Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-07-30
2001-11-27
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S13800J
Reexamination Certificate
active
06323437
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to clamps, and more particularly to spring clamps for electronic components.
BACKGROUND OF THE INVENTION
Components are usually integrated into a system by securing the components to an assembly. There are many ways to secure components to an assembly. Often, components are clamped to a circuit board. As shown in
FIG. 1
, components
14
,
18
are clamped to circuit board
20
to hold components
14
,
18
in place when components
14
,
18
are being soldered into place. Additionally, components are clamped to the circuit board rather than being soldered to the circuit board when it is difficult to provide a secure solder connection between the components and the circuit board or when it is useful to be able to rework the components. This is particularly advantageous for expensive components. For example, if a component is attached to a circuit board by solder, the entire circuit board has to be heated to melt the solder connection and remove the component. Clamping the component to the circuit board allows the component to be easily removed and replaced, without affecting the other components on the circuit board.
FIG. 2
a
shows assembly
50
having component
52
clamped to circuit board
54
with clamp
56
. Typically, circuit board
54
is connected to back plate
58
. Clamp
56
has rigid metal bar
72
, and more compliant bar
74
, for example fabricated from FR4. Bars
72
,
74
are fastened to circuit board
54
and back plate
58
with screws
76
,
78
. Circuit board
54
has an opening through which the bottom of component
52
contacts back plate
58
. Referring to
FIGS. 2
a
and
2
b
, component
52
is typically, one, or a plurality of semiconductor devices or integrated circuits (ICs)
60
housed in plastic or ceramic package
62
. Package
62
has walls
77
,
79
and lid
80
. There is a thin conductive layer on the bottom of package
62
referred to as a flange. Flange
64
is electrically coupled to the bottom of device or IC
60
. Leads
68
,
70
of component
52
contact circuit board
54
. Clamp
56
has to apply enough force to component
52
to press component
52
tightly enough to the rest of assembly
50
to ensure that there is a sufficient electrical connection between flange
64
and back plate
58
and between leads
68
,
70
and circuit board
54
. Screws
76
,
78
hold bars
72
,
74
tightly to component
52
so that bars
72
,
74
apply force to component
52
.
A problem with using clamp
56
to attach component
52
to circuit board
54
and back plate
58
is that when clamp
56
applies enough force to component
52
to ensure sufficient electrical connection a significant amount of force is asserted against lid
80
. For example, in an RF transistor 250 to 300 lbs./sq.in. of force may be needed to ensure sufficient electrical connection. The thin lid of the package of many components is too thin to withstand this much force, causing the package to crack.
Furthermore, the force exerted by clamp
56
varies based on the tolerances of screws
76
,
78
and the coefficient of friction between screws
76
,
78
and back plate
58
. This force will vary from clamp to clamp and screw to screw. Therefore, to ensure a sufficient electrical connection in the worst case, more force than the 250 to 300 lbs./sq.in. has to be applied. This force is often large enough to crack lid
80
of many components.
Another problem with using clamp
56
to attach component
52
to circuit board
54
and back plate
58
is that the tolerances of package
62
do not ensure that clamp
56
will evenly press against component
52
to ensure a sufficient electrical connection. The tolerances in manufacturing package
62
allow for a package that is not completely flat. When clamp
56
presses against component
52
, because metal bar
72
is rigid, gap
81
forms between bar
74
and component
52
, even though bar
74
is somewhat compliant. Clamp
56
does not apply enough force to the portion of component
52
under gap
81
. This may cause an insufficient electrical connection between the portion of flange
64
under gap
81
and back plate
58
, so component
52
does not function acceptably.
To get a better electrical connection, more force can be applied on component
52
by clamp
56
. However, now the force on taller side
82
of the package is even greater. Often this force is too great for lid
80
of many components to withstand, causing the package to crack and rendering component
52
useless.
Yet another problem with fastening component
52
to assembly
50
is that when clamp
56
is being fastened it can easily crack component
52
as shown in FIG.
3
. Clamp
56
can be fastened to assembly
50
by either first tightening screw
76
fully into place and then tightening the other screw, or by gradually tightening each screw while constantly alternating between the two screws. Tightening screw
76
fully places all of the force of clamp
56
on corner
82
of component
52
, crushing corner
82
. This can cause a crack to start in corner
82
, which will then spread to the rest of the top of the package of component
52
, rendering component
52
useless. Gradually tightening each screw while constantly alternating between the two screws reduces this problem, however, it is much more time and labor intensive, which greatly increases the time and cost of the assembly.
SUMMARY OF THE INVENTION
The invention solves the above problems by providing a spring clamp for fastening a component to an assembly. The spring clamp provides a sufficient and adequately even electrical connection between the component and the rest of the assembly by providing deflection in the frame of the clamp. The force applied by the clamp to the component can be adjusted because of the deflection of the clamp. This allows the clamp to apply enough force to produce a sufficient electrical connection between the component and the rest of the assembly, but not enough force to crack the component. One section of the frame can have a different angle of deflection than another section of the frame, allowing the clamp to adjust when the top of the package of the component is not flat. The fact that the sections of the frame can have different amounts of deflection, and the clamp's ability to adjust the force that it applies to the component allows the clamp's fasteners to be tightened independently without putting so much force on the side of the component closest to the fastener that this side cracks.
Furthermore, the spring clamp prevents cracking of the component's package by applying much of the clamping force on the walls of the package rather than on the center of the package lid. The walls can support more force than the lid because the walls of the package are more rigid than the lid. This allows the clamp to exert a larger force on the component without cracking the package.
The spring clamp has a frame, a spacer structure, and fasteners. Preferably, the spacer structure has a first and second spacer. In one embodiment of the invention, the frame of the clamp has a top section whose central portion is capable of deflection. The deflection in the frame varies based on the size and shape of the component. This allows the clamp to apply enough force to all of the component to produce a sufficient electrical connection between the component and the assembly. In another embodiment of the invention, one or both, of the spacers have an opening through at least a portion the spacer in the location where the spacer is positioned over the component. The opening places most of the force of the clamp on the walls of the component package.
REFERENCES:
patent: 4595794 (1986-06-01), Wasserman
patent: 5099392 (1992-03-01), Miller et al.
patent: 5282111 (1994-01-01), Hopfer
patent: 5435734 (1995-07-01), Chow
patent: 5561594 (1996-10-01), Wakefield
patent: 5761036 (1998-06-01), Hopfer et al.
Gaffin Jeffrey
Lager Irena
Lucent Technologies - Inc.
Norris Jeremy
LandOfFree
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