Abstract:
A printed circuit assembly for use in an implantable medical device comprises a plurality of panels having active and passive circuit components on one major surface thereof, the plurality of panels being interconnected with flexible flat cable segments allowing the assembly to be folded so as to place the individual panels carrying the circuit components in a stacked relationship. By providing conductive layers on predetermined surfaces of the panels, shielding is provided to inhibit noise generating circuitry from contaminating wanted signals passing between the components and the plural panels.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     This invention relates generally to implantable electronic tissue stimulating devices, and more particularly to the physical packaging of the electronic circuitry used in such devices in which circuit boards carrying hybrid circuitry are interconnected with flexible printed conductors, allowing the boards to be juxtaposed by folding the flexible interconnecting conductors. 
     II. Discussion of the Prior Art 
     The miniaturization of electronic devices has resulted in a widespread use of flexible printed circuit boards and interconnecting cabling. The use of flexible printed circuitry can minimize the space required to accommodate interconnected electronic circuits. The printed circuit boards are usually fitted into an hermetically sealed, moisture-impervious housing of such devices as pacemakers, defibrillators, neurostimulators, hearing aids and other small electronic devices. Typically, limits are imposed on the construction of the flexible printed circuit boards because of volume restrictions imposed by the allowable size of the housing of the implantable device in which the circuitry is contained. 
     Taking as an example a small electronic device, such as an implantable defibrillator, it typically requires a hybrid circuit including discrete and integrated circuit components that must be connected to and contained within a hermetically sealed housing with a battery power supply and energy storage capacitors. In prior art designs, the hybrid circuit is typically disposed on a multi-layer circuit board with active and passive circuit components mounted on the opposed major surfaces of the printed circuit board. While this approach generally permits an increased component count-per-unit volume occupied, it tends to increase the cost of manufacture in that multiple passes with pick-and-place machines are needed to populate both sides of the printed circuit boards with components. 
     It is known in the art to provide multiple printed circuit boards interconnected with one another by flexible conductors embedded in insulation layers that can also be flexed. See, for example, the Haas Patent 5,121,297. There is no teaching in this patent, however, of having the substrates on which circuit components are mounted in other than a coplanar relationship. 
     The Karabatsos Patent 5,949,657 describes an electronic assembly comprising a number of rigid substrates or panels that are connected by flexible wired jumpers, allowing the multiple boards to be folded so as to be non-coplanar. The &#39;657 patent does not address problems brought about by close proximity of circuit components upon the folding of the assembly as far as EMI is concerned. 
     Thus, a need exists for a printed circuit assembly that allows for a relatively high component density, the ability to populate the printed circuit panels with components using only a single pass with automated pick-and-place equipment and which incorporates requisite shielding to prevent noise-generating circuits from adversely affecting operation of other components comprising the overall circuit assembly. The present invention meets these needs and provides other advantages and improvements that will be evident to those skilled in the art upon review of the following description and drawings. 
     SUMMARY OF THE INVENTION 
     The present invention provides a packaging approach that utilizes a plurality of printed circuit panels interconnected by flexible interconnecting flat cabling so that components may be mounted on one major surface of the panels only. Thus, only a single pass with pick-and-place equipment is require to populate the panels which then may be juxtaposed in non-coplanar relationship by folding the flexible interconnecting cabling. During initial component layout, consideration is given to component placement so that noise-generating components will not be closely proximate other components that may be sensitive to such noise following the folding thereof. Further, by including conductive shield structures in the printed circuit board, and by folding the assembly so that the components face outward, the shielding layers will be interdispersed with the active and passive components, thereby further reducing radio frequency interference and noise. The configuration also allows for the direct connection of ancillary components, such as batteries and capacitors, thereby reducing the inter-complexity and the cost of manufacture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description from the preferred embodiment, especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts. 
     FIG. 1 is a front isometric view of a circuit assembly constructed in accordance with the present invention in an unfolded state; 
     FIG. 2 is a back isometric view of the printed circuit assembly of FIG. 1; 
     FIG. 3 is an isometric view of the assembly of FIG. 1 when being folded in half; 
     FIG. 4 is an isometric view of the circuit assembly of FIG. 1 in its fully folded state; and 
     FIG. 5 is an isometric view of the assembly of FIG. 4 inserted in a retainer. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is applicable to a variety of medical devices utilizing active and passive hybrid circuit components. The invention will be described generally in the context of a printed circuit board assembly for an implantable cardiac rhythm management device, but it is to be understood that the invention may find utility in other product areas as well. 
     The printed circuit assembly in FIG. 1 is indicated generally by numeral  10  and is illustrated as including four discrete printed circuit boards or panels  12 ,  14 ,  16  and  18  arranged in a 2×2 matrix that are interconnected with one another by means of flat, flexible printed cabling segments. More particularly, panel  12  is connected to panel  14  by a flexible flat printed conductor cable segment  20  and printed circuit panel  16  is joined to printed circuit panel  18  by flexible flat cable segment  22 . Printed circuit panel  12  is joined to printed circuit panel  16  using a flat conductor cable segment  24  and printed circuit panel  14  is joined to printed circuit panel  18  via flat conductor cable segment  26 . 
     As is further seen in FIG. 1, each of the printed circuit panels is populated on one major surface only with hybrid circuitry including integrated circuit chips  28  and  30  on panel  16  as well as discrete components including resistors, diodes, capacitors also located on the panel  16 . In a similar fashion, printed circuit panel  18  has mounted thereon a multi-chip module  32  and other electronic components as illustrated. Because the components are disposed only on one major surface, automated pick-and-place equipment is only required to make a single pass to fully populate the several interconnected panels. 
     Printed circuit panel  14  has a plastic surface mount multi-chip module which is connected by printed wiring to other points in the assembly. A portion of the printed circuit panel  14  includes a copper substrate that functions as a shield inhibiting EMI from adversely interfering with signals being developed and conducted between circuit components. 
     A plurality of input and output tie points are located on the flat cable conductor segment  21  and are identified by numeral  40 . These tie points are adapted to be connected to feed-through pins  41  (FIG. 4) that are conventionally used to connect lead terminal contacts in the molded plastic header portion of a pacemaker or defibrillator to the electronic circuit  10  contained within the hermetically sealed housing or can of the device. 
     The assembly includes a plurality of circuit test point terminals scattered through. For example, test points  42  are disposed on a small printed circuit panel  44  that connects to the printed circuit panel  16  by a flexible cable segment  46  and that can be folded in. Before the circuitry  10  is placed within its housing, test probes may be applied to the test points  42  to ensure that the circuitry is properly operating. 
     Flex circuitry  47  is also used to join a printed circuit panel  48  to the printed circuit panel  18 . The printed circuit panel  48  includes a plurality of contacts, as at  57 , that are adapted to connect to the energy storage capacitors utilized in implantable defibrillator circuits. Further contacts  50  on a panel  48  are adapted to connect to a battery (not shown) used to power the device. 
     Referring to FIG. 2, there is shown the reverse side of the interconnected circuit panels illustrated in FIG.  1 . The circuit panels  12 ,  14 ,  16 ,  18  and  44  include conductive ground planes serving as shield members  58 ,  60 ,  62 ,  64  and  66 , respectively. 
     Referring next to FIG. 3, it shows the circuit assembly  10  in the process of being folded through the flexible flat cable segments  20  and  22  so that the printed circuit panels  12  and  16  are juxtaposed in side-by-side relationship to the panels  14  and  18 . When so-folded, the active and passive circuit components visible in the view of FIG. 1 face away from one another and are effectively separated by conductive ground plane shield elements  58 ,  60 ,  62  and  64 . 
     FIG. 4 shows the circuit assembly  10  after it has again been folded, this time by folding flat conductor cable segments  24  and  26 , thereby placing the several panels in a substantially parallel, stacked orientation relative to one another. The four panels  12 ,  14 ,  16  and  18  with the electronic components in place form a 2×2 matrix when unfolded and a 1×4 stack when the cabling is folded in the manner shown. To maintain the circuit assembly in its fully folded configuration, it may be placed around an inner liner  61  in a basket retainer member as is illustrated in FIG.  5 . The retainer is indicated generally by numeral  66  and comprises a pair of molded plastic side members  68  and  70  which are hinged together along a back binding (not shown) that allows the first and second halves  68  and  70  to close about the folded circuit assembly  10 . Upper and lower pegs  72 - 74  and  76 - 78  on the inner liner and basket retain are adapted to fit within holes  80 - 82  and  84 - 86  with a predetermined friction fit to thereby clamp the folded circuit assembly  10  between the retainer halves  68  and  70 . 
     From what is depicted in the drawings and described herein, those skilled in the art will appreciate that the folded construction of the final assembly illustrated in FIG. 5 exchanges surface area for depth and permits economical planar construction of relatively dense electronics on a printed wiring board. In that the components themselves reside only on one surface of the unfolded assembly, conventional pick-and-place machines can be used to position the components onto the substrate as soldered connections between the components and the printed wiring terminal points on the substrates is effected. The flexible junctions between the several panels vary in the number of conductive layers used to accommodate the various signals exchanged between panels, while permitting the inclusion of electrical shield layers to protect signal integrity. 
     The use of auxiliary panels as low profile integrated shields permits noisy and sensitive circuits to be placed in close proximity without interference. The integrated nature of these shields reduces the number of manufacturing steps and final assembly costs. 
     As explained, auxiliary components, such as batteries and high voltage capacitors are adapted to be connected directly to the folded assembly, further reducing the interconnect complexity of the device and simplifying the manufacture of the device in question. The flat manufacturing configuration also permits ease of testing due to reduced fixture density and complexity. Once folded, however, the structure becomes very compact and can be readily fitted within the outer housing of the implantable device. By beveling one corner of each of the panels  12 ,  14 ,  16  and  18  (as best seen in FIG.  1 ), when the configuration is in its fully folded condition as illustrated in FIGS. 4 and 5, the resulting folded package is made to better conform to the profile of the housing in which the folded package is fitted. 
     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 construct and use such specialized components as are required. 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 equipment and operating procedures, can be accomplished without departing from the scope of the invention itself