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 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 claim 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 polymer.
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
[0001] 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
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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
[0007] 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.
[0008] 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
[0009] FIG. 1 is an exploded view of one preferred embodiment of
the present invention;
[0010] FIG. 2 is an exploded view of a second preferred embodiment
of the present invention; and
[0011] 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
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] FIG. 2 shows the area 20 that is exposed to the air when
the activation piece 12 is removed in the second preferred embodiment.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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. |