Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-03-30
2001-11-27
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06324428
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to improvements in the packaging of electronic components suitable for implantable medical devices. More particularly, this invention relates to methods and apparatus for constructing a multi-level high density electrical package which is optimally protected from dielectric breakdown, moisture, and other contaminants.
BACKGROUND OF THE INVENTION
It will be appreciated that the invention has utility with respect to improvements in electronic packaging that may be suitable for many applications. However, the present invention has some unique features which maximize utilization of space within an implantable medical device and provide enhanced protection for internal electronic components.
Implantable medical devices of the type having electrical circuit components are well known in the medical arts. In one particularly common form, the implantable device comprises a pacemaker, or other stimulation device, having an appropriate electrical power supply and related control circuitry for use in electrically stimulating a patient muscle, such as the heart. Such a pacemaker commonly includes a hermetically sealed case or housing within which a power supply and control circuitry are placed, in combination with one or more conductive pacemaker leads extending from the housing to the selected muscle structure within the patient.
Signals into and out of the circuitry within the housing of a common stimulation device are coupled through the housing by means of feedthrough terminals of various types known in the art. Examples of such stimulation devices may be found in commonly assigned U.S. Pat. No. 5,282,841 to Szyszkowski.
As is apparent from the Szyszkowski patent, the size of the housing is dependent upon that required to house both the battery and the electronic control circuitry constituting the pulse generator. A major factor which drives the electronic control circuit design is the need to fit large, generally rectangular or cylindrical components into a physiologically-shaped, curved housing. Of course, efforts are continually being made to minimize the size of the housing, and thus the size of the internal components, while maximizing the effectiveness of the device.
The control circuitry of implantable stimulation devices is often a multi-level hybrid circuit module. The multi-level module is ordinarily designed to achieve a low-volume configuration to facilitate placement within the limited confines of an associated device housing. Multi-level circuit modules may contain separate vertically stacked substrates, i.e., platforms, having individual circuit components mounted on the substrates. A protective cover, or lid, is typically placed over any exposed electronic circuitry of the multi-level module.
There have been many approaches documented in prior art publications for constructing a multi-layer, or three-dimensional, circuit module used in implantable devices. For example, in U.S. Pat. No. 5,222,014 issued to Lin, and Japanese publication No. 1-147850 issued to Kuwabara, independent circuit platforms are stacked above a substrate to create the multi-level structures. In each case a lid may be placed over the structure to protect the underlying circuitry.
As the electronic circuit modules of implantable medical devices become more complex and more densely configured, design constraints for closely configuring the associated electronic components become ever more significant. In particular, the electronic components must be free of errant particles and other ionic contaminants which could interfere with the electronic circuitry or damage miniature wirebond connections.
Some methods of sealing pacemaker devices and the like include those disclosed in U.S. Pat. No. 5,480,416 issued to Garcia et al., and U.S. Pat. No. 4,616,655 issued to Weinberg et al. In the Garcia et al. patent, an electrically insulative coating is applied over the entire surface of the implantable device case. In Weinberg et al., however, the electronic pulse generator of a cardiac pacer includes an internal chip carrier housing which is hermetically sealed.
In a high voltage system, such as an implantable cardioverter-defibrillator, the packaging density of the electronic components within an implantable device module is largely determined by the dielectric properties of the material separating the components. Previous methods of insulating electronic components have including using air as a natural dielectric, or as disclosed in the Lin patent, an encapsulating molding compound may be placed over the various electronic components for protection. Such methods achieve a certain level of dielectric breakdown protection which may not be suitable for the increased packaging density found in the most advanced implantable medical devices.
The present invention represents an improvement over previous implantable medical devices which allows for increased packaging density and improved protectability of internal electronic components.
SUMMARY OF THE INVENTION
The present invention comprises an implantable medical device having a multi-level electronic module which may be characterized by at least two stacked internal substrates for mounting electronic circuits. The electronic module has a protective lid for protecting the substrates and an external interconnect structure mounted on the lid which is also capable of mounting electronic components.
The electronic components of the present invention comprise a hybrid assembly including a first substrate for supporting passive and active electronic circuitry components and their electrical interconnections. The first substrate may be formed with a cavity on a first side which defines a depressed surface for mounting electronic components thereon.
The present invention further includes an intermediate substrate mounted on the first side of the first substrate, the intermediate substrate having a lower surface facing the depressed surface and having an upper surface. Both surfaces of the intermediate substrate are capable of supporting electronic circuitry including active and passive components and their electrical interconnections.
Advantageously, one or more air gaps are maintained between the first and intermediate substrates, such as along the edges, to establish fluid communication between the electronic components mounted on the first substrate and the upper surface of the intermediate substrate. A lid is placed over the substrates to protect the active components on the first and intermediate substrates. The lid is further capable of supporting and interconnecting the large, typically externally-mounted device components (such as inductors, telemetry coils, and a reed switch) to the hybrid assembly.
The lid is mounted on the first side of the first substrate overlying the upper surface of the intermediate substrate and has one or more notches for establishing fluid communication between an exterior portion of the lid and the underlying substrates. A protective coating, such as parylene, or other suitable polymer material, is vapor deposited over the entire hybrid assembly. The presence of the lid notches and the substrate air gaps allows for uniform coating of the underlying circuit components mounted on the first and intermediate substrates. Due to the high dielectric breakdown properties of materials such as parylene, increased packaging density of the circuit components can be maintained. The deposited coating also helps support the miniature electronic components and the delicate wirebond connections between such components. In addition, the parylene coating provides protection against moisture and contaminants interfering with electronic operations.
While the embodiment described above includes a vertically oriented hybrid circuit assembly, it is within the spirit of the invention to apply the principles of parylene coating, and in particular parylene coating throughout multi-cavity structures, to other assembly configurations.
Accordingly, a primary feature of the present invention is to provide impro
Silvian Sergiu
Weinberg Alvin
Yang Min-Yaug
Kamm William E.
Pacesetter Inc.
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