Patent Application
20240413058
This Disclosure relates to leadframe packaging of semiconductor devices and resulting packaged semiconductor devices.
A variety of semiconductor chip packages are known that provide support for an integrated circuit (IC) chip or die and associated bond wires, provide protection from the environment, and enable surface mounting of the die to and interconnection with a printed circuit board (PCB). One conventional package configuration includes a leadframe (LF) having leads on at least 2 sides of a die pad.
LF packages are well known and widely used in the electronics industry to house, mount, and interconnect a variety of ICs. A conventional LF strip is typically die-stamped from a sheet of flat-stock metal (e.g., copper), and includes a plurality of metal leads temporarily held together in a planar arrangement about a central region during package manufacture by a rectangular frame comprising a plurality of expendable “dam-bars.” A die pad may be provided for a semiconductor die supported in the central region by “tie-bars” that attach to the frame. The leads extend from a first end integral with the frame to an opposite second end adjacent to, but spaced apart from, the die pad.
Different packaged devices, mechanical stress, heat dissipation, mold locking features, and electrical parasitic components generally require a custom LF design. A LF is generally designed in a co-design process together with the IC die including mechanical, thermal, electrical modeling, which is time consuming and results in a high LF design cost. A change in a target specification can cause another iteration of the co-design process, including a change in the bump layout on the IC die and/or a change in the LF design.
This Summary is provided to introduce a brief selection of disclosed concepts in a simplified form that are further described below in the Detailed Description including the drawings provided. This Summary is not intended to limit the claimed subject matter's scope.
This Disclosure recognizes one can avoid the conventional requirement for a custom LF design for each new IC die design which typically results in a high development cost by using a standard LF and IC bump design, enabled by an additive manufactured metal process that adds printed LF traces that are coupled to leads of a standard LF. The printed LF portions are physically supported by a dielectric support material in the gaps between the metal structures of the standard LF, and include connections to leads of the standard LF to provide a custom LF design that provides routing between the leads of the standard LF and each bump feature (e.g., a solder bump or a solder capped copper pillar) on the IC die. This Disclosure enables quickly generating a new custom LF design digitally and then fabricating the actual custom LF. Also, this Disclosure enables standardizing the bump design for ICs which can reduce the number of die masks needed, such as by avoiding the need for redirect layers.
Disclosed aspects include a packaged semiconductor device comprising an IC die having bump features that are coupled to bond pads that are flip chip (FC) attached to a custom LF. The custom LF includes metal structures including metal leads on at least 2 sides, and printed metal providing a printed LF portion including printed metal traces that connect to and extend inward from at least one of the metal leads over the dielectric support material that are coupled to FC pads configured for receiving the bump features, including at least some of the printed metal traces coupled to the bond pads on the IC die. The IC die is flip chip mounted on the printed LF portion so that the bump features are connected to the FC pads.
Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, wherein:
Example embodiments are described with reference to the drawings, wherein like reference numerals are used to designate similar or equivalent elements. Illustrated ordering of acts or events should not be considered as limiting, as some acts or events may occur in different order and/or concurrently with other acts or events. Furthermore, some illustrated acts or events may not be required to implement a methodology in accordance with this Disclosure.
The custom LF 100 includes a dielectric support surface 131 in the gaps between the metal structures of the standard LF portion 110 that provides mechanical support beyond the area of the standard LF for the printed LF portion 120. The dielectric support surface 131 can be provided as the surface of a support 130 which generally comprises a pre-molded structure with the leads 110b being embedded leads having an exposed top surface so that there is dielectric material between adjacent ones of the leads 110b. The pre-molded structure can comprise a pre-molded standard LF that provides the standard LF portion 110 where the mold compound provides the dielectric support surface 131 and the leads 110b are exposed, or by a single level or a multi-level molded interconnect substrate (MIS) that comprises a pre-molded structure including an MIS leadframe providing the standard LF portion 110, where the top dielectric layer of the MIS is used as the dielectric support surface 131 and the leads 110b are exposed. The standard LF portion 110 can also be provided or processed to have a nano-roughened surface to improve adhesion of the traces 120a of the printed LF portion 120 to the leads 110b.
The printed LF portion 120 is formed by additively depositing (e.g., 3D printing, i.e., inkjet printing, or screen printing) a metal precursor (e.g., an ink or a paste including a plurality of metal particles) to generally deposit a printed metal precursor. The additively depositing is generally followed by sintering or curing to form the printed LF portion 120 including FC pads 120b and metal traces 120a that connect to and extend inward from at least one of the metal leads 110b over the dielectric support surface 131. A typical thickness for the printed metal precursor is 75 μm to 150 μm. The additively depositing process can comprise a plurality of coating and sintering steps, such as a sequence of powder coating followed by laser exposure.
For some devices some traces 120a may extend from one side of the custom LF 100 without any FC bond pad 120b in the path, such as to provide common ground or a thermal dissipation path. The IC die is then FC coupled to FC pads 120b that are configured for receiving bump features that are coupled to bond pads on an IC die to be mounted. Sintering or curing of the metal precursor is generally performed before FC mounting. The FC pads 120b are positioned for FC mounting the IC die on the printed metal so that the bump features (see bump feature 140a in
As known in the art of printing, an ink includes a material that is either solid (e.g., particles, such as nanoparticles) or a precursor for a solid that forms a solid (e.g., particles) upon curing or sintering to remove its liquid carrier including a solvent and/or a dispersant. For example, the ink can be a sinterable metal ink or an ultraviolet (UV)-curable polymer or a UV-curable polymer-based mixture. The ink is additively depositable by a printer platform into its programmed desired locations. The ink deposition apparatus can be an inkjet printer that uses piezoelectric, thermal, or acoustics, an electrostatic inkjet printer, or a screen or flexographic printer.
A metal paste, such as after being additively deposited by screen printing, can be processed including a heat up step in a reducing gas atmosphere and then a vacuum sintering step generally at a temperature of at least 200° C. for forming a sintered metal coating. Metal pastes can be conventionally sintered in a cure oven to remove the binder and solvent if present, and to densify for reducing the porosity the metal material.
A method of forming a disclosed custom LF can first determine a plurality of preliminary candidate LF designs which also satisfy device requirements for the IC die including the number of I/Os, voltage and/or current rating, and the mechanical and/or thermal stress. The preliminary candidate LFs can be narrowed in number to identify candidate LFs by simulating the preliminary candidate LFs to quantify their device performance. This narrowing process creates a set of candidate LF designs which satisfies all requirements for one particular IC device. The same process is repeated for other IC devices which have different voltage and/or current ratings, and mechanical and/or thermal stress, but some similarity in the number of I/Os and the package size. This process step creates a set of candidate custom LF designs for different IC devices which have a similar number of I/Os and die size.
One or more standard LFs will generally be designed based on common features two or more candidate LFs have. An algorithm can identify the common features among the candidate custom LF designs, which together determine the standard LF design. The standard design LF is then fabricated as a LF strip using conventional LF manufacturing technology. 3D printing technology is then used to fabricate the printed metal portions including printed traces that extend to contact on top of the edge of standard LF traces to reproduce the candidate LF designs. In this way, a standard LF design can be used for candidate LF designs for different devices.
There can be more than one standard LF design depending on how to categorize candidate LF designs. The candidate LF design can be categorized based on the similarity, such as the number of I/Os, package size, thermal dissipation performance, and mechanical strength.
As noted above the surface of the LFs 110 can include nano-roughening. Next, a metal precursor material is additively deposited and is then sintered or cured (e.g., laser processed) to provide metal traces and FC pads, and to connect the metal traces to leads of standard LFs for desired routing and for satisfying the other LF properties such as the number of I/O pins, thermal dissipation, and mechanical stress. The additively depositing can comprise inkjet printing using piezoelectric, thermal, or acoustics, or electrostatic inkjet printing, screen printing, or flexographic printing. Molding and singulating of the LF strip generally follows.
The printed metal precursor material can comprise an ink comprising a material that is a solid or a precursor for a solid that forms a solid upon the curing or the sintering. The ink includes copper or silver nanoparticles. The printed metal generally has a porosity greater than, a mechanical strength less than, and an electrical conductivity less than that of the metal of the LFs.
There are several standard LF options that can be used with disclosed aspects. Two or more standard LFs may be combined, such as a top leadframe on a bottom leadframe. Some of the leads of the standard LF may also be floating as shown in
Advantages provided by disclosed custom LFs include reducing the time and the cost of LF orders, standardizing the LF design and IC bump design to reduce the number of mask required. Moreover, additive manufacturing of metal layers allows a flexible design and fabrication of LFs.
Disclosed embodiments can be integrated into a variety of assembly flows to form a variety of different semiconductor integrated circuit (IC) devices and related products. The assembly can comprise single semiconductor die or multiple semiconductor die, such as PoP configurations comprising a plurality of stacked semiconductor die. A variety of package substrates may be used. The semiconductor die may include various elements therein and/or layers thereon, including barrier layers, dielectric layers, device structures, active elements and passive elements including source regions, drain regions, bit lines, bases, emitters, collectors, conductive lines, conductive vias, etc. Moreover, the semiconductor die can be formed from a variety of processes including bipolar, insulated-gate bipolar transistor (IGBT), CMOS, BiCMOS and MEMS.
Those skilled in the art to which this Disclosure relates will appreciate that many other embodiments and variations of embodiments are possible within the scope of the claimed invention, and further additions, deletions, substitutions and modifications may be made to the described embodiments without departing from the scope of this Disclosure.
The present application is a divisional of co-pending application Ser. No. 16/123,100 filed Sep. 6, 2018, titled “CUSTOM LEADFRAME FROM STANDARD PLUS PRINTED LEADFRAME PORTION” and is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16123100 | Sep 2018 | US |
| Child | 18810024 | US |
