Patent Application
20140374892
The present invention relates to integrated circuit packaging and, more particularly, to a lead frame and a semiconductor device packaged with the lead frame and method of packaging a semiconductor die.
A semiconductor die is an integrated circuit formed on a semiconductor wafer, such as a silicon wafer. Such a die is typically cut from the wafer and packaged, often using a lead frame. The lead frame is a metal frame, usually of copper or nickel alloy, that supports the die and provides external electrical connections for the packaged die or chip. The lead frame usually includes a flag (die pad), and associated proximal lead fingers (leads). The semiconductor die is attached to the flag and bond pads on the die are electrically connected to the lead fingers of the lead frame with bond wires. The die and bond wires are encapsulated with a protective encapsulation compound to form a semiconductor package. The encapsulation compound defines the package body. The lead fingers either project outwardly from the body or are at least flush with the body so they can be used as terminals, allowing the semiconductor package to be electrically connected directly to other devices or to a printed circuit board (PCB).
Semiconductor dies are being fabricated with an increased functionality, which requires an increased pin count, but at the same time, it is still desirable to have a small package size, making it difficult to accommodate additional pins (external terminals). This is partly because of improved silicon die fabrication techniques that allow die size reductions. However, the number of lead fingers is limited by the size of the package and the pitch of the lead fingers. When the flag (die pad) is downset from the lead fingers, the lead frame and angled sections of the associated tie bars are located in a recess and slots of a lead frame support that is typically a heater block. However, some of the lead fingers can be located relatively close to the tie bars and due to positioning tolerances (or indexing inaccuracy) a bonding end of a lead finger may be unsupported over one of the slots. This unsupported bonding end is subject to stress, bounce and bending during wire bonding. Consequently, this may lead to poor quality or faulty wire bonds especially when more than one wire bond is required at the unsupported bonding end. Thus, it would be advantageous to improve bond quality for currently unsupported bond ends (lead tips).
The invention, together with objects and advantages thereof, may best be understood by reference to the following description of preferred embodiments together with the accompanying drawings in which:
The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention, and is not intended to represent the only forms in which the present invention may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the invention. In the drawings, like numerals are used to indicate like elements throughout. Furthermore, terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that module, circuit, device components, method steps and structures that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such module, circuit, steps or device components. An element or step proceeded by “comprises” does not, without more constraints, preclude the existence of additional identical elements or steps that comprises the element or step.
Certain features in the drawings have been enlarged for ease of illustration and the drawings and the elements thereof are not necessarily in proper proportion. Further, the invention is shown embodied in a quad flat pack (QFP) type package. However, those of ordinary skill in the art will readily understand the details of the invention and that the invention is applicable to all leaded package types and their variations.
In one embodiment, the present invention provides for a frame member surrounding a die pad. There are tie bars attaching the die pad to the frame member, the tie bars being bent so that die pad is downset from the frame member. There are intermediate lead fingers extending from the frame member towards the die pad, the intermediate lead fingers each having a bonding end near the die pad. One outer lead finger is adjacent a respective edge of each one of the tie bars, and each outer lead finger extends from the frame member towards the die pad. Each outer lead finger includes a transverse region coupling two spaced longitudinal regions and the two spaced longitudinal regions each have a bonding region near the die pad.
In another embodiment, the present invention provides for a method of forming a semiconductor die package, the method includes providing a lead frame with a frame member surrounding a die pad, the lead frame having tie bars attaching the die pad to the frame member. The tie bars have an angled section that downsets die pad from the frame member, and intermediate lead fingers extend from the frame member towards the die pad. There is an outer lead finger adjacent a respective edge of each one of the tie bars, and each outer lead finger extends from the frame member towards the die pad. Also, each outer lead finger includes a transverse region coupling two spaced longitudinal regions each having a bonding region near the die pad. The two spaced longitudinal regions are a first longitudinal region and second longitudinal region located between the first longitudinal region and one of the tie bars.
The method also includes attaching a semiconductor die to the die pad and selectively electrically coupling, with bond wires, connection pads of the semiconductor die to the bonding regions of each outer lead finger. This coupling is characterized by no more than one of the bond wires is bonded to the bonding region of the second longitudinal region. The method further includes encapsulating the semiconductor die and bonding regions with an encapsulating compound. There is then performed a process of detaching from the frame member the tie bars, the intermediate lead fingers, and each outer lead finger to thereby provide the semiconductor die package.
In another embodiment, the present invention provides for semiconductor die package including a semiconductor die attached to a die pad. There are intermediate lead fingers extending from a periphery of the package towards the die pad, the lead fingers intermediate each having a bonding end near the die pad. There is an outer lead finger adjacent a respective edge of each one of the tie bars, each outer lead finger extending from the periphery of the package towards the die pad. Each outer lead finger includes a transverse region coupling two spaced longitudinal regions and wherein the two spaced longitudinal regions each have a bonding region near the die pad. A semiconductor die is attached to the die pad and bond wires selectively electrically couple connection pads of the semiconductor die to the bonding regions of each outer lead finger. No more than one of the bond wires is bonded to the bonding region of the second longitudinal region and an encapsulation compound covers the bond wires and semiconductor die.
Referring to
Referring to
The lead fingers 225 include an outer lead finger 240 adjacent a respective edge of one of the tie bars 215. In order to increase the number of lead fingers 225, the outer lead fingers 240 can be located relatively close to the tie bars 215. Consequently, due to positioning tolerances (or indexing inaccuracy) a bonding end 235 of one or more of the outer lead fingers 240 may be unsupported over one of the slots 130 as illustrated by magnified region 245. Accordingly, the unsupported bonding end 235 is subject to stress, bounce and bending during wire bonding. This may lead to poor quality or faulty wire bonds especially when more than one wire bond is required at the unsupported bonding end 235.
Referring to
There is also an outer lead finger 335 adjacent a respective edge 340 of each one of the tie bars 315. Each outer lead finger 335 extends from the frame member 305 towards the die pad 310. Each outer lead finger 335 includes two spaced longitudinal regions namely a first longitudinal region 350 and a second longitudinal region 355, and a transverse region 345 coupling the two spaced longitudinal regions 350 and 355. The second longitudinal region 355 is located between the first longitudinal region 350 and one of the tie bars 315, and the first and second longitudinal regions 350, 355 each have a respective bonding region 360, 365 near the die pad 310.
As illustrated, each outer lead finger 335 includes a fork with the transverse region 345 located between the frame member 305 and the bonding regions 360, 365 of each of the longitudinal regions 350, 355. There is also a support tape 370, in the shape of a rectangular frame, attached to an underside of the intermediate lead fingers 325 and the longitudinal regions 350, 355. The support tape 370 provides some rigidity and restricts movement of the intermediate lead fingers 325 and outer lead fingers 335.
Referring to
As will be apparent to a person skilled in the art, the intermediate lead fingers 325 extend from a periphery 710 of the device 700 towards the die pad 310 and the intermediate lead fingers 325 each have their bonding end 330 near the die pad 310. Each outer lead finger 335 also extends from the periphery 710 of the device 700 towards the die pad 310 with the two spaced longitudinal regions 350, 355 each having their bonding region 360, 365 near the die pad 310.
Referring to
Referring to
Each outer lead finger 935 includes a transverse region 945 coupling two spaced longitudinal regions namely a first longitudinal region 950 and a second longitudinal region 955. The second longitudinal region 955 is located between the first longitudinal region 950 and one of the tie bars 915, and the first and second longitudinal regions 950, 955 each have a respective bonding region 960, 965 near the die pad 910
In this embodiment, the transverse region 945 forms part of the bonding regions 960, 965 of each of the first and second longitudinal regions 950, 955. If required there may also be a support tape, in the shape of a rectangular frame, attached to an underside of the intermediate lead fingers 925 and the longitudinal regions 950, 955.
The lead frame 900 is used to form a semiconductor die package similar to the semiconductor die package 700 and to avoid repetition the bonding, encapsulation, singulation, and trim and form operations are not illustrated or described in detail.
At a block 1020 there is performed attaching the semiconductor die 405 to the die pad 310. Next, at a block 1030 there is performed a process of selectively electrically coupling, with the bond wires 505, the connection pads 410 of the semiconductor die 405 to the bonding regions of each outer lead finger. In this embodiment there is no more than one of the bond wires 505 bonded to the bonding region 365 of the second longitudinal region 355. Furthermore, there is typically more than one of the bond wires 505 bonded to the bonding region 360 of the first longitudinal region 350. The process of selectively electrically coupling also includes wire bonding the connection pads 410 of the semiconductor die to bonding ends 330 of the intermediate lead fingers 325.
At an encapsulating block 1040 the semiconductor die 405, the bonds wires 505, the bonding ends 330, bonding regions 360, 365 and the longitudinal regions 360, 365 are encapsulated with the encapsulant 605. At block 1050, the tie bars 315, the intermediate lead fingers 325, and each outer lead finger 335 are detached from the frame member 305 to provide the semiconductor device 700. Trimming and forming may be part of the detaching process or alternatively trimming and forming is performed at a block 1060. The trimming and forming process includes bending ends of all the intermediate lead fingers 325 and an end of each outer lead finger 335 to thereby provide the mounting feet 705 for the semiconductor device 700.
Advantageously, the present invention reduces or at least alleviates potential problems, during wire bonding, caused by unsupported bonding ends of leads being located over the slots 130. Since the outer lead fingers have two spaced longitudinal regions 360, 365 or 960, 965 then no more than one of the bond wires 505 need be bonded to the bonding region 365 or 395. Thus, if the bonding region 365 or 395 is unsupported over one of the slots 130 then the longitudinal region 365 or 395 is only subject to stress, bounce or bending for a single wired bond. Furthermore, the transverse region 345 provides for additional support when the bonding region 365 is over one of the slots 130.
The description of the preferred embodiments of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or to limit the invention to the forms disclosed. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment disclosed, but covers modifications within the spirit and scope of the present invention as defined by the appended claims.
