U.S. patent application number 15/055852 was filed with the patent office on 2016-10-20 for optoelectronic device packages.
This patent application is currently assigned to Intersil Americas LLC. The applicant listed for this patent is Intersil Americas LLC. Invention is credited to Sri Ganesh A Tharumalingam.
Application Number | 20160306072 15/055852 |
Document ID | / |
Family ID | 55589090 |
Filed Date | 2016-10-20 |
United States Patent
Application |
20160306072 |
Kind Code |
A1 |
A Tharumalingam; Sri
Ganesh |
October 20, 2016 |
OPTOELECTRONIC DEVICE PACKAGES
Abstract
An optical proximity sensor comprises a light detector die
including a light detector sensor area and at least one bond pad on
a portion of the light detector die not including the light
detector sensor area. A light source die, including anode and
cathode terminals, is attached to a portion of the light detector
die not including the light detector sensor area, such that at
least one of the terminals of the light source die, on a bottom of
the light source die, is attached to at least one of the bond pads
on the light detector die. An opaque barrier, formed off-wafer
relative to a wafer including the light detector die, is attached
to and extends upward from a top surface of the light detector die
between the light detector sensor area and the light source die.
Electrical connectors are on the bottom of the light detector
die.
Inventors: |
A Tharumalingam; Sri Ganesh;
(Fremont, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Intersil Americas LLC |
Milpitas |
CA |
US |
|
|
Assignee: |
Intersil Americas LLC
Milpitas
CA
|
Family ID: |
55589090 |
Appl. No.: |
15/055852 |
Filed: |
February 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14749169 |
Jun 24, 2015 |
9305967 |
|
|
15055852 |
|
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|
62148575 |
Apr 16, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 24/97 20130101;
H01L 25/167 20130101; H01L 31/167 20130101; H01L 24/94 20130101;
H01L 2224/48145 20130101; H01L 2924/181 20130101; H01L 2224/48091
20130101; G01V 8/12 20130101; H01L 2924/181 20130101; H01L
2924/00012 20130101; H01L 2224/48091 20130101; H01L 2924/00014
20130101; H01L 2224/48145 20130101; H01L 2924/00012 20130101 |
International
Class: |
G01V 8/12 20060101
G01V008/12 |
Claims
1. An optical proximity sensor, comprising: a light detector die
that includes a light detector sensor area and at least two bond
pads on a portion of the light detector die that does not include
the light detector sensor area; a light source die including anode
and cathode terminals and attached to a portion of the light
detector die that does not include the light detector sensor area,
such that at least one of the terminals of the light source die,
which is on a bottom of the light source die, is attached to at
least one of the bond pads on the light detector die; an opaque
barrier, formed off-wafer relative to a wafer including the light
detector die, attached to and extending upward from a top of the
light detector die between the light detector sensor area and the
light source die so that the entire light source die is on an
opposite side of the opaque barrier than the light detector sensor
area; electrical connectors for both the light detector sensor area
and the light source die on a bottom of the light detector die; and
vias in the light detector die that electrically connect the light
detector sensor area and the anode and cathode terminals of the
light source die to respective ones of the electrical connectors
that are on the bottom of the light detector die.
2. The optical proximity sensor of claim 1, wherein the opaque
barrier is adhered to the top of the light detector die, between
the light detector sensor area and the light source die, by an
opaque epoxy.
3. The optical proximity sensor of claim 1, wherein the opaque
barrier is made from one or more etched sheets of opaque material,
and wherein each of the one or more etched sheets of opaque
material is selected from the group consisting of a sheet of metal,
a sheet of silicon or a sheet of glass treated to be opaque.
4. The optical proximity sensor of claim 1, wherein the opaque
barrier is made from an opaque liquid crystal polymer.
5. The optical proximity sensor of claim 1, wherein the opaque
barrier is made from polyphthalamide.
6. The optical proximity sensor of claim 1, wherein the opaque
barrier is made from a high temperature thermo-plastic
material.
7. The optical proximity sensor of claim 1, wherein the anode and
cathode terminals of the light source die are both on the bottom of
the light source die and are attached to respective ones of the
bond pads on the light detector die by an electrically conductive
epoxy.
8. The optical proximity sensor of claim 7, wherein the optical
proximity sensor does not include any bond wires.
9. The optical proximity sensor of claim 8, further comprising a
light transmissive material that encapsulates the light detector
sensor region and the light source die.
10. The optical proximity sensor of claim 1, further comprising a
light transmissive material that encapsulates the light detector
sensor region and the light source die.
11. The optical proximity sensor of claim 1, wherein one of the
anode and cathode terminals of the light source die is on the
bottom of the light source die and is attached to one of the bond
pads on the light detector die by an electrically conductive epoxy,
and the other one of the anode and cathode terminals of the light
source die is on the top of the light source die and is attached to
another one of the bond pads on the light detector die by a bond
wire.
12. The optical proximity sensor of claim 11, wherein the bond wire
that attaches the one of the anode and cathode terminals of the
light source die, which is on the top of the light source die, to
one of the bond pads on the light detector die, is the only bond
wire of the optical proximity sensor.
13. The optical proximity sensor of claim 12, further comprising a
light transmissive material that encapsulates the light detector
sensor region, the light source die, and the only bond wire of the
optical proximity sensor.
14. An optical proximity sensor, comprising: a light detector die
that includes a light detector sensor area and at least two bond
pads on a portion of the light detector die that does not include
the light detector sensor area; a light source die including anode
and cathode terminals and attached to a portion of the light
detector die that does not include the light detector sensor area,
such that at least one of the terminals of the light source die,
which is on a bottom of the light source die, is attached to at
least one of the bond pads on the light detector die; an opaque
barrier, formed off-wafer relative to the light detector die,
attached to and extending upward from a top of the light detector
die between the light detector sensor area and the light source die
so that the entire light source die is on an opposite side of the
opaque barrier than the light detector sensor area; electrical
connectors for both the light detector sensor area and the light
source die on a bottom of the light detector die; and vias in the
light detector die that electrically connect the light detector
sensor area and the anode and cathode terminals of the light source
die to respective ones of the electrical connectors that are on the
bottom of the light detector die; wherein the opaque barrier is
made from at least two etched sheets of opaque material; wherein
each of the etched sheets of opaque material is selected from the
group consisting of a sheet of metal, a sheet of silicon or a sheet
of glass treated to be opaque; and wherein each of the etched
sheets of opaque material is adhered to the top of the light
detector die, or to another one of the etched sheets of opaque
material, by an opaque epoxy.
15. The optical proximity sensor of claim 14, wherein: the anode
and cathode terminals of the light source die are both on the
bottom of the light source die and are attached to respective ones
of the bond pads on the light detector die by an electrically
conductive epoxy; the optical proximity sensor does not include any
bond wires; the optical proximity sensor further comprises a light
transmissive material that encapsulates the light detector sensor
region and the light source die.
16. The optical proximity sensor of claim 14, wherein one of the
anode and cathode terminals of the light source die is on the
bottom of the light source die and is attached to one of the bond
pads on the light detector die by an electrically conductive epoxy,
and the other one of the anode and cathode terminals of the light
source die is on the top of the light source die and is attached to
another one of the bond pads on the light detector die by a bond
wire.
17. The optical proximity sensor of claim 16, further comprising a
light transmissive material that encapsulates the light detector
sensor region, the light source die, and the bond wire.
18. An optical proximity sensor, comprising: a light detector die
that includes a light detector sensor area and first and second
bond pads on a portion of the light detector die that does not
include the light detector sensor area; a light source die
including anode and cathode terminals that are both on a bottom of
the light source die and are attached to respective ones of the
first and second bond pads on the light detector die without using
any bond wires; an opaque barrier extending upward from the light
detector die between the light detector sensor area and the light
source die so that the entire light source die is on an opposite
side of the opaque barrier than the light detector sensor area;
electrical connectors for both the light detector sensor area and
the light source die on a bottom of the light detector die; and
vias in the light detector die that electrically connect the light
detector sensor area and the first and second bond pads, and
thereby the anode and cathode terminals of the light source die, to
respective ones of the electrical connectors that are on the bottom
of the light detector die.
19. The optical proximity sensor of claim 18, wherein the anode and
cathode terminals of the light source die are attached to
respective ones of the first and second bond pads on the light
detector die by an electrically conductive epoxy.
20. The optical proximity sensor of claim 18, wherein the optical
proximity sensor does not include any bond wires.
Description
PRIORITY CLAIM
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/749,169, filed Jun. 24, 2015, which claims priority to
U.S. Provisional Patent Application No. 62/148,575, filed Apr. 16,
2015. Priority is claimed to both of the above applications, which
are both incorporated herein by reference.
RELATED APPLICATIONS
[0002] This application is related to U.S. patent application Ser.
No. 13/761,708, entitled WAFER LEVEL OPTOELECTRONIC DEVICE PACKAGES
AND METHODS FOR MAKING THE SAME, filed Feb. 7, 2013 (Attorney
Docket No. ELAN-01285US1), U.S. patent application Ser. No.
14/671,619, entitled WAFER LEVEL OPTOELECTRONIC DEVICE PACKAGES AND
METHODS FOR MAKING THE SAME, filed Mar. 27, 2015 (Attorney Docket
No. ELAN-01285US2), and U.S. patent application Ser. No.
14/748,904, entitled WAFER LEVEL OPTOELECTRONIC DEVICE PACKAGES
WITH CROSSTALK BARRIERS AND METHODS FOR MAKING THE SAME (Attorney
Docket No. ELAN-01313US1), filed Jun. 24, 2015, each of which is
incorporated herein by reference in its entirety.
BACKGROUND
[0003] FIG. 1 is a perspective view of an exemplary prior art
optical proximity sensor 102 that includes a cover lid 122, which
is shown as being removed. The sensor 102 includes a light source
die 104 and a light detector die 106 spaced apart from on another
and attached to a base substrate 108 (e.g., a printed circuit board
(PCB)). The light source die 104 is encapsulated in a clear epoxy
114, and the light detector die 106 is separately encapsulated in a
clear epoxy 116. There is a gap 112 between the clear epoxy 116
encasing the light detector die 106 and the clear epoxy 118
encasing the light source die 104, wherein the gap 112 accepts a
crosstalk barrier 132 (that is part of the cover lid 122) when the
cover lid 122 is attached to the substrate 108. The cover 122,
which is likely made of metal, includes a window 124 for the light
source die 104 and separate window 126 for the light detector die
126. The opaque crosstalk barrier 132 (integrally formed with or
attached to the cover lid 122) is used to optically isolate the
light source die 104 from the light detector die 106.
[0004] As can be appreciated from the exemplary prior art optical
proximity sensor 102 described with reference to FIG. 1, current
packaging of optical proximity sensors involve many components and
many process steps, which increase the bill of materials, escalate
manufacturing costs, increase cycle times, and incur high yield
losses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a perspective view of an exemplary prior art
optical proximity sensor that includes a cover lid, which is shown
as being removed.
[0006] FIG. 2 is a perspective view of an optoelectronic device,
according to an embodiment of the present invention, which can be
an optical proximity sensor that can also provide ambient light
sensing.
[0007] FIG. 3, which includes cross-sectional FIGS. 3(a)-3(i), is
used to illustrate the fabrication of optoelectronic devices
according to certain embodiments of the present invention.
[0008] FIG. 4, which includes cross-sectional FIGS. 4(a)-4(d), is
used to illustrate the fabrication of optical crosstalk barriers,
specular reflection reducing shelves and peripheral optical
barriers according to certain embodiments of the present
invention.
[0009] FIG. 5, which includes cross-sectional views, is used to
illustrate the fabrication of optoelectronic devices according to
alternative embodiments of the present invention.
[0010] FIGS. 6A-6F are used to describe details of how to preform,
off-wafer, opaque vertical optical crosstalk barriers, opaque
peripheral barriers and opaque vertical shelves (to reduce specular
reflections) from sheets of opaque material.
[0011] FIG. 7 illustrates the fabrication of optical crosstalk
barriers, specular reflection reducing shelves and peripheral
optical barriers according to alternative embodiments of the
present invention.
[0012] FIG. 8 illustrate that lenses, e.g., bubble lenses, can be
formed over the light detector sensor regions and/or the light
source dies, in accordance with certain embodiments.
[0013] FIG. 9A illustrates a top view of an optoelectronic device
according to an embodiment of the present invention. FIG. 9B
illustrates a top view of the optoelectronic device of FIG. 9A,
with the light source die removed. FIG. 9C illustrates a bottom
view of the optoelectronic device of FIG. 9A.
[0014] FIG. 10 is used to illustrate that in accordance with
certain embodiments, dicing can be performed so that an array of
sensors is included in a single package.
[0015] FIG. 11 is a high level flow diagram that is used to
summarize methods for fabricating a plurality of optoelectronic
devices, according to certain embodiments of the present
invention.
[0016] FIG. 12 is a high level flow diagram that is use to describe
a method for forming, off-wafer, a preformed structure from an
opaque material and attaching the structure to a wafer.
[0017] FIG. 13 is a high level block diagram of a system according
to an embodiment of the present invention.
[0018] FIGS. 14A, 14B and 14C are used to describe why specular
reflections may occur, and the function of specular reflection
reducing shelves introduced in earlier FIGS.
DETAILED DESCRIPTION
[0019] Certain embodiments described below enable the entire
processing of optical proximity sensor devices (which can also be
used for ambient light sensing) to be performed at the wafer level,
thereby reducing the bill of materials and providing high yield
manufacturing, resulting in very low cost solutions. Beneficially,
the final devices, which can more generally be referred to as
optoelectronic devices, are about the size of the light detector
dies themselves, resulting in significant miniaturization, making
the devices well suited for handheld or other mobile
applications.
[0020] In the embodiments described below, there is no need for a
separate base substrate (e.g., a PCB substrate) to which are
connected a light source die and a light detector die. Rather, the
light source die is connected to the light detector die, such that
the light detector die acts as the base for the finished
optoelectronic device. This provides for a significant cost
reduction over other proximity sensor devices. Additionally, this
reduces the total package footprint to approximately that of the
light detector die itself.
[0021] FIG. 2 is a perspective view of an optoelectronic device
202, according to an embodiment of the present invention, which can
be an optical proximity sensor that can also provide ambient light
sensing. As will be understood from the discussion of FIGS. 3-6, in
accordance with specific embodiments of the present invention, each
of the elements shown in FIG. 2 is either fabricated as part of a
wafer, or attached to the wafer during wafer level processing,
prior to dicing of the wafer.
[0022] Referring to FIG. 2, a light detector sensor region 206 is
shown, which was formed within a portion of a wafer (also referred
to as the light detector die 204) using any know or future
developed wafer level device fabrication process and structure. For
example, the light detector sensor region 206 can include an
N.sup.+ region, which is heavily doped, and a P.sup.- region (e.g.,
a P.sup.- epitaxial region), which is lightly doped, all of which
is formed on a P.sup.+ or P.sup.++ substrate, which is heavily
doped. The N.sup.+ region and P.sup.- region form a PN junction,
and more specifically, a N.sup.+/P.sup.- junction. When this PN
junction is reversed biased, e.g., using a voltage source, a
depletion region is formed around the PN junction. When light is
incident on the light detector sensor region 206, electron-hole
pairs are produced in and near the diode depletion region.
Electrons are immediately pulled toward N.sup.+ region, while holes
get pushed down toward P.sup.- region. These electrons (also
referred to as carriers) are captured in N.sup.+ region and produce
a measurable photocurrent indicative of the intensity of the light.
This is just one example of the structure of the light detector
sensor region 206, which is not meant to be limiting. The light
detector sensor region 206 can alternatively include a P+/N-
junction, or a PIN, NPN, PNP or NIP junction, but is not limited
thereto. Further, it is noted that the light detector sensor region
206 can be made up of a plurality of smaller light detector sensor
regions connected together. Regardless of the exact structure of
the light detector sensor region 206, the light detector sensor
region 206 produces a signal (e.g., a photocurrent) in response to
and indicative of incident light.
[0023] In certain embodiments the light detector sensor region 206
is covered by a light transmissive material 208, which can be,
e.g., a light transmissive epoxy (e.g., a clear or tinted epoxy),
or other light transmissive resin or polymer. In certain
embodiments, the light transmissive material 208 may have a pigment
or other property that filters out light of certain wavelengths
that are not of interest, while allowing light of wavelengths of
interest to pass. The optoelectronic device 202 is also shown as
including a light source die 216 encapsulated within a light
transmissive material 218, which is likely the same as the light
transmissive material 208.
[0024] The light source die 216 includes a light emitting element,
which can be a light emitting diode (LED), an organic LED (OLED), a
bulk-emitting LED, a surface-emitting LED, a vertical-cavity
surface-emitting laser (VCSEL), a superluminescent light emitting
diode (SLED), a laser diode, or a pixel diode, but is not limited
thereto. The light source die 216 includes at least an anode
contact and a cathode contact. In accordance with certain
embodiments, one of the anode and cathode contacts is located on
the bottom of the light source die 216 and is connected to a bond
pad on the top surface of the light detector die 204; and the other
one of the anode and cathode contacts is located on the top surface
of the light source die 216 and is connected by a bond wire 224 to
a bond pad on the top surface of the light detector die 204. In
alternative embodiments, both the anode and cathode contacts are
located on the bottom of the light source die 216, and both the
anode and the cathode contacts are connected directly to respective
bond pads on the top surface of the light detector die 204, thereby
eliminating the need for a bond wire. Further, it is noted that the
light source die 216 can include a plurality of light emitting
elements connected together, e.g., serially and/or in parallel.
[0025] The light detector die 204 can also include other circuitry,
such as, a transimpedance amplifier that converts a current signal
to a voltage signal, and/or amplifier circuitry that is used to
amplify the photocurrent produced by the light detector sensor
region 206, and/or driver circuitry that is used to selectively
drive the light emitting element(s) of the light source die 216. It
would also be possible for the driver circuitry to alternatively be
part of the light source die 216, or to be external to the dies 204
and 216.
[0026] An opaque crosstalk barrier 232 is located between the light
detector sensor region 206 and the light source die 216 to thereby
optically isolate the light emitting element(s) of the light source
die 216 from the light detector sensor region 206. The opaque
crosstalk barrier 232 can be formed from an opaque material, which
can be, e.g., a black or other dark epoxy, or other resin or
polymer that is non-transmissive to the light generated by the
light source die 216. The opaque material that forms the opaque
crosstalk barrier 232 also forms a peripheral barrier 234 around
the entire periphery of the device 202, so as to optically isolate
the device 202 from one or more other optoelectronic device(s) that
may be located in the vicinity of the device 202. In specific
embodiments, the opaque crosstalk barrier 232 and peripheral
barrier 234 is formed using an opaque molding compound.
[0027] A window 210 is located over the light detector sensor
region 206, and a window 220 is located over the light source die
216. While the windows 210 and 220 are shown as being simple
apertures or openings, more complex windows can be formed.
[0028] FIG. 3, which includes cross-sectional FIGS. 3(a)-3(i), will
now be used to illustrate the fabrication of an optoelectronic
device (and more specifically, a plurality of such devices),
according to certain embodiments of the present invention. For
example, the process described with reference to FIG. 3 can be used
to produce the optoelectronic device 202, described above with
reference to FIG. 2.
[0029] Referring to 3(a), a plurality of light detector sensor
regions 306, which can also be referred to as light detector sensor
regions 306, are shown as being formed in a silicon wafer 304. Each
of the light detector sensor regions 306 can include one or more
PN, PIN, NPN, PNP or NIP junction(s), but is not limited thereto,
as was described above with reference to the light detectors sensor
region 206 in FIG. 2. In specific embodiments, each of the light
detector sensor regions 306 is a CMOS image sensor fabricated using
CMOS device fabrication. Additionally, while not specifically shown
in FIG. 3(a), bond pads can also formed on a top surface of the
silicon wafer 304, which can also be referred to herein simply as
the wafer 304. For example, such bond pads can be for connecting
anode and cathode contacts of light source dies to the wafer 304,
as will be described in additional detail below.
[0030] Referring to FIG. 3(b), wafer backgrinding is performed to
thin the wafer 304 to its final desired thickness. For example, the
wafer may start out having a 30 mil thickness, and may end up with
a thickness of about 5 mils after the backgrinding. This
significantly reduces the thickness of the final devices. These are
just exemplary initial and final wafer thicknesses, which are not
meant to be limiting.
[0031] Referring to FIG. 3(c), through silicon via (TSV) processing
is performed upward, from the bottom of the wafer 304, to form the
vias 308 that will provide electrical connections between
components connected to the top of the wafer 304 and the electrical
contacts (e.g., solder balls) which will be formed on a bottom of
the wafer 304. In other words, bottom-up TSV processing is
performed on the wafer 304. For example, standard TSV processing
with plasma etch can be used to form the openings (hole drilling).
At this stage there is no plastic material deposited on the wafer.
Accordingly, copper (Cu) seeding, Cu plating, via filling and
chemical mechanical polishing/planarization (CMP) can be performed
without process constraints.
[0032] Referring to FIG. 3(d), via plating and tenting is performed
to electrically connect contacts on the bottom of the wafer 304 to
contacts on the top of the wafer 304, and potentially within the
wafer. Additionally, pad redistribution and re-passivation may be
performed to relocate the final solder ball pads in an array and
size that is different from that of the TSV vias. More generally,
wafer back metallization can be performed to prepare the wafer for
bottom terminal connections, including, but not limited to, pad
redistribution.
[0033] Referring to FIG. 3(e), solder balls 342 are shown as being
mounted to the bottom of the wafer 304. More specifically, the
wafer 304 can be subjected to flux print, solder ball attachment
and reflow to produce the solder ball terminals on the bottom of
the wafer 304. It is also within the scope of the present invention
for alternative electrical contacts to be used instead of solder
balls. For example, electrically conductive lands, pads or pegs can
be used. Laser markings can also be added to the bottom of the
wafer 304.
[0034] Referring to FIG. 3(f), a plurality of light source dies 316
are connected to bond pads on the top surface of the wafer 304. For
example, the wafer 304 can be loaded onto a die attachment machine
and held in place by a wafer holder. The light source dies 316 can
be attached, e.g., using an electrically conductive epoxy, such as,
but not limited to, a silver (Ag) epoxy. This will connect either
the anode or the cathode contact of the light emitting element(s)
of each light source die 316 to a respective bond pad on the top
surface of the wafer 304. If both the anode and the cathode
contacts of the light source die are located on the bottom of the
light source die, then both the anode and the cathode contacts can
be connected directly to respective bond pads on the top surface of
the wafer 304 by an electrically conductive epoxy. The wafer then
goes through a baking process to cure the electrically conductive
epoxy (e.g., the Ag epoxy).
[0035] Referring to FIG. 3(g), a wafer level bonding machine can
then be used to connect a bond wire 324 from the other contact
(e.g., the cathode or anode) of the light emitting element of each
light source die 316 to a respective bond pad on the wafer 304. The
bond wires 324 can be made, e.g., of silver (Ag) or copper (Cu),
but are not limited thereto. This assumes that that one of the
anode and cathode contacts is located on the bottom of the light
source die 216, and the other one of the anode and cathode contacts
is located on the top surface of the light source die 216. The need
for bond wires 324 is eliminated if both the anode and cathode
contacts are located on the bottom of the light source die 216.
[0036] Referring to FIG. 3(h), the top surface of the wafer 304 and
the elements connected thereto, including the light source dies 316
(and the bond wires 324, if they are present) are encapsulated in a
light transmissive material 318. The light detector sensor regions
306 are also encapsulated in the light transmissive material 318.
The light transmissive material 318 can be, e.g., a light
transmissive epoxy (e.g., a clear or tinted epoxy), or other light
transmissive resin or polymer. In accordance with specific
embodiments, the light transmissive material 318 is a clear solder
mask material that is dispensed using solder mask deposition
equipment. In accordance with alternative embodiments, the light
transmissive material 318 (e.g., a clear epoxy) is formed using
liquid compression molding, with or without vacuum assist.
Alternatively, injection or transfer molding can be used.
[0037] Also shown in FIG. 3(h) are optical crosstalk barriers 332
that are used to block light from being transmitted directly from
one of the light source dies 316 to an adjacent one of the light
detector sensor regions 306. Also shown in FIG. 3(h) are specular
reflection reducing shelves 336 that extend from each of the
optical crosstalk barriers 332 towards an adjacent light source die
316. Additionally, specular reflection reducing shelves 338 extend
horizontally from each of the optical crosstalk barriers 332
towards an adjacent light detector sensor region 306. Such shelves
336, 338 are used to reduce specular reflections that may occur if
a light transmissive cover plate (e.g., made of glass, plastic, or
some other protective light transmissive material) is placed over a
finished optoelectronic device (e.g., optical proximity sensor).
For example, such a cover plate can be the glass covering a screen
of a mobile phone, portable music player or personal data assistant
(PDA), or the plastic covering a screen of a laptop computer. When
such a cover plate is placed over an optical proximity sensor, the
optical proximity sensor is often susceptible to specular
reflections. Just as it is desirable to minimize light being
transmitted directly from a light source die 316 to an adjacent
light detector sensor region 306, it is also desirable to minimize
the specular reflections because such reflections similarly reduce
the capability of the overall device to sense proximity or
distance, since specular reflections are essentially noise that
contain no information. Also shown in FIG. 3(h) are peripheral
barriers 334 used to optically isolate the finished optoelectronic
device (e.g., optical proximity sensor) from one or more other
optoelectronic device(s) that may be located in the vicinity of the
device.
[0038] Also shown in FIG. 3(h) are windows 310 that are left open
over at least a portion of each of the light detector sensor
regions 306, and windows 320 that are left open over at least a
portion of each of the light source dies 316. The windows 320 over
the light source dies 316 allow at least a portion of the light
emitted the light emitting elements of the light source dies 316 to
exit the devices, and the windows 310 over the light detector
sensor regions 306 allow emitted light, reflected off objects
within the fields of view of the devices, to be incident on and
detected by the light detector sensor regions 306. If the devices
are being used as ambient light sensors, the windows 310 over the
light detector sensor regions 306 allow ambient light to be
incident on and detected by the light detector sensor regions 306.
Such windows 310, 320 can also be referred to as apertures.
[0039] Additional details of how to encapsulate the light detector
sensor regions 306 and the light source dies 316 (and the bond
wires 324, if they are present) in the light transmissive material
318, and how to fabricate the opaque vertical optical crosstalk
barriers 332, the opaque horizontal shelves 336 (that extend from
each of the vertical crosstalk barriers 332 towards an adjacent
light source die 316), the opaque horizontal shelves 338 (that
extend horizontally from each of the vertical crosstalk barriers
332 towards an adjacent light detector sensor region 306), and the
opaque peripheral barriers 334, are described below with reference
to FIGS. 4, 5A and 5B.
[0040] Referring to FIG. 3(i), the wafer is then mechanically diced
(e.g., sawn) to singulate each optoelectronic device. In accordance
with an embodiment, after the dicing, the devices remain attached
to a tape (e.g., Mylar tape) medium used to mount the wafer. The
singulated devices can then be tested using an electrical tester
(e.g., a tester having probes) to check whether the individual
devices are operating properly. Alternatively, the testing can be
performed prior to the dicing. The singulated devices can then be
loaded onto a pick and place machine that is used to pick the
devices that operate properly (as determined using the testing) and
place them into tape and reel packing, at which point they are
ready for shipping to customers.
[0041] Still referring to FIG. 3, it is preferable to attach the
light source dies 316 to the top of the wafer 304, as shown in FIG.
3(f), after the steps described with reference to FIGS. 3(a)-3(e)
are performed. This is because it is beneficial that the top of the
wafer 304 is planar (without any topology) during the steps
described with reference to FIGS. 3(a)-3(e). Otherwise, wafer
mechanical integrity may be compromised. Further, it is beneficial
to mold the light transmissive material 318 over the light source
dies 316 and the light detector sensor regions 306 after wafer back
metallization is performed in order to avoid potentially
discoloring the light transmissive material 318 and/or causing
other thermal issues that may be caused by the heat required to
perform the wafer back metallization, which process typically has
the highest thermal budget. It may also be beneficial to mold the
light transmissive material 318 over the light source dies 316 and
the light detector sensor regions 306 before the solder balls 342,
or other electrical connectors, are mounted to the bottom of the
wafer 304, in order to avoid potentially discoloring the light
transmissive material 318 and/or causing other thermal issues that
may be caused by the heat required to attach the solder balls 342
or other electrical contact terminals. However, since the heat
required to attach solder balls (or other electrical connector) to
the bottom of a wafer is less than the heat required for wafer back
metallization, this is not as beneficial as performing wafer back
metallization before molding the light transmissive material 318
over the light source dies 316 and the light detector sensor
regions 306. Despite the aforementioned benefits, it is also within
the scope of embodiments of the present invention to perform the
steps described with reference to FIG. 3 in different orders than
described above. For example, in an alternative embodiment,
attachment of the light source dies 316 to the top of the wafer
304, as describe with reference to FIG. 3(f), can alternatively be
performed between the steps described with reference to FIGS. 3(a)
and 3(b), between the steps described with reference to FIGS. 3(b)
and 3(c), between the steps described with reference to FIGS. 3(c)
and 3(d), or between the steps described with reference to FIGS.
3(d) and 3(e). Other variations are also possible, and within the
scope of embodiments described herein. For example, the mounting of
the solder balls or other electrical connectors may be the last
step that is performing prior to the mechanical dicing of the wafer
to singulate each optoelectronic device.
[0042] FIG. 4, which includes cross-sectional FIGS. 4(a)-4(d), will
now be used to described additional details of how to encapsulate
the light detector sensor regions 306 and the light source dies 316
(and the bond wires 324, if they are present) in the light
transmissive material 318, and how to fabricate the optical
crosstalk barriers 332, the specular reflection reducing shelves
336 (that extend from each of the optical crosstalk barriers 332
towards an adjacent light source die 316), the specular reflection
reducing shelves 338 (that extend horizontally from each of the
optical crosstalk barriers 332 towards an adjacent light detector
sensor region 306), and the peripheral barriers 334. The specular
reflection reducing shelves 336 and the specular reflection
reducing shelves 338, individually, or collectively, can be
referred to as specular reflection reducing shelves. Referring to
FIG. 4(a), the top surface of the wafer 304 and the elements
connected thereto, including the light source dies 316 (and the
bond wires 324, if they are present) are encapsulated in the light
transmissive material 318. The light detector sensor regions 306
are also encapsulated in the light transmissive material 318. As
noted above, the light transmissive material 318 can be, e.g., a
light transmissive epoxy (e.g., a clear or tinted epoxy), or other
light transmissive resin or polymer. In accordance with specific
embodiments, the light transmissive material 318 is a clear solder
mask material that is dispensed using solder mask deposition
equipment. In accordance with alternative embodiments, the light
transmissive material 318 (e.g., a clear epoxy) is formed using
liquid compression molding, with or without vacuum assist.
Alternatively, injection or transfer molding can be used.
[0043] Referring to FIG. 4(b), grooves 312 are formed in the light
transmissive encapsulating material 318 to separate encapsulated
light detector sensor regions 306 from adjacent encapsulated light
source dies 316. In accordance with certain embodiments,
photolithography is used to form the grooves 312. In accordance
with other embodiments, the grooves 312 are cut, e.g., using a saw
or a laser.
[0044] In the embodiment just described above with reference to
FIGS. 4(a) and 4(b), the light detector sensor regions 306 and the
light source dies 316 (and the bond wires 324, if they are present)
are encapsulated in the light transmissive material 318 during one
step, and then the grooves 312 are formed during a further step.
These two steps can alternatively be replaced with a single step
during which a mold is used to encapsulate the light detector
sensor regions 306 and the light source dies 316 (and the bond
wires 324, if they are present) in a light transmissive material
318, and to form the grooves 312. Such a mold would include mold
features for forming the grooves at desired positions relative to
the light detector sensor regions 306 and the light source dies
316. More specifically, during a single molding step, the light
detector sensor regions (which can also be referred to a light
detector sensor areas) and the light source dies (and the bond
wires 324, if present) are encapsulated in a light transmissive
material with grooves in the light transmissive material between
the light detector sensor regions and adjacent light source dies.
The result of such a molding step would resemble what is shown in
FIG. 4(b).
[0045] Referring to FIG. 4(c), in accordance with certain
embodiments, an opaque material 330 is dispensed over the remaining
light transmissive material 318 and within the grooves 312
discussed with reference to FIG. 4(b). The opaque material 330 is
used to form an optical crosstalk barrier 332 (between each light
detector sensor region 306 and its adjacent light source die 316)
and a peripheral barrier 334, the purposes of which were discussed
above with reference to elements 232 and 234 in FIG. 2. The opaque
material 330 can be, e.g., a black or other dark epoxy, or other
resin or polymer that is non-transmissive to the light generated by
the light source die 316. In specific embodiments, the opaque
material is a black solder mask material that is dispensed using
solder mask printing. Referring to FIG. 4(d), windows 310 are
formed for the light detector sensor regions 306, and windows 320
are formed for the light source dies 316. In accordance with
specific embodiments, these windows 310, 320, which can also be
referred to as apertures, can be formed by removing portions of the
opaque material 330 (e.g., black solder mask material) using
photolithography.
[0046] In accordance with alternative embodiments, rather than
performing the two steps described above with reference to FIGS.
4(c) and 4(d), a further molding step is used to fill the grooves
312 with an opaque material 330 to form vertical optical crosstalk
barriers 332 between light source dies 316 and adjacent light
detector sensor regions 306. The opaque material 330 can be, e.g.,
a black or other dark molding compound, epoxy, or other resin or
polymer that is non-transmissive to the light generated by the
light source dies 316. Compression molding, injection molding or
transfer molding can be used, for example, to perform this molding
step.
[0047] The vertical optical crosstalk barriers 332 are used to
block light from being transmitted directly from one of the light
source dies 312 to an adjacent one of the light detector sensor
regions 306. During this molding step, shelves 336 that extend from
each of the vertical crosstalk barriers 332 towards an adjacent
light source die 316, are also formed. Additionally, shelves 338
that extend horizontally from each of the vertical crosstalk
barriers 332 towards an adjacent light detector sensor region 306,
can also be formed. Such horizontal shelves 336, 338 are used to
reduce specular reflections that may occur if a light transmissive
cover plate (e.g., made of glass, plastic, or some other protective
light transmissive material) is placed over a finished
optoelectronic device (e.g., optical proximity sensor). For
example, such a cover plate can be the glass covering a screen of a
mobile phone, portable music player or personal data assistant
(PDA), or the plastic covering a screen of a laptop computer. When
such a cover plate is placed over an optical proximity sensor, the
optical proximity sensor is often susceptible to specular
reflections. Just as it is desirable to minimize light being
transmitted directly from a light source die 316 to an adjacent
light detector sensor region 306, it is also desirable to minimize
the specular reflections because such reflections similarly reduce
the capability of the overall device to sense proximity or
distance, since specular reflections are essentially noise that
contain no information. The opaque material 330 can also be used to
form a peripheral barrier 334 used to optically isolate the
finished optoelectronic device (e.g., optical proximity sensor)
from one or more other optoelectronic device(s) that may be located
in the vicinity of the device. More generally, during a single
molding step an opaque material 330 is molded to form the optical
crosstalk barriers 332, the peripheral barriers 334, and the
specular reflection reducing shelves 336, 338. During this same
molding step, windows 310 are left open over at least a portion of
each of the light detector sensor regions 306, and windows 320 are
left open over at least a portion of each of the light source dies
316, as shown in FIG. 4(d).
[0048] In accordance with specific embodiments, the molding of the
light transmissive material 318, performed to achieve what is shown
in FIG. 4(b), and the molding of the opaque material 330, to
achieve what is shown in FIG. 4(d), are performed using a dual
molding process. For example, the dual molding process can be
dual-shot injection molding, but is not limited thereto.
[0049] In alternative embodiments, the steps described above with
reference to FIGS. 4(a) and 4(b), or the combination thereof,
is/are eliminated. In other words, in such alternative embodiments,
the light detector sensor regions 306 (which can also be referred
to a light detector sensor areas) and the light source dies 316
(and the bond wires 324, if present) are not encapsulated in a
light transmissive material.
[0050] In still other embodiments, the opaque barriers 332, 334 and
the shelves 336, 338 are formed from the opaque material 330 prior
to the light transmissive material 318 being used to encapsulate
the light detector sensor regions 306 and the light source dies 316
(and the bond wires 324, if present).
[0051] After the above described wafer level processing, e.g., to
form the light transmissive material and to form the opaque
barriers, the wafer can be attached to a wafer support system e.g.,
using an acrylic based adhesive. The wafer support system will help
prevent warping and help protect the light transmissive material
318 and the barriers from temperature excursions.
[0052] In accordance with certain embodiments of the present
invention, rather than forming the optical crosstalk barriers 332,
the peripheral barriers 334, and the opaque horizontal specular
reflection reducing shelves 336, 338 "on-wafer", these elements are
parts of a preformed opaque structure made "off-wafer" from an
opaque material. For example, referring to FIG. 5, in accordance
with specific embodiments, the opaque vertical optical crosstalk
barriers, the opaque peripheral barriers and the opaque vertical
shelves (to reduce specular reflections) are preformed "off-wafer",
and then attached to the wafer. For a more specific example, a
sheet of opaque material can be etched to produce the vertical
optical crosstalk barriers "off-wafer" that are thereafter adhered
to the wafer (before or after the light detectors and sources are
encapsulated with a light transmissive material). A further sheet
of opaque material can be etched to produce the specular reflection
reducing small apertures/windows, and the further sheet of opaque
material can adhered above/to the vertical optical crosstalk
barriers to provide the specular reflection reducing vertical
shelves, as can be appreciated from FIG. 5. In accordance with
embodiments of the present invention, the sheets of opaque material
can be sheets of metal, sheets of silicon, or sheets of glass
coated with an opaque material or otherwise treated to be opaque,
but are not limited thereto. The opaque vertical optical crosstalk
barriers and opaque vertical shelves (to reduce specular
reflections) that are preformed "off-wafer" can be attached to a
wafer after the light detector sensor regions 306 and the light
source dies 316 (and the bond wires 324, if present) are
encapsulated in a light transmissive material. Alternatively, the
opaque vertical optical crosstalk barriers and opaque vertical
shelves (to reduce specular reflections) that are preformed
"off-wafer" can be attached to a wafer wherein the light detector
sensor regions 306 and the light source dies 316 (and the bond
wires 324, if present) are not encapsulated in a light transmissive
material. Thereafter, the light detector sensor regions 306 and the
light source dies 316 (and the bond wires 324, if present) may, or
may not (depending upon implementation) be encapsulated in a light
transmissive material.
[0053] Elements are considered to be formed "on-wafer" if they are
formed directly on the wafer, as opposed to being formed separate
from the wafer and then attached to the wafer. Elements are
considered to be formed "off-wafer" if they are formed separate
from the wafer and then attached to the wafer. Elements are
considered to be formed at the wafer level if they are added or
attached to the wafer before the wafer is diced. Elements that are
formed "on-wafer" and elements that are formed "off-wafer" are
considered to be formed at the wafer level so long as they are
added or attached to the wafer before the wafer is diced. In the
embodiments described herein, the optical crosstalk barriers 332
and the peripheral barriers 334, which are formed at the wafer
level (whether formed on-wafer or pre-formed off-wafer and then
attached to the wafer prior to dicing), can also be referred to
individually or collectively as opaque vertical optical barriers.
Certain instances or portions of the opaque vertical optical
barriers may function as the optical cross talk barriers 332, while
others, or portions thereof, may function as the peripheral
barriers 334. The specular reflection reducing shelves 336 and/or
338, because they extend in a horizontal direction relative to the
opaque vertical optical barriers, can also be referred to as opaque
horizontal optical barriers. Certain instances or portions of the
opaque horizontal optical barriers may function as the specular
reflection reducing shelves 336 or 338. A discussion of why
specular reflections may occur, and the function of specular
reflection reducing shelves 336 and 338, is provided below with
reference to FIGS. 14A-14C.
[0054] Where a sheet of opaque material (e.g., a sheet of metal, a
sheet of silicon, or a sheet of glass coated with an opaque
material or otherwise treated to be opaque) is used to form the
opaque optical crosstalk barriers and peripheral barriers, and a
second sheet of opaque material (e.g., a sheet of metal, a sheet of
silicon, or a sheet of glass coated with an opaque material or
otherwise treated to be opaque) is used to form the opaque vertical
shelves (to reduce specular reflections) and windows, these two
sheets can be attached to one another off-wafer, and then attached
to the wafer. Alternatively, the first sheet of opaque material in
which the opaque optical crosstalk barriers and peripheral barriers
are formed can be attached to the wafer, and then the second sheet
opaque material in which the opaque vertical shelves (to reduce
specular reflections) and windows are formed can be attached, above
the first sheet, to the wafer.
[0055] FIGS. 6A-6F will now be used to describe additional details
of how to preform, off-wafer, the opaque vertical optical crosstalk
barriers, the opaque peripheral barriers and the opaque vertical
shelves (to reduce specular reflections) from sheets of opaque
material. In other words, FIGS. 6A-6F are used to describe specific
embodiments for forming opaque vertical optical barriers and opaque
horizontal optical barriers off-wafer, at the wafer level.
Referring to FIG. 6A, illustrated therein is a top view of a
portion of a sheet of opaque material 601, with openings
corresponding to the desired sizes of the apertures 310 and 320
etched in the sheet of opaque material 601. As mentioned above, the
sheet of opaque material 601 can be a sheet of metal, or a sheet of
silicon treated to be opaque, but is not limited thereto. FIG. 6B
illustrates a side cross-sectional view of the portion of the sheet
of opaque material 601 shown in FIG. 6A, along the dashed line B-B
in FIG. 6A. The etched sheet of opaque material 601 shown in FIGS.
6A and 6B is used to form opaque horizontal optical barriers, as
can be appreciated from FIG. 6F discussed below.
[0056] FIG. 6C illustrates a top view of a portion of a further
etched sheet of opaque material 603, which can be a sheet of metal,
or a sheet of silicon treated to be opaque, but is not limited
thereto. FIG. 6D illustrates a side cross-sectional view of the
portion of the sheet of opaque material 603 shown in FIG. 6C, along
the dashed line D-D in FIG. 6C. The etched sheet of opaque material
603 shown in FIGS. 6C and 6D is used to form opaque vertical
optical barriers, as can be appreciated from FIG. 6F discussed
below.
[0057] FIG. 6E illustrates a top view of an opaque structure formed
by attaching the etched sheet of opaque material 601 above the
etched sheet of opaque material 603, e.g., using an opaque epoxy.
FIG. 6F illustrates a side cross-sectional view of the portions of
the sheets of opaque material 601, 603 shown in FIG. 6E, along the
dashed line F-F in FIG. 6E. As shown in FIG. 6F, the etched sheet
of opaque material 601 is used to form opaque horizontal optical
barriers, including the shelves 336 and 338 that are used to reduce
specular reflections. As also shown in FIG. 6F, the etched sheet of
opaque material 603 is used to form opaque vertical optical
barriers, including the optical crosstalk barriers 332 and the
peripheral barriers 334. In view of the above description, the
structure shown in FIG. 6F can be referred to as a preformed opaque
structure 605 that is made off-wafer.
[0058] FIG. 7 illustrates another example of preformed opaque
structure 705 that is made off-wafer. Referring to FIG. 7, in this
embodiment, an opaque molding compound is molded (e.g., injection,
compression or transfer molded) to simultaneously form the optical
crosstalk barriers 332, the peripheral barriers 334, and the opaque
horizontal specular reflection reducing shelves 336 and/or 338
"off-wafer", and the preformed opaque structure 705 is thereafter
adhered to the wafer after light detector sensor regions 306 and
the light source dies 316 (and the bond wires 324, if present) are
encapsulated with a light transmissive material. The opaque molding
compound can be, for example, an opaque liquid crystal polymer,
polyphthalamide (PPA) or other high temperature thermo-plastic
materials, but is not limited thereto. The optical crosstalk
barriers 332, the peripheral barriers 334, and the specular
reflection reducing shelves 336 and/or 338 can alternatively be
adhered onto the wafer without the light detector sensor regions
306 and the light source dies 316 (and the bond wires 324, if
present) being encapsulated with a light transmissive material. The
optical crosstalk barriers 332, the peripheral barriers 334, and
the specular reflection reducing shelves 336 and/or 338 can be made
to the size of the wafer with a single pass attach or fabricated in
smaller segments and attached via multiple passes onto the
wafer.
[0059] In certain embodiments, lenses, e.g., bubble lenses, can be
formed over the light detector sensor regions and/or the light
source dies, as can be appreciated from FIG. 5C. Referring to FIG.
8, such lenses 826 can be formed, e.g., using liquid compression
molding of the light transmissive material 318 (e.g., a clear
epoxy). The lens over each light source die is used to focus light
being emitted from the light source die. The lens over each light
detector sensor region is used to focus light (reflected and/or
ambient light) that is incident on the lens.
[0060] In the embodiments described above, there is no need for a
separate base substrate (e.g., a PCB substrate) to which are
connected a light source die and a light detector die. Rather, the
light source die is connected to the light detector die, such that
the light detector die acts as the base for the finished
optoelectronic device. This provides for a significant cost
reduction over other proximity sensor devices. Additionally, this
reduces the total package footprint to approximately that of the
light detector die itself. The resulting optoelectronic device(s)
can be used for proximity detection, as well as for ambient light
detection.
[0061] In accordance with specific embodiments described above,
only a single bond wire is needed for each optical proximity sensor
device. The rest of the electrical connections are routed by vias
to the back of the die and finished with solder balls or other
external connectors. This allows for package miniaturization.
Additionally, the bill of materials is less prone to increase if
the price of commodities used to produce bond wires (such as silver
(Ag) or copper (Cu)) increase. In other embodiments, bond wires are
not needed, as explained above.
[0062] In specific embodiments, the components of the
optoelectronic devices are formed using wafer level chip scale
packaging (CSP), which provides for extensive miniaturization.
[0063] Embodiments described above can be used to fabricate a
plurality of optoelectronic devices which are optical proximity
sensors. Such optical proximity sensors may also be able to
function as ambient light sensors. Embodiments described herein can
also be used to fabricate a plurality of optoelectronic devices
which are ambient light sensors that are not configured to also
function as optical proximity sensors. In such latter embodiments,
where dedicated ambient light sensors are fabricated, light source
dies are not attached to the wafer
[0064] FIG. 9A illustrates a top view of an optoelectronic device
according to an embodiment of the present invention. FIG. 9B
illustrates a top view of the optoelectronic device of FIG. 9A,
with the light source die removed. FIG. 9B illustrates a bottom
view of the optoelectronic device of FIG. 9A.
[0065] In accordance with certain embodiments, rather than
performing the dicing so that each resulting device only includes a
single proximity sensor, the dicing can alternatively be performed
so that an array of such sensors is included in a single package,
as can be appreciated from FIG. 10. More specifically, FIG. 10
shows an array of four optoelectronic devices in one package 1002,
an array of two optoelectronic devices 1004 where the light source
dies are spaced close to one another, and an array of two
optoelectronic devices 1006 where the light source dies are spaced
farther apart from one another. Other configurations are also
possible.
[0066] FIG. 11 is a high level flow diagram that is used to
summarize methods for fabricating a plurality of optoelectronic
devices, according to certain embodiments of the present invention,
starting with a wafer that includes a plurality of light detector
sensor regions (e.g., 306). Referring to FIG. 11, step 1102
involves backgrinding a bottom of the wafer, which includes the
plurality of light detector sensor regions, to achieve a specified
thickness for the wafer. Step 1104 involves performing through
silicon via (TSV) processing on the wafer to thereby form a
plurality of vias. Step 1106 involves tenting and plating the vias
and performing wafer back metallization, after performing the TSV
processing.
[0067] The backgrinding (performed at step 1102) can be performed
before or after the TSV processing (performed at step 1104),
depending upon implementation. In accordance with certain
embodiments, if the backgrinding is performed after the TSV
processing, then tenting and plating the vias and performing wafer
back metallization will be done after the backgrinding.
[0068] In accordance with specific embodiments, where the TSV
processing (at step 1104) is performed after backgrinding the
bottom of the wafer (at step 1102), the TSV processing (at step
1104) is bottom-up TSV processing, as described above with
reference to FIG. 3(c). Performing TSV processing on a thin
backgrinded wafer improves process capability, cost and cycle time
due to a lower via depth requirement. This option also allows TSV
processing to be decoupled from a CMOS sensor device fabrication
process (used to form the light detector sensor regions) and to be
fully completed using a different process capability and
manufacturing site than the CMOS device fabrication site to
leverage better cost structure and manufacturing flow.
[0069] Still referring to FIG. 11, step 1108 involves attaching
each of a plurality of light source dies (e.g., 316) to a top
surface of the wafer, e.g., as described above with reference to
FIG. 3(f). More specifically, step 1108 can include attaching each
of the light source dies to a separate bond pad on a top surface of
the wafer. At step 1110, for each of the plurality of light source
dies, a bond wire (e.g., 324) can be attached from a top of the
light source die to a further separate bond pad on the top surface
of the wafer. Alternatively, if the bottoms of the light source
dies include both anode and cathode contacts, then both the anode
and the cathode contacts can be connected directly to respective
bond pads on the top surface of the wafer at step 1108. In other
words, step 1110 can be eliminated if both anode and cathode
contacts are located on the bottoms of the light source dies.
[0070] Step 1112 involves molding a light transmissive material
(e.g., 318) to encapsulate the light detector sensor regions and
the light sensor dies in the light transmissive material. More
generally, step 1112 involves encapsulating the light detector
sensor regions and the light sensor dies in a light transmissive
material. The light transmissive material can be, e.g., a light
transmissive epoxy (e.g., a clear or tinted epoxy), or other light
transmissive resin or polymer. In accordance with specific
embodiments, the light transmissive material is a clear solder mask
material that is dispensed using solder mask deposition equipment.
In accordance with alternative embodiments, the light transmissive
material (e.g., a clear epoxy) is formed using liquid compression
molding, with or without vacuum assist. Alternatively, injection or
transfer molding can be used, as was noted above.
[0071] In accordance with specific embodiments, molding the light
transmissive material to encapsulate the light detector sensor
regions and the light sensor dies in the light transmissive
material (at step 1112), is performed after tenting and plating the
vias and performing wafer back metallization (at step 1106), and
after attaching the plurality of light source dies to the top
surface of the wafer (at step 1108). A benefit of molding the light
transmissive material to encapsulate the light detector sensor
regions and the light sensor dies in the light transmissive
material, after tenting and plating the vias and performing wafer
back metallization, is that it avoids potentially discoloring the
light transmissive material and/or causing other thermal issues
that may be caused by the heat generated during wafer back
metallization, which process typically utilizes the highest
temperature and has the highest thermal impact.
[0072] Still referring to FIG. 11, step 1114 involves fabricating
opaque barriers including opaque optical crosstalk barriers (e.g.,
332). In accordance with specific embodiments, step 1114 also
includes fabricating opaque specular reflection reducing shelves
(e.g., 336 and/or 338) and opaque peripheral barriers (e.g., 334).
In accordance with certain embodiments, the opaque optical
crosstalk barriers, the specular reflection reducing shelves and
the opaque peripheral barriers are fabricated by molding an opaque
material to produce such barriers. In certain such embodiments, a
dual molding process, such as, but not limited to, dual-shot
injection molding, is used to mold of the light transmissive
material to encapsulate the light detector sensor regions and the
light sensor dies in the light transmissive material (at step
1112), and to mold an opaque material to produce the opaque optical
crosstalk barriers, reflection reducing shelves and peripheral
barriers (at step 1114).
[0073] In accordance with alternative embodiments, the fabricating
opaque optical crosstalk barriers, specular reflection reducing
shelves and peripheral barriers, at step 1114, involves attaching
preformed opaque optical crosstalk barriers, specular reflection
reducing shelves and peripheral barriers to the wafer, e.g., as was
described above with reference to FIGS. 5-7. More generally,
additional details of the opaque barriers that can be fabricated at
step 1114 were discussed above with reference to FIGS. 2-7, and are
also discussed below with reference to FIGS. 14A-14C.
[0074] In accordance with specific embodiments, the through silicon
via (TSV) processing performed on the wafer (at step 1106), and the
tenting and plating the vias and performing wafer back
metallization (at step 1106), are both performed before attaching
the light source dies to the top surface of the wafer (at step
1108), and before molding the light transmissive material to
encapsulate the light detector sensor regions and the light sensor
dies in the light transmissive material (at step 1112). A benefit
of performing the TSV processing and performing the tenting and
plating the vias and wafer back metallization, before the attaching
the light source dies to the top surface of the wafer, and before
molding the light transmissive material to encapsulate the light
detector sensor regions and the light sensor dies in the light
transmissive material, is that the tenting and plating of the vias
and the wafer back metallization (which can include, e.g., copper
(Cu) seeding, Cu plating and chemical mechanical
polishing/planarization (CMP)) can be performed without process
constraints, because at this stage there is light transmissive
material on the wafer.
[0075] In accordance with certain embodiments, the attaching of the
light source dies to the top surface of the wafer (at step 1108),
is performed after performing the backgrinding (at step 1102),
after performing the TSV processing on the wafer (at step 1104),
and after tenting and plating the vias and the performing wafer
back metallization (at step 1106). A benefit of attaching the light
source dies to the top surface of the wafer after performing the
backgrinding, after performing the TSV processing on the wafer, and
after tenting and plating the vias and performing wafer back
metallization, is that it is better to perform the aforementioned
steps while the top of the wafer is planar (without any topology).
Otherwise, wafer mechanical integrity may be compromised. This is
because the attachment of light source dies and the light
transmissive material encapsulation of the wafer top side may lead
to a non-planar and/or soft surface which may lead to wafer
breakage during the mechanical grinding of the wafer back surface,
if the wafer grinding were instead performed after the
aforementioned steps.
[0076] Step 1116 involves mounting solder balls or other electrical
connectors to the bottom of the wafer. For example, electrically
conductive lands, pads or pegs can be used as electrical
connectors, instead of solder balls. In accordance with certain
embodiment, the solder balls or other electrical connectors are
attached to the bottom of the wafer (at step 1116) after molding
the light transmissive material to encapsulate the light detector
sensor regions and the light sensor dies in the light transmissive
material (at step 1112). In accordance with alternative
embodiments, the solder balls or other electrical connectors are
attached to the bottom of the wafer (at step 1116) before molding
the light transmissive material to encapsulate the light detector
sensor regions and the light sensor dies in the light transmissive
material (at step 1112). Accordingly, depending upon
implementation, the steps described with reference to FIG. 11 may
be performed in the order shown therein, or in alternative orders,
many of which are described herein.
[0077] A benefit to attaching the solder balls or other electrical
connectors to the bottom of the wafer (at step 1116) before molding
the light transmissive material to encapsulate the light detector
sensor regions and the light sensor dies in the light transmissive
material (at step 1112) is that performing the steps in this order
would avoid potentially discoloring the light transmissive material
(e.g., 318) and/or causing other thermal issues that may be caused
by the heat required to attach the solder balls (e.g., 342) or
other electrical contact terminals. However, since the heat
required to attach solder balls (or other electrical connector) to
the bottom of a wafer is less than the heat required for wafer back
metallization, this is not as beneficial as performing wafer back
metallization before molding the light transmissive material (e.g.,
318) over the light source dies (e.g., 316) and the light detector
sensor regions (e.g., 306).
[0078] Still referring to FIG. 11, step 1118 involves dicing the
wafer to separate the wafer into a plurality of optoelectronic
devices. In accordance with certain embodiments, each of the
optoelectronic devices, resulting from dicing the wafer, includes
at least one of the light detector sensor regions (e.g., 306), at
least one of the light source dies (e.g., 308), one of the opaque
optical crosstalk barriers (e.g., 332) between the at least one of
the light detector sensor regions and the at least one of the light
source dies, and at least two of the solder balls or other
electrical connectors (e.g., 342).
[0079] The opaque barriers that are fabricated at step 1114 can be
formed on-wafer, e.g., as described above with reference to FIGS. 3
and 4. Alternatively, the opaque barriers that are fabricated at
step 1114 can be preformed off-wafer, e.g., as described above with
reference to FIGS. 5-7. For example, as was described above with
reference to FIG. 7, the opaque barriers can be molded off-wafer,
and then attached to the wafer. Alternatively, as was described
above with reference to FIGS. 6A-6F, and summarized below with
reference to FIG. 12, the opaque barriers can be a preformed opaque
structure made-off wafer from one or more etched sheets of opaque
material. As noted above, in certain embodiments a preformed opaque
structure, which is made off-wafer from an opaque material,
includes opaque vertical optical barriers and opaque horizontal
optical barriers. In specific embodiments, the opaque vertical
optical barriers and the opaque horizontal optical barriers are
made from two etched sheets of opaque material. The high level flow
diagram of FIG. 12 will now be used to describe a method for
forming, off-wafer, such a preformed structure, and attaching the
structure to a wafer.
[0080] Referring to FIG. 12, step 1202 involves etching, off-wafer,
a first sheet of opaque material to form the opaque vertical
optical barriers that function as optical crosstalk barriers and
peripheral barriers. Step 1204 involves etching, off-wafer, a
second sheet of opaque material to form the opaque horizontal
optical barriers that function as specular reflection reducing
shelves and to form windows for the light detector sensor regions
and the light source dies. Step 1206 involves attaching the first
etched sheet of opaque material to the wafer so that each of the
light detector sensor regions is separated from an adjacent one of
the light source dies by one of the vertical optical barriers that
functions as an optical crosstalk barrier. Step 1208 involves
attaching the second etched sheet of opaque material to the first
etched sheet of opaque material (before or after the first etched
sheet of opaque metal is attached to the wafer), so that there is a
window over at least a portion of each of the light detector sensor
regions and a window over at least a portion of each of the light
source dies. In certain embodiments, the first and second sheets of
opaque material are both sheets of metal. In other embodiments, the
first and second sheets of opaque material are both sheets of
silicon. In other embodiments, the first and second sheets of
opaque material are both sheets of glass coated with an opaque
material or otherwise treated to be opaque. It would also be
possible for one of the first and second sheets of opaque material
to be a sheet of metal, and the other one of the first and second
sheets of opaque material to be a sheet of silicon or a sheet of
glass treated to be opaque. More generally, the first and second
sheets of opaque material may be sheets of the same type of opaque
material, or the types of the first and second sheets of opaque
material may differ from one another. Exemplary additional details
of the steps described in FIG. 12 can be appreciated from the above
discussion of FIGS. 6A-6F.
[0081] In alternative embodiments, the preformed opaque structure
is molded (e.g., injection molded, compression molded or transfer
molded) from an opaque molding compound. The opaque molding
compound can be, e.g., an opaque liquid crystal polymer,
polyphthalamide (PPA) or some other high temperature thermo-plastic
materials, but is not limited thereto. Exemplary additional details
of how the preformed opaque structure can be molded, off-wafer,
from an opaque molding compound and then attached to the wafer can
be appreciated from the above discussion of FIG. 7.
[0082] In certain embodiments, the encapsulating the light detector
sensor regions and the light sensor dies in the light transmissive
material is at a time that is prior to the attaching the preformed
opaque structure. As shown, e.g., in FIG. 3(e), grooves (e.g., 312)
can be formed in the light transmissive material (e.g., 318)
between the light detector sensor regions and adjacent light source
dies. The light detector sensor regions and the light source dies
(and the bond wires, if present) can first be encapsulated in a
light transmissive material, and then the grooves can be
molded/formed, as was described above with reference to FIGS. 3(d)
and 3(e). Alternatively, the light detector sensor regions and the
light source dies (and the bond wires, if present) can be
encapsulated in a light transmissive material simultaneously with
the grooves being formed, as was described above with reference to
FIG. 3(e). Other variations are also possible and with the scope of
embodiments of the present invention.
[0083] Optoelectronic devices of embodiments of the present
invention can be used in various systems, including, but not
limited to, mobile-phones and other handheld-devices. Referring to
a system 1300 of FIG. 13, for example, an optoelectronic device
1302 (e.g., 202) can be used to control whether a subsystem 1306
(e.g., a touch-screen, backlight, virtual scroll wheel, virtual
keypad, navigation pad, etc.) is enabled or disabled. For example,
the optoelectronic device 1302 can detect when an object 1308, such
as a person's finger, is approaching, and based on the detection
either enable or disable the subsystem 1306. More specifically, a
driver 1303 selectively drives a light source die (e.g., 216) of
the optoelectronic device 1302, thereby causing the light source
die to emit light that reflects off of the object 1308. The driver
1303 can be external to the device 1302, as shown, or part of the
device 1302 (e.g., part of one of the dies of the device 1302). A
portion of the reflected light is detected by a light detector
sensor region (e.g., 306) of a light source die of the
optoelectronic device 1302. An output of the optoelectronic device
1302 is provided to a comparator or processor 1304 which can
compare the output of the optoelectronic device 1302 to a
threshold, to determine whether the object 1308 is within a range
where the subsystem 1306 should be enabled or disabled, depending
on what is desired. Multiple thresholds can be used, and more than
one possible response can occur based on the detected proximity of
the object 1308. For example, a first response can occur if the
object 1308 is within a first proximity range, and a second
response can occur if the object 1308 is within a second proximity
range. In the system 1300, the optoelectronic device 1302 is being
used to detect the proximity of the object 1308, and thus, the
device 1302 can also be referred to as an optical proximity
sensor.
[0084] FIGS. 14A, 14B and 14C will now be used to further describe
why specular reflections may occur, and the function of the
specular reflection reducing shelves 336 and 338 introduced above.
FIG. 14A illustrates an optoelectronic apparatus that includes a
light source die 316 and a light detector sensor region 306,
separated from one another by an opaque optical crosstalk barrier
332. Such an optoelectronic apparatus may be used as a proximity
detector. As shown in FIG. 14A, the optoelectronic apparatus
(including a light source die 316 and a light detector sensor
region 306) may be used with (e.g., placed behind or covered by) a
cover plate 1402, which can be made, e.g., of glass, plastic, or
some other protective light transmissive material. Such a cover
plate 1402 includes a close surface 1404 and far a surface 1406,
with a thickness of the plate 1402 therebetween. While the close
surface 1404 is shown as being a distance from the top surface of
the optoelectronic apparatus, it is also possible that the close
surface is in contact with (i.e., abuts against) the top surface of
the optoelectronic apparatus. The cover plate 1402 can be, e.g.,
the glass covering a screen of a mobile phone, personal music
player or personal data assistant (PDA), or the plastic covering
the screen of a laptop computer, but is not limited thereto.
[0085] Exemplary light rays 1403 are also shown in FIG. 14A. As can
be appreciated from FIG. 14A, at least some of the light rays, or
portions thereof, can be reflected back toward the light detector
sensor region 306 of the optoelectronic apparatus due to specular
reflections. Just as it is desirable to minimize light being
transmitted directly from the light source die 316 to the light
detector sensor region 306, it is also desirable to minimize the
specular reflections because such reflections similarly reduce the
capability of the overall device to sense distance since they are
essentially noise that contain no information. To reduce and
preferably prevent the detection of specular reflections by the
light detector sensor region, one or more specular reflection
reducing shelves can be added, as described below with reference to
FIGS. 14A and 14B.
[0086] Referring to FIG. 14B, the optical cross talk barrier 332
prevents light produced by the light source die 316 from travelling
directly to the light detector sensor region 306. Additionally, an
opaque vertical barrier 336, which can be referred to as a specular
reflection reducing shelf 336, reduces specular reflections. This
barrier 336, which extends from optical crosstalk barrier 332,
forms a shelf over the light source die 316, and in certain
embodiments, covers at least a portion of a light emitting
element(s) of the light source die 316, as shown in FIG. 14B. As
can be appreciated from a comparison between FIG. 14A and FIG. 14B,
the shelf 336 reduces the amount of specular reflections, and
thereby reduces (and preferably minimizes) the amount of light
detected by the light detector sensor region 306 that would
otherwise be due to specular reflections, if the optoelectronic
device is used with a cover plate (e.g., 1402). In this manner, the
specular reflection reducing shelf 336 increases the sensitivity of
the optoelectronic device. Stated another way, the specular
reflection reducing shelf 336 increases the percentage of light
that will be detected by the light detector sensor region 306 that
is actually due to reflections by an object on the far side of the
cover plate 1402 (as opposed to reflections from the cover plate
1402 itself).
[0087] Referring to FIG. 14C, in accordance with certain
embodiments, a further opaque vertical barrier 338 reduces the
detection of specular reflections. This barrier 338 forms a shelf
over the light detector sensor region 306, and in an embodiment,
covers at least a portion of the light detector sensor region 306,
as shown in FIG. 14C. As can be appreciated from a comparison
between FIG. 14A and FIG. 14C, the shelf 338 reduces the amount of
specular reflections that are detected by the light detector sensor
region 306, and thereby, increases the sensitivity of the
optoelectronic device. Stated another way, the specular reflection
reducing shelf 338 blocks at least some specular reflections that
would otherwise be detected by the light detector sensor region 306
if the shelf 338 were not included.
[0088] The forgoing description is of the preferred embodiments of
the present invention. These embodiments have been provided for the
purposes of illustration and description, but are not intended to
be exhaustive or to limit the invention to the precise forms
disclosed. Many modifications and variations will be apparent to a
practitioner skilled in the art. Embodiments were chosen and
described in order to best describe the principles of the invention
and its practical application, thereby enabling others skilled in
the art to understand the invention.
[0089] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example, and not limitation. It will be
apparent to persons skilled in the relevant art that various
changes in form and detail can be made therein without departing
from the spirit and scope of the invention.
[0090] The breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents.
* * * * *