Apparatus for spreading material onto a substrate

An apparatus for spreading and depositing a viscous liquid or paste-like material on a substrate includes a housing removably insertable into a diamond- or square-shaped squeegee blade holder, the blade holder itself mounted to a squeegee head assembly of a screen or stencil printer. The squeegee head assembly is driven in a linear direction over and above the substrate, dragging the blade over the substrate and forcing deposition of the material onto the substrate. The housing includes a pair of oppositely-disposed locking clamps that attach to both ends of the housing. A shaft having a blade secured thereto is disposed through the channels of the clamps and within a groove of the housing, and the shaft is rotatable within the housing and the locking clamps so that the angle of attack between the blade and substrate can be selectively adjusted and, once the appropriate angle of application is selected, the blade is fixed in position by tightening the clamps against the shaft.

BACKGROUND OF THE INVENTION 
The present invention comprehends an apparatus for spreading and pushing 
material onto a substrate, and more particularly pertains to an adjustable 
blade for spreading a viscous liquid or paste-like material onto printed 
circuit boards and other substrates. 
In the surface mount technology field and hybrid microelectronics field, 
manual, semi-automatic, or automatic screen and stencil printing equipment 
is typically used for printing solder paste, epoxies (both conductive and 
adhesive), conductive inks, resistive inks, and dielectric inks, for 
example, onto printed circuit boards and other substrates. 
The circuit board, or other substrate, is placed on the stencil or screen 
printer, and then one of the above-mentioned materials is printed onto the 
circuit board through either a metal mask stencil with open apertures or 
through a template having a plurality of interstices. In addition, the 
materials can be printed onto a circuit board through a cross-sectional 
screen mesh that has an emulsion in it, and the circuit or pattern to be 
printed on the circuit board is etched out of the emulsion. The various 
above-described materials are used for the purpose of attaching electrical 
components to the substrate and for manufacturing electrical circuits on 
the substrate. 
The typical screen or stencil printer includes a tooling plate upon which 
the circuit board is positioned and aligned, a squeegee assembly or 
squeegee head assembly, and a metal or polyurethane blade referred to in 
the industry as a "squeegee blade". A squeegee blade holder is mounted to 
the squeegee assembly, and both the squeegee blade holder and squeegee 
assembly are positioned above and extend transverse to the circuit board 
or other substrate horizontally positioned on the tooling plate which is 
part of the screen or stencil printer. 
A squeegee blade is inserted into the squeegee blade holder so that the 
squeegee blade is superjacent the circuit board and extends transverse 
thereto. The squeegee head assembly is driven over the screen, stencil, or 
template positioned between the circuit board and the 
downwardly-projecting squeegee blade by some type of electric or pneumatic 
motor or cylinder drive assembly. This movement is referred to as the 
"squeegee stroke". For most printers the squeegee head assembly can print 
in both directions (forward or backward), and the movement of each stroke 
can be individually controlled. In addition, many screen and stencil 
printers permit x, y, and theta (rotation) adjustments of the circuit 
board or other substrate placed on the printer. Moreover, some types of 
printers include features which permit adjustment of both the speed and 
stroke length of the squeegee head assembly and adjustment of the pressure 
of the squeegee blade against the material and/or substrate. Metal 
squeegee blades are typically used in place of polyurethane squeegee 
blades when a company is printing high viscosity materials, such as solder 
paste or epoxy, onto printed circuit boards or other substrates. 
In operation, the squeegee blade is driven down under pressure until it 
comes into contact with, or is just above, the top surface of the screen 
or stencil. With the squeegee blade forced down under pressure, the drive 
assembly drags the squeegee blade across the stencil. As the squeegee 
blade travels above the stencil, the solder paste--or other material 
previously described --is dragged and pushed along the top surface of the 
stencil by the squeegee blade. The simultaneous downward pressure and 
forward travel of the squeegee blade against the solder paste forces the 
paste through the stencil or screen and deposits the solder paste onto the 
circuit board. The downward pressure and longitudinal movement of the 
blade forces the solder paste through the stencil or screen apertures and, 
in the process, wipes clean the surface of the screen or stencil. The bead 
of solder paste is not dragged across the top surface of the screen or 
stencil; in fact, the bead of solder paste rolls across the top surface of 
the screen or stencil like a steam roller traveling over a road surface. 
The rolling action of the solder paste caused by the downward pressure and 
forward movement of the squeegee blade is what causes the paste to be 
pushed and passed through the screen or stencil apertures for deposition 
onto the circuit board. Once the solder paste is forced through the 
interstices of the template or the apertures of the stencil, capacitators, 
resistors, and other electrical components are mounted onto the wet paste 
deposited on the circuit board to complete the electrical circuitry of the 
board. Then the circuit board goes through a heating/curing process and 
the solder paste is transformed into what in the art is called pads and 
lines which create the electrical circuitry on the circuit board. 
Among the critical factors which affect the passing of solder paste through 
the screen or stencil apertures and deposition of solder paste onto the 
circuit board is the angle at which the squeegee blade meets the top 
surface of the screen or stencil. This is referred to in the industry as 
the "angle of attack". Varying this angle affects the amount of solder 
paste or other material deposited through the screen or stencil apertures 
and onto the substrate surface. 
The majority of metal squeegee blades currently in use comprise two flat, 
elongated, aluminum or steel plates between which a flat or bent piece of 
steel (the actual squeegee blade) is sandwiched. The plates are fastened 
together to hold the blade in position. This sandwich blade assembly is 
then inserted into a squeegee holder. The result is a metal squeegee blade 
whose angle of attack is fixed relative to the stencil or screen over 
which the blade will pass during the printing process. An alternative is 
to cut two elongated blocks of steel or aluminum at an angle so that the 
blade located therebetween is sandwiched at an angle. Moreover, some 
screen and stencil printers include a feature which permits adjustment of 
the entire squeegee head assembly so that the angle of attack can be 
varied. However, this feature is usually not standard on printers but 
comes as an option and is a separate mechanism from the blade. 
Therefore, there is a need for a squeegee blade which incorporates an 
adjustable "angle of attack" in its design, and is readily adaptable to 
the various squeegee blade holders and squeegee head assemblies in use in 
the surface mount technology field. 
SUMMARY OF THE INVENTION 
The present invention comprehends an apparatus for spreading and depositing 
material on a substrate and includes an elongated, square-shaped squeegee 
housing which is removably insertable in a blade holder. The blade holder 
is part of a squeegee head assembly which is located above and extends 
transverse to the substrate. The housing includes a circular-shaped groove 
coequal in length with the housing. A pair of oppositely-disposed, 
arch-shaped locking clamps are removably attachable to either end of the 
housing. Each clamp has a main body portion and a pair of 
oppositely-disposed, inwardly-curving legs which define a circular 
channel. Protruding horizontally from each end of the housing is a roll 
pin, and the locking clamps are attached to the housing ends by insertion 
on the roll pins. When the locking clamps are attached to the housing, the 
circular groove of the housing is axially aligned with the circular 
channels of the clamps. 
Disposed within the channels of the clamps and groove of the housing is an 
elongated, cylindrical shaft. The shaft has a longitudinal slot formed on 
its surface which is coequal in length with the shaft. The shaft is 
capable of rotatable movement within the channels of the clamps and the 
groove of the housing. Mounted within the slot of the shaft and rotating 
concomitant with the shaft is an elongated blade which can either be 
shorter than the slot or may be coequal in length with the shaft. The 
blade can be selectively adjusted within a predetermined number of degrees 
by rotating the shaft within the housing so that the proper angle of 
attack can be obtained. Once the proper angle between the blade and 
substrate is obtained, the legs of the clamps are tightened against the 
shaft and this fixes and holds the shaft within the housing so that the 
shaft does not rotate. Thus, the angle of attack of the blade with respect 
to the substrate is also fixed. By loosening a screw that is inserted 
through the main body portion of each clamp and against the ends of the 
shaft, the shaft can be rotated within the housing and the angle of attack 
of the blade can be selectively adjusted relative to the substrate. 
It is an objective of the present invention to provide an apparatus which 
allows adjustment of the angle of attack of the blade after the blade and 
shaft have been mounted to the blade holder, and after the blade holder 
has been inserted into a squeegee head assembly. 
Another objective of the present invention is to provide an adjustable 
blade which is insertable within diamond- or square-shaped blade holders 
and also can be used on trailing-edge-style holders. 
These and other objects and advantages will be readily evident upon a study 
of the following specification and accompanying drawings wherein:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Illustrated in FIGS. 1-11 is an apparatus 10 for spreading a variety of 
materials onto a substrate; and the apparatus 10 is adapted for removable 
insertion into the channel or open area of either a diamond-shaped or 
square-shaped squeegee blade holder which, in turn, is mounted to and part 
of a squeegee head assembly. The squeegee head assembly travels over a 
screen, stencil, or template superposed on a circuit board or other 
substrate which is supported on a base or tooling plate on any of a 
variety of manual, automatic, and semi-automatic screen and stencil 
printers. A spreading means securable to the apparatus 10 forces solder 
paste or other material through the apertures of the stencil, the 
interstices of the template, or the mesh of the screen, and onto the 
circuit board for the purpose of attaching electrical components and for 
manufacturing electrical circuits on the circuit board. 
Shown in FIGS. 1-4 and 11 is an elongated, cylindrical shaft 12 having a 
milled groove or slot 14 formed therein and extending coequal in length 
with the shaft 12. The slot 14 extends one-half the distance into the 
diameter of the shaft 12. The length of the shaft 12 can vary to 
accommodate the enormous variety of circuit board sizes and image areas to 
be printed by screen and stencil printers. One common shaft diameter is 
0.187 inches. 
Illustrated in FIGS. 1-4 and 11 is a blade 16 which may be referred to as a 
squeegee blade, a metal squeegee blade, or a metal blade. If the squeegee 
blade is metal, the blade is typically manufactured from a spring steel or 
stainless steel so that the metal blade can be plated with a special 
coating that will provide a non-stick surface. However, the blade 16 can 
be manufactured from a plastic material, such as polyurethane; but when 
high viscosity materials, such as solder paste or epoxies, are to be 
printed onto circuit boards, the metal blade is used. The thickness of the 
blade 16 ranges between 0.00010 and 0.00020 of an inch. In FIGS. 1-4 and 
11, the blade 16 is inserted into the slot 14 of the shaft 12 so that the 
blade 16 and shaft 12, which are separate elements, become a one-piece 
unit or assembly through the manufacturing process. The blade 16 is 
mounted to the slot 14 and secured thereto by an epoxy. In FIGS. 1-4 and 
11, the blade 16 is not as long as the shaft 12 but the extension of the 
blade 16 within the slot 14 can vary for each particular use as shall be 
hereinafter further described. With the blade 16 inserted into the slot 14 
and permanently affixed to the shaft 12 by an epoxy, any rotation or 
rotatable movement by the shaft 12 causes the blade 16 to rotate 
concomitant therewith. 
Shown in FIGS. 1, 3, 4, and 11 is an elongated, adjustable angle, blade 
shaft housing 18 having a generally circular-shaped groove 20 extending 
therethrough and which is coequal in length with the housing 18. The 
housing 18 also includes a locking means for fixing the angle of attack of 
the blade 16 and for preventing movement and rotation of the shaft 12 
within the housing 18. The locking means includes a pair of 
oppositely-disposed, arch-shaped locking clamps 22, shown in FIGS. 1-4 and 
11, which are removably attachable to either end 24 and 26 of the housing 
18. Each clamp 22 includes a main body portion 28 and oppositely-disposed, 
downwardly-projecting legs 30 which form a generally circular-shaped 
aperture or channel 32. On each flat end surface at each opposite end 24 
and 26 of the housing 18 is a blind hole 34 which is spaced slightly above 
the groove 20 of the housing 18. Inserted into each blind hole 34 is a 
dowel or roll pin 36 such that a portion of the pin 36 projects outwardly 
from each end surface perpendicular thereto. Cut into the main body 
portion 28 of each clamp 22, and extending upwardly from the top of the 
channel 32, is a slight gap 38 which also spaces the legs 30 from each 
other. The gap 38 terminates at a circular receiving or mounting hole 40 
which extends through the main body portion 28 of each clamp 22. 
As shown in FIG. 1, in order to mount the clamps 22 to the ends 24 and 26 
of the housing 18, the roll pins 36 are first inserted into the blind 
holes 34 and then each clamp 22 is slipped onto the respective pin 36 by 
the hole 40. The shaft 12 is then inserted into and through the channel 32 
of one clamp 22 and through the length of the groove 20 of the housing 18 
until the shaft 12 is received into the channel 32 of the opposite clamp 
22. There is a very slight gap or clearance between the shaft 14 and the 
inner surface of the groove 20. Once this insertion is completed, the 
shaft 12 is axially aligned and enclosed within the channels 32 and the 
groove 20. The housing 18 can then be mounted to the squeegee head 
assembly. 
The shaft 12 is freely rotatable within the housing 18, and in order to 
prevent the rotation of the shaft 12 and fix the angle of application of 
the blade 16 with respect to the substrate over which it will pass, a 
screw 42 is inserted into a threaded aperture 44 which extends 
transversely through the main body portion 28 of each clamp 22. With the 
shaft 12 inserted through the clamps 22 and into and through the housing 
18, tightening each screw 42 inserted in each aperture 44 causes the 
slight gap 38 in each clamp 22 to close, bringing the legs 30 together, 
compressing and pinching the legs 30 against the cylindrical surface of 
the shaft 12. This prevents rotation of the shaft 12 and fixes the shaft 
12 within the housing 18. Both screws 42 must be tightened within the 
clamps 22 for properly compressing the legs 30 against the shaft 12 so 
that rotation of the shaft 12 within the housing 18 is prohibited. It 
should be noted that the housing 18 itself does not pinch or in any way 
compress the cylindrical surface of the shaft 12; all that is necessary in 
order to prevent rotation of the shaft 12 and fix the angle of application 
of the blade 16 is for the legs 30 to be brought together and tightly 
compress and pinch against the end portions of the shaft 12. Loosening 
each screw 42 causes the legs 30 to slightly move away from each other and 
release their grip upon the end portions of the shaft 12. In order to 
provide backup for the clamps 22, a pair of set screws 46, shown in FIG. 
1, can be inserted through threaded apertures 48 extending from the upper 
surface of the housing 18 and registering with the groove 20 itself. The 
apertures 48 are adjacent the blind hole 34 for each roll pin 36, and 
inserting and tightening the screws 46 therein causes the screws 46 to 
contact the shaft 12 to further prevent the shaft 12 from rotating in the 
housing 18. 
The shaft 12 and blade 16 of FIG. 1 are removably insertable into the 
housing 18 of FIG. 1, and create an assembly 50 which is removably 
insertable into either a diamond-shaped blade holder 52, as shown in FIG. 
3, or a square-shaped blade holder 54, as shown in FIG. 4. FIG. 2 
illustrates one screw 42 completely inserted into the clamp 22 which 
causes the legs 30 to compress and contact the shaft 12 for preventing 
rotation of the shaft 12 and fixing the angle of the blade 16 relative to 
the substrate. The holders 52 and 54 shown in FIGS. 3 and 4 have a 
relatively simple method of holding the housing 18 therein. With the 
housing 18 inserted into the holder 52 of FIG. 3, a lever 56 which extends 
through a main block portion 58 and into and through a second block 
portion 60 is turned so that the second block portion 60 is drawn toward 
the main block portion 58. This closes down a clearance space 62 between 
the two block portions 58 and 60 and causes the second block portion 60 to 
compress and pinch against the housing 18 which holds the housing 18 in 
place within the holder 52. Roll pins or dowels (not shown) are inserted 
through apertures 64 on the face of the main block portion 58 and into 
both the second block portion 60 and a third block portion 66 for 
maintaining alignment of the block portions 58, 60, and 66. The 
square-shaped holder 54 of FIG. 4 employs essentially the same elements to 
hold and contain the housing 18 therein. Tightening one or several 
fasteners 68 which extend transversely through the holder 54 of FIG. 4 
causes an L-shaped portion 70 of the holder 54 and a vertical portion 72 
to draw and compress against each other. Tightening the fasteners 68 thus 
compresses the housing 18 within the L-shaped portion 70 and the vertical 
portion 72 of the holder 54 and thus maintains the housing 18 within this 
holder 54. 
The particular angle of attack of the blade 16 can be pre-set outside any 
particular holder or the blade 16 can be adjusted after the blade 16 is 
inserted into the holder, such as holders 52 and 54. This provides maximum 
flexibility for the blade 16 to achieve the appropriate angle of attack. 
In addition to the assembly 50 of the present invention being removably 
insertable into a variety of blade holders, such as are shown in FIGS. 3 
and 4, the adjustable angle of application of the blade 16 represents a 
significant improvement over the prior art. Illustrated in FIGS. 12-14 is 
the prior art. Currently, an elongated piece of steel or aluminum is cut 
longitudinally into two flat pieces of aluminum or steel plate 74. The 
squeegee blade, whether metal or non-metal, is then fastened between the 
plates 74 like a sandwich. Once the plates 74 are fastened together, the 
angle of attack of the blade 16 is permanently fixed. Furthermore, it is 
possible to cut an aluminum or steel block 76 at an angle so that the 
blade 16 is placed or sandwiched between two blocks 76 at an angle; but 
even in this embodiment, as shown in FIGS. 13 and 14, once the blocks 76 
are fastened together, the angle of attack of the blade 16 is fixed in 
place and non-adjustable. If the zero position is taken to be the position 
when the blade 16, as shown in FIG. 3, is perpendicular to the substrate, 
whether it be a screen, stencil, or template, then typical angles of 
attack for blades currently in use range from between 38.degree. and 
42.degree.. In contrast, the range of adjustment of the assembly 50 is 
much greater which permits a much more accurate and closer control of the 
amount of solder paste or other material deposited on the circuit board. 
From the zero position, the blade 16 shown in FIGS. 1-4 has a range of 
adjustment within the housing 18 of .+-.70.degree.. Hence, the total range 
of adjustment for the blade 16 illustrated in FIGS. 1-4 is from 20.degree. 
to 160.degree., with the zero position being at FIG. 90.degree.. FIG. 10 
illustrates a representative screen printer 78 with a circuit board 80 
resting upon a tooling plate 82 and a squeegee head assembly 84 adjacent 
the board 80. A blade 16 projects downwardly at an angle ready to sweep 
over the board 80 and stencil (not shown). FIG. 11 illustrates one 
possible angle of application of the blade 16 with regard to the solder 
paste 86, stencil 88, and circuit board 80. 
FIGS. 5-9 illustrate alternative embodiments for the blade and shaft 
assembly 50 shown in FIGS. 1-4. FIGS. 5-7 disclose a second alternate 
embodiment for the assembly 50 shown in FIGS. 1-4. FIGS. 5-7 disclose an 
elongated, cylindrical shaft 90 having a milled groove or slot 92 cut 
longitudinally along its length and extending approximately halfway into 
the shaft 90. A blade 94 is mounted into the slot 92 and is permanently 
secured thereto by the use of an epoxy. The two major differences between 
the shaft 90 and blade 94 of FIGS. 5-7 and the shaft and blade illustrated 
in FIGS. 1-4 are that in FIGS. 5-7 the blade 94 is coextensive in length 
with the shaft 90 and that the shaft 90 is enlarged to fill the area 
within the holders 52 and 54 of FIGS. 3 and 4 that would be filled by the 
housing 18 in the preferred embodiment. FIGS. 6 and 7 show the shaft 90 
disposed within the square-shaped blade holder 54 and the diamond-shaped 
blade holder 52; and the diameter of the shaft 90 completely fills the 
area which would be filled by the housing 18 of FIG. 1 in the preferred 
embodiment. As shown in FIGS. 6 and 7, the shaft 90 is rotatable within 
the respective holders 52 and 54 for permitting the selective adjustment 
of the angle of attack of the blade 94. By manually adjusting the lever 56 
as previously described in relation to FIG. 3, or tightening the fasteners 
68 that extend transversely through the holder 54 as previously described 
with respect to FIG. 4, rotation of the shaft 90 is prevented and the 
angle of attack of the blade 94 is fixed relative to the substrate. As in 
the preferred embodiment, the angle of attack for the blade 94 is fixed 
before the holder 52 or 54 is mounted to the squeegee head assembly 84. 
Illustrated in FIGS. 8 and 9 is a third alternative embodiment for the 
assembly 50. In FIGS. 8 and 9 the squeegee blade is formed from an 
elongated sheet of steel or aluminum and is shaped in the form of an eye 
hook with an elongated, tubular-shaped shaft portion 98 and an 
integrally-formed flat blade portion 100. A longitudinal slot 102 coequal 
in length with the tubular-shaped shaft portion 98 spaces the upper 
portion of the blade 100 from the inwardly-curved edge of the 
tubular-shaped shaft portion 98 so that the shaft portion 98 does not form 
a closed circle along its axial length. The integral shaft 98 and blade 
100 of FIGS. 5, 8, and 9 is disposed within the holder 52 in the same way 
that the enlarged shaft 90 embodiment of FIGS. 5-7 is disposed within the 
holders 52 and 54. FIG. 9 shows the shaft 98 and blade 100 inserted into 
the diamond-shaped holder 52, and this is the same holder 52 as shown in 
FIG. 3. The angle of the blade 100 in FIG. 9 is fixed relative to the 
substrate by manually tightening the lever 56 so that as the portions 58 
and 60 of the holder 52 are brought together the tubular-shaped shaft 
portion 98 is compressed and thus held in place. The blade 100 illustrated 
in FIG. 9 can also be disposed within the square-shaped holder 54 
illustrated in FIGS. 4 and 7, and it would be maintained within this 
holder 54 by simply tightening the transversely-extending fasteners 68 so 
that the holder 54 would compress and hold the tubular-shaped shaft 
portion 98 in a fixed, non-rotatable position which would fix the angle of 
attack of the blade 100. 
Although several embodiments of the present invention have been illustrated 
and described, it will be apparent to those skilled in the art that 
various changes and modifications may be made therein without departing 
from the spirit of the invention or the scope of the appended claims.