Rotation system for circuit board screener

A rotational system to be utilized in conjunction with a vertical screening apparatus, wherein a print head assembly and ink reservoir rotate about a pivot away from the coating chamber in order to allow ready access to the screen chase.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This application claims the benefit of U.S. provisional application No. 
60/006,129 filed Nov. 6, 1995. 
FIELD OF THE INVENTION 
This invention relates generally to the field of print screening devices. 
More particularly, the invention relates to the provision of a rotation 
system capable of rotating a print head assembly (i.e. squeegee and flood 
blade) and ink reservoir out of the coating chamber so that one can 
readily access the screen chase for adjustment and maintenance purposes. 
BACKGROUND OF THE INVENTION 
Photopolymers have found widespread application in the preparation of 
printed circuit boards and other electronic devices. These materials are 
applied to circuit boards by screen printing and/or stenciling techniques 
which are well known in the art. Applicant's prior U.S. Pat. No. 4,404,903 
describes a semi-automatic device that uses a horizontal print stroke to 
print a photoimagable soldermask ink simultaneously on both sides of a 
board. Applicant's prior U.S. Pat. No. 4,957,044 describes an automatic 
device that uses vertical flood and print strokes to print photoimagable 
soldermask ink simultaneously on both sides of a board. Applicant's prior 
U.S. Pat. No. 5,265,531 describes a reciprocally shuttled double sided 
screener with tiltable print squeegee assembly capable of printing both 
sides of a circuit board simultaneously. 
U.S. Pat. Nos. 5,265,531 and 4,957,044 both employ common methods of 
screening a circuit board. In particular, circuit boards are transported 
into a print zone between two pivotally mounted vertical screens where the 
boards are printed, and then to an output assembly. Both sides of a board 
are printed simultaneously by means of flood blades and squeegees 
operating sequentially to flood the screens with ink and press them into 
contact with the board. The print head support arm and ink reservoir arm 
are both bolted to the screen frame, so that in order to access the 
coating chamber, it is necessary to unbolt the print head support bar and 
ink reservoir. 
Most persons in the business of screening circuit boards work for a large 
number of different customers, and thus have many different small job 
orders. Typically, circuit boards are screened in groups of 25 to 50 
boards. Each new job order usually involves adjusting the screen chase in 
order to accommodate a new size of circuit board. Thus, ready access to 
the screen chase and coating chamber is a common problem in the industry. 
For example, when a job order comes in for a different size board, the 
machine needs to be opened up and worked on in order to define the new 
dimensions of the window of the chase for the new board size. The chases, 
which hold the screening membranes, have to be adjusted. In order to 
access the chases, the print head needs to be unbolted and removed, which 
is a messy, time consuming process. The ink remaining on the print head 
rubs off and spills over onto various parts of the machine and 
surroundings. The ink has a viscosity similar to honey, so that when the 
print head is removed, the remaining ink forms sticky strings that hang 
from the print head and sticks to various parts of the screening 
apparatus. This is a problem for many reasons. First, the ink is very 
expensive, and is about the third highest material cost in producing 
circuit boards. By having to open up the machine and remove the print 
heads, a large amount of ink is wasted. Second, adjusting the machine in 
order to accommodate a new job order takes time and cuts down on the 
number of circuit boards that can be printed during a set period of time. 
Third, without speedy access to the work area, the ink has a tendency to 
dry, which is not only wasteful, but also requires additional time to 
remove the old ink and replace with fresh ink. Fourth, during the time 
that the machine is being worked on, the ink that gets all over the 
machine either dries or accumulates on different parts of the machine, 
which could cause problems in the accuracy of the next printing. 
SUMMARY OF THE INVENTION 
The present invention overcomes the foregoing problems by providing a 
system to rotate the print head and ink reservoir out of the print zone so 
that one can quickly and easily adjust the machine in order to accommodate 
a different sized circuit board. Unlike the prior art, such as U.S. Pat. 
Nos. 5,265,531 and 4,957,044, where the print head support bar, which 
carries the print head (including the flood blade and one or more 
squeegees), and the ink trough are bolted into the machine, the present 
invention provides a hinged arm which rotates about a pivot and allows the 
print head support bar and an ink reservoir to swing out away from the 
machine. A lever is provided which, when in closed position, keeps the 
hinged arm flush against the housing blocks of the squeegee vertical drive 
system. When the machine needs to be worked on, for either maintenance 
work or for normal process setup (i.e. redefining a window on the chase or 
replacing the screen), the lever holding the hinged arm flush against the 
housing block is rotated to an open position, which allows the print head 
arm and print head to swing out along a generally horizontal plane away 
from the coating chamber. Because the flood blade generally resides within 
the ink reservoir, the ink reservoir swings out in conjunction with the 
print head arm. In this way, the ink reservoir remains in vertical 
alignment with the print head arm and acts to contain the ink that drips 
off the flood blade and print squeegees. The present invention also cuts 
down on the amount of time it takes to adjust the machine because the 
print head support bar and the ink reservoir no longer need to be unbolted 
from the screen frame, thus allowing ready access to the screen chase. 
The present invention can be used in conjunction with the squeegee vertical 
drive system as described in U.S. Pat. Nos. 5,265,531 and 4,957,044, the 
specifications of which are hereby incorporated by reference. The squeegee 
vertical drive system is formed by conjunctively mounting opposing flood 
blades and opposing print squeegees onto cross members. The cross members 
are slidably attached as hereinafter described, to guide bars, and they 
are screw driven in a vertical plane by screw systems which are mounted on 
each of the four corners of a system base plate. Further details of the 
squeegee vertical drive are described in U.S. Pat. Nos. 5,265,531 and 
4,957,044. 
The foregoing and additional features and advantages of this invention will 
become apparent from the detailed description and accompanying drawing 
figures that follow. In the figures and the written description, numerals 
indicate the various features of the invention, like numerals referring to 
like features throughout for both the drawing figures and the written 
description.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a system for rotating the print head and ink reservoir 
out of the coating chamber so that one can quickly and easily adjust the 
circuit board screening machine in order to accommodate a different sized 
circuit board is illustrated. In particular, an ink reservoir 2, 
containing ink 4, is provided so as to be positioned in flush parallel 
alignment beneath screening membrane 6 (commonly referred to as a screen) 
within chase 8. During the screening process, the screen 6 is flooded with 
ink 4. The ink reservoir 2 is connected to the upper generally horizontal 
plate 12 (shown in FIG. 4) of a rigid member 10. The rigid member 10 is 
comprised of an upper generally horizontal plate 12 connected to a 
generally vertical plate 14, which is in turn connected to a lower 
generally horizontal plate 16. The lower horizontal plate 16 is connected 
to a rigid ink reservoir arm 18, preferably made of steel, which rotates 
about pivot 20. The ink reservoir arm 18 is shaped so that when in a 
closed position (as further described below), it lies flush against the 
lower portion of the screen 6, then is offset by extending outward at an 
acute angle, and returns to a plane parallel to the chase frame 22, before 
it attached to pivot member 24. The ink reservoir 2 is held tight against 
screen 6 by cylinder 28 which pushes on linkage 30 which in turn pushes 
against ink reservoir arm 18. The ink reservoir 2 rotates about internal 
pivot 32 so that it stays in line with the screen 6 when in closed 
position. Internal pivot 32 allows ink reservoir 2 to remain in flush 
parallel alignment with screen 6 so as to contain any ink 4 dripping from 
screen 6. 
FIG. 2 shows the ink reservoir arm and print head arm in a closed, unlocked 
position. The print head 34 is comprised of a squeegee and flood blade 
assembly 36. In the preferred embodiment shown, the squeegee and flood 
blade assembly 36 is comprised of a flood blade 38, a print squeegee 40, 
and a spot suppressor squeegee 42. Many other alternative embodiments of 
the squeegee and flood blade assembly 36 are possible. For example, the 
spot suppressor squeegee can be omitted, or a roller could be used in 
place of the spot suppressor squeegee. 
The print head 34, including the squeegee and flood bar assembly 36, is 
attached to the upper surface of plate 44. Referring to FIG. 2 in 
conjunction with FIG. 3, the lower surface of the plate 44 is connected to 
the upper surface of the print head arm 46. The plate 44 is located 
generally in the center of the print head arm 46 in order to align the 
print head 34 with the circuit board (not shown) to be screened. As shown 
in FIG. 3, one end 35 of the print head arm 46 is pivotally attached to a 
pivot assembly 51, which includes top and bottom support blocks 50 and 52 
and pivot pin 56. In particular, between pivot 20 and plate 44, the front 
face 47 of print head arm 46 is attached to hinge 48, which is located 
between the pivot assembly blocks 50 and 52. The blocks 50 and 52 are 
attached to a housing block 54. A pivot pin 56 is held between the support 
blocks 50 and 52, thus allowing the print head arm 46 to pivotally rotate 
about the pivot pin 56. 
A scab plate 58 is attached to the other end 49 of the print head arm 46 
opposite the pivot assembly 51. A sensor 60 for indicating whether the 
print head arm 60 is in a closed or open position is located on the front 
face 59 of scab plate 58. A free end 53 of the scab plate 58 extends 
beyond the length of the print head arm 46. When the print head arm 46 is 
locked in a closed position, the scab plate 58 engages the housing block 
66 between upper and lower receiving blocks 62 and 64. The receiving 
blocks 62 and 64 are attached to the housing block 66 and are disposed 
generally parallel to one another with a space disposed therebetween for 
receiving the free end 53 of scab plate 58 when the print head arm 46 is 
in a closed position. A lever 68 is pivotally attached to housing block 
66. When the lever 68 is in an open position (FIG. 3), the lever 68 rests 
against an outer stop 70, which is attached to the front face of the 
housing block 66. 
Referring to FIG. 2, when print head arm 46 is in a closed and locked 
position (the locked position is shown by dotted lines), the free end 53 
of the scab plate 58 lies in intimate contact with the outer surface of 
the housing block 66. The lever 68 pivots about the pivot pin 72 so that 
when in a closed and locked position, the lever 68 rests against inner 
stop 74 extending from scab plate 58. The print head arm 46, when in a 
closed and locked position, is held in intimate contact with the front 
face of the housing block 66 by the lever 68. When the lever 68 is in its 
closed position, the sensor 60 indicates that the print head arm 46 is 
closed and that the machine is ready to run. 
In FIG. 2, the print head arm 46 is shown in the closed and unlocked 
position. Dotted lines are used to show the print head arm 46 in the 
closed and locked position. In FIG. 3, the print head arm is in the open 
position. When the lever 68 pivots into the open position (as indicated by 
arrows), the print head arm 46 swings out away from coating chamber 76 
along a horizontal plane (also indicated by arrows). 
In FIG. 4, the ink reservoir arm 18 is in an open position, and unaligned 
with print head arm 46. While generally, in accordance with the invention, 
ink reservoir arm 18 remains in vertical alignment with print head arm 46. 
As shown in FIG. 4, the two arms pivot separately and independently of one 
another. However, as a practical matter, because the flood blade 38 
generally rests within the ink reservoir 2, when the print head arm 46 
swings away from the coating chamber 76 (FIG. 1) along a horizontal plane, 
the ink reservoir arm 18, which freely pivots about the pivot pin 56, 
swings away from the coating chamber 76 in vertical alignment with the 
print head arm 46. 
It will be appreciated by persons skilled in the art that the present 
invention is not limited to what has been shown and described hereinabove, 
nor the dimensions of sizes of the physical implementation described 
immediately above. The scope of invention is limited solely by the claims 
which follow.