Patent Description:
One or more embodiments may be applied, in particular, to Quad-Flat No-leads (briefly, QFN) or Quad-Flat Package (QFP) exposed pad semiconductor packaging having exposed leads on the bottom of the package body thereof, and to a method of manufacturing thereof.

One or more embodiments may be applied to a pre-molded leadframe which is molded in a flat configuration and is adapted for use in package applications using surface mount technology (SMT).

IC dies are conventionally enclosed in plastic packages providing protection from the environment and facilitating electrical interconnection between the IC die and an underlying substrate such as a printed circuit board (PCB).

In a conventional arrangement, a packaged semiconductor device may include:.

The leadframe is the central supporting structure for the IC die, in particular during assembly of such a packaged semiconductor device, is adopted to shape external contactors (leads or pads). A portion of the leadframe may be completely surrounded by the plastic encapsulant. Portions of the leads of the leadframe extend externally from the package or are partially exposed within the encapsulant material for use in electrically connecting the package to another component. In certain packaged semiconductor devices, a portion of the die pad of the leadframe may also remain exposed within the exterior of the package for use as a heat sink.

One type of semiconductor package commonly known in the electronics field is referred to as a quad flat pack (QFP) package. A QFP package may comprises a thin, generally square package body defining four peripheral sides of substantially equal length. Protruding from each of the four peripheral sides of the package body are a plurality of leads which each have a generally gull-wing configuration. Portions of the leads are internal to the package body, and are electrically connected to respective ones of the pads or terminals of a semiconductor die also encapsulated within the package body. The semiconductor die is mounted to a die pad of the QFP package leadframe. In certain types of QFP packages referred to as QFP exposed pad (QFP-ep) packages, one surface of the die pad is exposed within the bottom surface of the package body.

Package may be stressed during reliability evaluation and the adhesion between all the parts can be ascertained for determining package reliability. The leadframe adhesion on the resin is an important figure of merit for the package hermeticity and its reliability.

In QFN, QFP package technology external contactors (leads or pads) can be shaped by photoetching and, as mentioned, a die pad portion of the leadframe sustaining the IC die silicon chip may be exposed to the exterior of the molded body.

In that respect, adhesion/strength is an issue, particularly with pre-molded leadframe and/or when using ribbon bonding (for high-power applications, for instance).

A molding compound shrinking on a die paddle may result in a compressive stress likely to produce a so-called "crying" warpage leading to resin detachment from leadframe due to lack of adhesion, that is to delamination between the molding compound and the die pad. Die pad/molding delamination can jeopardize package hermeticity, as the die pad may be pulled out from the molded body when mounted on PCB.

Existing solutions available to leadframe suppliers in order to improve reliability of resin-die pad coupling may comprise surface treatments to the die pad or tailored under (photo) etching of the leadframe.

Reliability tests performed on such arrangements indicate however that delamination between mold compound and under etch die pad can still take place, with the resulting gap compromising package hermeticity.

More specifically, the invention relates to a leadframe according to the preamble of claim <NUM>, which is known, for instance, from <CIT>.

Also documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, are of interest for the invention.

An object of one or more embodiments is to contribute in providing improved solutions addressing the issues discussed in the foregoing. The invention is disclosed by the appended claims.

According to one or more embodiments, that object can be achieved by means of a device /method having the features set forth in claim <NUM> that follows.

One or more embodiments facilitate an improved anchorage of the die pad to the molding compound by providing a through slot on the die pad periphery, formed by over-lapping of upper and lower half-cut patterns.

One or more embodiments may relate to a corresponding leadframe.

A leadframe comprising a die pad having a slot formation on one side and a stepped profile outline may be exemplary of such a leadframe.

One or more embodiments may relate to a corresponding semiconductor assembly.

One or more embodiments may relate to a corresponding method.

A method of manufacturing a leadframe or a semiconductor assembly having improved resilience to delamination may be exemplary of such a method.

One or more embodiments may facilitate providing QFP-ep packages with improved package hermeticity and delamination reduced (virtually removed).

In one or more embodiments, a feature may be included to the die pad area of the leadframe to increase its adhesion to subsequently applied molding compound. Such a feature may comprise a half etch done on an upper side of the die pad, the half etch overlapping partially a second half etch on the bottom of the die pad.

One or more embodiments may create a resin under lock that may facilitate preventing delamination on die pad and increasing die pad hermeticity in the semiconductor assembly.

In one or more embodiments, such a through slot perforating partially a half-etched area on die pad periphery may facilitate creating a strong locking by mold compound, preventing a die pad pulling from out from the molded body when mounted on a Printed Circuit Board (PCB).

One or more embodiments may be suited for use in QFN and QFP-ep semiconductor packages with photoetched leadframe.

In one or more embodiments, the die pad may be designed so as to comprise one or more engraved slots on one surface.

One or more embodiments may advantageously facilitate, among others:.

The claims are an integral part of the technical teaching provided herein with reference to the embodiments.

One or more embodiments will now be described, by way of non-limiting example only, with reference to the annexed Figures, wherein:.

The references used herein are provided merely for convenience and hence do not define the extent of protection or the scope of the embodiments.

The drawings are in simplified form and are not to precise scale. For the sake of simplicity, directional (up/down, etc.) or motional (forward/back, etc.) terms may be used with respect to the drawings. The term "couple" and similar terms do not necessarily denote direct and immediate connections, but also include connections through intermediate elements or devices.

Throughout the figures annexed herein, unless the context indicates otherwise, like parts or elements are indicated with like references/numerals and a corresponding description will not be repeated for brevity.

As mentioned, improving locking between leadframe and molding compound is an object of one or more embodiments as per the present disclosure.

In order to facilitate an improved locking, some solutions may comprise methods of under-etching the leadframe so as to form an inverted T-shape during an operation of half-cut etching of the leadframe, as exemplified in <FIG>.

<FIG> is a perspective view of a portion of a (metallic, for instance copper) lead-frame <NUM> subjected to back-etching as discussed in the following, the lead-frame <NUM> comprising an array of electrical contact formations <NUM> around a die pad portion.

In one or more embodiments, the array of electrical contact formations <NUM> may possibly have selectively plated parts provided thereon by known means.

As mentioned, the leadframe <NUM> may have a core or die pad area <NUM> configured to host a semiconductor die.

Specifically, the die pad <NUM> may comprise a first planar die-mounting surface and a second planar surface 14b opposed the first surface.

For instance, the semiconductor die may be glued onto such first surface (not visible in <FIG>) and the electrical contact formations <NUM> may be configured to provide electrical connection and accessibility to the semiconductor die functions once placed on the die pad area <NUM> of the leadframe <NUM>.

In one or more embodiments the die pad <NUM> may have a polygonal shape, for instance square, and comprises a generally planar top surface and an opposed, generally planar, bottom surface, as well as four peripheral edge segments.

As a result of the etching processing, for instance, a stepped profile <NUM> is engraved in the die pad rim or outline as well as in the rim or outline of the leads <NUM> of the leadframe.

Specifically, such a photoetching process may be configured to provide a half-etched leadframe <NUM> wherein the stepped profile <NUM> comprises a first step and a second step, the first step having a half-width with respect to the width of the leadframe before etching.

As mentioned, during the formation of the leadframe <NUM> via etching processing, also the leads <NUM> may be half-etched in a manner facilitating the formation of a continuous, recessed shoulder within the surface thereof, such shoulder extending continuously along the inner end and portions of the longitudinal sides of each lead <NUM>.

An assembly <NUM> of the leadframe <NUM> and a semiconductor die <NUM> may have a transverse section as exemplified in <FIG>, wherein the semiconductor die (or dice) may be placed on a first surface 14a of the die pad <NUM> of the leadframe <NUM>.

Subsequent to the mechanical and electrical connection of the semiconductor die <NUM> to the electrical contact formations <NUM>, for instance via through the use of the conductive wires (known as wire bonding, not visible in the Figures), the assembly <NUM> may be encapsulated or covered with an encapsulant material in a molding process, with the hardening of the encapsulant material resulting in the formation of a package body of the semiconductor package <NUM>. The encapsulant material is applied to the leadframe <NUM> such that in the completely formed package body, the bottom surface 14b of the die pad <NUM> and the "bottom" surfaces 16b (opposed to respective "top" surfaces 16a) of the electrical contact formations <NUM> may be exposed within a "bottom" surface of the package assembly <NUM>, wherein the bottom surface of the package assembly <NUM> may be configured to be coupled to a support S. In one or more embodiments, for instance, such a support S may comprise a Printed Circuit Board, briefly PCB.

For instance, the leadframe <NUM> may be assembled as a pre-molded leadframe <NUM> as exemplified in <FIG>, for instance having spaces between die pad <NUM> and leads <NUM> filled with a molding compound <NUM>', wherein the second surface 14b of the die pad <NUM> and a top surface 16b of the electrical contact formations <NUM> may remain visible to external inspection.

As mentioned, the packaged semiconductor device <NUM> or pre-molded leadframe <NUM> may have an improved resistance to delamination forces which may cause a deterioration of adhesion between molding and leadframe.

Specifically, such a resistance may result to the presence of the stepped profile outline or recessed shoulder <NUM> sculptured into the die pad rim, which may counter delamination forces acting parallel to the die pad planar surface 14a.

Nevertheless, such a shoulder <NUM> may hardly contribute to countering forces acting in other directions, for instance perpendicularly to the die-pad surface. Lack of protection from such (non-parallel) forces may cause in any case a deterioration of adhesion between molding and leadframe: for instance, the leadframe may tend to "slip" outside of its seat as a result of such forces.

One or more embodiments as per the present disclosure aim at providing such an improved adhesion between leadframe die pad <NUM> and molding compound <NUM> with respect to delamination forces acting in any direction.

In one or more embodiments as exemplified in <FIG> such an improvement may be facilitated via a die-pad <NUM> of a leadframe <NUM> comprising at least one engraved formation <NUM>, for instance having an oval shape or a mouth portion, going through 18a a first step in a stepped profile <NUM> outlining the die pad <NUM>.

The leadframe <NUM> may be formed from rolled strip metal stock by wet chemical etching or mechanical stamping using progressive dies. Photo Chemical etching (also known as chemical milling) is a process that uses photolithography and metal-dissolving chemicals to etch a pattern into a metal strip. The photoresist is exposed to ultraviolet light through a photo mask having a desired pattern, and is subsequently developed and cured. Chemicals are sprayed or otherwise applied to the masked strip, and exposed portions of the strip are etched away, leaving the desired pattern.

As mentioned, the lead frame <NUM> can be formed by photo-etching or chemically etching the rolled strip metal stock from both sides using a conventional liquid etchant. The etch process may be stopped early so as to provide an under-etching of various surfaces of the lead frame <NUM> to achieve the desired cross-sectional configuration, for instance as exemplified in <FIG> and/or 2B or in <FIG>.

Specifically, in one or more embodiments as exemplified in <FIG>, different masked strips may be used for different sides of the leadframe. For instance, a first mask <NUM> may be used to etch, for instance with a first etching flow from top <NUM>, the top surface 14a and a second mask <NUM> may be used to etch, for instance with a second etching flow from bottom <NUM>, the bottom surface 14b. In one or more embodiments, applying such a differentiated etching processing <NUM>, <NUM> may facilitate obtaining different (engraving) patterns on different leadframe surfaces 14a, 14b. <FIG> is exemplary of a section of one or more embodiments of an assembly <NUM> of the leadframe <NUM> and a semiconductor die <NUM> packaged with an encapsulating molding compound <NUM>.

For instance, the semiconductor die <NUM> may be coupled to the second surface or "top" surface 14a of the die pad <NUM> and may be coupled to contact formations <NUM> via (wire-bonded) contacts <NUM>. <FIG> is an enlarged view of a portion V of <FIG>. In one or more embodiments as exemplified in <FIG>, thanks to the presence of formation <NUM> which goes through the stepped profile <NUM> of the die pad <NUM>, the molding compound when poured is coupled to the die pad <NUM> via an anchoring portion <NUM> of the die pad <NUM> which is a result of the engraved formation <NUM> filled with the molding compound. The anchoring <NUM> may be of various sizes and ratios with respect to the die pad surface 14a as a function of the size of the steps in the rim, for instance of a first step <NUM> in the stepped profile <NUM> of the die pad <NUM>.

In one or more embodiments as exemplified in <FIG>, the formation <NUM> may have the shape of an oval slot, such a shape being purely exemplary and in no way limiting. For instance, the formation <NUM> may have other polygonal shapes or comprise a pattern of, e.g., parallel, oval or polygonal formations.

In one or more embodiments as exemplified in <FIG>, a method <NUM> of manufacturing a pre-molded leadframe and/or a semiconductor device as per the present disclosure may comprise:.

For instance, the leadframe <NUM> may be assembled as a pre-molded leadframe by applying, flush to the surface of the leadframe, a molding compound so as to fill spaces between die pad <NUM>, anchoring portion <NUM> and leads <NUM> filled with a molding compound <NUM>'.

As a result, the method <NUM> may comprise providing <NUM> at least one of a semiconductor device <NUM> and/or a pre-molded leadframe <NUM> having an improved robustness with respect to delamination forces acting in any direction.

One or more embodiments relate to a leadframe (for instance, <NUM>) for semiconductor devices which may comprise a die pad portion (for instance, <NUM>) having a first planar die-mounting surface (for instance, 14a) and a second planar surface (for instance, 14b) opposed the first surface, the first surface (for instance, 14a) and the second surface (for instance, 14b) having facing peripheral rims jointly defining a peripheral outline of the die pad, wherein the die pad comprises at least one package molding compound receiving cavity (for instance, <NUM>) opening at the periphery of said first planar surface.

In one or more embodiments, the peripheral rims of said first surface and said second surface are mutually offset to provide a stepped peripheral outline of the die pad with the periphery of said first planar surface having a peripheral region protruding with respect to the second planar surface, wherein said at least one package molding compound receiving cavity is provided at said protruding region of the first planar surface.

In one or more embodiments, the at least one package molding compound receiving cavity partially overlaps and goes through said stepped peripheral outline of the die pad.

In one or more embodiments, said at least one package molding compound receiving cavity may have a mouth portion at said first planar surface, said mouth portion having a closed contour and being at a distance from the peripheral rim of the first planar surface.

In one or more embodiments, said at least one package molding compound receiving cavity may comprise a buttonhole-like cavity.

In one or more embodiments, the leadframe may comprise a plurality of said package molding compound receiving cavities (for instance, <NUM>, <NUM>) distributed along the peripheral outline of the die pad.

In one or more embodiments, the leadframe may have package molding compound (for instance, <NUM>') molded thereon flush with said first planar die-mounting surface and said second planar surface, the package molding compound (for instance, <NUM>') filling said at least one package molding compound receiving cavity opening at the periphery of said first planar surface.

One or more embodiments relate to a semiconductor product (for instance, <NUM>), comprising:.

In one or more embodiments, the semiconductor product may comprise:.

One or more embodiments relate to a method which may comprise:.

In one or more embodiments, the method may comprise:.

Claim 1:
A leadframe (<NUM>) for semiconductor devices, the leadframe (<NUM>) comprising a die pad portion (<NUM>) having a first planar die-mounting surface (14a) and a second planar surface (14b) opposed the first surface (14a), the first surface (14a) and the second surface (14b) having facing peripheral rims jointly defining a peripheral outline of the die pad (<NUM>), wherein the die pad (<NUM>) comprises at least one package molding compound receiving cavity (<NUM>) opening at the periphery of said first planar surface (14a),
the leadframe (<NUM>) characterized in that:
the peripheral rims of said first surface (14a) and said second surface (14b) are mutually offset to provide a stepped peripheral outline of the die pad (<NUM>) with the periphery of said first planar surface (14a) having a peripheral region protruding with respect to the second planar surface (14b), wherein said at least one package molding compound receiving cavity (<NUM>) is provided at said protruding region of the first planar surface (14a),
wherein said at least one package molding compound receiving cavity (<NUM>) comprises a through cavity (18a) extending from said first planar surface (14a) to said second planar surface (14b), and
said at least one package molding compound receiving cavity (<NUM>) partially overlaps and goes through said stepped peripheral outline of the die pad (<NUM>).