US20040061217A1 - Thin and heat radiant semiconductor package and method for manufacturing - Google Patents

Abstract

A semiconductor package which is improved in thinness and heat radiation and a method for making the same. The package includes a semiconductor chip electrically connected to leads of a leadframe via input and output bond pads. The leadframe may have a ground ring formed therein. The leads and semiconductor chip are at least partially encapsulated by an encapsulant. The semiconductor chip and leads have bottom surfaces which are externally exposed to improve heat radiation and reduce the thickness of the package. The package is made by placing the leadframe having leads onto adhesive tape, affixing a semiconductor chip into an open space on the leadframe, pressurizing the leadframe and chip downwardly for securement to the adhesive tape, electrically connecting input bond pads and output bond pads on the chip to the leads; at least partially encapsulating the leads and semiconductor chip; removing the tape from the bottom surfaces of the leads and chip; and cutting the leadframe to form the package. In an alternate embodiment, a chip paddle is connected to the leadframe and the semiconductor chip is secured to the chip paddle via an adhesive.

Description

BACKGROUND OF THE INVENTION
• 1. Technical Field of the Invention[0001]
• The present invention relates to a packaged semiconductor, a semiconductor package and a method for fabricating the package, and more particularly but not by way of limitation, to a thin semiconductor package having improvements in heat radiation and a method for manufacturing the same.[0002]
• 2. History of Related Art[0003]
• It is conventional in the electronic industry to encapsulate one or more semiconductor devices, such as integrated circuit dies, or chips, in a semiconductor package. These plastic packages protect a chip from environmental hazards, and provide a method of and apparatus for electrically and mechanically attaching the chip to an intended device. Recently, such semiconductor packages have included metal lead frames for supporting an integrated circuit chip which is bonded to a chip paddle region formed centrally therein. Bond wires which electrically connect pads on the integrated circuit chip to individual leads of the lead frame are then incorporated. A hard plastic encapsulating material, or encapsulant, which covers the bond wire, the integrated circuit chip and other components, forms the exterior of the package. A primary focus in this design is to provide the chip with adequate protection from the external environment in a reliable and effective manner.[0004]
• As set forth above, the semiconductor package therein described incorporates a lead frame as the central supporting structure of such a package. A portion of the lead frame completely surrounded by the plastic encapsulant is internal to the package. Portions of the lead frame extend internally from the package and are then used to connect the package externally. More information relative to lead frame technology may be found in Chapter 8 of the book[0005]Micro Electronics Packaging Handbook,(1989), edited by R. Tummala and E. Rymaszewski and incorporated by reference herein. This book is published by Van Nostrand Reinhold, 115 Fifth Avenue, New York, N.Y.
• Once the integrated circuit chips have been produced and encapsulated in semiconductor packages described above, they may be used in a wide variety of electronic appliances. The variety of electronic devices utilizing semiconductor packages has grown dramatically in recent years. These devices include cellular phones, portable computers, etc. Each of these devices typically include a motherboard on which a significant number of such semiconductor packages are secured to provide multiple electronic functions. These electronic appliances are typically manufactured in reduced sizes and at reduced costs, consumer demand increases. Accordingly, not only are semiconductor chips highly integrated, but also semiconductor packages are highly miniaturized with an increased level of package mounting density.[0006]
• According to such miniaturization tendencies, semiconductor packages, which transmit electrical signals from semiconductor chips to motherboards and support the semiconductor chips on the motherboards, have been designed to have a small size. By way of example only, such semiconductor packages may have a size on the order of 1×1 mm to 10×10 mm. Examples of such semiconductor packages are referred to as MLF (micro leadframe) type semiconductor packages and MLP (micro leadframe package) type semiconductor packages. Both MLF type semiconductor packages and MLP type semiconductor packages are generally manufactured in the same manner.[0007]
• Such conventional semiconductor packages are not without problems. Specifically, a typical semiconductor package is difficult to make slim because the thickness of the internal leads is equivalent to the thickness of the chip paddle. Further, the mounting of the semiconductor chip on the chip paddle increases the overall thickness of the package. The thickness is increased because of the input/output pads on the semiconductor chip mounted on the chip paddle are positioned at a higher level than the internal leads, thereby increasing the loop height of the conductive wires. The increased height may contribute to wire sweeping, caused by the encapsulation material during encapsulation.[0008]
• In addition, mounting the semiconductor chip on a chip paddle having an externally exposed bottom surface has poorer heat radiation than having a direct externally exposed bottom surface of the semiconductor chip.[0009]
• Finally, after the chip-mounting step and wire-bonding step are performed, the semiconductor package is encapsulated only after the leadframe is positioned on a mold. Thus, although the leadframe is in close contact with the lower mold die, some encapsulation material infiltrates through the interface between the leadframe and the lower mold die, resulting in the formation of so-called “flash”. An extra de-flashing step must then generally be executed.[0010]
SUMMARY OF THE INVENTION
• In one embodiment of the present invention, there is provided a semiconductor package comprising a semiconductor chip having an upper surface and a bottom surface. A plurality of input bond pads and output bond pads on the upper surface of the semiconductor chip and along the circumference of the semiconductor chip are electrically connected to the semiconductor chip. A chip paddle may be provided which has a top surface, a side surface and a bottom surface. The chip paddle is bonded to the bottom surface of the semiconductor chip by an adhesive. The chip paddle has corners, a circumference and a half-etched section at the lower edge of the chip paddle along the chip paddle circumference.[0011]
• A lead frame is provided having a plurality of tie bars. Each of the tie bars has a side surface and a bottom surface. The plurality of tie bars are connected to the corners of the chip paddle. The plurality of the tie bars externally extend from the chip paddle and have a half-etched section. A plurality of dam bars are provided on the lead frame help limit flow of encapsulation material on the leadframe.[0012]
• A plurality of internal leads connect to the leadframe. Each of the leads has a side surface and a bottom surface. The leads are radially formed at regular intervals along and spaced apart from the circumference to the chip paddle and extend towards the chip paddle. Each of the leads has a step shaped half-etched section facing the chip paddle.[0013]
• A plurality of via conductive wires are electrically connected to and between the plurality of leads and the semiconductor chip. Encapsulating material encapsulates the semiconductor chip, conductive wires, chip paddle, and the leads to form a package body. The flow of the encapsulation material is limited by the dam bars formed on the leadframe. The dam bars also serve to stabilize the leads on the leadframe. After encapsulation, the chip paddle, leads, and tie bars are externally exposed at respective side and bottom surfaces.[0014]
• A ground ring may be provided on the leadframe having an upper surface and a lower surface. The conductive wires may be connected to the ground ring, which is exposed at the lower surface. The ground ring may further serve to function as a power ring.[0015]
BRIEF DESCRIPTION OF THE DRAWINGS
• A more complete understanding of the method and apparatus of the present invention may be obtained by reference to the following detailed description when taken in conjunction with the accompanying Drawings wherein:[0016]
• FIG. 1A is a cross-section of a semiconductor package made in accordance with one embodiment of the present invention;[0017]
• FIG. 1B is a cross-section of the semiconductor package of FIG. 1A with a ground ring included in the package;[0018]
• FIG. 2A is a cross-section of an alternate embodiment of a semiconductor package made in accordance with the teachings of the present invention;[0019]
• FIG. 2B is a cross-section of the semiconductor package of FIG. 2A with a ground ring included in the package;[0020]
• FIG. 3 is a top plan view of a leadframe;[0021]
• FIGS.[0022]4-9 are side-elevation cross-sections of a preferred embodiment of the semiconductor package of the present invention from the initial to final construction; and
• FIGS.[0023]10-14 are side-elevation cross-sections of an alternate embodiment of the semiconductor package of the present invention from the initial to final construction.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Referring first to FIGS. 1A and 1B, there is shown a cross sectional illustration of one embodiment of a[0024]semiconductor package10 construed in accordance with the principles of the present invention. Thesemiconductor package10 includes acorner12 andbottom surface15. Thesemiconductor package10 further includes asemiconductor chip20 having anupper surface30, acircumference40 and abottom surface50. A plurality ofinput bond pads60 andoutput bond pads70 are disposed on theupper surface30 of thesemiconductor chip20.Conductive wires75, including but not limited to gold or aluminum wires, electrically connect thesemiconductor chip20 to the respectiveinput bond pads60 oroutput bond pads70.
• In an alternate embodiment best seen in FIGS. 2A and 2B, a[0025]chip paddle80 having aupper surface90, aside surface100 and abottom surface110 is secured to thebottom surface50 of thesemiconductor chip20 via an adhesive120. Thechip paddle80 hascorners130, acircumference140 and may include a half-etchedsection150. The half-etchedsection150 is located at alower edge160 of thechip paddle80.
• Referring now to FIG. 3, a[0026]leadframe170 is shown having a plurality of tie bars180 and aside surface190. The tie bars180 are connected to thecorners130 of thechip paddle80 and externally extend from thechip paddle80. Theleadframe170 also includes a plurality of dam bars220.
• A plurality of[0027]leads230 are connected to theleadframe170 and have anupper surface235, aside surface240 and abottom surface250. In a first embodiment seen in FIGS. 1A and 1B, theleads230 are radially formed at regular intervals along thesemiconductor chip circumference40 and spaced apart from thecircumference40 of thesemiconductor chip20. The leads230 extend towards thechip20 and have a half-etchedsection260 facing thechip20.
• In an alternate embodiment best seen in FIGS. 2A and 2B, the[0028]leads230 are radially formed at regular intervals along thechip paddle circumference140 and spaced apart from thecircumference140 of thechip paddle80. The leads230 extend towards thechip paddle80, such that each of the plurality ofleads230 has a half-etchedsection260 facing thechip paddle80.
• Referring back to FIGS. 1B and 2B, there is shown a[0029]ground ring262 formed inpackage10. Theground ring262 is positioned between thesemiconductor chip20 and the plurality ofleads230, and may be interchangeably used as a power ring should circumstances require.Conductive wires75 can connect theground ring262 to the respectiveinput bond pads60 oroutput bond pads70, depending on the application. As seen in FIG. 1B, theupper surface264 of theground ring262 is planar with theupper surface30 of thesemiconductor chip20 and theupper surface235 of theleads230. However, as seen in FIG. 2B, theupper surface264 of theground ring262 may be planar with the upper surface of thechip paddle80 to minimize package thickness. Likewise, theupper surface235 of theleads230 is planar with theupper surface30 of the semiconductor chip20 (FIGS. 1A and 1B) to minimize package thickness. In the alternate embodiments shown in FIGS. 2A and 2B, theupper surface235 of theleads230 is planar with theupper surface90 of thechip paddle80 to reduce package thickness.
• Referring generally now to FIGS. 1A and 3, to enclose the[0030]semiconductor package10,encapsulation material280 at least partially encapsulates thesemiconductor chip20,conductive wires70, and leads230. In the alternate embodiment shown in FIGS. 2A and 2B, theencapsulation material280 encapsulates thechip paddle80 as well. Likewise, for the embodiments shown in FIGS. 1B and 2B, theencapsulation material280 encapsulates theground ring262.
• Referring now to FIGS. 1 through 3 in general, dam bars[0031]220 limit the flow of theencapsulation material280 on theleadframe170 and provide stability to theleads230 on theleadframe170. In the respective embodiment during encapsulation, thechip paddle80, leads230, and tiebars180 may be externally exposed at peripheral side and bottom surfaces. The externally exposed portions ofchip paddle80, leads230, and tiebars180 may, but do no necessarily have to be, electroplated with corrosion-minimizing materials such as but not limited to, tin lead, tin, gold, nickel palladium, tin bismuth, or any other similar material known in the art. The respective half-etchedsections150,260 of thechip paddle80 and leads230 are provided to increase the bonding strength of theencapsulation material280 in thepackage10. It is contemplated that the respective half-etchedsections150,260 may be eliminated without departing from the scope and spirit of this invention.
• Referring now to FIGS.[0032]4-9 in general, there is shown a cross-section of thesemiconductor package10 of FIG. 1A. It is to be recognized that the method for constructing thesemiconductor package10 of FIG. 1A may be used for constructing the embodiment shown in FIG. 1B without departing from the principles of this invention. The leadframe, although not shown in these figures, having leads230 and a space290 large enough to accommodate asemiconductor chip20, is first placed upon an adhesive tape300. Next, asemiconductor chip20 is fixed to the adhesive tape300 within the space290 as best seen in FIG. 5. Thesemiconductor chip20 and theleads230 are pressurized downwardly onto the tape300 at a suitable temperature to make the tape300 firmly adhere to thesemiconductor chip20 and leads230.
• As shown in FIG. 6, the[0033]input bond pads60 andoutput bond pads70 of thesemiconductor chip20 are next electrically connected to theleads230 viaconductive wires75.Upper surface235 ofleads230 may, but do not necessarily have to be, electroplated with a material that enhances electrical conductivity such as, for example, gold or silver. Typically, theconductive wires75 are connected via an automated process, but may be connected in any alternate method in the industry.
• The[0034]semiconductor chip20,conductive wires75, and leads230 are then at least partially encapsulated with theencapsulation material280, which may be an epoxy molding compound or a liquid encapsulation material, thereby forming apackage body10 as seen in FIG. 7. Referring to FIG. 8, the adhesive tape300 is next removed from thebottom surface15 of thepackage10. The leads230 are next severed from the leadframe (not shown) by cutting through the dam bars (not shown) or neighboring areas of thepackage body10 best seen in FIG. 9 as a singulation step. It is to be noted that this singulation step may occur before the adhesive tape300 is removed.
• After formation of the[0035]package body10, a marking process (not shown) may be carried out by the use of ink or lasers. The removal of the adhesive tape300 allows thesemiconductor chip20 and leads240 to be exposed to the outside, thereby improving heat radiation. By adhering theadhesive tape250 to the bottom surfaces15,250 of thesemiconductor chip20 and leads230, respectively, flashes, which are typically formed during the molding process are not generated, thereby eliminating or reducing any further deflashing steps.
• After the removal of the adhesive tape[0036]300, a predetermined thickness of solder (not shown) may be plated over thebottom surface250 of the of theleads230 to allow easy fusion of thepackage10 to a motherboard (not shown).
• Referring now generally to FIGS.[0037]10-14, there are shown cross-sections of thesemiconductor package10 of FIG. 2A during various stages of construction. It is to be recognized that the method for constructing thesemiconductor package10 of FIG. 2A may be used for constructing the embodiment shown in FIG. 2B without departing from the principles of this invention. The leadframe (not shown) having leads230 and achip paddle80 is first placed upon an adhesive tape300 best seen in FIG. 10. Thechip paddle80 and theleads230 are pressurized downwardly onto the tape300 at a suitable temperature to make the tape300 firmly adhere to thechip paddle80 and leads230.
• As shown in FIG. 11, the[0038]semiconductor chip20 is bonded to theupper surface90 of thechip paddle80 via an adhesive120. Theinput pads60 andoutput pads70 of thesemiconductor chip20 are next electrically connected to theleads230 viaconductive wires75.Upper surfaces235 ofleads230 may, but do not necessarily have to be, electroplated with a material that enhances electrical conductivity such as, for example, gold or silver. Typically, theconductive wires75 are connected via an automated process, but may also be connected in any alternate method in the industry.
• The[0039]semiconductor chip20,chip paddle80,conductive wires75, and leads230 are then at least partially encapsulated with theencapsulation material280, which may be thermoplastics or thermoset resins, with thermoset resins including, for example, silicones, phenolics, and epoxies. Theencapsulation material280 forms apackage body10 as seen in FIG. 12.
• Referring to FIG. 13, the adhesive tape[0040]300 is next removed from thebottom surface15 of thepackage10. The leads230 are next severed from the leadframe (not shown) by cutting through the dam bars (not shown) or neighboring areas of thepackage body10 best seen in FIG. 14 in a singulation step. It is noted that this singulation step may occur before the adhesive tape300 is removed.
• Once the[0041]package body10 is formed, a marking process (not shown) may be carried out by the use of ink or lasers. The removal of the adhesive tape300 allows thechip paddle80 and leads230 to be exposed to the outside, thereby improving heat radiation. By adhering the adhesive tape300 to the bottom surfaces110,250 of thechip paddle80 and leads230, respectively, flashes, which are typically formed during the molding process, are not generated, thereby eliminating or reducing any further deflashing steps. Bottom surfaces110,250 of thechip paddle80 and leads230, may be electroplated with corrosion-minimizing materials such as, but not limited to, tin lead, tin, gold, nickel palladium, tin bismuth, or other similar materials known in the art.
• After the removal of the tape[0042]300, a predetermined thickness of solder (not shown) may be plated over thebottom surface250 of the of theleads230 to allow easy fusion of thepackage10 to a motherboard (not shown).
• In such a semiconductor package as described and shown in FIGS. 1A and 1B, the[0043]bottom surface15 of thesemiconductor chip20 is in the same plane as thebottom surface250 of theleads230, so that thesemiconductor package10 is thin by limiting the height level of theconductive wires75. In addition, the direct exposure of thesemiconductor chip20 provides for higher thermal radiation.
• The following applications are all being filed on the same date as the present application and all are incorporated by reference as if wholly rewritten entirely herein:[0044]

  Attorney		First Named
  Docket No.	Title of Application	Inventor
  45475-00014	Lead Frame for Semiconductor	Young Suk
  	Package and Mold for Molding the	Chung
  	Same
  45475-00017	Method for Making a Semiconductor	Tae Heon Lee
  	Package Having Improved Defect
  	Testing and Increased Production	Yield
  45475-00018	Near Chip Size Semiconductor	Sean Timothy
  	Package	Crowley
  45475-00022	End Grind Array Semiconductor	Jae Hun Ku
  	Package
  45475-00026	Leadframe and Semiconductor Package	Tae Heon Lee
  	with Improved Solder Joint Strength
  45475-00027	Semiconductor Package Having	Tae Heon Lee
  	Reduced Thickness
  45475-00029	Semiconductor Package Leadframe	Young Suk
  	Assembly and Method of Manufacture	Chung
  45475-00030	Semiconductor Package and Method	Young Suk
  	Thereof	Chung

• It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description of the preferred exemplary embodiments. It will be obvious to a person of ordinary skill in the art that various changes and modifications may be made herein without departing from the spirit and the scope of the invention.[0045]

Claims (16)

What is claimed is:

1. A packaged semiconductor, comprising:

a semiconductor chip having a planar upper surface, a circumference and a bottom surface;

a plurality of input bond pads on the planar upper surface of said semiconductor chip along the circumference and electrically connected to said semiconductor chip;

a plurality of output bond pads on the planar upper surface along the circumference of said semiconductor chip and electrically connected to said semiconductor chip;

a leadframe having a plurality of tie bars, said tie bars having a side surface and a bottom surface, said leadframe having a plurality of dam bars;

a plurality of internal leads connected to said leadframe, said plurality of internal leads having a side surface and a bottom surface, said plurality of internal leads being radially formed at regular intervals along and spaced apart from said circumference of said semiconductor chip and extending towards said semiconductor chip, each of said plurality of internal leads having a half-etched section facing said semiconductor chip, each of said plurality of leads having an upper surface in the plane of said upper surface of said semiconductor chip;

a plurality of conductive wires for electrically connecting to said plurality of internal leads and to said semiconductor chip;

encapsulant material encapsulating said semiconductor chip, said plurality of conductive wires, and said plurality of internal leads to form a package body, wherein flow of said encapsulant material is limited by said plurality of dam bars formed on said leadframe; and

wherein said semiconductor chip, said plurality of internal leads and said plurality of tie bars are externally exposed at respective side and bottom surface.

2. The semiconductor package ofclaim 1, further comprising

a chip paddle connected to said leadframe, said chip paddle having a top surface, a side surface and a bottom surface, said chip paddle bonded to said bottom surface of said semiconductor chip by an adhesive, said chip paddle having corners, a circumference and a half-etched section at a lower edge of said chip paddle along said chip paddle circumference.

3. The semiconductor package ofclaim 2, wherein each of said plurality of tie bars are connected to said corners of said chip paddle.

4. The semiconductor package ofclaim 3, wherein each of said plurality of tie bars has a half-etched section, and whereas each of said plurality of tie bars externally extend from said chip paddle.

5. A packaged semiconductor, comprising:

a leadframe having a plurality of tie bars, said tie bars having a side surface and a bottom surface, said leadframe having a plurality of dam bars and a space for receiving a semiconductor chip;

a plurality of internal leads connected to said leadframe, said plurality of internal leads having a side surface and a bottom surface, said plurality of internal leads being radially formed at regular intervals along and spaced apart from said circumference of said semiconductor chip and extending towards said semiconductor chip, each of said plurality of internal leads having a half-etched section facing said semiconductor chip, each of said plurality of leads having an upper surface in the plane of said upper surface of said semiconductor chip;

a plurality of conductive wires for electrically connecting to said plurality of internal leads and to said semiconductor chip;

encapsulant material encapsulating said semiconductor chip, said plurality of conductive wires, and said plurality of internal leads to form a package body, wherein flow of said encapsulant material is limited by said plurality of dam bars formed on said leadframe; and

wherein said semiconductor chip, said plurality of internal leads and said plurality of tie bars are externally exposed at respective side and bottom surface.

6. The semiconductor package ofclaim 5, further comprising:

a semiconductor chip having a planar upper surface, a circumference and a bottom surface secured into said space on said leadframe.

7. The semiconductor package ofclaim 6, further comprising:

a plurality of input bond pads on the planar upper surface of said semiconductor chip along the circumference and electrically connected to said semiconductor chip; and

a plurality of output bond pads on the planar upper surface along the circumference of said semiconductor chip and electrically connected to said semiconductor chip;

8. The semiconductor package ofclaim 7, further comprising

a chip paddle connected to said leadframe, said chip paddle having a top surface, a side surface and a bottom surface, said chip paddle bonded to said bottom surface of said semiconductor chip by an adhesive, said chip paddle having corners, a circumference and a half-etched section at a lower edge of said chip paddle along said chip paddle circumference.

9. The semiconductor package ofclaim 8, wherein each of said plurality of tie bars are connected to said corners of said chip paddle.

10. The semiconductor package ofclaim 9, wherein each of said plurality of tie bars has a half-etched section, and whereas each of said plurality of tie bars externally extend from said chip paddle.

11. A method for making a semiconductor package, comprising the steps of:

placing a leadframe having a plurality of leads and a space for accommodating a semiconductor chip on an adhesive tape, said plurality of leads having a bottom surface;

affixing a semiconductor chip having a bottom surface, input bond pads and output bond pads within said space on said leadframe;

pressurizing said leadframe and said semiconductor chip downwardly onto said tape;

electrically connecting said input bond pads and said output bond pads of said semiconductor chip to said leads via wires;

encapsulating said semiconductor chip, said wires, and said leads by an encapsulant material to form a package body;

removing said adhesive tape from said package body while leaving said bottom surface of said leads and said bottom surface of said semiconductor chip externally exposed; and

cutting said package from said leadframe.

12. The method as inclaim 11, wherein the steps are performed sequentially.

13. A method for making a packaged semiconductor, comprising the steps of:

placing a leadframe having a plurality of leads, a ground ring having a bottom surface, and a space for accommodating a semiconductor chip on an adhesive tape, said plurality of leads having a bottom surface;

affixing a semiconductor chip having a bottom surface, input bond pads and output bond pads within said space on said leadframe;

electrically connecting said input bond pads and said output bond pads of said semiconductor chip to said leads via wires;

encapsulating said semiconductor chip, said ground ring, said wires, and said leads by an encapsulant material to form a package body;

removing said adhesive tape from said package body while leaving said bottom surface of said leads, said bottom surface of said ground ring, and said bottom surface of said semiconductor chip externally exposed; and

cutting said package from said leadframe.

14. The method as inclaim 13, wherein the steps are performed sequentially.

15. A method for making a packaged semiconductor, comprising the steps of:

placing a leadframe having a chip paddle having a bottom surface and a plurality of leads on an adhesive tape, said plurality of leads having a bottom surface;

affixing a semiconductor chip having a bottom surface, input bond pads and output bond pads onto said chip paddle via an adhesive;

electrically connecting said input bond pads and said output bond pads of said semiconductor chip to said leads via wires;

encapsulating said semiconductor chip, said wires, and said leads by an encapsulant material to form a package body;

removing said adhesive tape from said package body while leaving said bottom surface of said leads and said bottom surface of said semiconductor chip externally exposed; and

cutting said package from said leadframe.

16. The method as inclaim 15, wherein the steps are performed sequentially.

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