Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CONDUCTIVE INK FOR FLASH LAMP ARRAY CIRCUIT
CROS'S'REFERENCE TO 'REL'ATED' APPLICATIONS
In Canadian Patent Application Serial No. 394,651,
filed January 21, 1982 in the name of M.E. Suster,
there is described and claimed a modified conductive
carbon ink for a flash lamp array circuit containing a
particulated electrically conductive material such as
graphite or metal flakes, metal coated glass spheres,
and the like. Increased electrical conductivity is
obtained in this manner which improves flashability
and electrostatic flash out protection for the associated
flash lamps. The preferred embodiments further include
use of the same modified conductive ink to serve as
integral fuse elements in the circuit pattern by
narrowing the width of said circuit pattern at the
fuse locations and said preferred embodiments can
further locate both radiation switches and fuse elements
adjacent to the flash lamps for simultaneous actuation
when the adjoining flash lamp is flashed. The present
application represents a still further improvement in
the modified carbon ink composition with respect to
operation of the fuse elements in this type flash lamp
array circuit.
BACKGROUND':OF TH'E INVENTION
Addition of a particulated electrically conductive
material such as graphite or metal flakes, metal coated glass
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spheres, and the like to a conductive carbon ink as disclosed
in the cross-referenced patent application filed concurrently
herewith provides a desirable increase in electrical
conductivity to improve the operational reliability of a
flash lamp array circuit pattern using this type ink.
More particularly, such additives reduce the incidence
of lamp failures to ~lash by a considerable degree while
further enabling the modified inks to serve as integral
fuse elements in the circuit pattern. On the other hand,
there still exists a need to further improve the reliability
of fuse operation beyond that already obtained since
increasingly lower intensity flash lamps are now being
used which creates a greater likelihood of a short circuit
condition being experienced. It is a primary object of the
present invention, therefore, to provide a modified carbon
ink demonstxating still greater operational reliability
when used as integral fuse elements in the circuit pattern.
Another important object is to provide a modified carbon
ink exhibiting improved electrical resistance and dielectric
breakdown voltage characteristics after thermal decomposition
when serving as the fuse means in a flash lamp array circuit.
Such operative characteristics for the fuse means in this
type circuit helps prevent application of a successive
high voltage firing pulse to an already fla~hed lamp.
SUMMARY OF THE INVENTION
The foregoing objectives along with stiLl other
important ben~fits are achieved in accordance with the
present invention by modification of available carbon
inks contai~ing at least 25% by weight of powdered carbon
in the dry solid coating to further include a particulated
electrically conductive radiation-absorbing material.
More particularly, the presently modified conductive ink
is a mixture containing at least 25% in the dry solid
coating of powdered carbon and an organic polymer binder
with a particulatsd electrically conductive radiation-absorbing
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material imparting increased electrical conductivity before
thermal decomposition together with increased residual
electrical resistance after being thermally decomposed.
More particularly, the presently improved photoflash array
smploys a plurality of high voltage type flash lamps connected
to a lamp firing circuit pattern deposited on a circuit
board with radiation-sensitive switches and fuse elements
being connected to said circuit pattern for sequential
firing of said flash lamps, said fuse elements being
provided by narrowing the width of the circuit pattern
at the fuse locations and undergoing thermal decomposition
when activated with radiation, and wherein said improvement
comprises a conductive ink for said circuit pattern and
fuse elements which is a mixture containing at least 25~
by weight in the dry solid coating of powdered carbon with
a particulated electrically conductive radiation-absorbing
material and an organic polymer binder, said conductive
ink exhibiting increased electrical conductivity at said
fuse locations before the thermal decomposition together with
increased residual electrical resistance after thermal
decomposition. In one preferred embodiment, the radiation
switcnes and fuse elements are located adjacent said flash
lamps for simultaneous activation of an adjoining switching
fuse element. A different preferred embodiment electrically
connects the flash lamps in branch circuits having a radiation
switch connected between one side of each pair of successively
connected flash lamps and a radiation-sensitive ~use element
connected between the remaining side of each pair of
successively connected flash lamps, and wherein said fuse
elements are further electrically connected together in a
series circuit combination to increase the dielectric
breakdown voltage of said combination upon successive
actuation of the fuse elements. -
Suitable conductive inks providing improved
operation as above generally indicated can be prepared by
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proper modification of available commercial carbon inks.One commercially available ink suitable for modification
in accordance with the present invention is a product sold
by the Advance Process Supply Company under the trade name
designation "EL-796" which i5 reported to contain percentages
by weight 22.2% lamp black, 20~ organic polymer mixture,
with the remainder being various organic liquid vehicles.
Customary removal of the liquid vehicles from said ink
composition as well as other commercial carbon inks
produces a dry solid coating containing at least 25P6 by
weight of the powdered càrbon having a considerably higher
electrical resistance (génerally 30 or 40 times or more)
than previously employed silver-containing conductive inks.
Suitable particulated electrically conductive radiation-
absorbing materials for addition to said commercialcarbon inks are finely divided conductive solids
exhibiting a bulk resistivity characteristic less than
approximately 200 ohm-centimeters and which can be wet~ed
by the various organic liquid vehicles employed in said
commercial carbon inks by conventional milling in order
to increase the electrical conductivity of the dry solid
coating. Moreover, the present additives further impart
increased radiation absorption of light/heat to the dry
solid coating which does not occur with the particulated
électrically conductive additives disclosed in the afore-
mentioned concurrently filed application possibly by xeason
of optical reflection and larger particle size of said
former addîtives.
BRIEF DESCRIPTION OF THE DRA~I~GS
,
FIG. 1 is a perspective view of a flash array
circuit board in accordance with a preferred embodiment
of the invention;
FIG. 2 is an electrical schematic diagram
illustrating the circuit path for one group of four flash
lamps being sequentially fired by the circuit board
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configuration in FIG. l; and
FIG. 3 is a perspective view of the different
flash array circuit board in accordance with another
preferred em~odiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
-
In the preferred circuit board embodiment depicted
in FIG. 1, both radiation-sensitive switches and radiation-
sensitive fuse elements are deposited as part of the circuit
pattern on the circuit board adjacent the flash lamp
loca~ions for simul~aneous actuation of each adjoining
switch and fuse element by radiation being emi-tted from
an adjacent flash lamp. Accordingly, a lamp firing circuit
pattern 10 is shown having been deposited on a circuit board
member 11 preferably in the form of a thermoplastic organic
polymer material and with said circuit pattern being formed
with the modified ink composition according to the present
invention to urther include integral fuse elements of the
same modified conductive ink. The circuit board member 11
also includes connector tabs 12 and 14 located at each
end for insertion of said circuit board member into an
associated camera socket (not shown). The camera socket
contacts for conductor line 16, 18 and 20, of the lamp
firing circuit pattern to connect four flash lamps in
parallel between conductive lines 16 and 18 when connector
tab 12 has been inserted in the camera socket. Corres~ondingly,
the second group of four lamps is connected between conductor
lines 18 and 20 when connector tab 14 has been inserted
in the camera socket. While an entire illustrated circuit
board is shown, there is need to discuss only a single group
of four flash lamps since the operation o the second group
of four flash~lamps is essentially the mirror image of
the first lamp group. Conductor line 16 includes a
serially connected arrangement of radiation switches 22
to prevent flash lamps in said group from all being fired
together upon release of the camera shutter~ As can be
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noted, the switches 22 are each arranged in the region of
the flash lamp termination 24 so that heat and light released
when the flash lamp is fired operates to convert the
respective switch rom a non-conductive to an electrically-
conductive state, thus establishing a current path in thenext lamp to be flashed. Accordingly, when the particular
flash lamp in the circuit is to be flashed, then the
adjacent radiation switch is actuated providing a current
path to the next lamp to be flashed. Each of the radiation
switches is serially connecte~ between the branch circuits
connecting lamps in a parallel circuit arrangement to be
more fully described. Each of said radiation switches
employ a material exhibiting an open circuit or high
resistance condition and with said resistance thereafter
becoming zero or a low value when said material absorbs radiation
and/or heat from the adjoining flash lamp. Individual fuse
elements 26 are serially connected together in conductive
line 18 as well as being located adjacent to the flash
lamp terminations 24 so as also to be actuated by the
heat and light released when the adjacent fl~sh lamp is
flashed. As can be noted, each of said integral fuse
elements simply comprises a more narrow width of the
circuit pattern at the fuse location than the remaining
width o~ said circuit pa~tern elsewhere. When the particular
flash lamps adjacent to a given fuse element is flashed,
the radiation and/or heat created thereby is absorbed by
the circuit pattern at the fuse locations whereupon the
more narrow fuse element portions of said circuit pattern
become sufficiently thermally decomposed to disrupt the
electrical connection to the already fired flash lamp.
A more detailed description of the sequential
firing operation for the circuitry of the four-lamp group
in the above described circuit board configuration is
provided in connection with the schematic drawing shown
in FIG. 2. Accordingly, in FIG. 2 there is shown a
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plurality of flash lamps 24 electrically connected in
branch circuits to assure the branch circuit of each
lamp will become an open circuit upon flashing of the
lamp in that circuit. The desired mode of operation is
carried out starting with the topmost circuit when the
lamp in said circuit is flashed and causes fuse element
26 in the samR branch circuit to physically interrupt
the circuit path to said lamp while simultaneously closing
the circuit path and flash lamp in the adjacent branch
circuit by actuating the radiation-sensitive switch 22
which is serially connected between branch circuits to
the conductive state. This cooperative action is repeated
between successive branch circuits until all four lamps
in the group have been fired from simultaneous actuation
of adjoining switching fuse elements with radiation being
emitted from an adjacent flash lamp. By further serially
connecting all fuse elements 26 between said branch
circuits, the likelihood of developing a short circuit
condition with an already flashed lamp is understandably
reduced. Thus, when the firing pulse is applied to the
last branch circuit in a sequence, it becomes necessary to
overcome the dielectric breakdown voltage in the previously
opened fuse elements for short circuiting of the already
flashed lamps. The likelihood of developing a short
circuit condition in the topmost already flashed lamp
would be theoretically least in the present circuit
configuration by reason of being electrically isolated
by all three opened fuse elements.
To demonstrate the improved operational
reliability a~tributable to the presently modified
conductive ink, a comparative test evaluation was carried
out using the same type firing circuit configuration above
described. Electrical resistivity measurements were first
made at the tab areas of circuit board members prepared
with the EL-796 unmodified ink above disclosed for
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comparison with said ink when modified with approximately
15~ by weight graphite flakes as disclosed in the afore-
mentioned concurrently filed application as well as with
the modification of said commercial ink in accordance
with the present invention which contained approximately
5% by weigh~ added conductive carbon. Said resistivity
measurements provide a 15.1 ohms per square per mil
thickness for the unmodified carbon ink, 5.0 ohms per
square per mil thickness for the 15% graphite flake
addition, and 11.5 ohms per square per mil thickness for
the presently modified ink. Customary dielectric
breakdown voltage measurements were also conducted
upon each circuit board member after the fuse elements
had been actuated to provide an open circuit path by
lS thermal decomposition. When tested with a 2150 volts
piezoelectric pulse source, the converted fuse elemen~s
of the unmodified commercial ink exhibited an average
2089 volts breakdown whereas a comparative 1792 volts
breakdown was exhibited for the converted fuse elements
containing 15% graphite flakes while the converted fuse
elements using the presently modified ink withstood the
entire applied voltage. It will be apparent from all
of the foregoing measurements that while the presently
modified conductive ink exhibits increased electrical
conductivity at the fuse locations before thermal
decomposition as compared with the unmodified ink material,
there is also obtained increased residual electrical
resistance and dielectric standoff capability after
thermal decomposition which is superior to that obtained
with the previously modified ink materi~l.
In FIG. 3 there is shown a circuit board member
30 of the same general configuration already described
employing a circuit board pattern 32 of ~he conductive
carbon ink which is made wider in a particular manner
3s to provide greater protection of these flash lamps from
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accidental electrostatic flash out. More particularly,
a common electrical grounding circuit 34 extends from
one tab of the circuit ~oard member to the other ta~ and
i5 made wider than each of the conductive runs 36 and
38 which apply to firing pulses sequentially when the
flash lamps are connected thereto. As can be further
noted, the carbon ink material now occupies most of the
connector tab areas 40 and 42 which decreases electrical
resistance so that an electrostatic charge applied to
these terminals will more readily be carried to further
operatively associated electrical grounding means ~not
shown) instead of reaching the lamps to cause accidental
flashing. The wider common circuit run 34 also per~orms
an additional advantageous function acting as a supplemental
electrostatic shield behind the flash lamps which further
reduces the likelihood of accidental flashing of these
lamps. Parallel connected fuse elements 44 are provided
in the circuit pattern and thermally decompose in the
same manner already above described to prevent electrical
shorting by a lamp which has already been flashed. To
further demonstrate the improved operational reliability
attributable to the presently dified conductive ink,
another comparative test evaluation was carried out using
the above described firing circuit configuration. The
test evaluation compared the incidence of lamp failures
to flash in the four-lamp group using the above specified
unmodified carbon ink as compared with modifications to
said commercial conductive ink further con~aining either
approximately 15 weight percent graphite flakes or 5%
conductive carbon based on the weight of the dry solid
coating. In carrying out said test evaluation, actual
short circuiting of each already flashed lamp in the four-
lamp group was employed to create a more severe operational
test of the fuse elements in a circuit pattern. Accordingly,
the testing of 60 lamp groups under said conditions for each
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of the conductive inks being compared resulted in 0.8%
of the lamps nct flashing with the unmodified carbon
ink while 4.6 of the lamps did not flash with the 15~
graphite flakes modification and all lamps flashed for
S the present conductive ink. It will be apparent from
the said foregoing test evaluations that the presently
modified carbon ink provides still greater operational
reliability in the circuit pattern.
While preferred embodiments of the invention
have been shown and described, various other embodiments
and modifications thereto will become apparent to the
person skilled in the axt. It is thereby intended to
limit the present invention only by the scope of the
following claims.
