INTERCONNECT STRIPS

A method for forming integrated circuit (IC) packages includes mounting dies on a strip of interconnects and applying wire bonds in regions of the strip of interconnects proximate to mold shields. The method also includes adjusting the mold shields of the strip of interconnects. The method includes flowing a mold compound on the strip of interconnects to form a strip of IC packages. Mold injection pressure causes the mold compound to flow from a first end of the strip of interconnects across the strip of interconnects to a second end of the strip of interconnects, and the mold shields impede the flow of the mold compound through the regions of the strip of interconnects proximate to the mold shields. The method includes singulating the strip of IC packages to form the IC packages.

TECHNICAL FIELD

This disclosure relates to strips of interconnects for integrated circuit (IC) packages.

BACKGROUND

An interconnect (alternatively referred to as a lead frame) is a metal structure inside an integrated circuit (IC) package that carries signals from a die to the outside. The interconnect includes a die pad, where the die is placed, surrounded by leads, metal conductors leading away from the die to the external circuits. The end of each lead closest to the die ends in a bond pad. Small wire bonds connect the die to each bond pad. Mechanical connections fix these parts into a rigid structure, which makes the whole interconnect easy to handle automatically.

The die is glued or soldered to the die pad inside the interconnect, and then wire bonds are attached between the die and the bond pads to connect the die to the leads. In a process called encapsulation, a plastic case is molded around the lead frame and die, exposing only the leads. The leads are cut off outside the plastic body and any exposed supporting structures are cut away. The external leads are then bent (formed) to the desired shape. In various examples, interconnects are employed to manufacture a quad flat no-leads package (QFN), a quad flat package (QFP), or a dual in-line package (DIP).

SUMMARY

A first example relates to a method for forming IC packages. The method includes mounting dies on a strip of interconnects. The method also includes applying wire bonds in regions of the strip of interconnects proximate to mold shields. The method includes adjusting the mold shields of the strip of interconnects and flowing a mold compound on the strip of interconnects to form a strip of IC packages. Mold injection pressure causes the mold compound to flow from a first end of the strip of interconnects, across the strip of interconnects to a second end of the strip of interconnects, and the mold shields impede the flow of the mold compound through the regions of the strip of interconnects proximate to the mold shields. The method includes singulating the strip of IC packages to form the IC packages.

A second example relates to a strip of IC packages. The strip of IC packages includes a strip of interconnects comprising mold shields arranged in a center region of the strips of interconnects. The mold shields form a right angle or an acute angle. The strip of IC packages also includes dies mounted on the strips of interconnects and wire bonds in the center region of the strips of interconnects. The strip of IC packages includes a mold compound encapsulating the strip of interconnects, and the mold shields protrude out of the mold compound.

DETAILED DESCRIPTION

This description relates to a strip of IC packages and a method for forming integrated circuit (IC) packages from a strip of interconnects. The method includes mounting dies on the strip of interconnects. The strips of interconnects are a component of a frame of strips of interconnects. Wire bonds are applied to couple the dies to the interconnect and to couple dies together. In some examples, some of the wire bonds extend in a direction transverse (or nearly transverse) to a direction of a mold flow (e.g., a direction of flow of a mold compound).

The strips of interconnects include mold shields at a center region of the strips of interconnects. The mold shields are adjusted (e.g., bent) to form a right angle or an acute angle, such as an angle of 87.5 degrees with a 2.5 degree tolerance. A mold compound (e.g., plastic) is flowed on the strips of interconnects in a mold flow operation. The strips of interconnects are oriented horizontally, such that mold injection pressure causes the mold to flow from a first end of the strip of interconnects, across the strip of interconnects and to a second end of the strip of interconnects that opposes the first end of the strip of interconnects, and the mold shields impede the flow of the mold through regions of the strip of interconnects proximate to the mold shields. The mold shields protrude out from the mold compound. Accordingly, the mold shields operate as a marker for singulation.

The mold compound hardens to encapsulate the strip of interconnects and to form a strip of IC packages. In response to the hardening, the strip of IC packages is singulated to form IC packages. The singulation includes laser sawing the strip of IC packages with a laser saw. In some examples, two passes of the laser saw are implemented to remove the mold shields. By implementing the strip of interconnects, the frame of strips of interconnects is increased in density. More particularly, the mold shields obviate the need for other features, such as side gates, such that the strips of interconnects employ less space, thereby allowing for the increased in density. For instance, in some examples, there are 20 or more (e.g.,22) strips of interconnects in the frame of interconnects, and there are 7 interconnects on each strip of interconnects. Thus, there are 154 singulatable IC packages in the frame of strips of IC packages that utilize these strips of interconnects.

FIG.1illustrates a flowchart of an example method100for forming IC packages. The IC packages are formed from singulating IC packages from a strip of IC packages formed with a strip of interconnects. In some examples, the strip of interconnects is a component of a frame (array) of interconnects. The strip of interconnects is alternatively referred to as a bar of interconnects. In some examples, the strip of interconnects are a high density (HyDE) strip of interconnects. The interconnects in the strip of interconnects include pads for dies and pins for coupling the IC packages to external components. At110, dies are mounted on the strip of interconnects. In some examples, a single die is mounted on an interconnect of the strip of interconnects. In other examples, multiple dies are mounted on an interconnect of the strip of interconnects. The dies are mounted on the pads of the interconnects of the strip of interconnects.

The interconnects in the strip of interconnects include mold shields situated in a center region of the strip of interconnects. The mold shields are formed as tabs that extend parallel to a backplane of the strip of interconnects. At115, wire bonds are applied to electrically couple the dies to the interconnects of the strip of interconnects. In some examples, the wire bonds also electrically couple dies of a respective interconnect in the strip of interconnects. The wire bonds are positioned in the center region of the strip of interconnects. In some examples, the wire bonds, or some subset thereof, for each interconnect of the strip of interconnects are proximate to the corresponding mold shield.

At125, the mold shields are adjusted. Adjustment of the mold shields includes bending the mold shields. In some examples, the mold shields are bent to a right angle or an acute angle. More specifically, the mold shields are bent to form an angle of 87.5 degrees with a tolerance of 2.5 degrees. Thus, the angle in the mold shield is in a range of 90 degrees to 85 degrees.

At130, a mold compound, such as plastic, is flowed on the strip of interconnects to form a strip of IC packages in a mold flow operation. The interconnects are arranged horizontally, such that mold injection pressure pulls the mold compound across the strip of interconnects. The mold shields imped the mold flow (e.g., the flow of the mold compound) at the center region of the strip of interconnects. Moreover, the mold flow is unimpeded at a periphery of the strip of interconnects. This impeding of the mold flow reduces a pressure of the mold compound on the wire bonds, because the wire bonds are also at the center region of the strip of interconnects. Moreover, the mold compound flows and hardens and encapsulates the strip of interconnects to form the strip of IC packages. The mold shields protrude out of the mold compound, such that a location of the mold shields is readily identified.

At135, IC packages in the strip of IC packages are singulated. Singulation of the strip of the IC packages includes applying a laser saw to the strip of IC packages. In some examples, the mold shields are removed with two passes of the laser saw. In some examples, the resultant IC packages are dual in-line IC packages. In other examples, the resultant IC packages are dual flat no leads (DFN) IC packages.

Utilization of the mold shields obviates the need for features such as side gates to control the flow of the mold compound. Instead, the mold shields impede the flow of mold compound, such that a higher density of interconnects are enabled. For example, in a conventional approach using side gates, there are usually 16 strips of interconnects in a frame of strips of interconnects. Conversely, by including the mold shields, the number of interconnects in the strip of interconnects is increased to 20 strips of interconnects or more (e.g., 22 strips of interconnects) in a frame of strips of interconnects.

FIGS.2,3A and3Billustrate stages of a method for adjusting a mold shield in a strip of interconnects and for flowing a mold compound. For purposes of simplification of explanation,FIGS.2,3A and3Bemploy the same reference numbers to denote the same structure.

At200, in a first stage, as illustrated inFIG.2, a strip of interconnects300is provided. The strips of interconnects300is a high density (HyDe) strip of interconnects. The strip of interconnects includes a first interconnect304and a second interconnect308. The first interconnect304and the second interconnect308include pads312for mounting dies316. In the example illustrated, 4 dies316have been mounted on the pads312of the second interconnect308, but there are no dies mounted on the first interconnect304.

The second interconnect308includes wire bonds320(only some of which are labeled) that electrically couple the dies316to leads324(only some of which are labeled) of the second interconnect308. Some wire bonds326couple the dies316together. These wire bonds326extend in a direction transverse or nearly (e.g., a tolerance of +/−2%) transverse to a direction of mold flow indicated by an arrow330(e.g., a direction of flow of a mold compound).

The first interconnect304and the second interconnect308include a mold shield328. The mold shield328is a bendable tap arranged on and end and center of a periphery of the first interconnect304and the second interconnect308. The wire bonds326that extend in the direction transverse to the mold flow direction330are located in a center region of the second interconnect308. In an un-bended condition The mold shields328extend in a direction parallel to a backplane of the strip of interconnects300and in a direction parallel to the mold flow direction330. In some examples, in the un-bended condition, the mold shields328are 1.57 millimeters (mm) long, such that the first interconnect304and the second interconnect308are spaced about 1.57 mm apart.

At210, in a second stage, as illustrated inFIGS.3A and3B, the mold shields328are adjusted to imped the flow of the mold compound.FIG.3Billustrates a cross-sectional view of the interconnects300taken along line b-b. As illustrated inFIG.3B, the adjustment includes bending the mold shield328to form an angle between 90 degrees and 85 degrees. Thus, in some examples, the mold shield328is bent to form an 87.5 degrees, with a tolerance of 2.5 degrees. In the bent condition, the mold shield328includes a base portion332and a bent portion336. Thus, the mold shield328is bent such that the bent portion336is at an angle between 90 degrees and 85 degrees with respect to the base portion332. The base portion332has a length, for example of about 0.5 millimeters (mm). Moreover, the bent portion336has a length of about 1.07 mm. Unless otherwise stated, in this description, ‘about’ preceding a value means+/−10 percent of the stated value.

Also at210, a mold compound340illustrated inFIG.3Bflows in the mold flow direction330. In the example illustrated, it is presumed that the strip of interconnects300is oriented horizontally, such that mold injection pressure draws the mold compound from a first end of strip of interconnects300across the strip of interconnects300and to a second end (opposing the first end) of the strip of interconnects300, and in the direction of the mold flow direction330. As illustrated inFIG.3Athe flow of the mold compound340is impeded by the mold shield328and diverted to directions indicated by the arrows344and348. This impeding and redirection reduces a compressive force of the flowing mold compound340in the center region of the strip of interconnects300. Accordingly, the compressive force applied to the wire bonds326is reduced, thereby reducing a probability that the mold flow will damage the wire bonds326.

As illustrated inFIG.3B, after hardening, the mold compound340encapsulates the strip of interconnects300to form a strip of IC packages. The mold compound340has a thickness of about 1.016 mm on both sides of the strip of interconnects300. Accordingly, the thickness of the mold compound340on one side of the strip of interconnects is less than a length of the bent portion336of the mold shield328, such that a portion of the mold shield328protrudes out of the mold compound340, after the mold compound has hardened.

As demonstrated inFIGS.3A and3B, the mold shields328reduce the compressive force applied by the mold compound340to the wire bonds326that extend transverse to the mold flow direction330. This obviates the need for relatively large features such as side gate that are employed in a conventional approach. Accordingly the number strips of interconnects300in a frame of strips of interconnects is increased.

FIGS.4-6illustrate stages of a method for encapsulating a strip of interconnects in a mold compound and for singulating IC packages. For purposes of simplification of explanation,FIGS.4-6employ the same reference numbers to denote the same structure. Moreover,FIGS.4and5include a scale to show the flow of a mold compound flow as a function of time.

At400, in a first stage, as illustrated inFIG.4, a strip of interconnects500is provided. The strip of interconnects500is employable to implement the strip of interconnects300illustrated inFIGS.2,3A and3B. The strip of interconnects500include mold shields504that are in the bent condition. The strip of interconnects also includes dies508that are coupled with wire bonds512. At400, a mold compound516flows in a mold flow direction indicated by an arrow520. The wire bonds512extend in a direction transverse (or nearly transverse) to the mold flow direction520. The strip of interconnects300is oriented horizontally, such that the mold flow direction520is across the strip of interconnects300, and mold injection pressure causes the mold compound516to flow.

At410, in a second stage, as illustrated inFIG.5, the mold compound516has continued to flow in the mold flow direction520. However, as illustrated, the mold shields504impedes the flow of the mold compound near a center region of the strip of interconnects500. More particularly, as illustrated inFIG.5, in a region524below a mold shield504, there is less mold compound516in a region proximate to the mold shields504(the center region) than on peripheral regions of the strip of interconnects500. Thus, this reduction in mass reduces a compression force applied by the flowing mold compound. Further, as illustrated, the wire bonds512are proximate to the mold shields504and to the region524. Thus, the compressive force of the mold compound516applied to the wire bonds512proximate to the region524and the mold shields504is similarly reduced. This reduces a chance that the flowing of the mold compound516will damage the wire bonds512. Additionally, as demonstrated, the mold shields504are sufficiently long to protrude beyond the mold compound516. The mold compound hardens, such that the strip of interconnects500is converted to a strip of IC packages526.

Accordingly, as demonstrated inFIGS.4and5, the mold shields504reduce the compressive force applied by the mold compound516to the wire bonds512that extend transverse to the mold flow direction520. This obviates the need for relatively large features such as side gates that are employed in a conventional approach. Accordingly the number of interconnects in the strip of interconnects500is increased.

At420, in a third stage, as illustrated inFIG.6, the strip of IC packages526is singulated to provide IC packages. To singulate the strip of IC packages, a laser saw530makes a first cut534below a mold shield504and a second cut538above the mold shield504(or vice versa) for each mold shield504. Moreover, the mold shields504operate as guides for aligning the laser saw530. In this manner, the mold shields504are removed without the laser saw530cutting directly through a mold shield504. The resultant IC packages are dual in-line IC packages with pins542(only some of which are labeled) on opposing sides.

FIG.7illustrates a frame600of strips of IC packages604. The strips of IC packages604are employed to implement the strip of IC packages526ofFIGS.5-6. Each interconnect includes a mold shield608(only some of which are labeled) to impede the flow of a mold compound encapsulating the strips of IC packages604. The strips of IC packages604have interdigitated pins. Moreover, in the example illustrated, there are 7 interconnects in each strip of IC packages604, and there are 22 strips of IC packages604in the frame600of strips interconnects of IC packages604, such that there are 154 IC packages604in the frame600of strips of IC packages604.

IC packages are formed by singulating the strips of IC packages604. More specifically, a laser saw (e.g., the laser saw530ofFIG.6) makes cuts as indicated by the lines612. Moreover, by avoiding the use of features such as side gates, the number of strips of IC packages604can be increased to 22, such that the frame600of strips of interconnects is employable to singulate the 154 IC packages.