U.S. patent application number 13/188367 was filed with the patent office on 2011-11-17 for thin quad flat package with no leads (qfn) fabrication methods.
This patent application is currently assigned to SHANGHAI KAIHONG TECHNOLOGY CO., LTD. Invention is credited to Xiaolan Jiang, Zhining Li, Xiaochun Tan.
Application Number | 20110281398 13/188367 |
Document ID | / |
Family ID | 41063485 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110281398 |
Kind Code |
A1 |
Tan; Xiaochun ; et
al. |
November 17, 2011 |
THIN QUAD FLAT PACKAGE WITH NO LEADS (QFN) FABRICATION METHODS
Abstract
Embodiments of the present invention include a method of
packaging semiconductor devices. The method comprises the steps of
molding a surface of a wafer, sawing the wafer into individual
devices, attaching the individual semiconductor device to an
adhesive surface, molding the exposed surface, and sawing the wafer
into individual semiconductor devices. The step of molding forms a
continuous molded layer. The step of sawing results in each
individual semiconductor having a molded layer. This molded layer
corresponds to a portion of the continuous molded layer. The step
of attaching includes attaching the molded layer of the individual
semiconductor devices to the adhesive surface. The step of molding
the exposed area includes molding an exposed area above the
adhesive surface. This forms a solid expanse of material. The step
of sawing the wafer into individual semiconductor devices includes
sawing the solid expanse of material.
Inventors: |
Tan; Xiaochun; (Shanghai,
CN) ; Li; Zhining; (Shanghai, CN) ; Jiang;
Xiaolan; (Shanghai, CN) |
Assignee: |
SHANGHAI KAIHONG TECHNOLOGY CO.,
LTD
|
Family ID: |
41063485 |
Appl. No.: |
13/188367 |
Filed: |
July 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12728914 |
Mar 22, 2010 |
8008128 |
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13188367 |
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12109635 |
Apr 25, 2008 |
7713784 |
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12728914 |
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Current U.S.
Class: |
438/113 ;
257/E21.504; 257/E21.506; 257/E21.702 |
Current CPC
Class: |
H01L 2224/274 20130101;
H01L 2924/01075 20130101; H01L 2221/68359 20130101; H01L 2224/48247
20130101; H01L 2924/00014 20130101; H01L 21/6835 20130101; H01L
2924/181 20130101; H01L 24/48 20130101; H01L 2224/83 20130101; H01L
2224/48091 20130101; H01L 24/97 20130101; H01L 23/3121 20130101;
H01L 24/27 20130101; H01L 2924/181 20130101; H01L 24/85 20130101;
H01L 2924/04953 20130101; H01L 24/83 20130101; H01L 2924/10158
20130101; H01L 2924/18301 20130101; H01L 2224/97 20130101; H01L
2224/85 20130101; H01L 2224/85 20130101; H01L 2224/45015 20130101;
H01L 2924/01013 20130101; H01L 2924/15153 20130101; H01L 21/561
20130101; H01L 29/0657 20130101; H01L 2924/00014 20130101; H01L
2224/97 20130101; H01L 2224/48091 20130101; H01L 2924/00012
20130101; H01L 2924/01082 20130101; H01L 2924/00014 20130101; H01L
2924/1517 20130101; H01L 2924/18165 20130101; H01L 2224/45099
20130101; H01L 2224/73265 20130101; H01L 2924/00014 20130101; H01L
2924/207 20130101 |
Class at
Publication: |
438/113 ;
257/E21.504; 257/E21.506; 257/E21.702 |
International
Class: |
H01L 21/56 20060101
H01L021/56; H01L 21/782 20060101 H01L021/782; H01L 21/60 20060101
H01L021/60 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2008 |
CN |
200810034572.6 |
Claims
1. A method of packaging semiconductor devices comprising: molding
a first surface of a wafer with a first mold compound, and in
accordance therewith, forming a continuous molded layer; sawing the
wafer into individual semiconductor devices, each individual
semiconductor device includes a molded layer corresponding to a
portion of the continuous molded layer; attaching a surface of each
of the molded layers of each of the individual semiconductor
devices to an adhesive surface; molding an exposed area above the
adhesive surface with a second mold compound, and in accordance
therewith, forming a solid expanse of material; removing the
adhesive surface to expose each of the surfaces of each of the
molded layers of each of the individual semiconductor device; and
sawing the solid expanse of material, and in accordance therewith,
forming a plurality of individual packaged semiconductor
devices.
2. The method of claim 1, wherein the adhesive surface has a
leadframe attached thereto and the step of attaching the surface of
each of the molded layers of each the individual semiconductor
devices to the adhesive surface includes placing the individual
semiconductor devices in individual cavities of the leadframe.
3. The method of claim 1, further comprising attaching a bond wire
between a conductive pad of each of the individual semiconductor
device to a conductive surface of a portion of a leadframe, the
conductive surface corresponding to the conductive pad, wherein the
leadframe and the surface of each the molded layers of the each of
the individual semiconductor devices are attached to the adhesive
surface.
4. The method of claim 1, wherein the step of molding an exposed
area above the adhesive surface includes molding exposed areas of
the individual semiconductor devices and a leadframe, and wherein a
portion of the leadframe and a portion of the surface of each of
the molded layers of each of the individual semiconductor devices
are attached to the adhesive surface, and in accordance therewith,
said attached portions remain unexposed.
5. The method of claim 4, wherein the step of molding an exposed
area above the adhesive surface includes molding bond wires between
conductive pads of each of the individual semiconductor devices and
the leadframe.
6. The method of claim 1, wherein the first mold compound is the
same as the second mold compound.
7. The method of claim 1, wherein portions of the second mold
compound meld with portions of the first mold compound.
8. The method of claim 1, wherein portions of the second mold
compound adhere with portions of the first mold compound.
9. The method of claim 1, wherein the step of sawing the solid
expanse of material includes sawing the leadframe.
10. The method of claim 8, wherein the step of sawing the solid
expanse of material further includes sawing the second mold
compound overlying the leadframe.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of, and
claims priority from, U.S. patent application Ser. No. 12/728,914,
filed Mar. 22, 2010, titled "Thin Quad Flat Package with No Leads
(QFN) Fabrication Methods," of Tan et al., which is a continuation
application of, and claims priority from, U.S. patent application
Ser. No. 12/109,635, filed Apr. 25, 2008, titled "Thin Quad Flat
Package with No Leads (QFN) Fabrication Methods," of Tan et al.,
which claims priority from Chinese Patent Application No.
200810034572.6, filed Mar. 13, 2008, each of which is incorporated
by reference herein in its entirety for all purposes.
BACKGROUND
[0002] The present invention relates to semiconductor package
fabrication processes, and in particular, to thin quad flat package
no leads (QFN) fabrication methods.
[0003] Consumers are demanding that devices such as cell phones,
personal digital assistants, and music players be more reliable,
compact, and affordable. For example, consumers are requiring that
their cell phones be ultra thin and reliable. This requires thinner
packaging and fewer defects. Additionally, these low profile
applications may also require power electronics which require some
level of thermal dissipation from the package. Of course, these
package features need to be available at an affordable price.
[0004] Present QFN packages are fabricated using standard methods
using a lead frame and a die attach pad. These methods limit the
thinness of the device and may introduce additional process
elements which may be an additional source of potential defects.
These additional process elements may add additional cost to the
package fabrication. Present QFN package heat dissipation may be
limited and may require additional space for heat sinking on the
printed circuit board or substrate.
[0005] Thus, there is a need for improved package assembly methods.
The present invention solves these and other problems by providing
chip scale package assembly methods.
SUMMARY
[0006] Embodiments of the present invention improve fabrication
methods of packaging semiconductors. In one embodiment, a method of
packaging semiconductor devices includes molding a first surface of
a wafer with a first mold compound, and in accordance therewith,
forming a continuous molded layer, and sawing the wafer into
individual semiconductor devices, each individual semiconductor
device including a molded layer corresponding to a portion of the
continuous molded layer. The method further includes attaching a
surface of each of the molded layers of each of the individual
semiconductor devices to an adhesive surface, and molding an
exposed area above the adhesive surface with a second mold
compound, and in accordance therewith, forming a solid expanse of
material. The method further includes removing the adhesive surface
to expose each of the surfaces of each of the molded layers of each
of the individual semiconductor device; and sawing the solid
expanse of material, and in accordance therewith, forming a
plurality of individual packaged semiconductor devices.
[0007] According to a specific embodiment, the adhesive surface has
a leadframe attached thereto and the step of attaching the surface
of each of the molded layers of each the individual semiconductor
devices to the adhesive surface includes placing the individual
semiconductor devices within individual cavities of the
leadframe.
[0008] According to another specific embodiment, the method further
includes attaching a bond wire between a conductive pad of each
individual semiconductor device to a conductive surface of a
portion of a leadframe. The conductive surface corresponds to the
conductive pad. The leadframe and the surface of each the molded
layers of the each of the individual semiconductor devices are
attached to the adhesive surface.
[0009] According to another specific embodiment, the step of
molding an exposed area above the adhesive surface includes molding
exposed areas of the individual semiconductor devices and a
leadframe. A portion of the leadframe and a portion of the surface
of each of the molded layers of each of the individual
semiconductor devices are attached to the adhesive surface, and in
accordance therewith, said attached portions remain unexposed.
[0010] According to another specific embodiment, the step of
molding an exposed area above the adhesive surface includes molding
bond wires between conductive pads of each the individual
semiconductor devices and the leadframe.
[0011] According to another specific embodiment, the first mold
compound is the same as the second mold compound.
[0012] According to another specific embodiment, portions of the
second mold compound meld with portions of the first mold
compound.
[0013] According to another specific embodiment, portions of the
second mold compound adhere with portions of the first mold
compound.
[0014] According to another specific embodiment, the step of sawing
the solid expanse of material includes sawing the leadframe, and
may include sawing the second mold compound overlying the
leadframe.
[0015] In one embodiment, a method of packaging semiconductor
devices includes attaching a wafer, adding, sawing through the
wafer, attaching devices, molding, and sawing to form a plurality
of packaged semiconductor devices. The step of attaching includes
attaching a first side of the wafer to a first adhesive surface.
The step of adding includes adding a layer of metal to a second
side of the wafer. The layer of metal forms a metalized surface of
the wafer. The step of sawing the wafer includes sawing through a
plurality of saw streets of the wafer. This establishes individual
semiconductor devices. Each individual semiconductor device has a
metalized surface corresponding to a portion of the metalized
surface of the wafer. The step of attaching devices includes
attaching the metalized surface of each of the individual
semiconductor devices to a second adhesive surface. This makes the
metalized surface unexposed. The step of molding includes molding
an exposed area above the second adhesive surface. This forms a
solid expanse of material. The step of sawing to form a plurality
of packaged semiconductor devices includes sawing the solid expanse
of material.
[0016] In one embodiment, the method further comprises sawing from
the second side of the wafer. This establishes a notch. The step of
adding the layer of metal forms a discernable channel within the
notch. This provides surface details for alignment.
[0017] In one embodiment, the method further comprises sawing along
the plurality of saw streets on the second side of a wafer prior to
the sawing through the plurality of saw streets. This establishes a
first cut having a height less than a thickness of the wafer.
[0018] In one embodiment, the step of sawing through the wafer
creates a second cut having a width less than a width of the first
cut. This forms a ledge.
[0019] In one embodiment, a leadframe tape includes the second
adhesive surface. The leadframe tape has a leadframe attached. The
step of attaching the metalized surface of each of the individual
semiconductor devices to the second adhesive surface includes
placing the individual semiconductor devices within individual
cavities of the leadframe
[0020] In one embodiment, the step of molding the exposed area
includes molding exposed portions of the individual semiconductor
devices and the leadframe. A portion of the leadframe and the metal
surface of the individual semiconductor devices are attached to the
second adhesive surface. Therefore these portions remain
unexposed.
[0021] In one embodiment, the method further comprises re-taping
the individual semiconductor devices after the step of sawing
through a plurality of saw streets. The step of re-taping includes
attaching the metalized surface of the wafer to a third adhesive
surface after the sawing through the plurality of saw streets, and
removing the first adhesive surface from the first side of the
wafer.
[0022] In one embodiment, the step of attaching the metalized
surface of each of the individual semiconductor devices includes
picking the individual semiconductor devices from the third
adhesive surface.
[0023] Additional embodiments will be evident from the following
detailed description and accompanying drawings, which provide a
better understanding of the nature and advantages of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates a method of fabricating a thin QFN
package and the corresponding cut away side views according to one
embodiment of the present invention.
[0025] FIG. 2 illustrates another method of fabricating a thin QFN
package according to another embodiment of the present
invention.
DETAILED DESCRIPTION
[0026] Described herein are techniques for performing thin QFN
package fabrication methods. In the following description, for
purposes of explanation, numerous examples and specific details are
set forth in order to provide a thorough understanding of the
present invention. It will be evident, however, to one skilled in
the art that the present invention as defined by the claims may
include some or all of the features in these examples alone or in
combination with other features described below, and may further
include obvious modifications and equivalents of the features and
concepts described herein.
[0027] FIG. 1 illustrates a method 100 of fabricating a thin QFN
package according to one embodiment of the present invention. The
method 100 includes the steps of backside molding 101, front side
sawing 102, die attaching 103, wire bonding 104, molding 105,
de-taping 106, and singulation sawing 107.
[0028] The step of backside molding 101 includes adhering a mold
compound 109 to the back side of the wafer 110. The molding 101
forms a continuous molded layer 108 having a thickness 146.
[0029] The step of front side sawing 102 cuts through the front
side 137 of the wafer 110.
[0030] This saws the wafer into individual devices (139, 140, and
113). Each individual semiconductor device (139, 140, and 113) has
a molded layer (141, 142, and 114) corresponding to a portion of
the continuous molded layer 108. The wafer may be attached to a
tape 115 during the step of front side sawing 102, and the sawing
may remove a portion of the tape 115.
[0031] The step of die attaching 103 includes attaching molded
layer 141 of individual semiconductor device 117 to adhesive
surface 143 of tape 121. Leadframe 116 may be already attached to
the adhesive surface 143 of tape 121. The attaching the molded
layer 141 of individual semiconductor device 117 may include
placing the individual semiconductor device 117 within individual
cavity 144 of the leadframe 116. Another individual semiconductor
device 119 having a molded layer 142 attached to the adhesive
surface 143 within an individual cavity 145 of the leadframe 116 is
shown for clarity.
[0032] The step of wire bonding 104 includes connecting a wire 122
between a first conductive pad of individual semiconductor device
117 to a portion of a conductive surface of the leadframe 116
corresponding to the first conductive pad. Connected wires 123,
124, and 125 are shown for clarity. Wire 123 connects a second
conductive pad of individual semiconductor device 117 to another
portion of the conductive surface of the leadframe 116
corresponding to the second conductive pad. Wire 124 and 125
connect to the leadframe 116 and another individual die 119 in a
manner similar to wire 122 and 123.
[0033] The step of molding 105 includes molding an exposed area
above the adhesive surface 143 using mold compound 133. The molding
105 forms a solid expanse of material. The solid expanse of
material may include mold compound 109, mold compound 133, the
individual semiconductor devices (117, 119), and portions of the
leadframe 116. The molding 105 of the exposed areas above the
adhesive surface 143 may include molding exposed areas of the
individual semiconductor devices (117 and 119) and leadframe 116. A
portion of the leadframe 116 and a portion of the molded layer (141
and 142) of the individual semiconductor devices (117 and 119) are
attached to the adhesive surface 143 of tape 121 and are therefore
unexposed. Mold compound 109 may be the same as mold compound 133.
Mold compound 133 may meld with previously exposed portions (126,
127) of mold compound 109 of the molded layer of the individual
semiconductor device 117. Mold compound 133 may adhere with exposed
portion of mold compound 109 of the individual semiconductor
devices (117 and 199). Locations 126 and 127 are example regions
around individual semiconductor device 117 in which the melding or
the adhering may occur. Locations 128 and 129 are regions around
another individual semiconductor device 119 and are shown for
clarity.
[0034] The step of de-taping 106 removes the tape 121 used in the
steps of die attaching 103, wire bonding 104, and molding 105. This
step may or may not be required prior to the step of singulation
sawing 107.
[0035] The step of singulation sawing 107 includes sawing through
the wafer at location 132 between the devices (117 and 119) such
that a plurality of chip scale packages are formed. Packaged device
130 and 131 are examples of the plurality of chip scale
packages.
[0036] FIG. 2 illustrates another method 200 of fabricating a QFN
package according to another embodiment of the present invention.
The method 200 includes the steps of taping 201, first backside
sawing 202, adding back metal 203, second backside sawing 204,
third backside sawing 205, re-taping 206, die attaching 207, wire
bonding 208, molding 209, singulation sawing 210.
[0037] The step of taping 201 includes attaching the front side of
wafer 211 to an adhesive surface of a tape 212. The tape 212 may be
referred to as wafer tape.
[0038] The step of first backside sawing 202 includes sawing from
the backside 241 of the wafer 211 and establishing a notch 216.
Another notch 217 is shown for clarity. The sawing may be along a
plurality of saw streets. The notch 216 adds surface detail to the
backside of the wafer so that these details may be utilized for
alignment after the step of adding back metal 203. The notch 216 is
a cut having a width and height large enough to add the surface
detail required for alignment after the step of adding back metal
203. The height and width of the required notch may be controlled
by the attributes of the metallization such as thickness, for
example.
[0039] The step of adding back metal 203 includes adding a layer of
metal 246 (shown with angled hatched lines) to the backside 241 of
the wafer 211. The layer of metal 246 forms a metalized surface 220
of the wafer 211. The layer of metal 246 forms a discernable
channel 221 within notch 216. Another discernable channel 222
within notch 217 is shown for clarity.
[0040] The step of second backside sawing 204 includes sawing along
a plurality of saw streets on the back side 241 of the wafer 211.
The second backside sawing 204 results in a cut 223 which has a
height and a width. Another cut 224 is shown for clarity. The cut
223 may be centered on notch 216 such that cut 223 replaces notch
216. For example, cut 223 may have a larger width and height than
notch 216. Cut 223 may have a height that is greater than notch 216
but less than the thickness of the entire composite wafer,
including metal, so that the cut does not penetrate the entire
wafer. The step of second backside sawing 204 may include aligning
the wafer according to the discernable channel (e.g., 221, 222)
prior to applying the saw to the wafer 211.
[0041] The step of third backside sawing 205 includes sawing
through a plurality of saw streets on the back side 241 of the
wafer 211. This establishes individual semiconductor devices (225,
226, and 227) each having a metalized surface corresponding to a
portion of the metalized surface (218, 219, 220) of the wafer 211.
The step of third backside sawing 205 results in cut 228. Another
cut 229 is shown for clarity. Cut 228 may have a width narrower
than the width of cut 223. A difference of the widths of cut 228
and cut 223 may form a ledge 241. This ledge 241 may aid in
securing the semiconductor device 226 within the package after the
step of molding 209. The step of third backside sawing 205 may cut
into a portion of the width of the wafer tape 212, for example, but
not through the entire tape thickness.
[0042] The step of re-taping 206 includes attaching the metalized
surface (e.g., 218, 219, 220) to an adhesive surface of tape 213
and removing the wafer tape 212 from the front side of the wafer.
This step provides corresponding spacing between individual
semiconductor devices (225, 226, 227) on the wafer tape 212 and the
individual semiconductor devices (227, 226, 225) on tape 213 in
preparation for the step of die attaching 207.
[0043] The step of die attaching 207 includes attaching the
metalized surface 219 of the individual semiconductor device 226 to
an adhesive surface 242 of tape 214. The individual semiconductor
device may have been picked from an array of devices attached to
tape 213 and then placed onto tape 214. Tape 214 may be a leadframe
tape in which a leadframe 230 is already attached to the adhesive
surface 242. The attaching the metalized surface 219 of the
individual semiconductor device 226 to an adhesive surface 242
includes placing the individual semiconductor device 226 within an
individual cavity 243 of the leadframe 230. Another individual
semiconductor device 227 with a metalized surface 220 attached to
the adhesive surface 242 in another individual cavity 244 of the
leadframe 230 is shown for clarity.
[0044] The step of wire bonding 208 is similar to that discussed in
step 104 of method 100. Reference numbers 117, 119, 122, 123, 124,
and 125 of FIG. 1 correspond to reference numbers 226, 227, 233,
234, 235, and 236 of FIG. 2 respectively.
[0045] The step of molding 209 includes molding an exposed area
above the adhesive surface 242 using mold compound 237. The molding
209 forms a solid expanse of material 247. The solid expanse of
material 247 may include mold compound 237, portions of the layer
of metal 246, the individual semiconductor devices (e.g., 226,
227), and portions of the leadframe 230. The molding 209 the
exposed areas above the adhesive surface 242 may include molding
exposed areas of the individual semiconductor devices (226 and 227)
and leadframe 230. A portion of the leadframe 230 and a portion of
the metalized surface (219 and 220) of the individual semiconductor
devices (226 and 227) are attached to the adhesive surface 242 and
are therefore unexposed. The ledge 241 may help to secure the
individual semiconductor device 226 within the mold compound
237.
[0046] The step of singulation saw 210 includes sawing through the
wafer at location 240 between the devices (226 and 227) such that a
plurality of chip scale packages are formed. Packaged device 238
and 239 are example elements of the plurality of chip scale
packages.
[0047] The above description illustrates various embodiments of the
present invention along with examples of how aspects of the present
invention may be implemented. The above examples and embodiments
should not be deemed to be the only embodiments, and are presented
to illustrate the flexibility and advantages of the present
invention as defined by the following claims. For example,
switching systems and methods with current sensing according to the
present invention may include some or all of the innovative
features described above. Based on the above disclosure and the
following claims, other arrangements, embodiments, implementations
and equivalents will be evident to those skilled in the art and may
be employed without departing from the spirit and scope of the
invention as defined by the claims.
* * * * *