SMC filter and method of manufacture thereof

• US 4,714,905 A
• Filed: 10/08/1986
• Issued: 12/22/1987
• Est. Priority Date: 10/08/1986
• Status: Expired due to Term

• Current Assignee: Delaware Capital Formation Incorporated (Dover Corporation)
• Original Assignee: k & L Microwave, Inc (Dover Corporation)
• Inventors: Bernstein, Richard, Anthony, William H., Lupfer, David A.
• Primary Examiner(s): Nussbaum, Marvin L.
• Application Number:
  US06/916,559
• Time in Patent Office: 440 Days
• Field of Search: 333/12, 333/167, 333/181, 333/183, 333/184, 333/182, 333/185, 333/140, 333/168, 333/172, 333/174, 333/175, 333/176, 333/202, 333/204, 333/205, 361/424, 361/415, 361/399, 29/613, 29/832, 29/841
• US Class Current: 333/167
• CPC Class Codes: H03H 1/00 Constructional details of impedance networks whose electrical mode of operation is not specified or applicable to more than one type of network constructional details of electromechanical transducers H03H9/00
• CPC Class Codes: H03H 3/00 Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
• CPC Class Codes: H03H 7/1775 Parallel LC in shunt or branch path H03H7/1791 takes precedence
• CPC Class Codes: Y10T 29/4913 Assembling to base an electrical component, e.g., capacitor, etc.

Abstract

A microwave bandpass filter for frequencies in the range of 30-3000 MHz comprises a substrate formed from dielectric ceramic sheets fused together and stacked according to a dielectric constant required of the filter capacitors, the plates of which are formed on the substrate. Discrete air core coils, to provide greater frequency selectivity in this particular frequency range, are attached into the circuit on a top surface of the substrate, and a drawn metal can covers the circuitry on the top surface and is soldered to a metallized coating extending over substantially all of the rest of the substrate except for surface mounting lead portions and associated conductive paths. Thus, EMI and RFI shielding is provided by the combination of the metal can and the ground plane of the circuit. The metal can portion of the shield also provides physical protection for the fragile air core coils, while presenting a solid, uniform profile for engagement by a pick and place head during subsequent handling of the finished component.

Claims

1. A method of manufacturing a surface mount-type chip filter circuit for passing frequencies in a specified range generally greater than 30 MHz, and comprising the steps of:

determining a dielectric constant required for filter capacitors of said circuit and corresponding to said specified range;

providing at least two sheets of suitable dielectric green state ceramic which, when stacked and fused together, provide said dielectric constant, each of said sheets being generally rectangular in shape and having a top and a bottom surface connected by end and side edges;

providing holes through at least a top one of said sheets and filling said holes with an electrically conductive material to provide vias;

screening electrically conductive strips onto one of said sheets so as to prepare a bottom sheet for said stack, with each of said strips extending from said top surface of said bottom sheet and around an end edge and onto said bottom surface of said bottom sheet, and each strip being situated for connection to a corresponding one of said vias upon stacking of said sheets;

stacking and laminating said sheets together;

firing said sheets in a kiln sufficiently to center said ceramic and fuse said sheets together into a unitary module having said vias interconnected with said strips conductively to form thin conductive paths from a top area of said module to surface mounting lead portions on a bottom area of said module;

screening a metallized conductive layer over substantially all surface areas of said module, except for a center portion of said module top area and exposed portions of said conductive paths, and thus providing a ground plane for said filter circuit and a unitary second plate for each of said filter capacitors and a portion of an electromagnetic and radiofrequency interference shield for said filter circuit;

screening small conductve lands onto said central portion and separate from said ground plane and thus providing a corresonding individual first plate for each said filter capacitor;

attaching discrete air core inductors, commensurate with characteristics of said filter circuit, between said ground plane and corresponding ones of said first plates and thus providing a plurality of filter sections;

providing interconnection of said filter sections and said vias in order to complete said filter circuit with input and output paths from said filter circuit to said surface mounting lead portions on said module bottom area; and

attaching a metallic can to said ground plane spaced from and covering said inductors, thus completing said shield for said circuit while providing a physical shield for said inductors and providing a uniform profile adapted for subsequent handling of said chip.

2. The method as in claim 1, and further comprising the step of:

attaching discrete coupling capacitors between said filter sections.

3. In a method of manufacturing a surface mount chip-type filter circuit having conductive lands screened onto a dielectric substrate as first plate of filter capacitors, and discrete air core inductors attached thereto for said filter, the improvement comprising the steps of:

applying a metallic coating on substantially all surface areas of said substrate, except for a central top portion of said substrate containing said lands and exposed portions of vias from said centeral top portion to surface mounting lead portions on a bottom of said substrate, thus providing a second plate for said capacitors and a ground plane for said circuit and a portion of an EMI and RFI shield for said circuit; and

completing said EMI and RFI shield, while providing a physical shield for said inductors and a solid, uniform profile adapted for subsequent handling by a pick and place component handling head, by attaching a formed metallic cover to said ground plane and spaced from and covering said inductors and lands.

4. A filter circuit for passing frequencies in a specified range generally greater than 30 MHz, and comprising:

at least two sheets of suitable dielectric green state ceramic stacked and fused together to provide a unitary substrate with a dielectric constant required for filter capacitors of said circuit corresponding to said specified range, said substrate being generally rectangular in shape and having top and bottom areas connected by end and side edges;

vias comprising holes through at least a top one of said sheets and filled with an electrically conductive material;

electrically conductive strips on a bottom one of sheets with each of said strips extending from a top surface of said bottom sheet and around an end edge and onto a bottom surface of said bottom sheet, and each strip being connected to a corresponding one of said vias;

a metallized conductive layer over substantially all surface areas of said substrate, except for a central portion of said substrate top area and exposed portions of said conductive strips, said conductive layer thus providing a ground plane for said filter circuit and a unitary second plate for each of said filter capacitors and a portion of an electromagnetic and radiofrequency interference shield for said filter circuit;

small conductive lands screened onto said central portion and separate from said ground plane to provide a corresponding individual first plate for each said filter capacitor;

discrete air core inductors, commensurate with characteristics of said filter circuit, attached between said ground plane and corresponding ones of said first plates and in order to provide a plurality of filter sections;

means for interconnecting said filter sections and said vias in order to complete said filter circuit as a surface mountable-type chip with input and output paths from said filter circuit to said surface mounting lead portions of said strips on said substrate bottom area; and

a metallic can attached to said ground plane and spaced from and covering said inductors, thus completing said interference shield for said circuit while providing a physical shield for said inductors and providing a uniform profile adapted for subsequent handling of said chip.

5. In a surface mount-type chip providing a filter circuit having lands screened onto a dielectric substrate as first plates of filter capacitors, and discrete air core inductors attached thereto for said filter, the improvement comprising:

a metallic coating on substantially all surface areas of said substrate, except for a central top portion of said substrate containing said lands and exposed portions of vias from said central top portion to surface mounting lead portions on a bottom of said substrate, said coating providing a second plate for said capacitors and a ground plane for said circuit and a portion of an EMI and RFI shield for said circuit; and

a formed metallic cover attached to said ground plane and spaced from and covering said inductors and lands, said cover providing a remainder of said EMI and RFI shield, while providing a physical shield for said inductors, and a solid, uniform profile adapted for subsequent handling by a pick and place component handling head.