Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
2000-06-07
2002-11-26
Picardat, Kevin M. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
C257S712000, C257S796000, C438S108000, C438S122000, C438S124000
Reexamination Certificate
active
06486562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit device having a structure in which a flip chip and an interposer substrate are molded and a method of manufacturing the same.
2. Description of the Related Art
Conventional circuit devices such as an IC (integrated circuit) have been manufactured in the form of separate chip components for use in a variety of electronic instruments. In such a circuit device, a multiplicity of lead terminals are provided about a flip chip of a semiconductor circuit which has a plurality of connecting pads. These lead terminals and the connecting pads are connected by bonding wires, and the flip chip and inward portions of the lead terminals are molded with a resin material. In conventional circuit device having the above structure, the lead terminals project outwardly from the edge of the resin material. Therefore, when the circuit device is mounted on a printed circuit board (PCB) so that the lead terminals are connected to printed patterns, data transmission between a semiconductor circuit of the circuit device and the printed circuit board can be carried out.
However, since the circuit devices are now made smaller in the size and higher in the integration so that the number and density of lead terminals are increased, it becomes difficult for a user to precisely connect the lead terminals to the printed patterns of the printed circuit board. Additionally, the lead terminals are too narrow to have an improper degree of physical strength and may be often damaged or injured when the circuit device is handled.
For solving the foregoing problems, a BGA (ball grid array) package has been developed for protecting the circuit device. In such a BGA package, connecting leads are provided as spherical solder bumps which are arrayed in two dimensions over the lower surface of the device. Therefore, the density of the lead terminals is decreased to avoid damage to the lead terminals.
An example of the conventional circuit device having such a BGA structure will be described with reference to
FIGS. 1 and 2
.
FIG. 1
is a schematic cross sectional view of the internal structure of a BGA package in the circuit device.
FIG. 2
is a flowchart schematically showing an example of the conventional method of manufacturing the BGA package. For simplification of the description, the upward and downward directions in the drawings shall represent the upward and downward directions on the circuit device.
As shown in
FIG. 1
, the BGA package
1
includes a flip chip
2
in which a semiconductor circuit is integrated in a high density. The flip chip
2
is mounted above the upper surface of an interposer substrate
3
. The flip chip
2
has a multiplicity of connecting pads
4
provided on the lower surface thereof. Also, the interposer substrate
3
has a multiplicity of connecting pads
5
and
6
provided on the upper and lower surfaces thereof. More specifically, an array of the connecting pads
5
are mounted in a higher density on a central region of the upper surface of the interposer substrate
3
at the positions corresponding to the connecting pads
4
of the flip chip
2
, while an array of the connecting pads
6
are mounted in lower density on substantially the entire lower surface of the interposer substrate
3
. The interposer substrate
3
has a multi-layer structure in which printed wire patterns and through holes provided on its both surfaces and in the inside. The connecting pads
5
on the upper surface are connected to the connecting pads
6
on the lower surface by the printed wire patterns and the through holes.
The connecting pads
5
and
6
are coupled to solder bumps
7
and
8
. By the solder bumps
7
, the connecting pads
5
on the upper surface of the interposer substrate
3
are mechanically and electrically connected to the connecting pads
4
on the lower surface of the flip chip
2
. The space between the solder bumps
7
is filled with an under-fill resin
9
of epoxy resin which enhances the mechanical coupling between the lower surface of the flip chip
2
and the upper surface of the interposer substrate
3
.
The BGA package
1
of the example has side wall metal stiffeners
10
which are coupled to on the upper surface of the interposer substrate
3
in a peripheral portion of the flip chip
2
. In addition, a top cover or metal heat spreader
11
is mounted over and joined to the upper surfaces of the stiffeners
10
and the flip chip
2
by resign and metal paste
12
, respectively.
The flip chip
2
in the BGA package
1
of the conventional circuit device includes a high-density semiconductor circuit with the connecting pads
4
arrayed in the higher density. Each of the connecting pads
4
arrayed in the higher density on the lower surface of the flip chip
2
is connected by the solder bump
7
to corresponding one of the connecting pads
5
arrayed on the upper surface of the interposer substrate
3
. The connecting pads
5
are in turn connected to their corresponding connecting pads
6
arrayed in a lower density on the lower surface of the interposer substrate
3
. The connecting pads
6
arrayed in the lower density on the lower surface of the interposer substrate
3
in the BGA package
1
are preliminarily provided at their surfaces with solder bumps
8
, respectively. This allows the circuit device to be surface-mounted to a circuit board (not shown) of an electronic instrument with ease on the user side, preventing its connecting leads from being physically injured and protecting the BGA package
1
.
A conventional method of manufacturing the example of the BGA package will be described in brief. The method starts with preparing relevant components of the BGA package
1
including the flip chip
1
, the interposer substrate
3
, the stiffeners
10
, and the heat spreader
11
.
Next, the stiffeners
10
are bonded to the upper surface of the interposer substrate
3
in the peripheral portion and the flip chip
2
is mounted by the solder bumps
7
to the upper surface of the interposer substrate
3
in the central region. After flux is rinsed out, a resultant assembly is dried and subjected to O
2
plasma process. The space between the flip chip
2
and the interposer substrate
3
is filled with epoxy resin. The epoxy resin is hardened to produce the under-fill resin
9
.
Next, the upper surface of the flip chip
2
is coated by metal paste
12
while the upper surfaces of the stiffeners
10
are coated with an adhesive such as epoxy resin. Then, the heat spreader
11
is bonded to the flip chip
2
and the stiffeners
10
. Finally, the connecting pads
6
on the lower surface of the interposer substrate
3
are joined with the solder bumps
8
. Thus, the BGA package
1
is completed.
The BGA package
1
manufactured in the above manner has as connecting terminals, the solder bumps
8
arrayed in the lower density in two dimensions on the lower surface thereof. Accordingly, the BGA package
1
can easily be surface-mounted to a printed circuit board on the user side while its connecting terminals are hardly injured.
However, as described above, the under-fill resin
9
filled for enhancing the mechanical bonding strength between the flip chip
2
and the interposer substrate
3
during the fabrication of the BGA package
1
. For this filling, a considerable length of time is required for the epoxy resin of a high viscosity to infiltrate into the space by its capillary effect. At this time, the contact area of the under-fill resin
9
with the flip chip
2
and the interposer substrate
3
may not be enough large to increase the coupling strength.
Also, in the above BGA package
1
, the interposer substrate
3
and the stiffeners
10
are separately manufactured, and then coupled to each other by the epoxy resin. Then, the heat spreader
11
is coupled to the stiffeners
10
by the epoxy resin. As a result, both the number of manufacturing steps and the number of components are increased, resulting in low productivity. Moreover, the interposer substrate
3
, the stif
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