Adhesive connections and joints between one or more structures are used in many areas of manufacturing, including semiconductor manufacturing. In semiconductor manufacturing, adhesive connections may be used to connect a semiconductor chip to a chip carrier, or a chip contact pad to a printed circuit board or lead frame. Adhesive connections are furthermore used in flip-chip wafer level packages for adhering a side of a chip, e.g. a chip back-side to a wafer, a printed circuit board, or a lead frame.
Many factors affect the reliability of adhesive connections between two surfaces. The quality of an adhesive connection in semiconductor manufacturing may be affected by the quality of films, e.g. metal thin films, which may be formed over the surfaces of the chip, or which may form part of the electrical circuitry of a chip. The quality of an adhesive connection may be affected by the quality of the adhesive paste, glue or solder used to connect the chip to a chip carrier.
The issue of quality regarding the deposition of metal films over semiconductor wafers affects a standard and industry-wide process in semiconductor manufacturing for producing metal tracks, metal protective layers, boundary layers, intermediate layers, bond layers, solder layers, and electrical contacts. The properties of the layers are dependent on process parameters and process limitations. Some of the factors which may be used to determine the quality of layers produced, and which are considered in the production of layers in the semiconductor industry may include the thickness of the layers. As thicker layers result in higher costs, layers may be made too thin to produce a good quality layer. Layers, especially very thin layers, may be subject to high internal mechanical stress. High mechanical stress in the layers may further be caused by the mechanical properties of adjacent layers, e.g. adjacent silicon, oxide or nitride layers placing unsuitable amounts of stress on the layers. Layers may be brittle, and some layers may cause wafer bending due to the bi-metallic effect. Current techniques for avoiding some of the problems associated with metal film deposition include making changes to the design of the layers, e.g. through the introduction of meandering structures, variation of the critical layer thickness, or conductive track width. A common technique is to introduce additional layers to compensate for mismatches in the original layers.
Adhesive materials in an adhesive connection between a chip and a chip carrier have up till now, been an adhesive paste or adhesive foil. Depending on whether a conductive or isolating adhesive connection is required, an adhesive material with different conductive or isolation properties may be used to connect or glue a component, e.g. a semiconductor chip, to a carrier.
The adhesives foils and pastes used today are, however, insufficiently reliable against stress, e.g. mechanical stress and thermal stress. Another problem is coming-up with moisture. Processing problems may also exist due to the adhesive pastes running or spreading onto the chip surfaces, causing problems for electronics. Many adhesive foils and pastes do not meet the necessary requirements for being sufficiently electrically or thermally conductive.