Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Assembly of plural semiconductive substrates each possessing...
Reexamination Certificate
2001-04-10
2003-05-20
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Assembly of plural semiconductive substrates each possessing...
C438S613000, C257S778000, C257S780000
Reexamination Certificate
active
06566166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a substrate, particularly to a cavity-down plastic ball grid array (CD-PBGA) substrate.
2. Description of the Prior Art
With the sophistication of IC devices, the complexity of semiconductor dies has increased, leading to a greater number of slots for electric signals, plug-switches and conductive lines. This has lead to a variety of high-density substrates for packaging semiconductor dies, including CD-PBGA substrates. CD-PBGA substrates are used for ball grid array packaging, which has a excellent thermal dissipation characteristics. The traditional CD-PBGA substrate has between 300 to 800 ball counts, with an operating power of 5 to 10 watts or higher. The thermal dissipation capabilities of a CD-PBGA substrate can be improved using forced-air convection, such as by adding a cooling fan to the top of the CD-PBGA substrate with attached heat slug.
There are many prior art inventions in the field of cavity-down ball grid arrays (CD-BGA). For example, U.S. Pat. No. 5,027,191 provides a cavity-down padding array substrate for packaging a semiconductor die, and U.S. Pat. No. 5,420,460 provides a thin CD-BGA packaging structure for wire bonding.
Please refer to FIG.
1
and FIG.
2
.
FIG. 1
is a diagram of a traditional CD-PBGA substrate
10
, and
FIG. 2
is a cross-sectional view of the CD-PBGA substrate
10
of FIG.
1
. The CD-PBGA substrate
10
made according to the prior art comprises an organic substrate
12
and a Cu heat spreader
14
. The organic substrate
12
has in its center a squared or rectangular cavity for holding an IC die
18
. When the CD-PBGA
10
is positioned on a printed circuit board (PCB), the Cu heat spreader
14
will be positioned on top away from the printed circuit board so as to facilitate heat radiation.
As shown in FIG.
1
and
FIG. 2
, one side of the organic substrate
12
comprises a plurality of bonding fingers
20
, solder ball pads
22
, and conductive interconnects
23
(
FIG. 1
only shows a portion of the conductive interconnects
23
) for electrically connecting the bonding fingers
20
to the solder ball pads
22
. The organic substrate
12
has a Cu layer (Cu interconnects layer)
24
on its opposite side, and it has a plurality of conductive vias
26
for electrically connecting the bonding fingers
20
, the ball pads
22
, and the conductive interconnects
23
to the Cu layer
24
. A solder mask
28
covers the organic substrate
12
to protect the packaging substrate
10
, to isolate the conductive pads
20
and
22
, and to insulate the conductive interconnects
23
. The surface of each conductive pad
20
,
22
is plated with a layer of nickel
30
and a layer of gold
32
. An adhesive layer
34
is used to bind the organic substrate
12
to the Cu heat spreader
14
. The adhesive layer
34
is usually an epoxy-based prepreg. Additionally, the surface of the Cu heat spreader has a Ni-plated finish
36
for protecting the Cu heat spreader
14
and to prevent oxidation.
After the IC die
18
is fitted, with the help of epoxy, into the cavity
16
of the substrate
10
, the IC die
18
is, by wire bonding, electrically connected to the bonding fingers
20
through a plurality of conductive interconnects
38
. The cavity
16
is then filled to seal in the IC die
18
. A Pb/Sn or Sn solder ball
40
is fixed onto each of the solder ball pads
22
, in order to bond the substrate
10
to the printed circuit board (not shown). Signals from the IC die
18
are transmitted through the conductive interconnects
38
to the bonding fingers
20
of the substrate
10
, and through the conductive interconnects
23
to the solder ball pads
22
(or following a route from the conductive interconnects
23
to the conductive vias
26
, the Cu interconnects layer
24
, the conductive vias
26
, and to the conductive interconnects
23
). Finally, current from the IC die
18
is transmitted to the printed circuit board through the solder balls
40
. Following the same route in reverse, signals are transmitted back to the IC die
18
from the printed circuit board.
The method of manufacturing the substrate
10
according to the prior art is to first separately make the organic substrate
12
and the Cu heat spreader
14
, and then to combine the two. According to the conventional method, the bonding fingers
20
, the solder ball pads
22
, the conductive interconnects
23
, Cu conductive interconnects layer
24
and the conductive vias
26
are made on the organic substrate
12
without the cavity
16
. The solder mask
28
is then coated onto the substrate
12
on the same side as the ball pads
22
and bonding fingers
20
. An etching process is performed to transfer an appropriate pattern to the solder mask
28
.
After the solder mask
28
is made, a tape or film (not shown) is adhered to the other side of the organic substrate
12
(the same side as the Cu interconnects layer
24
) before performing a single-sided Ni/Au plating process (on the same side as the conductive interconnects
23
). The plating process is performed by plating each of the conductive pads
20
and
22
of the organic substrate
12
with a Ni layer
30
that is approximately 5 microns thick, and over which is plated a gold layer
32
that is approximately 0.5 microns thick. Upon the completion of the plating process, the tape or film is removed, and a squared or rectangular cavity
16
is cut into-the center of the organic substrate
12
, followed by a cleaning process.
After cutting out the cavity
16
, the manufacturer performs a single-sided Cu surface pre-treatment. An oxide layer
42
is formed over the Cu layer
24
of the organic substrate
12
in order to increase the surface adhesion of the organic substrate
12
by utilizing the coarse nature of the oxide layer
42
. The oxide layer
42
can comprise black oxide or brown oxide.
When making the organic substrate
12
, the manufacturer can at the same time fix a tape or a dry film (not shown) onto one side of the Cu heat spreader
14
before performing a single-side Ni plating process on the opposite side. After the Ni-plated finish
36
is formed, the tape or dry film is removed from the Cu heat spreader
14
, and another single-side Cu surface pretreatment process is performed, in which an oxide layer
44
is formed on one side (the same side as the Ni-plated finish
36
) of the Cu heat spreader
14
to increase the surface adhesion of the Cu heat spreader. The oxide layer
44
may comprise black oxide or brown oxide.
Please refer to FIG.
3
and FIG.
4
.
FIG. 3
shows the thermal laminating process in making the substrate
10
according to the prior art, and
FIG. 4
is a view of removing a release film
48
and a filler film
46
after completing the thermal laminating process. After the organic substrate
12
and the Cu heat spreader
14
are made as described above, a thermal laminating process is performed to laminate the two pieces.
As shown in
FIG. 3
, a filler film
46
is fixed onto the organic substrate
12
to prevent the sticky adhesive layer
34
from flowing into the cavity
16
during the thermal laminating process. The filler film
46
may comprise polyethylene or silicone rubber. After the completion of the thermal laminating process, the filler film
46
must be removed completely, so before placing the filler film
46
, the manufacturer places a release film
48
over the organic substrate
12
. The release film
48
can be peeled from the organic substrate afterwards so as to help with the removal of the filler film
46
.
Before performing the thermal laminating process, in addition to placing the release film
48
and the filler film
46
, the manufacturer must also cut a cavity
50
in the center of the sticky adhesive layer
34
that corresponds to the cavity
16
to prevent the sticky adhesive layer
34
from remaining in the cavity
16
when the substrate
10
is completed.
After the preparations described above are completed, the filler film
46
, the organic substrate
1
Elms Richard
Hsu Winston
VIA Technologies Inc.
Wilson Christian D.
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