U.S. patent application number 11/027920 was filed with the patent office on 2005-08-04 for integrated circuit package with transparent encapsulant and method for making thereof.
This patent application is currently assigned to Carsem (M) Sdn.Bhd.. Invention is credited to Chan, Meng Boon, Cheong, Tuck Mun, Khor, Lek Ah, Lee, Huat Kock, Thum, Kong Min, Tung, Mun Hong.
Application Number | 20050167790 11/027920 |
Document ID | / |
Family ID | 34709371 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050167790 |
Kind Code |
A1 |
Khor, Lek Ah ; et
al. |
August 4, 2005 |
Integrated circuit package with transparent encapsulant and method
for making thereof
Abstract
IC package with transparent encapsulant and method for making
thereof. The IC package includes a die pad including a pad bottom
surface, a die disposed on the die pad and including an integrated
circuit, a plurality of leads including a plurality of lead bottom
surfaces, a plurality of conductive wires connecting the die and
the plurality of leads, and an encapsulant material. The
encapsulant material is transparent for visible wavelengths. The
pad bottom surface is exposed without being covered by the
encapsulant material, and the plurality of lead bottom surfaces
each are exposed without being covered by the encapsulant
material.
Inventors: |
Khor, Lek Ah; (Ipoh, MY)
; Lee, Huat Kock; (Ipoh, MY) ; Chan, Meng
Boon; (Ipoh, MY) ; Thum, Kong Min; (Menglembu,
MY) ; Tung, Mun Hong; (Ipoh, MY) ; Cheong,
Tuck Mun; (Bercham, MY) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Carsem (M) Sdn.Bhd.
Ipoh
MY
|
Family ID: |
34709371 |
Appl. No.: |
11/027920 |
Filed: |
December 29, 2004 |
Current U.S.
Class: |
257/666 ;
257/E23.046; 257/E23.124 |
Current CPC
Class: |
H01L 2924/01029
20130101; H01L 2924/14 20130101; H01L 2924/181 20130101; H01L 24/73
20130101; H01L 2224/97 20130101; H01L 2924/00014 20130101; H01L
23/49548 20130101; H01L 2224/48091 20130101; H01L 2924/14 20130101;
H01L 2924/181 20130101; H01L 2924/01005 20130101; H01L 2224/32245
20130101; H01L 2924/16195 20130101; H01L 23/3107 20130101; H01L
24/48 20130101; H01L 24/97 20130101; H01L 2924/00014 20130101; H01L
27/14618 20130101; H01L 2924/01078 20130101; H01L 2924/01079
20130101; H01L 2224/97 20130101; H01L 2224/48247 20130101; H01L
2924/01006 20130101; H01L 2224/73265 20130101; H01L 2224/73265
20130101; H01L 2224/32225 20130101; H01L 2924/12042 20130101; H01L
2924/01019 20130101; H01L 2224/97 20130101; H01L 2924/00014
20130101; H01L 2924/01082 20130101; H01L 2224/48091 20130101; H01L
2224/48247 20130101; H01L 2224/73265 20130101; H01L 2224/45015
20130101; H01L 2924/00 20130101; H01L 2224/73265 20130101; H01L
2224/45099 20130101; H01L 2924/00012 20130101; H01L 2224/48247
20130101; H01L 2224/32225 20130101; H01L 2924/00 20130101; H01L
2224/48247 20130101; H01L 2224/48247 20130101; H01L 2224/32245
20130101; H01L 2224/83 20130101; H01L 2924/00 20130101; H01L
2924/207 20130101; H01L 2224/32245 20130101; H01L 2224/85 20130101;
H01L 2924/00 20130101; H01L 2924/00012 20130101; H01L 2224/32245
20130101; H01L 2924/00012 20130101; H01L 2924/00014 20130101; H01L
2224/73265 20130101; H01L 2224/73265 20130101; H01L 2924/01012
20130101; H01L 2224/97 20130101; H01L 2924/01033 20130101; H01L
2924/12042 20130101; H01L 2224/97 20130101; H01L 2224/97
20130101 |
Class at
Publication: |
257/666 |
International
Class: |
H01L 023/495 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 31, 2003 |
MY |
PI 20035051 |
Claims
What is claimed is:
1. A method for making an IC package with transparent encapsulant,
the method comprising: providing a leadframe, the leadframe
including a first die pad and a second die pad; disposing a first
die on the first die pad and a second die on the second die pad;
forming a cavity on the leadframe, the cavity including the first
die pad and the second die pad; injecting an encapsulant material
into the cavity; cutting the injected encapsulant material and the
leadframe to form a first IC package and a second IC package;
wherein: the encapsulant material is transparent for visible
wavelengths; and the injecting an encapsulant material is performed
at an encapsulant temperature ranging from 140.degree. c to
160.degree. c.
2. The method of claim 1 wherein the injecting an encapsulant
material comprising transferring the encapsulant material at a
pressure ranging from 1100 psi to 1400 psi.
3. The method of claim 2 wherein the injecting an encapsulant
material is further performed in an environment with a dust count
lower than or equal to about 30 k parts per million (PPM).
4. The method of claim 1 wherein the encapsulant material is
configured to provide a transmission rate higher than or equal to
80% for a wavelengths longer than or equal to 350 nm.
5. The method of claim 1 wherein the encapsulant material comprises
a plastic.
6. The method of claim 1 wherein the leadframe comprises an outer
frame surrounding a plurality of die pads, the plurality of die
pads including the first die pad and the second die pad.
7. The method of claim 6 wherein the plurality of die pads forms a
two dimensional array.
8. The method of claim 6 wherein the forming a cavity comprises
forming a plurality of side boundaries approximately on the outer
frame.
9. The method of claim 6 wherein the outer frame comprises a
plurality of elongated openings around the circumference of the
outer frame.
10. An apparatus for making an IC package with transparent
encapsulant, the apparatus comprising: a leadframe, the leadframe
including an outer frame and a plurality of connecting bars, the
plurality of connecting bars attached to the outer frame and
defining a plurality of inner frames arranged in a matrix pattern
within the outer frame, the plurality of inner frames including a
plurality of die pads respectively; a plurality of side boundaries
located approximately on the outer frame; wherein: the plurality of
side boundaries, the outer frame, and the plurality of inner frames
form at least parts of a cavity; the cavity is at least partially
filled with a transparent encapsulant material; and the encapsulant
material is transparent for visible wavelengths.
11. The apparatus of claim 10 wherein the encapsulant material is
configured to provide a transmission rate higher than or equal to
80% for a wavelengths longer than or equal to 350 nm.
12. The apparatus of claim 10 wherein the encapsulant material
comprises a plastic.
13. The apparatus of claim 10 wherein the cavity is configured to
receive an injection of the transparent encapsulant material
performed at an encapsulant temperature ranging from 140.degree. c
to 160.degree. c.
14. The apparatus of claim 13 wherein the cavity is further
configured to receive the injection of the transparent encapsulant
material at a pressure ranging from 1100 psi to 1400 psi.
15. The apparatus of claim 14 wherein the cavity is further
configured to receive the injection of the transparent encapsulant
material further performed in an environment with a dust count
lower than or equal to about 30 k parts per million (PPM).
16. The apparatus of claim 10 wherein the outer frame comprises a
plurality of elongated openings around the circumference of the
outer frame.
17. An IC package with transparent encapsulant, the package
comprising: a die pad including a pad bottom surface; a die
disposed on the die pad and including an integrated circuit; a
plurality of leads including a plurality of lead bottom surfaces; a
plurality of conductive wires connecting the die and the plurality
of leads; and an encapsulant material; wherein: the encapsulant
material is transparent for visible wavelengths; the pad bottom
surface is exposed without being covered by the encapsulant
material; the plurality of lead bottom surfaces each are exposed
without being covered by the encapsulant material.
18. The IC package of claim 17 wherein the encapsulant material is
configured to provide a transmission rate higher than or equal to
80% for a wavelength longer than or equal to 350 nm.
19. The IC package of claim 18 wherein the encapsulant material
comprises a plastic.
20. The IC package of claim 17 wherein: the die is disposed on the
die pad through a bonding layer; the die pad includes a pad plating
layer; the plurality of leads include a plurality of lead plating
layers respectively.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority to Malaysian Patent
Application No. PI 20035051, filed Dec. 31, 2003, commonly assigned
and incorporated by reference herein for all purposes.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] NOT APPLICABLE
REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER PROGRAM
LISTING APPENDIX SUBMITTED ON A COMPACT DISK.
[0003] NOT APPLICABLE
BACKGROUND OF THE INVENTION
[0004] The present invention relates in general to integrated
circuit (IC) packaging. More particularly, the invention provides
an IC package with transparent encapsulant and a method for making
thereof. Merely by way of example, the invention is described as it
applies to a package in compliance with certain JEDEC standard, but
it should be recognized that the invention has a broader range of
applicability.
[0005] Integrated circuits are usually packaged before being used
in electronic systems. Integrated circuit (IC) packages often
protect the integrated circuits from the surrounding environment
but also provide electrical connections to other components of the
electronic systems. For example, the IC packages include a
plurality of leads that are connected to the integrated circuits,
and such leads can transmit or receive electrical signals from
other components of the electronic systems. In another example, the
IC packages also include encapsulant materials that cover and
protect at least parts of the integrated circuits and/or the
electrical connections between the integrated circuits and the
leads.
[0006] For certain applications, the integrated circuits include
optical sensors, which are used in light sensitive or light
activated devices such as laser diodes. To meet this demand, IC
packages with transparent windows have been developed. FIG. 1 is a
conventional IC package with a transparent window. The IC package 1
can be used as a ceramic dual-in-line package (CERDIP) of a
charge-coupled device (CCD). As shown in FIG. 1, the package 1
includes a die 11, a ceramic lower plate 12, a leadframe 14, a
ceramic upper plate 15 and a window 10. The lower plate 12 serves
as a die pad. The die 11 includes an integrated circuit coupled to
a light sensor 19.
[0007] Additionally, a die sealant 13 is applied to one side of a
central portion of the die pad 12, and the die 11 is attached to
the die pad 12 through the die sealant 13 by a heat treatment.
Moreover, a ceramic sealant 16 is applied to top fringes of the die
pad 12, and the lead frame 14 is mounted on the die pad 12 through
the sealant 16. Also, the ceramic sealant 16 is applied to the lead
frame 14, and the upper ceramic plate 15 is fixed onto the
leadframe 14 through the sealant 16. Alternatively, the ceramic
plate sealant 16 is provided to the lower side of the ceramic upper
plate 15, and the ceramic upper plate 15 is mounted onto the lead
frame 14. Through a heat treatment, the ceramic plate sealant 16 is
molten to seal the lead framed 14 to the ceramic upper plate 15.
Additionally, the die 11 and the inner leads of the lead frame 14
are electrically connected by conductive wires 18. The transparent
window 10 is sealed by a transparent window sealant 17. For
example, the sealant 17 is melted to seal the transparent window 10
to the upper portion of the ceramic upper plate 15 through a heat
treatment. Moreover, the lead frame 14 is trimmed, and the
fabrication of the package 1 is completed.
[0008] The IC package 1 has various weaknesses. For example, the
fabrication process for coating the ceramic sealant 16 on the lower
side of the ceramic upper plate 15 is complex and costly.
Additionally, the desired sealant effect is difficult to achieve
between the ceramic upper plate 15 and the window sealant 17. If
the window 10 is peeled off from the ceramic upper plate 15, the IC
package 1 can be significantly damaged.
[0009] FIG. 2 is another conventional IC package with a transparent
window. A die 21 is placed on a die pad 22 of a lead frame 23. Lead
fingers of the lead frame 23 have electrical connections 25 with
the die 21. The die 21 includes an integrated circuit coupled to a
light sensor 26. The die 21 and the die pad 22 are covered by a
predetermined volume of transparent plastic 24. Thereafter the
transparent plastic 24 is molded to form an IC package 2 with a
transparent window. The transparent plastic 24 often has an
expansion coefficient larger than those of other types of molding
compounds. This large expansion coefficient can result in
disassociation of the transparent plastic 24 from other components
of the IC package 2 after some time of use. For example, the IC
package 2 includes a copper die pad, copper leads, and a die
surface. The die surface are made of silicon-based material. Such
disassociation often leads to cracks and thereby damages the IC
package.
[0010] Hence it is highly desirable to improve techniques for
integrated circuit packaging.
BRIEF SUMMARY OF THE INVENTION
[0011] The present invention relates in general to integrated
circuit (IC) packaging. More particularly, the invention provides
an IC package with transparent encapsulant and a method for making
thereof. Merely by way of example, the invention is described as it
applies to a package in compliance with certain JEDEC standard, but
it should be recognized that the invention has a broader range of
applicability.
[0012] According to one embodiment of the present invention, a
method for making an IC package with transparent encapsulant is
provided. The method includes providing a leadframe. The leadframe
includes a first die pad and a second die pad. Additionally, the
method includes disposing a first die on the first die pad and a
second die on the second die pad and forming a cavity on the
leadframe. The cavity including the first die pad and the second
die pad. Moreover, the method includes injecting an encapsulant
material into the cavity, and cutting the injected encapsulant
material and the leadframe to form a first IC package and a second
IC package. The encapsulant material is transparent for visible
wavelengths, and the injecting an encapsulant material is performed
at an encapsulant temperature ranging from 140.degree. c to
160.degree. c.
[0013] According to another embodiment of the present invention, an
apparatus for making an IC package with transparent encapsulant
includes a leadframe. The leadframe includes an outer frame and a
plurality of connecting bars. The plurality of connecting bars are
attached to the outer frame and defines a plurality of inner frames
arranged in a matrix pattern within the outer frame. The plurality
of inner frames includes a plurality of die pads respectively.
Additionally, the leadframe includes a plurality of side boundaries
located approximately on the outer frame. The plurality of side
boundaries, the outer frame, and the plurality of inner frames form
at least parts of a cavity, and the cavity is at least partially
filled with a transparent encapsulant material. The encapsulant
material is transparent for visible wavelengths.
[0014] According to yet another embodiment of the present
invention, an IC package with transparent encapsulant includes a
die pad including a pad bottom surface, a die disposed on the die
pad and including an integrated circuit, a plurality of leads
including a plurality of lead bottom surfaces, a plurality of
conductive wires connecting the die and the plurality of leads, and
an encapsulant material. The encapsulant material is transparent
for visible wavelengths. The pad bottom surface is exposed without
being covered by the encapsulant material, and the plurality of
lead bottom surfaces each are exposed without being covered by the
encapsulant material.
[0015] Many benefits are achieved by way of the present invention
over conventional techniques. Certain embodiments of the present
invention provide IC packages with transparent encapsulants. For
example, the transparent encapsulants are both reliable and
durable. Some embodiments of the present invention provide a method
that can easily apply transparent encapsulants. Certain embodiments
of the present invention can prevent or reduce delamination of
transparent encapsulants. For example, the delamination of
transparent encapsulants may occur during cooling and result in
warpage and delamination rejects of the IC packages. Some
embodiments of the present invention use stress-relief structures
in a leadframe. The stress-relief structures can prevent or reduce
the propagation of delamination of transparent encapsulants.
Certain embodiments of the present invention apply transparent
encapsulants to only one side of a leadframe. The amount of
transparent encapsulant used is reduced and the fabrication costs
are lowered. Some embodiments of the present invention provide
transparent IC packages with improved heat dissipation, smaller
size, and/or lighter weight. Certain embodiments of the present
invention use matrix arrays of packaging units. These packaging
units are singulated as an individual optical devices and/or
packages. For example, the matrix arrays allow the use of a single
mould for making packages of various sizes and shapes. Some
embodiments of the present invention provide locking mechanisms.
For example, the locking mechanisms include extended parts. During
encapsulation, the heat causes the encapsulants to melt and flow
under the extended parts. After cooling, the encapsulants under the
locking mechanisms can prevent or reduce the delamination of
transparent encapsulants
[0016] Various additional objects, features and advantages of the
present invention can be more fully appreciated with reference to
the detailed description and accompanying drawings that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a conventional IC package with a transparent
window;
[0018] FIG. 2 is another conventional IC package with a transparent
window;
[0019] FIG. 3 is a simplified cross section of an IC package
according to an embodiment of the present invention;
[0020] FIG. 4 is a simplified diagram for making an IC package with
transparent encapsulant according to an embodiment of the present
invention;
[0021] FIG. 5 shows a simplified leadframe according to an
embodiment of the present invention;
[0022] FIG. 6 shows a simplified leadframe used for making packages
with various sizes according to an embodiment of the present
invention;
[0023] FIG. 7 shows a simplified leadframe used for making packages
of the same size according to another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention relates in general to integrated
circuit (IC) packaging. More particularly, the invention provides
an IC package with transparent encapsulant and a method for making
thereof. Merely by way of example, the invention is described as it
applies to a package in compliance with certain JEDEC standard, but
it should be recognized that the invention has a broader range of
applicability.
[0025] FIG. 3 is a simplified cross section of an IC package
according to an embodiment of the present invention. This diagram
is merely an example, which should not unduly limit the scope of
the claims. One of ordinary skill in the art would recognize many
variations, alternatives, and modifications. An IC package 300
includes a die pad 320, leads 330, a bonding layer 340, a die 350,
conductive wires 360, and encapsulant material 370. Although the
above has been shown using a selected group of components for the
IC package 300, there can be many alternatives, modifications, and
variations. For example, some of the components may be expanded
and/or combined. Other components may be inserted to those noted
above. For example, the die 350 includes a light sensor 352. In
another example, the die 350 does not include the light sensor 352.
Depending upon the embodiment, the arrangement of components may be
interchanged with others replaced. Further details of these
components are found throughout the present specification and more
particularly below.
[0026] The die pad 320 includes extended parts 322 and a bottom
surface 334. For example, the extended parts 322 are formed by
shallowly machining away portions of the die pad. In another
example, the bottom surface is exposed without being covered by the
encapsulant material 370. The leads 330 each include an extended
part 332 and a bottom surface 334. For example, the extended parts
332 are formed by shallowly machining away portions of the die pad.
In another example, the bottom surface is exposed without being
covered by the encapsulant material 370. The die 350 is attached to
the die pad 320 through the bonding layer 340. As an example, the
bonding layer 340 includes an epoxy. Additionally, the die 350 is
connected to the leads 330 with the conductive wires 360. In one
embodiment, the die 350 includes an integrated circuit. Moreover,
the IC package 300 includes the encapsulant material 370. For
example, the encapsulant material 370 surrounds the die pad 320,
the leads 330, the bonding layer 340, the die 350, and the
conductive wires 360, but not the bottom surfaces 324 and 334. In
another example, the encapsulant material 370 also leaves side
surfaces 336 of the leads 330 exposed.
[0027] The encapsulant material 370 is transparent. In one
embodiment, the encapsulant material can be seen through by naked
human eyes. In another embodiment, the encapsulant material
provides a transmission rate higher than or equal to 80% for
wavelengths higher than or equal to about 350 nm. For example, the
wavelengths are in the range of visible light. In another example,
the wavelengths are in the range of visible and ultra-violet light.
In yet another embodiment, the encapsulant material is a clear
plastic. For example, the plastic includes at least one selected
from CV series of Matsushita Electric Works, Ltd, NT series of
Nitto Denko Corporation, and MG-97 series from Henkel
Corporation.
[0028] As discussed above and further emphasized here, FIG. 3 is
merely an example, which should not unduly limit the scope of the
claims. One of ordinary skill in the art would recognize many
variations, alternatives, and modifications. In one embodiment, the
package 300 is a micro leadframe package from Carsem. In another
embodiment, the package 300 is in compliance with certain JEDEC
standard. For example, the JEDEC standard is MO220 or MO229. In
another example, the package 300 is a quad flat no-lead (QFN)
package. In yet another example, the package 300 is a small outline
no-lead (SON) package. In yet another embodiment, the leads 330 are
fused with the die pad 320. In yet another embodiment, the package
300 includes two or more die pads.
[0029] FIG. 4 is a simplified diagram for making an IC package with
transparent encapsulant according to an embodiment of the present
invention. This diagram is merely an example, which should not
unduly limit the scope of the claims herein. One of ordinary skill
in the art would recognize many variations, alternatives, and
modifications. The method 400 includes a process 410 for separating
dies, a process 420 for attaching leadframes, a process 430 for
attaching dies, a process 440 for bonding wires, a process 450 for
applying transparent encapsulant, a process 460 for forming plating
layers, and a process 470 for singulating packages. Although the
above has been shown using a selected sequence of processes, there
can be many alternatives, modifications, and variations. For
example, some of the processes may be expanded and/or combined.
Other processes may be inserted to those noted above. Depending
upon the embodiment, the specific sequence of processes may be
interchanged with others replaced. For example, the method 400 is
used to make the package 300. Future detail of the present
invention can be found throughout the present specification and
more particularly below.
[0030] At the process 410, dies on the same wafer are separated.
For example, the separation includes a sawing process. In another
example, each die includes an integrated circuit. At the process
420, leadframes are attached to tapes. For example, the tapes are
used to protect bottom surfaces of the leadframes from being
covered by an encapsulant material.
[0031] FIG. 5 shows a simplified leadframe according to an
embodiment of the present invention. This diagram is merely an
example, which should not unduly limit the scope of the claims. One
of ordinary skill in the art would recognize many variations,
alternatives, and modifications. A leadframe 500 includes a
plurality of packaging units 510 arranged in a matrix array. For
example, each of the packaging units 510 includes the die pad 320
and the leads 330. The leads 330 are connected to metal strips 520,
some of which lie between adjacent packaging units. Additionally,
the leadframe 500 includes an outer frame 530 with stress-relief
structure. In one embodiment, the stress-relief structure includes
two rows of elongated openings 532 and 534. For example, the rows
532 and 534 surround a plurality of packing units on four sides. At
each side, a line 540 perpendicular to the side intersects at least
one elongated opening in the row 532 or the row 534. In another
embodiment, stress-relief structure is implemented with an
inter-locking structure as described in U.S. patent application
Ser. No. 09/909,934. U.S. patent application Ser. No. 09/909,934 is
incorporated by reference herein for all purposes. In yet another
embodiment, the stress-relief structure can prevent or slow down
the delamination of transparent encapsulant from propagating from
the plurality of packing units to packing units in other matrix
arrays at the process 450 as discussed below. In yet another
embodiment, the leadframe 500 also includes a plurality of
connecting bars. The plurality of connecting bars is attached to
the outer frame and defines a plurality of inner frames arranged in
a matrix pattern within the outer frame. The plurality of inner
frames includes a plurality of die pads respectively.
[0032] Returning to FIG. 4, at the process 430, the dies separated
at the process 410 are attached to the die pads. For example, the
die pads are the ones of the leadframe 500. In one embodiment, the
attachment is performed to the die pad 320 through the bonding
layer 340. For example, the bonding layer 340 is cured through a
heat treatment. At the process 440, conductive wires are bonded
between the dies and the leads. For example, the conductive wires
include the conductive wires 360.
[0033] At the process 450, a transparent encapsulant is applied. In
one embodiment, the encapsulant material is injected into a cavity.
The cavity includes four side boundaries that lie roughly on top of
the outer frame 530. For example, the injection is performed in an
environment with a dust count lower than or equal to about 30 k
parts per million (PPM). The temperature of the encapsulant
material ranges from 140.degree. c to 160.degree. c, and the
transfer pressure of the encapsulant ranges from 1100 psi to 1400
psi. After the injection, the encapsulant is baked with clamping.
For example, a clamping magazine and interleave are applied to the
encapsulant material. In another example, the baking process takes
about 3 to 6 hours with a temperature ranging from 125.degree. c to
160.degree. c.
[0034] In one embodiment, the transparent encapsulant is the
encapsulant material 370. For example, the encapsulant material can
be seen through by naked human eyes. In another example, the
encapsulant material provides a transmission rate higher than or
equal to 80% for wavelengths higher than or equal to about 350 nm.
In yet another example, the encapsulant material includes a clear
plastic, such as one selected from CV series of Matsushita Electric
Works, Ltd, NT series of Nitto Denko Corporation, and MG-97 series
from Henkel Corporation.
[0035] At the process 460, plating layers are formed on the bottom
surfaces of the leadframes. These bottom surfaces are taped at the
process 420 and not covered by the encapsulant material. At the
process 470, the IC packages are singulated. For example, the
singulation process uses the sawing technique and/or the punching
technique. In one embodiment, each IC package corresponds to a
packaging unit in FIG. 5. For each packaging unit, its leads are
severed from the metal strips 520. Additionally, the packaging
units within the outer frame 530 belong to the same cavity. The
encapsulant material that covers these packaging units are
connected to each other. The singulation process also separates the
encapsulant material into individual IC packages. In another
embodiment, the individual IC packages each are the package
300.
[0036] As discussed above and further emphasized here, FIG. 4 is
merely an example, which should not unduly limit the scope of the
claims herein. One of ordinary skill in the art would recognize
many variations, alternatives, and modifications. In one
embodiment, a process for providing package identifications is
performed after the process 410. For example, two-dimensional
markings are printed on the bottom surfaces of the leadframes. In
another embodiment, a process for detaching leadframes is performed
during the process 450. For example, the tapes are detached from
the leadframes at a temperature ranging from 80.degree. c to
120.degree. c after the transparent encapsulant is injected but
before the encapsulant is baked. In yet another embodiment, after
the process 470, a process for inspecting packages is performed.
For example, this process includes the inspection of the bottom
surfaces of the packages and the quality assurance inspection.
[0037] Some embodiments of the present invention, such as the
method 400, use a cavity with side boundaries that lie
approximately on top of the outer frame 530. For example, the outer
frame 530 includes the stress relief structure as shown in FIG. 5.
The leadframe 500 includes the plurality of packaging units 510
that are arranged in a matrix array. This arrangement enables
cavities with one common size to be used for making packages of
various sizes.
[0038] FIG. 6 shows a simplified leadframe used for making packages
with various sizes according to an embodiment of the present
invention. This diagram is merely an example, which should not
unduly limit the scope of the claims. One of ordinary skill in the
art would recognize many variations, alternatives, and
modifications. A leadframe 600 includes a plurality of regions.
Each region includes an array of packaging units 612, 622, 632, or
642 and is surrounded by an outer frame 610, 620, 630, or 640
respectively. The packaging units 612, 622, 632, and 642 are used
for making packages of different sizes. The outer frames 610, 620,
630, and 640 have approximately the same size and can be used for
cavities of the same size at the process 450. As shown in FIG. 6,
the outer frames 610, 620, 630 and 640 each include stress relief
structures, which may vary with different outer frames.
[0039] FIG. 7 shows a simplified leadframe used for making packages
of the same size according to another embodiment of the present
invention. This diagram is merely an example, which should not
unduly limit the scope of the claims. One of ordinary skill in the
art would recognize many variations, alternatives, and
modifications. A leadframe 700 includes a plurality of regions.
Each region includes an array of packaging units 712 and is
surrounded by an outer frame 710 respectively. The packaging units
712 are used for making packages of the same size. The outer frames
710 have approximately the same size and can be used for cavities
of the same size at the process 450. As shown in FIG. 6, the outer
frames 610 each include stress relief structures, such as the one
for the outer frame 530.
[0040] The use of one cavity to make a plurality of packages with
transparent encapsulants is a significant advancement in the field
of IC packaging. Without this improvement, each package is molded
with individual cavity pockets. The individual cavities often
require cavities of different sizes be used for different package
sizes. In contrast, using the same cavity for different package
sizes can significantly reduce costs and shortens turnaround
times.
[0041] The use of same cavities for different package sizes is
difficult to accomplish according to conventional techniques. One
reason for such difficulty is significant differences in thermal
expansion coefficient between a transparent encapsulant and a
leadframe or other components of an IC package. These components
include a bonding layer, a die, and conductive wires, and the
leadframe includes leads and a die pad. For example, the die is
made of silicon and the conductive wires are made of gold. During
cooling stage after high temperature molding, the transparent
encapsulant, the leadframe, and other components of the IC package
usually shrink differently. This difference in shrinkage often
causes warpage and mechanical stress to the molded package.
[0042] The warpage and mechanical stress can get worse as the
package size gets larger. Also, if the transparent encapsulant is
molded on only one side, instead of two sides, of the leadframe,
the warpage and mechanical stress usually exacerbate. If both sides
of the leadframe are covered by the transparent encapsulant, the
shrinkage of the top and bottom halves of the IC package can
neutralize each other and thus reduce the warpage.
[0043] Due to severe warpage and mechanical stress, the
conventional techniques cannot use one cavity to make a plurality
of transparent IC packages with the same size or different sizes.
If the warpage is larger than about 0.4 mm, the package singulation
process can cause the singulated packages to fly off from the
holder with sticky tape. If the holder uses a mechanical jig with
vacuum base to hold individual units, the tolerance for the warpage
becomes even tighter as the mechanical jig is not elastic like the
sticky tape.
[0044] In contrast, certain embodiments of the present invention
have overcome the above problems associated with warpage and
mechanical stress. As shown in FIGS. 5-7, the array molded design
of the present invention can share the common equipment between
different packages sizes, and thus avoid or reduce dedicated
tooling or equipment. These embodiments of the present invention
can lower capital expenses, improve equipment utilization, and
shorten lead times for tooling up different package sizes.
[0045] The problems associated with warpage and mechanical stress
have been overcome by using the method 400 according to some
embodiments of the present invention. The inventors have discovered
that using the transparent encapsulant with a temperature ranging
from 140.degree. c to 160.degree. c at the process 450 can
significantly reduce the warpage and stress.
[0046] Additionally, the inventors have discovered that for the
process 450, the injection of transparent encapsulant should be
preferably performed in an environment with a dust count lower than
or equal to about 30 k parts per million (PPM). Such dust count can
significantly reduce the number of foreign particles in the IC
package. Moreover, the transfer pressure of the transparent
encapsulant ranges from 1100 psi to 1400 psi according to an
embodiment of the present invention.
[0047] The present invention has various advantages. Certain
embodiments of the present invention provide IC packages with
transparent encapsulants. For example, the transparent encapsulants
are both reliable and durable. Some embodiments of the present
invention provide a method that can easily apply transparent
encapsulants. Certain embodiments of the present invention can
prevent or reduce delamination of transparent encapsulants. For
example, the delamination of transparent encapsulants may occur
during cooling and result in warpage and delamination rejects of
the IC packages. Some embodiments of the present invention use
stress-relief structures in a leadframe. The stress-relief
structures can prevent or reduce the propagation of delamination of
transparent encapsulants. Certain embodiments of the present
invention apply transparent encapsulants to only one side of a
leadframe. The amount of transparent encapsulant used is reduced
and the fabrication costs are lowered. Some embodiments of the
present invention provide transparent IC packages with improved
heat dissipation, smaller size, and/or lighter weight. Certain
embodiments of the present invention use matrix arrays of packaging
units. These packaging units are singulated as an individual
optical devices and/or packages. For example, the matrix arrays
allow the use of a single mould for making packages of various
sizes and shapes. Some embodiments of the present invention provide
locking mechanisms. For example, the locking mechanisms include
extended parts 322 and 332. During encapsulation, the heat causes
the encapsulants to melt and flow under the extended parts. After
cooling, the encapsulants under the locking mechanisms can prevent
or reduce the delamination of transparent encapsulants.
[0048] Although specific embodiments of the present invention have
been described, it will be understood by those of skill in the art
that there are other embodiments that are equivalent to the
described embodiments. Accordingly, it is to be understood that the
invention is not to be limited by the specific illustrated
embodiments, but only by the scope of the appended claims.
* * * * *