CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 90106703, filed on Mar. 22, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a wafer-level packaging. More particularly, the invention relates to a wafer-level packaging suitable for use with a flip-chip connection.

2. Description of the Related Art

As electronic technology progresses, the miniaturization of electronic products is increasingly emphasized. This miniaturization results in a more complicated and denser structure of electronic products. In electronic industries, the packaging of electronic devices thus requires package structures that have small dimensions and high density. In this context, many types of packaging structures are developed, such as ball grid array (BGA) packages, chip-scale packages (CSP), flip-chip (F/C) structure packages, multi-chip module (MCM) packages, etc.

Among the above-mentioned types of packaging structures, the flip-chip structure packages advantageously allow for a packaging structure that has a small surface, high pin counts, a short signal path, a low induction and a control of noise signals. Thus, the flip-chip structure is increasingly used in packaging electronic devices.

In the traditional flip-chip structure, an underfill must be filled between the chip and the carrier or printed circuit substrate onto which the chip is connected. The underfill can share the thermal stress generated between the carrier and the chip due to different coefficients of thermal expansion of the carrier and the chip. As a result, the bumps that electrically connect the chip to the carrier can be prevented from fatigue resulting from the thermal cycle.

However, with a packaging structure that is increasingly denser, the pitch between the bumps formed on the chip is consequently reduced. In a flip-chip structure, effectively filling the underfill without voids thus becomes difficult and increases the manufacturing cost. Solutions that can overcome the above-described problems to allow for a reliable flip-chip structure are thus needed.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a wafer-level packaging in which a patterned stress buffer layer is adequately formed over the wafer to substitute for a conventional underfill process, such that the packaging can be simply achieved with a reduced cost.

To attain the foregoing and other aspects, the present invention, according to a first preferred embodiment, provides a wafer-level packaging comprising: providing a wafer having a plurality of bonding pads thereon exposed through a passivation layer formed on the wafer, an under bump metal (UBM) being formed on each of the bonding pads; forming a stress buffer layer that can be patterned over the wafer, wherein using the pattern property of the stress buffer layer, a plurality of first openings are formed in the stress buffer layer exposing the under bump metals (UBM); filling a solder material in the first openings of the stress buffer layer; arranging either a stencil or a patterned photoresist having a plurality of second openings on the stress buffer layer such that the second openings expose the first openings; filling a solder material in the second openings; and performing a reflow process, wherein if the stencil is used, it is removed before the reflow process while if the patterned photoresist is used, it is removed after the reflow process.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,

FIG. 1

is a cross-sectional view schematically illustrating a wafer with a stress buffer layer formed thereon in an intermediary stage of a wafer-level packaging according to a preferred embodiment of the present invention;

FIG. 2

is a cross-sectional view schematically illustrating a wafer after solder material is filled in a patterned stress buffer layer, in an intermediary stage of a wafer-level packaging according to a preferred embodiment of the present invention; and

FIG. 3

is a cross-sectional view schematically illustrating a structure of the wafer after a wafer-level packaging has been achieved according to a preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description of the embodiments and examples of the present invention with reference to the accompanying drawings is only illustrative and not limiting.

Referring now to FIG.

1

through

FIG. 3

, various cross-sectional views schematically illustrate various stages in a wafer-level packaging according to a preferred embodiment of the present invention.

With reference to

FIG. 1

, a wafer

100

is provided with a plurality of bonding pads

102

thereon. A passivation layer

104

is formed on the surface of the wafer

100

and exposes the bonding pads

102

. An under bump metal (UBM)

106

is respectively formed on the exposed bonding pads

102

. Then, a stress buffer layer

108

is formed over the wafer

100

. The stress buffer layer

108

is made of a material that advantageously can share stress and be patterned.

Next referring to

FIG. 2

, a plurality of first openings

110

and a plurality of cutting paths

111

are formed in the stress buffer layer

108

. The first openings

110

are formed to respectively expose the under bump metals (UBM)

106

. The cutting paths

111

serves as mark zones after packaging, such that a subsequent dicing can be effectively performed without misalignment problems. The cutting paths

111

also can advantageously prevent the wafer

100

from warping when the wafer is heated during an encapsulating process.

Then, a stencil or patterned photoresist

114

having a plurality of second openings

116

therein, is formed on the stress buffer layer

108

in such a manner that the second openings

116

respectively expose the first openings

110

. Then, a solder material

112

is filled in the first and second openings

110

and

116

. The solder material can be filled by, for example, screen printing.

Next referring to

FIG. 3

, a reflow of the solder material then is performed. If a stencil

114

has been used to fill the solder material during screen printing, the stencil then should be removed before reflowing. If a patterned photoresist

114

has been used, then the reflow of the solder material is first performed, and then the patterned photoresist is removed.

Another possible example of the present embodiment is to fill the solder material in two steps. The solder material is first filled in the first openings

110

after the first openings

110

are defined in the stress buffer layer

108

. After the stencil or patterned photoresist

114

with the second openings

116

is arranged on the stress buffer layer

108

, the solder material is filled a second time in the second openings

116

such as described above.

During reflowing, an action of internal cohesion forces in the solder material turns the solder material into a plurality of round-shaped bumps

118

.

With the above method, the conventional underfill process that is difficult to perform thus can be advantageously substituted with a simple process in which a stress buffer layer is directly patterned to define therein the cutting paths and bumps. The cost of the wafer-level packaging thus is advantageously reduced. The cutting paths that are directly defined by patterning the stress buffer layer can advantageously prevent the wafer from being warped when subjected to subsequent heating during encapsulating. Moreover, the cutting paths conveniently serve as mark zones for subsequent dicing after the packaging of the wafer. Another advantage is that if the pitch of the bumps is reduced, the method of the present invention can effectively overcome the limitations of the conventional underfill process.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention.