A CIRCUIT CARD AND A CIRCUIT CARD ASSEMBLY
The present invention relates to a circuit card and a circuit card
assembly, and generally relates to printed circuit cards, and more specifically
to printed card assemblies having controiied vibrational properties.
Background of the Invention
Rapid advances in technology and increasing consumer'demand are
driving manufacturers and suppliers of electronics systems to increase the
population density of devices on circuit cards, and to populate the circuit cards
with more powerful circuit devices. As both the number and power
consumption of the circuit devices on a circuit card increase, more heat is
produced in the card. Dissipation of these large amounts of heat require the
use of more numerous, larger and more massive heat sinks.
The increased number and large mass of such heat sinks can
significantly alter the vibrational characteristics of the circuit card assemblies
on which they are mounted, by producing large displacements of the circuit
card that can overstress various physical components on the circuit card
assembly and lead to early failures. The size and location of these large
displacements can be controlled primarily by a single heat sink that is very
large, or by a distribution of heat sinks of varying sizes.
Failures due to vibration induced displacements can occur in different
applications. Of particular concern are applications that experience a
significant amount of vibration, such as those in mobile environments. Circuit
card assemblies mounted in mobile environments often endure significant
amounts of vibration, causing the circuit card assemblies to produce large
displacements.
For the reasons stated above, and for other reasons stated below which
will become apparent to those skilled in the art upon reading and
understanding the present specification, there is a need in the art for a method
and apparatus to control vibrational properties of circuit card assemblies.
Accordingly the present invention provides a circuit card
comprising a top side and a bottom side, a deformable block
affixed to the top side wherein the deformable block is
configured, to exhibit a controlled deformation as a function of
a voltage applied thereto, a second deformable block affixed to
the bottom side at a point substantially opposed to the
deformable block affixed to the top side, and a control system
coupled to the first and second deformable blocks, the control
system configured to detect displacement of the circuit card, to
apply the voltage to the deformable block as a function
thereof, and to apply a voltage to the second deformable block
that is substantially 180 degrees out of phase relative to the
voltage applied to the deformable block affixed to the top side,
wherein the voltage supplied to the first and second
deformable blocks are not of the same amplitude.
The present invention also provides a circuit card
assembly comprising a circuit card, a pair of piezoelectric
wafers mounted to opposite sides of a circuit card at a first at
a first anti-node region of the circuit card, a trigger wafer
mounted to the circuit card at a second anti-node region of the
circuit card, a voltage sensor coupled to the trigger wafer, and
a control system coupled between the voltage sensor and the
pair of piezoelectric wafers, the control system being
configured to supply separate electric potentials to the pair of
piezoelectric wafers responsive to a voltage received from the
voltage sensor, wherein the control system comprises a trigger
circuit configured to supply the separate electric potentials
when the voltage received from the voltage sensor exceeds a
threshold.
The present invention further provides a circuit card
assembly comprising a first side, and a second side opposing
the first side, a first piezoelectric wafer affixed to the first
side, the first piezoelectric wafer being configured to receive a
first voltage and deform in response thereto, a second
piezoelectric wafer affixed to the second side, the second
piezoelectric wafer being configured to supply a second
voltage in response to being deformed, a third piezoelectric
wafer affixed to the second side, the third piezoelectric wafer
being configured to receive a third voltage and deform in
response thereto, and a control system coupled to the first,
second and third piezoelectric wafers, to receive the second
voltage and to produce the first and third voltages
substantially 180 degrees out of phase, wherein the control
system is configured to produce first and third voltages of
different amplitudes.
The present invention still further provides a circuit card
comprising a top side and a bottom side, a deformable block
affixed to the top side, wherein the deformable block is
configured to exhibit a controlled deformation as a function of
a voltage applied thereto, a second deformable block affixed to
the bottom side at a point substantially opposed to the
deformable block affixed to the top side, and a control system
coupled to the first and second deformable blocks, the control
system configured to detect displacement of the circuit card, to
apply the voltage to the deformable block as a function
thereof, and to apply a voltage to the second deformable block
that is substantially 180 degrees out of phase relative to the
voltage applied to the deformable block affixed to the top side,
wherein the deformable blocks affixed to the top and bottom
sides are piezoelectric wafers, the circuit card also comprising
a trigger wafer affixed to the circuit card at a location that
flexes when the circuit card is vibrated, such that the control
system is responsive to a voltage produced by the trigger
wafer, and wherein the control system comprises a trigger
circuit coupled to the trigger wafer, the trigger circuit
configured to supply the voltages to the first and second
deformable blocks when the voltage received from the trigger
wafer exceeds a threshold.
The present invention still further provides a circuit card
assembly comprising a circuit card, a pair of piezoelectric
wafers mounted to opposite sides of a circuit card at a first at
a first anti-node region of the circuit card, a trigger wafer
mounted to the circuit card at a second anti-node region of the
circuit card, a voltage sensor coupled to the trigger wafer, and
a control system coupled between the voltage sensor and the
pair of piezoelectric wafers, the control system being
configured to supply separate electric potentials to the pair of
piezoelectric wafers responsive to a voltage received from the
voltage sensor, wherein the control system comprises an
amplifier that supplies the separate electric potentials
substantially 180 degrees out of phase relative to each other,
and wherein the separate electric potentials supplied to the
pair of piezoelectric wafers are not of the same amplitude.
Brief Description of the Accompanying Drawings
Figures 1A and IB show edge views of a generally planar circuit card
assembly in accordance with an embodiment of the invention; and
Figures 2 and 3 show edge views of alternate embodiments of circuit
card assemblies.
Description of Embodiments
In the following detailed description of the embodiments, reference is
made to the accompanying drawings that show, byway of illustration, specific
embodiments in which the invention may be practiced. In the drawings, like
numerals describe substantially similar components throughout the several
views. These embodiments are described in sufficient detail to enable those
skilled in the art to practice the invention. Other embodiments may be utilized
and structural, logical, and electrical changes may be made without departing
from the scope of the present invention. Moreover, it is to be understood that
the various embodiments of the invention, although different, are not
necessarily mutually exclusive. For example, a particular feature, structure, or
characteristic described in one embodiment may be included within other
embodiments. The following detailed description is, therefore, not to be taken
in a limiting sense, and the scope of the present invention is defined only by
the appended claims, along with the full scope of equivalents to which such
claims are entitled.
The method and apparatus of the present invention provide a mechanism
for altering the vibrational properties of circuit cards and circuit card
assemblies, m some embodiments, piezoelectric wafers are intimately affixed
to circuit cards to control expansion and contraction as a function of circuit
card displacement. The piezoelectric wafers can have a voltage imposed
thereon to control expansion. In some embodiments, piezoelectric wafers are
affixed to opposing sides of a circuit card. When the circuit card flexes, a
voltage is applied to one or more of the piezoelectric wafers, which in turn
expand or contract.
Piezoelectric wafers can also be used to detect when a circuit card is
flexing. In some embodiments, a piezoelectric wafer affixed to the circuit card
generates a voltage as the circuit card flexes, and provides the voltage to a
mntml svstem that applies a voltage to the other piezoelectric wafers. As a
result, displacement of the circuit card can be reduced when the circuit card is
vibrated.
Figure 1A shows an edge view of a generally planar circuit card
assembly. Circuit card assembly 100 includes circuit card 102 having
piezoelectric wafers 104, 106, and 110 affixed thereto. Piezoelectricity is a
property of certain classes of crystalline materials. When an electric field is
applied to a polarized piezoelectric material, the crystalline structure changes
shape, producing dimensional changes in the material in a specific plane,
governed by the polarization. Conversely, when mechanical pressure is
applied to one of these materials, the crystalline structure produces a voltage
proportional to the pressure.
Piezoelectric wafers 104, 106, and 110 are affixed to circuit card 102
during manufacture of the circuit card. Piezoelectric wafers 104, 106, and 110
can be any type of material having piezoelectric properties. One such exampl z
is PZT-5H Bimorph available from Morgan Mitroc, Inc. PZT-5H has high
permissiviry and coupling, and also has high piezoelectric constant.
Piezoelectric wafers 104, 106, and 110 are examples of deformable blocks that
deform in a controlled manner, causing the circuit card to deform in a
controlled manner. Any type of deformable block can be used without
departing from the scope of the present invention.
The method and apparatus of the present invention allows the
transformation from electrical energy to mechanical energy by affixing
piezoelectric material to circuit card 102. When an electrical potential is
applied between two electrodes on a piezoelectric wafer affixed to circuit card
102, the piezoelectric wafer expands or contracts and applies a flexing force
on the circuit card.
Piezoelectric wafers that are used to generate a voltage as a result of
mechanical pressure are hereinafter referred to as "trigger wafers."
Piezoelectric wafers that have a voltage applied thereto are hereinafter referred
to as "flex wafers." This terminology is in no way meant to limit the use to
which a particular piezoelectric wafer can be put. Rather, this terminology is
used to facilitate the explanation of the various embodiments that include
multiple piezoelectric wafers. In the embodiment of Figure 1A, wafers 104
and 106 are flex wafers, and wafer 110 is a trigger wafer.
Trigger wafer 110 generates a voltage as circuit card 102 flexes.
Voltage sensor 112 senses the voltage and supplies the voltage to control
system 114. Control system 114 applies a voltage to flex wafers 104 and 106
as a function of the voltage received from voltage sensor 112. A control loop
is formed by circuit card 102, trigger wafer 110, voltage sensor 112, control
system 114, and flex wafers 104 and 106. As circuit card 102 flexes, trigger
wafer 110 generates a voltage, and control system 114 applies a voltage to flex
wafers 104 and 106 to reduce the flexing of circuit card 102. In some
embodiments, control system 114 includes amplifiers and filters.
Figure IB shows an edge view of a flexing circuit card. As shown in
Figure IB, circuit card 102 has a mode shape in which node 120 remains
substantially still, and the areas about node 120 flex. The term "mode shape '
refers to the shape assumed by circuit card 102 as a result of being vibrated.
Circuit card 102 has a "dominant mode shape" which is the shape of circuit
card 102 when circuit card 102 flexes at a resonant frequency. Circuit card
102 can also flex at frequencies different from the resonant frequencies.
Displacements of circuit card 102 are generally largest when circuit card 102
flexes in the dominant mode shape. The amount of displacement for any
given mode shape is termed "modal displacement." Regions of largest modal
displacements are termed "anti-nodes" and are shown as anti-nodes 122 and
124. Trigger wafer 110, as a result of mechanical pressure -1-1-3- caused by the
flexing of circuit card 102, produces a voltage at node 111. As circuit card
102 flexes over time, voltage 111 changes accordingly.
Flex wafers 104 and 106 are configured to receive voltages on nodes
135 and 137 respectively. Control system 114 (Figure 1A) applies voltages t3
nodes 135 and 137, and forces 134 and 136 result. Flex wafer 104,
undergoing force 134, works against the deformation of circuit card 102
shown in Figure IB. Likewise, flex wafer 106, undergoing force 136, also
works against the current deformation of circuit card 102.
Circuit card 102, as shown in Figure IB, represents the deformation of i
circuit card at a fixed point in time. In some embodiments, circuit card 102
flexes back and forth such that the voltage at node 111 generated by trigger
wafer 110 oscillates. Referring now back to Figure 1A, control system 114
receives an oscillating voltage from voltage sensor 112 as circuit card 102
f, vibrates. In response, control system 114 applies oscillating voltages to flex
\wafers 104 and 106. For example the voltage generated by trigger wafer 11C
can be of the form:
Asin(4t) Eq. 1.
where A is the amplitude and 4 is the natural frequency of the dominant mode
shape that is desired to be controlled. In response to this voltage, control
system 114 produces two signals. One is of the form:

and is applied to flex wafer 104. The other signal is of the form:

and is applied to flex wafer 106. B and C represent the amplitudes of the
signals applied to flex wafers 104 and 106, respectively. In some
embodiments, B and C are the same. An offset angle, _, is applied to both
signals as appropriate by control system 114. Values for B, C, and _ can be
derived by one skilled in the art of control system theory. These values are
preferably chosen such that adequate gain and phase margins exist to keep the
control loop stable. Flex wafers 104 and 106 have signals 180 degrees out
phase applied thereto, as shown by the symbol ". This ensures that flex wafers
104 and 106 work together to counteract the flexing of circuit card 102.
Flex wafers 104 and 106 are shown mounted to opposing sides of circuit
card 102 at anti-node region 122. Trigger wafer lift-is- shown mounted at a
separate anti-node region 124. In some embodiments, trigger wafer 110 is
mounted near anti-node region 122, such that trigger wafer 110 is in close
proximity to flex wafers 104 and 106.
In the embodiment shown in Figure IB, a mode shape is shown having
node 120 and anti-nodes 122 and 124. A circuit card can take on more than
one mode shape. For example, under differing vibration environments, the
cross-section of circuit card 102 shown in Figure IB can have two or more
nodes 120, and three or more anti-nodes. In some embodiments, multiple
trigger wafers are positioned on circuit card 102 such that a trigger wafer is
located at at least one anti-node of each mode shade. In some embodiments, a
separate control system 114 (Figure 1 A) is incorporated for each mode shape,
such that deformation of circuit card 102 can be reduced for more than one
mode shape.
Figure 2 shows an edge view of an alternate embodiment of a circuit
card assembly having controlled vibrational properties. Circuit card 120
includes trigger wafer 110 and flex wafers 104 and 106. Control system 114
(Figure 1 A) is replaced in Figure 2 by trigger circuit 202 and oscillators 204
and 206. Trigger circuit 202 senses a voltage provided by voltage sensor 11?..
When the voltage exceeds a threshold, trigger circuit 202 triggers oscillators
204 and 206 that generate signals at the frequency of the standing wave
induced in circuit card 120 by vibratory forces. Oscillators 204 and 206 are
substantially 180 degrees out of phase such that the mechanical forces
produced by flex wafers 104 and 106 are substantially opposite. For example,
when flex wafer 104 is expanding, flex wafer 106 is contracting.
In some embodiments, trigger circuit 202 can include circuitry that
adjusts the amplitude of signals generated by oscillators 204 and 206 as a
function of the voltage received from voltage sensor 112. In other
embodiments, trigger circuit 202 senses when the voltage from voltage senso-
112 exceeds a threshold, and turns oscillators 204 and 206 on and off without
adjusting the amplitude of the signals produced.
In some embodiments, trigger circuit 202 includes circuitry to detect the
frequency of the signal produced by voltage sensor 112. When the frequency
of the signal from voltage sensor 112 matches the frequency of the mode
shape that flex wafers 104 and 106 suppress, then trigger circuit 202 turns on
oscillators 204 and 206. When the frequency does not match, then the currem
mode of circuit card 120 may be one different from that which flex wafers 104
and 106 suppress, and oscillators 204 and 206 are not turned on.
Figure 3 shows an edge view of an alternate embodiment of a circuit
card having controlled vibrational properties. Circuit card 120, as shown in
Figure 3, includes one flex wafer 104 at anti-node 122, and trigger wafer 110
at anti-node 124. Trigger wafer 110 can be affixed to circuit card 120 on
either the top or the bottom. In the embodiment shown in Figure 2, trigger
wafer 110 is shown on the bottom.
In some embodiments, trigger wafer 110 is affixed to circuit card 120
substantially opposite flex wafer 104. In these embodiments, modal
displacements can be reduced regardless of the mode shape, in part because
the voltage applied to flex wafer 104 is a function of its own displacement.
Since trigger wafer 110 is affixed substantially opposite flex wafer 104, they
both undergo substantially the same displacement, and the voltage generated
by trigger wafer 110 can provide useful feedback to flex wafer 104 regardless
of the mode shape. In some embodiments, locations other than nodes or
antinodes can be selected for affixing wafers in accordance with the present
invention.
It is to be understood that the above description is intended to be
illustrative, and not restrictive. Many other embodiments will be apparent to
those of skill in the art upon reading and understanding the above description.
The scope of the invention should, therefore, be determined with reference tc
the appended claims, along with the full scope of equivalents to which such
claims are entitled,
WHAT IS CLAIMED IS :
1. A circuit card comprising :
a top side and a bottom side ;
a deformable block affixed to the top side wherein the deformable
block is configured to exhibit a controlled deformation as a function of a
voltage applied thereto ;
a second deformable block affixed to the bottom side at a point
substantially opposed to the deformable block affixed to the top side ; and
a control system coupled to the first and second deformable blocks, the
control system configured to detect displacement of the circuit card, to apply
the voltage to the deformable block as a function thereof, and to apply a
voltage to the second deformable block that is substantially 180 degrees out
of phase relative to the voltage applied to the deformable block affixed to the
top side ;
wherein the voltage supplied to the first and second deformable blocks
are not of the same amplitude.
2. The circuit card as claimed in claim 1 wherein the deformable block
comprises a crystalline material having piezoelectric properties.
3. The circuit card as claimed in claim 1 wherein :
the circuit card exhibits a dominant mode shape when vibrated, the
dominant mode shape having a region of large modal displacement; and
the deformable blocks affixed to the top and bottom sides of the circuit
card are located at substantially the region of large modal displacement.
4. The circuit card as claimed in claim 3 wherein the deformable blocks
affixed to the top and bottom sides are piezoelectric wafers, the circuit card
also comprising :
a trigger wafer affixed to the circuit card at a location that flexes when
the circuit card is vibrated, such that the control system is responsive to a
voltage produced by the trigger wafer.
5. A circuit card assembly comprising :
a circuit card ;
a pair of piezoelectric wafers mounted to opposite sides of a circuit
card at a first at a first anti-node region of the circuit card ;
a trigger wafer mounted to the circuit card at a second anti-node region
of the circuit card ;
a voltage sensor coupled to the trigger wafer; and
a control system coupled between the voltage sensor and the pair of
piezoelectric wafers, the control system being configured to supply separate
electric potentials to the pair of piezoelectric wafers responsive to a voltage
received from the voltage sensor;
wherein the control system comprises a trigger circuit configured to
supply the separate electric potentials when the voltage received from the
voltage sensor exceeds a threshold.
6. The circuit card assembly as claimed in claim 5 wherein the separate
electric potentials supplied to the pair of piezoelectric wafers are of
substantially the same amplitude.
7. The circuit card assembly as claimed in claim 5 wherein the separate
electric potentials supplied to the pair of piezoelectric wafers are not of the
same amplitude.
8. A circuit card assembly comprising :
a first side, and a second side opposing the first side ;
a first piezoelectric wafer affixed to the first side, the first piezoelectnc
wafer being configured to receive a first voltage and deform in responss
thereto ;
a second piezoelectric wafer affixed to the second side, the seconc1
piezoelectric wafer being configured to supply a second voltage in response
to being deformed ;
a third piezoelectric wafer affixed to the second side, the third
piezoelectric wafer being configured to receive a third voltage and deform in
response thereto ; and
a control system coupled to the first, second and third piezoelectric
wafers, to receive the second voltage and to produce the first and third
voltages substantially 180 degrees out of phase ;
wherein the control system is configured to produce first and third
voltages of different amplitudes.
9. The circuit card as claimed in claim 8 wherein the second piezoelectric
wafer is affixed to the second side substantially opposite the first piezoelectric
wafer.
10. The circuit card as claimed in claim 8 wherein the first piezoelectric
wafer is affixed at a first anti-node of the circuit card, and the second
piezoelectric wafer is affixed at a second anti-node of the circuit card.
11. The circuit card as claimed in claim 10 wherein the third piezoelectric
wafer is affixed substantially opposite the first piezoelectric wafer.
12. A circuit card comprising :
a top side and a bottom side ;
a deformable block affixed to the top side, wherein the deformable
block is configured to exhibit a controlled deformation as a function of a
voltage applied thereto ;
a second deformable block affixed to the bottom side at a poirt
substantially opposed to the deformable block affixed to the top side ; and
a control system coupled to the first and second deformable blocks, tho
control system configured to detect displacement of the circuit card, to apply
the voltage to the deformable block as a function thereof, and to apply a
voltage to the second deformable block that is substantially 180 degrees oul
of phase relative to the voltage applied to the deformable block affixed to the
top side ;
wherein the deformable blocks affixed to the top and bottom sides are
piezoelectric wafers, the circuit card also comprising a trigger wafer affixed to
the circuit card at a location that flexes when the circuit card is vibrated, such
that the control system is responsive to a voltage produced by the trigger
wafer; and
wherein the control system comprises a trigger circuit coupled to the
trigger wafer, the trigger circuit configured to supply the voltages to the first
and second deformable blocks when the voltage received from the trigger
wafer exceeds a threshold.
13. A circuit card assembly comprising :
a circuit card ;
a pair of piezoelectric wafers mounted to opposite sides of a circuit
card at a first at a first anti-node region of the circuit card ;
a trigger wafer mounted to the circuit card at a second anti-node region
of the circuit card ;
a voltage sensor coupled to the trigger wafer; and
a control system coupled between the voltage sensor and the pair of
piezoelectric wafers, the control system being configured to supply separate
electric potentials to the pair of piezoelectric wafers responsive to a voltage
received from the voltage sensor;
wherein the control system comprises an amplifier that supplies the
separate electric potentials substantially 180 degrees out of phase relative to
each other, and wherein the separate electric potentials supplied to the pair of
piezoelectric wafers are not of the same amplitude.

Piezoelectric wafers (104, 106) are affixed to a circuit card (102) to control displacement of the circuit card (102) when vibrated. A trigger wafer (110) located at an anti-node of the dominant mode shape produces a voltage as a function of modal displacement. A control system (114) responsive to the trigger wafer (110) produces voltages that are applied to flex wafers (104, 106) at a different anti-node of the dominant mode shape. The flex wafers (104, 106) expand and contract in a manner that reduces the modal displacement of the circuit card (102). Multiple flex wafers (104, 106) can exist, affixed to the circuit card (102) substantially
opposite each other, or a single flex wafer (104) can exist with a single trigger wafer (110). The trigger wafer can be located substantially opposite the flex wafer or can be located elsewhere on the circuit card.