Method for building interconnect structures by injection molded solder and structures built

#The present invention generally relates to a method for building interconnect structures by injection molded solder and more particularly, relates to a method for building interconnect structures by injection molded solder wherein the solder is first injected into mold cavities contained in a mold, cooled and then transferred to a semi-conducting substrate by reflowing the solder and interconnect structures built by such method.

#In present semiconductor fabrication processes, semiconductor chips are frequently attached to other chips or other electronic structures. The attachment of a semiconductor chip is frequently accomplished by one of two techniques. The first technique is a wire bonding process in which each of a series of I/O bump terminals on a chip built on an aluminum bonding pad is sequentially bonded to the connecting pads on a substrate. The second technique is a flip chip attachment method in which all the I/O bumps on a semiconductor chip are first terminated with a solder material. A frequently used solder material is a lead/tin high melting temperature alloy. The semiconductor chip is then flipped over and the solder bumps are aligned and reflowed in a reflow furnace to effect all the I/O connections with the bonding pads on the substrate. One advantage achieved by the flip chip process is its applicability to very high density CMOS circuits and its high reliability in the interconnects formed when compared to the wire bonding process.

#In the more recently developed interconnect technology of C4 (controlled collapse chip connection) which is a method of using a lead-rich lead/tin alloy to mount chips directly to high temperature ceramic substrates, C4 flip chip structures can be built directly over exposed aluminum vias located at the top surface of a wafer. The flip chip structure consists of a ball limiting metallurgy (BLM) and a solder ball/bump. The BLM used is a multi-layer structure such as Cr-Cu-Au which provides a conductive path between solder and the aluminum wiring exposed through vias in the wafer. The BLM structure also seals the vias and thus provides a restricted solderable area such that the wafer surface outside the BLM regions is protected by either a glass or a polymer film to limit the lateral flow of solder during subsequent reflow process. A column structure during chip interconnect can thus be assured.

#These and other objects, features and advantages of the present invention will become apparent from the following detailed description and the appended drawings in which:

#FIG. 1 is an enlarged, partial cross-sectional view of a conventional electronic device that has a BLM structure and an evaporated solder ball formed on top.

#FIG. 2 is a flow chart illustrating the present invention parallel processing of a BLM structure and IMS formation.

#The present invention provides a method for building interconnect structures on a semiconductor wafer by first utilizing a substantially transparent mold for molding injection molded solder bumps of a predetermined shape and then transferring the solder bumps onto a wafer surface. The method presents several major benefits such as it allows the inspection of the quality of solder bumps molded prior to transferring; it allows an easy alignment process between the mold cavities and the BLM structures on the wafer surface to be carried out; and it allows a mold having a coefficient of thermal expansion substantially similar to that of the semi-conducting wafer to be used such that solder bumps can be accurately placed on the wafer surface.

#The present invention method provides novel enhancements to the injection molded solder technology and novel mold construction developments which when combined together provides a technique for transferring a molten solder bump onto a BLM for the fabrication of solder interconnect structures.

#The BLM structure used as a component of the present invention method can be a present state of the art BLM technology of tri-layers of chromium/copper/gold or similar composite layers produced by mask processes, or a BLM structure produced by photoprocesses and electroplating technique, or an aluminum/electroless nickel-gold BLM which can be applied by a self-registered, mask-less process. The aluminum/electroless nickel-gold BLM process is a more preferred method for the present invention.