The features, aspects, and advantages of the present invention will become more fully apparent from the following detailed description, appended claims, and accompanying drawings in which:
In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, one having an ordinary skill in the art will recognize that the invention can be practiced without these specific details. In some instances, well-known structures and processes have not been described in detail to avoid unnecessarily obscuring the present invention.
Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings.
A solder mask layer 104 is formed over substrate 108 and has an opening therein exposing a portion of bump pad 106. The material for forming solder mask layer 104 comprises a solder resistant material that may include ultraviolet type of solder mask and thermoset type of solder mask and the method for forming solder mask layer 104 may include, for example roller coating, curtain coating, screen curtain, dipping, and dry film, as is understood by those skilled in the art.
To allow for better bonding and wetting of a subsequently deposited solder material to the bump pad 106 and increase the bump pad area adhesion strength and stability thereby avoiding the occurrence of solder bump cracks and cavities, one important aspect of the present invention is the addition of a step of depositing a layer 120 of solder wettable material on the exposed surface of the bump pad 106 and the sidewalls and substantially the corners of the solder mask layer 104. Layer 120 is a solder wettable material and may comprise of copper (Cu), nickel (Ni), palladium (Pd), cobalt (Co), platinum (Pt), ruthenium (Ru), tin (Sn), silver (Ag), gold (Au), and combinations thereof. In one embodiment, layer 120 comprises of a Cu/Ni alloy. In another embodiment, layer 120 comprises of a Ni/Au alloy. Deposition techniques such as plating, electroless-plating, and sputtering may be used to deposit layer 120 on substrate 108. It is understood by those of ordinary skill in the art that alternative techniques may be used for applying layer 120. Layer 120 may comprise of a single layer or a multi-layer and in one embodiment, layer 120 has a thickness in the range of about 0.1 μm to about 15 μm. A solder material 102 is then formed over layer 120 and portions of the solder mask layer 104.
The strong, reliable solder bump joint to the solder mask layer 104 achieved with the use of layer 120 of solder wettable material provides flip chip packages with robust, higher densities and more reliable interconnections. An underfill material 115 may subsequently be employed to fill the space between the chip 100 and the substrate 108 to protect solder bump 122 from premature failure due to bump cracks from thermal stresses.
In the preceding detailed description, the present invention is described with reference to specifically exemplary embodiments thereof. It will, however, be evident that various modifications, processes, structures, and changes may be made thereto without departing from the broader spirit and scope of the present invention, as set forth in the claims. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that the present invention is capable of using various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.