CN105895612B

CN105895612B - Semiconductor device with heat dissipating lead frame

Info

Publication number: CN105895612B
Application number: CN201510097811.2A
Authority: CN
Inventors: 葛友; 赖明光; 王志杰
Original assignee: NXP USA Inc
Current assignee: NXP USA Inc
Priority date: 2015-01-15
Filing date: 2015-01-15
Publication date: 2020-04-24
Anticipated expiration: 2035-01-15
Also published as: CN105895612A

Abstract

The present invention relates to a semiconductor device with a heat dissipating lead frame. A packaged semiconductor device has a top and a bottom and includes a leadframe, a die, and an encapsulant encapsulating the die and a majority of the leadframe. The leadframe includes a die pad on which the die is mounted, leads electrically connected to the die, e.g., with bonding wires, and a die pad extension extending fan-like from the die pad. Each die pad extension has a proximal end segment and a distal end segment. The distal segment is interlaced with the lead. The bottom of the die pad and the proximal segment of the extension may be exposed from the bottom of the device. The top of the device may have a notch corresponding to the extension and portions of the distal segment may be exposed and bent into a corresponding notch in the top of the device.

Description

Semiconductor device with heat dissipating lead frame

Technical Field

The present invention relates to Integrated Circuit (IC) packages, and more particularly, to semiconductor devices with heat dissipating lead frames.

Background

A leadframe is an aggregate of metal leads and possibly other elements such as die paddle or flag and power bars, which are used to assemble one or more IC dies into a semiconductor package in a single packaged semiconductor device. The leadframe may have support structures (e.g., rectangular leadframes) that hold the components in place prior to assembly to the packaged device. The support structure may be removed in whole or in part during assembly. The term "leadframe" as used herein may be used to refer to an aggregate of components, whether or not these support structures are present, before or after assembly.

Fig. 1A is a plan view of a conventional lead frame 100. Fig. 1B is a cross-sectional view of the lead frame 100 of fig. 1A along the cut line Y-Y. The leadframe 100 is a patterned sheet metal cutout (cut-out) that includes a die pad or flag 101 and lead fingers 102(1) through 102(44) that wrap around the die pad 101. The leadframe 100 may be used in an IC package, such as a Quad Flat Package (QFP). The die pad 101 is used to mount at least one IC die (not shown) during assembly, wherein the die is attached to the die pad 101, for example by an adhesive (not shown). During assembly, the lead fingers 102, which will be converted into respective leads, are used to provide electrical connections between the device internal components of the die and the device external components.

The leadframe 100 has 11 lead fingers 102 on each side. The lead fingers 102(11 × (i-1) +1) to 102(11 × i) are supported by respective barrier rods (dam bar)103(i), where i is an integer from 1 (inclusive) to 4 (inclusive). For example, the lead fingers 102(1) to 102(11) are supported by the blocking rod 103(1), and the lead fingers 102(12) to 102(22) are supported by the blocking rod 103 (2). More generally, the relationship of QFPs can be described by the barrier bar numbered i supporting lead fingers numbered N × (i-1) +1 to N × i, where N is the number of lead fingers on each side. The blocking bar 103 is formed in a rectangular shape, which is supported at its corners by respective connecting bars 104(1) to 104(4), which hold the blocking bar 103 and the lead fingers 102 in place with respect to the die pad 101. Each tie bar 104 has a corresponding tie bar down-set 105 that includes two bends to allow the die pad 101 to lie on a first plane and the lead fingers 102 to lie on a second plane that is parallel to the first plane and at a different height from the first plane, as shown in fig. 1B.

During assembly, a die (not shown) is mounted on the die pad 101 and then electrically connected to the lead fingers 102 using, for example, bonding wires as known in the art.

After wire bonding, the assembly including the die, leadframe 100, and bonding wires is typically encapsulated in an encapsulant material (e.g., a mold compound), with the distal ends of the lead fingers 102 exposed. In some packages, the bottom of the die pad 101 is also left exposed, which allows for more efficient heat dissipation from the die.

In a typical assembly process, the leadframe 100 is only one leadframe in a one-or two-dimensional array of leadframes, where two adjacent leadframes in the array may share additional support structures (not shown). After encapsulation, the assembly body is singulated by saw cutting or laser cutting into individual IC devices, which also removes (if any) the additional support structure, and cuts off the inner lead segments of the barrier rods 103 to electrically insulate the lead fingers 102 from each other and to electrically insulate the lead fingers 102 from the connection strips 104. The lead fingers 102 of each IC device may also be trimmed (trim) and shaped, such as so-called gull-wing or j-leads, to form leads for packaging the semiconductor device, which is then to be mounted on a Printed Circuit Board (PCB). The bottom of the die pad 101 may be left exposed or mounted on a heat sink or on a thermally conductive element on the PCB.

As integrated circuits become more complex and include more transistors, they generate more heat. Thus, it is advantageous: the semiconductor device package has a lead frame so that it can dissipate heat well.

Drawings

Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals refer to similar or identical elements. It is noted that the elements of the drawings are not to scale.

Fig. 1A is a plan view of a conventional lead frame;

FIG. 1B is a cross-sectional view of the lead frame of FIG. 1A;

fig. 2A is a plan view of a lead frame according to one embodiment of the present invention;

FIG. 2B is a cross-sectional view of the lead frame of FIG. 2A;

fig. 3 is a plan view of an assembly including the leadframe of fig. 2A and 2B after mounting a die on a die pad and wire bonding the die to the lead fingers;

fig. 4 is a plan view of a packaged device corresponding to the assembly of fig. 3 after encapsulation, singulation, and wire trimming and shaping;

FIG. 5 is a bottom view of the packaged device of FIG. 4; and

fig. 6 is a side cross-sectional view of the packaged device of fig. 4 along cut line z-z after additional shaping.

Detailed Description

Detailed illustrative embodiments of the invention are disclosed herein. However, specific structural and functional details are disclosed herein for the purpose of describing example embodiments of the present invention only. Embodiments of the invention may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention.

As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "has," "having," "includes," and/or "including" specify the presence of stated features, steps, or components, but do not preclude the presence or addition of one or more other features, steps, or components. It should also be noted that, in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures.

In one embodiment of the invention, the leadframe includes a die pad extension that is fan-out (fan out) from the die pad. The extensions both extend the thermally conductive area of the bottom of the corresponding package and allow heat to dissipate from the sides and top of the package with a sufficiently long extension and suitable assembly.

Referring now to fig. 2A, shown is a plan view of an exemplary leadframe 200 according to one embodiment of the invention. Fig. 2B is a cross-sectional view of the lead frame 200 of fig. 2A along the tangent line z-z. Elements of the lead frame 200 that are substantially similar to corresponding elements of the lead frame 100 of fig. 1A-1B are similarly labeled, but with different prefixes.

The lead frame 200 includes a die pad 201, a plurality of lead fingers 202 (in this example, the lead frame has 44 lead fingers) surrounding the die pad 201, four blocking bars 203, four connecting bars 204, and four under-connecting-bar setting devices 205. These elements are substantially identical to the corresponding elements of leadframe 100. The leadframe 200 further includes a plurality of die pad extensions 206 (40 die pad extensions 206 in this example) that fan out from the die pad 201 and extend to the outer edge of the leadframe 200.

In the embodiment shown, leadframe 200 has ten (10) die pad extensions 206 on each side. The extension portions 206(10 × (i-1) +1) to 206(10 × i), and the lead fingers 202(11(i-1) +1) to 202(11 × i), where i is an integer from 1 (inclusive) to 4 (inclusive), are supported by the respective blocking rods 203 (i). For example, the die pad extensions 206(1) to 206(10) and the lead fingers 202(1) to 202(11) are supported by the barrier rods 203(1), and the extensions 206(11) to 206(20) and the lead fingers 202(12) to 202(22) are supported by the barrier rods 203 (2). More generally, the relationship of QFPs can be described as barrier bar numbered i supporting die pad extensions numbered N × (i-1) +1 to N × 1 (where N is the number of extensions per side) and lead fingers numbered M (i-1) +1 to M × 1 (where M is the number of lead fingers per side). Along each blocking rod 203, the lead fingers 202 are interleaved with the extensions 206, forming an interleaved pattern along the blocking rod 203. The distal ends of the die extensions 206 extend from the respective barrier rods to the same extent as the distal ends of the lead fingers 202.

Die pad extension 206 has a corresponding proximal segment 206p and a connected distal segment 206 d. Each proximal extension segment 206p flares out from the die pad 201 and may widen as it extends outward from the die pad 201. Each distal extension segment 206d is substantially parallel to the adjacent lead finger 202 on their support stop bar 203. At some point along each die pad extension 206 is a corresponding under-extension fixture 207, in this embodiment, the under-extension fixture 207 is at the end of a proximal section 206p that is connected to a distal section 206 d. It should be noted that in other embodiments, the under-extension-providing device 207 may be located elsewhere on the proximal extension segment 206p and/or the distal extension segment 206 d. The under-extension-set-up 207, similar to the under-bar-set-up 205, allows for (i) at least a portion of the proximal extension segment 206p to lie in a first plane with the die pad 201, and (ii) at least a portion of the distal extension segment 206d to lie in a second, different plane with the lead finger 202.

Fig. 3 is a plan view of an assembly 300 including the leadframe 200 of fig. 2A and 2B after a die 301 is mounted on the die pad 201 and the die 301 is electrically connected to the lead fingers 202 using bonding wires 302. Each bonding wire 302 connects a bonding pad (not shown) on the die 301 to a corresponding lead finger 202. For example, wire bonds 302(1) electrically connect the connection pads on die 301 to lead fingers 202 (1).

Fig. 4 is a plan view of a packaged semiconductor device 400 corresponding to assembly 300 of fig. 3 after packaging, singulation, and trimming and shaping of lead fingers 202. Fitting body 300 is encapsulated by encapsulating material 401 and blocking rod 203 is removed.

Fig. 6 is a cross-sectional side view of the packaged device 400 of fig. 4 along the cut line Z-Z. The lead fingers 202 are bent into a gull-wing shape for attachment to a corresponding Printed Circuit Board (PCB) (not shown). As can be seen, the die 301 is attached to the die pad 201 using a die attach paste 601.

The top of the packaged device 400 has a channel-like recess 402 in the encapsulation material 401 corresponding to the die pad extension 206. The exposed portions of the die pad extensions 206 extending from the encapsulated packaged device 400 are bent upward and into the corresponding recesses 402. In particular, a distal segment 206d of extension 206 (e.g., distal segment 206d (5)) is bent upward and into a corresponding one of notches 402 (e.g., notches 402 (5)). The bent extensions 206 allow heat generated by the encapsulated die 301 to dissipate from the sides and top of the packaged device 400, and additionally from the bottom of the packaged device 400. One method of embedding the extension 206 into the recess 402 is to first form the recess 402 (during the molding process) and then bend the extension 206 into the recess 402. Alternatively, the extension 206 may be bent into place prior to molding and then the notch 402 formed around the extension 206, in which case some additional finishing step (such as grinding) may be necessary to expose the extension 206 to improve its heat dissipation capability.

Fig. 5 is a bottom view of the packaged device 400 of fig. 4. The bottom of die pad 201 is exposed, as is a portion of proximal segment 206p of die pad extension 206. The exposed portion of die pad extension 206 helps to improve heat dissipation from die 301 through the bottom of device 400 as compared to heat dissipation from die pad 201 alone.

Embodiments of the invention are described herein in which the top of the packaged device has a recess corresponding to the die pad extension. However, the present invention is not limited thereto. In some alternative embodiments, the top of the packaged device does not have any recess to accommodate the die pad extension. In some embodiments, the die pad extension is bent over onto the top of the packaged device without a notch. In some embodiments, the die pad extensions are not bent to the top of the packaged device. In some embodiments, the die pad extensions do not extend out from the packaged device.

Embodiments of the invention are described herein in which a leadframe may be used in a quad-package device (e.g., a QFP device). However, the present invention is not limited to packaged devices having leads on four sides. In some alternative embodiments, the lead frame may be used for packaged devices having leads on both sides (e.g., small integrated circuit (SOIC) devices), with corresponding modifications as would be understood by one of ordinary skill in the art.

Embodiments of the present invention are described herein with exemplary numbers and shapes of lead fingers and die pad extensions. However, the present invention is not limited thereto. In alternative embodiments, lead frames with different numbers of lead fingers and/or die pad extensions are formed in the same or different shapes.

Embodiments of the present invention are described herein in which a die is electrically connected to a lead finger by wire bonding. However, the present invention is not limited thereto. The die may be electrically connected to the lead fingers using any suitable technique.

Embodiments of the invention are described herein in which, after trimming, the distal ends of the die pad extensions extend out of the packaged device the same distance as the adjacent leads. However, the present invention is not limited thereto. In some alternative embodiments, one or more die pad extensions extend further outward from the packaged device than adjacent leads. In some alternative embodiments, one or more die pad extensions terminate closer to the packaged device than adjacent leads. In some alternative embodiments, the die pad extension does not reach the blocking rod and terminates prior to reaching the blocking rod. Thus, in these embodiments, the distal segment of the die pad extension is not exposed and does not extend from the packaged device. In some embodiments, the die pad extension does not include an under-extension fixture.

Embodiments of the invention are described herein in which die pad extensions are interleaved with the lead fingers of each blocking bar of a lead frame, wherein no two die pad extensions are adjacent to each other and no two lead fingers are so adjacent on each side of the die. However, the present invention is not limited thereto. In alternative embodiments, the number and pattern of fan-shaped extensions extending out of the die pad have different relationships with adjacent lead fingers. In some alternative embodiments, the relationship between the die pad extensions and the lead fingers may be irregular.

It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims.

Reference herein to "one embodiment" or "an embodiment" is intended to: a particular feature, structure, or characteristic described in connection with the embodiments may be included within at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same is true for the use of the word "embodiment".

Unless otherwise expressly stated, each numerical value and range should be construed as about, as if the word "about" or "approximately" were used before the numerical value or range. As used in this application, the word "connected," unless expressly stated otherwise, is intended to cover both direct and indirect connections between two elements.

The use of figure numbers and/or reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter for facilitating an understanding of the claims. Such use should not be construed as: the scope of these claims is limited to the embodiments shown in the respective figures.

The embodiments covered by the claims in this application are not limited to the following embodiments: (1) the embodiments implemented by this specification, and (2) the embodiments that correspond to statutory subject matter. Embodiments that cannot be realized and embodiments that correspond to illegitimate subject matter are not expressly claimed even if they fall within the scope of the present claims.

In this specification, including any claims, the word "each" may be used to refer to one or more particular features of a plurality of the aforementioned elements or steps. The recitation of the word "each" when used with the open-ended word "comprising" does not exclude additional, unrecited elements or steps. Thus, it is to be understood that an apparatus may have additional, unrecited elements and a method may have additional, unrecited steps, wherein the additional, unrecited elements or steps are devoid of one or more specific features.

Although the steps of the following method claims are expressed in a particular order and with corresponding labeling, unless the claim recitations otherwise imply a particular order of implementing some or all of those steps, those steps are not necessarily intended to be limited to being implemented in that particular order. The abstract included in this application is provided with the understanding that it is not used for interpretation of the claims.

Claims

1. An apparatus comprising a lead frame for a packaged semiconductor device, the lead frame comprising:

a die pad;

a plurality of lead fingers; and

a plurality of die pad extensions extending fan-out from one or more sides of the die pad, wherein:

each die pad extension includes a proximal extension segment and a connected distal extension segment;

the proximal extending section extends out of the die pad in a fan shape; and is

The distal extension segment is substantially parallel to an adjacent lead finger;

the device further comprises:

a die attached to the die pad and electrically connected to the lead fingers; and

an encapsulation material encapsulating the die and at least a portion of the leadframe, thereby:

a bottom of the die pad and at least a portion of the die pad extension are exposed from a bottom plane of the encapsulant material; and is

At least a portion of the distal extension segment of each die pad extension is exposed and extends out from the encapsulant material.

2. The apparatus of claim 1, wherein the leadframe further comprises:

one or more blocking bars connected to hold the lead fingers in place relative to the die pad, wherein each blocking bar supports a respective subset of the plurality of lead fingers.

3. The apparatus of claim 2, wherein:

the set of connected blocking bars comprises four blocking bars arranged to form a rectangular frame; and is

Each die pad extension of a subset of the plurality of die pad extensions terminates inside the rectangular frame without contacting a blocking rod; and wherein:

the apparatus also includes four connecting bars, each connecting a corner of the die pad to a corresponding corner of the rectangular frame.

4. The apparatus of claim 2, wherein: each blocking rod supports a respective subset of the plurality of die pad extensions.

5. The apparatus of claim 1, wherein:

the die pad is located on a first plane;

the lead fingers are located on a second plane that is parallel to and at a different height than the first plane; and is

Each die pad extension includes under-extension provisions positioned along the die pad extension such that a first section of the die pad extension is located on the first plane and a second section of the die pad extension is located on the second plane.

6. The device of claim 1, wherein the proximal extension segment widens as it extends outwardly from the die pad.

7. The device of claim 1, wherein a top surface of the encapsulating material includes a recess that receives an exposed portion of the distal extension segment.

8. The device of claim 1, wherein the die pad extensions are interleaved with the lead fingers.

9. An integrated circuit device, comprising:

a lead frame including a die pad, a plurality of leads surrounding and electrically insulated from the die pad, and a plurality of die pad extensions extending in a fan-like fashion from one or more sides of the die pad;

a semiconductor die attached to the die pad and electrically connected to the leads; and

an encapsulation material encapsulating the die and at least the encapsulated segment of each of the plurality of leads and die pad extensions,

wherein:

each of the leads includes an exposed segment;

each of the die pad extensions comprises an exposed segment;

the die pad is exposed from a bottom plane of the encapsulant material; and is

The exposed segment of each of the die pad extensions is bent upward and over the top surface of the encapsulant material.

10. The device of claim 9, wherein:

the encapsulant material includes a recess in a top surface; and is

Each exposed segment of each of the die pad extensions is bent and into a corresponding recess in the top surface of the encapsulation material.