Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2001-11-20
2002-11-19
Gibson, Randy W. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S750000, C361S751000, C361S790000, C439S067000, C174S250000, C174S254000
Reexamination Certificate
active
06483713
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to multilayer circuit boards and folded flexible circuit boards.
2. Description of the Related Art
Primarily flexible circuits are used to solve problems with interconnection of rigid circuit boards. This new structure offers the advantages of increased reliability, weight and space savings, a reduction in mechanical connectors, and greater impedance control.
Four types of flexible circuits are prevalent today: single-side, double-sided, rigid-flex and multilayer. Single-sided circuits, consisting of a single layer of conductors on a base film, are most commonly used in interconnection applications. A double-sided flexible circuit has a single-etched conductive pattern on both sides of the base film. It is used when circuit density and layout cannot be routed on one layer, and in ground plane applications.
Rigid-flex circuitry traditionally consists of both rigid and flexible substrates selectively laminated together into a single cohesive construction, electrically interconnected with electroplated holes or ‘via’. The rigidized area can be used to mechanically reinforce the circuit board in an area subject to increased abrasion or other forms of stress.
Multilayer flexible circuits consist of a sandwich formed by many layers of copper, between the dielectric substrates, and are used primarily in high-density applications. Conventional multilayer printed circuit boards consist of a number of thin boards sandwiched together between layers of epoxy resin-impregnated glass cloth. Connections between layers are achieved by means of plated via holes.
In the prior art, there have been some attempts to provide foldable flexible circuit boards.
For example, U.S. Pat. No. 4,928,206 by Porter et al. discloses a number of rigid circuit boards connected by a number of flexible circuit panels. Integrated circuit boards are mounted on the rigid printed circuit boards. The boards are foldable to reduce the entire unfolded layout in one direction, either width or length. Such a configuration is attached serially and folds along the flexible portions from a completely unfolded position to a most compact folded position.
Another flexible printed circuit board, by Takao et al. (U.S. Pat. No. 5,917,158), discloses a single circuit board having a main body and a folding portion as part of the single circuit board and wherein a set of copper foil lines provided on both the main body and the folding portion so that the folding portion overlaps the main body so that terminals at the ends of the copper foil lines make electrical contact with each other.
Furthermore, U.S. Pat. No. 5,398,163 by Sano discloses a flexible printed circuit board having at least one electrically conductive layer, and a fold retainer pattern which is electrically isolated from the printed circuit pattern. The fold retainer pattern maintains its folded shape once the flexible sheet is folded.
In the above devices, as well as in other prior art devices, there are a series of rigid circuits which in one way fold via flexible connections, to reduce the open layout of the circuitry in one direction. In the above patents, the folding circuit board serves to reduce the unfolded area of the circuit board in order to minimize the space taken up by the circuit board, or fit a series of rigid circuit boards by flexible connectors in order to conform to the desired space available. No consideration is given to the nature of the folding, or situations where there are theoretical limitations to the space available or very low current signals where one seeks to minimize inter-channel crosstalk or capacitance.
However, in certain electronic devices further reductions in compactness is required, specifically in circuit boards utilizing high density of conductor lines where space constraints limit the circuit board size. For example, in a Kinestatic Charge Detector (KCD, U.S Pat. No. 4,764,679 by McDaniel et al.), a strip-beam, multielectrode ionization chamber is used to produce a high-resolution digital radiographic image of a subject. The XCD utilizes a high-pressure rare gas as the uniform detection medium enclosed in a tubular chamber. X-rays after passing through the subject enter the chamber and ionize the gas forming charge pairs (ion-electrons). An externally induced precisely controlled electric field within the chamber is used to direct the positive ions at a constant velocity towards the collector electrodes or channels. The collector electrodes accumulate the current induced by the ions and the signal from these electrodes is read out by the interfacing electronics. In other words, the uniform detection medium contains spatial information that is read out as the ions approach the collectors.
Current circuit board manufacturing technology sets the minimum separation between conductor lines of a KCD at 0.013 cm for a conductor width of 0.013 cm for large circuit boards. (For a much smaller circuit board area, smaller conductor widths and separations on the order of a couple of hundred nanometers are possible.) According to the current technology, it would require, at least, 15 cm of circuit board width just to lay 576 conductors (signal channels for the KCD). These conductors need to be taken out of the chamber with the help of vias that need a hole of bigger size to be drilled on the circuit board surface for each conductor. With the vias, the total width of circuit board needed is about 30 cm. However, the maximum available width of the circuit board is dictated by the inner diameter of the chamber, which in turn is limited by the minimization of the detector size needed for clinical efficacy and a maximum practical size for maximal imaging signal. For an inner diameter of 11.25 cm (as used for the prototype KCD detector designed for megavoltage imaging), the collector board can be, at the most, 10 cm wide for a 0.5 cm clearance all around the edge required for mechanical alignment.
To be able to route all the channels out of the chamber, one approach is to fabricate the collector board in two parts with half the number of channels on each. The total number of channels will still have to be reduced to 480 (which may be allowed) because of limited width available. Each board can be double-sided with the collecting electrodes on one surface and its routing path via the second surface (back surface). The two boards must be accurately aligned inside the chamber since even a small misalignment can cause a loss in resolution and/or damage to the circuit board and the grid.
Apart from alignment issues relating the two board parts, the collector board itself must be precisely positioned within the chamber, very close to the grid (typically 0.2 B 0.5 mm). Inserting the boards from both ends introduces a blindfolded step in the assembly process; since at least one board must be inserted through the end cap after the detector is assembled, making it difficult to determine when the two boards exactly meet. If the boards are pressed too hard against each other, they might damage each other and cause bowing of the board, ultimately short-circuiting the grid. On the other hand, if the boards are not pressed enough, they may not be touching each other at all, thereby causing a loss of signal and vital channel information. To ensure uniform signal collection, the two boards have to be on the same level and exactly touching, so that the spacing between the first conductors on the two boards is the same as the spacing between all other conductors. This spacing requires tight tolerances and a highly complicated design to get a working chamber, making this solution impractical.
Another approach to the above problem is to reduce the number of channels so that they can be accommodated in the available circuit board width i.e. 9 cm. This means fewer channels to collect the signal, or in other words, a lower spatial resolution or a reduced field of view, either of which is unacceptable. Yet another solution is to increase the tube diameter, which is not practical due to s
Jain Jinesh Jitendra
Laughter Joseph
Samant Sanjiv Singh
Gibson Randy W.
Gigante Stephen
Klauber & Jackson
Levi Dameon E.
St. Jude Children's Research Hospital
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