Patent Description:
In semiconductor devices, clip bonded packages are commonly used as lead frame arrangements to make connections from a semiconductor die to external contacts of the device. Clip bonded packages have a number of advantages over conventional wire bonded packages. For example, clip bonded packages are typically used for mechanically robust and reliable electrical connections to and from the semiconductor die in automotive applications. Furthermore, the conductive clip material may have increased thermal mass compared to the wire bond material and can thus act as a heat sink for the semiconductor die.

Existing known lead frame arrangements for semiconductor devices, such as the type shown in <FIG>, result in increased connection resistance between semiconductor die and the external leads. As shown in <FIG>, semiconductor device <NUM> comprises a semiconductor die <NUM> mounted on a die pad <NUM>. A clip member <NUM> electrically connects contact terminals on a top surface of the semiconductor die <NUM> to external leads <NUM>. As shown in <FIG>, the clip member is electrically connected to and mechanically bonded to the external leads <NUM> using a solder connection <NUM>. This solder connection <NUM> results in increased connection resistance which can result in increased device resistance. For example in a MOSFET semiconductor device, where the clip member is a source connection, the increased resistance may result in increased drain-source on resistance, Rdson.

Documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT> disclose prior art lead frame assemblies for a semiconductor chip.

Various example embodiments are directed to issues such as those addressed above and/or others which may become apparent from the following disclosure concerning improving lead frame arrangements for semiconductor devices.

In certain example embodiments, aspects of the present disclosure involve semiconductor devices comprising improved lead frame arrangements and a method of manufacturing such semiconductor devices.

The invention is disclosed by the appended claims.

So that the manner in which the features of the present disclosure can be understood in detail, a more particular description is made with reference to embodiments, some of which are illustrated in the appended figures. It is to be noted, however, that the appended figures illustrate only typical embodiments and are therefore not to be considered limiting of its scope. The figures are for facilitating an understanding of the disclosure and thus are not necessarily drawn to scale. Advantages of the subject matter claimed will become apparent to those skilled in the art upon reading this description in conjunction with the accompanying figures, in which like reference numerals have been used to designate like elements, and in which:.

In overview, a semiconductor device <NUM> prior to moulding and comprising a lead frame assembly <NUM> according to an embodiment is illustrated in <FIG>. The semiconductor device <NUM> generally comprises a die attach structure <NUM> and a clip frame structure <NUM>, forming the lead frame assembly <NUM>, and a semiconductor die <NUM> attached to both the die attach structure <NUM> and the clip frame structure <NUM>.

The die attach structure <NUM> is typically arranged for mounting a semiconductor die <NUM> thereon and providing support for the clip frame structure <NUM>. In addition the die attach structure <NUM> may, depending on the arrangement of contact terminals, such as source, gate or drain, of semiconductor die <NUM>, provide contact to a back-side or bottom contact of the semiconductor die <NUM>. The die attach structure <NUM> is typically formed of a metallic conductive material, such as copper. In this way the die attach structure <NUM> may provide a bottom external lead <NUM>, such as a drain contact or tab, to a back-side or bottom contact terminal arranged on the semiconductor die <NUM>. The bottom external lead <NUM> may extend outside of the moulded package material of the semiconductor device <NUM> to form a heat sink tab to the bottom of the semiconductor die <NUM>, as illustrated for example in <FIG>.

The semiconductor die <NUM> is fixedly arranged on the die attach structure <NUM>, and the clip frame structure <NUM> is fixedly connected to the semiconductor die <NUM> and the die attach structure <NUM>. In the embodiment of <FIG>, the clip frame structure <NUM> is formed of two distinct but integrally formed parts, namely: a die connection portion <NUM>; and a lead portion <NUM>. The die connection portion <NUM> may be generally rectangular in shape and/or may be dimensioned such that it substantially corresponds to the dimensions of a contact terminal on the top side of the semiconductor die <NUM> to which the die connection portion <NUM> is attached.

As discussed above, the bottom or backside contact terminal of the semiconductor die <NUM> may be fixedly attached to the die attach structure <NUM>. The semiconductor die <NUM> may be fixedly attached to and may be electrically connected, via a bottom contact terminal (not illustrated) to the die attach structure <NUM> using any suitable bonding material such as a solder or a conductive adhesive. The die connection portion of the clip frame structure <NUM> is fixedly attached to the contact terminal arranged on a top side of the semiconductor die <NUM>, using an appropriate bonding material, such as for example, a solder or a conductive adhesive.

The lead portion <NUM> is a continuous and merged section extending from the die connection portion <NUM>. The lead portion <NUM> is continuous in that forms a substantially elongate member extending away from and along the width of the die connection portion <NUM>. In this way, the lead portion <NUM> has a continuous width W and may be seen as a merged member, that is without bifurcation or plurality of finger like lead members, which extends substantially along the width of the die connection portion <NUM>. The lead portion <NUM> is arranged as a so-called "gull wing" lead having one or more angles or bends to allow the lead portion to contact the PCB. The lead portion <NUM> being continuous and merged may be arranged as a plate like member having the appropriate gull-wing bends formed therein.

The lead portion <NUM> can be dimensioned such that it aligns or corresponds to the footprint of the contacts on a PCB (not illustrated). By maximizing the width, W, of the lead portion <NUM> and thus the volume thereof (assuming a constant length and thickness of the lead portion <NUM>) current handling in terms of maximum allowable operating current, such as drain source current, of the clip frame structure <NUM> and semiconductor device <NUM> can be maximised. Likewise, the above discussed arrangement will minimise the spreading resistance of the clip frame structure <NUM> and thus reduce the on resistance of the semiconductor device <NUM>.

By arranging the lead portion in this way it is possible to reduce the package resistance of the lead frame assembly <NUM> and thus reduce the operating resistance, such as Rdson, of the semiconductor device <NUM>. However, the above arrangement does not significantly increase the inductance of the lead frame assembly <NUM>. For example, according to embodiments the resistance of the clip frame structure may be <NUM> mΩ with an inductance of <NUM> nH. Whereas, for a known arrangement the resistance of the clip frame structure may be <NUM> mΩ with an inductance of <NUM> nH.

The semiconductor die <NUM> and the clip frame structure <NUM> is then encapsulated using a moulding material <NUM> (as illustrated for example in <FIG>). The lead portion <NUM> and the bottom external lead <NUM> project through the mould compound <NUM> to allow the lead portion <NUM> and the bottom external lead <NUM> to contact an external carrier such as a PCB.

The clip frame structure <NUM> is typically formed from a single unitary sheet of metal, such as copper, which is formed or stamped to produce the desired structure. In this way the thickness of the die connection portion <NUM> and a lead portion <NUM> of the clip frame structure <NUM> may be equal. The choice of metal is entirely at the choice of the skilled person and may be chosen dependent on the required electrical characteristics of the lead frame assembly for the semiconductor device <NUM>.

<FIG> illustrate a further embodiment of the lead frame assembly <NUM>. Consistent with the arrangement described above with respect to <FIG>, the arrangement of <FIG> includes generally comprises a die attach structure <NUM> and a clip frame structure <NUM>, forming the lead frame assembly <NUM>, and a semiconductor die <NUM> attached to both the die attach structure <NUM> and the clip frame structure <NUM>.

The arrangement of <FIG> also includes a number of first slots or holes <NUM> formed through the continuous lead portion (<NUM>) and the bottom external lead <NUM>. The slots or holes <NUM> act as anchor or locking points for the mould compound <NUM> and allow for improved adhesion or attachment of the mould compound <NUM> to the lead frame assembly <NUM>. Improved adhesion of mould compound prevents can reduce stress and package cracking during lead forming, that is cutting and bending of the die connection portion <NUM> and or the bottom external lead <NUM> post moulding.

Second slots or holes <NUM> formed through the die connection portion <NUM> traverse or extend lengthways across the die connection portion <NUM>. This allows for both stress relief and solder protection.

In terms of stress relief, the holes or slots <NUM> formed in the die connection portion <NUM> reduce stress spreading across the surface of the die connection portion <NUM> as it is fixed to the terminal arranged on the top surface of the semiconductor die. In other words the holes or slots <NUM> distort the stress induced the die connection portion <NUM> so stress does not propagate across the die connection portion <NUM>. In terms of solder protection, the holes or slots <NUM> allow for gasses to escape from under the die connection portion <NUM> during solder reflow processes.

Third slots or holes <NUM> are also incorporated in the continuous lead portion <NUM> to prevent the leads from springing back, due to the elastic return of the metal after formation of the leads. This also makes the leads more flexible during board level temperature cycling which can prevent the solder joints of the leads to the PCB from breaking or cracking.

The arrangement of <FIG> and <FIG> also illustrate one or more optional lead end portions <NUM> arranged at one end of the lead portion <NUM> distal to the die connection portion <NUM>. The lead end portions <NUM> and the lead portion <NUM> may comprise one or more bends <NUM> intermediate the die connection portion <NUM> and an extremity of the lead end portions <NUM>, such that the leads are formed as so-called "gull wing" leads. The lead end portions <NUM> may be arranged in any standard lead geometry as required by the footprint of the contacts on a PCB. For example the lead geometry may be the Small Outline Integrated Circuit (SOIC) such as SO8, SO14, SO16 or any other appropriate package outline.

According to embodiments, clip frame structure <NUM> may form a source connection to a source terminal on top side of the semiconductor die <NUM>. A lead <NUM> may form a gate connection to a gate terminal also formed on the top side of the semiconductor die <NUM>. The bottom external lead <NUM> may form a drain connection to a drain terminal formed on the back side of the semiconductor die <NUM>. In this regard the semiconductor die <NUM> may be a field effect transistor.

Likewise, the semiconductor die <NUM> may be a bipolar junction transistor. The clip frame structure <NUM> may form a collector connection to a collector terminal on the top side of the semiconductor die <NUM>. The lead <NUM> may form a base connection to a base terminal also formed on the top side of the semiconductor die <NUM>. The bottom external lead <NUM> may form an emitter connection to an emitter terminal formed on the back side of the semiconductor die <NUM>.

<FIG>, illustrates the slots or holes <NUM> arranged in the bottom external lead <NUM> anchoring the mould compound <NUM> to the bottom external lead <NUM> so as to allow for improved adhesion or attachment of the mould compound <NUM> to the bottom external lead <NUM>.

<FIG> illustrate the process flow steps for manufacturing a semiconductor device according to embodiments.

As illustrated in <FIG>, the die attach structure <NUM> with a bottom external lead <NUM> extending therefrom is provided. The die attach structure <NUM> and bottom external lead <NUM> may be formed of any appropriate conductive material such as copper. The arrangement of <FIG> shows a single die attach structure <NUM>, however the skilled person will appreciate that a plurality of die attach structures may be arranged in a strip or matrix.

In the next step, as illustrated in <FIG>, a die attach material <NUM> is dispensed onto the die attach structure <NUM>. The die attach material <NUM> is arranged for fixedly mounting the semiconductor die <NUM> to the die attach material <NUM>, as illustrated in <FIG>. The die attach material <NUM> may be any appropriate adhesive material such as a solder or conductive adhesive.

Following placement of the semiconductor die <NUM>, a contact terminal attach material is dispended on the top side contact of the semiconductor die <NUM> for electrical and mechanical connection of the clip frame structure <NUM> to the semiconductor die <NUM> as illustrated in <FIG>. The die attach material may be applied by any appropriate process such as adhesive or solder printing or dispense.

Once the semiconductor die <NUM> is in place on the die attach structure <NUM>, the contact terminal attach material <NUM> is arranged on the one or more top contacts of the semiconductor die <NUM>. The clip frame structure <NUM> may then be arranged on the contact terminals, as illustrated in <FIG>. Whilst the arrangement of <FIG> illustrates a single clip frame structure <NUM> arranged on the semiconductor die <NUM>, the skilled person will appreciate that a plurality of such clip frame structures may be arranged in a strip or matrix corresponding to the plurality of die attach structures each having a semiconductor die arranged thereon. Following connection of the clip frame structure <NUM> the assembly undergoes solder re-flow to solidify the die attach material and the contact terminal attach material. Following re-flow, the assembly may be packaged in a mould material <NUM> as illustrated in <FIG>.

As illustrated in <FIG> the lead end portions <NUM> are formed by trimming the lead portion <NUM> and bending the leads to form the gull-wing arrangement. The process is completed in <FIG> by trimming of the bottom external lead <NUM>.

Claim 1:
A lead frame assembly for a semiconductor device, the lead frame assembly comprising:
a die attach structure (<NUM>) and a clip frame structure (<NUM>), the clip frame structure comprising:
a die connection portion (<NUM>) configured for contacting a contact terminal or a top side of the semiconductor die (<NUM>); and
a continuous lead portion (<NUM>) extending along the die connection portion (<NUM>);
wherein the continuous lead portion (<NUM>) is integrally formed with the die connection portion (<NUM>);
wherein the continuous lead portion (<NUM>) is a merged lead portion which extends substantially across the width of the die connection portion (<NUM>),
wherein the die connection portion (<NUM>) comprises a second hole or second holes (<NUM>) traverse or extend lengthways across the die connection portion (<NUM>),
characterized in that the continuous lead portion (<NUM>) comprises one or more first holes or slots (<NUM>) arranged to act as an anchor or locking points for a mould compound, and wherein the continuous lead portion (<NUM>) comprises one or more third holes or third slots (<NUM>) arranged to prevent the continuous lead portion (<NUM>) from springing back.