Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
1998-04-28
2001-08-21
Smith, Matthew (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S780000, C257S738000
Reexamination Certificate
active
06278180
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a ball-grid-array-type semiconductor device and its fabrication method and an electronic apparatus, particularly to an art effectively applied to an art for improving the reliability of external terminal connection of a ball-grid-array-type semiconductor device secured to a mounting board.
Because functions of electronic units have been improved, it is requested that a semiconductor device such as an IC (integrated circuit arrangement) or an LSI (large-scale integrated circuit arrangement) is provided with more external terminals (change to multiple pin). A QFP (Quad Flat Package) in which a lead is protruded from four sides of a rectangular sealing body (package) has corresponded to the change to multiple pin by decreasing the intervals between its external terminals to, for example, 0.4 mm and then 0.3 mm in order.
Moreover, as a package structure capable of decreasing the pitch between external terminals, a pin-grid-array-type semiconductor device and a ball-grid-array-type semiconductor device (hereafter also referred to as BGA-type semiconductor device) are developed.
In the case of a BGA-type semiconductor device, an external terminal serves as a ball electrode. The ball electrode is constituted with a metallic ball which does not deform or a solder ball which fuses and deforms.
The ball electrode is soldered to a land of a mounting board. Moreover, the mounting height of a semiconductor device is determined by the diameter of the solder ball (low-fusion-point solder ball which fuses at the time of reflow or high-fusion-point solder ball which does not fuse at the time of reflow) or that of the metallic ball.
A BGA-type semiconductor device is described in “Electron Materials”, the April 1997 issue issued on Apr. 1, 1997, pp. 103-105, edited by KOGYOCHOSAKAI (transliterated).
Moreover, the structure of an external terminal comprising a solder ball or the like and the external-terminal structure when mounted are disclosed in published patent journal No. “5-508736” and the official gazettes of Japanese Patent No. 2500109 and Japanese Patent Application Laid-Open No. 8-31974.
A BGA-type semiconductor device has a structure in which bumpy external terminals (external electrodes) are arranged on the back of a wiring board (package substrate) like an array.
As one of BGA semiconductor devices, a structure is known in which solder balls or metallic balls are arranged like an array as external terminals on the back of a package substrate made of low-temperature co-fired ceramic (LTCC)
The present applicant also develops a BGA-type semiconductor device using an LTCC plate.
FIG. 12
is a locally-cut-out sectional view of a BGA-type semiconductor device developed by the present applicant. Moreover,
FIG. 13
is an enlarged sectional view showing a ball-electrode support portion of the mounting structure of a BGA-type semiconductor device developed by the present applicant.
As shown in
FIG. 12
, a BGA-type semiconductor device
1
has a rectangular flat package substrate
2
comprising a multilayer wiring structure in which the top (principal plane) center is recessed in two stages. The package substrate
2
is constituted with a low-temperature co-fired ceramic multilayer substrate.
A semiconductor chip
5
is secured to the bottom of a deep recess
3
of the package substrate
2
through a joining material
4
. Moreover, wiring
7
is provided for the bottom of a shallow recess
6
. Furthermore, the front end portion extending toward the deep recess
3
of the wiring
7
is connected with a not-illustrated electrode of the semiconductor chip
5
by a conductive wire
9
.
Furthermore, an insulating sealing resin
10
is injected into the recesses
3
and
6
and cured so as to cover the semiconductor chip
5
and the wire
9
.
Furthermore, external terminals (external electrodes)
11
respectively constituted with a ball electrode are arranged like an array on the back (bottom) of the package substrate
2
. The external terminal
11
comprises an electrode
15
constituted with wiring formed at the bottom of the package substrate
2
and a metallic ball
17
secured onto the electrode
15
through a pedestal layer
16
made of low-fusion-point solder. The metallic ball
17
is made of, for example, oxygen-free copper.
Furthermore, a plated film
21
is formed on the surface of the electrode
15
in order to improve the adhesiveness of solder (see FIG.
13
). In the case of the plated film
21
, the lower layer is made of a nickel layer
22
and the upper layer is formed with a gold layer
23
.
Furthermore, the wiring
7
and joining material
4
to which the wire
9
of the package substrate
2
is connected are electrically connected to the bottom electrode
15
through a via
19
extending in the longitudinal direction and an internal wiring
20
extending in the horizontal direction in the package substrate
2
.
Furthermore, because the pedestal layer
16
is fused once when the metallic ball
17
is set, layer
16
is widely wet along a part of the spherical surface of the metallic ball
17
and the circumferential surface of the layer
16
forms a curved surface between the metallic ball
17
and the electrode
15
.
This type of the BGA-type semiconductor device
1
is built in a mounting board of an electronic apparatus.
A printed wiring board (PWB: FR-4) is generally used as a mounting board to be built in an electronic apparatus.
A BGA-type semiconductor device is mounted on paste solder printed by a metal mask by positioning the BGA-type semiconductor device so that external terminals of the BGA-type semiconductor device overlap, for example, lands on the surface of a mounting board, and then reflowing low-fusion-point solder previously provided for the surface of the land (ultimate temperature of 240° C., 180° C. for 40 sec), and securing the external terminals to the lands respectively. The solder on the land surface uses eutectic solder. In this case, because the top and the bottom of the metallic ball
17
are made of low-fusion-point solder (pedestal layer
16
and solder layer
33
) as shown in
FIG. 13
, the ball
17
automatically moves to a stable position due to the surface tension of the solder and securely electrically connects a land
31
of a mounting board
30
with the electrode
15
.
Moreover, the surface of the package substrate
2
is provided with a glass layer
12
. The electrode is formed with a conductor layer
13
exposed from the glass layer
12
. Furthermore, the surface of the mounting board
30
is also provided with an insulating film
32
. The land
31
is formed at a portion exposed from the insulating film
32
.
According to the method for mounting a BGA-type semiconductor device, the above reflow is performed at a temperature lower than the fusion temperature of high-fusion-point solder and higher than the fusion temperature of low-fusion-point solder. Therefore, the metallic ball
17
made of high-fusion-point solder does not fuse and the BGA-type semiconductor device
1
is kept at a predetermined height by the metallic ball
17
. Thus, it is possible to prevent an electrode short circuit from occurring due to a solder bridge between lands.
Moreover, the present inventor finds in a reliability test (temperature cycle test) of a mounted BGA-type semiconductor device that the joint between the land
31
and the electrode
15
may deform so as to inversely tilt at the both ends of the package substrate
2
or the portion of the package substrate
2
for supporting the external terminal
11
may be cracked. Moreover, it is found that extreme one of these phenomena causes electrode disconnection.
FIG. 14
is a schematic view of a package substrate showing a state of the joint between a BGA-type semiconductor device developed by the present applicant and a mounting board after mounting the semiconductor device on the mounting board and performing a heat cycle test, which is obtained by tracing a microphotograph.
The package substrate of the BGA-type semiconductor device used for th
Aoki Makoto
Ikeda Satoshi
Mizushima Kiyoshi
Tanagi Noriyuki
Mattingly Stanger & Malur, P.C.
Nikko Company
Smith Matthew
Yevsikov Victor
LandOfFree
Ball-grid-array-type semiconductor device and its... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ball-grid-array-type semiconductor device and its..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ball-grid-array-type semiconductor device and its... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2447824