Abstrict A human body implantable drug delivery pump has a housing including
at least a first shield and a second shield. The housing defines
an interior within the shields. The pump further includes a fluid
reservoir within the housing, a fluid conduit also within the housing
from the reservoir, an outlet from the fluid conduit to the exterior
of the housing, and a pump member in the housing adapted to move
fluid through the fluid conduit to the outlet. The fluid in the
reservoir and fluid conduit is isolated from the pump interior.
The pump further has a desiccant in the pump interior, the desiccant
absorbent of moisture in the pump interior, and preferably absorbent
of substantially all the moisture in the pump interior. The desiccant
also preferably has a moisture absorbent property dependent on temperature,
being lessened at higher temperatures, the desiccant being pre-baked
to improve its moisture absorbent property before being placed in
the pump.
Claims What is claimed is:
1. A human body implantable drug delivery pump comprising a housing
of assembled components including electronics, the pump further
comprising a desiccant located interiorly to the housing and in
the same environment as the electronics, whereby the desiccant absorbs
moisture within the environment of the electronics.
2. A human body implantable drug delivery pump as in claim 1 in
which the desiccant is absorbent of moisture within the housing
to a desired level.
3. A human body implantable drug delivery pump as in claim 2 the
desiccant absorbent of substantially all the moisture in the pump
interior.
4. A human body implantable drug delivery pump as in claim 2 in
which the desiccant is further absorbent of moisture, whereby the
desiccant may be placed within the housing during final assembly
of the pump when the pump housing is not completely sealed, and
the desiccant is absorbent during a time period of final assembly,
and remains absorbent of substantially all the moisture within the
housing after complete sealing of the housing.
5. A human body implantable drug delivery pump as in claim 2 the
desiccant absorbent of substantially all the moisture in the pump
interior.
6. A human body implantable drug delivery pump as in claim 1 in
which the moisture absorbent property of the desiccant is dependent
on temperature, being lessened at higher temperatures, the desiccant
being pre-heated to improve its moisture absorbent property.
7. A human body implantable drug delivery pump as in claim 1 in
which the desiccant is molded to fit free space within the housing.
8. A human body implantable drug delivery pump as in claim 1 in
which the desiccant comprises liquid silicon rubber.
9. A human body implantable drug delivery pump as in claim 1 in
which the desiccant comprises aluminum oxide.
10. A human body implantable drug delivery pump as in claim 1
in which the desiccant is absorbent of substantially all the moisture
in the pump interior, in which the moisture absorbent property of
the desiccant is dependent on temperature, being lessened at higher
temperatures, the desiccant being pre-heated to improve its moisture
absorbent property, in which the desiccant is further absorbent
of moisture, whereby the desiccant may be placed within the housing
during final assembly of the pump when the pump housing is not completely
sealed, and the desiccant is absorbent during a time period of final
assembly, and remains absorbent of substantially all the moisture
within the housing after complete sealing of the housing, and in
which the desiccant comprises liquid silicon rubber and aluminum
oxide.
11. A human body implantable drug delivery pump, the pump comprising
a housing including at least a first shield and a second shield,
the housing defining an interior within the shields, the pump further
including electronics and a fluid reservoir within the housing,
a fluid conduit also within the housing from the reservoir, an outlet
from the fluid conduit to the exterior of the housing, and a pump
member in the housing adapted to move fluid through the fluid conduit
to the outlet, the fluid in the reservoir and the fluid conduit
isolated from the pump interior, the pump further comprising a desiccant
in the pump interior and in the same environment as the electronics,
the desiccant absorbent of moisture in the pump interior.
12. A human body implantable drug delivery pump as in claim 11
in which the desiccant is absorbent of moisture within the pump
interior to a desired level.
13. A human body implantable drug delivery pump as in claim 11
in which the moisture absorbent property of the desiccant is dependent
on temperature, being lessened at higher temperatures, the desiccant
being pre-heated to improve its moisture absorbent property.
14. A human body implantable drug delivery pump as in claim 11
in which the desiccant is further absorbent of moisture, whereby
the desiccant may be placed within the housing during final assembly
of the pump when the pump housing is not completely sealed, and
the desiccant is absorbent during a time period of final assembly,
and remains absorbent of substantially all the moisture within the
pump interior after complete sealing of the housing.
15. A human body implantable drug delivery pump as in claim 11
in which the desiccant is molded to fit free space within the pump
interior.
16. A human body implantable drug delivery pump as in claim 11
in which the desiccant comprises liquid silicon rubber.
17. A human body implantable drug delivery pump as in claim 11
in which the desiccant comprises aluminum oxide.
18. A human body implantable drug delivery pump as in claim 11
in which the desiccant is absorbent of substantially all the moisture
within the pump interior, in which the moisture absorbent property
of the desiccant is dependent on temperature, being lessened at
higher temperatures, the desiccant being pre-baked to improve its
moisture absorbent property, in which the desiccant is further absorbent
of moisture, whereby the desiccant may be placed within the housing
during final assembly of the pump when the pump housing is not completely
sealed, and the desiccant is absorbent during a time period of final
assembly, and remains absorbent of substantially all the moisture
within the housing after complete sealing of the housing, in which
the desiccant is molded to fit free space within the housing, and
in which the desiccant comprises liquid silicon rubber and aluminum
oxide.
19. A human body implantable drug delivery pump, the pump comprising
a housing including at least a first shield and a second shield,
the housing defining an interior within the shields, the pump further
including a fluid reservoir within the housing and electronics exposed
to the first shield and non-exposed to the second shield, a fluid
conduit also within the housing from the reservoir, an outlet from
the fluid conduit to the exterior of the housing, and a pump member
in the housing adapted to move fluid through the fluid conduit to
the outlet, the fluid in the reservoir and fluid conduit isolated
from the pump interior, a desiccant being absorbent of substantially
all the moisture within an environment between the first shield
and the electronics, the desiccant having a moisture absorbent property
dependent on temperature, being improved after being raised to higher
temperatures, the desiccant being pre-baked to improve its moisture
absorbent property before being placed in the pump, the desiccant
being further absorbent of moisture, whereby the desiccant is placed
within the environment between the first shield and the electronics
during final assembly of the pump when the pump housing is not completely
sealed, and the desiccant is absorbent during a time period of final
assembly, and remains absorbent of substantially all the moisture
within the environment between the first shield and the electronics
after complete sealing of the housing, the desiccant being molded
to fit free space within the environment between the first shield
and the electronics, and the desiccant comprising liquid silicon
rubber and aluminum oxide.
20. A method of manufacturing a human body implantable drug delivery
pump, comprising forming the pump as having a housing including
at least a first shield and a second shield, the housing defining
an interior within the shields, the pump further including a fluid
reservoir within the housing, a fluid conduit also within the housing
from the reservoir, an outlet from the fluid conduit to the exterior
of the housing, and a pump member in the housing adapted to move
fluid through the fluid conduit to the outlet, the fluid in the
reservoir and fluid conduit isolated from the pump interior, the
method also comprising inserting in the pump interior a desiccant
and then sealing the housing in a final assembly step, the desiccant
being one that is absorbent of substantially all the moisture within
the pump interior, the desiccant having a moisture absorbent property
dependent on temperature, being improved after being raised to higher
temperatures, the desiccant being pre-baked to improve its moisture
absorbent property before being placed in the pump, the desiccant
also being formed in type and size to be further absorbent of moisture,
whereby the desiccant may be placed within the housing during final
assembly of the pump when the pump housing is not completely sealed,
and the desiccant is absorbent during a time period of final assembly,
and remains absorbent of substantially all the moisture within the
housing after complete sealing of the housing, the desiccant further
being molded to fit free space within the housing, and the desiccant
comprising liquid silicon rubber and aluminum oxide.
Description BACKGROUND OF THE INVENTION
This invention relates to medical devices, and more specifically,
to human body implantable drug delivery pumps.
PAIN
Briefly, the brain, not the point of an injury, registers any sensation
of pain. When pain is felt, it is a reaction to signals that are
transmitted throughout the body. These signals are sent from the
pain source, through the nerves in the spinal cord, to the brain,
where they are perceived as pain. Pain can be controlled by preventing
the pain signals from reaching the brain.
The origin of some pain is neuropathic, while other pain is nociceptive.
Neuropathic pain is pain that is caused by damage to nerve tissue.
Nociceptive pain means pain caused by an injury or disease outside
the nervous system.
Acute pain (such as spraining an ankle) acts as a warning to signal
harm or possible damage to tissues in the body. It prevents additional
damage by alerting you to react and remove the source of pain. However,
when pain lasts a long time (over six months) and is not relieved
by standard medical management, it is called "chronic"
pain. In chronic pain, the pain signal no longer helps, but hinders
the body. Pain is recognized as a major public health problem. In
the United States, it is estimated that chronic pain affects 15%
to 33% of the U.S. population, or as many as 70 million people.
In fact, chronic pain disables more people than cancer or heart
disease and costs the American people more than both combined. Pain
costs an estimated $70 billion a year in medical costs, lost working
days, and workers' compensation.
ADVANCED PAIN THERAPIES
APT.TM. Neurostimulation ("Advanced Pain Therapy Neurostimulation")
is available from Medtronic, Inc., and commonly used for neuropathic
pain. APT.TM. Intrathecal treatment, also available from Medtronic,
Inc., is commonly used for nociceptive pain.
APT.TM. Neurostimulation (including both spinal cord stimulation
and peripheral nerve stimulation) uses a small neurostimulation
system that is surgically placed under the skin to send mild electrical
impulses to the spinal cord. The electrical impulses are delivered
through a lead (a special medical wire) that is also surgically
placed. These electrical impulses block the signal of pain from
reaching the brain. Peripheral nerve stimulation works in the same
way, but the lead is placed on the specific nerve that is causing
pain rather than the spinal cord.
APT.TM. Intrathecal uses a small pump that is surgically placed
under the skin of the abdomen to deliver medication directly into
the intrathecal space (where fluid flows around the spinal cord).
The medication is delivered through a small tube called a catheter
that is also surgically placed. The spinal cord is like a highway
for pain signals on their way to the brain, where the feeling of
pain is experienced by the body. Because the medication goes directly
to the site of action in the spinal cord, where pain signals travel,
APT.TM. Intrathecal offers many people significant pain control
with much lower doses of medication than would be required by oral
medications (pills). This helps minimize the side effects that often
accompany other treatments.
A doctor can do a screening test to see if APT.TM. Intrathecal
will relieve pain, before the patient commits to the therapy. In
addition, APT.TM. Intrathecal is non-destructive and reversible.
Typically, people who have success with APT.TM. Intrathecal experience
greater than 50% reduction in their pain and improved ability to
go about activities of daily living.
The SynchroMed.RTM. Infusion System is a fully implantable, programmable
APT.TM. Intrathecal system available from Medtronic. The SynchroMed.RTM.
Infusion System has two parts that are both placed in the body during
a surgical procedure: the catheter and the pump. The catheter is
a small, soft tube. One end is connected to the catheter port of
the pump, and the other end is placed in the intrathecal space (where
fluid flows around the spinal cord). The pump is a round metal device
that stores and releases prescribed amounts of medication directly
into the intrathecal space. It is about one inch (2.5 cm) thick,
three inches (8.5 cm) in diameter, and weighs about six ounces (205
g). It is made of titanium, a lightweight, medical-grade metal.
The reservoir is the space inside the pump that holds the medication.
The fill port is a raised center portion of the pump through which
the pump is refilled. The doctor or a nurse inserts a needle through
the patient's skin and through the fill port to fill the pump. Some
pumps have a side catheter access port that allows the doctor to
inject other medications or sterile solutions directly into the
catheter, bypassing the pump.
The SynchroMed.RTM. pump automatically delivers a controlled amount
of medication through the catheter to the intrathecal space around
the spinal cord, where it is most effective. The exact dosage, rate
and timing prescribed by the doctor are entered in the pump using
a programmer, an external computer-like device that controls the
pump's memory. Information about the patient's prescription is stored
in the pump's memory. The doctor can easily review this information
by using the programmer. The programmer communicates with the pump
by radio signals that allow the doctor to tell how the pump is operating
at any given time. The doctor also can use the programmer to change
your medication dosage.
CURRENT TECHNIQUE FOR HUMIDITY PROTECTION
As indicated, an APT.TM. Intrathecal pump is a sophisticated electromechanical
device. In addition to its reservoir, fill port, and other mechanical
components, the device includes microelectronics in an electronic
chamber. Implantation of an APT.TM. Intrathecal pump is also a significant
life event. Given the electronics in the units and the significance
of implantation, long-term excellence in the performance of the
units is highly desirable. Unfortunately, one common failure mode
(way things fail) for implantable device electronics is corrosion
of conduction pathways, or short circuiting of the pathways, caused
by the presence of water vapor and salts. The short circuiting of
the pathways often occurs from dendrites which form between circuits
which are at different voltage potentials, when in the presence
of ionic vapors. Plastic components in the electronics (e.g., chip
carriers), absorb trace amounts of water vapor in normal air, and
these vapors can leave the plastics after implantation, risking
corrosion.
Consistently, the electronics of the devices are protected. They
are protected against liquids, and against humidity. Liquid protection,
by surrounding the electronics in a hermetic enclosure, prevents
entry of fluids from the human body or drugs from the drug pathway.
Humidity protection provides for a dry environment for the internal
electronic components. A dry interior promotes long life and accuracy
in the performance of the electronic components.
In current device manufacture, a last or near-last step of manufacture
is the humidity protection step. The device is fully assembled,
with only a pinhole called a "tig" hole remaining as an
opening to the interior. The unit is then "baked" by bringing
it to a temperature of about 100 degrees Fahrenheit (37 degrees
C.) while a vacuum is created in the heating chamber or "oven".
The air inside the unit is pulled by the vacuum through the tig
hole, bringing internal moisture, including moisture previously
absorbed in plastic components, out with it. Typically, the tig
hole is so small that the time necessary to pull the air from the
unit is a day to two days. The external vacuum is then reduced and
in a short time, the baked unit is "backfilled" with helium,
meaning the vacuum inside the unit is filled with helium, also through
the tig hole. Within the short time available, the tig hole is then
welded closed.
This vacuum bake time can be a significant time constraint for
assembling the implantable pump.
SUMMARY OF THE INVENTION
A primary object of the invention is to substantially advance the
construction of human body implantable drug delivery pumps.
Another primary object is to substantially advance the manufacturing
methods employed for manufacturing such pumps.
Another primary object is to minimize the consumption of time required
by the current technique for humidity protection, and the complication
of the rigors of time, temperature, vacuum, and location of its
use.
Another primary object is to imbue the human body implantable drug
delivery pump with structure eliminative of the current technique
for humidity protection; that is, to provide a construction of the
unit that permits assembly without use of the current technique
for humidity protection.
Another object is to imbue the pump with structure that allows
the reduction of a hermetic barrier between the electronics area
and the motor area; that is, to provide a construction that works
with a hermetic seal of the electronics area and motor area together,
assuming the motor system has an impermeable barrier tubing that
contains the drug being delivered.
Other primary objects include providing a pump structure eliminative
and potentially eliminative of the unit baking and its use and complication,
eliminative and potentially eliminative of the vacuum creation and
its use and complication, and eliminative and potentially eliminative
of the tig hole and its use and complication.
In a first aspect, then, the invention includes an improvement
in a human body implantable drug delivery pump that comprises a
housing including at least a first shield and a second shield. The
housing defines an interior within the shields. The pump further
includes a fluid reservoir within the housing, a fluid conduit also
within the housing from the reservoir, an outlet from the fluid
conduit to the exterior of the housing, and a pump member in the
housing adapted to move fluid through the fluid conduit to the outlet.
The fluid in the reservoir and fluid conduit is isolated from the
pump interior. The pump further comprises a desiccant in the pump
interior, the desiccant absorbent of moisture in the pump interior,
and preferably absorbent of substantially all the moisture in the
pump interior.
In another principal aspect, the invention is directed specifically
to improvement in a human body implantable drug delivery pump of
the type described in which the desiccant has a moisture absorbent
property dependent on temperature, being lessened at higher temperatures,
the desiccant being pre-heated to improve its moisture absorbent
property before being placed in the pump. The desiccant is also
further absorbent of moisture, whereby the desiccant may be placed
within the housing during final assembly of the pump when the pump
housing is not completely sealed, and the desiccant is absorbent
during a time period of final assembly, and remains absorbent of
substantially all the moisture within the housing after complete
sealing of the housing. Most preferably, the desiccant is molded
to fit free space within the housing, and the desiccant comprises
a mixture of liquid silicon rubber and aluminum oxide.
These and other objects, aspects and advantages of the invention
and its preferred embodiments are best understood by a complete
reading of the detailed description of the preferred embodiment
of the invention, which follows a brief description of the accompanying
drawing.
BRIEF DESCRIPTION OF THE DRAWING
A drawing accompanies this specification, and includes a variety
of figures. They are each briefly described as follows:
FIG. 1 is a diagrammatic view of a human patient in which a representative
form of human implantable drug delivery pump is implanted for pain
treatment.
FIG. 2 is a pictorial view of the pump of FIG. 1 as implanted,
with human skin in phantom;
FIG. 3 is an exploded view of the representative pump;
FIG. 4 is a plan view of a desiccant body of the invention;
FIG. 5 is a side elevation view of the desiccant body; and
FIG. 6 is an exploded view similar to FIG. 3 of a pump with dessicant
body. FIGS. 2 and 3 are taken from U.S. Pat. No. 4692147 for economy.
As will become apparent, the specific internal and external construction
of the pump associated with the invention is not particularly significant
to the application of the invention. Except as claimed, the detail
of the pump is not considered critical or limiting of the claims
made to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As in FIG. 1 APT.TM. Intrathecal in the form of the SynchroMed.RTM.
Infusion System from Medtronic, Inc. uses a small pump 10 that is
surgically placed under the skin of the abdomen of a human patient
13 to deliver medication directly into the intrathecal space in
the spinal column 12 (where fluid flows around the spinal cord).
The medication is delivered through a small tube 14 called a catheter
that is also surgically placed. APT Intrathecal treatment offers
many people significant pain control with much lower doses of medication
than would be required by oral medications (pills). The pump 10
as shown is a round metal--titanium--device, in this case about
one inch (2.5 cm) thick, three inches (8.5 cm) in diameter. It weighs
about six ounces (205 g). Inside it has a reservoir, i.e., a space
that holds medication.
Turning to FIG. 2 a fill port 15 is in a raised center portion
or septum 17 of the pump 10 through which the pump is refilled.
The doctor or a nurse inserts a needle 19 through the patient's
skin 23 and through the fill port to fill the pump. Some pumps have
a side catheter access port that allows the doctor to inject other
medications or sterile solutions directly into the catheter, bypassing
the pump.
The SynchroMed.RTM. pump 10 automatically delivers a controlled
amount of medication through the catheter 14 to the intrathecal
space around the spinal cord, where it is most effective. The exact
dosage, rate and timing are prescribed by the treating physician.
These factors are entered in the internal electronic controls of
the pump using a programmer, not shown, which is an external computer-like
device that controls the pump's internal memory. Information about
the patient's prescription is then stored in the pump's memory.
The programmer communicates with the pump by radio signals.
Much additional information about APT.TM. Intrathecal, specifically
the SynchroMed.RTM. Infusion System, and most specifically the advantages
of the available medical treatments are available from implanting
physicians, from Medtronic, Inc., and from the medical and scientific
literature. All those who are potential candidates for treatment
are encouraged to seek reliable medical information from authoritative
sources. For the purpose of this detailed description of the invention,
the focus will be on the invention in its desiccant and the invented
manufacturing method. Broader information on drug delivery pumps
is also available in the patent literature, as for example in U.S.
Pat. No. 6036459 to Robinson issued Mar. 14 2000 U.S. Pat. No.
4692147 issued to Duggan Sep. 8 1987 U.S. Pat. No. 4576556
issued Mar. 18 1986 to Thompson, and U.S. Pat. No. 4978338 issued
to Melsky Dec. 18 1990 and the prior art they cite.
Attention is also directed to U.S. Pat. No. 6146743. This patent
discusses barrier metalization in ceramic substrates for implantable
medical devices. The patent is intended for multi-layer ceramic
substrates and the processing necessary to protect the substrate
and hybrid from moisture. A desiccant shield or cover 80 is in FIG.
14. The electronics packing for the pump 10 does not use ceramic,
but uses printed wiring board (PWB) technology. The substrate and
subsequent components available for surface mounting for PWB are
mainly plastic packages subject to water absorption. The high density
nature of the electronics (i.e., pitch <0.025 inches) makes it
imperative that water vapor and salts are controlled as distance
between electrical pathways continues to shrink.
Referring to FIG. 3 two shields or shells 20 22 form the housing
of the pump 10 and define its exterior and interior. The shields
20 22 come together about a center plate or bulkhead 24. The lower
portion of the pump, between the bulkhead 24 and lower shield 22
includes two sealed areas: a reservoir chamber, and an outer chamber.
A bellows 26 separates and defines the two chambers. The reservoir
holds medication or infusate introduced through the fill port 15
and the bellows 26 expands and contracts in response to the pressure
applied externally to the bellows by a two-phase fluid in the outer
chamber, maintaining pressure in the reservoir.
A fluid conduit extends through a flexible tube from the reservoir,
to an outlet or catheter port 28 extending from the exterior of
the pump housing. As stated in the Duggan U.S. Pat. No. 4692147
at column 3 lines 17-38 incorporated by reference, the conduit
extends through a pump member in the form of a motor-driven peristaltic
roller pump, where rollers move or press the fluid or infusate forward
toward the outlet when activated.
As stated in Duggan at column 3 lines 11-12 incorporated by reference,
the pump 10 further includes an electronic circuit module driven
by suitable capacitive energy storage units. The circuit module
provides instruction to the roller pump, and includes a microprocessor,
memory, and such other electronic componentry as necessary to have
the pump function as indicated above.
As appropriate to implantation in the human body, the pump 10 is
hermetically sealed as the pump is in its final manufactured form.
To achieve the sealing, the shields are welded to the center plate.
The welds are tested to withstand internal and external pressures,
pull forces, and leakage.
Referring to FIGS. 4 5 and 6 in contrast with the above-described
"Current Technique for Humidity Protection," a desiccant
body 30 is formed to fit in free space within the pump 10'. The
body 30 fits between the shield 20' and the bulkhead 24'. The pump
also includes its bellows 26' and second shield 22'. Primarily to
fit within available space, the body 30 includes a thin plate section
32 and an integral knob section 34. Four protuberances or bumps
such as the one designated 36 are spaced across the plate section
32. These abut the shield 20' and the plate section 32 abuts underlying
structure(s) to hold the body 30 in place under the compression
of the fit between the shield 20' and the bulkhead 24'. The protuberances
also expose the upper surface of the plate section 32 to gases within
the pump 10', allowing more rapid moisture absorption as will be
explained.
The body 30 is formed of a high percentage of aluminum oxide (AlO)
and a high percentage of liquid silicone rubber (LSR). Most preferably,
the percentages are 40-50%.+-.2% aluminum oxide by weight and 50-60%.+-.2%
LSR by weight. The AlO percentage is measured after exposure to
air for 24 hours minimum, while the AlO is in powder condition in
a layer no thicker than 0.5 inch (12.7 mm). The AlO powder is mixed
in the LSR, and the mixture molded to the shape shown. Care is taken
to assure the part is not exposed to heptane, alcohol or other solvents
other than water. The resulting body 30 is moisture absorbent.
The desiccant body 30 has a moisture capacity based on its composition
and size. As most preferred, the capacity of the body is sufficient,
once moisture has been baked out, to absorb moisture in the interior
components of the pump above the bulkhead 24', once the pump 10'
is backfilled with helium and welded sealed, to a desired or predetermined
level of dryness, and most preferably to substantially complete
dryness. The pumps 10' will have been assembled in clean rooms,
where relative humidity is typically specified in the range of 45%
to 60%, and the electronic and perhaps other components will have
absorbed moisture. Also as most preferred, the body, once baked,
has sufficient moisture capacity to absorb moisture as indicated,
and also to absorb moisture in advance of sealing of the pumps 10',
during a time period of exposure of the desiccant body to the atmosphere
of the clean room during final assembly of the pump and before the
pump is welded. As most preferred, the capacity of the body 30 is
sufficient for ninety minutes of assembly time in the clean room
and substantially complete dryness of the pump interior.
To assure the body 30 is sized properly for the unique circumstances
addressed by others of skill in the art, test bodies can be formed
and installed under expected working conditions. Test pumps may
be sealed. The devices may then be warmed, to drive deeply embedded
moisture into the gases in the pumps, and after an appropriate time
period such as two days, the pumps may be pierced. The gases may
be tested for moisture content, and the desiccant body composition
and size validated, or varied for further testing.
Thus, as can be fathomed at this point, the method of manufacturing
a human body implantable drug delivery device with the desiccant
body 30 includes pre-baking the body. The desiccant of the body
has a moisture absorption capacity depend on temperature that is
improved on baking. Baking drives moisture from the body.
The pump 10' in contrast, does not need to be baked. It also need
not be placed in a vacuum. The desiccant body allows substrate,
usually FR-4 components and metal components to be assembled without
vacuum baking or a humidity controlled environment. On arrival at
the final stage of assembly, the stage including sealing by welding,
the pump may be maintained in clean room conditions, at room temperature,
room humidity, and room pressure. The desiccant body may be placed
in the unit, and final assembly accomplished while the desiccant
body is exposed to clean room atmosphere. The assembly time period
should extend for no longer than the time for which the body has
been validated for exposure, by testing for composition and size,
but the assembly may occur with the body exposed. In completion
of final assembly, the pump may be helium filled and sealed by welding.
The desiccant of the body will remain absorbent within its tested
capacity, and if composition and size has been well chose, the desiccant
will absorb substantially all the moisture in the electronic chamber
of the pump.
For this specification, the term "absorb moisture" means
to absorb some moisture, whether all moisture is absorbed, a significant
portion of moisture is absorbed, or only some moisture is absorbed.
"Absorb" means to take in, for a significant period of
time. Other terms shall have the meaning ascribed to those terms
by persons of ordinary skill in the art.
The preferred embodiments of the invention, and the invention itself,
are now described in such full, clear, concise and exact terms as
to enable a person of ordinary skill in the art to make and use
the invention. To particularly point and distinctly claim the subject
matters regarded as invention, the following claims conclude this
specification. To the extent variations from the preferred embodiments
fall within the limits of the claims, they are considered to be
part of the invention, and claimed. |