Data processing: measuring – calibrating – or testing – Testing system – Of circuit
Reexamination Certificate
1998-03-02
2001-07-17
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Testing system
Of circuit
C702S124000, C324S527000
Reexamination Certificate
active
06263294
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to an on-line impedance spectroscopy system that characterizes the rheologic and thixotropic properties of solder paste and residues by measuring its impedance at various frequencies.
BACKGROUND OF THE INVENTION
A need for real time solder paste process control is critical due to the dynamic nature of solder paste. The rheology and thixotropic properties of solder paste can change dramatically during manufacture which can cause significant problems in the printablity of circuit boards using the solder paste. These changes are dependent on the manufacturing environment, the characteristics and age of the paste, and the previous treatment of the paste. A high humidity environment can cause an increase in slump and an increase in the occurrence of solder balls due to moisture absorption. Solder paste can also increase or decrease in viscosity with age. Changes in the flux material can impact the rheologic nature of the paste due to excessive build-up of reaction products between the flux activators and the metal oxides.
Methods currently used for measuring the rheology of solder paste include the use of a viscometer. A viscometer can measure the viscosity of solder paste at different shearing rates. In this way the viscosity of a solder paste can be tracked from a reference shear rate and the thixotropic character of the paste can be tracked by calculating the change in viscosity from the change in shear rate. Viscometer systems allow a manufacturer to calculate both viscosity and thixotropic behavior. However, these systems are primarily designed to make bulk rheologic measurements as an incoming inspection tool and typically require a large amount of paste for an accurate measurement.
A related patent is U.S. Pat. No. 5,656,933 issued Aug. 12, 1997. U.S. Pat. No. 5,103,181 discloses a composition and monitoring process that uses impedance measurements. U.S. Pat. No. 4,939,469 discloses a method for evaluating printed circuit boards using the impedance spectra of the board. U.S. Pat. Nos. 3,482,161; 3,440,529 and 3,448,380 all use spectroscopic analysis for analyzing samples.
SUMMARY OF THE INVENTION
The invention consists of both hardware and software which forms an on-line impedance spectroscopy system that characterizes the rheologic and thixotropic properties of solder paste and residues by measuring its impedance at various frequencies. The hardware provides voltage and current inputs to a sample at various frequencies and measures the resulting impedance. The software stores equivalent circuit parameters for multiple solder pastes and residues, controls the hardware inputs to the sample, displays measurement data in real-time, displays results, and notifies the operator if results exceed preset limits. The invention supports two probe, three probe and four probe surface and bulk measurements of the solder paste and associated residues in manufacturing.
It is an object of the present invention to support an auto-collection mode wherein a series of impedance spectroscopy tests can be set up by the operator and then occur without further operator intervention. The measurements and results from the auto-collection tests are stored for later review.
It is also an object of the present invention to provide a switch matrix through which multiple output probe interfaces are selectable for spectroscopy measurements. The output probe interfaces being in contact with one or more samples to be characterized
Additional objects, advantages and novel features of the invention are set forth in the description that follows, and will become apparent to those skilled in the art upon reviewing the drawings in connection with the following description.
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patent: 5656933 (1997-08-01), Frederickson et al.
patent: 6005399 (1999-12-01), Frederickson et al.
Guy et al., “Analyzing Residues Using AC Impedance Techniques”, Technical Paper presented at NEPCON West '97 Conference, Anaheim, CA, Feb. 23-27, 1997.
Kendig, Martin W., “Overview of the Science and Capability of Impedance Spectroscopy” (Date Unknown).
Seitz et al., “Monitoring Solder Pastes Using AC Impedance Spectroscopy”, Alpha Metals Technical Brief, (Date Unknown).
“IS-4000 Monitor Your Process in Real Time”, Alpha Metals brochure, 1997.
Cragoe Alex E.
Frederickson Michael D.
Latham Jeff K.
American Competitiveness Institute, Inc.
Bose McKinney & Evans LLP
Hoff Marc S.
Miller Craig Steven
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