U.S. patent application number 12/081792 was filed with the patent office on 2008-09-04 for thermal bonding structure and manufacture process of flexible printed circuit board.
Invention is credited to Li-Hui Chen, Ya-Ting Ho.
Application Number | 20080209717 12/081792 |
Document ID | / |
Family ID | 36683047 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080209717 |
Kind Code |
A1 |
Ho; Ya-Ting ; et
al. |
September 4, 2008 |
Thermal bonding structure and manufacture process of flexible
printed circuit board
Abstract
A thermal bonding structure and manufacture process of a
flexible printed circuit (FPC) board are disclosed, and the thermal
bonding structure includes a laminated structure having a first
insulating layer with a solder pad area and showing parts of a
first conductive layer, the first conductive layer, a second
insulating layer, a second conductive layer, and a third insulating
layer with a bonding area such that a part of the second conductive
layer is exposed, and at least a through hole passing through the
first conductive layer to the second conductive layer for
propagating heat energy to fuse a solder. Accordingly, the
reduction of heat energy lost in the third insulating layer
improves the bonding quality, shortens the bonding period, and
maintains the material stability under high temperature resulted
from high heat energy.
Inventors: |
Ho; Ya-Ting; (Hsin-Chu,
TW) ; Chen; Li-Hui; (Hsin-Chu, TW) |
Correspondence
Address: |
ROSENBERG, KLEIN & LEE
3458 ELLICOTT CENTER DRIVE-SUITE 101
ELLICOTT CITY
MD
21043
US
|
Family ID: |
36683047 |
Appl. No.: |
12/081792 |
Filed: |
April 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11085097 |
Mar 22, 2005 |
7385143 |
|
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12081792 |
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Current U.S.
Class: |
29/830 ;
29/852 |
Current CPC
Class: |
Y10T 29/49126 20150115;
H05K 1/0212 20130101; Y10T 29/49165 20150115; H05K 3/363 20130101;
H05K 3/281 20130101; H05K 2203/0195 20130101; H05K 3/3494 20130101;
H05K 2201/09781 20130101; H05K 1/0206 20130101; H05K 3/42
20130101 |
Class at
Publication: |
29/830 ;
29/852 |
International
Class: |
H05K 3/00 20060101
H05K003/00; H05K 3/36 20060101 H05K003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 14, 2005 |
TW |
094101091 |
Claims
1. A method for manufacturing a flexible printed circuit board,
comprising the steps of: providing a laminated structure having a
first insulating layer, a first conductive layer, a second
insulating layer, a second conductive layer and a third insulating
layer laminated in sequence; dividing the laminated structure into
a first portion, a second portion and a third portion, wherein the
second portion is between the first portion and the third portion;
forming at least one through hole in the second insulating layer of
the first portion and the third portion, respectively; forming a
solder pad area by removing a part of the first insulating layer of
the third portion to expose the first conductive layer; and forming
a bonding area by removing a part of the third insulating layer of
the third portion to expose the second conductive layer, wherein
the at least one through hole is formed beyond the range of the
solder pad area and the bonding area.
2. The method of claim 1, further comprising a step of: removing
the second conductive layer and the third insulating layer of the
second portion.
3. The method of claim 1, wherein the step of forming at least one
through hole further comprises a step of: forming a conductive
material in the at least one through hole.
4. The method of claim 1, wherein the first conductive layer and
the second conductive layer are comprised of copper.
5. The method of claim 1, further comprising a step of: forming an
adhesive layer disposed between the first insulating layer and the
first conductive layer.
6. The method of claim 1, further comprising a step of: forming an
adhesive layer disposed between the first conductive layer and the
second insulating layer.
7. The method of claim 1, further comprising a step of: forming an
adhesive layer disposed between the second insulating layer and the
second conductive layer.
8. The method of claim 1, further comprising a step of: forming an
adhesive layer disposed between the second conductive layer and the
third insulating layer.
Description
RELATED APPLICATIONS
[0001] This application is a Divisional patent application of
co-pending application Ser. No. 11/085,097, filed on 22 Mar. 2005.
The entire disclosure of the prior application Ser. No. 11/085,097,
from which an oath or declaration is supplied, is considered a part
of the disclosure of the accompanying Divisional application and is
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention generally relates to a flexible
printed circuit board, and more particularly relates to a thermal
bonding structure and manufacture process of a flexible printed
circuit board that can improve the issues of bonding burns and
material quality.
BACKGROUND OF THE INVENTION
[0003] As our living standard is improving gradually, various
electronic consumer products are introduced to meet extensive
consumer requirements, and thus promoting the prosperity of various
industries directly and driving the growth of related
sub-industries indirectly. To further meet the consumer
requirements and trends for various functions, portability,
operability and appearance, in hope of improving consumer's
willingness to buy and brand loyalty, various electronic consumer
products tend to be designed thinner and lighter. For example, the
market share of color mobile phones with a photographic function
and other combined functions grows drastically, and the demand of
color LCD panels and camera modules for mobile phones rises
accordingly. Color LCD panel industry is divided into the area of
color super twisted nematic (CSTN) LCDs and thin-film transistor
(TFT) LCDs, and the key components including light emitting diodes
(LEDs) and flexible printed circuit (FPC) boards also grow with the
high demand for flexibility, 3-D circuit layout and light weight of
a miniaturized foldable design of mobile phones. The estimated
quantity of flexible printed circuit boards used in a color mobile
phone is increased from 3-4 pieces to 6-7 pieces, and the design of
flexible printed circuit boards tends to follow a high-end small
circuit specification. A flexible printed circuit board is made by
raw materials including a flexible insulating substrate material
and a circuit conductor material (generally copper clad), and the
raw materials are divided into resins, copper clads, adhesives,
coverlays, and flexible copper cladded laminates (FCCL). Since
polyimide (PI) has good expansibility and heat resistance,
therefore PI is generally used as a resin material and serves as a
middle layer and a substrate in the manufacture of flexible copper
substrates and also as a coverlay film.
[0004] PI manufacturers can produce different PI films from
different PI monomers according to different technologies in three
main aspects: formula, manufacture process and processing method,
and thus different manufacturers achieve different applications and
performance of the materials. Further, the flexible copper
substrate is divided into two main types: an adhesive three-layer
structure and an adhesiveless two-layer structure, and both adopt
different manufacture processes, methods and applications, and thus
the properties of the materials are different. In general, the
adhesive three-layer structure is usually applied to the production
of a large number of flexible printed circuit board products and
the adhesiveless two-layer structure is usually applied to the
manufacture of high-end flexible printed circuit boards, such as
the rigid and flexible printed circuit boards and some of the
multi-layer boards. It is believed that the adhesiveless two-layer
structure will take over some of the adhesive three-layer flexible
copper cladded laminates used for the flexible printed circuit
boards with high resolution and good dimensional stability.
[0005] Referring to FIG. 1, a schematic view of the relation
between the raw materials and the finished goods of a prior art
flexible printed circuit board is illustrated. In the manufacture
of the flexible printed circuit board 150, an insulating substrate
material 100 and a circuit conductor material 110 are used to
produce an adhesiveless two-layer flexible copper cladded laminate
130 first, and then a coverlay, a stiffener, and an anti-static
layer are used to produce the flexible circuit board 150. On the
other hand, an adhesive three-layer flexible copper cladded
laminate 140 is made of an insulating substrate material 100, a
circuit conductor material 110 and an adhesive 120, and a flexible
printed circuit 150 is made of such laminate 140. At present,
flexible printed circuit boards are generally used in electronic
products, particularly mobile phones and LCDs showing a drastic a
growth of using flexible circuit boards in their applications.
[0006] Referring to FIG. 2, a top view of a flexible printed
circuit board and a cross-sectional view of a bonding head
according to a prior art are illustrated. The flexible printed
circuit board 2 comprises a first insulating layer 200, an adhesive
layer 210, a conductive layer 220 and a second insulating layer
240; wherein the first insulating layer 200 and the second
insulating layer 240 are made of the same material or different
materials, and the first insulating layer 200 includes a solder pad
area 270 and the second insulating layer 240 includes a bonding
area 250, such that a bonding head 260 is in direct contact with
the bonding area 250 for soldering the flexible printed circuit
board 2 with another flexible printed circuit board. In actual
practices, the boding area 250 is usually situated at a position
substantially parallel to the solder pad area 270, so that heat
energy can be conducted from the bonding area 250 to the adhesive
layer 210, conductive layer 220 and solder pad area 270 for
bonding. However, it is necessary to increase the temperature of
the bonding head 260 for bonding, and the high temperature will
burn the first insulating layer 200 and the adjacent adhesive layer
210 black, and thus causing poor bonding quality and appearance of
the product, or even deteriorating the materials in the bonding
area. For example, a bonding machine sets a temperature for the
bonding head for a thermal compression, and the temperature of the
bonding head is set to 330.degree. C. for a predetermined time
(such as 3 seconds for temperature rise) and then the operating
temperature of the bonding machine is set to 470.degree. C. for
another predetermined time (such as 3.5 seconds for the bonding),
then the solder will be fused to complete the bonding process.
However, the first insulating layer 200 and its adjacent adhesive
layer 210 will be burned black at the temperature of 470.degree.
C., and such phenomenon is particularly severe for lead-free
solders because the melting point of lead-free solders is higher
than that of lead solders. For example, the melting points of the
solders of the Sn--Ag--Cu series and Sn--Cu--Ni series are
227.degree. C. and 217.degree. C. respectively. Compared with the
melting point 183.degree. C. of solder of the Sn--Pb series, there
is a difference of 34.about.44.degree. C. Therefore, it is
necessary to increase the temperature of the bonding head 260 for
lead-free solders in compliance with the environmental protection
and international standard requirements. As a result, the burning
effect produced in the bonding area 250 becomes obvious and
severe.
[0007] Therefore, developing a thermal bonding structure and
manufacture process for a flexible printed circuit board to
overcome the foregoing shortcomings of the prior arts, improving
the burning situation in the bonding area, and further conducting
heat energy to the solder so as to lower the bonding temperature
and supply less heat energy for saving bonding time and costs are
important topics for manufactures and users and demand immediate
attentions and feasible solutions. The inventor of the present
invention based on years of experience on related research and
development of the optoelectronic component industry to invent a
thermal bonding structure and manufacture process for flexible
printed circuit boards to overcome the foregoing shortcomings.
SUMMARY OF THE INVENTION
[0008] Therefore, it is a primary objective of the present
invention to provide a thermal bonding structure of a flexible
printed circuit board that comprises: a laminated structure and the
laminated structure includes a first insulating layer, a first
conductive layer, a second insulating layer, a second conductive
layer and a third insulating layer in sequence; at least a through
hole for passing through the first conductive layer, the second
insulating layer and the second conductive layer. The first
insulating layer includes a solder pad area for exposing the first
conductive layer, and the third includes a bonding area for
exposing the second conductive layer, such that the bonding head is
in direct contact with the bonding area, and the heat energy can be
conducted to the solder pad area through the through hole quickly
for bonding.
[0009] Another objective of the present invention is to provide a
flexible printed circuit board comprising a first area, and the
first area includes a laminated structure having a first insulating
layer, a first conductive layer, a second insulating layer, a
second conductive layer and a third insulating layer arranged in
sequence; a second area including a laminated structure coupled to
the first area and having a first insulating layer, a first
conductive layer, and a second insulating layer arranged in
sequence; and a third area including a laminated structure disposed
away from the first area and coupled to the second area and having
the foregoing first insulating layer, first conductive layer,
second insulating layer, second conductive layer and third
insulating layer arranged in sequence; and at least one through
hole passing through the foregoing first conductive layer, second
insulating layer and second conductive layer. The first insulating
layer in the third area includes a solder pad area for exposing the
first conductive layer and being in contact with the solder, and
the third insulating layer includes a bonding area for exposing
part of the second conductive layer to define a bonding area, such
that the heat energy of the bonding head can be conducted to the
solder pad area through the through hole quickly to reduce bonding
time and heat supply costs.
[0010] A further objective of the present invention is to provide a
manufacture process of a flexible printed circuit board that
comprises the steps of: providing a laminated structure and the
laminated structure is divided into a first area, a second area and
a third area, and the second area is disposed between the first
area and the third area, and the laminated structure in the first
and third areas includes a first insulating layer, a first
conductive layer, a second insulating layer, a second conductive
layer and a third insulating layer arranged in sequence, and the
second area includes a first insulating layer, a first conductive
layer, a second insulating layer, and at least one through hole
formed in the first area and third area separately and passing
through the first conductive layer, the second insulating layer and
the second conductive layer; removing a part of the third
insulating layer to expose the second conductive layer and define a
bonding area; removing a part of the first insulating layer in the
third area to expose the first conductive layer and define a solder
pad area; and removing a part of the third insulating layer in the
third area to expose the second conductive layer and define a
bonding area.
[0011] Thus, the thermal bonding structure and manufacture process
of a flexible printed circuit board in accordance with the present
invention has the following advantages. Since the heat consumption
at the insulating layer is reduced, therefore the bonding head can
achieve the bonding effect with less heat energy and the cost for
the bonding process can be lowered. Furthermore, the bonding head
is applied to the bonding area, and the through hole is used to
conduct heat energy to the solder pad area to accomplish the
bonding process, and thus the temperature of the bonding head can
be controlled to improve the burning phenomenon caused by the high
temperature of the bonding head and occurred at the bonding area,
so as to enhance the soldering process, the material quality, and
the appearance of the product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic view of the relation between the raw
materials and the finished goods of a prior art flexible printed
circuit board;
[0013] FIG. 2 shows a top view of a finished goods of a flexible
printed circuit board and a cross-sectional view of a bonding head
according to a prior art;
[0014] FIG. 3 shows a top view of a thermal bonding structure of a
flexible printed circuit board and its corresponding
cross-sectional view according to a preferred embodiment of the
present invention;
[0015] FIG. 4 shows a top view of a flexible printed circuit board
and its corresponding cross-sectional view according to a preferred
embodiment of the present invention; and
[0016] FIG. 5 shows a flow chart of the manufacture process of a
flexible printed circuit according to a preferred embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] To make it easier for our examiner to understand the
objective of the invention, its innovative features and
performance, a detailed description and technical characteristics
of the present invention are described together with the drawings
as follows.
[0018] Referring to FIG. 3, a top view of a thermal bonding
structure of a flexible printed circuit board and its corresponding
cross-sectional view according to a preferred embodiment of the
present invention are illustrated. In the preferred embodiment, a
thermal bonding structure 3 of a flexible circuit board comprises:
a laminated structure having a first insulating layer 310, an
adhesive layer 320, a first conductive layer 330, an adhesive layer
320, a second insulating layer 340, an adhesive layer 320, a second
conductive layer 350, and a third insulating layer 360; and at
least one through hole 380 passing through each layer between the
first conductive layer 330 and the second conductive layer 350. The
first insulating layer 310 includes a solder pad area 390 for
exposing the first conductive layer 330, and the third insulating
layer 360 includes a bonding area 365 for exposing the second
conductive layer, and the through hole 380 is formed beyond the
range of the solder pad area 390 and the bonding area 365. In other
words, there is a gap between the solder pad area 390 and the
bonding area 365. Referring to FIG. 3 for a cross-sectional view of
a thermal bonding structure of a flexible printed circuit board
according to a preferred embodiment of the present invention, the
through hole 380 is formed beyond the range of the solder pad area
390 and the bonding area 365. It is noteworthy that each conductive
layer can be stacked on top of each insulating layer directly as
disclosed in another embodiment, since the laminated structure of
the thermal bonding structure of the flexible printed circuit board
can only have a first insulating layer 310, a first conductive
layer 330, a second insulating layer 340, a second conductive layer
350 and a third insulating layer 360. The through hole 380 of this
embodiment includes an electric conductive material on its internal
wall, and the materials used for making the first conductive layer
330 and the second conductive layer include a copper clad, and the
surface of the second conductive layer 350 of the bonding area 365
further includes a metal layer for protecting the second conductive
layer 350. The metal layer could be single-layer or multiple-layer
and made of gold, nickel, tin, other metal, or an alloy of the
foregoing metals. In this embodiment, a nickel layer and a gold
layer are formed in sequence on the surface of the second
conductive layer 350 of the bonding area 365, and the materials
used here are provided for the purpose of describing the present
invention and not intended to limit the invention. Further, the
quantity and size of the through holes 380 vary with the speed and
time of the heat conduction, and thus the positions of the through
holes and the bonding area described in this embodiment are
provided for example only, and not limited to the same number and
size of the through holes 380 as depicted in FIG. 3.
[0019] A lithographic etching is adopted to remove a part of the
third insulating layer 360 to define a bonding area 365, so that
heat energy can be conducted directly and quickly from the second
conductive layer 350 to the first conductive layer 330 and fuse a
solder such as a solder paste in the solder pad area 390. With the
same conditions as the prior art, a solder can be fused to complete
a bonding process with a lower temperature, if the temperature of
the bonding machine is set to 330.degree. C. for a predetermined
time (such as 3 seconds for temperature rise) and the operating
temperature of the bonding machine to 400.degree. C., and the
bonding head 370 is operated for a bonding time (such as 3.5
seconds), and thus improving or avoiding the burning phenomenon at
the bonding area 365 and the third insulating layer 360.
[0020] Referring to FIG. 4, a top view of a flexible printed
circuit board and its corresponding cross-sectional view according
to a preferred embodiment of the present invention are illustrated.
In this embodiment, the flexible printed circuit board 4 is divided
into a first area 410, a second area 430 coupled to the foregoing
first area 410 and a third area 450 disposed away from the first
area 410 and coupled to the second area 430. The flexible printed
circuit board 4 comprises a laminated structure, and the first area
410 (which is a connecting area for components such as the light
emitting diodes) and the third area 420 include a first insulating
layer 411, a first conductive layer 412, a second insulating layer
413, a second conductive layer 414 and a third insulating layer 415
arranged in sequence, and the second area 430 includes a first
insulating layer 431, a first conductive layer 432, a second
insulating layer 433 arranged in sequence and considered as a
circuit area; and at least one through hole 458 passing through the
first conductive layer 452, the second insulating layer 453 and the
second conductive layer 454. The first insulating layer 451 in the
third area 450 includes a solder pad area 456 for exposing the
first conductive layer 452, and the third insulating layer 455
includes a bonding area 457 for exposing the second conductive
layer 454 and contacting a bonding head 459. The surface of the
second conductive layer 454 exposed from the bonding area 457 could
include a metal layer, which is a single-layer metal layer such as
a gold layer, or a double-layer metal layer such as a nickel layer
and a gold layer. These materials are used for example to describe
the present invention and not intended to limit the invention.
[0021] It is noteworthy that the through hole 458 is formed beyond
the range of the solder pad area 456 and the bonding area 457, and
the through hole 458 includes an electric conductive material such
as nickel or any other substance having a thermal conductive
property. In addition, the materials used for the first conductive
layer 452 and the second conductive layer 454 could include a
copper clad, and an adhesive layer could be included between
layers.
[0022] Referring to FIGS. 4 and 5, a flexible printed circuit board
and a flow chart of a manufacture process of a flexible printed
circuit board according to a preferred embodiment of the present
invention are illustrated. In the embodiment, the manufacture
process of a flexible printed circuit board 4 comprises the steps
of: (Step S51) providing a laminated structure, which is a
four-layer structure as shown in the figure, and the laminated
structure is divided into a first area 410, a second area 430 and a
third area 450, and the second area 420 is disposed between the
first area 410 and the third area 450 and includes a first
insulating layer 411, a first conductive layer 412, a second
insulating layer 413, a second conductive layer 414 and a third
insulating layer 415; and at least one through hole 458 being
formed at the first area 410 and the third area 450 and passing
through the first conductive layer 412, second insulating layer 413
and second conductive layer 414; (Step S52) removing a part of the
first insulating layer 411 in the third area 450 to expose the
first conductive layer 412 to define a solder pad area 456; and
(Step S53) removing a part of the third insulating layer 415 in the
third area 450 to expose the second conductive layer 414 to define
a bonding area 457.
[0023] In another preferred embodiment of the present invention, a
manufacture process of a flexible printed circuit board further
comprises the steps of removing the second conductive layer 414 and
the third insulating layer 415 in the second area 430, such that
the laminated structure in the first area 410 and the third area
450 includes a first insulating layer 411, a first conductive layer
412, a second insulating layer 413, a second conductive layer 414
and a third insulating layer 415 arranged in sequence, and the
laminated structure in the second area 430 includes a first
insulating layer 411, a first conductive layer 412 and a second
insulating layer 413 arranged in sequence; depositing an electric
conductive material in at least one through hole 458 after forming
at least one through hole 458 that passes through the first
conductive layer 412, the second insulating layer 413 and the
second conductive layer 414; and forming a metal layer on the
surface of the bonding area 457 after forming the bonding area 457.
It is noteworthy that the laminated structure further comprises at
least one adhesive layer disposed between the first insulating
layer, the first conductive layer 412, the second insulating layer
413, the second conductive layer 414 and the third insulating layer
415.
[0024] While the invention has been described by way of example and
in terms of a preferred embodiment, it is to be understood that the
invention is not limited thereto. To the contrary, it is intended
to cover various modifications and similar arrangements and
procedures, and the scope of the appended claims therefore should
be accorded the broadest interpretation so as to encompass all such
modifications and similar arrangements and procedures.
[0025] In summation of the description above, the present invention
is novel and useful and definite enhances the performance over the
conventional structure and further complies with the patent
application requirements and is submitted to the Patent and
Trademark Office for review and granting of the commensurate patent
rights.
* * * * *