Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2001-10-30
2003-10-28
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C228S248100
Reexamination Certificate
active
06638858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a hole metal-filling method, and more particularly, to a hole filling and electroplating method for a printed circuit board which has been mechanically drilled with holes.
2. Description of the Related Art
In addition to the great demand in functionality, the consumers also require the electronic product to be light, thin, short and small. Therefore, the integration has to be higher and higher with more and more powerful functions. Consequently, the printed circuit board (PCB) to equip the electronic devices is fabricated with more and more layers, for example, from a single layer to 2, 6, 8 or even 10 layers. The electronic devices can thus be formed on the printed circuit board more densely with a smaller occupancy of surface area.
However, as layers of the multi-layer circuit board increase, the fabrication process becomes more complex, and the production time is also lengthened. The subsequent testing process is also increased with more complex steps and longer time.
In
FIG. 1A
, an inner substrate
14
with two layers of circuit
12
is shown. The circuit
12
can be located at two sides of the insulation layer
10
and formed using photolithography and etching process.
In
FIG. 1B
, a surface of the inner circuit
12
is oxidized to obtain a coarse surface, so as to improve the bonding performance between the inner circuit
12
and the insulator. A layer of rubber sheet
16
and a layer of copper foil
18
are located and laminated at two sides of the substrate
14
. The next layer of circuit is then fabricated at two sides of the substrate
14
. However, the fabrication of the next layer of circuit has to be performed after bonding and curing the rubber sheet
16
with the inner circuit
12
. To bond the rubber sheet
16
with the inner circuit
12
, the rubber sheet
16
has to be heated and pressed with a process called thermal press. The rubber sheet
16
can then be hardened and closely adjacent to the inner circuit
12
. The temperature is then reduced, while the press is continuously applied in a cold pressing process.
In
FIG. 1C
, the interconnecting holes and the component holes
20
to install components and to interconnect various layers have to be drilled first. The holes
20
are then plated with copper with a plating through hole (PTH) process to form a copper foil in the holes. An outer circuit layer is then formed using photoresist layer to etch the copper foils
18
,
22
.
Generally speaking, an electroplating process is used to form the copper foil
22
in the hole
20
. To plate a cylindrical shape of copper in the hole
20
, a very long plating time is required. Thus, the cost is high, and the applicability of the hole
20
with a diameter more than 0.2 mm is not desired.
SUMMARY OF THE INVENTION
The invention provides a metal-filling method of a hole. After forming and electroplating a hole in a printed circuit board, this method is performed. In this method, a substrate is provided. A plurality of holes is drilled through the substrate. The substrate is placed on a platform, and a plurality of metal balls is disposed on the substrate. By vibrating the platform, a part of the metal balls roll into the holes. The metal balls not rolling into the holes after vibrating the platform are removed. The substrate is then placed on a press down unit and pressed until the metal balls within the holes are level with the surface of the substrate. An electroplating step is performed on the substrate directly to form a plating layer closely adjacent to the metal balls.
While applying the above method to printed circuit board, as copper is selected as the material of the metal balls, the diameter of the holes in the substrate can be increased. Due to the good electrical and thermal conductivity, the copper metal balls can also used as heating dissipation members such as ball grid array (BGA) package device. In addition, while replacing laser via with mechanical via in the product with high density interconnection (HDI), the fabrication cost is greatly reduced.
The laser used typically includes gas laser, solid laser such as CO
2
laser, yttrium-aluminum-garnet (YAG) laser with a wavelength of 10.6 micron, 1.064 micron and a beam size of 0.1 mm and 0.05 mm, respectively.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 5465898 (1995-11-01), Schulz-Harder et al.
patent: 5921462 (1999-07-01), Gordon
patent: 5941449 (1999-08-01), Le Coz et al.
patent: 6270002 (2001-08-01), Hayashi et al.
patent: 6428328 (2002-08-01), Haba et al.
J. C. Patents
Lattin Christopher
Niebling John F.
Unimicron Taiwan Corp.
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