one of the corresponding pre-solder blocks. 8. The flip-chip bonding process described in item 7 of the scope of the patent application, wherein the material of the pre-solder blocks is a tin-lead alloy, and the tin-lead ratio of the pre-solder blocks is 6 3: 37. 9 · A flip-chip bonding process suitable for bonding a wafer to a substrate, wherein the wafer has an active surface and a plurality of bumps, and the bumps are arranged on the active surface, and the bumps have An oxide layer respectively covers the surfaces exposed by the bumps, and the substrate further has a substrate surface and a plurality of bonding pads, and the bonding pads are disposed on the substrate surface, and the flip-chip bonding process is at least The method includes the following steps: (a) forming a soldering film on the outer surfaces of the bumps, and respectively coating the soldering film on one of the corresponding oxide layers; (b) removing the soldering films; The oxide layers that are part of the bumps; (c) contacting the bumps to one of the corresponding bonding pads respectively; and 10550twf.ptd Page 15 1228805 6. The scope of the patent application (d) The solder bumps are re-soldered, so that the bumps are respectively bonded to one of the corresponding bonding pads, and the flux films are removed separately. One of the oxide layers corresponding to it. I 0. According to the flip-chip bonding process described in item 9 of the scope of patent application, at step (a), the partially removed oxide layers are located at one end of the bumps away from the wafer. II. The flip-chip bonding process according to item 9 of the scope of the patent application, wherein the material of the bumps is a tin-lead alloy. 12. The flip-chip bonding process as described in item 11 of the scope of patent application, wherein the tin-lead ratio of these bumps is one of 5: 9 5 and 6 3: 3 7. 13. The flip-chip bonding process described in item 9 of the scope of patent application, in step (a), includes forming the flux films by attaching a flux. 14. The flip-chip bonding process as described in item 9 of the scope of patent application, at step (b), includes removing the oxide layers locally by grinding. 1 5. The flip-chip bonding process as described in item 9 of the scope of patent application, wherein the substrate further has a plurality of pre-soldering blocks, which are respectively connected to one of the bonding pads corresponding to them, and in step (c) At this time, the bumps are indirectly in contact with one of the corresponding bonding pads respectively through one of the corresponding pre-soldering blocks, and at step (d), the bumps are It is respectively joined to one of the corresponding pre-solder blocks. 16. The flip-chip bonding process described in item 15 of the scope of the patent application, wherein the material of the pre-solder blocks is tin-lead alloy, and the tin-lead of the pre-solder blocks 10550twf.ptd Page 16 1228805 10550twf.ptd Page 17