Space-saving memory module

• US 5,412,538 A
• Filed: 07/19/1993
• Issued: 05/02/1995
• Est. Priority Date: 07/19/1993
• Status: Expired due to Fees

• Current Assignee: PDACO LIMITED
• Original Assignee: Cordata, Inc.
• Inventors: Seller, William J., Kikinis, Dan
• Primary Examiner(s): LEDYNH, BOT L
• Application Number:
  US08/093,774
• Time in Patent Office: 652 Days
• Field of Search: 361/748, 361/749-751, 361/760, 361/761, 361/764, 361/767, 361/784-791, 361/792, 174/260, 174/262, 257/685, 257/686, 257/777, 29/832, 437/208, 437/915
• US Class Current: 361/792
• CPC Class Codes: G06F 13/409 Mechanical coupling back panels H05K7/1438
• CPC Class Codes: H04M 1/725 Cordless telephones user interfaces specially adapted therefor H04M1/724
• CPC Class Codes: H04M 3/42323 PBX's with CTI arrangements
• CPC Class Codes: H05K 1/182 associated with components mounted in the printed circuit board, e.g. insert mounted components [IMC]
• CPC Class Codes: H05K 3/4611 by laminating two or more circuit boards H05K3/4652 takes precedence
• CPC Class Codes: H05K 3/4691 Rigid-flexible multilayer circuits comprising rigid and flexible layers, e.g. having in the bending regions only flexible layers

Abstract

A low-profile printed circuit board has discrete components mounted within openings provided in a rigid substrate forming art of the board. The components are mounted with leads soldered to mounting pads on the surface of the board, and arranged around the periphery of the openings. The stand-off design of discrete components for mounting to the surfaces of boards allows such components to be mounted within openings simply by reversing the orientation of the components relative to the board. In a preferred embodiment a DRAM card is a four-level board with circuitry on each side of a thin, flexible substrate and each side of a rigid substrate, the two substrates spaced apart by a thin, insulating layer. The rigid substrate has openings with DRAM modules mounted within the openings, and further modules are mounted on the opposite surface in the conventional manner.

Claims

1. A multi-layer primed circuit board comprising:

a first flexible substrate formed of a polymer film and having first and second sides for supporting circuitry and discrete components, the discrete components each having a maximum overall height H;

first and second connection circuitry for providing electrical connection to leads of the discrete components, the first and second connection circuitry arrayed on the first and second sides of the first substrate, the first connection circuitry comprising first mounting pads for connecting to electrical leads of the discrete components;

a second substrate having third and fourth sides for supporting circuitry and the discrete components and thickness T equal to or greater than H, the second substrate having openings therethrough from the third side to the fourth side, providing spaces wherein the discrete components may be completely enclosed within the third and fourth sides;

third and fourth connection circuitry for providing electrical connection to the discrete components, the third and fourth connection circuitry arrayed on the third and fourth sides of the second substrate and comprising second mounting pads arrayed around the openings for connecting to the electrical leads of the discrete components;

an insulator layer fixedly mounted between the second and the third connection circuitry thereby spacing apart the first and the second substrates and forming a four layer printed circuit board; and

through-hole connections for providing electrical communication between the first, second, third, and fourth connection circuitry.

2. A multi-level printed circuit board as in claim 1 comprising discrete components mounted on the first side with leads connected to the first mounting pads and discrete components mounted on the fourth side with leads connected to the second mounting pads, the discrete components mounted on the fourth side enclosed within the openings.

3. A multi-layer printed circuit board as in claim 2 further comprising first gull-wing design DRAM packaged integrated circuits mounted to the first mounting pads and second gull-wing design DRAM packaged integrated circuits mounted to the second mounting pads, the second DRAM packages enclosed within the openings.

4. A four-level DRAM memory card for providing memory to a host computer, comprising:

a polymer-film flexible substrate having circuitry paths on first and second sides;

first DRAM memory modules mounted on the first side with electrical leads connected to the printed circuitry.;

a rigid substrate having circuitry paths on third and fourth sides and openings through the thickness of the rigid substrate;

second DRAM memory modules mounted wholly within the openings with electrical leads connected to the circuitry paths on the fourth side;

an insulator layer affixed to and spacing apart the second and third sides, spacing apart the flexible and rigid substrates;

through-hole connections for providing electrical communication between the circuitry paths on the first, second, third, and fourth sides; and

an edge connector for providing electrical connection from the circuitry paths to a host computer'"'"'s parallel bus.

5. A method for making a four-level printed circuit board for mounting and interconnecting discrete components, comprising the steps of:

(a) preparing a rigid substrate having a thickness greater than the maximum height of any of the discrete components to be mounted by forming openings therethrough of an extent to completely enclose the discrete components to be mounted;

(b) forming connective circuitry on first and second sides of the rigid substrate, including mounting pads arranged around the openings on the second side for connecting to electrical leads of the discrete components;

(c) preparing a substrate of polymer film by forming connective circuitry on third and fourth sides of the flexible substrate, including mounting pads for connecting to electrical leads of discrete components on the fourth side;

(d) laminating the rigid substrate and the flexible substrate together with an insulator layer therebetween, forming thereby a four-level board with the second and forth sides exposed; and

(e) fabricating through-hole connectors through the layers and substrates for connecting the four levels of connective circuitry.

6. The method of claim 5 further comprising steps:

(f) mounting discrete components to the mounting pads on the fourth side; and

.

(g) mounting discrete components fully enclosed within the openings in the rigid substrate and connecting leads of the discrete components so mounted to the mounting pads around the openings on the second side.

7. The method of claim 6 wherein the discrete components mounted are memory modules, forming thereby a compact and low-profile memory card.

8. The method of claim 7 wherein the memory modules are DRAM modules.