Lead-frame method and assembly for interconnecting circuits within a circuit module

The present invention relates generally to circuit modules, and more specifically, to a method and assembly for interconnecting circuits within a circuit module.

Circuit modules or cards are increasing in use to provide storage and other electronic functions for devices such as digital cameras, personal computing devices and personal digital assistants (PDAs). New uses for circuit modules include multimedia cards and secure digital cards.

Typically, circuit modules contain multiple integrated circuit devices or “dies”. The dies are interconnected using a circuit board substrate, which adds to the weight, thickness and complexity of the module. Circuit modules also have electrical contacts for providing an external interface to the insertion point or socket, and these electrical contacts are typically circuit areas on the backside of the circuit board substrate, and the connection to the dies are provided through vias through the circuit board substrate. Producing vias in the substrate adds several process steps to the fabrication of the circuit board substrate, with consequent additional costs.

Therefore, it would be desirable to provide a method and assembly for interconnecting circuits within modules that require no circuit board substrate.

A circuit module assembly and method for interconnecting circuits within modules to provide a circuit module that may be fabricated without a circuit board substrate. A lead-frame assembly is connected to one or more dies and external contacts may be provided by an extension of the lead-frame assembly out of the plane of the die interconnect.

The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings.

FIG. 1A is a pictorial diagram depicting a top view and FIG. 1B is a pictorial diagram depicting a cross section of a prior art circuit module;

FIG. 2A is a pictorial diagram depicting a top view and FIG. 2B is a pictorial diagram depicting a cross section of a lead-frame in accordance with an embodiment of the invention; and

FIG. 3A is a pictorial diagram depicting a top view and FIG. 3B is a pictorial diagram depicting a cross section of a circuit module in accordance with an embodiment of the invention.

Common reference numerals are used throughout the drawings and detailed description to indicate like elements.

Referring now to the figures and in particular to FIG. 1A a top view of a prior art circuit module 10 is depicted. Circuit module 10 is depicted as a circuit module as used in various multimedia card memory applications. The present invention is also applicable to cards and modules having other outlines such as secure digital cards and to peripheral device cards (I/O cards), as well.

A carrier 14 to which integrated circuit dies 12 are attached and circuit contacts 13 are included on the bottom side, is covered by a cover 11 that is bonded to carrier 14 . The circuit module housing may be completely formed from an encapsulant, or the circuit may be encapsulated and a lid 19 applied over the encapsulant. Dies 12 are coupled to each other and to circuit contacts 13 by circuit traces 16 , which are typically etched from a metal layer on the top of carrier 14 . Circuit contacts 13 are coupled by means of plated-through holes 15 that pass through carrier 14 . The bottom side of carrier 14 is also typically etched from a metal layer on the bottom side forming electrical contacts 13 that are generally plated with a corrosion resistant material such as gold and circuit contacts 13 connect on the bottom side of carrier 14 to plated through holes 15 by circuit traces on the bottom side of carrier 14 . Circuit traces 16 include wire bonding areas 17 that may also be plated, permitting a wire bonding apparatus to electically couple dies 12 by wires 18 .

Referring now to FIG. 1B , a cross section end view of circuit module 10 is depicted. Dies 12 are covered by cover 11 and are bonded to carrier 14 . Circuit contacts 13 are disposed on the bottom side of carrier 14 to provide electrical connections to the external circuits via a socket in which circuit module 10 is inserted.

The present invention provides a circuit module that does not require a separate carrier, wherein the circuit paths between dies 12 and electrical contacts 13 are provided by a conductive lead-frame to which dies 12 are bonded and an encapsulant applied surrounding the lead-frame to provide support and electrical insulation.

Referring now to FIG. 2A , a top view of a lead-frame 20 in accordance with an embodiment of the invention is depicted. Circuit traces 16 A are supported by a dam bar 22 that surrounds the periphery of the lead-frame, providing rigidity during the fabrication and integration processes. Lead-frame 20 is generally stamped from a metal, such as copper, and integrated circuit dies are bonded to lead-frame in die bonding areas 21 . Wire bonding pads 17 A are provided on circuit traces 16 A to permit attachment of wires from dies to the lead-frame. The lead-frame is then encapsulated and portions of dam bar 22 are cut, resulting in electrical isolation of circuit traces 16 A, after mechanical rigidity has been provided by the encapsulant.

In addition or in alternative to wire bonding pads 17 A, pads may be included for attachment of surface mounted passive components by soldering or conductive adhesive attachment, and pad grids may be included for attachment of pre-packaged integrated circuits.

Referring now to FIG. 2B , a cross-section side view of lead-frame 20 is depicted. Dam bar 22 is shown at ends of the lead-frame and is cut-away along the sides in the figure to illustrate that circuit traces 17 A are a half-thickness of metal with respect to dam bar 22 . This half-thickness may be produced by etching the bottom side of lead-frame after applying an etchant resistant coating to dam bar and circuit contacts 13 A. Circuit contacts 13 A are also partially a half-thickness of metal, produced by etching the top side of lead-frame after applying an etchant resistive coating to circuit traces 16 A and dam bar 22 . The etching of both sides of lead-frame 20 results in a circuit that has circuit contacts 13 A disposed as an extension out of the plane of circuit traces 16 A, while the full thickness portion of the electrical contacts/circuit trace combination produces a continuous conductive and mechanically rigid connection from circuit traces 16 A to circuit contacts 13 A. Thus, encapsulant may be applied beneath circuit traces and the circuit contact 13 A surfaces may protrude from the encapsulant, providing an interface connection external to a circuit module.

As an alternative, circuit contacts 13 A may be fabricated is in the same plane as circuit traces 16 A and additional length supplied so that the circuit traces may be bent to provide an extension out of the plane of circuit traces 16 A so that circuit contacts 13 A may protrude from an encapsulant applied beneath lead-frame 20 .

The illustrative embodiments herein depict an etched lead-frame, but lead-frames may also be stamped in accordance with an embodiment of the present invention. The alternative embodiment depicted, wherein circuit traces are bent to provide circuit contacts especially lends itself to stamping, because the circuit traces may be formed and bent in a single stamping operation.

Referring now to FIG. 3A , a top view of a circuit module 30 , in accordance with an embodiment of the invention is depicted. The depiction shows the internal features after dies 12 have been bonded to lead-frame 20 , an encapsulant cover 11 A applied and the dam bar 22 is singulated from circuit module 30 . The resulting circuit module 30 has circuit traces 16 A that are isolated (but supported by the encapsulant) and wires 18 have been bonded from dies 12 to bonding pads 17 A. Circuit contacts 13 A are located at the bottom surface of encapsulant cover 11 A and protrude from or are conformal to the bottom surface to provide an external electrical connection.

Referring now to FIG. 3B , a cross-section end view of a circuit module 30 , in accordance with an embodiment of the invention is depicted. The plane of circuit traces 16 A adjacent to the plane of electrical contacts 13 A may be seen from the figure. Die 12 is shown as mounted above the plane of circuit traces 16 A, but a mounting within the plane of circuit traces is also possible. Additionally, circuit contacts 13 A may be attached using plating techniques to attach to circuit traces 16 A rather than including the circuit contacts within the lead-frame.

This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.