Patent ID: 12224181

DETAILED DESCRIPTION

This description relates generally to electronic circuits, and more particularly to a laser-cut lead-frame sheet for integrated circuit (IC) packages. As described herein, the lead-frame sheet that is formed from a conductive metal material sheet is laser-cut (e.g., via a laser graphic process) instead of etched. For example, the lead-frame sheet can be laser-cut to include all of the features of a lead-frame sheet that is typically etched, such as including through-holes, three-dimensional locking features for mating with corresponding holes in packaging material of an IC package (e.g., a quad flat no-lead (QFN) IC package). As another example, the lead-frame sheet can also include additional features associated with lead-frame sheets, such as an index through-hole, a mold-flow vent feature, and a stress-release feature. The lead-frame sheet can thus be fabricated with a laser-cutting process on a conductive metal material sheet to include all of the features of a typical etched lead-frame sheet.

IC dies can be coupled to the lead-frame sheet and to the packaging material to form an IC package block. The IC package block can thus include a plurality of IC packages that are conjoined by the packaging material and the lead-frame sheet. The IC packages can thus be singulated based on laser-cutting the IC package block, as opposed to a typical fabrication process in which the IC package block is mechanically cut (e.g., with a saw or other cutting tool). Such mechanical cutting for a typical fabrication procedure is provided along a tie-bar, which is typically required for an etched lead-frame sheet. However, laser-cutting the lead-frame sheet can obviate the need for tie-bars and cross-bars in the lead-frame sheet, thus facilitating a simpler arrangement for the lead-frame sheet and a cleaner singulation of the IC packages from the IC package block. Furthermore, one or more grooves can be laser-cut in the packaging material and the lead-frame sheet of each of the IC packages (e.g., a bottom surface of the IC packages) to electrically isolate portions of the lead-frame sheet from each other. For example, the groove(s) can isolate a plurality of leads from the ground pad in each of the IC packages. As described herein, the term “leads” can refer to signal pads, such as in the example of the IC packages being arranged as QFN IC packages.

FIG.1is an example of a block diagram100of a process for fabricating integrated circuit (IC) packages. The diagram100can correspond to a simplistic example of fabrication of any of a variety of different types of IC packages. As an example, the IC packages can be fabricated as quad flat no-lead (QFN) IC packages.

The diagram100includes an IC fabrication tool102that is configured to fabricate a plurality of IC dies104, such as on a semiconductor wafer. For example, the IC fabrication tool102can be configured to provide material deposition, chemical etching, and a variety of other IC fabrication processes to fabricate the IC dies104on the semiconductor wafer. As an example, the semiconductor wafer can include a substrate (e.g., formed from any of a variety of substrate materials) on which the IC dies104are fabricated.

The diagram100also includes a laser-cutting tool106that is configured to laser-cut a lead-frame sheet108. The laser-cutting tool106can correspond to any of a variety of graphical lasers that provide sufficient power to cut through the materials of an IC package (e.g., silicon, metal, plastic, etc.), as described in greater detail herein. For example, the lead-frame sheet108can be formed from a conductive metal material sheet (e.g., a copper sheet), such that the laser-cutting tool106cuts predetermined shapes into the conductive metal material sheet to form the lead-frame sheet108. As an example, the laser-cutting tool106can cut at least one through-holes and three-dimensional locking features into the conductive metal material sheet to form the lead-frame sheet108. As another example, the laser-cutting tool106can also cut additional features associated with a traditional lead-frame sheet into the conductive metal material sheet to form the lead-frame sheet108, such as an index through-hole, a mold-flow vent feature, and a stress-release feature.

In the example ofFIG.1, the lead-frame sheet108is combined with the IC dies104, previously singulated from a semiconductor wafer (e.g., via the laser-cutting tool106or another cutting tool), to form an IC package block110. As an example, the IC package block110can also include packaging material (not shown), such as a plastic molding material, that can substantially surround the singulated IC dies104and can surround portions of the lead-frame sheet108to form IC package block110. Therefore, the IC package block110can correspond to a group of IC packages that are conjoined by the lead-frame sheet108and the packaging material. As described in greater detail herein, the lead-frame sheet108thus provides multiple lead-frames that each include at least one ground pad and a plurality of leads for each of the IC packages in the IC package block110.

As described herein, implementing laser-cutting to form the lead-frame sheet108provides for a significantly more efficient and cost-effective manner of fabricating the lead-frame sheet108, and by extension the IC package block110, than a typical manner of fabricating a lead-frame sheet. Typical lead-frame sheets are fabricated based on an etching (e.g., chemical etching) process. Chemical etching can result in a much less precise shaping of the through-holes and/or three-dimensional locking features of the lead-frame sheet than implementing an indexed laser to cut the same features in the lead-frame sheet108. Additionally, etching a lead-frame sheet can limit a minimum size of a given IC and a given input/output (I/O) count, for a given lead-frame of the lead-frame sheet108, based on imprecise etching tolerance and a minimum etching space, thereby limiting meeting the demand for miniaturization of IC packages. Additionally, etching lead-frame sheets can be significantly more expensive than laser-cutting the lead-frame sheet108. For example, the etching process can be more costly and can take a significantly longer time to complete than programming the laser-cutting tool106. Furthermore, many fabrication facilities outsource lead-frame sheet etching, and may require a minimum order quantity and/or large stocking quantities. Such a fabrication system can provide significant delays, particularly in the event of etching errors or changes to the fabrication of the IC packages. However, by implementing an in-house laser-cutting tool106, such delays and costs can be greatly mitigated. For these reasons, laser-cutting the lead-frame sheet108via the laser-cutting tool106can provide for a significantly more efficient fabrication process than etching a lead-frame sheet.

FIG.2is an example diagram200of a laser-cut lead-frame sheet202. The diagram200demonstrates a conductive metal material sheet204that can correspond to a thin sheet of conductive metal from which the laser-cut lead-frame sheet202is formed. As an example, the conductive metal material sheet204can be a thin sheet of copper or other conductive metal that can be cut and shaped via a laser (e.g., the laser-cutting tool106). The diagram200also demonstrates the laser-cut lead-frame sheet202in a top view206and in a bottom view208. The laser-cut lead-frame sheet202is demonstrated as including through-holes210, visible in both the top and bottom views206and208, which are formed from laser-cutting through the conductive metal material sheet204.

The laser-cut lead-frame sheet202also includes three-dimensional locking features212, visible in the bottom view208. In the example ofFIG.2, the three-dimensional locking features212are demonstrated as partial removal of the thickness of the conductive metal material sheet204, such that the three-dimensional locking features212include thinner portions of the conductive metal material sheet204. The three-dimensional locking features212can facilitate coupling of the laser-cut lead-frame sheet202with packaging material, such that a portion of the laser-cut lead-frame sheet202in a resulting IC package can be exposed while the remainder of the laser-cut lead-frame sheet202can be surrounded by and held in place by the packaging material. Therefore, as described in greater detail herein, the laser-cut lead-frame sheet202can form lead-frames that include ground pads and leads of the resultant IC packages. Furthermore, the laser-cut lead-frame sheet202can include additional features that are formed by the laser-cutting tool106, such as index through-holes, mold-flow vent features, and/or stress-release features.

As an example, the packaging material can be formed by a plastic molding material that is flowed onto the combined laser-cut lead-frame sheet202and respective IC dies (e.g., via an injection molding process), followed by a post-mold cure (PMC) process.FIG.3is an example of an IC package block300. The IC package block300is demonstrated as a combination of the laser-cut lead-frame sheet202in the diagram200of the example ofFIG.2and packaging material302(as well as the IC dies, not shown in the example ofFIG.3). The IC package block300therefore includes a plurality of IC packages that are conjoined by the laser-cut lead-frame sheet202and the packaging material302. In the example ofFIG.3, portions of the laser-cut lead-frame sheet202are exposed on the surface of the IC package block300. Thus, the exposed portions, demonstrated at304, can correspond to respective lead-frames (e.g., including ground pads and leads) of the resultant IC packages.

FIG.4is another example of a block diagram400of a process for fabricating IC packages. The diagram400can correspond to a simplistic example of fabrication of any of a variety of different types of IC packages. As an example, the diagram400can correspond to a portion of the fabrication process subsequent to the formation of the IC package block, demonstrated in the example ofFIG.4at402.

The diagram400also includes a laser-cutting tool404. As an example, the laser-cutting tool404can correspond to the same laser-cutting tool106demonstrated in the example ofFIG.1. Therefore, as described in greater detail herein, the laser-cutting tool404can be used for multiple stages and functions during the fabrication of the IC packages. In the example ofFIG.4, the laser-cutting tool404is provided to the IC package block402to cut around each of the IC packages that are conjoined together on the IC package block402. As a result, the laser-cutting tool404can singulate the IC packages as discrete IC packages relative to each other, thus providing singulated IC packages406. Therefore, as opposed to implementing a mechanical separation of the IC packages, as is provided in a typical fabrication process, the laser-cutting tool404can laser-cut the IC package block402to provide the singulated IC packages406. In addition, as described in greater detail herein, the laser-cutting tool404can cut one or more grooves into each of the IC packages (e.g., before or after singulation) to electrically isolate portions of the laser-cut lead-frame sheet202. Therefore, the groove(s) can form the ground pads and the leads of each of the IC packages from the laser-cut lead-frame sheet202.

FIG.5is an example diagram500of singulated IC packages. The diagram500includes the IC package block402in the example ofFIG.4. In the example ofFIG.5, the IC package block402is marked with dashed lines502to demonstrate the borders of IC packages, demonstrated at504. As an example, the laser-cutting tool404can cut along the dashed lines502to singulate the IC chips in the IC package block402to provide the IC packages504. Additionally, the IC package block402is marked with dotted lines506that can correspond to a location of a groove that the laser-cutting tool404can cut into each of the IC packages504. The groove can correspond to a partial cut through the IC package block402, as opposed to a through-cut that is implemented for the singulation of the IC packages504. The groove along the dotted line506can thus be sufficient to cut through a portion of the lead-frame sheet202to electrically isolate portions of the lead-frame of the resultant IC packages504, thereby providing electrical isolation between leads a ground pad for each of the IC packages504.

FIG.6is an example diagram600of an IC package602. The diagram600demonstrates three views of the IC package602, including a first view604along an XY-plane of the IC package602, a second view606along an XZ-plane of the IC package602, and a third view608of the IC package602corresponding to a cross-sectional view taken along “A” in the first view604. The IC package602can correspond to one of the IC packages504in the example ofFIG.5. Therefore, the IC package602can be formed from singulating the IC packages504in the IC package block402via the laser-cutting tool404. As an example, the IC package602corresponds to a QFN IC package, with the first view604corresponding to a view of the bottom of the IC package602.

The IC package602includes packaging material610that substantially surrounds the portions of the lead-frame, formed form the lead-frame sheet202, which correspond to a first electrode612and a second electrode614. As an example, one of the electrodes612and614can correspond to a ground pad and the other one of the electrodes612and614can correspond to a lead (or multiple leads, as dictating the laser-cutting tool404). The packaging material610also surrounds an IC die616that can be directly conductively coupled to the second electrode614, and is conductively coupled to the first electrode612via a conductive coupling wire618. The outer periphery of the packaging material610can thus be formed during the singulation of the IC package block402via the laser-cutting tool404. In the example ofFIG.6, the first and second electrodes612and614are electrically isolated via a groove620. As an example, the groove620can be formed by the laser-cutting tool404, such that the first and second electrodes612and614can both initially be part of the laser-cut lead-frame sheet202, and can be separated by the laser-cutting tool404to electrically isolate the respective portions of the conductive metal of the resultant lead-frame.

FIG.7is an example of a plan view of an IC package700. The IC package700can correspond to another example of a QFN IC package. The IC package700includes a ground pad702and a plurality of leads704that are arranged along the periphery of the IC package700. The ground pad702and the leads704can be electrically isolated via a groove that substantially surrounds the ground pad702.

FIG.8is another example diagram800of the IC package700. The diagram800demonstrates two views of the IC package700, including a first view802along an XY-plane of the IC package700and a second view804of the IC package700corresponding to a cross-sectional view taken along “A” in the first view802. Similar to as described above, the IC package700can be formed from singulating IC packages in an IC package block via the laser-cutting tool404. As an example, the IC package700corresponds to a QFN IC package, with the first view802corresponding to a view of the bottom of the IC package700.

The IC package700includes packaging material806that substantially surrounds the portions of the lead-frame that correspond to the ground pad702and the leads704. The packaging material806also surrounds an IC die808that is directly conductively coupled to the ground pad702, and is conductively coupled to each of the leads704via conductive coupling wires810. The outer periphery of the packaging material806can thus be formed during the singulation of a respective IC package block via the laser-cutting tool404. In the example ofFIG.8, the ground plane702and the leads704are electrically isolated via a groove812. As an example, the groove812can be formed by the laser-cutting tool404, such that ground plane702and the leads704can both initially be part of the laser-cut lead-frame sheet202, and can be separated by the laser-cutting tool404to electrically isolate the respective portions of the conductive metal of the resultant lead-frame.

As an example, prior to forming the groove812, the IC package700(e.g., before or after singulation) can undergo an electrolytic plating process to deposit a corrosion-resistant material (e.g., Tin (Sn)) on the exposed portions of the lead-frame or lead-frame sheet202(e.g., external to the packaging material610, such as the ground pad702and the plurality of leads704). The electrolytic plating can substantially mitigate oxidization and/or corrosion of the material (e.g., Copper) that forms the lead-frame sheet202, and can also enable the IC package700to be mounted on a corresponding printed circuit board (PCB) by an end user of the IC package700(e.g., using a surface mount technology (SMT) process). Such an electrolytic plating process can be more cost effective than plating the entire conductive metal sheet with other materials (e.g., Nickel/Palladium/Gold) prior to laser-cutting the conductive metal material sheet204into the lead-frame sheet202, particularly when part of the plating is removed and wasted by forming the groove812.

In view of the foregoing structural and functional features described above, a methodology in accordance with various aspects of the present invention will be better appreciated with reference toFIG.9. While, for purposes of simplicity of explanation, the methodology ofFIG.9is shown and described as executing serially, it is to be understood and appreciated that the present invention is not limited by the illustrated order, as some aspects could, in accordance with the present invention, occur in different orders and/or concurrently with other aspects from that shown and described herein. Moreover, not all illustrated features may be required to implement a methodology in accordance with an aspect of the present invention.

FIG.9is an example of a method900for fabricating IC packages (e.g., the IC packages602or700). At902, a plurality of IC dies (e.g., the IC dies104) are fabricated. At904, a conductive metal material sheet (e.g., the conductive metal material sheet204) is provided. At906, a lead-frame sheet (e.g., the lead-frame sheet108) is formed from the conductive metal material sheet. At908, the IC dies are coupled to the lead-frame sheet. At910, the lead-frame sheet and the IC dies are coupled to packaging material (e.g., the packaging material302to form an IC package block (e.g., the IC package block300) comprising the IC packages. At912, at least one groove (e.g., the grooves620or812) is laser-cut in the packaging material and the lead-frame sheet of each of the IC packages to electrically isolate portions of the lead-frame sheet from each other.

In this description, the term “couple” may cover connections, communications, or signal paths that enable a functional relationship consistent with this description. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first example, device A is directly coupled to device B; or (b) in a second example, device A is indirectly coupled to device B through intervening component C if intervening component C does not substantially alter the functional relationship between device A and device B, so device B is controlled by device A via the control signal generated by device A.

Also, in this description, a device that is “configured to” perform a task or function may be configured (e.g., programmed and/or hardwired) at a time of manufacturing by a manufacturer to perform the function and/or may be configurable (or reconfigurable) by a user after manufacturing to perform the function and/or other additional or alternative functions. The configuring may be through firmware and/or software programming of the device, through a construction and/or layout of hardware components and interconnections of the device, or a combination thereof. Furthermore, a circuit or device described herein as including certain components may instead be configured to couple to those components to form the described circuitry or device. For example, a structure described as including one or more semiconductor elements (such as transistors), one or more passive elements (such as resistors, capacitors, and/or inductors), and/or one or more sources (such as voltage and/or current sources) may instead include only the semiconductor elements within a single physical device (e.g., a semiconductor wafer and/or integrated circuit (IC) package) and may be configured to couple to at least some of the passive elements and/or the sources to form the described structure, either at a time of manufacture or after a time of manufacture, such as by an end user and/or a third party.

Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.