Method for magnetically separating integrated circuit devices

Details Method for magnetically separating integrated circuit devices Method for magnetically separating integrated circuit devices

2001-07-12

2003-10-21

Walsh, Donald P. (Department: 3653)

Classifying, separating, and assorting solids

Magnetic

Paramagnetic

C209S636000

Reexamination Certificate

active

06634504

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the sorting and classification of integrated circuit (IC) devices. More specifically, the present invention relates to the use of magnetism to separate and sort IC devices based upon the material content of the IC devices.
2. State of the Art
In the art of manufacturing IC devices (also known as semiconductor devices), inspection for quality is routine and often rigorous. Inspection of IC devices may include various techniques known in the art such as subjecting the devices to emission microscopy or X-ray analysis, connecting the IC devices to test circuits cycling the devices at temperature extremes and excessive power inputs and other methods well-known in the art. Such tests are employed to verify an IC device's functionality as well as its structural integrity. The process of inspecting IC devices is integral to any company's goal of efficiently producing devices that are stable, reliable and of sufficient longevity. Such tests are typically tailored to verify that a particular type of IC device will function properly in its intended capacity. In other words, testing standards are set for a specific IC device design, or lot of such devices, depending on an expectation of ultimate use. For example, memory chips designed for use in a typical home (personal) computer are inspected and tested to confirm operability and reliability for that particular purpose. IC devices of a different nature are tested to a different standard.
While the electronics industry has made great strides in producing high quality IC devices, defects are not uncommon. Because IC devices are produced in extremely high volumes, even the smallest defect occurrence rate will result in numerous IC devices being determined to be unsuitable for their intended use. As a result, IC devices are rejected and normally discarded. However, while an IC device may have been discarded based on a certain set of quality standards, the IC device may still have operational characteristics suitable for use in another application.
Discarded IC devices may be salvaged and retested using a second set of quality standards. The retesting is performed to determine suitability for a use independent of that for which the IC device was originally produced. Often, an IC device which fails a quality test for a specific use in terms of, for example, memory capacity or operation speed will satisfy the quality standards set forth for another defined use. For example, an IC device designed for use in a personal computer may fail to meet the quality standards set for such a use while still meeting the standards required for use in a household appliance. Thus, the IC device is not entirely unusable. Rather, it is simply redesignated as to the end use of the device. Redesignation of IC devices based on satisfaction of independent quality standards allows for greater efficiency of production. While the overall number or percentage of IC devices having defects as defined for a specified use is not reduced, the economic loss concerning those defects may be substantially ameliorated upon a proper redesignation or reclassification for a different use.
Prior to any retesting procedures, it may be necessary to properly sort rejected IC devices, as such rejected IC devices may be collected in massive quantities including a number of different types of IC devices with little or no effort made in classifying such devices at the time of testing and rejection. Therefore, a segregating and sorting operation is required. Such an operation is conventionally done by hand, sorting according to predefined criteria. For example, one sort operation may be directed to dividing out devices which are classifiable as “flip chips” from those which are not. Likewise, devices having certain types of lead frames may be separated from other in the lot. Regardless of the base criteria defined for preliminary sorting operations, the sorting is usually done by hand. Sorting by hand requires some training of the individuals performing the sort and tends to be rather inefficient, tedious and time consuming.
In a typical scenario, a fifty-five gallon drum or other large container of rejected IC devices is delivered for sorting and retesting. Perhaps fifty percent, or less, of the devices are of a desired preliminary classification suitable for potential testing and use. One or more individuals will laboriously sift through the entire lot, visually inspect each of the IC devices and determine whether they satisfy a preliminary sort criteria. Sorting by hand is, therefore, a rather time intensive task and is susceptible to human error.
In view of the shortcomings in the state of the art of sorting large quantities of such IC devices, providing an apparatus and method for an automated preliminary sorting of large quantities of IC devices would be advantageous based on a defined device characteristic. Such an apparatus or method should, among other things, be easy to implement, reduce the test time as well as the required amount of human effort, be accurate, and increase the overall efficiency of the retesting process.
BRIEF SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method is provided for sorting a plurality of IC devices, such as memory chips or other packaged semiconductor devices. Based on a preliminary sorting criteria of lead frame metallurgical characteristics, the method includes subjecting the plurality of IC devices to a magnetic field. Ferrous metal containing IC devices, such as those manufactured with a ferrous alloy lead frame, are attracted by the magnetic field, while nonferrous IC devices do not respond to the pressure of the magnetic field. The nonferrous IC devices may thus be isolated for removal and gathered or binned to a first collection category. The remaining IC devices responsive to the magnetic field are ferrous alloy containing IC devices which may then be gathered or binned to a second collection category.
The inventive method may include transporting the IC devices through the magnetic field by means of a conveyor. While various sources are contemplated for providing the magnetic field, the method preferably includes providing a conveyor with an end pulley, or roller, having permanent magnets installed on an interior surface of a stainless steel shell. The magnetic field may advantageously be assisted by gravity in sorting ferrous and nonferrous IC devices. For example, the conveyor may be configured and oriented to carry the IC devices through a magnetic field subjecting the IC devices to be sorted to both a magnetic field as well as a conflicting gravitational field contemporaneously. The nonferrous IC devices thus respond to the gravitational field but not the magnetic field to facilitate collecting them in a common location, while the ferrous IC devices are carried to another collection location.
In accordance with another aspect of the invention, an apparatus for sorting IC devices based on ferrous metal content is provided. The apparatus includes a roller having a stainless steel shell and housing a plurality of permanent magnets. A circuitous belt partially circumscribes the roller and is adapted to convey a plurality of IC devices to an area proximate the roller's surface. The belt is preferably formed or coated with an antistatic (ESD) material so as to not damage the IC devices or further impair their operation and performance. The apparatus may include a grounding mechanism to assist in preventing electrostatic discharge between the belt and the devices.
Various additional features may be incorporated into the apparatus such as a feeding mechanism for distributing the IC devices onto the conveyor at a predetermined rate. Other features might include, for example, individual collection bins, guides for maintaining the chips on the conveyor when not in a sorting zone, tensioning and tracking devices for proper operation and maintenance of the belt, secondary conveyors for transporting the so

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