Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
2000-07-28
2003-07-22
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
C356S630000, C438S005000, C438S007000, C438S016000, C228S180220
Reexamination Certificate
active
06597444
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to semiconductor packaging technology and the manufacture of package assemblies. The present invention has particular applicability to methods of inspecting flux that has been applied to a substrate during assembly of a device package.
BACKGROUND
Integrated circuit devices are typically electronically packaged by mounting one or more integrated circuit (IC) chips or dies to a substrate, sometimes referred to as a carrier. In a flip chip assembly or package, the die is “bumped” with solder to form a plurality of discrete solder balls over metal contacts on the surface of the die. The chip is then turned upside down or “flipped” so that the device side or face of the IC die can be mounted to a substrate having a corresponding array of metal contacts. Typically, the metal contacts of the substrate are coated or formed with a solder alloy. Electrical interconnection of the die to the substrate is conventionally performed by aligning the die to the substrate and reflowing the solder on the die and/or the substrate to electrically and mechanically join the parts. Directly coupling the die immediately below the substrate allows for an increased number of interconnections and improves voltage noise margins and signal speed.
Typically, a flux composition is applied to either the die or the substrate to facilitate the formation of the interconnect. Flux acts as an adhesive to hold the placed components in place pending soldering and further acts to minimize metallic oxidation that occurs at soldering temperatures thereby improving the electrical and mechanical interconnection and reliability between the soldered component and substrate. Soldering fluxes fall into three broad categories: rosin fluxes, water-soluble fluxes, and no-clean fluxes. Rosin fluxes, which have a relatively long history of use, are still widely used in the electronics industry. Water-soluble fluxes, which are a more recent development and which are increasingly used in consumer electronics, are highly corrosive materials. No-clean fluxes, a very recent development, reportedly do not require removal from the circuit assemblies. The most common flux for IC die attach packaging comprises a suspension liquid of various acids suspended in an alcohol base.
It has been observed that controlling the amount of applied flux is important irrespective of the type of flux employed in a particular packaging process, since enough flux must be used to effect a reliable metallurgical bond to electrically and mechanically interconnect the component to the substrate. Too much applied flux, however, can undesirably cause displacement of the placed component due to flux boiling. Excess flux further adversely impacts other circuit board manufacturing processes. For example, traces of the soldering flux residues which remain after solder reflow can lead to circuit failure, delamination of underfill, etc.
Accordingly, a continual need exists for improved processes and/or assemblies for the packaging of electronic components on to substrates employing solder fluxes.
SUMMARY OF THE INVENTION
An advantage of the present invention is a high yield, high through-put process for inspecting the coverage and/or uniformity of applied flux during assembly of a device package.
Additional advantages and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a method of inspecting the application of flux on a substrate. The method comprises applying flux to the substrate over a preselected area, e.g. over an array of conductive contacts suitable for mounting a device to form a flux zone having an area. In an embodiment of the present invention, the flux is applied to cover approximately the same area occupied by an array of conductive contacts, e.g. an array of landing pads, on the substrate.
In practicing the invention, the flux zone area is inspected by optical or electro-optical spectroscopy. Embodiment of the present invention include applying a rosin flux to a chip area on a laminate substrate and inspecting the coverage and/or uniformity of the applied flux by fluorescence and/or infrared spectroscopy.
Another aspect of the present invention is a method of manufacturing an interconnected device assembly. The method comprises: providing a substrate having conductive contacts thereon for mounting a device, providing a device having a plurality, e.g. an array, of solder contacts thereon; applying a flux to the substrate to form a flux zone on the substrate; inspecting the flux zone area by optical or electro-optical spectroscopy; contacting the device and substrate such that the solder contacts of the device are aligned with the conductive contacts on the substrate to form a substrate/assembly; and forming an electrical connection between the solder contacts of the device and the conductive contacts on the substrate. The amount of flux that will be satisfactory depends on several factors, often requiring empirical determinations.
By monitoring the coverage of the applied flux prior to assembling the semiconductor device and substrate, the present invention advantageously provides an essentially instant and continuous method for determining adequate coverage and/or uniformity of the applied flux during the packaging process. In an embodiment of the present invention, the flux covering an area defined by the perimeter of the array of conductive contacts on the substrate is from about 50% to about 150%, e.g. approximately 100% of the area defined by the perimeter of the array of conductive contacts on the substrate.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.
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Brownfield Terri J.
Halderman Jonathan D.
Advanced Micro Devices , Inc.
Pham Hoa Q.
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