Data processing: measuring – calibrating – or testing – Measurement system – Temperature measuring system
Reexamination Certificate
2000-07-07
2003-05-13
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Temperature measuring system
Reexamination Certificate
active
06564166
ABSTRACT:
TECHNICAL FIELD
The present invention is generally related to a method and apparatus for measuring warpage in a specimen and, more particularly, is related to a method and apparatus using a projection moiré technique to measure warpage in a temperature controlled environment which simulates on-line manufacturing processes or facilitates laboratory development processes.
BACKGROUND OF THE INVENTION
The surface flatness of objects, such as printed circuit boards, integrated circuit (IC) packages, ceramic and metal substrates, papers, plastics, woven items and the like, can be very important and is often of special concern. For example, the manufacture of printed circuit boards, IC packages and other electronic interconnection products is a multi-billion dollar global industry, and the flatness of these products is critical to their ability to undergo further manufacturing steps and to their ultimate reliability in operation as parts of computer, automobile, telecommunications, aerospace, military and other electronic systems. Non-flatness, or warpage, is a frequent problem in manufacturing due to inadequacies in design, materials, and/or processing of components, which are typically complex devices composed of several different materials. The ability to analyze surface flatness, especially changes in surface flatness (warpage) associated with changing temperatures, plays an important role in the designing, manufacture, processing and maintaining of objects for which surface flatness is an important characteristic.
One method of analyzing surface flatness is projection moiré interferometry. Projection moiré is a full-field, noncontact method of measuring out-of-plane displacements for in-plane deformations of a structure. A typical projection moiré fringe pattern is a series of light and dark fringe lines of equal change in surface position which map out the contour change of an object much the same way a topography map delineates the contour of land.
FIG. 1
illustrates a simplified projection moiré system
20
. Generally, projection moiré interferometry fringe lines are formed by a plurality of phase shifted laser beams
22
projected onto a workpiece
24
. A laser
26
generates a laser beam
28
which is projected into a shearing interferometer
30
. The laser beam
28
is expanded by beam expander
32
and transmitted to beam splitter
34
. The shearing interferometer
30
is thus able to generate a plurality of interfering laser beams that form fringe patterns fanning out onto workpiece
24
. The spatial frequency of the fringes may be adjustable to a desired horizontal and/or vertical spacing. Some projection moiré systems employ an actuated mirror (not shown) which sweeps the beam
22
across workpiece
24
in a manner which further improves the analysis of the moiré patterns projected onto workpiece
24
. A camera
36
detects the moiré fringe patterns and provides the image of the workpiece
24
and the projected fringe patterns to processor
38
. The image detected by camera
36
is displayed on the video display screen
40
. The operator may interface with and/or control the projection moiré system and camera through an interface, such as keyboard
42
.
Shadow moiré fringe analysis is another fringe pattern analysis technique employing a light source projected through a glass plate having overlaying grating lines (reference grating) which are projected onto the workpiece as specimen gratings. The interference of the reference and specimen gratings produce moiré fringes. Like the projection moiré method, a camera captures the fringe image created by the shadow moiré system and a processor processes the images detected by the camera.
Typically, an image of an un-deformed workpiece
24
(
FIG. 1
) is recorded by the camera
36
and stored within processor
38
for comparison against a deformed workpiece
24
(or the same workpiece
24
after deformation). By comparing the differences in the projected fringe patterns on the un-deformed and the deformed workpiece
24
, the nature of any warpage and/or deformations in the workpiece
24
can be analyzed. However, the technique of comparing a deformed workpiece with an un-deformed workpiece (or comparing a change in deformation in the same workpiece) limits the analysis to two static points in time. That is, two views of a workpiece
24
are compared. For example, images of the initial un-deformed conditions and the subsequent deformations of workpiece
24
after a process may be compared.
The deformations experienced by a workpiece
24
as the workpiece is subjected to a process cannot be analyzed with this static projection moiré analysis approach. A dynamic analysis approach would provide a much better overall picture of the deformation process. For example, if the workpiece is a printed circuit board traveling down an assembly line through a series of reflow oven zones wherein various components are soldered to the circuit board, the circuit board would presumably start out in an initial un-deformed state, and then be subjected to a series of heating and cooling cycles which may induce various degrees of warpage at various locations on the circuit board at different times during the process as the electronic components are soldered to the printed circuit board.
Furthermore, tracking a workpiece
24
with a camera
36
and a projection moiré system
20
as the workpiece travels down the manufacturing assembly line presents numerous and nearly insurmountable difficulties. The oven enclosures which solder components to the circuit board provide restricted access to the projection moiré system
20
. If a single projection moiré system
20
is used, the laser
26
, shearing interferometer
34
, and camera
36
need to travel along the same path as the workpiece in a manner such that fringe patterns can be projected on the workpiece
24
and detected by camera
36
during the entire manufacturing process, including the soldering process conducted inside of the oven enclosures. Alternatively, a plurality of projection moiré interferometer systems
20
might be used at pre-selected locations along the manufacturing assembly line, however, this approach would have the higher costs of having multiple lasers
26
, shearing interferometers
30
and cameras
36
. Also, difficulties will have to be overcome in image synchronization between the plurality of cameras spaced along the assembly manufacturing line. Additionally, any of the projection moiré systems
20
viewing the workpiece
24
in an oven enclosure would have to overcome special design problems associated with operation in the high temperature environment of an oven enclosure. Thus, the above-described prior art projection moiré analysis method is not practically able to dynamically detect and analyze the entire warpage process that a workpiece
24
may be subjected to during a manufacturing process.
One prior art technique employs a shadow moiré analysis system in which a work sample is placed in a heating chamber. The shadow moiré illumination source is directed into the heating chamber and onto the sample. Subsequently, the temperature in the heating chamber. may be adjusted over time to approximate a predefined temperature/time profile. The camera captures the entire deformation process as the workpiece is subjected to changes in temperature during the simulation of the temperature/time profile. The temperature/time profile in the heating chamber can be designed to simulate an actual manufacturing process, or be specified such that a process engineer can conduct laboratory experiments for use in process and manufacturing method design. The use of a heating chamber for housing and heating a sample for analysis by a shadow moiré system is taught in Ume, U.S. Pat. No. 5,601,364, which is incorporated herein by reference. However, the shadow moiré analysis system taught in Ume contains a single fixed heating source and a single variable heating source. It would be desirable to have additional flexibility in the heating sources, a way to circulate air within the chamber, a
Petriccione Gregory James
Ume Ifeanyi Charles
Barlow John
Dougherty Anthony T.
Georgia Tech Research Corporation
Thomas Kayden Horstemeyer & Risley, L.L.P.
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