Hermetically sealed housing having a flex tape electrical connector

Disclosed is a hermetically sealed housing assembly for protecting electrical equipment. The housing assembly includes a hermetically sealed housing member having an exterior wall and an interior region for containing the electrical equipment. A flex tape electrical signal conductor extends through an opening in the exterior wall, and transmits electrical signals between the electrical equipment in the interior region and electrical components in a region exterior to the housing member. The flex tape signal conductor is hermetically sealed to the exterior wall of the housing member at the opening to maintain the integrity of the hermetic seal of the housing member even after temperature-cycling for a period of time.

BACKGROUND OF THE INVENTION 
This invention relates to hermetically sealed housings for protecting 
electrical equipment. In particular, the present invention is a 
hermetically sealed housing using a flex tape electrical connector to pass 
electrical signals between the interior and the exterior of the 
hermetically sealed housing. The flex tape electrical connector maintains 
the integrity of the hermetic seal of the housing while using 
non-hermetically sealed plug connectors. 
In certain environments, it is necessary to isolate electrical equipment 
from the outside world. In many applications, this is accomplished by 
placing the electrical equipment and other necessary elements within some 
type of housing or container. The housing is then hermetically sealed to 
avoid any environmental contamination of the electrical equipment such as 
caused by humidity and/or undesired gases. 
When using hermetically sealed housings, it is typically necessary to 
transmit electrical signals between the electrical equipment within the 
interior of the housing and electrical components exterior to the housing. 
These electrical signals, for example, may be power supplies, control 
signals or readout signals. Typically, electrical plug connectors are 
bonded or welded to the housing and are used to transmit these electrical 
signals between the interior and the exterior of the housing through a 
housing wall. In order to provide acceptable performance, the electrical 
plug connectors must adequately maintain the integrity of the hermetic 
seal of the housing. As such, expensive hermetically sealed electrical 
plug connectors are used. 
Besides their high cost, a further problem with known hermetically sealed 
electrical plug connectors is their inability to maintain the integrity of 
their hermetic seal after they have been temperature-cycled for a period 
of time. Once the hermetic seal of an electrical plug connector begins to 
leak, undesired gases and humidity enter the housing causing operation of 
the electrical equipment within the interior of the housing to degrade. 
Many of the aforementioned leaks result from inadequate sealing 
techniques. For example, the use of incorrect sealants or potting 
materials, results in unnecessary stresses in the electrical plug 
connector due to a coefficient of thermal expansion (CTE) differential. 
Other inadequate sealing techniques occur when bubbles or voids are 
entrapped in the components during the sealing process. These voids 
contribute to a CTE differential as well as provide leak paths through the 
plug connectors. This CTE differential within the sealant, in conjunction 
with any inherent CTE differential within the electrical plug connector 
itself and/or between the electrical plug connector and the housing, 
causes stress fractures in the cured sealant during thermal cycling. These 
stress fractures result in leaks that ruin the integrity of the hermetic 
seal of the housing. 
There is a need for improved hermetically sealed housings for electrical 
equipment. In particular, there is a need for an hermetically sealed 
housing using an electrical connector that will maintain the integrity of 
the hermetic seal of a housing even after having been temperature-cycled 
for a period of time. 
SUMMARY OF THE INVENTION 
The present invention is a hermetically sealed housing assembly for 
protecting electrical equipment. The housing assembly includes a 
hermetically sealed housing member having an exterior wall that defines an 
interior region for containing electrical equipment. Extending through the 
exterior wall is an opening that forms a passageway between the interior 
region and a region exterior to the housing member. An electrical 
connector device transmits electrical signals between electrical equipment 
in the interior region and electrical components in the region exterior to 
the housing member. The electrical connector device includes a flex tape 
electrical signal conductor that extends through the opening and is 
coupled to the electrical equipment and the electrical components. The 
flex tape electrical signal conductor is hermetically sealed to the 
exterior wall of the housing member at the opening. The hermetically 
sealed flex tape electrical signal conductor maintains the integrity of 
the hermetic seal of the housing member even after temperature-cycling for 
a period of time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A hermetically sealed housing assembly 10 in accordance with the present 
invention is illustrated generally in FIGS. 1-3. As seen best in FIG. 3, 
the sealed housing assembly 10 includes a hermetically sealed housing 
member 12 and a flex tape electrical connector device 14. The hermetically 
sealed housing member 12 is defined by a top cover element 16 and a bottom 
cover element 18. The top and bottom cover elements 16 and 18 are 
hermetically sealed together at a lap joint interconnect 20 by welding or 
an epoxy based adhesive 22. In one preferred embodiment, the top and 
bottom cover elements 16 and 18 are manufactured of aluminum, and 
Scotch-weld.TM. 2214 - High Temp, an epoxy based adhesive manufactured by 
Minnesota, Mining and Manufacturing Corporation of St. Paul, Minn. is used 
to hermetically seal the lap joint interconnect 20. 
As seen best in FIG. 3, once the top and bottom cover elements 16 and 18 
are hermetically sealed together, the top and bottom cover elements 16 and 
18 together form an exterior wall 23 of the housing member 12. The 
exterior wall 23 defines an interior region 24 for housing electrical 
equipment 25. The hermetically sealed housing member 12 contains and 
protects the electrical equipment 25 from environmental contamination such 
as may be caused by humidity and/or undesired gases. The electrical 
equipment 25 is mounted within the interior region 24 of the housing 
member 12 prior to the lap joint interconnect 20 being hermetically sealed 
by the sealant 22. In one preferred embodiment, the electrical equipment 
25 is a ring laser gyro and its associated electronics. 
As seen best in FIGS. 1 and 3, the top cover element 16 of the housing 
member 12 has a rectangular shaped recessed region 26 defined by a portion 
of the exterior wall 23 that forms a circumferential ledge 28. The ledge 
28 surrounds a rectangular shaped opening 30 that extends through the 
exterior wall 23 and forms a passageway between the interior region 24 and 
a region exterior to the housing member 12. The opening 30 has an edge 
wall 32. 
The flex tape electrical connector device 14 transmits electrical signals 
between the electrical equipment 25 in the interior region 24 and 
electrical components 33 in the region exterior to the housing member 12. 
As seen in FIGS. 2 and 3, the flex tape electrical connector device 14 
includes a flex tape electrical signal conductor 34 having first and 
second plug connectors 36 and 38, respectively. The first plug connector 
36 is coupled to a first end 40 of the signal conductor 34, and the second 
plug connector 38 is coupled to a second opposite end 42 of the signal 
conductor 34. The first and second plug connectors 36 and 38 are 
non-hermetically sealed plug connectors. The second plug connector 38 is 
secured to the exterior wall 23 by an epoxy based adhesive 39 similar to 
adhesive 22. 
In one preferred embodiment, the signal conductor 34 is a Polyimide flex 
tape with copper foil and an acrylic adhesive manufactured by Litchfield 
Precision, of Litchfield, Minn. and the first and second plug connectors 
36 and 38 are non-hermetically sealed 28 pin micro D connectors or 
multipin custom connectors manufactured by ITT Cannon of Santa Anna Calif. 
or Microdot of South Pasadena Calif. 
As seen best in FIG. 3, the signal conductor 34 extends through the opening 
30 and is coupled between the electrical equipment 25 and the electrical 
components 33. To this end, the first plug connector 36 is releasably 
coupled to a corresponding mating plug connector 44 of the electrical 
equipment 25. In addition, the second plug connector 38 is releasably 
coupled to a comparable mating plug connector 46 connected to the 
electrical components 33 through signal lines 48. In one preferred 
embodiment, the electrical components 33 are other ring laser gyros and 
associated electronics of an inertial navigation system. 
As seen best in FIGS. 2 and 3, in one preferred embodiment of the 
hermetically sealed housing assembly 10, the rectangular shaped opening 30 
is dimensioned to allow passage of the first and second plug connectors 36 
and 38 and the signal conductor 34. By dimensioning the opening 30 in this 
manner, the first and second plug connectors 36 and 38 can be assembled to 
the signal conductor 34 prior to the threading of the connector device 14 
through the opening 30. It is to be understood that in the one preferred 
embodiment described above, that the first and second plug connectors 36 
and 38 are identical, and that as such both the first plug connector 36 
and the second plug connector 38 can pass through the opening 30. However, 
if the first plug connector 36 is not dimensionally identical to the 
second plug connector 38, the opening 30 could be dimensioned to allow the 
passage of the signal conductor 34 and only the first plug connector 36 or 
the second plug connector 38. This arrangement would still allow 
dimensionally dissimilar first and second plug connectors 36 and 38 to be 
assembled to the signal conductor 34 prior to the threading of the 
connector device 14 through the opening 30. In one preferred embodiment, 
the rectangular shaped opening 30 has a length of 1.25 inches and a width 
of 0.40 inches, while each of the first and second plug connectors 36 and 
38 has a length of 1.20 inches, a width of 0.35 inches and a height of 
0.40 inches. 
As seen in FIGS. 2 and 3, a joining mechanism 50 secures the signal 
conductor 34 of the connector device 14 to the exterior wall 23 at the 
opening 30. The joining mechanism 50 hermetically seals the signal 
conductor 34 to the housing member 12 to define the hermetically sealed 
housing assembly 10. The joining mechanism 50 includes a filler element 52 
and a sealant 54. As seen best in FIG. 4, the filler element 52 is a 
U-shaped member 56 (preferably manufactured of aluminum) having first and 
second legs 58 and 60, respectively, joined by a bight portion 62. The 
first and second legs 58 and 60 and the bight portion 62 define a slot 64 
that is dimensioned to receive the signal conductor 34. As seen in FIGS. 2 
and 3, circumferential ledge 28 is dimensioned to receive and support the 
U-shaped member 56 with a portion of the signal conductor 34 passing 
through the slot 64 and the opening 30. The U-shaped member 56 bridges 
some of the gaps between the edge wall 32 of the opening 30 and the signal 
conductor 34. These gaps being a result of the use of the oversized 
opening 30, which is dimensioned so as to allow passage therethrough not 
only of the signal conductor 34, but also the larger first and second plug 
connectors 36 and 38. In one preferred embodiment, the slot 64 has a 
length of 0.85 inches and a width of 0.05 inches to receive the signal 
conductor 34 which has a length of 0.80 inches and a width of 0.01 inches. 
The sealant 54, as best seen in FIGS. 2 and 3, hermetically seals the 
signal conductor 34 to the U-shaped member 56, and hermetically seals the 
U-shaped member 56 to the edge wall 32 of the opening 30 in the exterior 
wall 23. Hermetically sealing the signal conductor 34 to the U-shaped 
member 56 and the U-shaped member 56 to the housing member 12, creates a 
hermetically sealed housing assembly 10 that protects electrical equipment 
25 from environmental contamination that may be caused by humidity and/or 
undesired gases entering the housing member 12. 
The sealant 54 is a high temperature resistant compound having high lap 
shear adhesion properties to ensure strong adhesion to the signal 
conductor 34, the U-shaped member 56 and the exterior wall 23. In 
addition, the sealant 54 exhibits a uniform coefficient of thermal 
expansion (CTE) throughout the sealing compound. This uniform CTE ensures 
consistent thermal expansion and contraction throughout the cured sealant 
54 during temperature-cycling. Consistent thermal expansion and 
contraction throughout the cured sealant 54 virtually eliminates stress 
fractures in the cured sealant caused by temperature cycling. By virtually 
eliminating stress fractures in the cured sealant, leaks that ruin the 
integrity of the hermetic seal of the housing assembly 10 are also 
essentially eliminated. 
Examples of the type of compound used for the sealant 54 are 
Scotch-weld.TM. 2214 a product of Minnesota, Mining and Manufacturing 
Corporation of St. Paul, Minn., and Scotch-weld.TM. 2216 with Cabosil.RTM. 
both products of Minnesota, Mining and Manufacturing Corporation of St. 
Paul, Minn. In one preferred embodiment, Scotch-weld.TM. 2214 was used as 
the sealant 54 and was allowed to oven cure per the manufacturer's 
recommendations for one hour at a temperature of 250.degree. F. to create 
a hermetic seal that can maintain leak rates below 1.times.10.sup.-7 atm. 
cm..sup.3 /sec. at a pressure differential of 1 atm. when exposed to 
temperature cycles ranging from -65.degree. F. to 230.degree. F. 
Alternatively, Scotch-weld.TM. 2216 with Cabosil.RTM. was used as the 
sealant 54 and was allowed to oven cure per the manufacturer's 
recommendations for twenty-four hours at a room temperature of) 77.degree. 
F. to create a hermetic seal that could also maintain leak rates below 
1.times.10.sup.-5 atm. cm..sup.3 /sec. at a pressure differential of 1 
atm. when exposed to temperature cycles ranging from -65.degree. F. to 
230.degree. F. 
FIGS. 5-7 illustrate an alternative embodiment of the hermetically sealed 
housing assembly 110. Like parts are labeled with like numerals except for 
the addition of the prescript 1. In the housing assembly 110, the 
rectangular shaped recessed region 26, the circumferential ledge 28 and 
the filler element 52 have been eliminated. In addition, the rectangular 
shaped opening 30 has been replaced by elongated opening 130. The 
elongated opening 130 is dimensioned to only allow passage therethrough of 
the signal conductor 134 and not the first and second plug connectors 136 
and 138. By dimensioning the elongated opening 130 in this manner, the 
first plug connector 136 or the second plug connector 138 (or both the 
first and second plug connectors 136 and 138) needs to be assembled to the 
signal conductor 134 after the signal conductor 134 is threaded through 
the opening 130. It is to be understood that in the alternative embodiment 
described above, that whether the first and second plug connectors 136 and 
138 are identical or dissimilar, that at least one of the first and second 
plug connectors 136 and 138 will have to be assembled to the signal 
conductor 134 after the signal conductor 134 is threaded through the 
opening 130. In one preferred embodiment, the elongated opening 130 has a 
length of 0.85 inches and a width of 0.05 inches, while the signal 
conductor 134 has a length of 0.80 inches and a width of 0.01 inches. As 
can be seen in FIGS. 6 and 7, the sealant 154 hermetically seals the 
signal conductor 134 directly to the edge wall 132 of the opening 130 in 
the exterior wall 123. 
The combination of the housing member 12, 112, the connector device 14, 114 
and the joining mechanism 50, 150 creates a hermetically sealed housing 
assembly 10, 110 that is capable of maintaining the integrity of the 
hermetic seal even after temperature-cycling for a period of time. 
Although the present invention has been described with reference to 
preferred embodiments, workers skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.