Manufacturing method for reflowed solder balls and their under bump metallurgy structure

Abstract

Provided is a method of manufacturing a semiconductor package, the method including a first step for forming a primary solder ball on an under bump metallurgy (UBM) structure, and a second step for forming a secondary solder ball on an upper surface of the UBM structure by performing a reflow process on the primary solder ball while a side wall of the UBM structure is exposed.

Claims

1. A semiconductor package comprising: an under bump metallurgy (UBM) structure having a side wall; and a solder ball formed on an upper surface of the UBM structure, wherein an antioxidant layer is disposed on the side wall of the UBM structure, and wherein the antioxidant layer comprises a tin (Sn) component of the solder ball.

2. The semiconductor package of claim 1, wherein a thickness of the UBM structure is greater than a thickness of an intermetallic compound formed at an interface of the solder ball and the UBM structure.

3. The semiconductor package of claim 2, wherein the thickness of the UBM structure is 20 μm to 50 μm.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1, 3, 4, 5, and 6 are cross-sectional views for sequentially describing the steps of a method of manufacturing a semiconductor package, according to an embodiment of the present invention.

(2) FIG. 2 is a cross-sectional view of describing one of the steps of a method of manufacturing a semiconductor package, according to a comparative example of the present invention.

(3) FIG. 7 is a graph showing a temperature profile of a reflow process used in the method of manufacturing a semiconductor package, according to an embodiment of the present invention.

MODE OF THE INVENTION

(4) Hereinafter, the present invention will be described in detail by explaining embodiments of the invention with reference to the attached drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to one of ordinary skill in the art. In the drawings, the sizes of elements may be exaggerated or reduced for convenience of explanation.

(5) FIGS. 1, 3, 4, 5, and 6 are cross-sectional views for sequentially describing the steps of a method of manufacturing a semiconductor package, according to an embodiment of the present invention, and FIG. 7 is a graph showing a temperature profile of a reflow process used in the method of manufacturing a semiconductor package, according to an embodiment of the present invention.

(6) Referring to FIG. 1, a semiconductor chip or device including a conductive electrode pad 20 on a substrate 10 is initially prepared. The substrate 10 may include, for example, a wafer containing silicon (Si) or a substrate containing polymer and ceramic including glass. The conductive electrode pad 20 may be formed by coating and patterning metal on the substrate 10. In this case, the metal may include aluminum (Al) or tungsten (W). The conductive electrode pad 20 may be electrically connected to a rewiring pattern 50 formed to efficiently establish an electrical connection with an external circuit to be coupled onto the semiconductor device. The rewiring pattern 50 may be electrically connected to an under bump metallurgy (UBM) structure 70 formed on the rewiring pattern 50. To prevent unnecessary electrical shorts and physical or chemical damages due to an external factor, a first passivation pattern 40 and a second passivation pattern 60 may be formed between the conductive electrode pad 20 and the rewiring pattern 50 and between the rewiring pattern 50 and the UBM structure 70.

(7) The UBM structure 70 may serve as a wetting layer for good adhesion of solder thereto in a subsequent process, and also serve as a diffusion barrier to prevent permeation of a solder component into the semiconductor chip. The UBM structure 70 provided between solder and the semiconductor device needs to have a low electrical resistance.

(8) The UBM structure 70 may have various configurations and may include, for example, a structure in which a copper (Cu) layer, a nickel (Ni) layer, and a gold (Au) layer are sequentially stacked on one another, or a structure in which a Cu layer and a Ni layer are sequentially stacked on one another. As another example, the UBM structure 70 may include a structure configured as a Cu layer. Alternatively, the UBM structure 70 may include a Cr/Cr—Cu/Cu structure, a TiW/Cu structure, or an Al/NiV/Cu structure.

(9) A primary solder ball 80a may be formed on the UBM structure 70. For example, the primary solder ball 80a may be formed on at least an upper surface 70u of the UBM structure 70 and, in this case, at least a part of a side wall 70s of the UBM structure 70 may be exposed. The primary solder ball 80a is an initial element to be implemented as a final solder ball 80 through a subsequent reflow process.

(10) The final solder ball 80 may be understood as a sort of a bump. The bump may serve to increase an electrode height to facilitate implementation of a flip chip and also serve to replace an electrode material with a material easily connectable to an external electrode. In terms of a bump shape, a solder bump may be formed in, for example, a ball shape due to a surface tension effect after a reflow process. A material of the primary solder ball 80a may include CuSn or include AuSn, PbSn, PbSn.sub.5, AgSn, or the like. The primary solder ball 80a may be formed by mounting a solder ball by using a nozzle, or be formed using an electroplating method, a screen printing method, a Super-Juffit method, or the like.

(11) Referring to FIGS. 3 and 4, a reflow process is performed on the primary solder ball 80a while the side wall 70s of the UBM structure 70 is exposed. In this case, the primary solder ball 80a is melted or softened to entirely cover the side wall 70s of the UBM structure 70. As a temperature of the reflow process increases, a solder ball 80b having a concave part gradually changes into a hemispherical solder ball 80c due to the UBM structure 70.

(12) Referring to FIG. 5, as the temperature of the reflow process decreases, a molten solder ball 80d is cooled and contracted. Particularly, a part of the solder ball 80d adjacent to the side wall 70s of the UBM structure 70 may have a very small thickness.

(13) Referring to FIG. 6, the molten solder ball 80d is continuously cooled and contracted to form a secondary solder ball 80 on the upper surface 70u of the UBM structure 70. In this case, a tin (Sn) component of the secondary solder ball 80 may be coated on the side wall 70s of the UBM structure 70 to prevent oxidation of the UBM structure 70. Ultimately, an antioxidant layer may be formed on the side wall 70s of the UBM structure 70 and the secondary solder ball 80 may be formed on the upper surface 70u of the UBM structure 70.

(14) More specifically, the antioxidant layer may be formed the side wall 70s of the UBM structure 70 and the secondary solder ball 80 may be formed not on the side wall 70s of the UBM structure 70 but on only the upper surface 70u of the UBM structure 70.

(15) Herein, the antioxidant layer serves to at least reduce or prevent oxidation of the side wall 70s of the UBM structure 70. When energy-dispersive x-ray (EDX) composition analysis is performed on the conductive electrode pad 20 having the above-described configuration, a layer containing Sn is observed on the side wall 70s of the UBM structure 70.

(16) A comparative example of the present invention to be compared to the configuration of FIG. 1 is illustrated in FIG. 2.

(17) Referring to FIG. 2, before a reflow process is performed on the primary solder ball 80a, an additional passivation pattern 75 is formed not to expose the side wall 70s of the UBM structure 70. The additional passivation pattern 75 may prevent oxidation of the side wall 70s of the UBM structure 70 in a reflow process. However, since additional deposition and photolithography processes are required to form the passivation pattern 75, manufacturing costs are increased.

(18) FIG. 7 is a graph showing a temperature profile of the reflow process used in the method of manufacturing a semiconductor package, according to an embodiment of the present invention.

(19) Referring to FIG. 7, a temperature (unit: ° C.) profile of the reflow process based on time (unit: sec.) is shown. In the graph, ‘step1’ corresponds to the step of FIG. 1, ‘step2’ corresponds to the step of FIG. 3, ‘step3’ corresponds to the step of FIG. 4, and ‘step5’ corresponds to the step of FIG. 5. In the method of manufacturing a semiconductor package, according to an embodiment of the present invention, the primary solder ball 80a may be formed to expose the side wall 70s of the UBM structure 70 in ‘step1’ before the temperature is increased for the reflow process. As such, oxidation of the UBM structure 70 may be effectively prevented without forming the additional passivation pattern 75 as illustrated in FIG. 2.

(20) The above-described configuration may be easily implemented when the UBM structure 70 has a thickness equal to or greater than a certain thickness. The thickness of the UBM structure 70 may be greater than a thickness (e.g., about 8 μm) of an intermetallic compound formed at an interface of the UBM structure 70 and the solder ball. In this case, the thickness of the UBM structure 70 may be 20 μm to 50 μm. For example, when the thickness of the UBM structure 70 is 30 μm, the antioxidant layer may be effectively formed.

(21) While the present invention has been particularly shown and described with reference to embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention as defined by the following claims.