U.S. patent application number 10/189645 was filed with the patent office on 2002-11-14 for detection of defects by thermographic analysis.
This patent application is currently assigned to ART Advanced Research Technologies Inc.. Invention is credited to Pastor, Marc, Schlagheck, Jerry.
Application Number | 20020167987 10/189645 |
Document ID | / |
Family ID | 24599597 |
Filed Date | 2002-11-14 |
United States Patent
Application |
20020167987 |
Kind Code |
A1 |
Schlagheck, Jerry ; et
al. |
November 14, 2002 |
Detection of defects by thermographic analysis
Abstract
A mechanism is provided for detecting a defect in a populated
sample having a thickness dimension substantially smaller than the
length and width dimensions thereof, the populated sample having a
first side and an opposite second side, at least said first side of
said populated sample having one or more Surface Mounted
Components. The mechanism exploits a standard thermographic image
which may be used in a detection method comprising 1) directing a
thermal wave at said second side of said populated sample 2)
recording a thermographic image of the first side of said populated
sample once a surface thereof reaches a predetermined transit
temperature or a predetermined transit time period has elapsed; and
3) analyzing the obtained thermographic image by comparing the so
obtained thermographic image with a standard thermographic
image.
Inventors: |
Schlagheck, Jerry; (West
Chester, OH) ; Pastor, Marc; (Saint-Hubert,
CA) |
Correspondence
Address: |
Timothy E. Nauman
FAY, SHARPE, FAGAN, MINNICH & McKEE, LLP
7th Floor
1100 Superior Avenue
Cleveland
OH
44114-2518
US
|
Assignee: |
ART Advanced Research Technologies
Inc.
|
Family ID: |
24599597 |
Appl. No.: |
10/189645 |
Filed: |
July 3, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10189645 |
Jul 3, 2002 |
|
|
|
09648140 |
Aug 25, 2000 |
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Current U.S.
Class: |
374/5 |
Current CPC
Class: |
G01N 25/72 20130101 |
Class at
Publication: |
374/5 |
International
Class: |
G01N 025/72 |
Claims
We claim:
1. An inspection system for the detection of an anomaly in a sample
comprising a thermal heater array comprising a plurality discrete
individually controllable heat source elements capable of imparting
heat to a sample a heat diffuser component an infrared camera
component for monitoring infrared emissions from a side of the
sample and deriving a signal indicative of the temperature profile
of this side of the sample, a sample support component for
supporting a sample for inspection said sample support component,
said heat diffuser component and said thermal heater array being
configured and disposed such that, when said support component
supports a sample for inspection, the sample has an observation
side and an opposite heat exposure side, the infrared camera is
disposed on the observation side for monitoring the observation
side and the diffuser component and the thermal heater array are
disposed on the heat exposure side for exposing the heat exposure
side to thermal radiation, the heat diffuser component being
disposed between the sample and the thermal heater array.
2. A method for detecting a defect in a populated circuit board,
said populated circuit board having a first side and an opposite
second side, at least said first side being populated with one or
more Surface Mounted Components, said method comprising 1)
directing a thermal wave at the second side of said populated
circuit board 2) recording a thermographic image of the first side
of said populated circuit board once a surface thereof reaches a
predetermined transit temperature or a predetermined transit time
period has elapsed; and 3) analysing the obtained thermographic
image by comparing the so obtained thermographic image with a
standard thermographic image wherein a) the thermal wave is
developed by a thermal heater array comprising a plurality of
discrete individually controllable heat source elements, said
elements each delivering a respective individual energy intensity
reflecting the respective energy parameter information therefor
comprised in a first block of energy parameter information; b) said
first block of energy parameter information comprising, for each of
said heat source elements, individual energy parameter information
whereby the thermal heater array may be induced to provide a
thermal wave giving rise to a thermographic image indicative of
uniform temperature of the surface of the first side of an
predetermined unpopulated circuit board; and c) said standard
thermographic image having been obtained by i) subjecting the
second side of a predetermined populated circuit board to a thermal
wave developed by said thermal heater array, said thermal field
being applied until a surface of the first side of the
predetermined populated circuit board reaches said predetermined
transit temperature or said predetermined transit time period has
elapsed, said elements of said thermal heater array each being set
to deliver a respective individual energy intensity reflecting the
energy parameter information of said first block of energy
parameter information, and ii) taking said standard thermographic
image from the first side of said predetermined populated circuit
board once said predetermined transit temperature is reached or
said predetermined transit time period has elapsed.
3. A method for detecting a defect in a populated circuit board,
said populated circuit board having a first side and a second
opposite side, at least said first side being populated with one or
more Surface Mounted Components, said method comprising 1)
directing a thermal wave at the second side of the populated
circuit board 2) recording a thermographic image of the first side
of the populated circuit board once a predetermined transit
temperature is reached on this side of the populated circuit board
or a predetermined transit time period has elapsed; and 3)
analysing the obtained thermographic image by comparing the so
obtained thermographic image with a standard thermographic image
wherein the standard thermographic image has been obtained by a)
monitoring the temperature of a surface of the first side of an
predetermined unpopulated circuit board b) subjecting the second
side of the unpopulated circuit board to a thermal wave developed
by a thermal heater array comprising a plurality of discrete
individually controllable heat source elements, said elements each
being initially set to deliver an individual energy intensity such
that the thermal array delivers a thermal wave of predetermined
contour; c) adjusting the individual energy intensity of each of
said elements until the thermal array delivers a thermal wave such
that the surface being monitored provides a thermographic image
thereof indicative of uniform temperature d) storing a first block
of energy parameter information corresponding to the individual
energy intensity of each of said heat source elements found to
provide the recorded thermographic image indicative of uniform
temperature e) monitoring the temperature of the first side of a
predetermined populated circuit board f) subjecting the second side
of the predetermined populated circuit board to a thermal wave
developed by a thermal heater array comprising a plurality of
discrete individually controllable heat source elements, said
elements each being set to deliver a respective individual energy
intensity reflecting the energy parameter information of said first
block of energy parameter information, said thermal wave being
applied until a surface site of the first side of the predetermined
populated circuit board reaches said predetermined transit
temperature or said predetermined transit time period has elapsed
and taking a second thermographic image; and, if desired, g)
storing a block of image information corresponding to the second
thermographic image, said second thermographic image being said
standard thermographic image.
4. A method for detecting a defect in a populated sample having a
thickness dimension substantially smaller than the length and width
dimensions thereof, said populated sample having a first side and
an opposite second side, at least said first side of said populated
sample having one or more Surface Mounted Components, said method
comprising 1) directing a thermal wave at said second side of said
populated sample 2) recording a thermographic image of the first
side of said populated sample once a surface thereof reaches a
predetermined transit temperature or a predetermined transit time
period has elapsed; and 3) analysing the obtained thermographic
image by comparing the so obtained thermographic image with a
standard thermographic image wherein a) the thermal wave is
developed by a thermal heater array comprising a plurality of
discrete individually controllable heat source elements, said
elements each delivering a respective individual energy intensity
reflecting the respective energy parameter information therefor
comprised in a first block of energy parameter information; b) said
first block of energy parameter information comprising, for each of
said heat source elements, individual energy parameter information
whereby the thermal heater array may be induced to provide a
thermal wave giving rise to a thermographic image indicative of
uniform temperature of the surface of the first side of an
unpopulated sample; and c) said standard thermographic image having
been obtained by i) subjecting the second side of a predetermined
populated sample to a thermal wave developed by said thermal heater
array, said thermal field being applied until a surface of the
first side of the predetermined populated sample reaches said
predetermined transit temperature or said predetermined transit
time period has elapsed, said elements of said thermal heater array
each being set to deliver a respective individual energy intensity
reflecting the energy parameter information of said first block of
energy parameter information, and ii) taking said standard
thermographic image from the first side of the predetermined
populated sample once said predetermined temperature is reached or
said predetermined transit time has elapsed.
5. A method for detecting a defect in a populated sample having a
thickness dimension substantially smaller than the length and width
dimensions thereof, said sample having a first side and a second
opposite side, at least said first side of said populated sample
having one or more Surface Mounted Components, said method
comprising 1) directing a thermal wave at the second side of said
populated sample 2) recording a thermographic image of the first
side of said populated sample once a predetermined transit
temperature is reached on this side of the populated sample or a
predetermined transit time period has elapsed; and 3) analysing the
obtained thermographic image by comparing the so obtained
thermographic image with a standard thermographic image, wherein
the standard thermographic image has been obtained by a) monitoring
the temperature of a surface of the first side of an predetermined
unpopulated sample b) subjecting the second side of the unpopulated
sample to a thermal wave developed by a thermal heater array
comprising a plurality of discrete individually controllable heat
source elements, said elements each being initially set to deliver
an individual energy intensity such that the thermal array delivers
a thermal wave of predetermined contour; c) adjusting the
individual energy intensity of each of said elements until the
thermal array delivers a thermal wave such that the surface being
monitored provides a thermographic image thereof indicative of
uniform temperature d) storing a first block of energy parameter
information corresponding to the individual energy intensity of
each of said heat source elements found to provide the recorded
thermographic image indicative of uniform temperature e) monitoring
the temperature of the first side of a predetermined populated
sample f) subjecting the second side of the predetermined populated
sample to a thermal wave developed by a thermal heater array
comprising a plurality of discrete individually controllable heat
source elements, said elements each being set to deliver a
respective individual energy intensity reflecting the energy
parameter information of said first block of energy parameter
information, said thermal wave being applied until a surface site
reaches a predetermined transit temperature or a predetermined
transit time period has elapsed and taking a second thermographic
image; and, if desired, g) storing a block of image information
corresponding to the second thermographic image, said second
thermographic image being said standard thermographic image.
6. A method for obtaining a standard thermographic image for use in
detecting a defect in a populated circuit board, said populated
circuit board having a first side and a second opposite side, at
least said first side being populated with one or more Surface
Mounted Components, said method comprising a) monitoring the
temperature of a surface of the first side of an predetermined
unpopulated circuit board b) subjecting the second side of the
unpopulated circuit board to a thermal wave developed by a thermal
heater array comprising a plurality of discrete individually
controllable heat source elements, said elements each being
initially set to deliver an individual energy intensity such that
the thermal array delivers a thermal wave of predetermined contour;
c) adjusting the individual energy intensity of each of said
elements until the thermal array delivers a thermal wave such that
the surface being monitored provides a thermographic image thereof
indicative of uniform temperature d) storing a first block of
energy parameter information corresponding to the individual energy
intensity of each of said heat source elements found to provide the
recorded thermographic image indicative of uniform temperature e)
monitoring the temperature of the first side of a predetermined
populated circuit board f) subjecting the second side of the
predetermined populated circuit board to a thermal wave developed
by a thermal heater array comprising a plurality of discrete
individually controllable heat source elements, said elements each
being set to deliver a respective individual energy intensity
reflecting the energy parameter information of said first block of
energy parameter information, said thermal wave being applied until
a surface site of the first side of the predetermined populated
circuit board reaches said predetermined transit temperature or
said predetermined transit time period has elapsed and taking a
second thermographic image; and, if desired, g) storing a block of
image information corresponding to the second thermographic image,
said second thermographic image being said standard thermographic
image.
7. A method for obtaining a standard thermographic image for
detecting a defect in a populated sample having a thickness
dimension substantially smaller than the length and width
dimensions thereof, said sample having a first side and a second
opposite side, at least said first side of said populated sample
having one or more Surface Mounted Components, said method
comprising a) monitoring the temperature of a surface of the first
side of an predetermined unpopulated sample b) subjecting the
second side of the unpopulated sample to a thermal wave developed
by a thermal heater array comprising a plurality of discrete
individually controllable heat source elements, said elements each
being initially set to deliver an individual energy intensity such
that the thermal array delivers a thermal wave of predetermined
contour; c) adjusting the individual energy intensity of each of
said elements until the thermal array delivers a thermal wave such
that the surface being monitored provides a thermographic image
thereof indicative of uniform temperature d) storing a first block
of energy parameter information corresponding to the individual
energy intensity of each of said heat source elements found to
provide the recorded thermographic image indicative of uniform
temperature e) monitoring the transit temperature of the first side
of a predetermined populated sample f) subjecting the second side
of the predetermined populated sample to a thermal wave developed
by a thermal heater array comprising a plurality of discrete
individually controllable heat source elements, said elements each
being set to deliver a respective individual energy intensity
reflecting the energy parameter information of said first block of
energy parameter information, said thermal wave being applied until
a surface site reaches a predetermined transit temperature or a
predetermined transit time period has elapsed and taking a second
thermographic image; and, if desired, g) storing a block of image
information corresponding to the second thermographic image, said
second thermographic image being said standard thermographic image.
Description
[0001] The present invention relates to the detection of defects in
an object by means of thermal analysis.
[0002] Although the invention may be used for other types of
(analogous) products the invention will be discussed herein in
relation to printed circuit boards by way of example only, i.e.
insulating base boards (e.g. epoxy resin boards) populated with
electronic components such as resistor, transistors, integrated
circuits, etc . . . These components are usually soldered to a base
board; such solder joints are a source of defects, i.e. defects due
to absence or poor quality of the solder joint.
[0003] It is known that an object such as a populated circuit board
may be inspected for defects by a procedure wherein such a board is
heated in order to obtain a thermographic image. The obtained image
is then analysed by being compared to a standard thermographic
image of a defect free populated circuit board; i.e. one image is
differenced from the other. Please see for example U.S. Pat. Nos.
5,208,528 and 5,775,806, the entire contents of which are
incorporated herein by reference.
[0004] It would be advantageous to have a method which facilitates
the obtaining of images under conditions of high thermal contrast.
It would in particular be advantageous to be able to tune out
background thermal noise attributable to thermal characteristics of
a base board itself.
[0005] It would be advantageous to be able to use or exploit an
array of discrete heat sources during a thermal analysis; each
individual heat source element may, for example, be an infra-red
light emitting diode. It would be advantageous to be able to use
the array in the context of inspecting sample objects such as, for
example, electronic circuit, boards.
[0006] It would in particular be advantageous with respect to
circuit boards to have an inspection technology based on an
apparatus which is relatively easy to make and use and which
relatively more reliable. It would more particularly be
advantageous for example to have a method system apparatus etc.
which may be exploited to inspect a circuit card without the use of
an isothermal housing.
STATEMENT OF INVENTION
[0007] The present invention in accordance with one aspect relates
to an (infrared) inspection system for the detection of an anomaly
(defects) in a sample comprising
[0008] a thermal heater array comprising a plurality (e.g. of rows
and columns of) discrete individually controllable heat source
elements capable of imparting heat (i.e. thermal radiation) to a
sample (an examination object)
[0009] a heat diffuser component
[0010] an infrared camera component for monitoring infrared
emissions from a side of the sample and deriving a signal
indicative of the temperature (profile) of this side of the
sample.
[0011] a sample support component for supporting a sample for
inspection
[0012] said sample support component, said heat diffuser component
and said thermal heater array being configured and disposed such
that, when said support component supports a sample for inspection,
the sample has an observation side and an opposite heat exposure
side, the infrared camera is disposed on the observation side for
monitoring the observation side and the diffuser component and the
thermal heater array are disposed on the heat exposure side for
exposing the heat exposure side to thermal radiation, the heat
diffuser component being disposed between the sample and the
thermal heater array.
[0013] The present invention in accordance with a related aspect
provides a method for obtaining a standard thermographic image
(video, still, monitor, etc . . . ) for use in detecting a defect
in a populated sample having a thickness dimension substantially
smaller than the length and width dimensions thereof, said sample
having a first side and a second opposite side, at least said first
side of said populated sample having one or more Surface Mounted
Components, said method comprising
[0014] a) monitoring the temperature of a surface of the first side
of an predetermined unpopulated sample
[0015] b) subjecting the second side of the unpopulated sample to a
thermal wave developed by a thermal heater array comprising a
plurality of discrete individually controllable heat source
elements, said elements each being initially set to deliver an
individual energy intensity (i.e. deliver an energy load) such that
the thermal array delivers a thermal wave of predetermined
contour;
[0016] c) adjusting the individual energy intensity of each of said
elements until the thermal array delivers a thermal wave such that
the surface being monitored provides a recorded thermographic image
thereof indicative of uniform temperature
[0017] d) storing (e.g. electronically--computer memory means) a
first block of energy parameter information corresponding to the
individual energy intensity (i.e. deliverable energy load) of each
of said heat source elements found to provide the recorded
thermographic image indicative of uniform temperature
[0018] e) monitoring the temperature of the first side of a
predetermined populated sample
[0019] f) subjecting the second side of the predetermined populated
sample to a thermal wave developed by a thermal heater array
comprising a plurality of discrete individually controllable heat
source elements, said elements each being set to deliver a
respective individual energy intensity (i.e. deliver an thermal
energy load) reflecting the energy parameter information of said
first block of energy parameter information, said thermal wave
being applied until a surface site reaches a predetermined transit
temperature or a predetermined transit time period has elapsed and
taking (i.e. recording or capturing) a second thermographic image
(e.g. by infra red camera--video or still); and, if desired,
[0020] g) storing (e.g. electronically--computer memory means, etc
. . . ) a block of image information corresponding to the second
thermographic image, said second thermographic image being said
standard thermographic image. The (standard) thermographic image(s)
may as desired be presented on a computer monitor or be reduced to
a hard copy picture format using a suitable colour printer.
[0021] In accordance with a further aspect the present invention
provides a method for detecting a defect in a populated sample
having a thickness dimension substantially smaller than the length
and width dimensions thereof, said sample having a first side and
an opposite second side, at least said first side being populated
with one or more Surface Mounted Components, said method
comprising
[0022] 1) directing a thermal wave (i.e. field or front) at said
second side of said populated sample
[0023] 2) recording a thermographic image of the first side of said
populated sample once a surface thereof reaches a predetermined
transit temperature or a predetermined transit time period has
elapsed; and
[0024] 3) analysing the obtained thermographic image by comparing
the so obtained thermographic image with a standard thermographic
image
[0025] wherein
[0026] a) the thermal wave (i.e. field or front) is developed by a
thermal heater array comprising a plurality of discrete
individually controllable heat source elements, said elements each
delivering a respective individual energy intensity (i.e. deliver
an thermal energy load) reflecting the respective energy parameter
information (e.g. intensity, duration, etc . . . ) therefor
comprised in a first block of energy parameter information (e.g.
intensity, duration, etc . . . );
[0027] b) said first block of energy parameter information
comprising, for each of said heat source elements, individual
energy parameter information whereby the thermal heater array may
be induced (i.e. in response thereto) to provide a thermal wave
giving rise to a thermographic image (i.e. as an image captured by
an infra red camera--video or still) indicative of uniform
temperature of the surface of the first side of a predetermined
unpopulated sample (i.e. no Surface Mounted Components on either
side thereof); and
[0028] c) said standard thermographic image having been obtained by
i) subjecting the second side of a predetermined (e.g. defect free)
populated sample to a thermal wave (i.e. field or front) developed
by said thermal heater array, said thermal field being applied
until a surface of the first side of the sample reaches said
predetermined transit temperature, said elements of said thermal
heater array each being set to deliver a respective individual
energy intensity (i.e. deliver an energy load) reflecting the
energy parameter information of said first block of energy
parameter information, and ii) taking (i.e. recording or capturing)
said standard thermographic image (i.e. as an image captured by an
infra red camera--video or still) from the first side of said
predetermined populated sample once said predetermined temperature
is reached or said predetermined transit time period has
elapsed.
[0029] In accordance with an additional aspect the present
invention provides a method for obtaining a standard thermographic
image for use in detecting a defect in a populated circuit board,
said populated circuit board having a first side and a second
opposite side, at least said first side being populated with one or
more Surface Mounted Components, said method comprising
[0030] a) monitoring the temperature of a surface of the first side
of an predetermined unpopulated circuit board
[0031] b) subjecting the second side of the unpopulated circuit
board to a thermal wave developed by a thermal heater array
comprising a plurality of discrete individually controllable heat
source elements, said elements each being initially set to deliver
an individual energy intensity (i.e. deliver an energy load) such
that the thermal array delivers a thermal wave of predetermined
contour;
[0032] c) adjusting the individual energy intensity of each of said
elements until the thermal array delivers a thermal wave such that
the surface being monitored provides a thermographic image thereof
indicative of uniform temperature
[0033] d) storing (e.g. electronically--computer memory
means--video--hard copy picture) a first block of energy parameter
information corresponding to the individual energy intensity (i.e.
deliverable energy load) of each of said heat source elements found
to provide the recorded thermographic image indicative of uniform
temperature
[0034] e) monitoring the transit temperature of the first side of a
predetermined populated circuit board
[0035] f) subjecting the second side of the predetermined populated
circuit board to a thermal wave developed by a thermal heater array
comprising a plurality of discrete individually controllable heat
source elements, said elements each being set to deliver a
respective individual energy intensity (i.e. deliver an energy
load) reflecting the energy parameter information of said first
block of energy parameter information, said thermal wave being
applied until a surface site of the first side of the predetermined
populated circuit board reaches said predetermined transit
temperature or said predetermined transit time period has elapsed
and taking (i.e. recording or capturing) a second thermographic
image; and, if desired,
[0036] g) storing (e.g. electronically--computer memory
means--video--hard copy picture, etc . . . ) a block of image
information corresponding to the second thermographic image, said
second thermographic image being said standard thermographic
image.
[0037] In accordance with the present invention there is also
provided a method for detecting a defect in a populated sample
having a thickness dimension substantially smaller than the length
and width dimensions thereof, said populated sample having a first
side and a second opposite side, at least said first side of said
populated sample having one or more Surface Mounted Components,
said method comprising
[0038] 1) directing a thermal wave (i.e. field or front) at the
second side of said populated sample
[0039] 2) recording (e.g. electronically--computer memory
means--video--hard copy picture, etc . . . ) a thermographic image
of the first side of said populated sample once a predetermined
transit temperature is reached on this side of the populated sample
or a predetermined transit time period has elapsed; and
[0040] 3) analysing the obtained thermographic image by comparing
(e.g. picture image by picture image, pixel by pixel, etc . . . )
the so obtained thermographic image with a standard thermographic
image (e.g. electronic image (monitor)--video image--hard copy
picture)
[0041] wherein the standard thermographic image has been obtained
by
[0042] a) monitoring the temperature of a surface of the first side
of an predetermined unpopulated sample
[0043] b) subjecting the second side of the predetermined
unpopulated sample to a thermal wave developed by a thermal heater
array comprising a plurality of discrete individually controllable
heat source elements, said elements each being initially set to
deliver an individual energy intensity such that the thermal array
delivers a thermal wave of predetermined contour;
[0044] c) adjusting the individual energy intensity (i.e.
deliverable energy load) of each of said elements until the thermal
array delivers a thermal wave such that the surface being monitored
provides a thermographic image thereof indicative of uniform
temperature
[0045] d) storing (e.g. electronically--computer memory
means--video--hard copy picture, etc . . . ) a first block of
energy parameter information corresponding to the individual energy
intensity (i.e. derivable energy load) of each of said heat source
elements found to provide the recorded thermographic image
indicative of uniform temperature
[0046] e) monitoring the temperature of the first side of a
predetermined (e.g. defect free) populated sample
[0047] f) subjecting the second side of the predetermined (e.g.
defect free) populated sample to a thermal wave developed by a
thermal heater array comprising a plurality of discrete
individually controllable heat source elements, said elements each
being set to deliver a respective individual energy intensity (i.e.
deliver an energy load) reflecting the energy parameter information
of said first block of energy parameter information, said thermal
wave being applied until a surface site reaches said predetermined
transit temperature or said predetermined transit time period has
elapsed and taking (i.e. recording or capturing) a second
thermographic image; and, if desired
[0048] g) storing (e.g. electronically--computer memory
means--video--hard copy picture, etc . . . ) a second block of
image information corresponding to the second recorded
thermographic image, said second recorded image being said standard
thermographic image.
[0049] In accordance with a further aspect the present invention
provides a method for detecting a defect in a populated circuit
board, said populated circuit board having a first side and an
opposite second side, at least said first side being populated with
one or more Surface Mounted (e.g. soldered) Components, (i.e. said
second side may be unpopulated or also populated with Surface
Mounted (e.g. soldered) Components as desired or necessary), said
method comprising
[0050] 1) directing a thermal wave (i.e. field or front) at said
second side of said populated circuit board
[0051] 2) recording a thermographic image of the first side of said
populated circuit board once a surface thereof reaches a
predetermined transit temperature or a predetermined transit time
period has elapsed; and
[0052] 3) analysing the obtained thermographic image by comparing
the so obtained thermographic image with a standard thermographic
image
[0053] wherein
[0054] a) the thermal wave is developed by a thermal heater array
comprising a plurality of discrete individually controllable heat
source elements, said elements each delivering a respective
individual energy intensity (i.e. deliverable energy load)
reflecting the respective energy parameter information therefor
comprised in a first block of energy parameter information;
[0055] b) said first block of energy parameter information
comprising, for each of said heat source elements, individual
energy parameter information whereby the thermal heater array may
be induced (i.e. in response thereto) to provide a thermal wave
(i.e. field) giving rise to a thermographic image (e.g. an image
captured by an infra red camera--video/still, etc . . . )
indicative of uniform temperature of the (a) surface of the first
side of an predetermined unpopulated circuit board (i.e. a board
with no Surface Mounted Components on either side); and
[0056] c) said standard thermographic image having been obtained by
i) subjecting the second side of a predetermined (e.g. defect free)
populated circuit board to a thermal wave (i.e. field) developed by
said thermal heater array, said thermal wave being applied until a
surface of the first side of the predetermined (e.g. defect free)
populated circuit board reaches said predetermined temperature,
said elements of said thermal heater array each being set to
deliver a respective individual energy intensity (i.e. deliver an
energy load) reflecting the intensity information of said first
block of intensity information, and ii) taking (i.e. recording or
capturing) said standard thermographic image (e.g. by an infra red
camera video/still, etc . . . ) from the populated side of the
circuit board once said predetermined temperature is reached.
[0057] In accordance with another aspect the present invention
provides a method for detecting a defect in a populated circuit
board, said populated circuit board having a first side and a
second opposite side, at least said first side being populated with
one or more Surface Mounted (e.g. soldered) Components, said method
comprising
[0058] 1) directing a thermal wave (i.e. field or front) at the
second side of said populated circuit board
[0059] 2) recording a thermographic image of the first side of the
board once a predetermined transit temperature is reached (observed
at a predetermined surfaces site) on this side of the populated
circuit board or a predetermined transit time period has elapsed;
and
[0060] 3) analysing the obtained thermographic image by comparing
the so obtained thermographic image with a standard thermographic
image
[0061] wherein the standard thermographic image has been obtained
by
[0062] a) monitoring the temperature of a surface of the first side
of an predetermined unpopulated circuit board
[0063] b) subjecting the second side of the predetermined
unpopulated circuit board to a thermal wave (i.e. field) developed
by a thermal heater array comprising a plurality of discrete
individually controllable heat source elements, said elements each
being initially set to deliver an individual energy intensity (i.e.
deliver an energy load) such that the array delivers a thermal wave
of predetermined contour;
[0064] c) adjusting the individual energy intensity (i.e.
deliverable energy load) of each of said elements until the array
delivers a thermal wave such that the surface being monitored
provides a thermographic image thereof indicative of uniform
temperature
[0065] d) storing (e.g. electronically--computer memory
means--video--hard copy picture, etc . . . ) a first block of
energy parameter information corresponding to the individual energy
intensity of each of said heat source elements found to provide the
recorded thermographic image indicative of uniform temperature
[0066] e) monitoring the temperature of the first side of a
predetermined (e.g. defect free) populated circuit board
[0067] f) subjecting the second side of the predetermined (e.g.
defect free) populated circuit board to a thermal wave developed by
a thermal heater array comprising a plurality of discrete
individually controllable heat source elements, said elements each
being set (i.e. controlled) to deliver a respective individual
energy intensity (i.e. deliver an energy load) reflecting the
energy parameter information of said first block of intensity
information, said thermal field being applied until a surface
(site) of the first side of the predetermined (e.g. defect free)
circuit board reaches a predetermined temperature, for example
30.degree. C., and taking (i.e. recording or capturing) a second
thermographic image; and, if desired,
[0068] g) storing (e.g. electronically--computer memory
means--video--hard copy picture, etc . . . ) a block of image
information corresponding to the second thermographic image, said
second thermographic image being said standard thermographic
image.
[0069] The methodology, apparatus, systems etc. of the present
invention may for example be used with electronic circuit boards
wherein electronic components are attached to an underlying base
board; such base boards do not have a homogeneous heat transfer
characteristic across their entire cross section from one end
thereof to the other, i.e. heat will travel slower through some
parts of the base board as compared to other parts of the same base
board.
[0070] In accordance with the thermal analysis technology of the
present invention each of the discreet heat sources are to be
individually connected in suitable manner to an electrical control
device which in turn is connected to a controlling computer system
comprising means for storing blocks of information each block of
information corresponding to a respective recorded thermal image.
The controlling computer would also be connected to an infra-red
camera. The sample to be tested would be disposed such that the
infra-red camera is on one side of the sample whereas the array of
individual discreet heat sources will be on the opposite side of
the sample.
[0071] A system in accordance with the present invention may be
calibrated in a two step process.
[0072] The first calibration step is carried out in order to obtain
and store in computer memory the parameter settings (i.e.
intensity, shape, duration, repetition rate, etc.) for each
individual discrete heating unit or element which after a heating
cycle provides the surface of a standard sample (i.e. the base
board on both sides thereof is component free) facing the infra-red
camera with an at least essentially uniform (i.e. reference)
temperature (i.e. the surface facing the infra-red camera will
provide a video image of essentially uniform colour indicative of a
homogeneous temperature across the surface thereof).
[0073] For this calibration a preselected target area on the base
board where the emissivity is very close to 1 (0.95 minimum) is
used as a temperature reference to monitor the temperature (or
Infra-red radiations) of the board during the pre-heat phase (Bare
Board or Populated Board), i.e. the individual intensity levels are
manipulated with a view to obtain a uniform thermal profile across
the board which reflects the average temperature of the target
area.
[0074] In other words, once the individual parameters (e.g.
intensity levels, etc.) of each of the discrete heat sources has
been found which will provide the surface of the sample (i.e. base
board) facing the camera with a uniform temperature, these
parameters (e.g. intensity levels, etc) are placed into computer
memory and will herein be referred to as the "standard homogeneous
base board parameters".
[0075] The second step in the calibration process is to take a
thermal image of a predetermined (e.g. defect free) "electronic
circuit card", comprising an above mentioned base board on which is
included electronic components. The obtained thermal image may then
be used as a standard against which other thermal images of other
"electronic circuit card" of the same construction are to be
compared as discussed below.
[0076] For the second calibration step a standard or predetermined
(e.g. defect free) "electronic circuit board" is placed into the
system and the intensity levels of each of the individual discreet
heat (i.e. thermal energy) sources is set by the computer at the
values initially determined for the "standard homogeneous base
board parameters". The "electronic circuit board" is then heated
for a pre-determined time period and/or until an area of the
upperside of the "electronic circuit board" facing the camera
registers a pre-determined temperature. At this point, the computer
places into memory the thermal image of the side of the circuit
board facing the infra-red camera. This thermal image is then to be
used as the "standard thermal image" of a defect free "electronic
circuit board" or to be used as a member of a set of images to
build a model (statistical or otherwise). For instance, a
statistical model will need around 30 images to give a good
confidence interval.
[0077] Once the above "standard homogeneous base board parameters"
and "standard thermal image" are obtained for a given circuit board
construction testing of a production line "electronic circuit
board" may proceed as follows:
[0078] i) each individual circuit board to be tested is subjected
to a heating cycle exploiting the above mentioned "standard
homogeneous base board intensity levels" for a pre-determined time
and/or until an area of the upperside of the "electronic circuit
board" facing the infra-red camera registers a pre-determined
temperature.
[0079] ii) Once the pre-determined time has passed or the
predetermined temperature (e.g. Infra red radiation level) is
achieved, the thermal image of the inspected circuit board is
captured and compared with the "standard thermal image", i.e. the
thermal image of the tested sample is compared to that of the
"standard thermal image" in order to determine whether or not there
is a defect based on differences between the two thermal
images.
[0080] In essence the first "standard homogeneous base board
intensity levels" is used so as to be able to essentially render
the base board thermally transparent during inspection of a sample
"electronic circuit board".
[0081] In drawings which illustrate an example embodiment of the
present invention:
[0082] FIG. 1 is a schematic perspective side view of a base (i.e.
unpopulated) circuit board (i.e. no Surface Mounted Components on
either broad side thereof);
[0083] FIG. 2 is a schematic perspective side view of a populated
circuit board (i.e. Surface Mounted Components on disposed on one
board side thereof);
[0084] FIG. 3 is a block diagram of showing the operational
components of an example system;
[0085] FIG. 4 illustrates in more detail in schematic block diagram
fashion a system in accordance with the present invention;
[0086] FIG. 5 illustrates un schematic fashion an array of discrete
heat elements each element being shown in association with an
intensity value;
[0087] FIG. 6 is a graph showing a typical temperature evolution of
a circuit board from the time the board is entering in a test
enclosure. The board has to be at a temperature less than a testing
enclosure in order to be heated by the heating elements.
[0088] Referring to FIGS. 1 and 2 these figures respectively
illustrate example samples, namely an unpopulated circuit board and
a populated circuit board. The unpopulated sample and the populated
sample each having a thickness dimension 1 substantially smaller
than the length and width dimensions (3, 5) thereof. The samples
each have a first (broad) side and an opposite second (broad) side.
As may be seen from FIG. 2, the populated board is provided on one
side thereof with a number of Surface Mounted Components, one of
which is designated with the reference numeral 7. Both sides of the
populated board may however be provided with such Surface Mounted
Components. The components may for example be solder mounted.
[0089] FIG. 3 shows a simplified block diagram of components of a
thermal analysis system of the present invention. The system
comprise a computer which is suitably connected to a an I/O timing
mechanism as well as to thermal image capture hardware. The system
includes a pulsed thermal generator as well as an infra red
detector. The computer is configured (i.e. with any suitable
software) so as to be able to induce the generation of a shaped
digital pulse (via a digital to analog converter) which connected
to the thermal heater array so as to produce a correspondingly
shaped thermal field or wave. The pulse generated by the computer
may be a square wave, a saw tooth wave, a half sine wave or any
other form that it is desired or necessary so as to be able to
apply sufficient or desired thermal stimulation in a desired or
predetermined time (e.g. shortest) duration to the unit under test.
The computer will simultaneously initiate a timing circuit to
acquire data, initiate the thermal heater array in a free running
capture mode, monitor the temperature of the target array and
acquire data when triggered by an event (temperature threshold and
time-out).
[0090] The system is configured in any suitable (known) manner such
that at specific (predetermined) time duration or temperature
threshold the computer will acquire a thermal image via an infra
red detector (e.g. camera) which transfers the acquired thermal
image data (image) to the computer by a suitable digital interface.
The computer then will process the image against a previously
calculated thermal standard (CTS). The CTS has both an upper and
lower control limits and any thermal data found to be outside these
limits may be displayed on a computer monitor as for example red
(exceeding limit) or blue (exceeding lower limit). The computer is
of course configured in any suitable fashion so as to automatically
build and define a model by allowing the user to acquire images of
acceptable units device etc . . . The software may of course be
designed so as to automatically define the CTS for each pixel of
the infra red detector array. The computer may be configured in any
suitable fashion so as to archive all acquired data in a Data Base
Management System. The system may be configured so as to allow a
user to recalculate the CTS and add/remove thermal images from the
CTS.
[0091] FIG. 4 shows in a more detailed schematic block diagram form
a system in accordance with the present invention. The system may
be disposed in a housing and include means for supporting a sample
in the housing during inspection.
[0092] As may be seen the infra-red optical component comprising an
infra-red camera and associated infrared optics. The infrared
optical system is disposed so as to monitor the heat profile of the
one side of the sample to be tested.
[0093] The system also includes a thermal heat array which is
disposed on the opposite side of the sample to be tested. The
thermal heat array comprises a plurality of individually
controllable heat source elements, i.e. the intensity of the energy
being given off by each heat source element may be independently
controlled or regulated.
[0094] A heat diffuser component is disposed between the sample to
be tested and the thermal heat array. If desired or necessary this
heat diffuser component may be omitted from the system; this may
however require a more vigilante control by the computer system of
the heater elements so as to obtain the desired thermal front
wave.
[0095] As shown the example system may also include a mask element
for masking or blocking heat energy from those parts of the sample
which are not to be exposed to the energy being emitted from the
thermal heat array. If desired or necessary this mask may be
omitted from the system
[0096] As mentioned above, the thermal heat array comprises a
plurality of discrete thermal energy elements each of which may be
independently regulated so as to emit energy of a desired
intensity. Thus each element may, for example, be individually
electrically controlled with respect to the amplitude, shape and
duration of a heating duty cycle using a suitable or an appropriate
electrical driver connected to computer. The parameters for each
element are stored in the Computer (PC in FIG. 2). The thermal heat
array may for example be built up using IR LED (Infra-Red Light
Emitting Diodes) elements, Laser diode elements, miniature Quartz
or incandescent filament lamp elements, etc . . . ; in particular
the thermal heating array may be composed of IR elements. Although
the individual elements may each be separately controlled if
desired the elements may be controlled in banks groups if so
desired or necessary.
[0097] The thermal heater array may for example itself be composed
of a plurality of juxtaposed basic array modules; for example each
such basic array module of may be made up of an 8.times.8 array of
elements, i.e. an array comprising eight columns and eight rows of
heater elements, each column and row comprising eight heater
elements (for a total of 64 elements).
[0098] FIG. 5 illustrates in schematic fashion the individual heat
intensity developed by each individual heater element. For FIG. 2
the X and Y axis represent the plane of a thermal heater array, the
intersection of a column and row representing a discrete heater
(e.g. IR) element. The Z axis on the other hand represents the
instantaneous heat intensity generated by each element; each arrow
upstanding from an intersecting column and row being representative
of a heat or energy intensity. Because each element is controlled
independently by an electronic way, each element can generate a
programmable intensity given by an analog signal through a driver
amplifier. The duration of the pulse is also programmable.
[0099] The heat diffuser component is configured and disposed on
the basis that it will permit or facilitate a more uniform,
repeatable and plane (or contoured) heat wavefront than if such
diffuser was not present. The heat diffuser component may for
example take the form of a mesh or screen like element; it may for
example be comprised of a certain number of layers of mesh screens
(e.g. of silver, copper, stainless steel or any metal with low
thermal conductivity coefficient); the mesh size may be of any
suitable size keeping in mind the purpose is to obtain
thermographic images.
[0100] A mask element for masking or blocking heat energy from
those parts of the sample which are not to be exposed may if
desired or required be exploited by the system. Such a masking
component may be used to select an area where the heat has to pass
through (aperture) and an area where the heat has to be blocked
(mask). The mask element is to be of a thermally non-conductive
material; it may for example be a non conductive thermal material
such as of a Phenolic resin.
[0101] The thermal heater (e.g. IR) array module and the heat
diffuser may as desired or required be subject to being cooled down
to avoid any undesired increase in temperature outside the limits
of the preheat process. This can be done by forced air with fans
with/without TE cooler. The warm air will be evacuated outside the
enclosure.
[0102] PASS/FAIL inspection for a Component at the micro inspection
level (BGA for instance). To "see" the B GA balls (or any Flip-Chip
pads), the spatial resolution has to be big enough to discriminate
balls with defects (voids for instance) from standard "good!`balls.
The optics should accommodate a board size of 1".times.I".
[0103] The two optics can be mounted on a slide mechanism to be
remotely selected.
[0104] The inspection process may for example proceed as
follows:
[0105] First, it consists in a calibration process to determine the
operational parameters of the unit. There are two calibration
procedures:
[0106] 3.2.1. First Calibration for the Bare (Blank) Board:
[0107] BB means a Blank (or Bare) Board with no Surface Mounted
Components on either side.
[0108] A pre-selected area on this board is used as a temperature
target to monitor the Bare Board temperature,
[0109] 1. BB has to be between 20.degree. C. and 25.degree. C.,
before entering in the test enclosure.
[0110] 2. BB on test enclosure fixture.
[0111] 3. program all the heating elements at the same intensity
level.
[0112] 4. turn on all heating elements of the array.
[0113] 5. monitor the IR radiation of the target (or temperature of
the target) until it gets the Test Temperature (30.degree. C. for
instance).
[0114] 6. when Test Temperature is reached, capture and record an
image (average of 3 or more consecutive frames).
[0115] 7. Compute all the IR radiations of the elements of the
array and adjust their electrical driver to the lowest value. This
will reduce all the other IR elements intensity. This will enable
to get an uniform intensity wave passing through the board material
and to compensate for the non uniformity of the IR array and the
PCB material.
[0116] Second Calibration for the Populated Board Called CCA
(Circuit Card Assembly); Board with Surface Mounted Components on
at Least One (Board) Side Thereof
[0117] 1. Populated Board (CCA) has to be between 20.degree. C. and
25.degree. C., before entering in the test enclosure.
[0118] 2. CCA on test enclosure fixture.
[0119] 3. Program all the heating elements at the previously
computed value, stored in the Computer.
[0120] 4. Turn on all heating elements of the array.
[0121] 5. Monitor the IR, radiation of the target (or temperature
of the target) until it gets the Test Temperature (30.degree. C.
our example),
[0122] 6. When Test Temperature is reached, capture and record the
image (average of 3 or more consecutive frames),
[0123] 7. Repeat all of the above process,
[0124] 8. When sufficient number of CCA images have been captured
(around 30 boards), the process will in the operational phase.
[0125] 3.2.2. Operational Phase.
[0126] From the previous boards, the PC will compute the
statistical or typical model to find the two limits for a pixel of
the image. For process details please see U.S. Pat. Nos. 5,803,303
and 5,294,198 (Jerry Schlagheck), the entire contents of which are
incorporate herein by reference. The building of the models and the
Pass/Fail are explained in these patents.
[0127] 4. Temperature Profile Over the Time.
[0128] This graph of FIG. 6 illustrates a typical temperature/time
evolution of the board from the time the board is entering in a
test enclosure, namely:
[0129] t1 is time install on inspection fixture;
[0130] t2 is time Start target monitoring;
[0131] t3 is time heat array placed ON; Continue target
monitoring;
[0132] Tt is reached at Time t4; IR array is turned OFF; Capture
Reference images;
[0133] t5 is time start Electrical Stimulation;
[0134] t6 is time Stop Electrical Stimulation; Capture Powered
images;
[0135] For the graph in FIG. 6:
[0136] Ti: Initial Temperature of the board (between 20.degree. C.
and 25.degree. C.)
[0137] Tt.,Test Temperature at which the Reference image is
captured (30.degree. C. in our case)
[0138] TfFinal Temperature of the board after Electrical
Stimulation.
[0139] delay 1: Time to initiate the process for heating the
board--(around 20 msec)
[0140] heat up: Time the board will reach the Test temperature Tt
(around 2 to 5 sec)
[0141] delay 2: Time to initiate the electrical stimulation signals
sequence (around 20 mscc).
[0142] Timing sequence, Time of the electrical stimulation sequence
(between 5 and 20 sec)
[0143] 2.6. Infra-Red Optics.
[0144] Depending of the device to be screened, the IR optics has to
be changed to get the maximum resolution in the selected Field Of
View. PASS/FAIL inspection for a CCA (at the board level). To "see"
the devices at the macro inspection level (CCA Infra-Red mode), the
optics should accommodate a board size of 14".times.14"
* * * * *