Method of backside grinding a bumped wafer

A method for backside grinding a bumped wafer is disclosed. A wafer has a plurality of bumps formed on the active surface thereof. Prior to grinding the back surface of the wafer, a hot-melt adhesive layer is formed on the active surface of the wafer so as to be adhered to the active surface and cover the bumps. Also a grinding film is attached to the hot-melt adhesive layer. After grinding the back surface of the wafer, the grinding film is removed but the hot-melt adhesive layer is remained on the wafer for the following wafer-dicing step.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to a method of backside grinding a bumped wafer. More particularly, the present invention is related to a method of backside grinding a bumped wafer for protecting the devices and the bumps formed on the active surface of the wafer from being damaged at the duration of processing.

2. Related Art

In this information explosion age, integrated circuits products are used almost everywhere in our daily life. As fabricating technique continue to improve, electronic products having powerful functions, personalized performance and a higher degree of complexity are produced. Nowadays, most electronic products are relatively light and have a compact body. Hence, in semiconductor production, various types of high-density semiconductor packages have been developed. Flip chip is one of the most commonly used techniques for forming an integrated circuits package. Moreover, compared with a wire-bonding package or a tape automated bonding (TAB) package, a flip-chip package uses a shorter electrical path on average and has a better overall electrical performance. In a flip-chip package, the bonding pads on a chip and the contacts on a substrate are connected together through a plurality of bumps formed on the chip by a conventional bumping process and then an underfill material is filled into the gap between the chip and the substrate to encapsulate the bumps so as to well protect the bumps. In such a manner, the reliability of such flip chip package is enhanced.

As mentioned above, in order to have a thinner package, the step of backside grinding a wafer in a package process is necessary before the wafer is diced into a plurality of chips. Therein, before the wafer is diced, the active surface of the wafer is placed on a grinding film, and then the back surface of the wafer is thinned under a backside grinding process. However, usually, there are electronic devices formed on the active surface of the wafer, such as bumps, passive components, and metal posts, and are protruded from the active surface of the wafer without appropriate protection, so the electronic devices are easily fell away from the wafer at the duration of removing the grinding film from the wafer.

In order to well protect the electronic devices, there is a backside grinding method for a wafer level packaging disclosed in TW Pat. 516116, which utilizes an organic layer formed on a surface of a bumped wafer and a UV film (ultraviolet film) attached to the organic layer, regarded as a grinding film, to protect the bumps of the wafer at the processing steps. Therein, the organic layer is usually made of a material selected from Benzotriazoles and substituted Benzotriazoles as well known organic solderability preservatives (OSP). Usually, the organic layer is easily fell off from the wafer when the thickness of the organic layer is larger than 1 um. However, in order to well protect the bumps and similar electronic devices, the organic layer is usually required to have a thickness larger than 10 um. Therefore, the organic layer cannot be well adhered to the wafer to keep the bumps from being damaged. Besides, when the grinding film is removed, the organic layer is usually removed off with the grinding film so that the organic layer cannot be regarded as a protection layer when the wafer is diced.

As disclosed in US Publications 2002/0166625, there is disclosed another backside grinding method by using a grinding film with a base and a thicker adhesive layer provided therein. Therein, the thicker adhesive layer is made of a material, such as acrylic adhesive and ultraviolet film (UV film) so as to cover ten to sixty percents of bumps area. However, the interfaces between the bumps and the wafer are not well protected so that the interfaces are easily damaged. Besides, when the grinding film is removed from the wafer, the bumps are easily to be damaged so as to have some bumps fell off from the wafer.

Therefore, providing another method to solve the mentioned-above disadvantages is the most important task in this invention.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems, an objective of this invention is to provide a method of backside grinding a bumped wafer by utilizing the steps of forming a hot-melt adhesive layer (HMA layer) on an active surface of the bumped wafer so as to cover the bumps. Therefore, the bumps can be well protected. Besides, a grinding film is provided and then attached to the hot-melt adhesive layer for proceeding the step of grinding the back surface of the wafer. Furthermore, after the back surface is ground and the grinding film is removed, the hot-melt adhesive layer is still disposed on the active surface of the wafer to enhance the reliability of the step of dicing the wafer into a plurality of chips. Besides, when the back surface of the wafer is ground, the hot-melt adhesive layer is disposed on the active surface of the wafer, so the bumps formed on the wafer are well protected. To be noted, the method is also applicable to a wafer having a plurality of electronic devices formed thereon and protruded from the active surface of the wafer, such as passive components, metal posts, wires and solder balls, so as to well protect the electronic devices at the duration of processing the steps of grinding back surface of the wafer.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention specifically provides a method of providing a bumped wafer having an active surface with a plurality of bumps or electronic devices formed thereon and a back surface; forming a hot-melt adhesive layer on the active surface, wherein the hot-melt adhesive layer covers at least sixty percents of the area of each bump; applying a grinding film onto the hot-melt adhesive layer; grinding the back surface of the wafer; removing the grinding film and keeping the hot-melt adhesive layer remained on the active surface of the wafer for protecting the bumps or electronic devices when the step of grinding the back surface of the wafer is performed; dicing the wafer into a plurality of chips; and removing the hot-melt adhesive layer out of the wafer to have the bumps exposed.

DETAILED DESCRIPTION OF THE INVENTION

The forming method thereof according to the preferred embodiment of this invention will be described herein below with reference to the accompanying drawings, wherein the same reference numbers are used in the drawings and the description to refer to the same or like parts.

As shown inFIG. 1, it illustrates a process flow of a method of backside grinding a bumped wafer. The method mainly comprises the following steps of providing a bumped wafer as shown in step1, forming a hot-melt adhesive layer on the active surface of the wafer as shown in step2, providing a grinding film on the hot-melt adhesive layer as shown in step3, grinding a back surface of the bumped wafer as shown in step4, attaching a dicing film on the back surface of the wafer as shown in step5, removing the grinding film form the wafer as shown in step6, dicing the bumped wafer as shown in step7and removing the hot-melt adhesive layer as shown in step8.

Referring toFIG. 1again withFIGS. 2B and 2C, the step2of forming a hot-melt adhesive layer20on the active surface11of the bumped wafer10comprises attaching the hot-melt adhesive layer20on the active surface11and performing a heating process, wherein the hot-melt adhesive layer20is made of a thermoplastic material. Referring toFIG. 2Cagain, a heating process is performed at a temperature equal to or higher than the melting point of the hot-melt adhesive layer so as to have the hot-melt adhesive layer20enclosed the bumps13, wherein the meting point of the hot-melt adhesive layer is about 80° C. and the hot-melt adhesive layer covers at least sixty percents of the area of each bump. Preferably, the hot-melt adhesive layer20covers at least eighty percents of the area of each bump. After the temperature returns to room temperature, the hot-melt adhesive layer is securely attached to the bumps13. To be noted, the dam14located at the periphery of the active surface11of the wafer10can block the hot-melt adhesive layer to flow out at the duration of performing heating process. Usually, the height of the dam14can vary according to the design of the thickness of the hot-melt adhesive layer20. Besides, the hot-melt adhesive layer20is made of a material with elasticity and transparency so as to provide the identification for dicing wafer and the protection for bumps.

Afterwards, referring toFIGS. 1 and 2D, as shown in the step3of providing a grinding film30on the active surface11of the wafer10, wherein the grinding film30, with a base layer and an adhesive layer, such as ultrasonic violet film or similar film made of a material without adhesion under heating process or ultraviolet radiation by ultraviolet light at a temperature lower than 80° C., is attached on the active surface11of the wafer10.

Then, referring toFIGS. 1 and 2Eagain, the back surface12of the wafer10is ground so as to have the wafer10thinned as shown in the step4. The active surface11of the wafer10is covered by the hot-melt adhesive layer20and the bumps13are also enclosed by the hot-melt adhesive layer20so that the hot-melt adhesive layer20is disposed between the wafer10and the grinding film30. Therefore, the interface between the bumps13and the wafer10are well protected from being damaged.

Next, the step5of attaching a dicing film40on the back surface12of the wafer10and the step6of removing the grinding film40are preformed. To be noted, the step5can be performed after or before the step6is performed. In this embodiment, after the step4is performed, the thickness of the wafer10is smaller than 6 mils. Therefore, in order to prevent the wafer10from being warped, the step5is performed to solve this disadvantage. Referring toFIG. 2Fand the step5as shown inFIG. 1, a dicing film40is attached to the back surface12of the wafer10and then a heating process or ultraviolet radiation by ultraviolet light at a temperature lower than 80° C. is performed to reduce the adhesion of the grinding film30to the hot-melt film so as to have the grinding film30removed. Because the hot-melt adhesive layer20encloses the bumps13and covers the active surface11of the wafer10, the bumps13are well protected when the step6is performed and not removed from the wafer10with the grinding film30.

Next, referringFIG. 2Hand the step7as shown inFIG. 2H, wherein when the step7is performed, the wafer10is diced into a plurality of chips20disposed at the dicing film40. Meanwhile, the hot-melt adhesive layer20is remained on the active surface11of the wafer10and the bumps13of each chip15are still enclosed by the hot-melt adhesive layer20so as to prevent the bumps from being damaged and prevent the chip15from being contaminated. Preferably, the hot-melt adhesive layer20are made of a material with good transparence so as to align the sawing line with the sawing blade through CCD.

Finally, referring toFIG. 1andFIG. 2I, wherein the step8of removing the hot-melt adhesive layer20from the wafer10is performed by cleaning the chips20, regarded as singulated wafer10, disposed on the dicing film40through the DI water (deionize water) and appropriate solution so as to remove the hot-melt adhesive layer20out and have the bumps13of each chip20exposed.

Accordingly, the process of grinding the back surface12of the bumped wafer10in this invention is performed by attaching the hot-melt adhesive layer20onto the active surface11of the wafer10through heating process so as to have the hot-melt adhesive layer20to enclose the bumps13. Therefore, the bumps13can be well protected in the step4of grinding the back surface12of the wafer10, the step of removing the dicing film40and the step7of dicing wafer. Besides, this invention can be applied to the steps of grinding and dicing the wafer10with a device formed thereon, wherein the device can be a surface mount device, such as wire-bonding chip, flip-chip, resistor, capacitor and inductance, or the wire, solder ball, metal column and bump, or the combination thereof.

Referring toFIG. 3showing the second embodiment of this invention, it illustrates a wafer50having a hot-melt adhesive layer20. Therein, the wafer50has an active surface51and a back surface52. The back surface52of the wafer50has a plurality of bumps53and a flip chip54formed thereon. The area of having the flip chip54thereon is smaller than the area of having the chip54thereon defined on the active surface51of the wafer50. For example, a processed wafer has a memory flip-chip54, and a hot-melt adhesive layer20is formed on the active surface51of the wafer50and attached to the active surface51by heating process so as to have the bumps53and the bottom thereof covered thereby. The hot-melt adhesive layer20has a surface exposed for having a grinding film attached thereto so as to have the bumps well protected by the hot-melt adhesive layer at the duration of processing the steps4,6, and7for that the hot-melt adhesive layer20can be utilized for enhancing the attachment of the bumps53to the flip chip54and the wafer50.

Referring toFIG. 4showing the third embodiment of this invention, it illustrates a wafer60having a hot-melt adhesive layer20. Therein, the wafer60has an active surface61and a back surface62. The back surface62of the wafer60has a plurality of bumps63, a passive component66and a wire64. The wire64connects the bonding pads65of the wafer. However, the bump63, the passive component66and the wire64are protruded from the active surface61of the wafer60and the hot-melt adhesive layer20is attached to the active surface61and encloses the bump63, the passive component66and the wire64so as to prevent the bump63, the passive component66and the wire64from being damaged at the step4of grinding the back surface of the wafer, the step6of removing the grinding tape.

Although the invention has been described in considerable detail with reference to certain preferred embodiments, it will be appreciated and understood that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.