Flexible geometry circuit board

A circuit board has one or more planar sections each connected to another portion of the circuit board by springs. The springs allow the sections of the circuit board connected by the springs to move in the planes of the sections relative to the remainder of the circuit board. An electrical device such as an automotive instrument cluster uses the circuit board in conjunction with gauges and a face plate. A method of producing an automotive instrument cluster includes the steps of attaching the gauges to the circuit board and mounting the gauges to a face plate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a circuit board. Further, the invention 
relates to an electrical device which contains the circuit board. Finally, 
the invention relates to a method of producing the electrical device. 
2. Description of the Related Art 
It is well-known in the art to use circuit boards in automotive instrument 
clusters. Such instrument clusters frequently contain several gauges to 
display particular quantities related to the operation of the automobile 
(for example, oil pressure, battery voltage, and engine RPM). Each gauge 
typically has a shaft which protrudes through a face plate of the 
instrument cluster. A pointer is mounted on the shaft. The pointer 
indicates, with reference to graduations on the front of the face plate 
and visible to the driver of the automobile, the value of the particular 
quantity being reported by the gauge. Each gauge further has several 
terminals, typically cylindrical, for electrical connections to the gauge. 
The terminals are typically attached to a circuit board, often an 
inflexible or "hard" circuit board. 
A problem is encountered in the assembly of instrument clusters. The gauges 
are typically attached to a hard circuit board early in the assembly of an 
instrument cluster. Typically, the terminals of the gauges are inserted 
through holes in the circuit board. The terminals are then soldered to the 
circuit board to effect attachment and electrical connection of the gauges 
to the circuit board. Once the attachments to the circuit board are made, 
the gauges are mounted to the face plate of the instrument cluster. This 
mounting is typically done with screws which are inserted through holes in 
flanges in the gauges and which are then driven into holes in the back of 
the face plate. The problem encountered is in making all of the holes in 
the flanges of all of the gauges line up with all of the corresponding 
holes in the face plate. This problem is encountered due to the relative 
positions of all of the gauges having been fixed by the prior soldering of 
the gauge terminals to the circuit board. 
One solution to this problem is to employ multiple circuit boards, each 
with holes to accommodate the terminals of some of the gauges. The 
relative positions of all of the gauges are therefore not fixed when the 
gauges are soldered to the circuit boards. This solution has several 
problems, including the proliferation of parts needed to build an 
instrument cluster and the need to provide electrical connections between 
the multiple circuit boards. 
A second well-known solution to the problem is to mount conductive metal 
clips to the circuit board. One clip is provided for each terminal of each 
gauge. Each clip has a hole with deflectable tangs protruding into the 
hole. The clips allow some tolerance for misalignment of the terminals of 
the gauges and the holes in the clips. Each terminal of each gauge is 
seated in the hole in a clip and retained by tension of the deflected 
tangs. The use of these clips, while helping to solve the gauge alignment 
problem, has a number of disadvantages. For example, the clips are much 
more expensive than simple holes in the circuit board and the use of the 
clips proliferates the number of parts needed in assembly of the circuit 
board. 
The prior art also recognizes the use of flexible material for use as the 
circuit board. Such material is typically a very thin plastic. A circuit 
board made of such flexible material does provide flexibility to help 
overcome the problem of misalignment of the gauges and their mounting 
holes. However, there are disadvantages to the use of such flexible 
material, including higher cost than traditional hard circuit board 
material and reduced reliability. 
U.S. Pat. No. 5,008,496 discloses a circuit board made of thermoplastic 
with flexible sections and non-flexible sections. The flexible sections 
are thinner than the non-flexible sections. Electronic components are 
mounted on the non-flexible sections of the circuit board. This circuit 
board, while providing flexibility to a rigid circuit board, is more 
suited to circuit boards intended to be bent into three-dimensional 
shapes. Considerable flexibility is provided to allow the circuit board to 
be bent into a box shape, while flexibility in the two dimensions in the 
plane of each non-flexible section is not assured. 
Given the lack of attractive solutions to the problem of assembling an 
instrument cluster, a hard circuit board whose gauge-mounting sections can 
be moved to allow the mounting of the gauges to the face plate of the 
instrument cluster would provide significant advantages over the prior 
art. 
SUMMARY OF THE INVENTION 
The present invention provides a circuit board with sections which can be 
moved relative to one another. 
The circuit board of this invention comprises at least one planar section 
with means for attaching electrical components such as gauges. The circuit 
board further comprises spring means which connect each planar section to 
another portion of the board so that each planar section can be moved in 
two axes which define the plane of the section. 
The circuit board of the present invention solves the problem described 
above in the production of instrument clusters. The sections of the 
circuit board can be moved to facilitate mounting of the gauges to holes 
in the face plate of the instrument cluster. Clips, which add cost and 
unreliability to the instrument cluster, can therefore be eliminated. 
Furthermore, flexible circuit board material is not required to provide 
the flexibility possessed by the circuit board of the present invention. 
Hard circuit board, which provides cost and reliability advantages over 
flexible circuit board, can be used. 
The present invention further provides an electrical device, such as an 
instrument cluster, which uses the circuit board of the present invention. 
In addition to the circuit board, the electrical device comprises a 
plurality of gauges attached to the circuit board. Further, the electrical 
device comprises a face portion, such as a face plate of an automotive 
instrument cluster. The gauges are mounted to this face portion, in 
addition to being attached to the circuit board. 
Finally, the present invention provides a method of producing an electrical 
device such as an automotive instrument cluster. The method comprises the 
step of attaching gauges to a circuit board which has movable sections. 
The method further comprises the step of mounting the gauges to a face 
plate of the instrument cluster, moving the movable sections of the 
circuit board so as to facilitate mounting the gauges to the face plate.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a circuit board 10 according to this invention. The circuit 
board has planar sections 20, 21, 22, 23, and 24, each section connected 
to another portion of the circuit board by springs 30, 31, 32, 33, 34, 35, 
and 36. FIG. 2 shows an enlargement of a part of FIG. 1, showing sections 
22 and 23 and springs 34 and 35 in greater detail. 
Sections 20, 21, 22, 23, and 24 of circuit board 10 include holes for 
attaching gauges to the sections. For example, section 22 has four holes 
221, 222, 223, and 224 through which terminals of a gauge can pass for 
attachment of the gauge to the circuit board. Section 23 similarly 
contains holes 231, 232, 233 and 234. 
In the embodiment of the invention shown in FIG. 1, springs 30, 31, 32, 33, 
34, 35, and 36 are composed of two or more beams. Referring to FIG. 2, 
spring 34 is composed of beams 341 and 342 and spring 35 is composed of 
beams 351 and 352. The beams are joined at an angle such that the beams 
are not collinear. The springs thus formed can flex. This allows the 
sections connected by the springs to be moved in relation to one another 
and in relation to the rest of the circuit board in the two orthogonal 
axes designated "x" and "y" in FIGS. 1 and 2. 
Considerable advantage is gained if circuit board 10 is made of fiberglass 
circuit board material, one of the materials commonly known in the art as 
"hard" circuit board material. (Circuit board material composed of paper, 
epoxy, fiberglass, or composites of those materials is commonly called 
"hard" circuit board material). The springs provided by the invention 
allow flexibility of circuit board 10 while maintaining the advantages of 
hard circuit board material. Those advantages include low cost and high 
durability. 
When fiberglass circuit board material is used, a very advantageous way of 
fabricating circuit board 10 of FIG. 1 is by stamping. If this method of 
fabricating circuit board 10 is chosen, the width of the beams should be 
at least twice the thickness of the circuit board. This allows circuit 
board 10 to survive the stamping process without breaking. Note, however, 
that this requirement applies if circuit board 10 is fabricated by 
stamping. If other methods of fabricating circuit board 10 are employed, 
this requirement does not necessarily apply. 
A particular type of fiberglass circuit board material widely used in 
automotive applications is known as FR-4. This type of material comes in 
standard thickness of approximately 1.5 millimeters. Therefore, if circuit 
board 10 depicted in FIG. 1 were fabricated by stamping from FR-4 circuit 
board material, the beams would be approximately 1.5 millimeters thick and 
at least 3 millimeters wide. For maximum flexibility, this lower limit of 
approximately 3 millimeters would ideally be used. 
Further flexibility of springs 30, 31, 32, 33, 34, 35, and 36 is gained 
because notches are removed from the beams which compose the springs. FIG. 
2 illustrates two such notches 50 and 51. Note that in FIG. 1, all of the 
notches in circuit board 10 are located at the point of intersection of 
two beams (as are notches 50 and 51 in FIG. 2). However, removing the 
notches from anywhere in a beam provides added flexibility. 
Notice also in FIG. 1 that some sections are joined by multiple springs 
(for example, section 22 and section 23 are joined by springs 34 and 35). 
On the other hand, some sections are joined by a single spring (for 
example, section 20 and section 21 are joined by spring 30). The use of 
multiple springs provides added strength (that is, greater resistance to 
breakage of the springs as they flex). The use of multiple springs, 
however, provides relatively less flexibility than the use of a single 
spring. 
FIGS. 3 and 4 show alternate construction of the springs of the present 
invention. Note that in FIGS. 1 and 2, all of the springs 30, 31, 32, 33, 
34, 35, and 36 are composed of two beams. Spring 37 in FIG. 3 is composed 
of three beams, 371, 372, and 373. Springs 38 and 39 in FIG. 4 are both 
composed of five beams. Spring 38 is composed of beams 381, 382, 383, 384, 
and 385. Spring 39 is composed of beams 391, 392, 393, 394, and 395. In 
general, springs composed of a greater number of beams (for example, three 
or five) tend to provide greater flexibility than springs composed of a 
smaller number of beams (for example, two). 
FIG. 5 shows another embodiment of the present invention, an automotive 
instrument cluster 60, in a partially assembled configuration. Instrument 
cluster 60 contains circuit board 10 of FIG. 1. Furthermore, instrument 
cluster 60 contains a face portion 70, which is commonly called a face 
plate in the art. Instrument cluster 60 further includes gauges 80, 81, 
82, 83, and 84. Gauge 83, representative of gauges 80, 81, 82, 83, and 84, 
is shown in FIG. 6. Gauge 83 has terminals 835, 836, 837 and 838. Gauge 83 
further has holes 831 and 832 by which gauge 83 can be mounted with screws 
to face portion 70 of instrument cluster 60. 
Referring to FIGS. 5 and 7, gauge 83 is attached to circuit board 10 by 
terminals 835, 836, 837, and 838 of gauge 83 going through holes 231, 232, 
233, and 234 in section 23 of circuit board 10. Terminals 835, 836, 837, 
and 838 are then soldered to circuit board 10. Gauges 80, 81, 82, and 84 
are attached to circuit board 10 in a similar manner. Gauge 83 is then 
mounted to face portion 70 of instrument cluster 60, by screws 91 and 92 
through holes 831 and 832 in gauge 83 and into corresponding holes 71 and 
72 in face portion 70. Gauges 80, 81, 82, and 84 are mounted to face 
portion 70 in a similar manner. 
A final embodiment of the present invention is a process for assembling an 
automotive instrument cluster. This process is illustrated with reference 
to FIG. 5. In this process, gauges 80, 81, 82, 83, and 84 are attached to 
circuit board 10. Gauges 80, 81, 82, 83, and 84 are then mounted to face 
plate 70 of instrument cluster 60. However, attaching gauges 80, 81, 82, 
83, and 84 to circuit board 10 fixes the relative positions of the gauges. 
Tolerance stack-ups make it highly unlikely that all of holes in all of 
the gauges (for instance, holes 831 and 832 in gauge 83) will then line up 
properly with all of the holes in face plate 70 (for instance, holes 71 
and 72). Therefore, the process of this embodiment of the invention 
further comprises the step of moving sections 20, 21, 22, 23, and 24 as 
required so the holes in gauges 80, 81, 82, 83 and 84 line up with the 
holes in face plate 70. Gauges 80, 81, 82, 83 and 84 are then mounted to 
face plate 70. 
Various modifications and variations will no doubt occur to those skilled 
in the arts to which this invention pertains. Such variations which 
generally rely on the teachings through which this disclosure has advanced 
the art are properly considered within the scope of this invention. For 
example, it was mentioned that "hard" circuit board is an ideal choice as 
a material for circuit board 10 of FIG. 1. However, the invention can also 
be employed to advantage if other circuit board materials are used. The 
same advantage is gained whenever a circuit board of sufficient thickness 
as to be substantially not moveable in the x-y plane illustrated in FIG. 1 
is employed. "Sufficient" thickness is a function of the particular 
material used to make the circuit board.