This application claims the priority benefit of Italian Application for Patent No. 102023000000849 filed on Jan. 20, 2023, the content of which is hereby incorporated by reference in its entirety to the maximum extent allowable by law.
The description relates to manufacturing semiconductor devices.
Solutions as described herein can be applied to power (integrated circuit) semiconductor devices such as power QFN packages, for automotive products, for instance.
In power integrated circuit semiconductor devices, the current transferred from the high-power section to the output pads of the device can be significant. Clips, ribbons or multiple wires can be used for that purpose in the place of single wires.
Clips are currently stamped from flat material. Pins with the purpose of centering the clip on the leadframe can also be created in the clip material by punching. Recesses are created at corresponding leadframe positions to house the clip pins for centering purposes.
In small packages (power Quad-Flat No Leads (QFN), for instance) and/or if several channels are desired to be provided in the final package, more pads are needed and the dimensions for recesses on leadframe and clips may become relatively small.
The relatively small dimensions may lead to difficulties in the manufacturing and handling of the clips.
Another approach is based on bonding using multiple wires; such a method involves wedge-bonding a plurality of wires and may thus be undesirably time consuming.
Yet another approach is based on the use of electrically conductive ribbons to provide electrical coupling between the power section of a (integrated circuit (IC)) semiconductor device and the outer pads.
These ribbons are bonded via ultrasonic wedge-bonding and such a bonding method may severely damage the (relatively small) outer pads.
There is accordingly a need in the art to address the issues discussed in the foregoing.
One or more embodiments relate to a method.
One or more embodiments relate to a ribbon for use in a method as described herein.
One or more embodiments relate to an apparatus for use in manufacturing ribbons as described herein.
One or more embodiments relate to a corresponding (integrated circuit) semiconductor device.
In solutions as described herein electrical coupling between the power section of a semiconductor device and the outer pads is provided via ribbon bonding.
In solutions as described herein a ribbon is provided with a reduced bonding area to reduce the mechanical stress applied during wedge-bonding.
Solutions as described herein may involve dispensing a conductive material, such as solder paste or glue, at the ends of the ribbon in order to increase conductivity of the electrical coupling via the ribbon.
Solutions as described herein may involve a (slight) modification of the ultrasonic wedge-bonding apparatus.
Solutions as described herein contemplate providing a leadframe, mounting a die thereon, forming electrical connections between the die and leads in the leadframe via ribbon bonding.
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 one or more specific details are illustrated, aimed at providing an in-depth understanding of examples of embodiments of this 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 certain aspects of 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” or “in one embodiment” that may be present in one or more points of the present description do not necessarily refer to one and the same embodiment.
Moreover, particular conformations, 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.
For simplicity and ease of explanation, throughout this description, and unless the context indicates otherwise, like parts or elements are indicated in the various figures with like reference signs, and a corresponding description will not be repeated for each and every figure.
As used herein, the terms chip/s and die/dice are regarded as synonymous.
An array of leads 12B is arranged around the die pads 12A having the low-power and the high-power dice 14 mounted thereon.
As illustrated herein by way of example, an integrated circuit semiconductor device such as the device 10 comprises, in addition to a substrate (leadframe) 12 having one or more semiconductor chips or dice 14 arranged thereon: electrically conductive formations 16, 18 coupling the semiconductor chip(s) 14 to leads (outer pads) 12B in the substrate; and an insulating encapsulation ER (e.g., an epoxy resin, whose outline is partly illustrated in dashed lines only in
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 12 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 (IC) semiconductor chip or die attached thereon. This may be via conventional means such as a die attach adhesive (a die attach film or DAF, for instance).
In certain cases, a leadframe can be of the pre-molded type, that is a type of leadframe comprising a sculptured metal (e.g., copper) structure formed by etching a metal sheet and comprising empty spaces that are filled by an insulating compound (a resin, for instance) “pre-molded” on the sculptured metal structure.
In current manufacturing processes of semiconductor devices, plural devices are manufactured concurrently to be separated into single individual device in a final singulation step. For simplicity and ease of explanation, the following description will refer to manufacturing a single device.
As noted, electrically conductive formations 16, 18 are provided coupling the semiconductor chip(s) 14 to leads (outer pads) 12B in the substrate.
In power semiconductor devices (e.g., the device 10 illustrated in
For instance, as illustrated on the right-hand side of
Wires 16 can still be used, as shown on the left-hand side of
That is, as illustrated in
Conversely, clips 18 (as illustrated in
As illustrated, clips 18 are provided with pins 181 (provided via punching, for instance) at their terminal (distal) part (on the right-hand side of
The proximal ends (on the left side in
The pins 181 and corresponding recessed portions 182 of the leads 12B in the leadframe 12 facilitate centering of the clip when mounting the clip 18 on the leadframe-chip assembly as well as keeping the clip in position during processing (e.g., during reflow).
As noted, when manufacturing small-sized power devices or when several electrical channels are involved, the method just described for providing electrical coupling to the power section of the device via clips may be faced with various difficulties.
In such a case, providing electrical coupling between the die bonding pads 22 and the corresponding (power) leads 12B via clips as discussed in the foregoing may be difficult; in fact, as a consequence of the (relatively) smaller size of the clips, providing pins 181 by stamping or punching may be impractical and one has to renounce to the centering feature.
It is noted that, in case of small package devices, those problems may already appear when more than two channels (and thus more than two clips) are desired.
One possible approach to provide electrical coupling to the high-power section of a device as exemplified in
As mentioned, due to the high current transferred from the high-power section of the device 10, a simple (single) wire bonding may prove to be inadequate. For that reason, in order to electrically couple one die pad 22 to one outer lead 12B, a plurality of wires (notionally of the same type of the wires 16 illustrated in
Such a solution would involve wedge-bonding a plurality of wires for each desired electrical coupling (thus, four couplings in the case exemplified in
Increasing the cross-section of the wires or using a different material with better electrical performance may possibly reduce the number of wires to be wedge-bonded, and thus possibly reduce bonding time, but will eventually involve undesirably higher production cost.
As illustrated in
The terminal parts 191 of the ribbons 19 may be bonded to the underlying die bonding pads 22 or leads 12B via ultrasonic wedge-bonding technique as known to those skilled in the art.
Ultrasonic wedge-bonding is essentially based on the application of ultrasound and (mechanical) pressure to form an electrical connection between the terminal part 191 of a ribbon and an underlying surface (of the die bonding pad 22 or the lead 12B).
While advantageous for certain aspects, wedge-bonding may have undesired effects on the device structure as a consequence of the mechanical stress applied during bond formation.
For instance, it is observed that ultrasonic wedge-bonding may cause cratering and/or cracking of the semiconductor material (e.g., silicon) of the die 14 beneath the die bonding pads 22 when forming the bond between die pads 22 and the terminal end of the ribbons 191.
Due to the mechanical stress applied, bond formation between leads 12B and ribbons 19 may also have detrimental effects on the leadframe 12; in certain cases, deformation and/or laceration of the leadframe 12 (especially in the proximity of the leads 12B) may cause the device under processing to be discarded, thus increasing overall manufacturing time and costs.
The parameters of the wedge-bonding process (e.g., ultrasound energy and mechanical pressure applied) may depend on the area of the surface to be bonded (the area of the portions 191, in the case exemplified in
It is observed that a larger area generally results in more “stressful” parameters. On the other hand, a reduction of the width of the ribbons 19 (that is, a reduction of the width of the central portion 190 and the terminal portions 191) may have the undesired effect of reducing the conductivity of the ribbon 19, leading to poor electrical performance.
Such reduction in conductivity could be (at least notionally) counterbalanced by the use of a different (e.g., more conductive) material for the ribbons; this would however cause higher production costs.
To summarize, according to the approaches as discussed in the foregoing: electrical coupling to the high-power section of (power) semiconductor device may be provided via clips 18, ribbons 19 or multiple wires; and such solutions may be unsatisfactory and/or involve higher costs/processing time when several (e.g., more than two) power electrical channels are desired.
Solutions as described herein aim at improving electrical coupling via ribbons with a modified design.
Solutions as described herein involve providing ribbons with a reduced area at (at least one of) the terminal portions configured to be connected to the leads or the die bonding pads.
Solutions as described herein may involve a modification of the wedge-bonding apparatus in order to provide ribbons according to embodiments of the present description. In solutions as described herein ribbons modified according to the present description may be wedge-bonded applying less mechanical stress to the structure of the device.
In solutions as described herein solder material may be dispensed at the bonding regions of the ribbons to increase overall conductivity of the coupling thus improving the electrical performance of the coupling.
In such a ribbon 19, the terminal portions 191 (only one terminal portion is visible in
A ribbon 20 according to embodiments of the present description includes an (enlarged) central portion 200 with a first width (this may be the same width W1 of the whole ribbon 19) and (one or two) tapered end portions 201 having a second width W2, smaller than the first width W1.
That is, electrically conductive ribbons 20 as proposed herein have: substantially constant thickness (in the “vertical” direction, transverse to the plane of the substrate 12) at the first and second end portions 201 and at the body portion 200; and different widths (W1, and W2, respectively) in the “horizontal” direction, parallel to the plane of the substrate 12.
As already mentioned, the parameters of the wedge-bonding process, and consequently the mechanical stress applied to the various parts of the device (e.g., the die 14 or the leads 12B) may depend on the area of the surface to be bonded in the sense that a larger area generally involves more “stressful” parameter.
In view of this fact, the terminal portion 201 of the ribbon 20 (that is, the portion of the ribbon configured to be wedge bonded) is advantageously shaped in such a way to reduce the area that is to be wedge-bonded (to the lead 12B or the die bonding pad 22). The area of the terminal portion 201 is thus reduced by reducing the width W2 of the terminal portion 201 (W2<W1).
It is noted that, once a reduced area is used at the terminal portion(s) 201 as illustrated in
It is noted that only the terminal portion of the ribbon 201 is reduced in size; the central portion 200 of the ribbon 20 may be advantageously maintained (e.g., width W1) in order to preserve satisfactory electrical performance.
As illustrated in
The tool PT may be implemented in different ways with different active members P1, P2 acting on the tape.
For instance, the members P1, P2 can comprise reciprocating punches P1, P2 acting on opposed sides of the strip RT to plastically deform the material of the strip RT by squeezing the strip RT therebetween at the desired narrowed portions.
Alternatively, the members P1, P2 can comprise blanking or milling heads P1, P2 acting at opposed sides of the strip RT to form therein cutouts at the desired narrowed portions.
These implementations facilitate providing electrically conductive ribbons 20 having a substantially constant thickness (in the “vertical” direction, transverse to the plane of the substrate 12) at the first and second end portions 201 and at the body portion 200.
This is in contrast to the different widths (W1, and W2, respectively) in the “horizontal” direction, parallel to the plane of the substrate 12.
The metal strip with the alternation of “wide” and “narrow” portions is provided to a wedge bonding tool. The narrow portions of the metal strip are bonded to desired locations. For example, a one of the narrow portions of the metal strip may be wedge bonded to one of the semiconductor die or an electrically conductive leads to provide a first end portion of the ribbon. The wedge bonding tool advances to the location of the location of other of the semiconductor die or electrically conductive leads. At this location, another one of the tapered portions of the metal strip is wedge bonded. The metal strip is then cut after this second wedge bond is completed. The cut is made at the another one of the tapered portions to provide the second end portion of the ribbon.
To summarize,
Still other implementations can be devised (e.g., where the wide body portions 200 of a ribbon 20 result from squeezing a strip that is left unsqueezed where narrow end portions 201 are intended to be provided).
Whatever the implementation of the tool PT, the strip RT having formed therein an alternation of “wide” and “narrow” portions can be fed to a cutting station C (e.g., as used to produce ribbons 19 as in
The specific parameters describing a desired shape of the ribbons 20 (W1, W2 or the length L of the ribbons, for instance) depend on the design of the device where they are intended to be used. An apparatus as illustrated in
It will be appreciated that an apparatus as illustrated in
As illustrated in
As a consequence of the reduced area of the portions that are bonded, compared to a ribbon 19 as in
As already mentioned, the shape of the ribbons 20 as illustrated, for instance, in
In particular, the ribbons 20 have been illustrated having a symmetrical shape, that is having both terminal portions 201 of reduced area. This feature should not be construed in a limiting sense of the embodiments: just by way of example, depending on the particular design of the “final” device 10, ribbons 20 may be provided with only one terminal portion 201 of reduced area and/or have terminal portions 201 of reduced area provides both ends with an asymmetrical shape (e.g., by bestowing on the ribbons 20 a sort of lozenge shape).
In order to counter the possible (relatively small) reduction in conductivity due to the reduced contact area provided by the terminal portions of the ribbons 201, an optional further step may be added to the manufacturing process as discussed so far.
As illustrated, solder material SM may be dispensed at the narrow terminal portion(s) of the ribbons 201 (and the die bonding pads 22 or the leads 12B there beneath). It is noted that the solder material SM may be dispensed in such a way to extend beyond the terminal portion 201 of reduced area of the ribbons 20. The larger area provided by the (electrically conductive) solder material SM increases the conductivity as provided by the ribbons 20, thus improving the electrical performance thereof.
Moreover, as those skilled in the art may appreciate, dispensing solder material SM at the terminal portions 201 wedge-bonded to the die pads 22 or the leads 12B, may desirably “strengthen” the bonding thus reducing the risk of detachment of the ribbon from the die pad/lead.
Further steps in semiconductor device manufacturing process may comprise: a molding step, wherein a molding compound (such as an epoxy resin, for instance: see ER in
The claims are an integral part of the technical teaching provided in respect of the embodiments.
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 extent of protection is determined by the annexed claims.
Number | Date | Country | Kind |
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102023000000849 | Jan 2023 | IT | national |