This application claims the priority benefit of Italian Application for Patent No. 102021000028553, filed on Nov. 10, 2021, the content of which is hereby incorporated by reference in its entirety to the maximum extent allowable by law.
The description relates to semiconductor devices.
Semiconductor devices in Quad-Flat No-leads (QFN) packages may be exemplary of devices where embodiments can be advantageously applied.
Laser direct structuring (LDS) technology (oftentimes referred to also as direct copper interconnect (DCI) technology) has been recently proposed to replace conventional wire bonding in die-to-lead electrical connections in semiconductor devices.
In LDS technology as currently used today, after laser structuring (activation) in an LDS material, electrical conductivity of formations such as vias and lines or traces is facilitated via plating (e.g., electro-less metallization followed by galvanic deposition) to reach a metallization thickness of tens of microns of metal material such as copper.
An issue arising when applying laser direct structuring in providing electrical connections in semiconductor devices such as QFN devices lies in the nearly 1:1 aspect ratio constraint related to the formation (e.g., electroplating) of frusto-conical vias.
The designation “aspect ratio” is currently adopted to denote the ratio of the width to the height of an image or an object in general.
Aspect ratio constraints in forming vias affect via landing on leads for fine pitch leadframes (0.4 mm or less) or for packages where molding thickness is high (so-called “slug-up” QFNs, for instance). An increase in via diameter can undesirably lead to undesired misalignment with respect to the leads and may result in metal short-circuits (“shorts”).
There is a need in the art to contribute in adequately dealing with such an aspect ratio issue.
One or more embodiments relate to a method.
One or more embodiments relate to a corresponding semiconductor device.
Semiconductor devices in a Quad-Flat No-leads (QFN) package may be exemplary of devices where embodiments can be advantageously applied.
One or more embodiments provide an approach in producing through mold vias (TMVs) that adequately addresses the aspect ratio issue discussed in the foregoing.
One or more embodiments improve manufacturability and package miniaturization.
For instance, embodiments as discussed herein improve manufacturability of fine-pitch Quad-Flat No-leads (QFN) packages using laser direct structuring (LDS) technology.
Examples as disclosed herein involve providing through mold vias comprising an upper collar, larger than a bottom via portion.
Examples as disclosed herein involve laser machining a through mold via in two ablation steps, to form first a collar recess and then a frusto-conical via extending from a bottom of the collar recess.
Examples as disclosed herein offer one or more of the following advantages: the formation of a collar facilitates creating vias that are not constrained by a 1:1 aspect ratio, e.g., creating vias with a diameter smaller than mold cap (encapsulation) thickness; a simpler molding process derives from the possibility of avoiding thin mold caps; a simpler metallization process (e.g., Cu plating) can be implemented; molding compound downsizing facilitates obtaining vias with a (global) aspect ratio no longer limited to 1:1 (that is, “lean” through mold vias can be produced having a height higher than their width); and no additional process steps are involved over conventional package solutions based on LDS technology.
One or more embodiments will now be described, by way of example only, with reference to the annexed figures, wherein:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated.
The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.
The edges of features drawn in the figures do not necessarily indicate the termination of the extent of the feature.
In the ensuing description, various specific details are illustrated in order to provide an in-depth understanding of various examples of embodiments according to the description. The embodiments may be obtained without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail so that various aspects of the embodiments will not be obscured.
Reference to “an embodiment” or “one embodiment” in the framework of the present description is intended to indicate that a particular configuration, structure, or characteristic described in relation to the embodiment is comprised in at least one embodiment. Hence, phrases such as “in an embodiment”, “in one embodiment”, or the like, that may be present in various points of the present description do not necessarily refer exactly to one and the same embodiment. Furthermore, particular configurations, structures, or characteristics may be combined in any adequate way in one or more embodiments.
The headings/references used herein are provided merely for convenience and hence do not define the extent of protection or the scope of the embodiments.
As used herein, the terms chip/s and die/dice are regarded as synonymous.
The designation “leadframe” (or “lead frame”) is currently used (see, for instance the USPC Consolidated Glossary of the United States Patent and Trademark Office) to indicate a metal frame that provides support for an integrated circuit chip or die as well as electrical leads to interconnect the integrated circuit in the die or chip to other electrical components or contacts.
Essentially, a leadframe comprises an array of electrically-conductive formations (or leads, e.g., 12B) that from an outline location extend inwardly in the direction of a semiconductor chip or die (e.g., 14) thus forming an array of electrically-conductive formations from a die pad (e.g., 12A) configured to have at least one semiconductor chip or die attached thereon. This may be via conventional means such as a die attach adhesive (a die attach film (DAF) 140 for instance).
A device as illustrated in
For simplicity, in
Laser direct structuring (LDS), oftentimes referred to also as direct copper interconnection (DCI) technology, is a laser-based machining technique now widely used in various sectors of the industrial and consumer electronics markets, for instance for high-performance antenna integration, where an antenna design can be directly formed onto a molded plastic part. In an exemplary process, the molded parts can be produced with commercially available insulating resins that include additives suitable for the LDS process; a broad range of resins such as polymer resins like PC, PC/ABS, ABS, LCP are currently available for that purpose.
In LDS, a laser beam can be used to transfer (“structure”) a desired electrically-conductive pattern onto a plastic molding that may then be subjected to metallization to finalize a desired conductive pattern.
Metallization may involve electroless plating followed by electrolytic plating.
Electroless plating, also known as chemical plating, is a class of industrial chemical processes that creates metal coatings on various materials by autocatalytic chemical reduction of metal cations in a liquid bath.
In electrolytic plating, an electric field between an anode and a workpiece, acting as a cathode, forces positively charged metal ions to move to the cathode where they give up their charge and deposit themselves as metal on the surface of the work piece.
Reference is made to United States Patent Application Publication Nos. 2018/0342453 A1, 2019/0115287 A1, 2020/0203264 A1, 2020/0321274 A1, 2021/0050226 A1, 2021/0050299 A1, 2021/0183748 A1, and/or 2021/0305203 A1 (all assigned to the same assignee of the present application, and which are incorporated herein by reference) which are exemplary of the possibility of applying LDS technology in manufacturing semiconductor devices.
For instance, LDS technology facilitates replacing wires, clips or ribbons with lines/vias created by laser beam processing of an LDS material followed by metallization (growing metal such as copper via a plating process, for instance).
Still referring to
Electrically conductive die-to-lead coupling formations can be provided (in a manner known per se: see the commonly assigned applications cited in the foregoing, for instance) in the LDS material 16 (once consolidated, e.g., via thermosetting).
As illustrated in
Providing the electrically conductive die-to-lead formations 181, 182, and 183 essentially involves structuring these formations in the LDS material 16, for instance, laser-drilling (blind) holes therein at the desired locations for the vias 181, 182, followed by growing electrically-conductive material (a metal such as copper, for instance) at the locations previously activated (structured) via laser beam energy.
As illustrated in
Further details on processing as discussed in the foregoing can be derived from the commonly-assigned patent application publications referred to in the foregoing, for instance.
Briefly, using LDS technology, through mold vias (TMVs) 181, 182 and traces 183 are created to electrically interconnect one or more semiconductor dice 14 to a leadframe (leads 12B) thereby replacing conventional wire bonding used for that purpose.
With LDS technology, the interconnection is created using laser structuring (to create vias and lines or traces) and metal plating is used to fill the laser-structured formations with metal such as copper.
Plating design rules allow only a nearly 1:1 aspect ratio (diameter vs. depth) for through mold blind vias, in order to have a proper metal (e.g., copper) filling of the vias.
As illustrated in
Being constrained to a nearly 1:1 aspect ratio, vias such as the vias 182 formed at the leads 12B may have proximal ends (opposite the leads 12B) that are undesirably large in comparison with the leads: for instance, these proximal ends (that is, the upper ends of the vias 182 in
Package design is adversely affected by this fact, primarily when a fine pitch (close spacing) is desired for the leads 12B.
For instance, assuming a 1:1 aspect ratio for vias design, the (larger) diameter of frusto-conical vias such as the vias 182 intended to connect to leads 12B can be chosen considering the thickness of the die attach material (140 in
This may result in an undesired constraint in so far as only thin dice 14 (in a thickness range of 70 to 150 microns, assuming a die attach material thickness of 15 to 25 microns) can avoid the risk of having too large a vias (top) diameter, with possible “fall out” of the vias from the leads (having a width of 200 to 300 microns).
In conventional arrangements as illustrated in
Reference is also made to U.S. patent application Ser. No. 17/872,893 (corresponding to Italian Patent Application 102021000020537) and U.S. patent application Ser. No. 17/872,774 (corresponding to Italian Patent Application 102021000020540), both assigned to the same assignee of the present application, incorporated herein by reference, and not yet available to the public at the time of filing of the present application. The patent applications disclose the possibility of extending the use of LDS processing from producing die-to-lead coupling formations as discussed in the foregoing to producing die-to-die coupling formations.
Issues similar to the issues discussed in the foregoing in connection with forming vias in die-to-lead coupling formations may thus arise when forming vias in die-to-die coupling formations.
While disclosed for simplicity in connection with forming vias in die-to-lead coupling formations, the examples herein can be advantageously applied to forming vias in die-to-die coupling formations. Similarly, these examples can be advantageously applied to vias in metallization-to-metallization level coupling formations as discussed in United States Patent Application Publication No. 2021/0183748 A1 (already cited).
Consequently, the embodiments herein shall not be regarded as limited to forming vias in die-to-lead coupling formations.
Throughout
In the examples to which
In the examples to which
The first (outer) portion or layer 161 of the LDS material 16 is molded “on top” of the second (inner) portion or layer 162.
The first (outer) portion 161 thus extends from a (notional) intermediate plane 1612 of (or intermediate level 1612 within) the LDS encapsulation 16 up to a front or top surface 1613 of the (whole) LDS encapsulation 16.
A second section or portion 182B of the vias 182 comprises an (otherwise conventional) frusto-conical via formed through the second (inner) portion or layer 162 of the encapsulation of LDS material 16 that extends from the intermediate plane 1612 of the LDS encapsulation 16 towards the leadframe 12A, 12B.
The second portion 162 of the LDS encapsulation 16 is thus adjacent to the substrate 12A, 12B and borders on the first portion 161 at the intermediate plane 1612 of the encapsulation.
Like in the case of
The vias 181 thus extend from the front or top surface 1613 of the (whole) LDS encapsulation to die pads (not visible for reasons of scale) at the front or top surface of the die 14.
As illustrated, the front or top surface of the die 14 lies (at least approximately) at or in the vicinity of the intermediate plane 1612. As used herein, the expression “approximately” refers to a technical feature within the technical tolerance of the method used to manufacture and/or measure it.
Electrically conductive lines or traces 183 can be formed (in a manner likewise known to those of skill in the art) at the front or top surface 1613 of the (whole) LDS encapsulation 16 to electrically couple the vias 181 to (the collars 182A of) the vias 182.
Examples as presented in
The collars 182A formed in the first portion or layer 161 of the encapsulation 16 can be larger than the (larger diameter of the) vias 182B formed in the second portion or layer 162 of the encapsulation 16.
The size and dimensions of the collars 182A are largely independent of the sizes of the leads 12B. Collar dimensions can be (much) larger than the diameter of the frusto-conical vias 182B (ad measured in the plane 1612).
As visible, e.g., in
This (also) facilitates plating metal (e.g., Cu) flow into the collars 182A to reach (and fill) the frusto-conical via portions 182B.
Vias 182 with a collar 182A may show (as a whole) a lean “cylindrical” shape (in contrast to the general frusto-conical shape of conventional vias 182 as illustrated in
This facilitates achieving a larger bottom diameter of the vias 182 (at the leads 12B) while avoiding the limitations related to a 1:1 aspect ratio.
Such a sequence involves laser machining a through mold via in two ablation steps, to form first a collar recess (e.g., a collar section 182A) and then a frusto-conical bottom via (e.g., a frusto-conical section 182B), that is forming first the enlarged collar section 182A and then forming the frusto-conical section 182B subsequent to forming the enlarged collar section 182A.
It will be otherwise appreciated that the sequence of
Also, unless the context indicates differently, the individual steps illustrated in
The sequence of steps of
In that respect it is noted that the designation Quad-Flat No-leads (QFN) designation currently applied to devices such as the devices 10 illustrated herein refers primarily to the fact that, while including leads such as the leads 12B, these devices have no leads protruding radially from the package.
As noted, plural semiconductor chips or dice 14 can be arranged at the (front or top) surface of each die pad 12A: one chip or die 14 is illustrated here for simplicity.
The step of
While in most instances applied as a single mass of LDS material, the encapsulation 16 can be regarded as comprising: an inner portion or layer (designated 162) having the chips or dice 14 embedded therein and extending up to the (notional) plane 1612 essentially flush with the front or top surface of the chips or dice 14, and an outer portion or layer (designated 161) molded “on top” of the inner layer 162 (and the chips or dice 14), with the outer portion or layer 161 extending from the plane 1612 to the front or top surface 1613 of the (whole) LDS encapsulation 16.
In
In
As illustrated, applying LDS processing to the encapsulation 16 of LDS material comprises: applying laser beam energy LB to the LDS material 16 to provide therein laser-ablated regions for the collars 182A′ as well as for the vias 181′, 182B′ and the lines or traces 183′, and growing (via plating P, for instance) electrically conductive material at the laser-activated/ablated regions 181′, 182A′, 182B′ and 183′.
As illustrated in
In terms of process flow, cavities for the collar sections 182A′ can be formed first—via laser ablation, for instance—through the outer layer 161 of the encapsulation of LDS material molded “on top” of the inner layer 162.
A frusto-conical section can then be formed (e.g., laser-drilled as 182B′) at and extending from the bottom of the collar section 182A′, with the frusto-conical section 182B′ extending through the inner layer 162 of the encapsulation 16 of LDS material from the notional plane 1612 (essentially flush with the front or top surface of the chip or die 14) to a respective lead 12B.
Metal material (e.g., copper) can then be grown into the sections 182A′ and 182B′ to facilitate electrical conductivity of the via 182 (collar 182A plus the frusto-conical via 182B) extending through the mold material 16 (layers 161 and 162) from the front or top surface 1613 of the (whole) LDS encapsulation 16 to the leads 12B passing through the (notional) intermediate plane 1612.
Without prejudice to the underlying principles, the details and embodiments may vary, even significantly, with respect to what has been described by way of example only without departing from the extent of protection.
The claims are an integral part of the technical teaching provided herein in respect of the embodiments.
The extent of protection is determined by the annexed claims.
Number | Date | Country | Kind |
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102021000028553 | Nov 2021 | IT | national |