Flip-chip package and fabricating process thereof

A flip-chip package is described. The flip-chip package includes a chip, a substrate, supporters and electrically conductive adhesive bumps. The electrically conductive adhesive bumps are located between the chip and the substrate electrically connecting the bonding pads on the former and the bump pads on the latter, wherein each electrically conductive adhesive bump has a smaller diameter at the central portion thereof than at the end portions thereof. The supporters are also disposed between the chip and the substrate surrounding the active area of the chip, so that the chip can be supported on the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 92104000, filed on Feb. 26, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flip-chip package and a process for fabricating the same. More particularly, the present invention relates to a flip-chip package with electrically conductive adhesive bumps disposed between a chip and a substrate, and to a process for fabricating the same.

2. Description of the Related Art

Flip-chip (FC) interconnect technology has been widely used in the package industry because it facilitates reduction of package area, shortening of signal transmission paths, and fabrication of package structures having high pin counts. In a FC packaging process, a chip is provided with bonding pads disposed on the active surface thereof and arranged in an area array, and bumps are disposed on the bonding pads. Then, the chip is flipped and situated over a carrier, and the bonding pads on the chip and the bump pads on the carrier are electrically and mechanically connected via the bumps. Consequently, the chip is electrically connected to the carrier via the bumps, and further to outer electronic devices via the inner circuits of the carrier. Among all types of package structures utilizing the FC technology, the flip-chip ball grid array (FC/BGA) package and the flip-chip pin grid array (FC/PGA) package are frequently used.

FIG. 1illustrates a cross-sectional view of a conventional flip-chip package. As shown inFIG. 1, the flip-chip package100includes a substrate110, bumps120and a chip130. The substrate110has a top surface112, a bottom surface114opposite to the top surface112, and bump pads116thereon. In addition, the chip130has an active surface132, a back surface134opposite to the active surface132, and bonding pads136thereon. The active surface132of the chip130is the surface formed with the active devices (not shown) of the chip130. The bonding pads136are disposed on the active surface132opposite to the bump pads116serving as a medium for signal input/output, wherein each bump120electrically and mechanically connects a pair of bonding pad136and bump pad116. Thereby, the signals from the chip130can be transmitted to the substrate110via the bumps120, and further to an outer electronic apparatus like a printed circuit board (PCB) or a main board via contacts (not shown) disposed on the bottom surface114of the substrate110.

Ordinary types of bump include solder bump, gold bump, electrically conductive adhesive bump and polymer bump, wherein the solder bump is the most popular one, but is also relatively complicated and expensive in fabrication. Referring toFIG. 1, solder bumps120are conventionally fabricated with the following steps. An under-bump metallurgy (UBM)138composed of multi metal layers is formed on the bonding pads136on the chip130, wherein the metal layers usually include an adhesion layer constituted of Sb, W, Ni, Au, Cu or the alloys thereof, a barrier layer and a wetting layer that are formed with evaporation or sputtering. Thereafter, solder bumps120are formed on the under-bump metallurgy138on the bonding pads136by using a printing method or an electric-plating method, and are melted into spherical bumps in a reflow step and then cooled. The flux (not shown) on the surfaces of the solder bumps120are cleaned, and then the chip130is electrically and mechanically connected to the substrate110via the solder bumps120. However, since the equipment for fabricating solder bumps is quite expensive and the fabricating process is relatively complicated, flip-chip packages cannot be fabricated with low cost in the prior art.

SUMMARY OF THE INVENTION

In view of the forgoing, this invention provides a flip-chip package and a process for fabricating the same to reduce the number of steps and the cost in fabrication of flip-chip packages.

The flip-chip package of this invention includes at least a chip, a substrate, supporters and electrically conductive adhesive bumps. The chip has an active surface with bonding pads disposed thereon, and the substrate has a carrying surface with bump pads disposed thereon opposite to the bonding pads. The supporters are disposed between the chip and the carrying surface, and are distributed at the periphery of the active surface. Each electrically conductive adhesive bump connects a bonding pad and a corresponding bump pad, and has a smaller diameter at the central portion thereof than at the end portions thereof.

The process for fabricating the aforementioned flip-chip package of this invention includes at least the following steps. Some supporters are disposed at the periphery of the active surface, and an uncured electrically conductive adhesive bump is formed on each bump pad. The chip is situated over the carrying surface to contact the latter via the supporters. The chip is pressed toward the substrate to decrease the distance between the active surface and the carrying surface, so as to cause elastic strain in the supporters and increase the contact area between each pair of electrically conductive adhesive bump and bonding pad. Thereafter, the pressure on the chip is removed to release the strain energy in the supporters, so that the height of the supporters relative to the substrate, i.e., the distance between the active surface and the substrate surface, is increased to make the diameter of the central portion of each electrically conductive adhesive bump smaller than those of the end portions of the same. Then, the electrically conductive adhesive bumps are cured.

In a preferred embodiment of this invention, each supporter may be a gold bump that is formed by, for example, bonding a gold wire to the chip, and then pulling the gold wire apart to leave a portion thereof on the chip as a gold bump. In addition, the electrically conductive adhesive bumps are preferably formed on the bump pads with a screen printing method.

Since this invention uses electrically conductive adhesive bumps that are cheaper to fabricate than solder bumps to connect the chip and the substrate, the flip-chip package can be fabricated with a lower cost. Moreover, the fabrication of electrically conductive adhesive bumps is simple and rapid, and the number of steps in the packaging process can be decreased.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2A–2Dillustrate a process flow of fabricating a flip-chip package according to the preferred embodiment of this invention. Referring toFIG. 2A, a chip210having an active surface212with bonding pads214disposed thereon is provided, and supporters230are disposed at the periphery of the active surface212of the chip210. The supporters230may be disposed outside the four corners of the active surface212, and are formed as gold bumps, for example. Each gold bump can be formed by, for example, bonding a gold wire to the chip210with a wire bonding method, and then pulling the gold wire apart to leave a portion thereof on the chip210as a gold bump. During the wire-bonding step, a portion of each softened gold wire can be extruded into a spherical gold bump by using an existing fully-developed wire bonding apparatus, and then the other portion of the gold wire is pulled apart from the gold bump. Since the gold bumps are formed with an existing fully-developed wire bonding technique, the cost for fabricating a flip-chip package can be lowered.

Referring toFIG. 2Aagain, a substrate220having a carrying surface222with bump pads224disposed thereon is also provided, wherein each bump pad224is disposed at a position corresponding to that of a bonding pad214. An uncured electrically conductive adhesive bump240is formed on each bump pad224. The electrically conductive adhesive bumps240are preferably constituted of a polymeric material like polyimide or epoxy resin doped with many electrically conductive particles like silver particles. Each electrically conductive adhesive bump240can be formed on a corresponding bump pad224with a screen printing method.

Referring toFIG. 2B, the chip210is placed over the carrier surface222so that the bonding pads214on the chip210are aligned with the electrically conductive adhesive bumps240on the substrate200. At this moment, the chip210indirectly contacts the carrier surface222via the supporters230. The supporters230support the chip210on the substrate220, and the height “G” thereof is equal to the distance between the chip210and the substrate220.

Referring toFIG. 2C, the chip210is pressed toward the substrate220to decrease the distance between the active surface212and the carrying surface222from “G” to “G1”. Thereby, the supporters230are compressed to store elastic strain energy therein, and contact is made between each pair of electrically conductive adhesive bump240and bonding pad214. Consequently, each electrically conductive adhesive bump240connects a bonding pad214on the chip210and a corresponding bump pad224on the substrate220.

Referring toFIG. 2D, the pressure on the chip210toward the substrate220is removed, so that the strain energy in the supporters230is released. Thereby, the height of the supporters230relative to the substrate surface222, i.e., the distance between the active surface212and the substrate surface222, increases from “G1” to “G2”. At this moment, the diameter “D1” of the central portion of an electrically conductive adhesive bump240gets smaller than the diameters “D2” of the end portions because of the surface tension of the electrically conductive adhesive bump240. Thereafter, the electrically conductive adhesive bumps240may be cured with a heating step to complete to flip-chip package200.

As mentioned above, the flip-chip package disclosed in this invention includes a chip, a substrate, supporters like gold bumps, and some electrically conductive adhesive bumps. The electrically conductive adhesive bumps are disposed between the chip and the substrate electrically connecting the bonding pads on the former and the bump pads on the latter, wherein each electrically conductive adhesive bump has a smaller diameter at the central portion thereof than at the end portions thereof. The supporters are also disposed between the chip and the substrate surrounding the active area of the chip, so that the chip can be supported on the substrate with a distance between them equal to the height of the supporters.

Since this invention utilizes the adhesion effect of the electrically conductive adhesive bumps to connect the bonding pads and the bump pads with the distance between them being controlled by the supporters, the chip can be rapidly and easily mounted on the substrate. Therefore, the number of steps in the flip-chip packaging process can be decreased. Moreover, since the electrically conductive adhesive bumps are fabricated with a screen printing method, they are cheaper than the conventional solder bumps in fabrication. Therefore, flip-chip packages can be fabricated with a lower cost by using the method of this invention.