(12) United States Patent
`Glenn
`
`I 1111111111111111 11111 lllll lllll lllll lllll lllll lllll 111111111111111 11111111
`US006433277Bl
`US 6,433,277 Bl
`*Aug. 13, 2002
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) PLASTIC INTEGRATED CIRCUIT PACKAGE
`AND METHOD AND LEADFRAME FOR
`MAKING THE PACKAGE
`
`5,200,362 A
`5,200,809 A
`5,214,845 A
`
`4/1993 Lin et al. .................... 437/207
`4/1993 Kwon ........................ 257/707
`6/1993 King et al.
`. . . . . . . . . . . . . . . . . . . 29 /841
`
`(75)
`
`Inventor: Thomas P. Glenn, Gilbert, AZ (US)
`
`(73) Assignee: Amkor Technology, Inc., Chandler, AZ
`(US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by O days.
`
`This patent is subject to a terminal dis(cid:173)
`claimer.
`
`(21) Appl. No.: 09/615,107
`Jul. 13, 2000
`
`(22) Filed:
`
`Related U.S. Application Data
`
`(63) Continuation of application No. 09/103,760, filed on Jun.
`24, 1998, now Pat. No. 6,143,981.
`
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`
`19734794 Al
`0794572 A2
`55-163868
`57-45959
`59-227143
`60-52050
`60-195957
`61-39555
`62-9639
`63-205935
`63-233555
`6-54749
`
`8/1997
`9/1997
`12/1980
`3/1982
`12/1984
`3/1985
`10/1985
`2/1986
`1/1987
`8/1988
`9/1988
`3/1989
`
`........... H0lL/23/50
`. ... ... .. H0lL/23/495
`........... H0lL/23/48
`........... H0lL/23/28
`........... H0lL/23/12
`........... H0lL/23/48
`........... H0lL/23/48
`........... H0lL/23/36
`........... H0lL/21/56
`........... H0lL/23/28
`........... H0lL/23/30
`........... H0lL/23/28
`
`(List continued on next page.)
`
`DE
`EP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`
`Primary Examiner-Dean A. Reichard
`Assistant Examiner----Carmelo Oliva
`(74) Attorney, Agent, or Firm----Stetina Brunda Garred &
`Brucker
`
`(51)
`
`Int. Cl.7 ................................................ H0lL 23/28
`
`(57)
`
`ABSTRACT
`
`(52) U.S. Cl. ..................... 174/52.4; 174/52.2; 257/670;
`257/676; 257/787
`
`(58) Field of Search ............................... 174/52.4, 52.2;
`257/678, 684, 687, 690, 692, 778, 787,
`670, 676; 438/123, 124; 361/717, 718,
`722, 723, 763, 764
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,838,984 A
`4,054,238 A
`4,530,152 A
`4,707,724 A
`4,756,080 A
`4,812,896 A
`5,041,902 A
`5,157,480 A
`5,172,213 A
`5,172,214 A
`
`10/1974 Crane et al. ............... 29/193.5
`10/1977 Lloyd et al.
`................. 29/588
`7/1985 Roche et al.
`11/1987 Suzuki et al. ................. 357 /71
`7/1988 Throp, Jr. et al.
`............ 29/827
`3/1989 Rothgery et al.
`............. 357 /70
`8/1991 McShane ..................... 357/79
`10/1992 McShane et al. ............. 357/74
`12/1992 Zimmerman ................ 257/796
`12/1992 Casto ......................... 257 /676
`
`Packages for an integrated circuit die and methods and
`leadframes for making such packages are disclosed. The
`package includes a die, a die pad, peripheral metal contacts,
`bond wires, and an encapsulant. The die pad and contacts are
`located at a lower surface of the package. The die pad and
`the contacts have side surfaces which include reentrant
`portions and asperities to engage the encapsulant.
`
`A method of making a package includes providing a metal
`leadframe having a die pad in a rectangular frame. Tabs
`extend from the frame toward the die pad. The die pad and
`tabs have side surfaces with reentrant portions and asperi(cid:173)
`ties. A die is attached to the die pad. The die is electrically
`connected to the tabs. An encapsulant is applied to the upper
`and side surfaces of the leadframe. Finally, the leadframe is
`cut in situ so that the die pad and tabs are severed from the
`frame, the sides of the package are formed, and the package
`is severed from the leadframe.
`
`25 Claims, 5 Drawing Sheets
`
`57
`
`31
`55
`
`51
`
`24
`
`40
`
`57
`
`55
`
`33
`
`53
`
`VIZIO Ex. 1034 Page 00001
`
`

`

`US 6,433,277 Bl
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`5,216,278 A
`5,221,642 A
`5,258,094 A
`5,273,938 A
`5,277,972 A
`5,278,446 A
`5,279,029 A
`5,332,864 A
`5,336,931 A
`5,343,076 A
`5,406,124 A
`5,424,576 A
`5,435,057 A
`5,474,958 A
`5,521,429 A
`5,604,376 A
`5,608,267 A
`5,639,990 A
`5,640,047 A
`5,641,997 A
`5,646,831 A
`5,650,663 A
`5,683,806 A
`5,696,666 A
`5,701,034 A
`5,710,094 A
`5,776,798 A
`5,783,861 A
`5,835,988 A
`5,859,471 A
`5,866,939 A
`
`6/1993 Lin et al. . . . . . . . . . . . . . . . . . . . . 257 /688
`6/1993 Burns ......................... 437 /207
`11/1993 Furui et al. ... .. ... ... ... ... 156/634
`12/1993 Lin et al. .................... 437/207
`1/1994 Sakumoto et al. .......... 428/355
`1/1994 Nagaraj et al.
`............. 257/707
`1/1994 Burns .......................... 29/856
`7/1994 Liang et al.
`............... 174/52.4
`8/1994 Juskey et al. ............... 257 /787
`8/1994 Katayama et al. .......... 257/717
`4/1995 Morita et al. ............... 257/783
`6/1995 Djennas et al. ............. 257 /666
`7/1995 Bindra et al. ................. 29/830
`12/1995 Djennas et al. ............. 437/211
`5/1996 Aono et al. ................. 257/676
`2/1997 Hamburgen et al. ........ 257/676
`3/1997 Makulikar et al. .......... 256/796
`6/1997 Nishihara et al. .......... 174/52.2
`6/1997 Nakashima ................. 257/738
`6/1997 Ohta et al. .................. 257/788
`7/1997 Manteghi .................... 361/813
`7/1997 Parthasarathi ............... 257 /706
`11/1997 Sakumoto et al. .......... 428/343
`12/1997 Miles et al.
`................ 361/764
`12/1997 Marrs ......................... 256/706
`1/1998 Song et al.
`................. 437/220
`7/1998 Quan et al. ................. 438/112
`7/1998 Son ............................ 253/693
`11/1998 Ishii ........................... 257 /684
`1/1999 Kuraishi et al.
`............ 256/666
`2/1999 Shin et al. . . . . . . . . . . . . . . . . . . 257 /666
`
`5,877,043 A
`5,894,108 A
`5,977,613 A
`5,977,630 A
`5,981,314 A
`5,986,885 A
`6,001,671 A
`6,025,640 A
`6,072,228 A
`6,130,115 A
`6,130,473 A
`6,140,154 A
`6,143,981 A
`6,198,171 Bl
`6,225,146 Bl
`6,229,200 Bl
`6,242,281 Bl
`6,281,568 Bl
`
`3/1999 Alcoe et al. ................ 438/123
`4/1999 Mostafazadeh et al. .... 174/52.4
`11/1999 Takata et al. ............... 257/666
`11/1999 Woodworth et al. ........ 257/712
`11/1999 Glenn et al. ................ 438/127
`11/1999 Wyland
`12/1999 Fjelstad ...................... 438/112
`2/2000 Yagi et al.
`6/2000 Hinkle et al.
`10/2000 Okumura et al.
`10/2000 Mostafazadah et al. . . . . . 257 /666
`10/2000 Hinkle et al.
`11/2000 Glenn ....................... 174/52.4
`3/2001 Huang et al.
`5/2001 Yamaguchi et al.
`5/2001 Mclellan et al. ............ 257 /666
`6/2001 Mclellan et al.
`8/2001 Glenn et al.
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`KR
`KR
`
`1106456
`6092076
`7-312405
`8-125066
`8-306853
`9-8205
`9-8206
`9-8207
`9-92775
`94-1979
`97-72358
`
`4/1989
`4/1995
`11/1995
`5/1996
`11/1996
`1/1997
`1/1997
`1/1997
`4/1997
`1/1994
`11/1997
`
`........... B42D/15/10
`........... H0lL/23/50
`........... H00L/23/12
`........... H0lL/23/50
`........... H0lL/23/50
`........... H0lL/23/50
`........... H0lL/23/50
`........... H0lL/23/50
`........... H0lL/21/56
`........... H0lL/23/50
`
`VIZIO Ex. 1034 Page 00002
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 1 of 5
`
`US 6,433,277 Bl
`
`PROVIDE A THIN METAL LEADFRAME INCLUDING A FRAME,
`A DIE PAD WITHIN THE FRAME, AND TABS WHICH
`EXTEND FROM THE FRAME TOWARDS THE DIE PAD
`
`r--
`
`PLACE AN INTEGRATED CIRCUIT DIE ONTO THE DIE PAD
`
`ELECTRICALLY CONNECT BONDING PADS ON THE DIE TO THE TABS
`
`!
`!
`i
`APPLY AN ENCAPSULANT MATERIAL TO A SURFACE OF THE LEADFRAME, - 4
`COVERING THE FRAME, DIE, DIE PAD, AND PERIPHERAL SIDE SURFACES
`OF THE DIE PAD AND TABS WITH ENCAPSULANT MATERIAL,
`AND HARDEN THE ENCAPSULANT MATERIAL
`
`2
`
`3
`
`!
`i
`
`PLATE EXPOSED SURFACES OF THE LEADFRAME WITH METAL
`
`5
`
`CUT THE ENCAPSULATED LEADFRAME AND ENCAPSULANT MATERIAL WITH; 1--- 6
`A SAW, SEVERING THE DIE PAD AND TABS FROM THE FRAME AND
`FORMING A COMPLETED PACKAGE
`
`FIG. 1
`
`VIZIO Ex. 1034 Page 00003
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 2 of 5
`
`US 6,433,277 Bl
`
`~ ,-20
`I
`21
`I
`
`=
`
`25
`
`27
`
`=
`
`I
`~30
`I
`29 I
`I
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`-
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`----C
`
`22
`
`8
`I
`I
`I
`
`23
`
`,---
`1
`2 4 --.,,,_
`I
`~
`I
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`c---- -
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`22A
`
`t 3--
`D - - L - - ' - - - - -+ - - -~
`
`t
`--3
`' - - - -+ - - - - ' - _J __ D
`
`28
`
`-
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`I
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`31
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`31
`
`23A
`
`FIG. 2
`
`31
`
`33 27
`
`25
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`~ j (~ (
`30
`24
`
`FIG. 3
`
`~;sI~
`
`\ 33
`30
`FIG. 4
`
`26 (
`24
`
`32
`
`•:~fijJ
`
`32 \ 37
`30
`
`37
`
`26 (
`24
`
`-~~-
`
`39
`
`26 ~
`l
`24
`
`32 '
`30
`
`39
`
`FIG. 5
`
`FIG. 6
`
`VIZIO Ex. 1034 Page 00004
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 3 of 5
`
`US 6,433,277 Bl
`
`I
`I
`C--------- - -L - - - - - - - - -L -
`1
`I
`I
`I
`
`I
`
`I
`
`I
`
`I
`
`I
`
`I
`
`B
`I
`I
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`I
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`I
`
`I
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`I
`I
`I
`I
`D---------~---------r-
`1
`I
`
`I
`
`I
`
`-
`
`22A
`
`I
`_-1
`I
`
`I
`
`I
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`I
`
`I
`
`I
`
`I
`B
`
`I
`
`I
`
`I
`
`I
`
`I
`I
`23A 1
`I
`I
`
`I
`
`I
`A
`
`57
`
`31
`55
`
`32 53 33
`
`26
`
`51
`
`24
`
`FIG. 8
`
`A
`I
`
`I
`
`I
`
`20 ----c
`
`I
`
`I
`
`FIG. 7
`
`f50
`
`40
`
`57
`
`55
`
`33
`
`53
`
`VIZIO Ex. 1034 Page 00005
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 4 of 5
`
`US 6,433,277 Bl
`
`f50
`
`60
`
`FIG. 9
`
`PROVIDE A THIN METAL LEADFRAME INCLUDING A PLURALITY
`OF INTERCONNECTED FRAMES, EACH FRAME HAVING A DIE PAD
`WITHIN THE FRAME, AND TABS WHICH EXTEND FROM THE FRAME
`TOWARDS THE DIE PAD
`
`!
`i
`
`PLACE AN INTEGRATED CIRCUIT DIE ONTO EACH DIE PAD
`
`ELECTRICALLY CONNECT BONDING PADS ON EACH DIE TO THE
`TABS WHICH EXTEND TOWARD THAT DIE
`
`60
`
`f--
`
`2
`
`- 3
`
`!
`APPLY AN ENCAPSULANT MATERIAL TO A SURFACE OF THE LEADFRAME, - 4
`COVERING THE FRAMES, DIES, DIE PADS, AND PERIPHERAL SIDE SURFACES
`OF THE DIE PADS AND TABS WITH ENCAPSULANT MATERIAL,
`AND HARDEN THE ENCAPSULANT MATERIAL
`
`!
`!
`
`PLATE EXPOSED SURFACES OF THE LEADFRAME WITH METAL
`
`5
`
`,...._ 6
`CUT THE ENCAPSULATED LEADFRAME AND ENCAPSULANT MATERIAL WITH -
`A SAW, SEVERING THE DIE PADS AND TABS FROM THEIR RESPECTIVE
`FRAMES AND FORMING A PLURALITY OF COMPLETED PACKAGES
`
`FIG. 10
`
`VIZIO Ex. 1034 Page 00006
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 5 of 5
`
`US 6,433,277 Bl
`
`--
`
`27
`24
`
`27
`76
`30
`
`78
`
`--
`
`74
`
`77
`
`r
`
`73
`
`71
`
`--
`
`t:9_
`
`-
`-
`
`-=-
`
`=
`
`-=-
`
`-
`-
`
`=
`
`29
`
`77
`
`78
`
`--
`
`72
`
`=
`
`30
`
`~-=-
`
`--
`
`--
`
`1=-k
`(78
`
`--
`
`75
`
`FIG. 11
`
`-=
`
`I
`
`70
`
`VIZIO Ex. 1034 Page 00007
`
`

`

`US 6,433,277 Bl
`
`1
`PLASTIC INTEGRATED CIRCUIT PACKAGE
`AND METHOD AND LEADFRAME FOR
`MAKING THE PACKAGE
`
`RELATED APPLICATIONS
`
`The present invention is a continuation of U.S. application
`Ser. No. 09/103,760 entitled PLASTIC INTEGRATED CIR(cid:173)
`CUIT PACKAGE AND METHOD AND LEAD FRAME
`FOR MAKING THE PACKAGE filed Jun. 24, 1998, U.S.
`Pat. No. 6,143,981.
`
`FIELD OF THE INVENTION
`
`The present invention is to directed toward an improved
`plastic package for an integrated circuit die, and a method of
`making such a package.
`
`BACKGROUND OF THE INVENTION
`
`20
`
`2
`sive to make than conventional plastic packages, and are
`more reliable and efficiently-sized than conventional pack(cid:173)
`ages.
`In one embodiment of an assembly method for a package
`5 within the present invention, Step 1 provides a metal lead(cid:173)
`frame. The leadframe includes a rectangular frame, e.g., a
`square frame. A substantially planar die pad is within and
`connected to the frame. A plurality of finger-like rectangular
`tabs extend from the frame toward the die pad without
`10 contacting the die pad. The number and location of the tabs
`around the frame may vary. The die pad and the tabs have
`peripheral side surfaces which include a reentrant portion(s)
`and asperities. The reentrant portions and asperities enhance
`the connection of the die pad and tabs to the plastic encap-
`15 sulating material.
`Step 2 places and attaches an integrated circuit to a first
`surface of the die pad.
`Step 3 electrically connects a bond wire or an equivalent
`conductor between each bonding pad of the die and a first
`surface of one of the tabs.
`Step 4 places the leadframe on a flat surface, with the die
`facing upwards, and applies a viscous encapsulant material
`onto the upward facing first surface of the leadframe. The
`encapsulant material is then hardened. The encapsulant
`material covers the die, the bond wires, a first surface of the
`tabs, the first surface of the die pad, the side surfaces of the
`die pad and tabs, and all or part of the frames around the die
`pad. A lower second surface of the leadframe, including a
`30 lower second surface of the die pad and tabs, is not covered
`with encapsulant.
`Step 5 plates the exposed surfaces of the leadframe,
`including the exposed second surfaces of the die pad and
`tabs with a metal, such as copper, gold, lead-tin solder, tin,
`35 nickel, palladium, or any solderable metal.
`Step 6 cuts the encapsulated portions of the leadframe
`with a saw. In particular, step 6 either obliterates the dis(cid:173)
`posable portions of the leadframe, or severs the disposable
`portions of the leadframe from other components of the
`40 leadframe, such as the die pad and tabs, which are to be
`included in the package. Step 6 also trims the encapsulant
`material and thereby forms the peripheral sides of the
`package.
`A feature of the packages built by the above described
`method is that the die pad and contacts (i.e., the severed tabs
`of the leadframe) of the package are located at the lower first
`surface of the package. The first surfaces and side surfaces
`of the die pad and tabs are internal to the package, i.e.,
`covered with encapsulant material, but the second surfaces
`of the die pad and tabs are not covered by encapsulant
`material. The die pad and tabs are isolated from each other
`by encapsulant material.
`In a completed package, only the encapsulant material
`holds the die pad and contacts to the package. The connec(cid:173)
`tion of the encapsulant material to the die pad and contacts
`is enhanced by the reentrant portion(s) and asperities of the
`side surfaces of the die pad and contacts. The reentrant
`portions and asperities of the side surfaces of the die pad and
`contacts function as encapsulant fasteners or lead locks.
`Numerous variations of the leadframe, package, and
`assembly method described above also are described in this
`application. In one alternative assembly method, a leadframe
`is provided which allows a plurality of packages to be
`65 constructed simultaneously.
`A leadframe for constructing a plurality of packages
`simultaneously includes, for example, a matrix of intercon-
`
`Integrated circuit die are conventionally enclosed in plas(cid:173)
`tic packages that provide protection from hostile environ(cid:173)
`ments and enable electrical interconnection between the
`integrated circuit die and printed circuit boards. The ele(cid:173)
`ments of such a package include a metal leadframe, an
`integrated circuit die, bonding material to attach the inte(cid:173)
`grated circuit die to the leadframe, bond wires which elec- 25
`trically connect pads on the integrated circuit die to indi(cid:173)
`vidual leads of the leadframe, and a hard plastic encapsulant
`material which covers the other components and forms the
`exterior of the package.
`The leadframe is the central supporting structure of such
`a package. A portion of the leadframe is internal to the
`package, i.e., completely surrounded by the plastic encap(cid:173)
`sulant. Portions of the leads of the leadframe extend eter(cid:173)
`nally from the package and are used to connect the package
`externally.
`Further background information concerning conventional
`plastic integrated circuit packages and leadframes is con(cid:173)
`tained in chapter 8 of the book Microelectronics Packaging
`Handbook (1989), which was edited by R. Tummala and E.
`Rymaszewski, and is published by Van Nostrand Reinhold,
`115 Fifth Avenue, New York, N.Y.
`A problem with conventional plastic packages is that their
`internal leadframes limit reduction of the size of the pack(cid:173)
`ages. Practitioners have attempted to reduce the size of 45
`packages by eliminating internal leadframes, as is shown in
`U.S. Pat. No. 4,530,152 to Roche et al and U.S. Pat. No.
`5,172,214 to Castro, but these packages have numerous
`disadvantages. The contacts of the package shown by Roche
`in the
`'152 patent have orthogonal side surfaces. 50
`Accordingly, the packages are believed to be unreliable
`because the contacts could easily be pulled from the encap(cid:173)
`sulant material. The package shown by Castro in the '214
`patent has leads which extend into the body of the package
`from a lower external surface of the package to the top of the 55
`die. These leads are large, and have complex bends. Includ(cid:173)
`ing such leads in a package would increase manufacturing
`costs and limit reductions in the lateral size of the package.
`By contrast, the contacts of the packages within the present
`invention are simpler, do not have such bends, and allow for 60
`packages of smaller lateral size.
`
`SUMMARY OF THE INVENTION
`
`The present invention is to directed toward improved
`plastic packages for housing an integrated circuit die, and to
`leadframes and methods for making such packages. The
`packages of the present invention are easier and less expen-
`
`VIZIO Ex. 1034 Page 00008
`
`

`

`US 6,433,277 Bl
`
`3
`nected rectangular frames. A die pad is within and connected
`to each of the interconnected frames. A set of tabs extend
`from each frame toward the sides of the enclosed die pad
`without contacting the die pad. A subsequent encapsulation
`step includes applying an encapsulant material onto the
`surface of the leadframe to which the dies are attached. This
`step covers the dies and the side surfaces of the die pads and
`tabs within a single block of encapsulant material. The
`encapsulant material is then hardened. A cutting step sepa(cid:173)
`rates individual packages from each other and from the 10
`disposable portions of the leadframe. The cutting step also
`severs the connection between each of the interconnected
`frames and the die pad and tabs within each frame.
`
`20
`
`4
`includes a circle and dashed line 3-3, which indicate the
`view of FIG. 3.
`Leadframe 20 of FIG. 2 includes a peripheral rectangular
`frame 21. Frame 21 consists of four rectilinear members.
`5 The two intersecting pairs of parallel members of frame 21
`are denoted as members 22 and 22A and 23 and 23A.
`Artisans should understand that the terms "rectangular" or
`"rectangle" as used herein include a square, which is a
`rectangle with four equivalent sides.
`A rectangular die pad 24 is within and connected to frame
`21. Die pad 24 has a planar or substantially planar upper first
`surface 25 and, although it is not shown in FIG. 2, an
`opposite planar or substantially planar lower second surface
`26. Die pad 24 also has peripheral side surfaces 27 between
`15 upper first surface 25 and lower second surface 26.
`A connector 28 connects two parallel side surfaces 27 of
`die pad 24 to members 22 and 22A of frame 21 of FIG. 2.
`Each connector 28 includes a mushroom-shaped anchor 29,
`although other shapes may be used for anchor 29.
`Three finger-like rectangular tabs 30 are connected to and
`extend from members 23 and 23A toward an adjacent side
`surface 27 of die pad 24 without contacting side surfaces 27.
`As a result of this configuration, the completed package will
`have a single row of three contacts on two parallel sides of
`the package. Tabs 30 ultimately are severed from members
`23 and 23A along cut lines C-C and D-D of FIG. 2, and
`become the contacts of the package.
`The number, location, and shape of tabs 30 may vary. For
`30 example, instead of having tabs 30 only on members 23 and
`23A of frame 21 of leadframe 20, as in FIG. 2, sets of tabs
`30 may be placed on all four members of frame 21. This
`alternative embodiment would result in the formation of a
`quad package.
`Each tab 30 of FIG. 2 has a planar or substantially planar
`upper first surface 31 and, although it is not shown in FIG.
`2, an opposite planar or substantially planar lower second
`surface 32. Each tab 30 also has three peripheral side
`surfaces 33 between upper first surface 31 and lower second
`surface 32.
`FIGS. 3-6 show an enlarged cross-sectional side view of
`the circled portion of FIG. 2 along line 3-3. In particular,
`FIGS. 3-6 show, in accordance with the present invention,
`a side surface 27 of a die pad 24 and a side surface 33 of a
`tab 30 of leadframe 20 of FIG. 2.
`Side surface 27 of die pad 24 and side surface 33 of tab
`30 of FIG. 3 have reentrant portions. In particular, the upper
`and lower portions of side surfaces 27 and 33 are reentrant
`such that there is a central peak 34 which extends outward
`from side surfaces 27 and 33 of die pad 24 and tab 30,
`respectively. Encapsulant material flows into the reentrant
`portions of side surfaces 27 and 33. Central peak 34 extends
`into the encapsulant material.
`The reentrant portions of side surfaces 27 of die pad 24
`and side surfaces 33 of tabs 30 of FIG. 3 have the function,
`in a completed package, of enhancing the connection
`between the encapsulating material, on the one hand, and die
`pad 24 and the contacts of the package (i.e., severed tabs 30),
`on the other hand.
`In addition to having reentrant portions, side surface 27 of
`die pad 24 and side surface 33 of tab 30 of FIG. 3 have a
`roughly-textured surface which includes numerous asperi(cid:173)
`ties. Encapsulant material flows into the areas of the asperi(cid:173)
`ties. The asperities also enhance the connection between the
`encapsulant material and die pad 24 and the contacts of the
`package (i.e., the severed tabs 30).
`
`BRIEF DESCRIPTION OF DRAWINGS
`FIG. 1 is a flow chart of a method of making a package.
`FIG. 2 is a top view of leadframe used for making a
`package.
`FIGS. 3 is an enlarged cross-sectional side view of a
`circled portion of FIG. 2. FIGS. 3 shows an embodiment of
`a side surface of a die pad and tab.
`FIG. 4 is a first alternative embodiment of a side surface
`of a die pad and tab.
`FIG. 5 is a second alternative embodiment of a side 25
`surface of a die pad and tab.
`FIG. 6 is a third alternative embodiment of a side surface
`of a die pad and tab.
`FIG. 7 is a top view of the leadframe of FIG. 1 after
`encapsulation. The dashed lines are cutting paths for a
`subsequent sawing step.
`FIG. 8 is a cross-sectional side view of a completed
`package.
`FIG. 9 is a cross-sectional side view of the package of 35
`FIG. 8 further including solder interconnection bumps on
`the package contacts.
`FIG. 10 is a flow chart of a method for making a plurality
`of packages simultaneously.
`FIG. 11 is a top view of a leadframe used for making a 40
`plurality of packages simultaneously.
`
`DETAILED DESCRIPTION
`FIG. 1 shows an exemplary method of assembling a
`package in accordance with the present invention. FIG. 8 45
`shows a completed package.
`Step 1 of FIG. 1 provides a metal leadframe. FIG. 2 is a
`top view of a first embodiment of a metal leadframe 20 in
`accordance with the present invention. For ease of view, 50
`shading is used in FIG. 2 to distinguish the metal portions of
`leadframe 20 from empty spaces between the various ele(cid:173)
`ments of leadframe 20.
`Leadframe 20 of FIG. 2 is planar or substantially planar
`and is made of a conventional leadframe metal, such as 55
`copper or copper alloys, plated copper or plated copper
`alloys, Alloy 42 ( 42% nickel, 58% iron), or copper plated
`steel, depending on the application. The opposing upper and
`lower surfaces of leadframe 20 may be plated with different
`metals. For example, the tabs 30 and/ or other portions of 60
`leadframe 20 which ultimately are enclosed within the
`package may be plated with silver, gold, nickel palladium, or
`copper. Such plating, for example, may enhance attachment
`of bond wires to tabs 30.
`FIG. 2 includes dash lines A-A, B-B, C-C, and 65
`D-D. These are lines which indicate where leadframe 20 is
`cut in Step 6 of FIG. 1. Step 6 is described below. FIG. 2 also
`
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`US 6,433,277 Bl
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`5
`FIG. 4 shows a first alternative profile for side surfaces 27
`of die pad 24 and side surfaces 33 of tabs 30 of leadframe
`20 of FIG. 2. In the embodiment of FIG. 4, side surfaces 27
`and 33 each have a central depression 35 and a roughly(cid:173)
`textured surface which includes numerous asperities. Encap-
`sulant material flows into central depression 35 and in the
`areas of the asperities. The reentrant portion and asperities of
`side surfaces 27 and 33 of FIG. 4 have the function, in a
`completed package, of enhancing the connection between
`the encapsulant material and die pad 24 and the contacts of
`the package (i.e., the severed tabs 30).
`FIG. 5 shows a second alternative profile for side surfaces
`27 of die pad 24 and side surfaces 33 of tabs 30 of leadframe
`20 of FIG. 2. In the embodiment of FIG. 5, side surfaces 27
`and 33 include a rounded lip 36 adjacent to upper surface 25
`and 31 of die pad 24 and tab 30, respectively. Lip 30 has,a
`roughly-textured surface which includes numerous asperi(cid:173)
`ties. Side surfaces 27 and 33 also have a reentrant orthogonal
`portion 37 beneath lip 36, adjacent to lower second surface
`29 and 32 of die pad 24 and tab 30, respectively. Encapsulant
`material flows beneath lip 36 and into the area of the
`asperities. Like the embodiments of FIGS. 3 and 4, the
`reentrant portions and asperities of side surface 27 of die pad
`24 and side surface 33 of tab 30 of FIG. 5 have the function,
`in a completed package, of enhancing the connection 25
`between the encapsulant material and die pad 24 and the
`contacts of the package (i.e., tabs 30 after they are severed
`from members 23 and 23A).
`FIG. 6 shows a third alternative for side surfaces 27 of die
`pad 24 and side surfaces 33 of tabs 30 of leadframe 20 of
`FIG. 1. In this embodiment, side surfaces 27 and 33 each
`include a rectangular lip 38 adjacent to upper surface 25 and
`31 of die pad 24 and tab 30, respectively. Side surfaces 27
`and 33 also have a reentrant orthogonal portion 39 beneath
`lip 38 adjacent to lower second surface 29 and 32 of die pad
`24 and tab 30, respectively. Encapsulant material flows
`beneath lip 38. Like the embodiments of FIGS. 3-5, the
`reentrant portions of side surface 27 of die pad 24 and side
`surface 33 of tab 30 of FIG. 6 have the function, in a
`completed package, of enhancing the connection between
`the encapsulant material and die pad 24 and the contacts of
`the package (i.e., severed tabs 30).
`As discussed above, Step 1 of FIG. 1 provides a metal
`leadframe having features like those shown in FIG. 2 and
`either FIG. 3, 4, 5, or 6, or equivalents thereof. Leadframe
`20 of FIG. 2 is formed from rolled strip metal stock by wet
`chemical etching or mechanical stamping using progressive
`dies.
`As is well known, chemical etching (also known as
`chemical milling) is a process that uses photolithography
`and metal-dissolving chemicals to etch a pattern into a metal
`strip. The photoresist is exposed to ultraviolet light through
`a photo mask having a desired pattern, and is subsequently
`developed and cured. Chemicals are sprayed or otherwise
`applied to the masked strip, and exposed portions of the strip
`are etched away, leaving the desired pattern.
`As is also well known, progressive stamping uses sets of
`progressive dies to mechanically remove metal from a metal
`strip. Each of a plurality of stamping stations uses one of the 60
`dies to punch a distinct small area of metal from the strip as
`the strip moves through the stations.
`A leadframe 20 having side surfaces like FIG. 3 can be
`formed by chemically etching the rolled strip metal stock
`from both sides using a conventional liquid etchant. The etch 65
`process is stopped early so that there is an underetching of
`all of the side surfaces of the components of leadframe 20,
`
`6
`including side surfaces 27 of die pad 24 and side surfaces 33
`of tabs 30, compared to the time it would take to form
`vertical side surfaces. The size and shape of central peak 34
`of FIG. 2 is controlled by the amount of underetching.
`A leadframe 20 having side surfaces like FIG. 4 can be
`formed by chemically etching the rolled strip metal stock
`from one side using a conventional liquid etchant. The etch
`process is continued beyond the time required to form
`orthogonal side surfaces for the components of leadframe
`10 20. The size and shape of central depression 35 of FIG. 3 is
`controlled by the amount of overetching.
`A leadframe 20 having side surfaces like FIG. 5 can be
`formed in a two step process. The first step of such a process
`involves forming a leadframe 20 by chemical etching or
`15 progressive stamping so that the side surfaces of the com(cid:173)
`ponents of leadframe 20, including die pad 24 and tabs 30,
`have an orthogonal profile. The second step involves coining
`the upper first surface of the leadframe 20, that is, applying
`a high pressure impact to the upper first surface of the
`20 leadframe 20. This step deforms the side surfaces of lead(cid:173)
`frame 40 adjacent to the impacted surface so that the
`rounded, asperity-marked protruding lip 36 of FIG. 5 is
`formed.
`A leadframe 20 having side surfaces like FIG. 6 can be
`formed by progressive stamping. The side surfaces of the
`components of leadframe 20, including side surfaces 27 of
`die pad 24 and the side surfaces 33 of tabs 30, can be
`provided with a rectangular lip 38 and a reentrant orthogonal
`portion 39 by including intermediate stamping steps which
`do not fully cut through the rolled strip metal stock before
`finally cutting through the rolled strip sheet. The interme(cid:173)
`diate stamping steps and the final cutting steps combine to
`form the rectangular, protruding lips 38 of side surfaces 27
`and 33 of FIG. 5.
`Step 2 ofFIG. l places an integrated circuit die onto upper
`first surface 25 of die pad 24. The placement and attachment
`of the die onto die pad 24 may be performed using a
`conventional die attach machine and conventional die attach
`adhesives. During Step 2 and the subsequent assembly steps,
`leadframe 20 of FIG. 2 is grounded to protect against
`electrostatic discharge ("ESD").
`Step 3 of FIG. 1 electrically connects a conductive metal
`bond wire between individual bonding pads on the inte(cid:173)
`grated circuit die and the upper first surface 31 of individual
`tabs 30 on leadframe 20 of FIG. 2. Tabs 30 ultimately
`become contacts in the completed package, after tabs 30 are
`severed from members 23 and 23A of frame 21. Conven(cid:173)
`tional bond wire attachment equipment may be used for Step
`50 3. Leadframe 20 of FIG. 2 is grounded during this wiring
`step to prevent damage to the integrated circuit dies due to
`electrostatic discharge. At the completion of Step 3, each
`bonding pad of each die is electrically connected to a tab 30
`of leadframe 20 of FIG. 1, which is grounded. Tabs 30 of
`55 leadframe 20 are all shorted together, which facilitates ESD
`protection.
`In Step 4 of FIG. 1, the lower second surface of leadframe
`20 of FIG. 2 is placed on a flat surface, and a viscous
`adhesive encapsulating material is applied onto the upward(cid:173)
`facing upper first surface of leadframe 20. The encapsulating
`material is applied so that the encapsulating material covers:
`the integrated circuit die; the bond wires; any exposed
`peripheral portions of upper first surface 25 of die pad 24
`around the die; side surfaces 27 of die pad 24; upper first
`surface 31 of tabs 30; side surfaces 33 of tabs 33; and part
`or all of the width of members 22, 22A, 23, and 23A of
`frame 21. The encapsulant material also fills the empty
`
`30
`
`35
`
`40
`
`45
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`US 6,433,277 Bl
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`7
`spaces between the components within frame 21 of lead(cid:173)
`frame 20. The encapsulant material does not, however, cover
`lower second surface 26 of die pad 24 or lower second
`surfaces 32 of tabs 30 of FIG. 2. In an alternative
`embodiment, die pad 24 may be up set during the encapsu(cid:173)
`lation step so that a thin layer of encapsulant material forms
`under lower second surface 26 of die pad 24. If such a step
`were used, die pad 24 would be completely internal to the
`package. Finally, the encapsulant material is hardened.
`There are several methods by which Step 4 of FIG. 1 may 10
`be accomplished, depending on the application. For
`example, as a first step, leadframe 20 of FIG. 2 is placed on
`a horizontal surface. As a second step, a contiguous bead of
`a conventional hardenable viscous adhesive material, such
`as HYSOL 4451 epoxy from the Dexter-Hysol Company of
`City of Industry, California, is applied onto the upper first 15
`surface of side members 22, 22A, 23, and 23A of frame 21
`