Note: Descriptions are shown in the official language in which they were submitted.
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CONDUCTIVE INK FOR FLASH LAMP ARRAY CIRCUIT
CROSS REFERENCE_TO ~ELATED APPLICATIONS
In Canadian Patent Appln. Serial No. 365,805
filed November 28, 1980, in the name of E.J. Collins and
assigned to the present assignee, there is described and
claimed a photoflash lamp array circuit board including
radiation-sensitive fuse elements provided by a circuit
pattern utilizing an organic resin matrix having particulated
electrically conductive material and a radiation-absorbing
material dispersed therein. The fuse elements are formed
~ lQ by narrowing the width of the circuit pattern at fuse
; locations while further reducing the thickness of the
underlying dielectric substrate of the circuit board
member relative to the remaining thickness of said
dielectric substrate.
Another Canadian Patent Appln. Serial No~ 391,068,
filed November 27, 1981, in the names of M.E. Suster and
V.H. ~eber, and which is also assigned to the present
assignee, describes a flash lamp array having a printed
circuit which is formed with a conductive ink utilizing
carbon particles bonded to the circuit board with an
organic polymer binder. Electrostatic flash out protection
of the associated flash Iamps is provided in said patent
application with a particular grounding circuit to help
offset the high electrical resistance characteristic of
this type conductive ink.
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Still another Canadian Patent Appln. Ser. NOA
391,058, filed November 27, 1981, in the names of E.J.
Collins, M.E. Suster, and V.H. Weber, and also
assigned to the present assignee, discloses a flash
lamp array having a printed circuit formed with the
same type high resistance characteristic conductive ink
but which employs wider circuit path means to help solve
the problem of adequately pro-tecting the associated
lamps from accidental flashing due to electrostatic
charges when the circuitry encounters various charged
objects, such as persons and the like.
BACKGROUND OF THE~INVENTION
The present inven-tion is in the field of photoflash
lamp arrays, such as the FlipFlash type of array. In all of
-the above referenced patent applications, there is generally
disclosed a circuit board member having a plurality of high
voltage flash lamps connected to a lamp firing circuit pattern
deposited on the circuit board member and which further
includes radiation-sensitive switches being connected in
said circuit pattern for sequential firing of the flash
lamps. Fuse elements are commonly included in the circuit
pattern with the lower intensity flash lamps now being
used for cost and energy saving considerations to help
produce a more reliable means to interrupt the circuit path
with the lesser amount of radiation being available from
such type flash lamps. A more recent introduction of lower
cost conductive inks utilizing carbon particles with an
organic polymer binder to replace the conductive ink generally
employing silver particulate has now created a need to modify
the circuit pattern in various ways to insure that the
associated flash lamps still remain adequately pro-tected
from accidental electrostatic flash out. It would be
desirable, however, to provide said protection in the lower
cost conduc-tive ink itself so that modification of the
circuit pattern to provide additional electrical grounding
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is less necessary.
SUMMARY OF THE lNV~NTION
m e principal objects of the present invention
are to provide an improved photoflash array utilizing a
modified conductive ink of powdered carbon which exhibits
greater el~ctrical conductivity togPther with increased
electrostatic *lash out protection of the associated flash
lamps~ The present modified conductive ink is a mixture
containing at least 25% in said mixture of the powdered
carbon in the liquid ink with particulated electrically
conducti~e material and an organic polymer binder. More
particularly, the present improved photoflash array employs
a plurality of high voltage type flash lamps connected to
a lamp firing circuit pattern deposited on the circuit
board member with radiation-sensitive switches being
connected in said circuit pattern for sequential firing
of said flash lamps, wherein the improvement comprises
using said modified conductive ink for the circuit pattern.
Since the presently modified conductive ink further demonstrates
operational characteristics suitable for use as the fuse
elements in this~type *ircuit application, it is also possible
to have said modified conductive ink serve both functions
in the same embodiment. In said preferred embodiment,
the width of the circuit pattern at the fuse locations is
narr~wed for reliable ~hermal decomposition thereat when
actuated by heat and radiation emitted from an adjoinins
flash lamp when flashed. A still further preferred
embodiment utilizing the present conductive ink to serve
in said dual capacity locates both radiation switches and
the fuse elements adjacent said flash lamps for simultaneous
actuation of both circuit components when the adjoining
1ash lamp is flashed. Interruption of the circui~ path
is obtained to tha activating flash lamp in this manner
while ~he cooperating radiation switch provides an
electrical path to the next unflashed lamp in the customary
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manner. Since the above referenced patent applications
all further contain a detailed description of the manner
in which the flash lamps are sequentia~ly flashed in a
predetermined order by such an arrangement of radiation
actuated switches and fuse elements disposed in the
circuit pattern, it is only further necessary in the
present application to describe the nature of the
improvements obtained in the m~dified circuit operation.
A suitable conductive ink providing improved
operation as above generally ~ndicated can be prepared by
proper modification o~ available commercial carbon inks.
One commercially available in~ suitable for modification
in accordance with the present invention is a product sola
by the Advance Process Supply Company under the trade name
designation "EL-796" which is reported to contain in
percentages by weight 22.2% lamp blac~, 20% organic
polymer binder mixture, with the remainder being various
organic liquid vehicles. Customary remo~al of the liquid
vehicles from said ink compositions as well as other
commercial carbon inks produces a dry solid coating
containing at least 25~ by weight of the powdered carbon
hav~ng a considerably higher electrical resistance (generally
30 or 40 times or more) than previously employed silver-
containing conductive inks. Said higher resistance char-
acteristic has not only been found heretofore to requireadditional circuit means for adequate protection of the
associated f lash lamps from acciden~al electrostatic
flash out but has now ~een discovered to adversely
influence flashing o flash lamps when the customary high
voltage pulse is applied. With respect to- the fuse
operation, it has now been discovered that the fuse
elements constructed from available carbon inks exhibit
a considerable resistive characteristic interfering with
reliable conductivity of the circuit path before said fuse
elements are actuated. All of the foregoing problems wi~h
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commercial carbon inks are substantially ameliorated in
accordance with the pre~ent invention by incorporating
up to approximately 50~ by weight in t7ne dry soli
coating of a particulated electrically conductive 7naterial.
The particulated electrically conductive material proYiding
improved electrical conducti~rity in said circuit pattern
can be selected from a partic7llatPd electrically conductive
metal a~d/or a particulated electrically conductive metal
containing material which can further contain up to
approximately 15% by weight of said particulated
electrically conducti~e material in flake form with an
aspect ratio of diameter to thickness greater ~han 20.
Graphite and metal flakes as well as metal coated glass
spheres can thereby be added to the commercial carbon
ink~ to produce improved electrostatic flash out protection
and flashability of the assoçiated flash lamps.
DESCRIPTION OF THE DRAWINGS
FIG~ 1 is a perspective view of a flash array
circuit board in accordance with a preferred embodiment of
the invention; and
FIG. 2 is a perspective view of a dif~erent
flash array circuit ~oard in accordance with another
preferred embodiment of this invention.
DESCRIP`rION OF THE PREFERRED EMBODIMENTS
.
In the preferred circuit board embodiment depicted
in FIG. 1, ther~ is depicted a circuit configuration
wherein the lamp firing circuit pattern includes an
electrical ground or "common" terminal connecting one
lead-in wire of each associated flash lamp. The remaining
lead~in wire of each flash lamp in this circuit pattern
- is electrically connected to a conductor line interco~necting
a four-lamp group in the flash lamp array for application
of the high voltage firing pulses to individual lamps in
the group. F7lnctionally, such interconnection o~ the
individual lamps in each four~lamp group produces a parallel
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cixcuit connection of said flash lamps for sequential
firing in a predetermined order when the high voltage
firing pulses are applied. Accordingly, a lamp firing
circuit pattern 10 is shown having been deposited on a circuit
board member 11 preferably in the form of thermoplastic
organic polymer material and with said circuit pattern
being formed with the modified ink composition of the
present invention, The circuit board member 11 also
includes connector tabs 12 and 14 located at each end
for insextion of said circuit board member into an
associated camera socket (not shown). The camera socket
has contacts for conductor lines 16, 18 and 20 of the
lamp firing circuit pattern to connect four flash lamp~
in parallel between conductive line 16 and the common ground
line 20 when connector tab 12 has been inserted in the
camera socket, Correspondingly, the second group of four
lamps is connected between conductor,line 18 and said
common yround,line 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 of
the second group of ~our flash lamps is essentially the
mirxor image of the first lamp group. Conductor line 16
includes a serially ~onnected arrangement of radiation
switches 22 to prevent the flash lamps of the group from
all be~ng fired together on release of the camera shutter.
Functionally, each of said radiation switches is serially
connected between ~he parallel connected lamp branch
circuits and the switches employ a material exhibiting
an open d r~uit or high resistance condition before actuation
which converts to a low resistance by absorptio.~ of radiation
and/or heat from an adjoining flash lamp when flashed. As
can be noted, said radiation switches are each located adjacent
to a flash lamp ~ermination 24 so that the light and heat
35 released when the lamp is flashed operates to convert ~he
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adjacent switch to an electrically conductive state
thereby establishing a current path to the next lamp to
be flashed. Assuming that none of the four lamps in
the upper four~lamp group of said circuit pattern have
5 been flashed, upon occurrence of the first firing pulse
across the conductor lines 16 and 20, this pulse is appliea
to the lead-in wires o~ the ~irst connected flash lamp
and fla~hes this lamp to become an open circuit between
its lead-in wires. Actuation of the radiation-sensitive
switch located adjacent said lamp at this time provides
a low resistance circuit path to the lead-in wires of
the second lamp in the four-lamp sequence thereby
connecting the second lamp to the circuit board terminals
for flashing when the next firing pulse is applied.
Successive flashing of the remaining lamps in the four-
lamp group facilitated by closing of the cooperating
radiation switches completes the desired sequential mode
of operation.
To demanstrate the improved operational reliability
attributable to the presently modified conductive ink, a
comparative test evaluation was carried out using the same
type firing circuit configuration above described. The
test evaluation compared the incidence of lamp failure
to ~lash in the four-lamp group using the above specified
unmodified carbon ink as compared with said commercial
conductive ink further containing approximately 15 weight
percent graphite flakes based on the weight of the liquid
ink coating. Of the 60 lamp groups tested with the
unmodified commercial ink composition, 4.6% of the lamps
did not flash when actuated with the customary high
voltage firing pulses. Operating reliability increased
wi~h the m~dified composition when only 0.4~% of the
lamps did not fire in the proper sequence~ Comparative
dielectric breakdown voltage measurements carried out
during said lamp flashability test further confirmed ~he
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nature o said improvement in that an average 1,523 volts
dielectric breakdown voltage was measured for the flash
lamp groups using the unmodified conductive ink in
contrast to an average 1,036 volts dielectric breakdown
voltage for the present conductive ink.
In FIG. 2 there is shown a circuit board member
30 having the same general configuration already described
but ~urther including fuse elements and employing a
circuit board pattern 32 of the conductive carbon ink
which is made wider in a particular manner to provide
greater protection of the associated flash lamp~ from
accidental electrostatic 1ash out. More particulariy,
a comm~n electrical grounding circuit run 34 extends from
ane end of the circuit board member to the other end and
is made wider than each of ~he conductive runs 36 and 38
which apply the firing pulses sequentially when the flash
lamps are connected thereto. As can be further noted,
the carbon i~k 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.
miS wider common circuit run 34 also permits a more
conducti~e r~n in each firing circuit for improved 1ash-
ability. Integral fuse elements 44 are provided in
~he circuit patternt as distinct from the previously
described circuit embodiment in FIG. l, and with said
fuse elements simply constituting a narrowing of the
circuit pattern at the fuse locations for reliable thermal
decomposition thereat when actuated by heat and rad~ation
emitted from an adjoining flash lamp when 1ashed. Said
indi~idual fuse elements 44 are parallel connected in
the common electrical grounding circuit run 34 as well
as being located approximate to the flash lamp terminations
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46 so as to also be activated by the heat and light
released when the adjacent flash lamp is flashed.
Fur~her,location of radiation-sensitive switch elements
48 are adjacent to said flash lamps. Simultaneous
activation of both swi~ch and fuse elements when the
adjoining flash lamp i5 flashed provides interruption
of the circuit path to the activating flash lamp while
the cooperating radiation switch furnishes an electrical
path to the next unflashed lamp in the customary manner.
Fuse operation entails absorption of radiation and/or
heat by the circuit pattern at the fuse location whereupon
the more narrow fuse element portion of said circuit
pattern becomes sufficiently thermally decomposed to
disrupt cr impede the electrical connection to the
already fired flash lamp. Comparative evaluation of
the electrostatic flash out protection a~orded in
this circuit configuration with the conductive carbon
ink above specifically disclosed as compared with the
also above disclosed modification thereto containing
approximately 26% graphite flakes based on the weight
of the ~olid coating demonstrated considerable
improvement attributable to said modification. Specifically,
5.6% of the lamps tested using the unmodified commercial
in~ were found to experience electrostatic flash out as
compared with only .6% flash out for the improved ink.
While preferred embodiments of the invention
.:
have been s~own and described, various other embodiments
and modifications thereto will become apparent to persons
sXilled in the art. It is thereby intended to limit ~he
present invention only by the scope of the following claims.
