Patent Application
20130034956
The disclosed subject matter generally relates to packaging technologies.
In some integrated circuit (IC) devices that employ wafer level chip scale packaging (WLCSP), liquid molding compound is applied to the WLCSP solder bump side of the IC devices and cured to improve the reliability of the solder bumps in the field. The cured molding compound surrounding the WLCSP solder bumps provide similar role as underfill, which are generally applied after the IC devices are diced and mounted onto a next level substrate, and eliminated the need for underfill in many device packages. After the liquid molding compound is cured, some amount of extraneous cured molding compound are present on the surface of the solder bumps. However, because the solder bumps are subsequently mounted to a next level substrate, any extraneous cured molding compound that are present on the surface of the WLCSP solder bumps are cleaned using wet chemical cleaning process or plasma cleaning process. The wet chemical cleaning processes tend to be costly and they often leave behind some residual cured molding compound which results in solder hump wettability defects when the IC devices are diced and subsequently mounted onto a substrate.
This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description, In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.
A method of forming solder bumps according to an implementation of the present disclosure will be described with references to
On the substrate 10 are wiring layers 20 that provides an array of a plurality of under hump metallurgy (UBM) pads 30 (one example shown) for forming solder bumps 40 thereon. In one embodiment, the wiring layers 20 include a passivation layer 23, a polymer layer 25 and redistribution metal wiring feature(s) 26 that connect certain bond pads 22 on the substrate 10 to the UBM pads 30.
The UBM pads 30 have a metal composition suitable for desired wetting of a solder bump 40 thereon. In many devices, the UBM pads 30 are formed of a thin film of Ni. In some embodiments, the UBM pad 30 includes a diffusion barrier layer and/or a seed layer. The diffusion barrier layer may be formed of tantalum nitride, although it may also be formed of other materials such as titanium nitride, tantalum, titanium, or the like. The seed layer may be a copper seed layer formed on the diffusion barrier layer. The seed layer may be formed of copper alloys that include silver, chromium, nickel, tin, gold, and combinations thereof.
In one embodiment, the passivation layer 23 is formed of a non-organic material selected from un-doped silicate glass (USG), silicon nitride, silicon oxynitride, silicon oxide, and combinations thereof. In another embodiment, the passivation layer 23 is formed of a polymer layer, such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like. The redistribution metal wiring feature(s) 26 may be formed of a conductive material including, but not limited to, for example copper, aluminum, copper alloy, nickel, or other mobile conductive materials. The polymer layer 25 may be formed of an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like, although other relatively soft, often organic, dielectric materials can also be used.
In
Referring to the flow chart 100 in
In one implementation, the UV laser having a wavelength in the range of 100 nm-400 and energy level in the range of 300-1500 mJ/cm2 is used. The beam size of the UV laser is in the range of 1 mm×1 mm-50 mm×50 mm, According to another implementation of the present disclosure, the cleaning step is conducted with a UV laser whose energy level is in the range of 400-1400 mJ/cm2.
Although the subject matter has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments, which may be made by those skilled in the art.
