Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-09-21
2001-04-17
Gandhi, Jayprakash N. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S762000, C361S763000, C361S779000, C174S050510, C174S255000, C174S256000, C174S257000, C174S260000, C439S066000, C439S068000, C428S901000, C165S185000
Reexamination Certificate
active
06219253
ABSTRACT:
This invention relates to the construction of a packaged electronic circuit comprising a molded-plastic support base having a capacity to accept and hold electronic devices or subassemblies thereof in a pocket within the molded substrate, and positioning them for interconnection (hereinafter referred to as “Molded Electronic Package”). The connection to the electronic devices or subassemblies is intricately formed with the placement of the circuit traces on the substrate. This is usually done at the surface level. This is an advantage over existing technology because it offers savings both in cost and space. The formation of the circuit traces by Build Up Technology is a way of creating circuitry with high precision and very fine lines. The attachment to electronic devices may also be achieved with Build Up Technology by forming the circuit traces with a plating process that simultaneously forms electrical connections to the electronic devices inserted in the pockets of a molded substrate on which the traces are formed. In some cases, there are an advantages to combining Polymer Thick Film technology and Build UP Technology when forming the circuit traces on the molded plastic containing electronic devices inserted into the molded plastic. The electronic devices may be semiconductors, integrated circuits, electromechancial devices, silicon chips, gallium arsenide chips, other active components, passive components such as Thick Film resistors or capacitors, or other devices as defined later. While molded substrates are not new, and the use of Build Up Technology and Thick Film Technology are not new, the combination of a molded substrate with a Pocket built into the molded substrate and interconnecting the electronic devices in the pocket with Build Up Technology is new and fulfills a long-felt need to be able to reserve the surface area above the trace area for other circuits traces and electronic devices. Others have tried to accomplish this by other means of interconnecting by layering circuit boards as discussed below, but only with the advent of the Build Up Technology and the new molded plastic resins which have only recently become available can we now accomplish the connecting of the electronic device in the pocket of the substrate material. The pocket permits the electronic device to be supported by the substrate instead of being supported on the trace which allows for the use of the Build Up Technology to connect the electronic devices. This long felt need to further reduce the size of circuit boards for ever smaller products while containing or reducing costs of the resulting circuits has until now been unanswered by conventional methods.
BACKGROUND OF THE INVENTION
A traditional printed circuit board comprises a supporting substrate and copper-foil circuit traces. These traces are usually formed by the chemical etching of a pattern defined onto a laminated copper surface. Sometimes both front and back sides of the substrate carry circuit traces. Two-sided, or double-sided designs usually are interconnected through vias (holes) that have copper deposited around the hole walls. A related technology exists known as Thick Film. Here the supporting substrate comprises flat, thin pieces of alumina (Al
2
O
3
) on which the traces are printed with an ink containing metal, glass frit, and other additives. When fired at the correct temperatures the ink fuses to form conductive traces to which components can be soldered. An important feature to Thick Film technology is that conductive traces can be interconnected by printed inks having specific electrical resistivity after being heated in a kiln (firing).
“Build Up Technology” is a way of creating multi-layer circuitry with high precision and very fine lines. It is therefore, like the Molded Electronic Package, a way of making things smaller. By adding multiple layers of circuit traces you can achieve more functions per unit area than can be achieved with a single layer. By using very fine traces one can achieve even more density. Traditional imaging, and the imaging processes used in the Molded Electronic Package, is screen printing where lines as fine as 0.125 mm are difficult to achieve. Build Up Technology is a known photo process, and lines in the 0.050 to 0.075 mm range are possible.
Countless variations of printed circuit boards exist, and many variations of the Build Up Technology process also exist. One application of both the printed circuit board process, and the Polymer Thick Film process is the Molded Circuit board. Here the process of converting a laminated sheet of material into the proper circuit board dimensions and having all the necessary holes, slots, and shapes are replaced by molding these features into the board. Circuit traces are applied to a board either during or after the molding process. Different methods exist for adding the electrically conductive traces to a surface. This includes such the use of Polymer Thick Film inks, sputtering, and vacuum deposition. Another method for adding the electrically conductive traces is to use Build Up Technology.
In the past the molded board with Polymer Thick Film traces (baking of the Polymer Thick Film ink creates the conductive circuit traces) found limited acceptance for a number of reasons. Printed Polymer Thick Film conductive traces have more resistance than copper foil traces. Also, electronic devices cannot be soldered to most Polymer Thick Film traces. Those electronic devices that were attached to solderable Polymer Thick Film inks did not have good adhesion to the molded substrate after the soldering process. Some Polymer Thick Film conductive inks contain lead which causes environmental concerns and which limits the ability to recycle the materials. Additionally, the molded plastic that could withstand soldering temperatures without warping were the engineering grade materials which are higher quality performing materials. These are more expensive, however, and when used, the cost advantage of the molding process is often lost. Some simple applications of the Molded Board with Polymer Thick Film traces but without components in Pockets and designed to fit into a connector have been used commercially, but in general commercial production of this type product has been limited.
Printing conductive layers over circuit board traces that are connected to and grounded by a ground plane is a known way to achieve shielding of the traces covered. The circuit traces are first sealed in an insulating layer, and then overprinted with a conductive layer. With this traditional approach it is not possible to shield the components which are attached to the circuit traces, but only the traces themselves.
Lassen's U.S. Pat. No. 4,602,318 describes achieving high density electronic networks by depositing filaments onto a substrate and encapsulating the filaments to achieve dimensional stability. Filaments are conductive or made conductive by various means. Access to these conductive traces is produced with the use of a high -energy beam to cut through and expose the filaments. Lassen claims the use of epoxy resin sheets, and polyimide resin sheets to create his circuitry.
Parker's U.S. Pat. No. 4,912,844 describes using a heated punch to define grooves and holes in a substrate. The grooves are then filled with solder to create a circuit trace which connects electronic devices.
Beaman's U.S. Pat. No. 5,371,654 describes a three dimensional electronic package with a plurality of assemblies interconnected by aligning the assemblies so they are adjacent, and interconnected by some means such as an elastomeric material, but other than a Polymer Thick Film.
Capote's U.S. Pat. No. 5,376,403 describes ink formulations which can be used to form circuit traces, but Capote does not describe or claim uses for his ink.
Hiller's U.S. Pat. No. 5,420,755 places a component in a hole cut into standard circuit board material, but does not claim using molded pockets in circuit boards. The component is attached with a standard solder connection. Placement of the
Elpac (USA), Inc.
Foster David
Gandhi Jayprakash N.
Otto Frederick J.
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