Patent ID: 12199019

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings. It may be evident, however, to one skilled in the art that one or more aspects of the disclosure may be practiced with a lesser degree of the specific details. In other instances, known structures and elements are shown in schematic form in order to facilitate describing one or more aspects of the disclosure. In this regard, directional terminology, such as “top”, “bottom”, “left”, “right”, “upper”, “lower” etc., is used with reference to the orientation of the Figure(s) being described.

In addition, while a particular feature or aspect of an example may be disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features or aspects of the other implementations as may be desired and advantageous for any given or particular application, unless specifically noted otherwise or unless technically restricted. Furthermore, to the extent that the terms “include”, “have”, “with” or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprise”. The terms “coupled” and “connected”, along with derivatives thereof may be used. It should be understood that these terms may be used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other; intervening elements or layers may be provided between the “bonded”, “attached”, or “connected” elements. However, it is also possible that the “bonded”, “attached”, or “connected” elements are in direct contact with each other. Also, the term “exemplary” is merely meant as an example, rather than the best or optimal.

The semiconductor chip(s) mentioned further below may be of different types, may be manufactured by different technologies and may include for example integrated circuits and/or passives, logic integrated circuits, control circuits, microprocessors, memory devices, etc.

The examples of a semiconductor package described in the following may use various types of semiconductor chips or circuits incorporated in the semiconductor chips, among them AC/DC or DC/DC converter circuits, power MOSFETs, power Schottky diodes, JFETs (Junction Gate Field Effect Transistors), power bipolar transistors, power integrated circuits, etc. The semiconductor chip(s) may have contact pads (or electrodes) which allow electrical contact to be made with the integrated circuits included in the semiconductor chip(s). The electrodes may be arranged all at only one main face of the semiconductor chip(s) or at both main faces of the semiconductor chip(s).

The semiconductor chip(s) may be covered with an encapsulation material in order to be embedded in an encapsulant after being bonded to a device carrier (substrate). The encapsulation material may be electrically insulating. The encapsulation material may comprise or be made of any appropriate plastic or polymer material such as, e.g., a duroplastic, thermoplastic or thermosetting material, and may e.g. contain filler materials. Various techniques may be employed to encapsulate the semiconductor chip(s) with the encapsulation material, for example any suitable molding technique.

FIG.1Ashows a sectional view of a semiconductor package100that comprises a semiconductor chip110, a molded body120and a plurality of electrical contacts130.FIG.1Bshows a view of the semiconductor package100along the arrow A inFIG.1A.FIG.1Cshows the same view asFIG.1A, however inFIG.1Cthe molded body120is depicted opaque.

In semiconductor package100the molded body120encapsulates the semiconductor chip110. For example, the molded body120may encapsulate the semiconductor chip110on all sides. The molded body120comprises a top face121and an opposing bottom face122and four side faces123connecting the top and bottom faces121,122.

The plurality of electrical contacts130may e.g. be arranged on two of the four side faces123of the molded body120, for example on opposing ones of the four side faces123. The other two side faces123(i.e. those side faces123that do not comprise any electrical contacts130) are metal-free side faces. “Metal-free” in particular may mean that the respective side face does not comprise any form of metal part, like a metal contact, a metal stud, a metal peg, remains of a metal tie-bar, etc. that is exposed on the respective side face. In other words, a metal-free side face is comprised solely of the molded body120but it does not comprise any exposed metal.

Furthermore, “metal-free” may mean that the surface of the molded body120on the respective side face is free of contamination with metal particles. In particular, the molded body120may be fabricated by using a molding tool, wherein a molding cavity is formed by a top part and a bottom part. The side faces123of the molded body may comprise a small ridge at the interface between the top part and the bottom part of the molding tool as described in greater detail further below with respect toFIGS.4A and4B. “Metal-free” may mean that this ridge is free of any metal residue like leadframe residue.

As shown inFIG.1C, the molded body120may comprise a cut surface140. The cut surface140may e.g. be the place of an inlet or an outlet of the molding cavity (e.g. allowing mold material to flow into the molding cavity or allowing gas to flow out of the molding cavity, compareFIGS.5A and5B). After the mold material in the molding cavity has been cured, waste material filling the inlet or outlet may be cut off or stamped off, leaving the cut surface140.

The molded body120comprises a cut surface140at no more than one of the side faces123. The other side faces123, in particular the side face123opposite the side face123with the cut surface140are free of any cut surface.

The cut surface140may for example be arranged on one of the two side faces123that do not comprise the electrical contacts130. The cut surface140may have any suitable size and may for example occupy no more than 30%, no more than 20%, or no more than 10% of the surface area of the respective side face123.

The semiconductor chip110may e.g. be a power semiconductor chip, configured to operate with a high voltage and/or a high electrical current. According to an example, the semiconductor chip110may be arranged on one or more of the electrical contacts130. However, it is also possible that the semiconductor chip110is arranged on a die carrier that is not contiguous with an electrical contact130(as shown in the example ofFIG.1A). The semiconductor package100may comprise a single semiconductor chip110or it may comprise more than one semiconductor chip110. The electrical contacts130may e.g. be coupled to load electrodes (e.g. a source electrode and a drain electrode or an emitter electrode and a collector electrode) as well as to a control electrode (e.g. a gate electrode) of the semiconductor chip110.

The molded body120may e.g. comprise a polymer material or a resin. According to an example, the molded body120may also comprise a filler material, which may e.g. be configured to reduce the thermal resistance of the molded body120.

The semiconductor package100may for example be a small outline package. Neighboring electrical contacts130may for example have a distance of 1.27 mm. The side faces123without electrical contacts130may have a length l of 7 mm or more. The side faces123with electrical contacts may e.g. have a width w of 5 mm or more, 8 mm or more, or 10 mm or more.

The electrical contacts130may for example have a gull wing shape, wherein an outer tip of the electrical contacts130is bent downwards as shown inFIGS.1A and1C. The electrical contacts130may comprise or consist of a metal like Al, Cu, Fe or any other suitable material.

FIG.2shows a sectional view of a semiconductor package200, which may be similar or identical to the semiconductor package100, except for the differences described in the following.

In addition to the parts described with respect to the semiconductor package100, the semiconductor package200further comprises a coating210covering the electrical contacts130. The coating210may in particular cover every one of the electrical contacts130. The coating210may for example be a Sn coating, a NiPd coating, a NiAu coating or a coating comprising any other suitable metal or metal alloy. The coating210may for example be deposited on the electrical contacts130galvanically, by using vapor deposition or by using any other suitable technique.

The coating210completely covers every surface of each electrical contact130, except for an end face131at the tip of each electrical contact which is not covered by the coating210. In other words, the material of the electrical contacts130is exposed to the outside solely at the end faces131. The end faces131are not covered by the coating210because the electrical contacts130are still connected to a connecting bar at the end faces131during deposition of the coating210(this is explained in greater detail further below with respect toFIGS.3C and3D).

According to an example, the coating210may be configured to act as a protection layer for the electrical contacts130, in particular as an oxidation prevention layer. The coating210may have any suitable thickness, e.g. a thickness in the nanometer range or a thickness in the micrometer range.

FIGS.3A to3Dshow a semiconductor package300in various stages of fabrication. The semiconductor package300may be similar or identical to the semiconductor packages100and200.

FIG.3Ashows a leadframe310prior to arranging the semiconductor chip110on the leadframe, encapsulating the semiconductor chip110with the molded body120and singulating the semiconductor package300from the rest of the leadframe310.

The leadframe310comprises the electrical contacts130, a frame320and connecting bars330. The leadframe310may further comprise one or more die pads340for one or more semiconductor chips110.

The frame320may be arranged left and right of the other parts of the leadframe310and it may run along the length of the leadframe stripe. The frame320may be the part of the leadframe stripe that connects consecutive sections of the leadframe that are used in the fabrication of individual semiconductor packages300.

The electrical contacts130are connected to the frame320by the connecting bars330. The connecting bars330are connected to the electrical contacts130at the tip of each electrical contact130and the connecting bars330may be arranged essentially perpendicular to the electrical contacts130and the frame320.

According to an example, the electrical contacts130may further be connected to the frame320by connecting pieces350. The connecting pieces350may be arranged essentially parallel to the connecting bars330. In some embodiments, the connecting pieces350may take the form of a dambar. The connecting pieces350may be connected to the electrical contacts130at lateral sides of the electrical contacts130. During fabrication of the semiconductor package300, the connecting pieces350may be cut away. However, after the connecting pieces350have been cut away the electrical contacts130are still connected to the frame320by the connecting bars330.

FIG.3Bshows a stage of fabrication of the semiconductor package300, wherein the one or more semiconductor chips110have been arranged on the die pad(s)340and the molded body120has been formed.

As shown inFIG.3B, the molded body120does not come into contact with the frame320. Instead, a gap360is arranged between the molded body120and the frame320, completely separating the two. In particular, the leadframe310does not comprise any form of tie bar which at any point during the fabrication of the semiconductor package300bridges the gap360. The gap360may for example have a width of 200 μm or more, 300 μm or more, 400 μm or more, or 500 μm or more.

FIG.3Cshows the semiconductor package300in a stage of fabrication, wherein the connecting pieces350have been cut away. The electrical contacts130(and by extension, the semiconductor package300) are connected to the frame320by the connecting bars330and by dummy leads370, wherein a dummy lead370is arranged at each end of each connecting bar330. A first end of each dummy lead370is connected to one of the connecting bars330and an opposing second end of each dummy lead370is connected to the frame320.

As shown inFIG.3C, the dummy leads370may essentially have the same shape and the same spatial orientation as the electrical contacts130. The only difference between the dummy leads370and the electrical contacts130may be that the second end of each dummy lead370is attached to the frame320, whereas the second end of each electrical contact130is arranged within the molded body120.

The coating210may be deposited on the electrical contacts130in the state of fabrication shown inFIG.3C. Since the connecting pieces350have been cut away beforehand, the coating210may cover the surface of the electrical contacts130completely, except for the tips where the electrical contacts130are connected to the connecting bar330.

Furthermore, the electrical contacts130may be subjected to a forming process, for example a stamping process, in order to obtain a gull wing shape, as shown inFIG.3C. This forming process may e.g. be performed prior to depositing the coating210. The dummy leads370may also be subjected to the forming process and may therefore obtain the same gull wing shape as the electrical contacts130.

FIG.3Dshows the semiconductor package300after singulation from the frame320. Singulation comprises cutting the electrical contacts130away from the connecting bars330. Since in the state of fabrication shown inFIG.3Cthe semiconductor package300is connected to the frame320solely by the connecting bars330and dummy leads370, the singulation process does not require cutting at any other location.

FIG.4Ashows a view of the leadframe310along the arrow A inFIG.3A. InFIG.4Aa molding tool410is arranged around part of the leadframe310. The molding tool410forms a molding cavity420, wherein the electrical contacts130are arranged within the molding cavity420and the frame320is arranged outside the molding cavity420. A mold material may be allowed to flow into the molding cavity420in order to fabricate the molded body120. For this purpose, the molding tool410may comprise a single opening, e.g. at a side face123of the molded body120(compareFIG.5A).

The molding tool410may comprise an upper half411and a lower half412, wherein both halves411,412may be pressed together to form the molding cavity420. In particular, the upper half411and the lower half412may touch within the gap360of the leadframe310. The upper and lower halves411,412may be arranged in the gap360such that they do not come into contact with the frame320. Instead, the upper and lower halves411,412may be spaced apart from the frame by a distance d>0. For this reason, mold material filling the molding cavity420does not come into contact with the frame320. The leadframe310in particular comprises no tie bar reaching from the frame320into the molding cavity420.

FIG.4Bshows the fabricated molded body120after the molding tool410has been removed. Since the frame320is not clamped between the two halves411,412the molded body120does not comprise a pronounced mold flash in the plane of the leadframe310. Instead, the molded body120may e.g. comprise no more than a thin ridge430at the interface of the upper and lower halves411,412. A thickness of the ridge430may be much smaller than a thickness z of the leadframe310.

Since the molded body120does not come into contact with the frame320, the side faces123of the molded body120without electrical contacts130may be free of any contamination with metal particles. Such a contamination would occur if the frame320was clamped between the two halves411,412of the molding tool410such that the mold material comes into contact with the frame320. After curing of the mold material, the frame320would have to be removed from the molded body120, leaving behind a smear of metal particles on the surface of the molded body120. Such a metal particle contamination could reduce the creepage distance of the semiconductor package to a value smaller than the length1of the semiconductor package (compareFIG.1C).

Furthermore, since no tie bar connects the molded body120to the frame320no such tie bar has to be truncated or pulled out of the molded body120. For this reason, the metal-free side faces123do not comprise any residues of such a tie bar, i.e. no truncated tie bar part and also no cavity where a tie bar used to be.

FIG.5Ashows a schematic top down view of the molding tool410. The molding tool410comprises a single inlet510connected to the cavity420and configured to allow a mold material flow into the cavity420as indicated by the arrow.

FIG.5Bshows the molded body120after the mold material has been cured and the molding tool410has been removed. At the location of the inlet510there is a protrusion520formed of excess mold material attached to the molded body120. Removing the protrusion520from the molded body120may produce the cut surface140in the respective side face123of the molded body120(compareFIG.1C). The protrusion520may for example be cut away or stamped away.

The protrusion520may e.g. be removed while the semiconductor package300is still connected to the frame320or it may be removed after the semiconductor package has been singulated from the frame320.

Since the semiconductor package300is connected to the leadframe310by the dummy leads370prior to singulation, the protrusion520does not have to be configured to mechanically couple the semiconductor package300to the frame320. It is in particular not necessary to provide several protrusions, e.g. arranged on opposing side faces123of the molded body120, to mechanically couple the semiconductor package300to the frame320prior to singulation.

Not having more than one protrusion that needs to be removed may be beneficial because cutting or stamping the protrusion520may produce mold material particles which may sediment on the semiconductor package300, for example on the electrical contacts130. This may for example impair the electrical properties and/or the solderability of the electrical contacts130.

FIG.6is a flow chart of a method600for fabricating a semiconductor package according to one embodiment of this disclosure. The method600may for example be used to fabricate the semiconductor packages100,200and300.

The method600comprises at601an act of providing a leadframe comprising a die carrier, a plurality of electrical contacts, four dummy leads and a frame, wherein the die carrier and the plurality of electrical contacts are connected to the frame by the four dummy leads, at602an act of arranging a semiconductor chip on the die carrier, at603an act of molding over the semiconductor chip and the die carrier, thereby fabricating a molded body, the molded body comprising a top face and an opposing bottom face and four side faces connecting the top and bottom faces, wherein the plurality of electrical contacts is exposed on two of the side faces and wherein the other two side faces are metal-free side faces that do not come into contact with the leadframe, at604an act of covering the exposed electrical contacts with a coating, and at605an act of singulating the semiconductor package from the frame by cutting the four dummy leads.

The act of providing601the leadframe may for example comprise providing the leadframe310as shown inFIG.3A. The act of arranging602a semiconductor chip may e.g. comprise arranging the semiconductor chip110on the die pad340. The act of molding603may comprise fabricating the molded body120as e.g. shown inFIGS.4A,4BandFIGS.5A,5B.

According to an example, the act of molding603may be performed while the electrical contacts130are still connected to the frame320by the connecting pieces350, as shown inFIGS.3A and3B.

The act of covering604may comprise covering the electrical contacts130with the coating210as described with respect toFIG.2. The act of covering604may e.g. be performed after the act of molding603. The act of covering604may e.g. be performed after the connecting pieces350have been removed. This way, the exposed electrical contacts130may be completely covered by the coating210except for the tips which are still connected to the connecting bars330.

The act of singulating605may be performed after the act of covering604. According to an example, an act of bending the electrical contacts130and the dummy leads370may be performed prior to the act of singulating605in order to obtain the gull wing shape shown e.g. inFIGS.3D and3C. The act of bending may e.g. be performed after the act of covering604.

EXAMPLES

In the following, the semiconductor package and the method for fabricating a semiconductor package are further explained using specific examples.Example 1 is a semiconductor package, comprising: a semiconductor chip, a molded body encapsulating the semiconductor chip and comprising a top face and an opposing bottom face and four side faces connecting the top and bottom faces, and a plurality of electrical contacts arranged on two of the side faces of the molded body, wherein the other two side faces are metal-free side faces, and wherein the molded body comprises a cut surface at no more than one of the side faces.Example 2 is the semiconductor package of example 1, further comprising: a coating covering the electrical contacts such that no more than the tips of the contacts are left uncovered.Example 3 is the semiconductor package of example 1 or 2, wherein the metal-free side faces are free of any smear with metal particles.Example 4 is the semiconductor package of example 2, wherein the coating comprises or consists of Sn.Example 5 is the semiconductor package of one of the preceding examples, wherein the metal-free side faces have a length of 7 mm or more.Example 6 is the semiconductor package of one of the preceding examples, wherein the metal-free side faces are free of any cavity arranged in a plane comprising the electrical contacts.Example 7 is the semiconductor package of one of the preceding examples, wherein the electrical contacts comprise or consist of Cu.Example 8 is the semiconductor package of one of the preceding examples, wherein a length of the side faces comprising the electrical contacts is greater than a length of the metal-free side faces.Example 9 is the semiconductor package of one of the preceding examples, wherein a creepage distance along the metal-free side faces is 8 mm or more.Example 10 is the semiconductor package of one of the preceding examples, wherein a thickness of a mold flash at the metal-free side faces is smaller than a thickness of the electrical contacts, measured perpendicular to the top and bottom faces.Example 11 is a method for fabricating a semiconductor package, the method comprising: providing a leadframe comprising a die carrier, a plurality of electrical contacts, four dummy leads and a frame, wherein the die carrier and the plurality of electrical contacts are connected to the frame by the four dummy leads, arranging a semiconductor chip on the die carrier, molding over the semiconductor chip and the die carrier, thereby fabricating a molded body, the molded body comprising a top face and an opposing bottom face and four side faces connecting the top and bottom faces, wherein the plurality of electrical contacts is exposed on two of the side faces and wherein the other two side faces are metal-free side faces that do not come into contact with the leadframe, covering the exposed electrical contacts with a coating, and singulating the semiconductor package from the frame by cutting the four dummy leads.Example 12 is the method of example 11, wherein a gap is arranged between the metal-free side faces and the frame of the leadframe.Example 13 is the method of example 11 or 12, wherein the plurality of electrical contacts is arranged in two rows along the respective side faces of the molded body, and wherein the four dummy leads are arranged at both ends of both rows.Example 14 is the method of one of examples 11 to 13, wherein the four dummy leads are connected to the plurality of electrical contacts by connecting bars, the connecting bars being arranged at the tips of the electrical contacts and perpendicular to the electrical contacts and the four dummy leads.Example 15 is the method of example 14, wherein during the covering of the electrical contacts with the coating the semiconductor package is mechanically coupled to the frame solely by the connecting bars and dummy leads.Example 16 is the method of one of examples 11 to 15, further comprising: bending the plurality of electrical contacts and the four dummy leads such that the electrical contacts and the four dummy leads obtain a gull-wing shape.Example 17 is the method of one of examples 11 to 16, wherein the electrical contacts are coated such that no more than the tips of the electrical contacts are left uncovered by the coating.Example 18 is an apparatus comprising means for performing the method of one of examples 11 to 17.

While the disclosure has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure.