Abstrict An apparatus for drying the air inside of hermetically sealed electronic
devices. The apparatus includes a desiccant part and an activation
piece that is attached to the desiccant part. The desiccant part
and activation piece are attached together and then covered, except
for the portions where the two pieces are attached, with a polymer
that has a low moisture vapor transmission rate, such as parylene.
The apparatus may be added into an electronic device during assembly.
The desiccant, or drying agent, is not activated, by removal of
the activation piece, until prior to closure of the hermetically
sealed electronic device.
Claims What is claimed is:
1. An apparatus for drying the air inside of a hermetically sealed
electronic device comprising: a. a desiccant part; b. an activation
piece that is attached to said desiccant part; c. a coating of a
material with a low moisture vapor transmission rate that coats
said activation piece and said desiccant part except the portions
of said activation piece and said desiccant part where said activation
piece and said desiccant part are attached.
2. The apparatus as claimed in claim 1 wherein said desiccant part
comprises a desiccant.
3. The apparatus as claimed in claim 1 wherein said desiccant part
comprises a carrier component that is impregnated with a desiccant.
4. The apparatus as claimed in claim 3 wherein said carrier component
is silicone and said desiccant is molecular sieve.
5. The apparatus as claimed in claim 1 wherein said desiccant part
is in a form and shape such that said apparatus can be incorporated
into said electronic device.
6. The apparatus as claimed in claim 1 wherein said activation
piece is removably attached to said desiccant part.
7. The apparatus as claimed in claim 6 wherein said activation
piece includes a means for removing said activation piece from said
desiccant part.
8. The apparatus as claimed in claim 7 wherein said removing means
is a portion of said activation piece that is not attached to said
desiccant part.
9. The apparatus as claimed in claim 1 wherein said activation
piece includes a means for securing said desiccant part and said
activation piece while said desiccant part and said activation piece
are being coated with said coating.
10. The apparatus as claimed in claim 9 wherein said securing means
is a portion of said activation piece that is not attached to said
desiccant part.
11. The apparatus as claimed in claim 1 wherein said activation
piece comprises a flexible sheet having opposite first and second
major side surfaces and having a layer of adhesive along one of
the major side surfaces that attaches to said desiccant part.
12. The apparatus as claimed in claim 1 wherein said activation
piece comprises a flexible sheet having first and second major side
surfaces and having first and second opposite end portions and having
adhesive on a second end portion of one of said major side surfaces
while being free of adhesive on both of said major side surfaces
along a first end portion thereof.
13. The apparatus as claimed in claim 1 wherein said material is
a polymer.
14. The apparatus as claimed in claim 13 wherein said polymer is
parylene.
15. The apparatus as claimed in claim 1 wherein said electronic
device is an implantable cardiac rhythm management device.
16. An apparatus for drying the air inside of a hermetically sealed
electronic device comprising: a. means for drying the air inside
of said hermetically sealed electronic device; b. means for activating
said drying means that is attached to said drying means; c. means
for preventing moisture vapor transmission to said drying means
prior to activating said drying means, that coats said drying means
and said activating means except the portions of said drying means
and said activating means where said drying means and said activating
means are attached.
17. The apparatus in claim 16 wherein said drying means is a desiccant.
18. The apparatus in claim 16 wherein said activating means is
removably attached to said drying means.
19. The apparatus as claimed in claim 16 and further comprising
a means for removing said activating means from said drying means.
20. The apparatus as claimed in claim 19 wherein said removing
means is a portion of said activating means that is not attached
to said drying means.
21. The apparatus as claimed in claim 16 and further comprising
a means for securing said drying means and said activating means
while said drying means and said activating means are being coated
with said means for preventing moisture vapor transmission.
22. The apparatus as claimed in claim 21 wherein said securing
means is a portion of said activating means that is not attached
to said drying means.
23. The apparatus in claim 16 wherein said means for preventing
moisture vapor transmission is a coating of a material with a low
moisture vapor transmission rate that coats said activating means
and said drying means except the portions of said activating means
and said drying means where said activating means and said drying
means are attached.
24. The apparatus as claimed in claim 23 wherein said material
is a polymers.
25. The apparatus as claimed in claim 24 wherein said polymer is
parylene.
26. The apparatus as claimed in claim 16 wherein said electronic
device is an implantable cardiac rhythm management device.
Description FIELD OF THE INVENTION
This invention relates generally to hermetically sealed electronic
devices and, more particularly, to an apparatus for drying the inside
of such devices.
BACKGROUND OF THE INVENTION
Electronic assemblies for use in a variety of harsh environments,
such as in space, marine applications, or the human body, are sealed
from the outside conditions by use of gas-tight (hermetically sealed)
containers. Such containers, while sealing out external dust, air
or moisture, also trap in whatever is inside the devices. Water
vapor is one of the things that are trapped inside such devices.
Since any water vapor that is present inside of an electronic enclosure
is a potential contributor to corrosion and circuit shorting, it
is desirable to somehow remove the water vapor from the air inside
the device after it is sealed.
The moisture in the air inside of a sealed electronic device can
be removed from the air by including a desiccant inside of the device.
A desiccant is usually placed inside electronic devices immediately
prior to closure of the devices. The desiccant removes the moisture
from the air inside the device by trapping or absorbing it. A dry
desiccant in some form is placed inside an electronic device as
one of the last steps prior to closure of the device. The step of
adding the desiccant to the device is usually done in a "dry
box," or "weld glove box," and, that way, the desiccant
is kept basically dry prior to placement in the device. If a desiccant
was added to a device earlier and/or allowed to be exposed to the
air for some time while the electronic device was being assembled,
the desiccant would absorb an appreciable amount of moisture from
the air and would thereby be ineffective in absorbing moisture from
the air inside of the electronic device once it is sealed shut.
The fact that the desiccant must be added as one of the last steps
in assembly of an electronic device places limits on the design
and form of the desiccant and also on the design of the electronic
device itself. Currently, the design of both must allow the desiccant
to be easily added to a near completely assembled electronic device.
In addition, the need for use of a "dry box" or "weld
glove box" in the assembly of electronic devices obviously
places limits on where the assembly of the device may take place.
A need, therefore, exists for an apparatus that allows a desiccant
to be incorporated into an electronic device well prior to closure
of the device without the desiccant adsorbing an appreciable amount
of moisture from the air. A need also exists for a way to control
when the desiccant will begin to absorb moisture. The present invention
meets these needs, and more. The present invention includes a coating
over a desiccant that is an effective barrier to moisture for a
definable period of time. The present invention also provides a
way to activate the desiccant at a specific time to begin absorbing
moisture. The present inventive apparatus may be made in different
shapes, sizes and forms that allow for different designs of the
electronic devices themselves. The present invention also meets
other needs that will become apparent from a review of the description
of the present invention.
There is prior art that discloses coating desiccants with a surface
treatment to limit adsorption by the desiccant. However, the prior
art does not include any kind of activation strip or mechanism to
begin the absorption at a certain time.
SUMMARY OF THE INVENTION
In its simplest embodiment, the present invention is an apparatus
for drying the air inside of a hermetically sealed electronic device
that comprises a desiccant part, an activation piece that is attached
to said desiccant part, and a coating of a material with a low moisture
vapor transmission rate that coats said activation piece and said
desiccant part except where said activation piece and said desiccant
part are attached.
The advantages of the present invention will become readily apparent
to those skilled in the art from a review of the following detailed
description of the preferred embodiment especially when considered
in conjunction with the claims and accompanying drawings in which
like numerals in the several views refer to corresponding parts.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded view of one preferred embodiment of the present
invention;
FIG. 2 is an exploded view of a second preferred embodiment of
the present invention; and
FIG. 3 is a perspective view of the activation piece of the second
preferred embodiment, which shows the reverse side of the activation
piece.
DETAILED DESCRIPTION
FIG. 1 shows an exploded view of one embodiment of the present
invention. In this embodiment, the desiccant part 10 of the present
invention comprises desiccant impregnated in a carrier component.
The desiccant part 10 can also be described as a means for drying
the air inside of a hermetically sealed electronic device. The desiccant
part 10 is in the shape of a square or rectangular sheet. However,
the desiccant part can be in many different shapes and sizes and
is not limited to the shape and size shown in FIG. 1. The desiccant
in the preferred embodiment shown in FIG. 1 is molecular sieve,
and the carrier component is silicone. However, other possible desiccants
or desiccants and carrier compounds may be used.
The preferred embodiment shown in FIG. 1 includes an activation
strip or piece 12 which is removably attached to the desiccant
part 10. The activation piece is also described as a means for activating
said drying means. The activation piece 12 is in a rectangular shape,
however, it is not limited to that shape and can be in many different
shapes and sizes. The activation piece 12 in the preferred embodiment
in FIG. 1 has opposite first and second major side surfaces 15
16. The activation piece 12 is removably attached to the desiccant
part 10 and may be removably attached through the use of an adhesive
or other material on one major side surface 16 which is the major
side surface that is attached to the desiccant part 10. The material
or adhesive could be any kind of material or adhesive that will
allow the activation strip 12 to be attached to the desiccant part
10 but that will also allow the activation strip 12 to be later
removed from the desiccant part 10. A preferred material or adhesive
would be one that does not leave behind a significant amount of
residue on the desiccant part 10 when the activation piece 12 is
removed. A preferred type of adhesive is a pressure sensitive adhesive,
although other types may be used.
As shown in the preferred embodiment shown in FIG. 1 both the
activation piece 12 and the desiccant part 10 are attached and are
coated with a coating 18 of parylene. The coating 18 covers the
desiccant part 10 and the activation piece 12 except the portions
of the activation piece 12 and desiccant part 10 where the activation
piece 12 and desiccant part 10 are attached. Parylene is the preferred
coating 18 however, other materials may be used. The material used
to coat the desiccant part 10 and activation piece 12 except where
the activation piece 12 and desiccant part 10 are attached, should
have a low moisture vapor transmission rate. The coating 18 may
be a polymer. Basically, the coating is a means for preventing moisture
vapor transmission to said drying means prior to activation of said
drying means, which coats said drying means and said activating
means except the portions of said drying means and said activating
means where said drying means and said activating means are attached.
FIG. 1 also shows an area 20 of the desiccant part 10 that is not
covered by the parylene or other material used for the coating 18
when the activation piece 12 is removed. As a result of the activation
piece 12 being removed, the area 20 is exposed to the air. This
allows the desiccant in the desiccant part 10 to absorb moisture
much more quickly and easily than through the parylene, or other
material, coating 18. In the assembly of electronic devices for
which the present invention is used, the activation piece 12 should
not be removed from the desiccant part 10 as shown, until some
time right before the electronic device is closed and hermetically
sealed. The desiccant in the desiccant part 10 is then able to absorb
the required or calculated amount of moisture from the air inside
of the hermetically sealed electronic device.
A desiccant is a hydrating agent that attracts moisture from the
atmosphere. It adsorbs and holds particles of water to itself. There
are many different kinds of desiccants. They include naturally occurring,
modified, and synthetic aluminosilicates, aluminas, silica gels,
molecular sieves or zeolites, activated carbon, and activated alumina.
It is possible that any of these desiccants, or other desiccants,
could be used in the present invention.
The preferred desiccant for the present invention is molecular
sieve. The molecular sieve is a network of uniform pores and empty
cavities. Molecular sieve is derived from sodium potassium or calcium
alumina silicate. It is a non-hazardous material. Molecular sieve
is the desiccant of choice for most demanding and unique applications.
Molecular sieve is the most aggressive and expensive of the primary
desiccants.
The desiccant part 10 in the preferred embodiment, and as shown
in FIG. 1 is made by using a process that is well known. First,
desiccant powder is removed from a can and spread out in a thin
layer. Second, the desiccant powder is exposed in a humidity chamber
for several hours to allow the desiccant powder to become fully
saturated. Next, the desiccant is then removed from the humidity
chamber and the saturated desiccant powder is then mixed with liquid
silicone rubber in a pot. The mixture in the preferred embodiment
is 45% desiccant and 55% silicone by weight, however it may be a
different ratio. The mixture is then poured into an injection molding
machine and injected into a sheet mold, for example, and cured.
The sheet is then removed from the mold and die-cut to correct the
shape of the part. The part is then placed in a vacuum oven and
dried out, which removes virtually all of the water. The part is
then sealed in an airtight container.
There are other methods that may be used to make the desiccant
part in the present invention. In addition, the desiccant part may
be made in different shapes, forms and sizes. The flexibility in
the shape, form and size of the desiccant part will enable the electronic
devices themselves to be made in different shapes and sizes.
The feature of the present invention that allows it to be made
into different shapes and sizes is especially important in the design
and manufacture of implantable cardiac rhythm management devices.
It is desirable to make such devices smaller than previous devices.
The flexibility that the present invention allows for the form,
size and shape of the drying apparatus allows implantable cardiac
rhythm management devices to be made smaller. For example, they
may be made smaller because the drying apparatus could be fit into
an already existing space inside of the devices. One such example
of an embodiment of the present invention is that the apparatus
is in the form of the liner of the implantable cardiac rhythm management
device.
In the present invention, the activation piece 12 may be added
to the desiccant part 10 before or after the desiccant part 10 has
been dried out. If it is added before the drying step, then the
activation piece 12 must be able to withstand, for example, the
260-degree drying temperature necessary to dry the desiccant part
10.
Parylene is the generic name for members of a unique family of
thermoplastic polymers that are formed on a surface exposed to a
rarified gas in a vacuum. The resulting linear crystalline polymer
coating possesses superior barrier properties per unit thickness,
has extreme chemical inertness, and is free from pinholes. There
are three commonly used forms of parylene dimers, which are Parylene
N, Parylene C and Parylene D. Each has unique properties that suit
them for particular types of coating applications. In particular,
Parylene C is superior to almost all other polymeric material for
having a low moisture vapor transmission rate.
Parylene coatings are obtained by means of a well-known vapor deposition
process in which the dimer is vaporized, pyrolized, i.e. cleaved
into a monomer vapor form, and fed into a deposition chamber wherein
the monomer molecules deposit and polymerize onto a substrate disposed
within the deposition chamber. Due to their ability to provide thin
films and conform to substrates of varied geometric shapes, parylene
polymers are ideally suited for use as a conformal external coating
in a wide variety of fields, such as for example, in the electronics,
automotive and medical industries.
There is a second preferred embodiment of the present invention,
as shown the exploded view in FIG. 2 that will result in uniform
coverage of parylene, or other coating material 18 on the desiccant
piece 10 that is free from any holes. As can be seen in FIGS. 2
and 3 the activation piece 12 is a flexible sheet comprising a
layer of material having opposite top and bottom major side surfaces,
15 and 16 respectively, and first and second opposite end portions,
13 and 14 respectively, such as that claimed in U.S. Pat. No. 4770320
issued to Miles et al. The activation piece 12 as in the first
preferred embodiment, is removably attached to the desiccant part
10. There may be a coating of adhesive 22 on the second opposite
side surface 16 of the second end portion 14 which attaches the
activation piece 12 to the desiccant part 10. The first end portion
13 is free of adhesive on both of said side surfaces 15 16.
In the second preferred embodiment shown in FIG. 2 the combination
of the desiccant part 10 and the activation piece 12 are coated
with parylene, 18 or some other material that has a low moisture
vapor transmission rate. When the combination is being coated with
parylene, or another material, in the deposition chamber, as described
above, it must be held by something so that it may be completely
coated. The preferred embodiment shown in FIG. 2 allows the combination
of the desiccant part 10 and the activation piece 12 to be held
by the end portion 13 of the activation piece 12. This results in
no areas of the desiccant part 10 being left uncovered by the coating
18. Therefore, this provides the apparatus with a means for securing
said drying means and said activating means while said drying means
and said activating means are being coated with said means for preventing
moisture vapor transmission. The securing means may be a portion
of said activating means that is not attached to said drying means.
The end portion 13 also provides a place for a person or machine
to grab and remove the activation piece 12 from the desiccant part
10. Therefore, this also provides the apparatus with a means for
removing said activation piece from said drying means. The removing
means may be a portion of said activating means that is not attached
to said drying means.
FIG. 2 shows the area 20 that is exposed to the air when the activation
piece 12 is removed in the second preferred embodiment.
It should be noted that the preferred embodiment shown in FIG.
2 is just one example of the present invention. The desiccant part
10 and activation piece 12 can be in different shapes and sizes
from those illustrated. In addition, the end portion 13 of the activation
piece 12 that can be used to secure the desiccant part 10 and activation
piece 12 combination while it is being coated, does not necessarily
have to extend beyond the desiccant part 10 as shown. It could,
for example, extend perpendicular to the activation piece 12 and
desiccant part 10 combination. In addition, the present invention
is not limited to the proportions of the portions 13 14 of the
activation piece 12 shown in the present application. There are
many different examples that are possible, and the present invention
is not limited to those shown or described in the specification.
Although the present invention may be used in all kinds of hermetically
sealed electronic devices, it is particularly useful for the pulse
generators of implantable cardiac rhythm management devices. The
claimed apparatus allows an electronic device, such as a pulse generator,
to be assembled in a humid environment. All of the components of
the pulse generator, including the desiccant part, could be assembled
in any order. The desiccant part would not have to be put into the
pulse generator in a weld glove box or dry box, which is commonly
used, and would not have to be done just prior to closure of the
device. The desiccant part of the present invention could be placed
in the pulse generator of the implantable cardiac rhythm management
device, and the desiccant could then be activated prior to closure
of the device by removing the activation piece 12.
The advantage of the present invention is that it allows for the
design of a drying apparatus that can be an integral part of the
electronic device assembly, yet that doesn't need special handling
or storage conditions. The space inside of devices, such as pulse
generators, is limited and, thus, it is highly preferable that the
drying apparatus be easily formed into a shape that can easily conform
to the inside of the sealed device.
This invention has been described herein in considerable detail
in order to comply with the patent statutes and to provide those
skilled in the art with the information needed to apply the novel
principles and to make and use such a device. However, it is to
be understood that the invention can be carried out by specifically
different equipment and devices, and that various modifications,
both as to the components and structure, can be accomplished without
departing from the scope of the invention itself.
|