Solder bump structure and method for forming a solder bump
A solder bump structure includes a contact pad, an intermediate layer located over the contact pad, a solder bump located over the intermediate layer, and at least one metal projection extending upwardly from a surface of the intermediate layer and embedded within the solder bump. Any crack in the solder bump will tend to propagate horizontally through the bump material, and in this case, the metal projections act as obstacles to crack propagation. These obstacles have the effect of increasing the crack resistance, and further lengthen the propagation path of any crack as it travels through the solder bump material, thus decreasing the likelihood device failure.
1. Field of the Invention
The present invention generally relates to integrated circuit (IC) chips and devices, and more particularly, the present invention relates to solder bump structures of IC chips and devices, and to methods of forming solder bump structures.
2. Description of the Related Art
As integrated circuits (IC's) advance toward higher speeds and larger pin counts, first-level interconnection techniques employing wire bonding technologies have approached or even reached their limits. New improved technologies for achieving fine-pitch wire bonding structures cannot keep pace with the demand resulting from increased IC chip processing speeds and higher IC chip pin counts. As such, the current trend is to replace wire bonding structures with other package structures, such as a flip chip packages and a wafer level packages (WLP).
Flip chip packages and WLP structures are partially characterized by the provision of solder bumps which connect to interconnection terminals of the IC chip. (Herein, unless otherwise specified, the term solder “bumps” is intended to encompass solder “balls” as well.) Device reliability is thus largely dependent on the structure and material of each solder bump and its effectiveness as an electrical interconnect.
A conventional solder bump structure will be described with reference to
In
The UBM layers 6 and 7 functions to reliably secure the bump 5 to the chip pad 2, and to prevent moisture absorption into chip pad 2 and IC chip 1. Typically, the first UBM layer 6 functions as an adhesion layer and is deposited by sputtering of Cr, Ti, or TiW. Also typically, the second UBM layer 7 functions as a wetting layer and is deposited by sputtering of Cu, Ni, NiV. Optionally, a third oxidation layer of Au may be deposited as well.
Referring to
Mechanical stresses on the solder bump are a source of structural which can substantially impair device reliability. That is, when the chip heats up during use, both the chip and the PCB expand in size. Conversely, when the chip cools during an idle state, both the chip and the PCB substrate contract in size. The chip and the PCB substrate have mismatched coefficients of thermal expansion, and therefore expand and contract at different rates, thus placing mechanical stress on the intervening solder bump.
According to a first aspect of the present invention, a method for manufacturing a solder bump is provided, which includes forming at least one metal protrusion extending upwardly over a contact pad, and embedding the at least one metal protrusion in a solder material.
According to another aspect of the present invention, a method for manufacturing a solder bump is provided, which includes depositing an intermediate layer over a contact pad, forming a photoresist over a surface of the intermediate layer, patterning the photoresist to define at least one opening which partially exposes the surface of the intermediate layer, filling the at least one opening of the photoresist with a metal, removing the photoresist to expose the metal, wherein the metal forms at least one metal protrusion extending upwardly from the surface of the intermediate layer, and embedding the at least one metal protrusion in a solder material formed over the intermediate layer.
According to yet another aspect of the present invention, a method for manufacturing a solder bump is provided, with includes depositing an intermediate layer over a contact pad, forming a photoresist over a surface of the intermediate layer, patterning the photoresist to define at least one opening which partially exposes the surface of the intermediate layer, filling the at least one opening of the photoresist with a metal to a first depth, filling the at least one opening of the photoresist with a solder material to a second depth such that the solder material is stacked on the metal within each of the at least one opening, removing the photoresist to expose the metal and the first solder material, wherein the metal and first solder material form at least one protrusion extending upwardly from the surface of the intermediate layer, and reflowing the solder material to form a solder bump having the metal embedded therein.
According to still another aspect of the present invention, a method for manufacturing a solder bump is provided, which includes depositing an intermediate layer over a contact pad, forming a photoresist over a surface of the intermediate layer, patterning the photoresist to expose a solder bump region over the surface of the intermediate layer, growing at least one metal dendrite having a plurality of branches which project upwardly in the solder bump region from the surface of the intermediate layer, filling the solder bump region with a solder material so as to embed the at least one metal dendrite within the solder material, and removing the photoresist.
According to another aspect of the present invention, a solder bump structure is provided, which includes a contact pad, an intermediate layer located over the contact pad, a solder bump located over the intermediate layer, and at least one metal projection extending upwardly from a surface of the intermediate layer and embedded within the solder bump.
BRIEF DESCRIPTION OF THE DRAWINGSThe aspect and advantages of the present invention will become readily apparent from the detailed description that follows, with reference to the accompanying drawings, in which:
FIGS. 5(a) through 5(i) are cross-sectional views for use in describing a process for manufacturing a solder bump structure according to a preferred embodiment of the present invention;
FIGS. 6(a) through 6(g) are cross-sectional views for use in describing a process for manufacturing a solder bump structure according to another embodiment of the present invention;
FIGS. 8(a) and 8(b) are cross-sectional views of solder bump structure having dendrite configuration embedded therein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSThe present invention is at least partially characterized by the inclusion of one or more metal projections within the solder bump material to form an obstacle which impedes the propagation of a crack within the solder bump material. While the metal projections can take any number of forms, the invention will be described below with reference to several preferred embodiments.
The solder bump 405 is located over the intermediate layer 407. An example of the solder bump dimensions is 100×100 μm, and examples of a material constituting the solder bump include Sn, Pb, Ni, Au, Ag, Cu, Bi and alloys thereof. In addition, at least one metal projection 411 extends upwardly from a surface of the intermediate layer 407 and is embedded within the solder bump 405. In this embodiment, as shown in FIGS. 4(a) and 4(b), a plurality of metal projections 411 extend upwardly from the surface of the intermediate layer 407 and are embedded within the solder bump 405. Preferably, because of reflow of the solder material during fabrication, a melting point of a material of the solder bump 405 is less than a melting point of the metal projections 411. An example of the width of each projection 411 is about 5 to 70 μm, and examples of the material constituting the metal projections 411 include Ni, Cu, Pd, Pt and alloys thereof.
As best shown in
Many other patterns of metal projections 411, both regular and irregular, may be adopted, such as off-set parallel rows of projections or concentric sets of patterns. In addition, the individual projections 411 may have cross-sections which differ from the generally square cross-sections of
A method for manufacturing a solder bump structure according to an embodiment of the invention will now be described with reference to FIGS. 5(a) through 5(i). At
Next, at
Then, at
Next, as shown in
Then, at
A method for manufacturing a solder bump structure according to another embodiment of the invention will now be described with reference to FIGS. 6(a) through 6(g). At
Next, at
Then, at
Next, at
Then, at
Another embodiment of the present invention will now be described with reference to FIGS. 7(a), 7(b), 8(a) and 8(b). This embodiment is characterized by metal projections which are formed of dendrite structures instead of the columnar structures of the previous embodiments. In particular, after deposition of the intermediate (UBM) layers, a photoresist is patterned having an opening which exposes a bump region of the intermediate layers. Then dendrite crystal structures are grown within the bump region. In this regard, reference is made to U.S. Pat. No. 5,185,073, entitled “Method Of Fabricating Nendritic Materials”, which is incorporated herein by reference, and which describes techniques which may be used to form a dendrite structure within the bump region according to the present invention. Examples of materials of the dendrite structure of the present embodiment include Ni, Cu, Pd, Pt and alloys thereof.
After formation of the dendrite structure, the bump region is filled with a solder material so as to embed the dendrite structure within the solder material. Then, the photoresist is removed, the intermediate (UBM) layers are etched outside the bump region, and the solder material is reflowed to obtain the structure illustrated in
Any crack in the solder bump 705 will tend to propagate horizontally through the bump material, and in this case, the metal dendrite projections 711 act as obstacles to crack propagation. These obstacles have the effect of increasing the crack resistance, and further lengthen the propagation path of any crack as it travels through the solder bump material, thus decreasing the likelihood device failure.
In the drawings and specification, there have been disclosed typical preferred embodiments of this invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the present invention being set forth in the following claims.
Claims
1-29. (canceled)
30. A solder bump structure, comprising:
- a contact pad;
- an intermediate layer located over the contact pad;
- a solder bump located over the intermediate layer; and
- at least one metal protrusion extending upwardly from a surface of the intermediate layer and embedded within the solder bump.
31. The solder bump structure of claim 30, comprising a plurality of metal protrusions extending upwardly from the surface of the intermediate layer and embedded within the solder bump.
32. The solder bump structure of claim 31, wherein a cross-section of the plurality of protrusions define a mesh pattern in a plane parallel to the contact pad.
33. The solder bump structure of claim 31, wherein the plurality of metal protrusions are dendrites grown on the surface of the intermediate layer.
34. The solder bump structure as claimed in claim 31, wherein a material of the metal is selected from the group consisting of Ni, Cu, Pd, Pt or alloys thereof.
35. The solder bump structure as claimed in claim 31, wherein a material of the solder bump is selected from the group consisting of Sn, Pb, Ni, Au, Ag, Cu, Bi or alloys thereof.
36. The solder bump structure as claimed in claim 31, wherein a melting point of a material of the solder bump is less than a melting point of the metal.
37. The solder bump structure as claimed in claim 31, wherein the contact pad is located on a semiconductor chip contained a flip chip package or a wafer level package.
Type: Application
Filed: Jun 3, 2005
Publication Date: Sep 22, 2005
Inventors: Se-Yong Oh (Hwasung-City), Nam-Seog Kim (Cheonan-City)
Application Number: 11/143,983