Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-05-21
2001-12-04
Picard, Leo P. (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S710000, C361S722000, C257S719000, C165S080300, C174S016300
Reexamination Certificate
active
06327146
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to an apparatus and method for a power device assembly, and more particularly, to an apparatus and method for integrating power device assembly into a SMD (Surface Mounted) assembly line.
2. Description of Related Art
High power devices in a chip, such as transistors, have high heat dissipation. To cool down the high power devices effectively, a low thermal resistance from the device to the outside is required. To make a low thermal resistance, manufacturers often use a metallic flange at the bottom of a high power device. The metallic flange attaches the power device to a mechanical member, such as a heat sink. The heat in the power device can be easily dissipated to the heat sink through the metallic flange.
In a chip assembly line, to address the heat dissipation problem, a power device with a flange is usually attached to a printed circuit board through a hole in the printed circuit board with two screws. The power device connects to the printed circuit board at its electric leads coming to the device and going out of the device. The metallic flange itself is to be attached to the mechanical member under the printed circuit board.
FIGS. 1 and 2
illustrate a traditional attaching method between the metallic flange and the mechanical member. In
FIGS. 1 and 2
, a printed circuit board
100
has a hole
102
to receive an active high power device
104
. The device
104
has two electric leads
106
,
108
. The two leads
106
,
108
are soldered to conductive strips
110
,
112
, respectively on the printed circuit board. The device
104
includes a device portion
114
and a flange portion
116
. The flange portion
116
is attached to the bottom of the device portion
114
. Screws
118
,
120
are used to mount the flange portion
116
of the device
104
onto a mechanical member
122
. In
FIG. 2
, a cover
124
is used to enclose the assembled printed circuit board
100
between the cover and the mechanical member
122
. The heat generated in the device
104
is dissipated to the mechanical member
122
via the flange portion
116
of the device
104
. To ensure a low thermal resistance between the device
104
and the mechanical member
122
, the screws
118
,
120
are used to fixedly attach the flange portion
106
to the mechanical member
122
.
Accordingly, a traditional method of assembling electrical components including the above active high power device on the printed circuit board requires at least the following phases in the assembly line:
1. SMD (Surface Mounted) components are assembled by a pick and place machine and mounted on the printed circuit board;
2. SMD components are soldered in a reflow oven;
3. The printed circuit board is attached to the mechanical member with a few screws (other than the screws
118
,
120
) to fix the printed circuit board in place;
4. The active power device with the flange portion is placed in the hole of the printed circuit board;
5. The screws (
118
,
120
) are assembled and tightened to fix the flange portion of the device to the mechanical member;
6. The electric leads of the device are soldered by hand; and
7. The cover is attached onto the top of the printed circuit board by a few screws (other than the screws
118
,
120
).
The traditional method has at least the following disadvantages:
Additional phases (e.g. the above phases
3
-
6
) are required in comparison to the phases used in a normal SMD (Surface Mounted) reflow process. Thus, the assembly makes the manufacturing process slow and expensive.
Hand soldering is required. The amount of soldering materials, e.g. tin, has an effect on an RF performance of the device. This effect would cause a process variation and a degraded yield.
Accordingly, it can be seen that there is a need for an apparatus and method for integrating the power device assembly into a SMD (Surface Mounted) assembly line. There is also a need for such an apparatus and method still resolving the heat problem in an active high power device.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is directed to an apparatus and method for a power device assembly, and more particularly, to an apparatus and method for integrating power device assembly into a SMD (Surface Mounted) assembly line.
The present invention provides an automatic pick-and-place and solder assembly with a heat dissipation mechanism. The assembly comprises electrical components including a power device, a circuit board on which the electrical components including the power device are assembled and the power device being assembled with the other electrical components in a same pick-and-place and solder process.
Other embodiments of a system in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the power device has a device portion and a flange portion integral to the device portion. The circuit board includes a hole for receiving the power device. The device portion of the power device is disposed in the hole, the flange portion projects from the hole.
Another aspect of the present invention is that the device portion is disposed below the flange.
Another aspect of the present invention is that a cover is attached onto the top of the flange portion and opposite from the device portion of the power device. The flange portion is thermally connected to the cover, and the flange portion dissipates the heat in the power device to the cover.
Another aspect of the present invention is that the cover is directly connected to the flange portion. Alternatively, an elastic member is disposed between the cover and the flange portion of the power device. The elastic member is made of a thermally conductive material such that the heat is dissipated from the flange portion to the cover via the elastic member.
And yet another aspect of the present invention is that the active power device includes electric leads (signal leads) which are soldered onto the circuit board. The flange portion is soldered (SMD) to metal ground on top of the circuit board. The flange can be connected by electrically conductive material to the cover to improve thermal conductivity and to minimize tolerance problems between the cover and the flange.
The present invention also provides a method of automatically pick-and-place assembling electrical components including a power device on a circuit board. The method comprises picking and placing the electrical components including the power device on the circuit board in a same pick and place process; soldering the electrical components including the power device on the circuit board in a same solder process; and covering the circuit board assembled with the electrical components including the power device, heat in the power device being dissipated to a cover.
The present invention allows the automatic assembly and soldering of high power devices, such as transistors, on a printed circuit board along with the other electrical components. Accordingly, a separate assembly or additional phases for solving heat dissipation of a power device is not required. All electrical components can be assembled in a same pick and place process and in a same solder process.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.
REFERENCES:
patent: 4517585 (1985-05-01), Ridout et al.
patent: 4715115 (1987-12-01), King et al.
patent: 5838
Altera Law Group LLC
Datskovsky Michael
Nokia Telecommunications OY
Picard Leo P.
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