Printed circuit board retainer assembly

An assembly is provided for holding a printed circuit board between spaced surfaces. The assembly comprises a plurality of wedge-shaped members slidably mounted end-to-end on a rod, with at least one of those members being movable in a transverse direction relative to the rod and to its respective adjacent members upon effective shortening of the rod to thereby bring a clamping surface of the transversely movable member into contact with a printed circuit board and to apply a clamping force thereto. The retainer is disposed in a recess of a base structure which includes an abutment formed at one end of the recess. The retainer is activated by rotating the rod thereby urging the slidably mounted members towards one another. Bevelled washers are disposed on the rod between the abutment and one of the end-most members which, when compressed upon tightening of the retainer, provide a force tending to urge the members away from the abutment. When the retainer assembly is loosened the urging force of the bevelled washers tends to move the members along the rod to overcome any surface tension and friction between the clamping surface of the movable member and the circuit board which may tend to preclude quick release of the clamping surface from the board.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
The present invention relates to a retainer assembly for clamping a printed 
circuit board between spaced surfaces within a chassis, and particularly 
to a retainer assembly which facilitates entry and removal of a card from 
between those surfaces and which efficiently applies and relieves the 
clamping force between the board and the retainer. 
II. Background of the Invention 
Circuit board retainers have been developed to handle a broad range of 
applications. For example, such known retainers comprise a plastic guide 
that aligns the printed circuit board with an interface connector, or 
high-performance retainers that will captivate a printed circuit board 
under the most extreme shock and vibration conditions as encountered by 
military aircraft and spacecraft. 
Of the known printed circuit board retainers one type, described in U.S. 
Pat. No. 4,823,951 comprises a partially threaded screw or rod and a 
plurality of members slidably mounted end-to-end on the rod. The members 
disposed on the rod have end portions which are wedge-shaped and 
engageable with one another and designed to move at least one of the 
members in a transverse direction relative to the rod when the members are 
moved towards one another along the rod. 
The transverse direction in which at least one of the members is moved when 
the retainer is being locked acts to engage a clamping surface of that 
member against an edge of the printed circuit board. The opposite edge of 
the board is thereby brought into contact with and clamps against a spaced 
surface fixedly connected to or integral with the chassis in which the 
board is to be mounted. Typically, the rod in these prior art retainers is 
threaded on one end and the rod is rotated with an appropriate tool at the 
opposite end such that the threads of the rod engage with mating threads 
on a nut attached to one of the end-most members mounted on the rod. In 
this manner, the members are moved toward one another as the threaded rod 
is tightened. 
In the above described retainers a problem is encountered upon unlocking of 
the retainer because the surface tension and friction between the clamping 
surface of the transversely movable member and the edge of the circuit 
board sometimes does not permit release of the board from the clamping 
surface of the member when the retainer is unlocked. Further contributing 
to this problem is the friction between the wedge-shaped end portions of 
adjacent members of the retainer. Since these wedge-shaped end portions 
engage with end portions of adjacent members to move at least one of the 
members into clamping engagement with the printed circuit board, when the 
retainer is unlocked the friction between the respective end portions 
sometimes restrains the members from returning to their unlocked positions 
thereby interfering with removal of the board from the chassis. 
The amount of clamping force between the members of the retainer and the 
edge of the circuit board is dependent upon the torque applied to rotate 
the rod. Thus, for purposes of locking and unlocking the retainer to clamp 
or remove the printed circuit board from its chassis, efficient transfer 
and release of the torque, and hence the force applied to move the 
slidably mounted members, will result in improved operability of the 
retainer. 
Printed circuit board chassis in most of the high-performance applications 
are sealed boxes which do not allow any air to pass over the circuit 
boards for the purpose of cooling the electronic components. The heat 
generated by these components is conducted through a metal heat sink 
attached to the printed circuit board and then transmitted to a heat 
exchanger or plenum. The critical thermal interface of the heat transfer 
path becomes the printed circuit board retainer. The amount of heat that 
can be transferred depends on the surface area of the retainer, the 
surface finish of the retainer, and the clamping pressure between the 
retainer and the printed circuit board. 
It is, accordingly, an object of the present invention to provide a 
retainer and an assembly incorporating the retainer which efficiently 
transmits and releases forces applied between the rod and the slidably 
mounted members, and which acts to relieve surface tension between the 
board and the clamping surface of the members or the retainer. 
Additional objects and advantages of the invention will be set forth in the 
description which follows and in part will be obvious from the description 
or may be learned by practice of the invention. 
SUMMARY OF THE INVENTION 
To achieve the foregoing objects and in accordance with the purposes of the 
invention as embodied and broadly described herein, an assembly for 
holding a printed circuit board between spaced surfaces is provided, 
comprising: a rod, and a plurality of members slidably mounted end-to-end 
on the rod with a least one of the members having an internal longitudinal 
channel with a transverse dimension greater than the corresponding outside 
dimension of the rod to thereby permit movement of the member along a 
transverse path relative to the rod. The member which moves transversely 
relative to the rod and the members adjacent to that member each have end 
portions engageable with one another and shaped to force the transversely 
movable member in its transverse direction upon forcing of the members 
towards one another along the rod. With sufficient movement in the 
transverse direction the member engages and clamps the printed circuit 
board against a fixed surface. The assembly further includes a mechanism 
for selectively applying the force to move the adjacent members towards 
one another on the rod. The rod and slidably mounted members are received 
in a recess defined by first and second side walls of a base structure. 
The recess has a width greater than the combined width of the transversely 
movable member and the edge of the printed circuit board which is to be 
retained by the assembly. The base structure further includes an abutment 
fixedly disposed at one end of the recess. The abutment includes an 
aperture therethrough for receiving the rod. Finally, means are provided, 
disposed between the abutment and one of the end-most adjacent members, 
for urging said members away from said abutment upon release of said 
selectively applied force. 
The mechanism for applying force to move the members towards one another on 
the rod preferably comprises a head piece formed on one end of the rod and 
screw-like threads formed on the opposite of the rod for engaging mating 
threads to advance and retract the rod through the internal longitudinal 
channel of the transversely movable member as the rod is rotated. The 
threads to which the rod threads mate are preferably formed in a nut which 
is attached to one of the end-most slidably mounted members. 
Preferably, a cylindrically shaped collar piece having an internal 
longitudinal channel adapted to receive the rod is disposed within the 
aperture of the abutment to transmit the force from the rod head to the 
slidably mounted members. The collar also acts a spacer permitting the 
headed end of the rod to remain easily accessible when the assembly is 
tightened down. Also, the collar is dimensioned so as to fit in the 
aperture of the abutment of the base structure thereby permitting the rod 
to "float" within the base structure by preventing the headed end of the 
rod from engaging the abutment. 
In the preferred embodiment, the means for urging the members away from the 
abutment upon loosening of the assembly includes bevelled washers disposed 
on the rod between the abutment of the base structure and an end-most 
slidably mounted member. These bevelled washers are flattened when the 
retainer is in a loaded or locked state to provide a biasing force tending 
to oppose the applied force of the rod. The bias force of the bevelled 
washers aids in releasing the retainer by exerting a force which acts to 
overcome any surface tension or friction between the circuit board and the 
member clamping the board in place.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will now be made in detail to the present preferred embodiment of 
the invention as illustrated in the accompanying drawings. 
FIG. 1 is an end view of retainers 10 disposed in respective base 
structures 12. Each retainer 10 clamps a respective printed circuit board 
13 within its base structure. Base structures 12 are fixedly mounted to an 
inner surface of a chassis wall 15 by brazing or by screws (not shown). 
Base structure 12 may also be integrally formed with wall 15. For purposes 
of example, only one of the retainers 10 and base structures 12 will be 
described below. 
Base structure 12 includes side walls 14 and 16 which define a recess 18 
which receives retainer 10. Recess 18 has a width which is greater than 
the width of the retainer 10 such that an edge of printed circuit board 13 
may be inserted into recess 18 to be clamped between the retainer 10 and 
one of the side walls, in this instance side wall 14. Base structure 12 
includes an abutment 40 formed at one end of recess 18. Abutment 40 has an 
aperture 43 formed therethrough. 
With reference to FIG. 2, which is a top view of retainer 10 and base 
structure 12 with the printed circuit board removed, the retainer 
comprises a rod 20 and a plurality of members slidably mounted on the rod. 
In the preferred embodiment shown, the plurality of slidably mounted 
members includes end members 22 and 24, and intermediate members 26, 28, 
and 30. Intermediate members 26 and 30 are disposed adjacent member 28 and 
adjacent to respective ones of end members 22 and 24. With reference to 
FIG. 6A, each intermediate member 26, 28, and 30 is configured with an 
internal longitudinal channel 31 having a transverse dimension greater 
than the corresponding outside dimension of the rod so as to permit 
movement of the members along transverse directions 56 and 58 relative to 
the rod as will be described in detail below. End members 22 and 24 also 
are configured with an internal longitudinal channel for receiving rod 20, 
although the channel formed in the end members need not be formed with as 
great a transverse dimension as the channels of the intermediate members, 
since the end members are not required to move transversely relative to 
the rod. 
Each end of intermediate members 26, 28, and 30 is configured with an 
inclined surface 32 which mates and slidably contacts the inclined surface 
32 of an adjacent member. Similarly, the end members 22 and 24 each have 
an inclined surface 32 formed on one end thereof which mates and slidably 
contacts one end of a respective intermediate member 26 and 30. 
Intermediate members 26 and 30 have clamping surfaces 33 which engage with 
printed circuit board 13 as will be described below. 
Retainer 10 further includes means for selectively applying force to move 
the slidably mounted members 22, 24, 26, 28, and 30 towards one another on 
the rod 20. As embodied herein, the means for selectively applying force 
to the slidably mounted members comprises a head piece 34 formed on one 
end of rod 20, and screw-like threads 36 formed on the opposite end of the 
rod. In this manner, as rod threads 36 engage with mating threads, the rod 
may be rotated to be advanced through the internal longitudinal channels 
31 of the slidably mounted members, thereby causing the inclined 
edge-shaped surfaces 32 of respective members to "ride up" on the mating 
surface 32 of its adjacent member as the members are moved toward one 
another on rod 20 by effective shortening of the rod. Comparison of FIGS. 
2 and 3 shows the relative movement of the members relative one another as 
the assembly is moved between the unlocked state of FIG. 2 and the locked 
state of FIG. 3. 
In the preferred embodiment, a nut 39 having internal threads 38 is fixedly 
attached to end member 24 and aligned with the channel in end member 24 
through which rod 20 is inserted. The threads 38 of nut 39 comprise the 
mating threads with which rod threads 36 engage. With reference to FIG. 3, 
as rod 20 is rotated in a first direction to engage rod threads 36 with 
mating threads 38 of nut 39, slidably mounted members 22, 24, 26, 28, and 
30 are forced to move towards one another on rod 20 and the configuration 
of the inclined surfaces 32 of those members forces transverse members 26 
and 30 in transverse direction 58 such that clamping surfaces 33 of 
members 26 and 30 engage an edge surface of printed circuit board 13 and 
force the opposite edge surface of the printed circuit board into contact 
with side wall 14 of base structure 12 thereby anchoring the printed 
circuit board in place. 
As previously described, base structure 12 includes an abutment 40 disposed 
at one end of recess 18. Abutment 40 includes an aperture 43 therethrough 
for receiving rod 20. It is further preferable that base structure 12 
includes a second abutment 41 formed at the opposite end of recess 18. 
Abutment 41 is formed with an indentation 45 for receiving the end-most 
threaded portion of rod 20. Indentation 45 does not extend completely 
through abutment 40. In this manner, rod 20, when inserted in indentation 
45, is maintained and aligned in a substantially constant position 
relative to base structure 12 in both the locked and unlocked positions of 
the retainer assembly. 
The assembly of the present invention includes means, disposed between the 
abutment of the base structure and one of the end-most slidably mounted 
members, for urging the members away from the abutment upon release of the 
force applied to move the members towards one another. As embodied herein, 
the urging means comprises at least one, and preferably a pair, of 
bevelled washers 51 disposed on rod 20 as illustrated in FIGS. 5A and 5B. 
Each washer 51 includes a substantially flat inner portion 53 having an 
aperture formed therethrough for receiving rod 20, and a bevelled 
circumferential outer portion 55 surrounding inner portion 53. The 
bevelled configuration of outer portions 55 is best illustrated in FIG. 
5B. 
Bevelled circumferential portions 55 of washers 51 are flattened against 
one another, against the end-face of end member 22, and against the 
opposing inner face of abutment 40 as rod 20 is tightened down to move the 
slidably mounted members towards one another. This flattened configuration 
of bevelled washers 51 is best illustrated in FIG. 5A. When flattened, 
bevelled circumferential portions 55 apply a force which opposes the force 
applied by tightening rod 20. Upon release of the force apply to move the 
slidably mounted members towards one another by counter-rotation of 
threaded rod 20, the bevelled circumferential portions 55 tend to assume 
their original configuration, thereby urging end member 22 and the 
remaining slidably mounted members disposed on rod 20 away from abutment 
40. This urging force transferred to the slidably mounted members 22, 24, 
26, 28, and 30 tends to move those members along rod 20 and thus parallel 
to the edge surface of printed circuit board 13 thereby tending to 
overcome any surface tension or friction between printed circuit board 13 
and clamping surfaces 33 of intermediate members 26 and 30. Such movement 
of members 26 and 30 as washers 51 assume their original state assists in 
making a clean release between clamping surfaces 33 and the edge of the 
printed circuit board when the retainer assembly is being unlocked. 
A "sticking" phenomenon sometimes occurs between clamping surfaces 33 and 
the edge of printed circuit board 13. This "sticking" phenomenon is caused 
by surface tension and friction between the clamping surfaces and the 
board, and is also caused by friction between engaged inclined surfaces 32 
of the slidably mounted members, which friction tends to resist and 
prevent intermediate members 26, 28, and 30 from returning to their 
relaxed or unlocked positions as illustrated in FIG. 2. Because the urging 
force applied by bevelled washers 51 as they return to their original 
configuration tends to move the slidably mounted members in a direction 
parallel to the clamped edge of printed circuit board 13, that urging 
force is effective in overcoming the surface tension and friction forces 
between the printed circuit board and clamping surfaces 33, thereby 
facilitating removal of the printed circuit board from the retainer 
assembly of the present invention. 
In a second embodiment of the present invention, the assembly includes 
collar means, disposed on the rod, for transferring the applied force 
between the rod and one of the end members, in this instance end member 
22. As embodied herein, the collar means is illustrated in FIG. 4 and 
comprises a cylindrically shaped collar piece 42 having an internal 
longitudinal channel adapted to receive rod 20. Collar piece 42 is 
dimensioned so as to fit within aperture 43 of abutment 40. When head 
piece 34 of rod 20 is rotated through use of an appropriate tool such as 
an allen wrench (not shown) to move the slidably mounted members into a 
locked state wherein clamping surfaces 33 engage the edge of printed 
circuit board 13, collar piece 42 is engaged on one end by head piece 34 
and engages end member 22 at the other end. Where the collar piece and the 
bevelled washers are both employed in the assembly of the present 
invention, collar piece 42 engages the bevelled washers and not end member 
22 directly. 
Collar piece 42 acts to efficiently transmit the force applied by rod 20 to 
end member 22, and therefrom to the remaining slidably mounted members on 
the pivot rod. Collar piece 42 also acts as a buffer between head piece 34 
and end member 22 so that as the head piece and rod are torqued down, 
rotation of the rod is not transferred into rotation and wear on end 
member 22. Collar piece 42 also acts as a spacer between end member 22 and 
head piece 34 of rod 20 so as to maintain head piece 34 in a position 
extending beyond abutment 40 thereby facilitating use of an appropriate 
tool for engaging head piece 34 to rotate rod 20. Also, because rod 20 
extends within collar piece 42 and does not engage abutment 40, the rod 
"floats" within the assembly and is more easily rotated to lock and unlock 
the retainer. 
Retainer 10 may also include means, attached at least to certain ones of 
the intermediate members, for applying a spring bias between those 
intermediate members and the rod. The means for applying such spring bias 
is embodied in leaf springs 60, 62, and 64 which bias a respective one of 
intermediate members 26, 28, and 30 against rod 20 as illustrated in FIGS. 
6A and 6B. That spring bias opposes movement of a respective intermediate 
member in the transverse directions 56 and 58 relative to rod 20. 
FIGS. 6A and 6B illustrate in detail a representative one of the leaf 
springs, in this instance leaf spring 60, disposed so as to bias 
intermediated member 26 against rod 20. In FIG. 6A, leaf spring 60 is 
flexed such as when intermediate member 26 is moved transversal relative 
to the rod to engage its clamping surface 33 against circuit board 13. 
FIG. 6B illustrates the position of leaf spring 60 when the retainer is in 
an unlocked position and clamping surface 33 of member 26 does not contact 
the circuit board. Leaf springs 60, 62, and 64 serve to maintain the 
alignment of intermediate members relative to rod 20 to thereby facilitate 
removal and insertion of the printed circuit board from its chassis. As 
rod 20 is rotated to unscrew rod threads 36 from mating threads 38, the 
spring bias action of leaf springs 60, 62, and 64 act to align the 
intermediate members and end members relative to one another. 
When the retainer embodying the features described above is activated by 
means of torquing and rotating rod 20, pressure between clamping surfaces 
33, circuit board 13, and side wall 14 is generated. The contact between 
these members also comprises the thermal interface between the circuit 
board and the heat sink of the chassis. The high clamping pressure 
achievable with the present invention results in the circuit board being 
tightly held even during high shock or vibration environments. Transfer of 
heat from the components mounted on board 13 in the conduction mode 
depends on the surface area, surface finish, and clamping pressure of the 
contact and clamping surfaces comprising the heat transfer path. With 
reference to FIG. 1, the conduction heat transfer path is as follows: heat 
is generated by the components 70 mounted on the printed circuit board 13. 
A heat sink 72 is disposed between components 70 and circuit board 13. As 
the components generate heat, that heat is conducted through heat sink 72 
to the clamping surfaces 33 of retainer 10 and from there through base 
structure 12 and into chassis wall 15. When the chassis is hermetically 
sealed, cooling air flows only over the outer surface 74 of chassis wall 
15 and removes heat in a convection heat transfer mode. 
Because heat transfer is influenced by the amount of clamping pressure 
between clamping surfaces 33, side wall 14, and circuit board 13, the 
present invention acts to increase the effective amount of heat transfer 
from the circuit board due to its ability to efficiently transfer the 
force applied by rotating rod 20 into the transversely directed clamping 
force of clamping surfaces 33. 
Although a retainer employing a total of five members is disclosed as the 
preferred embodiment of the present invention, retainers with less or more 
members are also contemplated, depending on the length of the circuit 
board to be mounted. 
Additional advantages and modifications will readily occur to those skilled 
in the art. The invention in its broader aspects is, therefore, not 
limited to the specific details, representative apparatus, and 
illustrative examples shown and described. Accordingly, departures may be 
made from such details without departing from the spirit or scope of 
Applicant's inventive concept.