Note: Descriptions are shown in the official language in which they were submitted.
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B~CE~GROUND OF TIIE INVENTION
Field of the Invention
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This invention relates generally to an apparatus
for applying adhesive resin on a surface, and, more particularly,
is directed to an apparatus for applying adhesive resin in a
pattern on a circuit board, for example, for use in temporarîly
holding chip-type circuit ele~ents or parts on the circuit
board.
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~escription of the Prior Art
Printed circuit boards are used for mounting parts
to be included in a desired circuit. Such parts are normally
temporarily affixed to holes or ?ins in the circuit board by
their wire leadsJ and a subsequent soldering operation per-
manently af~ixes the parts to the circuit board.
`~Chip-type circuit parts are used to increase the
density of the circuit parts and to permit reduction of the
size of the printed circuit board. Chip-ty e circuit parts
are generally cylindrical objects having cap-like contact
pads on their ends rather than wire leads. Accordingly, chip-
type circuit parts cannot be temporarily attached to the prin-
ted circuit board by wire leads in the normal manner prior to
soldering.
Adhesive resin may be used for temporarily attaching
chip-type parts to a printed circuit board. The adhesive resin
is applied to the printed circuit board in a predetermined pat-
tern corresponding to the positions where chip-~ype parts are
to be mounted. The chip-type parts are then temporarily
attached by the adhesive resin to be printed circuit board with
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their contact pads aligned with metallic conductors previously
printed on the substrate. The printed circuit board with the
attached chip-~ype and other parts is soldered in a conventional
soldering operation. In this way, the contact pads of the
chip-type parts are soldered to the printed circuit board for
permanent mechanical and electrical attachment thereto.
A preferred method of producing the predetennined
pattern of adhesive resin includes a silk screening operation
in which a fabric screen formed of silk, organdy but preferably
of polyester, and having a pattern~of pervious printing areas
and impervious non-printing areas formed thereon, is stretched
across a supporting frame and is disposed in confronting or
face to face relation to the printed circuit board. The adhe-
sive resin is squeezed through the pervious printing areas
onto the surface of the printed circuit board to duplica~e
the pattern thereon. The supporting frame is then an~ularly
displaced ~way From the printed circuit board. When the sup-
porting frame is thus displaced, resin threads bridging the
space between the screen and the printed circuit board are ~
stretched and laterally inclined until they break and fall on
the printed circuit board adjacent the desired resin-receiving
areas. Portions of the printed circuit board which are not
intended to receive resin, such as the conductive patterns,
may be covered by the collapsed resin threads. When portions
of the conductive patterns which are provided for solder attach-
ment of the contact pads of the chip-type parts become covered
with the resin threads, a good solder joint cannot be made.
The thicker the layer of adhesive resin deposited on the cir-
cuit board, the more difficulty is encountered by covera~e with
resin threads outside the desired resin-receiving areas~
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OBJECTS AND SUM?~ARY OF THE INVEl`ITIOM
_
An object of this invention is to provide an appara-
tus for applying adhesive resin in a predetermined pattern to
a circuit board in which the adhesive resin is limited to the
?redetermined pattern.
Another object of this invention is to provide an
apparatus for applying a predetermined pattern of adhesive
resin to a circuit board, and which avoids the formation of
resin threads between the circuit board and the screen which
fall to the circuit board outside the predetermined pattern.
A further object of this invention is to provide a
method for applying a predetermined pattern of adhesive resin
to a circuit board and which avoids the deposit of resin on
portions of the circuit board not :included within the predeter-
mined pattern.
`According to an aspect o~ the invention, an apparatus
for ap~lying a pattern of adhesive resin on a surface fixed in
a predetermined position comprises a screen having pervious
printing areas in the pattern, means for positioning the screen
parallel to the surface, means for squeezing the adhesive resin
through the printing areas onto the surface, and means for hold-
ing the screen parallel to and spaced a predetermined distance
from the surface for a predetermined time after actuation of
the means for squeezing.
According to a feature of the invention, a method
of applying a pattern of adhesive resin on a substantially
planar surface by means of a screen stretched across a frame
and having pervious printing areas in the pattern comprises
scraping the adhesive resin over the screen to scrape the adhe-
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sive resin into the pervious printing areas, holding the screen
parallel to and spaced a predetermined distance from the sur-
~: face, contacting the screen with a squeegee with sufficientforce to deflect the screen into contact with the surfac~,
translating the squeegee across the screen whereby the adhe-
sivP resip in the pervious printing areas is adhered ~o the
surface, moving the squeegee away from the screen to permit
the screen to resume its undeflected condition parallel to
and spaced the predetermined distance from the surface, and
continui~ng to hold the screen parallel to and spaced the
predetermined distance from the surface until resin threads
bridging the space between the surface and the screen brea~
and fall~back into respective printed areas on the surface.
More particularly, there ~s p:rovided:
A method of applying a desired pattern of an ad-
hesive resin on a substantially horizolltal planar surface using
a tensioned screen having p~svi~us printing areas arranged in
: said pattern compris~ng;
scraping said adhesive resin over said screen to scrape
amounts o~ said adhesi~e xesin into said pervious printing
areas;
holding said screen in an operative position parallel
to and spaced a predetermined distance above said substantially
horizontal surface;
pressing a squeezing blade downwardly against the
operatively positioned screen with ~u~ficient force to deflect
a portion of said ten~ioned screen engaged by said blade down-
wardly into contact with said surface;
translating the down~ardly;pressed squeezing blade
30 acrosS said screen whereby said amounts of adhesive resin in
said perviou~ printin~ areas are squeezed therefrom and adherPd
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to underlying respective areas of ~aid surface;
moving ~aid blade away from the operatively positioned
screen to permi~ the tension of the latter to cause said screen
to resume its undeflected condition parallel to and spaced up-
wardly said predetermined distance from said eurface with threads
of said adhesive resin initially bridging said distance between
said printing areas of the screen and said underlying areas of
the surface;
continuin~ to hold said screen in said operative po
sition parallel to and spaced said predetermined distance from
aid surface as said resin threads break and fall back substan~
tially vertically into the respecti~e ones of said underlying
areas; and
removing said screen from said operative position only
after all of said resin threads have broken and fallen back into
said respective underlying areas for ensuring that the margins
of the latter are sharply defined.
There is also provided.
~ Apparatus for applying a desirea pattern of adhesive
:~: 20 resin to a substantially horizontal plane surface comprising:
a screen having pervious printing areas in said pat- :
tern;
: a frame across which said screen is stretched;
means for pivoting said frame between first and second
positions;
said first position being effective to normally dis
pose said screen parallel to, and spaced from, said surface;
said second position being effective to dispose said
screen a substantial distance away from said surface;
a scraping blade;
means for contacting said scraping blade with said
screen across a first dimension of the latter;
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means for translating said scxaping blade in contact
with said screen acro-~s a second dimensi~n of said screen where-
by an amount of said adhesive resin is scraped into said per-
vious printing areas;
a squeezing blade;
means, effective when said frame is in said first
~` position~ for pressing said squeezing blade against said screenacross a first dimension of said screen with sufficient force
to deflect a portion o said screen contacted by said squeezing
blade in~o contact with said surface;
means for translating said squeezing bla~e in contact
with said screen across a second dimension of said screen whereby
said adhesive resin in said pervious printing areas i.s squeezed
from the latter and deposited in respective areas on said surface; :~
means or moving said squeezing blade out of contact
with said screen while said frame remains in said first position;
and ~:
mean~ for holding said frame in said first position
for a sufficient time after actuation of said means for moving
the squeezing blade to permit resin threads bridging between
said screen and the deposited areas on said surface to bxeak and ~-
fall back into the respective deposited areas. ::
There Is also provided:
A method of applyi~g a desired pattern of adhesive
re~in on a su~stantiall~ horizontal planar surface using a screen
having perYious printing areas arranged in said pattern compris-
i~g:
scraping said adhesive resin over said screen to scrape
said adhesive resin înto said pervious printing areas;
holding said screen parallel to and spaced a predeter-
mined distance from said surface;
pre~sin~ a squeezin~ blade again t said screen with
sufficient force to deflect a portion of said screen engaged
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by said blade into contact with said sur~ace;
translating said blade across said scxeen whereby
said adhesiv~ resin in said pervious printin~ areas is squeezed
therefrom and adhered to underlying respective areas o said
surface;
moving said blade away from said screen to permit said
~ screen to resume its undeflected condition parallel to and
: spaced said predetermined distance from said surface; and
continuing to hold said screen parallel to and spaced :
said predetermlned distance from said surface until resin
threads bridging between said printin~ areas of said screen and
said underlying areas of the surface break and fall back into
said underlying areas.
The above, and other obj ects, features and advan- .
tages of the present invention, will become apparent fro~ the
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following~description read in con~unction with the acco~any-
ing drawings in which li~e reference nunerals designate the
same elements.
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BRIEF DESCRIPTIO~I OF THE DR~JIN~S
Fig. 1 iS an overall schematic side elevational view
of an ap~aratus for applying adhesive resin to a ~rinted cir-
cuit board according to one embodiment of the invention; : -~
Fig. 2 is an enlarged cross-sectional view taken .` .
along the line II-II of Fig. l;
Fig. 3 is an enlarged cross-sectional view taken
along the line III-III of Fig. l;
Fig. 4 is a cross-sectional view taken along the
line IY-IV of Fig. 3; '
Figs. 5-8 and 10-12 are diagram~atic side views of
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the apparatus of Fig. 1 to which reference will be made in
describing the operation thereof in accordance with the pre-
sent invention; and
Fig. 9 is a diagrammatic side view similar to that
of Fig. 12, but to which reference will be made in describing
the problem encountered with the prior art.
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D~TAI~ED DESCRIPTIOr~ OF THE PREF~RR~D EMBODI~NT
Referring to Fig. 1, it will be seen that an apparatus
for applying adhesive resin on a printed circuit board in accor-
dance with one embodiment of this invention includes a base 1
on a supporting pla~e 11 for carry:ing a mounting plate 2 on
which a printed circuit board 3 may be mounted. ~ bracket 4
is fixed at each side of base 1 and supports a respective pivot
pin 5. A rectangular frame 6 is p:ivotally supported, at one
end, on pins 5. A crank arm 7 is fixedly attached to frame 6,
and the lower or free end of crank arm 7 is connected through
a pin 10 to a piston rod 9 of a hydraulic or oil pressure cylin-
der ~ and to a link 12. Link 12 and oil pressure cylinder 8
are hinged at their lwoer ends to supporting plate 11. ~Frame
~. may thus be angularly displaced about pins 5 by extension
and retraction of pi.ston rod 9 of oil pressure cylinder 8.
Crank arm 7, oil pressure cylinder 8, piston rod 9, link 12
and pin 10 mlay optionally be duplicated at the opposite side of
frame 6 for balanced actuation thereof.
Referring now also to Figs. 2 and 3, frame 6 is
shown to have a screen 13 stretched across it at a predetermined
tension. Screen 13 is a fabric mesh of any suitable material,
but is preferably a polyester synthetic fiber, such as the
rnaterial sold under the -trademark Tetoron. Both surfaces of
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screen 13 are coated with an impervious resin except for per-
vious printing areas 14 which permit the passage of liquid or
semi-liquid adhesive through the uncoated meshes thereof. The
thickness of the impervious non-printing areas of screen 13
is approximately equal to the thickness of adhesive resin
which it is desired to apply to selected areas of printed ~cir-
cuit board 3. In the preferred embodiment, the thickness of
the impervlous areas is about 400~ to about 500~. Adhesiv~e
resin is squeezed through the meshes of printing areas 14 of
screen 13 onto printed circuit board 3 by a squeeze member or
squeegee to be described hereinafter.
Supportlng members 15 (Fig. 1), at each side of the
front and rear of frame 6, support a pair of rods 16 substan-
tially parallel to the sides of frame 6. Slide blocks 17 on
slide bearings 18 (Fig. 3) are slideable along rods 16 either
manually Qr by conventional drive ~eans (not shown).
A pair of air cylinders l9 and 20 are provided for
each slide block 17 and have their piston rods attached to
: : .
stepped portions 17a of the respective slide blocks 17. A ~ -
bar 21 is connected between air cylinders 1~ (Fig. 3). A
squeegee consisting of a U-shaped support bar 23 holding a
resiliently flexible wiping blade 24, is connected to bar 21
by adjustable screws 22. Blade 24 extends over substantially
the entire width of screen 13 and is preerably of rubber-like
material, such as, urethane rubber.
A second bar 21' is connected between air cylinders
20. A scraper consisting of a U-shaped support bar 25 holding
a scraping blade 26 is attached through adjustable screws 22'
to bar 21'. Scraping blade also extends over substantially
the entire width of screen 13 and is also preferably of a
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resilient Material, such as, urethane rubber.
As will be eviden~ to one skilled in the art, actua-
tion of air cylinders 19 is effective to move wiping blade 2
toward and away from screen 13. Similarly, actuation of air
cylinders 20 is effective to move scraping blade 26 toward
and away from screen 13.
Although air cylinders 19 and 20 are shown with
their piston rods attached to slide blocks 17 and their cyjlin-
ders attached to bars 21 and 21', respectively, it is apparent
that the cylinders of air cylinders 19 and 20 may alternative-
ly be attached to slide blocks 17 while their piston rods are
there connected to bars 21 and 21', respectively.
iping or squeegee blade 24 and scraping blade 26
are inclined relative to the normal or undeflected plane of
screen 13 (Fi~. 4) in opposite directions at angles of from
45 to 60. Such inclination of blades 2~ and 26 and the use
of resilient urethane rubber for these parts reduces the inci-
:
dence of damage to, and increases the life of screen 13.
P~eferrinw now to Fi~. 5, it will be seen that frame
6 is initially angularly displaced by cylinder 8 in the clock-
wise direction about pins 5 into the illustrated inclined
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elevated posi~ion. An amount of adhesive resin 27 is applied
across screen 13 by any conventional means (not sho~m) and air
cylinders 20 are actuated to lower scraping blade 26 toward,
or into contact with, the upper surface or screen 13, as indi-
cated by the arrow.
As shown on Fig. 6, support bar 25 and scraping
blade 26 are moved leftward with slide blocks 17 by a conven-
tional drive apparatus (not sho~m) or manually during which
the semi-fluid adhesive resin 27 is scraped across screen 13
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by scraping blade 26. Printirlg areas 14 are thus filled with
adhesive resin, and then air cylinders 20 are actuated to raise
scraping blade 26 from screen 13.
Frame 6 is angularly displaced in the counter-clock-
wise direction about pins 5 into the ~osition shown in Fig. 7,
and in which frame 6 is parallel to but spaced a predetermined
distance from the horizontal surface of printed circuit board 3.
Air cylinders 19 are actuated to force squeegee or
wiping blade 24 downward against screen 13, as shown by the
arrow, with sufficient force to deflect screen 13 from its
normal plane shown in dot-dash lines on Fig. 7 into contact
with the surface of printed circuit board 3 as shown by the
solid line.
Slide blocks 17 are now moved rightward (in Figs.
7 and 8) drawing squeegee or wiping blade 24 with them. The
adhesive resin previously scraped into printing areas 14 by
scraying blade 26 is now pressed therethrough and adhered to
the surface of printed circuit board 3 as blade 24 presses
screen 13 into contact therewith, thus leaving a thickness
of adhesive resin 27 on printed circuit board 3 in a pattern
corresponding to pervious printing areas 14 of screen 13.
Any excess adhesive resin is moved alon~ ahead of blade 24.
Squee~ee blade 24 is moved fully to the right, as
shown in Fig. 10, and air cylinders 19 are actuated to raise
blade 24 from screen 13. This permits screen 13 to resume
its undepressed shape in which it is parallel to, but spaced
from printed circuit board 3.
. , Immediately after forming the desired areas of adhe-
sive resin 27 on printed circuit board 3 and the return of
screen 13 to its undepressed shape, resin threads 28 (Fig. 10)
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brldge the space between the individual pattern areas of adhe-
sive resin 27 deposited on printed circuit board 3 and the
respective printin~ areas 14 i~mediately thereabove.
In the prior art, frame 6 and screen 13 are angularly
displaced to their initial inoperative positions shown in
Fig. 9 immediately following the return of blade 24 to the
position shown on Fig. 10. Such angular displacement of frame
6 and screen 13 stretches resin threads 28 until the latter
break. Due to the elongation and breaking of resin threads
28, the material thus pulled from adhesive resin 27 may fall
upon unintended areas of printed circuit board 3 and make satis-
factory solder connections thereto impossible. This problem
is especially severe at the printing areas 14 nearer to pivot
pins 5 due to the fact that these areas are relatively closer
to the center of rotation and the elon~ated resin threads 2~
extending therefrom are thus more inclined to the surface of
printed circuit board 3.
In ordPr to solve the above proble~, in accordance
with this invention, frame 6 and screen 13 are maintained in
the position of Fig. 10 for a long enough period, suitably
two to six seconds after the return of blade 24 to the position
shown on Fig. 10, until the fluidity of the resin and its sur-
face tension cause resin threads 28 to break, as is shown on
Fig. 11. Since resin threads 28 extend straight upward or ver~
tically from coated areas of circuit board 3 until they are
broken as described above, there is no tendency for these
threads to fall over onto unintended areas of printed circuit
board,3. After resin threads 28 break and fall to the surface
of their respective pattern areas, surface tension smooths the
tops of the pattern areas.
