U.S. patent application number 14/488814 was filed with the patent office on 2016-03-17 for method for mounting chip on printed circuit board.
This patent application is currently assigned to SUNASIC TECHNOLOGIES, INC.. The applicant listed for this patent is SUNASIC TECHNOLOGIES, INC.. Invention is credited to Zheng-Ping HE, Chi-Chou LIN.
Application Number | 20160079289 14/488814 |
Document ID | / |
Family ID | 55410522 |
Filed Date | 2016-03-17 |
United States Patent
Application |
20160079289 |
Kind Code |
A1 |
LIN; Chi-Chou ; et
al. |
March 17, 2016 |
METHOD FOR MOUNTING CHIP ON PRINTED CIRCUIT BOARD
Abstract
A method for mounting a chip on a printed circuit board (PCB) is
disclosed. The method includes the steps of: providing a chip
having a plurality of bonding pads and a PCB having a recess
portion and a plurality of connectors; gluing the recess portion;
placing the chip into the recess portion; and forming circuit
patterns linking associated bonding pad and connector. A bottom of
the recess portion is substantially flat and a shape of the recess
portion is similar to that of the chip but large enough so that the
chip can be fixed in the recess portion after being glued.
Inventors: |
LIN; Chi-Chou; (New Taipei
City, TW) ; HE; Zheng-Ping; (New Taipei City,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUNASIC TECHNOLOGIES, INC. |
New Taipei City |
|
TW |
|
|
Assignee: |
SUNASIC TECHNOLOGIES, INC.
New Taipei City
TW
|
Family ID: |
55410522 |
Appl. No.: |
14/488814 |
Filed: |
September 17, 2014 |
Current U.S.
Class: |
438/66 |
Current CPC
Class: |
H01L 2224/29139
20130101; H01L 2224/2919 20130101; H01L 2924/15153 20130101; H01L
21/4867 20130101; H01L 27/146 20130101; H01L 2224/73267 20130101;
H01L 23/5389 20130101; H01L 2224/484 20130101; H01L 2224/32225
20130101; H01L 2224/92244 20130101; H01L 24/24 20130101; H01L 24/82
20130101; H01L 2224/04105 20130101; H01L 21/4857 20130101; H01L
24/19 20130101; H01L 2224/24227 20130101; H01L 27/1469 20130101;
H01L 2224/0401 20130101 |
International
Class: |
H01L 27/146 20060101
H01L027/146 |
Claims
1. A method for mounting a chip on a printed circuit board (PCB),
comprising the steps of: providing a chip having a plurality of
bonding pads and a PCB having a recess portion and a plurality of
connectors; adding glue into the recess portion; placing the chip
into the recess portion of the PCB; and linking the bonding pads to
the connectors of the PCB by inkjet printing or screen printing to
form circuit patterns, wherein a bottom of the recess portion is
substantially flat and a shape of the recess portion is similar to
that of the chip but large enough so that the chip can be fixed in
the recess portion of the PCB after the glue is being added; and
wherein step difference between a level of a top surface of the
chip and that of the PCB after the placing the chip into the recess
portion step is less than 0.1 mm.
2. The method according to claim 1, wherein the gluing step is
achieved by a conductive adhesive.
3. The method according to claim 2, wherein an auxiliary
nonconductive adhesive is further placed over the conductive
adhesive and sealing a gap between the chip and edges of the
PCB.
4. (canceled)
5. The method according to claim 1, wherein a conductive ink is
used for the inkjet printing or screen printing.
6. The method according to claim 1, wherein a conductive paste is
used for the inkjet printing or screen printing.
7. The method according to claim 1, wherein the PCB has at least 3
conductive layers and 2 insulation layers formed interleaved.
8. The method according to claim 1, wherein the forming circuit
patterns step is achieved by forming a layer of copper and etching
out an unnecessary portion of the copper.
9. The method according to claim 1, wherein the chip is an image
sensor.
10. The method according to claim 1, wherein the image sensor is a
fingerprint reader sensor.
11. (canceled)
12. The method according to claim 1, further comprising a step of
forming a protection layer over an off-chip area.
13. The method according to claim 12, wherein the protection layer
is made of organic coating material.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for mounting a
chip. More particularly, the present invention relates to a method
for mounting a chip on a printed circuit board.
BACKGROUND OF THE INVENTION
[0002] A silicon chip, or integrated circuit (IC), is the core
element of an electronic device and usually comes in packaged form.
With the development of manufacturing technology and requirement of
compact design for end products, various packaging methods were
invented to meet the demand. At most of the time, silicon chips are
sealed within a protection material such as epoxy resin. There are
certain cases, particularly when the silicon chip is a sensor
device such as a fingerprint sensor chip, that the silicon chip
needs to be mount on a substrate and has the surface exposed.
Meanwhile, for a fingerprint reader device, the thickness of the
packaged sensor must be as low as possible. Hence, the technique of
bonding the silicon chip to the substrate plays a very important
role. The bonding needs to ensure good circuit connectivity formed
therebetween, and to be rigid enough to sustain the fingerprint
reader sensor with shear force exerted by a finger.
[0003] Flip chip technology is a suitable means for better
interconnecting between the die and the PCB. Processing a flip chip
is similar to the conventional IC fabrication, with a few
additional steps. Please refer to FIG. 1. Near the end of the
manufacturing process, the attachment pads 2 of a chip 1 are
metalized to make them more receptive to solders. This typically
consists of several treatments. Small dots of solder balls 3 are
then deposited on each metalized pad 2. The chips 1 are then cut
out of the wafer as normal. To attach the flipped chips 1 into a
PCB 4, the chip (die) 1 is inverted to bring the solder balls 3
down onto connectors 5 on the underlying PCB 4. The solder balls 3
are then re-melted to produce an electrical connection, typically
using a thermosonic bonding or alternatively using a reflow solder
process. This also leaves a small space between the chip's
circuitry and the underlying mounting. In most cases an
electrically-insulating adhesive 6 is then underfilled to provide a
stronger mechanical connection.
[0004] One challenge of the flip chip technology is heat
dissipation for thermal stress in the chip 1. The adhesive 6 is
used as a heat bridge to ensure that the solder balls 3 are not
stressed due to differential heating of the chip 1 and the PCB 4.
The adhesive 6, distributing the thermal expansion mismatch between
the chip 1 and the PCB 4, prevents stress concentration in the
solder balls 3 which would lead to premature failure. When fan-outs
of logic gates of a chip increases and associated pads for
soldering become more and tiny, the efficiency of heating
dissipation of such adhesive for the solder balls get worse. In
other words, the tiny solder balls will easily get hurt to cause
open-circuit failure since limited quantity of the adhesive applied
to take away unnecessary heat. Meanwhile, for a fingerprint reader
sensor chip, the binding ability between the chip and the PCB may
not sufficient to resist the force exerted by a finger.
[0005] A better solution to settle the problem could be available
from the U.S. Pat. No. 5,045,921. Please see FIG. 2. An electronic
pad array carrier IC device 10 for mounting on a PCB is disclosed.
It has a thin and flexible "tape" substrate 11 which has a number
of traces 12. The substrate 11 can withstand relatively large
lateral mechanical displacement. An integrated circuit die 13 is
mounted in proximity with or on the substrate 11. The substrate
traces 12 are provided at their outer ends 14 with solder balls 15
for making connections to the PCB. A package body 16 covers the die
13. Alternatively, a carrier structure may be provided around the
periphery 17 of the substrate 11 to add rigidity during handling,
testing and mounting, but which may also provide the stand-off
function. The thin, flexible substrate 11 can absorb a relatively
large lateral or even vertical mechanical displacement over a
rather large package area that may accommodate as few as 20 or as
many 500 or more connections. The solder balls 15 may be joined to
a via 18 through the substrate 11 at least partially filled with
electrically conductive material to permit back side testing before
or after mounting of a package to the PCB. Additionally, a heat
sink structure 19 may be directly bonded to the die 13 in the pad
array carrier IC device 10. Although '921 was an innovative
invention to provide bonding between a die and a PCB with a special
tape substrate, it is the tape substrate causes complexity in
mounting and extra cost.
[0006] Therefore, an improved method for mounting a chip on a PCB
is still desired. More particularly, the binding ability between
the chip and the PCB should resist external force exerted onto the
chip.
SUMMARY OF THE INVENTION
[0007] This paragraph extracts and compiles some features of the
present invention; other features will be disclosed in the
follow-up paragraphs. It is intended to cover various modifications
and similar arrangements included within the spirit and scope of
the appended claims.
[0008] In accordance with an aspect of the present invention, a
method for mounting a chip on a printed circuit board (PCB)
includes the steps of: providing a chip having a plurality of
bonding pads and a PCB having a recess portion and a plurality of
connectors; gluing the recess portion; placing the chip into the
recess portion; and forming circuit patterns linking associated
bonding pad and connector. A bottom of the recess portion is
substantially flat and a shape of the recess portion is similar to
that of the chip but large enough so that the chip can be fixed in
the recess portion after being glued.
[0009] Preferably, the gluing step is achieved by a conductive
adhesive. An auxiliary nonconductive adhesive is further placed
over the conductive adhesive and in sealing the gap between the
chip and edges of the PCB. The forming circuit patterns step is
achieved by ink-jet or screen printing. A conductive ink or
conductive paste is used for the ink-jet or screen printing. The
PCB has at least 3 conductive layers and 2 insulation layers formed
interleaved. The forming circuit patterns step is achieved by
forming a layer of copper and etching out an unnecessary portion of
the copper. The chip is an image sensor. The image sensor is a
fingerprint reader sensor. Step difference between a level of a top
surface of the chip and that of the PCB after the placing the chip
into the recess portion step is less than 0.1 mm.
[0010] According to the present invention, the method further
includes a step of forming a protection layer over the off-chip
area. The protection layer is better made of organic coating
material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is used to illustrate a conventional flip chip
process.
[0012] FIG. 2 shows an electronic pad array carrier IC device in a
prior art.
[0013] FIG. 3 is a flow chart of a method for mounting a chip on a
printed circuit board according to the present invention.
[0014] FIG. 4 to FIG. 9 illustrate steps of the method.
[0015] FIG. 10 shows a top view of the chip and the printed circuit
board after the method has applied.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] The present invention will now be described more
specifically with reference to the following embodiment.
[0017] Please refer to FIG. 3 to FIG. 10. An embodiment is
illustrated. FIG. 3 is a flow chart of the method for mounting a
chip on a printed circuit board (PCB) according to the present
invention. FIG. 4 to FIG. 9 illustrates steps of the method. FIG.
10 shows a top view of the chip 300 and the PCB 100 after the
method has been applied.
[0018] The first step of the method is to provide a chip 300 and a
PCB 100 (S01). According to the present invention, the chip 300 is
in form of a die rather than a packaged integrated circuit. Without
the package portion in a conventional packaged integrated circuit,
the chip 300 can have lower thickness for assembly and is possible
to reduce the thickness of a final product applied this chip 300.
In application, the chip 300 is better an image sensor since it is
not necessary to be enclosed for protection. Instead, image sensors
must expose a portion of themselves to the external environment so
that they can function normally. Moreover, some of them would be
encountered extra forced exerted. Protection against friction
should be well done. For example, the chip 300 in the embodiment is
a fingerprint reader sensor chip in form of a die. Before further
processes of the method of the present invention are applied, a
layer of protection should be ready. Please refer to FIG. 10 first.
From the top view of the chip 300, it is obvious that the chip 300
has a sensing portion 320 and a number of bonding pads 340 on the
same side. In the embodiment, for illustrative purpose, there are
fifteen bonding pads 340 used. In practice, the number of bonding
pads 340 is not limited to fifteen. It can be more, for example
tens to hundreds, depending on the fan-outs of its design. The
bonding pads 340 are used to link to external circuitry for the
fan-outs.
[0019] The PCB 100 can be any types except a flexible circuit
board. According to the present invention, it is better to have at
least 3 conductive layers and 2 insulation layers formed
interleaved. Please refer to FIG. 4. The PCB 100 has a first
conductive layer 110, a first insulation layer 120, a second
conductive layer 130, a second insulation layer 140 and a third
conductive layer 150. Each of the conductive layers forms a
specified circuitry. There can be many vias (not shown) used to be
filled with conductive material, such as copper. Vias can be used
to conduct current between two or three conductive layers. The
first insulation layer 120 and the second insulation layer 140
substantially block electrical connections for two adjacent
conductive layers. Since each of the conductive layers may not be
completely formed or populated to occupy the entire space between
the first insulation layer 120 and the second insulation layer 140,
there are some portions of the first insulation layer 120 and the
second insulation layer 140 contacted with each other. For
illustration purpose, dashed lines are used to separate the two
insulation layers. In fact, the interface is not so clear.
[0020] It is appreciated that the illustration of the PCB 100
comparing with other components in all figures is not in
proportion. In order to have a better understanding of the present
invention, length and thickness of the PCB 100 comparing with other
components are shrunk. In practice, the PCB 100 would be much wider
than it is shown in FIG. 4 to FIG. 9. It is not necessary a limit
to the scope of claims of the present invention. The PCB 100 has a
recess portion 160 which may be formed by cutting a portion of the
first insulation layer 120. A bottom of the recess portion 160 is
substantially flat and formed by the second conductive layer 130. A
shape of the recess portion 160 is similar to that of the chip 300
but large enough so that the chip 300 can be fixed in the recess
portion 160 after the chip 300 gets glued in the coming step. The
first conductive layer 110 has a number of portions which are used
to link to the related bonding pads 340, so that a complete
circuitry run as a sensor can be implemented after all linkages
between that portions and the bonding pads 340 are formed.
[0021] The next step is gluing the recess portion 160 (S02). Please
see FIG. 5. A conductive adhesive 200 is used for gluing.
Preferably, the conductive adhesive 200 is a silver paste. The
reason the conductive adhesive 200 is used is the chip 300 and the
PCB 100 need to be fixed while electrical conductivity must exist
therebetween. Actually, the amount of the conductive adhesive 200
is not as much as the figures show as long as the PCB 100 and the
chip 300 can be glued. Then, place the chip 300 into the recess
portion 160 (S03). Please see FIG. 6. After the chip 300 is placed
on the conductive adhesive 200, there might be space where the
conductive adhesive 200 is not filled. The space forms a gap
between the chip 300 and edges of the PCB 100. An auxiliary
nonconductive adhesive 210 is further used to place over the
conductive adhesive 200 and in the gap. Please refer to FIG. 7.
Heat conductive glues are preferred to be used as the auxiliary
nonconductive adhesive 210. Epoxy resin is recommended.
[0022] It should be noted the step S03 is not soon after the step
S02. It should be time to wait for the conductive adhesive 200
becoming the maximum stickiness before it is fixed. It should be
noticed that a level of a top surface of the chip 300 may be
substantially the same as that of the PCB 100 after step S03 is
finished. This is because the two top surfaces must be closer
enough for the next step to be applied so that circuitry formed
across the two surfaces would not be damaged due to a large step
(or difference of height) formed therebetween. In practice, step
difference between the level of the top surface of the chip 300 and
that of the PCB 100 after step S03 should be less than 0.1 mm. The
chip 300 could be a slightly higher than the PCB 100 since the chip
300 may be enclosed by a housing (not shown) but the sensing
portion 320 must be exposed through an opening.
[0023] Next step is forming circuit patterns 400 linking associated
bonding pad 340 with connector 140 (S04). It is depicted by FIG. 8.
This step is achieved by inkjet printing or screen printing.
However, the ink used here should be specified. It is a conductive
ink used for the inkjet printing or screen printing. The conductive
ink contains conductive materials. After it is dried, circuit
connection can be available by the conductive materials left as the
circuit patterns 400. The circuit patterns 400 can be formed by
other means. For example, it is achieved by forming a layer of
copper and etching out an unnecessary portion of the copper. In
addition, the conductive ink can be replaced by a conductive paste
if further fixtures are used over the bonding pad 340.
[0024] Mounting of the chip 300 on the PCB 100 can be ready after
the aforementioned steps. However, according to the spirit of the
present invention, the method can further comprise a step to form a
protection layer 500 over the off-chip and the non-image sensing
area (S05). Please refer to FIG. 9. This is because the left
conductive materials of the conductive ink (paste) may not be
wearable. In order to protect the circuit patterns 400, the
protection layer 500 exists. Preferably, the protection layer 500
is made of organic coating material.
[0025] From the description of the embodiment above, it is known
that there are some features of the present invention comparing
with conventional methods. First, the recess portion 160 in the PCB
100 is just large enough to accommodate the chip 300 and the
conductive adhesive 200. After gluing, the chip 300 can be firmly
fixed in the PCB 100. The chip 300 can resist the force exerted by
the finger for fetching fingerprint image patterns with the help of
the conductive adhesive 200 and the reaction from the PCB 100.
Second, no soldering is applied to form the circuitry across the
chip 300 and the PCB 100. No more problems of heat dissipation
could happen.
[0026] While the invention has been described in terms of what is
presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention needs not be
limited to the disclosed embodiment. On the contrary, it is
intended to cover various modifications and similar arrangements
included within the spirit and scope of the appended claims, which
are to be accorded with the broadest interpretation so as to
encompass all such modifications and similar structures.
* * * * *