Replaceable air seal for force cooled removable electronic units

A rubber seal vulcanized to a removable strip is shown for forming a replaceable air seal for a plug-in printed circuit board or the like which is removeably mounted in a frame. The rubber seal defines upwardly outwardly extending sealing lips in a configuration having generally parallel sides and closed ends and dimensioned to sealingly engage the opposed facing surfaces of a pair of pre-assembled spaced circuit boards having the electrical components mounted thereon disposed in the space therebetween. The strip supporting the rubber seal is slidably received within machined grooves in opposed facing mounting plate members for the boards. Apertures in the opposed mounting plates and apertures in the strip are in alignment therewith when the strip is properly inserted within the plates. The rubber seal surrounds the aperture of the strip and seals against the opposed facing boards and attached supports to direct cooling air into the space between the boards through the aligned apertures. As the rubber sealing lips become damaged through repeated removal and reinsertion of the board pair assembly, the seal is readily replaced by removing and inserting a new strip having a seal bonded thereto.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an air seal for sealingly engaging a printed 
circuit board to deliver cooled air across electrical components mounted 
thereon and more particularly to a removable air seal which is easily 
replaced as it becomes damaged. 
2. Description of the Prior Art 
It is common practice to mount printed circuit boards in a frame wherein 
the boards are removably retained in side-by-side array in generally 
parallel planes. The boards are spaced from one another to provide 
clearance for the electrical elements that are mounted on each board. 
Operation of the circuit of each board produces heat, which at least in 
the generally large arrays of circuit boards, must be dissipated or the 
components would overheat. Thus, it is also common to direct cooling air 
between the spatially separated circuit boards to provide a means of 
removing the heat. Further, it is not uncommon for such array to be used 
in an environment, such as an airplane, where the amount of cooling air is 
rather limited and thus its effect must be optimized. 
As more clearly explained in reference to the figures describing the prior 
art, it has been common practice to pre-assemble two adjacent circuit 
boards in spatially separated orientation with the surfaces of each board 
on which the electrical components are mounted in facing arrangement. This 
permits the cooling air to be directed between the two boards to cool the 
components of each board. The assembled board pairs are then removably 
mounted in a frame with each pair bridging an elongated opening therein 
that permits cooling air to be fed therebetween. Flexible seals are 
provided, between the inner face of the boards and the elongated aperture 
in the base plate of the frame through which the air flows, to provide a 
seal between the air opening and the interior space to limit cooling air 
leakage. However, after repeated removal and replacement of the paired 
board assembly, as for checking and/or repair, the flexible stationarily 
mounted seals become damaged to the extent it is necessary to replace 
them. Heretofore, this has essentially required the replacement of the 
plate member on which the seals are attached which in turn could result in 
the removal of all boards and the replacement of all seals even though 
only the replacement of a few seals is required. Alternatively, the repair 
could be made by removal of sufficient number of paired circuit boards 
from the frame to permit replacement of individual seals by forcefully 
removing the seals from their supposedly permanent attachment to the frame 
plate and re-gluing new seals in their position, all of which is 
relatively laborious and time consuming. 
SUMMARY OF THE INVENTION 
The invention provides a replaceable air seal of a silicon rubber bonded 
(i.e. as by vulcanizing) to a planar strip of material which in turn is 
slideably received in a tongue-and-groove arrangement for retention in the 
opposed supporting plates of the frame which mount the aligned circuit 
boards. The strip has an elongated aperture corresponding to and, when 
assembled in the plate, generally coterminous with, the air openings in 
the plates. As before, the seals seal the air opening to the interior 
space of a pair of pre-assembled spatially separated circuit boards 
(hereinafter called a board pair assembly). Each strip is slid into its 
position and is retained therein so as not to be displaced by removal or 
insertion of the board pair assembly however, upon becoming ineffective as 
a seal, each single strip is readily removed and replaced by an effective 
seal on a new strip.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 through 3, a typical printed circuit board and 
mounting frame assembly for a modular electronic system is shown along 
with an air seal arrangement which is illustrative of the prior art as 
heretofore generally described. Thus it is seen that the modular system 10 
for receiving pluggable, removable circuit board assemblies 11 includes a 
pair of spaced, opposed generally horizontal rectangular plates 12, 14 
with the upper plate 14 being generally a duplicate of the lower plate 12 
and thus the description of plate 12 will be sufficient to describe both 
plates. The plates are mounted in any well known manner and form a part of 
a frame 16 which, at one end supports a plurality of vertically oriented 
electrical connectors 18 for connection to the apparatus being operated or 
controlled through the circuits of the board assemblies 11 of this system. 
The opposed facing surfaces of the plates 12, 14 define aligned circuit 
board receiving channels 20 sized to slidably receive a pair of circuit 
boards 11a, 11b, pre-assembled in a spaced facing relationship, as 
explained subsequently, with the electrical components (see FIG. 3) 
mounted on each board disposed in the space provided between them. Each 
channel 20 for receiving the board pair assembly 11 is defined by a pair 
of ribs 22 extending the full width of the plate 12, 14 and having at the 
receiving end a tapered nose 24. The ribs are spaced so as to closely 
receive the board pair assembly therebetween with the rib face 26 closely 
adjacent the outside surface of the board pair assembly 11. An 
intermediate raised portion 28, inset from the receiving edge 30, extends 
substantially to the opposite edge 32 of the plates 12, 14 and projects 
upwardly a short distance (i.e. less than the height of the separating 
ribs 22) so that the sides 34 of the raised portion are in opposed facing 
relationship with an adjacent rib 22 and cooperates therewith to define a 
groove 36 sized to slidingly receive an individual circuit board 11a or 
11b of the board pair assembly 11. 
The intermediate portion 28 contains slits 38 throughout its length closely 
adjacent each side in the portion and also defines an elongated aperture 40 
through the plates 12, 14 to place the space 42 between the boards 11a, 11b 
of the board pair assembly 11, as mounted therein, in cooling air flow 
communication with pressurized cooling air, such as from a plenum chamber 
44 below the lower plate 12. The receiving end 46 of the raised 
intermediate portion 28 is seen to define an initial shoulder taller than 
the remaining portion and also has mounted adjacent its front face, a 
block 48 of sealing material for engaging in sealing relationship certain 
internal surfaces of the board pair assembly 11 (to be defined) when the 
assembly 11 is properly positioned between the plates 12, 14 and plugged 
into the connector 18. Likewise the opposite end of the raised portion 28 
supports a block 50 of sealing material for sealing engagement with 
appropriate internal structure of the board pair assembly 11. 
A thin strip of rubber or resilient material 52 is inserted into each slit 
38 in the raised portion 28 and extends the length thereof. (Generally 
this requires depositing a bonding material in each slit and manually 
inserting one edge of the flexible rubber strip therein, which, upon 
curing of the bonding material, results in a relatively permanent 
attachment of the rubber seal within the slit.) 
The strip 52 is pre-formed to, in its normal, unbiased position, provide a 
flap portion 54 extending outwardly toward and generally overlying the 
adjacent groove 36. It should be noted that upon insertion of a circuit 
board 11a, 11b into the groove 36, the flap 54 is deformed into a 
generally vertical configuration (see FIG. 3) with an inherent bias into a 
sealing relationship with the inner surface of the board. 
As previously stated, the circuit boards 11a, 11b are pre-assembled into 
spaced facing pairs by being attached in a co-terminous relationship on 
vertical struts 56, generally adjacent each end. A vertical electrical 
plug-in connector 58 for mating with the connector 18 on the frame 16 is 
secured to each board along one vertical edge to, in the assembled 
arrangement, provide a common end for connection into the stationary 
connector 18. The internal facing surfaces of the struts 56 support 
vertical U-shaped members 60 extending generally the height of the 
associated strut. Also, it will be understood that the ends of the strut 
56 adjacent the connector 58 are inset from the top and bottom edge of the 
board pair assembly to provide clearance over the intermediate raised 
portion 28 of the plates 12, 14; however, upon complete engagement of the 
plug-in connectors 58, 18, the ends of this strut 56 sealingly engage the 
sealing blocks 50 on the adjacent end of the raised portion 28. Likewise, 
the opposite strut 56 is of a vertical length to sealingly engage the 
sealing block 48 adjacent the receiving end of the intermediate portion 
28. 
Thus, with the circuit board pair assembly 11 in place as shown in these 
FIGS. (1-3), the rubber sealing strip 52 engages the inner facing surfaces 
of the boards 11a, 11b and the U-shaped vertical members are sealingly 
engaged by blocks 48, 50 to form a seal generally at the interface of the 
boards and their support plates 12, 14. The U-shaped vertical members 
complete the vertical seal of the space between the boards so that cooling 
air entering the slots 40 in the plate 12 is confined to flow in the space 
42 between the assembled boards, cooling the electrical components within 
the space and exit through the top plate 14, for recirculation, or for 
continued circulation into the next upper adjacent similar circuit board 
mounting arrangement, with minimal air leakage. 
However, after repeated removal and reinsertion of the pluggable board pair 
assembly 11, the flap portion 54 of the rubber seals 52 which extend out 
over the grooves 36 and are deformed by inserting the boards, sometimes 
get caught by the boards and are torn, or, over a period of time, become 
worn and damaged to the extent that they no longer provide the desired air 
seal with the surface of the boards. The repair of these individual bonded 
seals generally requires the circuit board assemblies to be removed for 
access to the plates 12, 14, and the rubber strip manually removed and the 
slit 38 cleaned, a bead of glue or bonding material deposited in the slit 
and a new rubber strip 52, cut to size, inserted and left sufficient time 
for the bonding material to dry before that seal can again be used. Also, 
the blocks 48, 50 of sealing material adjacent each end of the raised 
portion 28 for sealingly engaging the struts of the board pair assembly 11 
becomes damaged and requires complete removal and replacement in a process 
similar to their original installation and, in the assembly, requires 
manually bonding them in the proper position. In all cases, both initially 
and especially for subsequent repair, the time for manual assembly is 
considerable and relatively expensive and during the repair process 
requires the electrical components associated therewith to be 
disconnected. 
The air seal of the present invention is clearly shown in FIGS. 4 through 8 
and as therein seen, the board pair assembly 11 remains unchanged as does 
the frame 16, however, the opposed support plates, only lower plate 12a 
being shown, define aligned channels 20a separated by raised ribs 22a 
extending across the width of the plate 12a. Each rib 22a is under-cut as 
at 62 flush with the lower surface of the channel 20a to provide a 
horizontal slit for slidingly receiving the longitudinal edges of a planar 
strip 64 having a width sufficient to extend across and into the opposed 
under-cut slits 62 in a sliding tongue-in-groove arrangement. Each channel 
22a defines an elongated centrally disposed aperture 40a through the plate 
12a and the planar strip 64 includes a like elongated aperture 66 for 
alignment therewith when the strip 64 is assembled in proper position by 
being slid within the slits 62 in the ribs 22a. 
A rubber-like gasket member 68 such as a silicon rubber is bonded (i.e. as 
by vulcanization) directly to one planar side of the strip 64 surrounding 
the aperture 66 and itself defines an aperture 70 co-terminous with the 
aperture 66 in the strip 64. The gasket member 68 also defines, as a 
typical cross-section along generally three sides of the elongated 
aperture (i.e. the two opposing lengthwise sides and the arcuate nose 
portion 80 adjacent the board receiving end of the gasket 68 as it is 
disposed within the plate member 12a), an upstanding generally vertical 
leg portion 72 which defines a board receiving slot between it and the 
facing surface of the adjacent rib 22a and terminating in an upwardly, 
outwardly projecting sealing lip 74 extending over the slot. The end of 
the gasket 68 adjacent the pluggable connector 58 defines a generally 
rectangular portion 76 having an upwardly projecting wedge-shaped crown 
78. The outer dimensions of the sealing lip 74 of the gasket member 68 are 
such as to be deformably received in a sealingly biased condition within 
the spacial separation of the board pair assembly 11 with the arcuate 
sealing nose portion 80 of the receiving end deformed to be sealingly 
received within the arcuate portion of the U-shaped upright member 60 and 
the wedge-shaped projection on the opposite end sealingly engaging the 
under surface of the inset forward strut 56 adjacent the connector end. It 
is noticed that the rounded nose portion 80 of the sealing lip 74 includes 
a slit 82 to prevent wrinkles in the nose as it assumes a lesser arcuate 
extent when compressed within the U-shaped upright 60 to more effectively 
seal with the inner surfaces of the upright. 
The planar strip 64 supporting the gasket is easily slideably removable 
from the plate 12a, and upon insertion into the undercut slits 62 is 
seated therein by the end adjacent the connectors abutting a frame member 
16 and by a dimple 84 and socket 86 arrangement between the strip 64 and 
the plate 12a to also maintain the strip 64 within the assembled 
arrangement when the board pair assembly is removed. However, under 
deliberate manual force, the strip 64 can easily be removed and a new 
strip with a new rubber seal 68 vulcanized thereto inserted whenever the 
existing seal needs to be replaced. Also, the initial fabrication of the 
seal is facilitated as compared to that of the described prior art in that 
the sealing blocks adjacent each end of the aperture for mating sealing 
engagement with the struts of the board pair assembly are no longer a part 
of the present seal structure in that the end seals configuration of the 
present invention are formed as an integral portion, namely the end seals 
are provided by the upper surface 78, wedge-shaped rectangular member 76 
at one end and the arcuate nose portion 80 at the opposite end. Both are 
biased into sealing engagement with the strut or the U-shaped vertical 
member when the board pair assembly 11 is fully inserted into the modular 
frame assembly. 
Thus, an easily replaceable air seal is provided for sealingly engaging the 
internal surfaces of a board pair assembly of a modular circuit board 
plug-in assembly to direct cooling air flow in the space defined between 
the boards of the assembly to cool the electrical components projecting 
into this space. Also, it is contemplated that under certain conditions a 
solid strip (one of the removable strips 64 without any aperture 
therethrough) may be inserted within opposite grooves of opposed plates 12 
and 14 when the board pair assembly generally associated with such groove 
is not going to be replaced. Such space will then remain empty and it will 
be unnecessary to deposit therein a dummy board pair assembly to direct the 
air flow therethrough as the solid strips will prevent cooling air from 
entering through the plate aperture 40a.