Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-02-18
2001-06-12
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S314000, C430S319000, C438S612000
Reexamination Certificate
active
06245490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of manufacturing the external connections of a circuit board, and to methods of manufacturing a semiconductor device package comprising a circuit board having such external connections. More particularly, the present invention relates to methods of manufacturing a circuit board having metal bumps as its external connections, and to methods of manufacturing a semiconductor device package comprising the same.
2. Description of the Related Art
Semiconductor device packages are progressively becoming faster, smaller, and thinner in order to meet the pressing demands for the miniaturization and multi-functionalization of electronic apparatus. A Ball Grid Array Package (hereinafter, referred to as a ‘BGA package’) has been developed in connection with these trends. The BGA package is a type of surface mount package which uses a printed circuit board (PCB) and solder balls or solder bumps, instead of a lead frame, for electrically connecting the semiconductor chip and the main circuit board. The BGA package has a comparatively large number of the I/O pins, and thus possesses a high mounting density.
As mentioned above, the BGA package has a structure in which the semiconductor chip is attached and electrically connected to the PCB. Also, circuit wiring patterns formed on a surface of the PCB, to which the semiconductor chip is attached, are electrically connected to external connections formed on the other surface of the PCB through a plurality of via holes. Because the external connections are not formed on the surface to which the semiconductor chip is attached, the BGA package can have a mounting area, i.e., an area over which the BGA package is mounted to the main board, that is smaller than that of other conventional plastic packages. In conventional BGA packages, solder bumps are used as the external connections.
FIG. 1
depicts such a conventional BGA package. The BGA package
200
includes a semiconductor chip
130
which is electrically connected to solder bumps
128
. A PCB
110
is positioned between the semiconductor chip
130
and the solder bumps
128
and is used as a means for connecting the semiconductor chip
130
and the solder bumps
128
.
A copper (Cu) pattern layer is formed on upper and lower surfaces of the PCB
110
so as to facilitate the electrical connection of the semiconductor chip
130
to the solder bumps
128
. A plurality of via holes
124
are formed in the PCB
110
in order to interconnect the Cu pattern layers which are deposited on the upper and the lower surfaces of the PCB
110
. In addition, Cu forms the inner walls of the via holes
124
.
The Cu pattern layer on the upper surface of the PCB
110
forms a chip mounting area
132
and circuit patterns
123
. The chip mounting area
132
is the region on which the semiconductor chip
130
will be mounted. The respective circuit patterns
123
are positioned around the chip mounting area
132
. One end of each circuit pattern
123
serves as a wire bonding area
125
which is electrically connected to the semiconductor chip
130
by a bonding wire
134
.
The Cu pattern layer on the lower surface of the PCB
110
consists of a plurality of solder ball pads
126
. The solder ball pads
126
are made of a metal, and solder balls will be attached thereto. The via holes
127
which are formed below the chip mounting area
132
are for transferring the heat generated during the operation of the semiconductor chip
130
to the outside. Hereinafter, these via holes
127
will be referred to as ‘the emission via holes’
127
.
Before electrically connecting the semiconductor chip
130
to the PCB
110
with the bonding wires
134
, the upper and the lower surfaces of the PCB
110
are coated with solder resist
120
. The solder resist
120
is applied over all portions of the upper and lower surfaces except for the chip mounting area
132
, the wire bonding area
125
, and the area of the solder ball pads
126
. After that, the upper surface of the PCB
110
is encapsulated with thermosetting resin to protect the semiconductor chip
130
and the circuit patterns
123
. This encapsulant results in the formation of a package body
136
. The solder balls are attached to the solder ball pads
126
on the lower surface of the PCB
110
to thereby form the solder bumps
128
.
FIG. 2A
depicts a step of a screen printing method in which the PCB is coated with flux by using a metal mask.
FIG. 2B
depicts a step of attaching the solder balls to the flux.
With reference to these figures, a screen printing method for forming the solder bumps
128
will now be described. Generally, after the PCB
110
is turned over so that the lower surface on which the solder ball pads
126
are formed faces upwards, the solder balls
128
are attached to the solder ball pads
126
. More specifically, a metal mask
150
in which holes
154
are formed in a pattern corresponding to that of the solder ball pads
126
is placed on the PCB
110
. Then, flux
140
is supplied onto the metal mask
150
and is forced through the holes
154
using a squeegee
156
. Next, solder supplied to the metal mask
150
forms solder balls which attach to the flux
140
.
The solder bumps
128
are produced by using a reflow soldering process, which is carried out under a temperature of 230° C. or more. In this process, solder balls are attached to the solder ball pads
126
.
After the reflow soldering process is carried out, the residue of the flux
140
which remains around the solder bumps
128
may contaminate the PCB
110
, and disrupt the subsequent manufacturing processes. Therefore, it is necessary to remove the residue of the flux
140
with an organic solvent. Note, the main component of the flux
140
is a rosin.
As the number of the solder ball pads
126
increases, the pitch between the solder ball pads becomes smaller, and it becomes accordingly more difficult to align the solder balls exactly with the solder ball pads
126
using the metal mask
150
. Furthermore, because the solder balls are attached to the solder ball pads
126
by the reflow soldering process, it is difficult to produce solder bumps
128
having a uniform height.
In addition, the organic solvent, which is used for removing the rosin component of the flux
140
, is harmful to the environment. Another problem is that the small pitch between the solder ball pads
126
is oftentimes responsible for failures, such as shorts between adjacent solder balls. In other words, the adjacent solder bumps
128
adhere to each other causing a short between the solder bumps
128
.
Also, among the semiconductor device packages which use the solder bumps as electrical connections, a micro BGA package (hereinafter, referred to as a ‘&mgr;-BGA package’) developed by Tessera Co. (U.S.) has a problem in that the small size and pitch of the via holes of a polyimide tape, which is attached to the solder balls, can cause misalignment of the solder balls. Note also that the ratio of the height of the solder bumps to the thickness of the &mgr;-BGA package is very large, that is, the height of the solder bumps is 300~350 &mgr;m for a &mgr;-BGA package having a thickness of 784~847 &mgr;m.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide methods of manufacturing a printed circuit board having metal bumps as external means of connections and to provide methods of manufacturing a semiconductor device package using the same, in which the aligning of the metal bumps with their underlying conductive pattern is not problematic.
Another object of the present invention is to provide methods of manufacturing a printed circuit board having metal bumps and to provide methods of manufacturing a semiconductor device package using the same, which do not require the use of flux and are therefore safer for the environment.
Still another object of the present invention is to provide methods of manufacturing a printed circuit board and to provide methods of manufacturing a semicond
Chung Myung Kee
Hong In Pyo
Kim Yong
Park Gi Bum
Yoon Jin Hyun
Barreca Nicole
Huff Mark F.
Jones Volentine, L.L.C.
Samsung Electronics Co,. Ltd.
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