Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-09-13
2002-10-08
Martin, David (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S752000, C361S759000, C361S808000, C174S268000, C174S050510, C439S620040
Reexamination Certificate
active
06462955
ABSTRACT:
BACKGROUND OF THE INVENTION
In today's electronics market, manufacturers are placing emphasis on increasing their product's reliability and reducing assembly costs to remain competitive. A primary focus of each manufacturer is to reduce the cost and increase the circuit density associated with interconnecting the sub-assemblies and components found within its products. Another emerging focus in today's electronics market is to pack more electronic functions into smaller packages. This means higher density modules, each requiring multiple high density interconnections to other modules.
In electrical systems, flexible printed circuits are employed as electrical jumpers or cables for interconnecting rows of terminal pins or pads of printed circuit board. Such flexible printed circuits are generally connected to a printed circuit board using a connector. Conventional connector manufacturers compete with each other using the same basic technology, individual stamped contacts molded into a plastic housing. This structure is then soldered to a printed circuit board (PCB) and is then ready to receive a flexible jumper or interconnect circuit. Many of these conventional connectors are of the zero insertion force (ZIF) variety, which require the application of minimal forces during the process of inserting the flexible circuit into the connector. These ZIF connectors thus reduce the likelihood of circuit damage during the connection process.
All of today's ZIF connectors use either the edge of the interconnect circuit or a precisely located hole to accurately align the conductors of the flexible circuit to the connector's contacts. This requires circuit manufacturers to precisely control both the thickness and width of a flexible circuit's terminating ends. Generally, tolerances must be maintained within 0.003 inches. To accurately outline a circuit and control the required tolerances requires an expensive precise outline die. Another obstacle encountered in conventional circuit connector technology centers around a tendency of flexible circuits to shrink somewhat after their manufacture. When working with larger flexible circuits, the shrinkage problem can be significant enough to result in significant alignment problems. As such, outline dies are usually constrained to outline a 6 inch by 6 inch area. This size restriction adds labor costs and reduces yield.
In addition to size restrictions, flexible circuits also require the precise attachment of a support stiffener. This stiffener is required to lift the circuits into connection with a conventional connector's contacts and add the structural support necessary to ensure the thin flexible circuit enters into the connector's opening. The precise outlining and stiffener attachment process is cumbersome and costly and frequently the cause of poor yields and system failures.
Conventional connectors also utilize internal spring assemblies in order to ensure that jumpers or flexible circuits maintain adequate contact with the connector's contacts. However, until now, these connectors have incorporated a single spring assembly for each conductor. The physical size required to manufacture an acceptable spring contact eliminates this technology in high-density circuits using microminiature connectors which will eventually require conductors on 0.006 inch pitch centers.
Thus there is a need for a microminiature apparatus to properly attach surface mounted components to flat flexible cable, or flexible printed circuit, and which requires minimal manufacturing and assembly costs, yet provides high quality connection.
SUMMARY OF THE INVENTION
A preferred embodiment of the present invention is a connection assembly or system to assemble surface mountable components to flat flexible cable (FFC), flexible printed circuits (FPC), and round wire interconnect (RWI). It is not a connector itself. The invention comprises surface mountable connector components (headers, receptacles, LED's etc.); prepared components such as FFC, FPC, or RWI, which are prepared by removing the insulation and exposing the traces; an alignment base having alignment ribs; and a cover. To assemble the component alignment casing system, the prepared component (FFC, FPC or RWI) is overlaid on to the alignment base, by hand if desired, the surface mountable component is applied to the alignment base overlaying the prepared component, by hand if desired. Then the exposed traces of the prepared component are soldered to the exposed leads of the surface mountable component (for example, a header, receptacle, LED, etc.), and the cover is attached, by hand if desired.
The system of the present invention aligns a surface mountable connector or component to an FFC, FPC or RWI. It does not align the internal components of a connector, and it is not an electrical connector by itself or by nature, it is an assembly system. The system is an apparatus that is used to properly attach surface mountable components to FFC, FPC or RWI. The system does so by ensuring an accurate alignment between the leads or traces of a surface mountable component and the leads or traces of the FFC, FPC or RWI, while maintaining isolation between the opposing leads or traces of the FFC, FPC, or RWI, thereby insuring against bridging (when a trace makes contact with another trace of the came component) using the alignment ribs or fins. This allows for “blind assembly”, an assembly which can take place without the use of magnifying optics which are typically needed for similar assemblies.
The component alignment system of the present invention can be disassembled for reworking rejects, or for other reasons, without damaging either the flexible interconnection medium or the connector components. The cover is removable and provides positive force to the leads of a surface mountable component to assure contact between the surface mountable component and the prepared component (FFC, FPC, or RWI). The solder can be reflowed and the surface mountable component, and the prepared flexible interconnection component or medium, can be removed from each other and from the alignment base. The simple design provides multiple manufacturing options for handling different production volumes. The assembly of the system can be done manually, semi-automated, or fully automated. The simple design makes it possible to be assembled by customers, because there is no custom assembly equipment needed. Because all of the involved parts align off of the same source, i.e. the base of the casing, the alignment tolerance stack up is lower than conventional practices.
The alignment ribs prevent bridging between conductors of the same component (leads or traces) during soldering, which in turn eliminates the requirement for expensive precision soldering equipment and lowers the reject rate. Typical manufacturing methods to mount surface mountable components to the FFC, FPC, or RWI have no manner to prevent solder bridging.
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Devine Millimet & Branch PA
Miraco, Inc.
Remus Paul C.
Sullivan Todd A.
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