Semiconductor device manufacturing: process – With measuring or testing – Packaging or treatment of packaged semiconductor
Reexamination Certificate
2000-08-22
2001-07-10
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
With measuring or testing
Packaging or treatment of packaged semiconductor
C438S005000, C438S007000, C438S014000, C438S016000, C073S29000R, C073S293000, C073S314000, C073S327000, C073S427000, C148S508000, C148S510000, C033SDIG004, C356S028500
Reexamination Certificate
active
06258612
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 determining the amount of flux applied to a substrate or semiconductor device in the manufacture of a semiconductor 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 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 and 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 application of 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 monitoring flux application. The method comprises applying flux to a substrate and/or a semiconductor device to coat either or both parts with flux, i.e. to form a thin film of the flux on the part. Once the flux has been applied to the part, it is monitored to determine the amount applied, e.g. the thickness of applied flux is determined.
Embodiments of the present invention include applying a rosin flux to a solder alloy on an organic or ceramic substrate and monitoring the thickness of the applied flux by impinging a light on the flux film and detecting the reflected light. The impinging light can be that of a laser, e.g. a He—Ne laser, and the detector can be a photodetector or a photomultiplier tube as, for example, in an interferometer.
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 of solder contacts thereon, e.g. solder bumps; applying a film of flux to the substrate and/or the device; monitoring the thickness of the applied flux; mounting the device on the substrate such that the solder contacts of the device are aligned with the conductive contacts on the substrate to form a substrate/device assembly; and forming an electrical connection between the solder contacts of the device and the conductive contacts on the substrate.
By monitoring the thickness of the applied flux prior to assembling the device and substrate, the present invention advantageously provides an in-situ method for optimally determining the uniformity and amount of flux applied to a particular packaging assembly thereby minimizing waste.
Embodiments of the present invention include mounting the device to the substrate in response to monitoring the thickness of the applied flux above a predetermined thickness value, e.g. monitoring the thickness above 5 mils, or cleaning and re-applying flux to the substrate and/or the device in response to the thickness being below a predetermined value, e.g. below 0.05 mils.
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Halderman Jonathan D.
Master Raj N.
Advanced Micro Devices , Inc.
Niebling John F.
Zarneke David A
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