Circuit board leveling apparatus

An apparatus for leveling (136) a circuit board (105) against a rail (128, 130) of a part placement machine (102) comprises a plate (200) and at least one spring (404, 506, 507, 508). The circuit board (105) can have any one of a plurality of different predetermined thicknesses. The plate (200) is positioned beneath the rail (128, 130) and has first and second sides (204, 300). The first side (204) is dimensioned to support the circuit board (105). The plate (200) is moveable to a first predetermined distance from the rail (128, 130). The first predetermined distance is no smaller than a smallest one of the plurality of different predetermined thicknesses of the circuit board (105). The at least one spring (404, 506, 507, 508) is carried on the second side (300) of the plate (200) to bias the plate towards the rail (128, 130). The at least one spring (404, 506, 507, 508) is compressible to accommodate the circuit board (105) between the plate (200) and the rail (128, 130).

FIELD OF THE INVENTION 
This invention relates generally to circuit boards and, more specifically, 
to an apparatus for leveling circuit boards. 
BACKGROUND OF THE INVENTION 
Many electronic devices include one or more circuit boards comprising 
electronic components assembled on a circuit board panel. In order to 
manufacture high quality electronic devices in a cost effective manner, it 
is necessary to assemble the electronic components to the circuit board 
panel at a high speed and with great precision. These goals are achieved 
through automated assembly. 
In an automated manufacturing environment, the circuit board is created by 
assembling the electronic components on an empty circuit board panel via 
an automated part placement machine. An example of such a machine is the 
model FCP-IV chip part placement machine manufactured and sold by Fuji 
Machine Manufacturing Company. The automated part placement machine 
receives the empty circuit board panel from a conveyor. A leveling 
apparatus of the part placement machine lifts the circuit board panel off 
of the conveyor and positions it for part placement. A placement head of 
the part placement machine places the electronic components or "parts" in 
predetermined locations on the circuit board panel. The leveling apparatus 
then places the assembled circuit board onto the conveyor. 
To remain competitive in the industry, manufacturers must be able to 
manufacture different circuit boards via a single assembly line. This 
often requires that manufacturing equipment be capable of assembling 
circuit boards from panels having different thicknesses. Because of the 
high cost of the automated part placement machine, it is desirable that 
all the circuit boards be assembled using one automated part placement 
machine. 
To accommodate circuit board panels having different thicknesses, the 
height of the leveling apparatus of the automated part placement machine 
must be manually adjusted or "hard tooled" to compensate for the different 
thicknesses of the circuit board panels. Currently, the procedure for 
adjusting the leveling apparatus has several undesirable characteristics. 
To make adjustments, the automated part placement machine is taken off 
line. This results in costly production down time. Additionally, adjusting 
the height of the leveling apparatus is a tedious and time consuming task 
that requires trial and error techniques to perfect each time an 
adjustment is made. Placement of parts on the circuit board following 
manual adjustments is often marked with a reduction in quality, including 
incidents in which circuit board panels become damaged due to 
mispositioning attributable to improper height adjustment. The height 
adjustment must be compensated repeatedly until such errors are 
eliminated. 
Therefore, what is needed is a leveling apparatus that does not require 
manual height adjustment between sequential manufacturing runs of circuit 
board panels or substrates having different thicknesses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An apparatus for leveling or positioning a circuit board against a rail to 
facilitate assembly of electrical components on the circuit board 
comprises a plate and at least one spring. The circuit board can have any 
one of a plurality of different predetermined thicknesses. The plate is 
positioned beneath the rail and has first and second sides. The first side 
is dimensioned to support the circuit board. The plate is moveable to a 
first predetermined distance from the rail. The first predetermined 
distance is no smaller than a smallest one of the plurality of different 
predetermined thicknesses of the circuit board. The at least one spring is 
carried on the second side of the plate to bias the plate towards the 
rail. The at least one spring is compressible to accommodate the circuit 
board having any one of the plurality of predetermined different 
thicknesses between the plate and the rail. 
FIG. 1 illustrates a section of assembly line 100. Assembly line 100 
includes automated part placement machine 102 and conveyance 104. Circuit 
board panel 105 is transported via conveyance 104. Automated part 
placement machine 102 includes tape reels 106 containing electronic 
components. Automated part placement machine 102 includes side openings, 
such as side opening 107, placement head 108, and placement table 110, all 
viewable via cutaway 112. Side openings permit extension of conveyance 104 
into automated part placement machine 102. Circuit board panel 105 enters 
automated part placement machine 102 via conveyance 104. Circuit board 
panel 105 is positioned in placement table 110. Placement head 108 picks 
electronic components from tape reels 106 and places the electronic 
components at predetermined locations on circuit board panel 105. Circuit 
board panel 105, once assembled, exits automated part placement machine 
102 via conveyance 104 and side opening 107. 
Conveyance 104 includes conveyor belts 116 and 118 (viewable via cutaway 
120 in circuit board panel 105 ). Conveyor belts 116 and 118 extend along 
the length of conveyance 104. Conveyor belts 116 and 118 contact edges of 
circuit board panel 105 and propel circuit board panel 105 from right to 
left (or left to right, if desired) with respect to FIG. 1, into automated 
part placement machine 102. 
Circuit board panel 105 can have any one of a plurality of different 
thicknesses. In the illustrated embodiment, circuit board panel 105 has a 
thickness ranging from 0.5 mm to 1.1 mm. Circuit board panel 105 is 
comprised of any suitable material, such as polyimide or epoxy-based flame 
retardant industrial fiberglass (G10-FR4). 
Placement table 110 includes conveyor belts 122 and 124 (viewable via 
cutaway 126), rails 128 and 130, clamping rails 132 and 134 (viewable via 
cutaway 126), and leveling apparatus 136. Conveyor belts 122 and 124 are 
in alignment with conveyor belts 116 and 118 of conveyance 104, 
respectively, and work in conjunction therewith to deliver circuit board 
panel 105 into placement table 110 as shown in dotted line in FIG. 1. 
Rails 128 and 130 overhang conveyor belts 122 and 124, respectively. 
Clamping rails 132 and 134 are moveably disposed both next to and beneath 
conveyor belts 122 and 124, respectively. Clamping rails 132 and 134 
coplanarly engage leveling apparatus 136. Leveling apparatus 136, which is 
further described below, positions circuit board panel 105 for assembly. 
Leveling apparatus employs a spring device that adjusts to accommodate any 
of the different thicknesses of circuit board panel 105 and to ensure 
planarity across circuit board panel 105. 
Although illustrated in automated part placement machine 102, which can be 
any commercially available automated part placement machine, such as, for 
example, model FCP-IV manufactured and sold by Fuji Machine Manufacturing 
Co. or model GSM 1000 manufactured and sold by Universal, it will be 
recognized that leveling apparatus 136 can find application in a variety 
of other machines utilized in the manufacturing environment that require 
the circuit board panel to be positioned such that its top surface is 
level or planar. These machines include, but are not limited to, laser 
marking machines, automated optical inspection machines (which require a 
constant focal plane across the surface of the positioned circuit board), 
screen printing machines, and automated labeling machines. 
Leveling apparatus 136 is further illustrated in FIGS. 2 and 3. Leveling 
apparatus 136 includes top plate portion 200 and base plate portion 202. 
Top plate portion 200 includes top side 204. Top side 204 is substantially 
planar. Top side 204 is dimensioned to substantially support circuit board 
panel 105. In the illustrated embodiment, circuit board panel 105 has a 
width of approximately 215 mm and a length of approximately 265 mm and top 
side 204 has a width, W, of approximately 200 mm and a length, L, of 
approximately 265 mm. 
Top side 204 includes vacuum cups 205 recessed therein. Vacuum cups 205 
provide a passage for air which creates vacuum suction to fix circuit 
board panel 105 of FIG. 1 against top side 204 during positioning. In the 
illustrated embodiment, vacuum cups 205 are arranged in two rows of two 
vacuum cups. Vacuum cups 205 are manufactured from any suitable material 
such as molded polymer or rubber, and can be any suitable, commercially 
available vacuum cups, such as those manufactured and sold by PIAB. 
Top plate portion 200 includes cut-outs 206 and 208 that extend 
longitudinally along rear and front edges, respectively, of top plate 
portion 200. Cut-outs 206 and 208 engage clamping rails 132 and 134 of 
FIG. 1, respectively. Cut-outs 206 and 208 are sized to correspond to a 
thickness of clamping rails 132 and 134, respectively. In the illustrated 
embodiment, the 15 mm of width of circuit board panel 105 that overhangs 
top side 204, is substantially supported by clamping rails 132 and 134. 
Top plate portion 200 can be of any suitable construction, such as tooled 
from a durable material, such as 6061 T6 aluminum or the like. 
Top plate portion 200 includes bottom side 300 of FIG. 3. Bottom side 300 
includes manifolds 302 and 304. Manifolds 302 and 304 are mounted beneath 
vacuum cups 205 of FIG. 2. Manifolds 302 and 304 direct vacuum suction 
from air hoses 306 and 308, respectively, to vacuum cups 205. Air hoses 
306 and 308 are further coupled to a vacuum pump (not shown) of automated 
part placement machine 102. In the illustrated embodiment, each one of 
manifolds 302 and 304 provides an air passage to one row of two vacuum 
cups of vacuum cups 205. 
Bottom side 300 further includes bushings 310, 311, and 312. Bushings 
310-312 are arranged to provide added stability to leveling apparatus 136 
and ensure planarity of top surface 204 of top plate portion 200 during 
positioning of circuit board panel 105 of FIG. 1. Although three bushings 
are shown, one skilled in the art will recognize that leveling apparatus 
136 could properly function via a single, centrally positioned bushing, 
two bushings, or more than three bushings. In the illustrated embodiment, 
bushings 310-312 are press fit into bottom side 300. Bushings 310-312 are 
tooled to extend approximately 20 mm from bottom side 300 and have a 
diameter of approximately 20 mm. Bushings 310-312 can be of any suitable 
construction, such as tooled from a durable material, such as 6061 T6 
aluminum or the like. Bushings 310-312 employ linear bearing guides 314, 
315, and 316, respectively. In the illustrated embodiment, linear bearing 
guides 314-316 are press fit into bushings 310-312. Linear bearing guides 
314-316 have a bore lined with ball bearings (not shown). The bore may be 
5-10 mm in diameter. Linear bearing guides 314-316 can be any suitable 
guides, such as those manufactured and sold by THK Co., Ltd. 
Referring back to FIG. 2, base plate portion 202 includes top surface 210. 
Top surface 210 includes linear guide posts 212, 213, and 214. Linear 
guide posts 212-214 are arranged on top surface 210 to engage linear 
bearing guides 314-316 of bushings 310-312 of FIG. 3, respectively, when 
leveling apparatus 136 is assembled. Although, three posts are shown, one 
skilled in the art will recognize that leveling apparatus 136 could 
properly function via a single, central, post, two posts, or more than 
three posts. In the illustrated embodiment, linear guide posts 212-214 are 
press fit into top surface 210. Linear guide posts 212-214 are tooled to 
extend approximately 30 mm above top surface 210 and have a diameter that 
slidably engages linear bearing guides 314-316. Base plate portion 202 and 
linear guide posts 212-214 can be of any suitable construction, such as 
tooled from a durable material, such as 6061 T6 aluminum or the like. 
Top surface 210 of base plate portion 202 includes spring plungers 216, 
217, 218, and 219. In FIG. 4, each one of spring plungers 216-219 is shown 
to include body 400, nose 402, spring 404, and plug 406. Body 400 includes 
inner bore 407 extending between top and bottom openings 408 and 409 of 
body 400, as shown in dotted line. Inner bore 407 includes neck 410, 
central portion 412, and threaded portion 414. Nose 402 includes radial 
flange 416. Plug 406 is threaded so as to mate with threaded portion 414 
of body 400. 
Spring 404 is a compression spring exhibiting a predetermined spring force. 
Spring 404 compresses to accommodate different thicknesses of circuit 
board panel 105 when circuit board panel 105 of FIG. 1 is positioned 
against rails 128 and 130 of FIG. 1. The predetermined spring force must 
be large enough to hold the thinnest accommodated circuit board panel 105, 
yet not large enough to damage the thickest accommodated circuit board 
panel 105. In a reduction to practice, force gauge testing (using, for 
example, a force gauge manufactured and sold by Chatillon Inc.) indicated 
that the maximum force or load that circuit board panel 105 could 
withstand was 2.9 lbs. As such, the force supplied by spring 404 was set 
to be less than 2.9 lbs for circuit board panel 105 having a thickness of 
1.1 mm. 
Spring plungers 216-219 are assembled by inserting nose 402 into neck 410 
of inner bore 407 via bottom opening 409 until nose 402 extends through 
top opening 408 and radial flange 416 of nose 402 abuts neck 410 of inner 
bore 407. Next, spring 404 is inserted into central portion 412 of inner 
bore 407 via bottom opening 409 until a first end of spring 404 abuts nose 
402. Next, plug 406 is screwed into threaded portion 414 of inner bore 
407. Plug 406 engages a second end of spring 404 and compresses, or 
preloads, spring 404. In the illustrated embodiment, spring plungers 
216-219 are of type S-61N/no. 1/2 - 13 manufactured by Vlier and sold by 
McMaster-Carr. This spring plunger is preloaded to 2.7 lbs with a final 
end force of 9.3 lbs. A spring, such as spring 404, employed by this 
spring plunger has a spring constant (k) of 0.114 lbs/mm. If this spring 
is deflected 1.1 mm to accommodate the thickest one of circuit board panel 
105, Hookes Law of F=k*x (where F is the exerted force or load, k is the 
spring constant, and x is the amount of deflection) indicates that this 
spring exerts a force or load of F=(0.114 lbs/mm)*(1.1 mm)=0.1254 lbs. 
Adding this force to the preloaded value of this spring, the largest total 
force exerted on circuit board panel 105 becomes 2.8254 lbs (2.7 
lbs+0.1254 lbs). This is less than the maximum allowable force of 2.9 lbs 
that circuit board panel 105 is capable of withstanding. 
Spring plungers 216-219 are arranged to uniformly provide spring forces 
across the bottom surface 300 of top plate portion 200 when leveling 
apparatus 136 is assembled. In the illustrated embodiment shown in FIGS. 2 
and 3, spring plungers 216-219 are press fit into base plate portion 202. 
An alternative base plate portion 500 is shown in FIG. 5. Base plate 
portion 500 includes linear guide posts 502, 503, and 504. Linear guide 
posts 502-504 are similar in dimension and arrangement to linear guide 
posts 212-214 of FIGS. 2 and 3. Rather than employing spring plungers 
216-219 of FIGS. 2 and 3, base plate portion 500 includes unloaded springs 
506, 507, and 508. Unloaded springs 506-508 are positioned such that 
linear guide posts 502-504, respectively, extend therethrough. That is, 
unloaded springs 506-508 reside coaxially with linear guide posts 502-504, 
respectively. In the illustrated alternative embodiment, unloaded springs 
506-508 are chosen such that the force exerted thereby does not exceed 2.9 
lbs. Applying Hookes Law of F=k*x and again assuming that the thickest 
accommodated circuit board panel 105 is 1.1 mm, the spring constant (k) of 
unloaded springs 506-508 must not exceed k=F/x=2.9 lbs/1.1 mm=2.636 
lbs/mm. Assuming that the spring constant (k) is 2.636 lbs/mm and 
deflection due to the thinnest accommodated circuit board panel 105 is 0.5 
mm, unloaded springs 506-508 exert 1.318 lbs (F=(2.636 lbs/mm)*(0.5 mm)) 
of force. Such force is sufficient to maintain positioning of the thinnest 
accommodated circuit board panel 105 during part placement. 
Referring back to FIG. 3, top plate portion 200 and base plate portion 202 
(as well as base plate portion 500 of FIG. 5) are assembled by inserting 
linear guide posts 212-214 (or linear guide posts 502-504 of FIG. 5) into 
linear guide inserts 314-316 of bushings 310-312, respectively. Such 
assembly is illustrated by dotted lines 318, 319, and 320. To prevent 
disengagement of base plate portion 500 of FIG. 5 once leveling apparatus 
136 is assembled, unloaded springs 506-508 extend to only a portion, such 
as three-fourths, of the height of linear guide posts 502-504. This allows 
linear guide inserts 314-316 to engage at least the remaining portion, 
such as one-fourth, of linear guide posts 502-504. Once assembled, 
unloaded springs 506-508 extend between and abut top surface 210 of base 
plate portion 202 and linear guide inserts 314-316 and/or bushings 
310-312. 
Although three or four spring devices (e.g., four spring plungers or three 
unloaded springs) are shown in FIGS. 2-5, those skilled in the art will 
recognize that a single, centrally positioned, spring device containing a 
single spring could provide sufficient force across the top plate portion 
200 of leveling apparatus 136 and ensure proper positioning of circuit 
board panel 105 thereby. One skilled in the art will also recognize that 
two, five, or more of such spring devices could alternatively be used. 
Once assembled, bottom side 300 of top plate portion 200 rests against nose 
402 of spring plungers 216-219 in the manner specifically illustrated in 
FIG. 6 by spring plungers 218 and 219. Also, linear guide posts 212-214 
reside in linear bearing guides 314-316 of bushings 310-312, respectively, 
in the manner specifically illustrated by linear guide post 213, linear 
bearing guide 315 and bushing 311. Base plate portion 202 include 
throughholes (not shown) that engage posts (not shown) of automated part 
placement machine 102 so as to securely fasten leveling apparatus 136 to 
automated placement machine 102. In FIG. 6, leveling apparatus 136 is 
shown in rest position 600. In rest position 600, circuit board panel 105 
remains positioned on conveyor belts 122 and 124. 
To position circuit board panel 105 against rails 128 and 130 for part 
placement by placement head 108 of FIG. 1, automated part placement 
machine 102 raises leveling apparatus 136. As leveling apparatus 136 is 
raised, clamping rails 132 and 134 engage cut-outs 206 and 208 in top 
plate portion 200, respectively. As leveling apparatus 136 is further 
raised, top side 204 of top plate portion 200 and clamping rails 132 and 
134, which together form a planar support surface, lift circuit board 
panel 105 off of conveyor belts 122 and 124. When top side 204 contacts 
circuit board panel 105, vacuum cups 205 of FIG. 2 juxtapose with circuit 
board panel 105. Suction secures circuit board panel 105 in position upon 
top side 204 to prevent shifting during further raising. For clarity, 
manifolds 302 and 304 of FIG. 3 have been removed from FIGS. 6 and 7. The 
arrangement of linear guide posts 212-214 and bushings 310-312 (see FIGS. 
2, 3, and 5) prevents lateral movement and twisting of the top plate 
portion 200 and, thus, ensures that circuit board panel 105 remains level 
during raising. 
Automated part placement machine 102 always assumes that the thinnest 
accommodated circuit board panel 105 is being positioned for part 
placement. As such, automated part placement machine 102 always raises 
base plate portion 202 of leveling apparatus 136 to a predetermined 
position, which is engagement position 700 of FIG. 7. In the illustrated 
embodiment, assuming top side 204 is initially 20 mm from bottom edges of 
rails 128 and 130 when leveling apparatus 136 is in rest position 600 and 
the thinnest accommodated circuit board panel 105 is 0.5 mm, base plate 
portion 202 is raised slightly more than 19.5 mm. 
Prior to reaching engagement position 700, top side edges of circuit board 
panel 105 engage bottom edges of rails 128 and 130. At such time, bottom 
side 300 of top plate portion 200 will deflect nose 402 of spring plungers 
216-219 to accommodate circuit board panel 105 between rails 128 and 130 
and top side 204 of top plate portion 200 and clamping rails 132 and 134 
as base plate portion 202 keeps moving. The selection and arrangement of 
spring plungers 216-219 ensures even, uniform application of the spring 
force across circuit board panel 105. The arrangement of linear guide 
posts 212-214 and bushings 310-312 ensure that circuit board panel 105 
remains level during deflection. Deflection of spring plungers 216-219 
will continue until leveling apparatus 136 reaches engagement position 
700. In this manner circuit board panel 105 with a large thickness is 
accommodated without manual adjustment or injury to circuit board panel 
105. Once in engagement position 700, part placement by placement head 108 
of FIG. 1 can begin. 
Thus it can be seen that a leveling apparatus in an automated part 
placement machine can be self adjusting to accommodate circuit board 
panels having any one of a plurality of different thicknesses. By 
employing spring devices, such as spring plungers, one can avoid the 
costly production down time necessary to manually adjust the leveling 
apparatus between sequential production runs of circuit boards having 
different thicknesses. As such, the self adjusting leveling apparatus 
provides for a more versatile manufacturing environment.