Patent Application
20070267745
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the features, advantages, and principles of the invention.
In the drawings:
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same or similar reference numbers will be used throughout the drawings to refer to the same or like parts.
Embodiments consistent with the present invention provide for a method of manufacturing a semiconductor device, including a solder bump with an over-bump passivation layer for protecting the bump from oxidation before bonding of the semiconductor device to the substrate, and for preventing the solder cold joint phenomenon.
To solve problems associated with the approaches in the related art discussed above and consistent with an aspect of the present invention, a semiconductor device and its method of manufacture will next be described.
An electrically conductive bump material 220, such as a solder material including Pb (or any other suitable bumping material) may be deposited over the UBM 215 by conventional means. Preferably, the electrically conductive bump material 220 is solder in any suitable composition including, for example, a known composition of 3-5 weight % (w/o) Sn and 97-95 weight % (w/o) Pb. The electrically conductive bump material 220 may be deposited, for example, by any of a variety of methods including electroplating, screen or stencil printing, evaporation, jet printing thermomechanical/pressure through nozzle, by means of electromechnical/piezoelectric device, magneto-fluidynamic or electromagneto-fluidynamic devices, micro-punching or any other known method.
As with conventional bump forming methods, the electrically conductive bump material 220 may be oxidized if left exposed to air. In the case of a solder bump for the electrically conductive bump material 220, for example, lead oxide (PbO2) may form upon exposure to air for even short periods of time. The presence of an oxide on the electrically conductive bump material 220 can lead to the undesirable solder cold joint phenomenon discussed previously.
In order to eliminate solder cold joints and repeated oxide formation on the electrically conductive bump material 220, the inventors have devised an improved solder bump by providing an over-bump passivation layer 230 for protecting the electrically conductive bump material 220 from oxidation before subsequent device processing steps, such as flip-chip bonding. The over-bump passivation layer 230 is formed by selectively covering the electrically conductive bump material 220 with an inert and dissolvable metal, such as gold (Au), or an organic material, such as an organic solderability preservative (OSP). Gold easily diffuses into solder bumps, such as the electrically conductive bump material 220, when the bump material 220 is melted for bonding. An OSP readily evaporates upon melting the solder bumps in subsequent processing steps. In either case, the over-bump passivation layer 230, formed by gold or OSP, will not adversely affect later solderability of the bump material 220. Alternatively, deposition of a separate layer of tin as the over-bump passivation layer over bump material 220 is contemplated, since an oxide of tin formed on the surface of the bump material 220 may act as a protective layer, impeding further oxidation into the bulk of bump material 220 once surface passivation occurs.
If an inert metal is used as the over-bump passivation layer 230, it is selectively coated only on the bump material 220 because the conductivity of the inert metal could otherwise adversely affect device operation if deposited on areas other than on the bump material 220. In
Alternatively, as noted above, the layer 230 can be provided as an organic material, such as OSP (a liquid, insulating, material), which can be spun or sprayed on the semiconductor device 100, or the semiconductor device 100 may be dipped in a solution of OSP. The semiconductor device 100 is then baked so that the solvent in the OSP is driven out, leaving behind an OSP-based over-bump passivation layer.
Thus, embodiments consistent with the present invention provide a solder bump with an over-bump passivation layer for protecting the bump from oxidation before bonding of the IC chip to the substrate, and for preventing the solder cold joint phenomenon. Embodiments consistent with the invention may also permit prolonged shelf-life of semiconductor devices with bumps, independent of the storage environment used. Further, embodiments consistent with the present invention which utilize gold or OSP as the over-bump passivation layer, may eliminate the need to apply solder flux normally during the flip chip assembly process, an otherwise essential step, since oxidation has already been prevented by the gold or OSP passivation. OSP also acts as a flux when melting of solder takes place upon bonding.
It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed structures and methods without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
