Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2002-02-05
2002-11-26
Cuneo, Kamand (Department: 2827)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C174S255000, C174S256000, C174S260000
Reexamination Certificate
active
06487084
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printed circuit board (PCB), and more particularly, to a printed circuit board comprising an embedded internal functional element.
2. Description of the Prior Art
Since the portable electronic products (such as cellular phone, notebook computer, hand-held camera and personal digital assistant, etc.) are getting more and more popular nowadays, over-current protection apparatuses for avoiding the occurrence of over-current or the over-temperature of the portable electric products are increasingly important.
In the protection apparatuses, a positive temperature coefficient (PTC) over-current protection apparatus is used extensively because of its characteristics of being resettable, sensitive to temperature and stable in reliability. Thus, the PTC over-current protection apparatus has been widely applied to protect batteries, especially second batteries, such as the nickel-hydrogen battery or the lithium battery, etc.
A PTC conductive composition material (PTC material) is utilized as a current sensitive element of the PTC over-current protection apparatus, because the resistance of the PTC material is very sensitive to temperature variation. Because the resistance of the PTC material is very low at its normal temperature, the circuit can operate normally. However, if the over-current or over-temperature of the battery occurs because of improper usage, the resistance of the PTC material will increase immediately for at least ten thousand times (such as 10
4
ohm) so that the PTC material will be at a high-resistance state. Therefore, the over current will be counterchecked and thereby the object of protecting circuit elements of the battery is achieved.
FIG. 1
is a schematic diagram showing connection of a conventional PTC over-current protection apparatus. One terminal of the PTC over-current protection apparatus
12
, mounted on the surface of a printed circuit board
10
, is connected to a power supply
11
and the other terminal is connected to a first integrated circuit
13
. Generally, the normal value of the electrical resistance of the PTC over-current protection apparatus
12
is obtained according to the conventional formula:
R
=
ρ
×
l
A
,
in which R is the resistance in ohms, &rgr; is the resistivity in ohms-cm of the PTC material, l is the length between two electrodes and A is the effective area of the protection apparatus
12
. Since the size of the printed circuit board of the portable electronic product becomes smaller and smaller, the footprint of the PTC over-current protection apparatus
12
mounted on the printed circuit board also needs to be decreased comparatively. According to the above formula, as the normal resistance of the PTC over-current protection apparatus
12
is increased, the power consumption will increase such that the working voltage of the first integrated circuit
13
connected with the protection apparatus will be dropped.
Furthermore, the printed circuit board has the trend of small size and high density at the present day. Therefore, the number of internal layers of the PCB has increased to be even more than 12, especially in small, thin and light products, such as cellular phone, personal digital assistant (PDA) and digital camera, etc. Generally, a main process of processes for manufacturing the multi-layer printed circuit board is a so-called build-up process. The build-up process forms the printed circuit board by stacking a circuit layer and an insulation layer one by one, such that a multi-layer PCB having vias and high density is formed.
FIGS.
2
(
a
) to
2
(
e
) depicts a conventional build-up process. In FIG.
2
(
a
), a substrate
20
is provided, which is composed of a glass fiber and a resin. A first conductive layer
21
, such as a copper foil, is applied to the surface of the substrate
20
. In FIG.
2
(
b
), the first conductive layer
21
is etched by a chemical method for forming an isolating area
22
. In FIG.
2
(
c
), an insulating layer
23
is applied to the surface of the first conductive layer
21
. In FIG.
2
(
d
), the insulating layer
23
is etched by a laser or chemical method for forming a conductive via
24
. In FIG.
2
(
e
), a second conductive layer
25
is applied to the insulating layer
23
by a method of plating or electroless plating. In the above-mentioned plating process, the conductive via
24
will be filled with a conductive material to conduct the first conductive layer with the second conductive layer. Therefore, the conductive layer and the insulating layer can be stacked one by one if the above steps are repeated over and over, and thus a multi-layer printed circuit board is formed. Moreover, any two conductive layers of the printed circuit board can also be connected by a electrically conductive hole. The electrically conductive hole is formed by mechanical drilling and plating the hole, electrolessly plating the hole or filling the hole with a conductive paste so as to connect two conductive layers together.
FIG. 3
depicts a diagram of the electrically conductive hole; wherein a first conductive layer
31
is connected to a second conductive layer
32
and a second terminal point
36
through a first conductive hole
33
. However, if the first conductive layer
31
needs to be connected to a first terminal point
35
without being connected to a second conductive layer
32
, an etched area
37
is formed around a second conductive hole
34
in the second conductive layer
32
, and thus the second conductive hole
34
and the second conductive layer
32
are isolated.
Since the size of the printed circuit board
10
is decreased, the area for mounting the electrical apparatus is limited. Therefore, how to increase the utilization area of the printed circuit board is a critical problem to be tackled with. For this purpose, the present invention discloses a printed circuit board having an embedded internal over-current protection apparatus to increase the utilization area of the PCB and decrease the normal resistance. Moreover, the surface of the PCB can accommodate more devices, since the over-current protection apparatus mounted on the PCB surface is not necessary. On the other hand, an external damage to the surface mount over-current protection apparatus will be avoided.
SUMMARY OF THE INVENTION
A major object of the present invention is to provide a printed circuit board (PCB) with an increased area of an embedded internal functional element for the benefit of decreasing the normal resistance. Thus, the power consumption of this invention is much lower than an over-current protection apparatus being surface mounted on the PCB surface and the dropping of the working voltage will also be significantly reduced.
A second object of the present invention is to make the embedded functional element constituted by one or more than one internal layers of the printed circuit board. Since this embedded functional element design utilizes more effective area of over-current protection apparatus without utilizing any area of PCB surface, the resulted electrical rating of embedded functional element in the printed circuit board such as maximum working current is higher.
A third object of the present invention is to make the functional element to constitute a resistive or sensing element, and thus the number of the apparatuses mounted on the surface of the PCB is decreased and the utilization rate of the PCB is improved.
In order to achieve the above objects and to avoid the disadvantages of the prior art, the present invention discloses a PCB, characterized in that besides the conductive layer and the insulating layer, the PCB further comprises at least one functional element either current-sensitive or temperature-sensitive layer, such as the positive temperature coefficient (PTC) element,negative temperature coefficient (NTC) element, or zero temperature coefficient (ZTC) element. The functional element comprises a functional material, an upper electrode and a lower electrode, and the functional m
Chu Edward Fu-Hua
Ma Yun-Ching
Wang David Shau-Chew
Cuneo Kamand
Norris Jeremy
Polytronics Technology Corporation
Shaw Seyfarth
LandOfFree
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