Some of the embodiments of the present invention relate generally to the field of implantable medical devices, and more particularly, to a method for forming a connector assembly having a sectional interconnect ribbon embedded therein for use with an implantable medical device.
Implantable medical devices (IMDs) are becoming increasingly prevalent for the treatment of a wide variety of medical conditions. For example, cardiac pacemakers and implantable cardioverter-defibrillators have been developed for maintaining a desired heart rate during episodes of bradycardia and/or for applying cardioversion or defibrillation therapies to the heart upon detection of serious arrhythmias. In addition, tissue-stimulating IMDs are known for stimulating various nerves, muscles and organs to treat a variety of conditions.
Most IMDs include a hermetically-sealed housing that encloses a power source and electronic circuitry, at least one medical lead that bears at least one electrode and/or sensor, and a connector assembly (sometimes referred to as a header or block assembly) that electrically and mechanically couples the electronic circuitry in the housing to the electrodes and/or sensors via the medical leads. The specific electronic circuitry and lead configuration of the IMD depend upon the desired functionality of the IMD (i.e., whether it is a pacemaker, a nerve stimulator, or some other medical device).
Because the IMD housing is hermetically sealed, the medical leads preferably do not penetrate the housing, but rather are coupled to electrical connectors located within the connector assembly. To allow electrical signals to pass between the electronic circuitry of the IMD housing and the sensors and/or electrodes carried by the medical leads, the IMD housing is conventionally configured with feed-through conductors located on its outside surface yet electrically coupled to its internal circuitry. Once the connector assembly is physically attached to the IMD housing, the pass-through conductors are routed from the IMD housing to one of the conductors of the connector assembly. The pass-through conductors are then covered with a medical adhesive, and the adhesive is cured to form a protective, insulating layer that isolates the wires from external elements. Although this method is relatively straight forward, it requires manual routing of the conductors and application of the adhesive, which in turn introduces undesired variables into the manufacturing process.
An alternative approach to the use of adhesives involves the positioning of one or more conductors within a mold in a predetermined orientation. An insulating material is then injected into the mold to encapsulate the conductors. While this process eliminates the variables associated with a manual step, it is nevertheless difficult to implement with other than a simple design. This is because the introduction of the plastic into the mold at high pressures generally causes the position of the conductors to shift. Accordingly, in the molding process, shorts may form between conductors, or conversely, a desired electrical connection may be lost. While injection molding systems of this type generally include mechanisms to hold the conductors in place during the injection process, the components may shift regardless of efforts to prevent such shifting. Additionally, the difficulty associated with maintaining isolation between multiple conductors places limits on the assembly dimensions. That is, an assembly cannot be made too small because shorts are more likely to occur between closely spaced conductors that shift during the injection molding process. This may lead to a higher scrap rate than would otherwise exist.
U.S. Pat. No. 6,817,905 (which is hereby incorporated, in relevant parts, by reference) improves upon this method with the introduction of a two-shot method of forming a connector assembly. This method allows for the electrical conductors to be embedded within the connector assembly while reducing the likelihood of the electrical conductors shifting positions during the manufacturing process. According to this method, a core is formed of a first insulating material during a first injection molding step. The core is then loaded with various electrical connector elements. Next, the electrical conductors are secured to the core and are attached to a desired one of the electrical connector elements. In one embodiment, the electrical conductors are formed as a circuit assembly (i.e., an interconnect ribbon) that can be handled as a single unit during the assembly process. The circuit assembly may be stamped, or otherwise formed, from a single planar sheet of conductive material and then shaped for attachment to the core. In alternate embodiments, the electrical conductors are (1) individually loaded onto the core, (2) joined in a single circuit member via insulated material, or (3) integrally formed with the electrical connector elements.
In a second injection molding step, the electrical conductors (except for the electrical conductor pads), electrical connector elements, and the core are overmolded with a second insulating material. The electrical conductor pads are then separated, both electrically and mechanically, from each other.