Method for manufacturing semiconductor devices

Details Method for manufacturing semiconductor devices Method for manufacturing semiconductor devices

2000-10-03

2004-04-20

Coleman, W. David (Department: 2823)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S613000

Reexamination Certificate

active

06723627

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for manufacturing semiconductor devices and, more particularly, to the method for manufacturing semiconductor devices by packaging a semiconductor chip onto a wiring board by use of a flip-chip approach.
2. Description of the Related Art
To manufacture a semiconductor device represented by an LSI (Large Scale Integration) such as a microprocessor, a memory, or a like, it is necessary to package onto a wiring board a semiconductor chip in which desired circuits are incorporated. To thus package the semiconductor chip, there have been known the following two approaches conventionally.
One approach is a face-up approach, whereby the semiconductor chip is packaged onto a wiring board with its right face facing upward on which pads are formed electrodes. According to this face-up approach, pad electrodes of the semiconductor chip are bonded with a wire to their corresponding wiring portions on the wiring board, thus being connected to an outside of the semiconductor chip. An other approach is a face-down approach, whereby the semiconductor chip is packaged onto the wiring board with its right face facing downward on which its pad electrodes are formed, an outgrowth of which approach is known as a flip-chip approach using ball-like solder electrodes (solder bumps) for connection. According to this approach, the ball-like solder electrode is formed at each pad of the semiconductor chip and connected to its corresponding wiring portion on the wiring board, thus being connected to the outside of the semiconductor chip.
As can be appreciated from comparison between the above-mentioned two approaches of packaging, the flip-chip approach eliminates a process of wire bonding and, moreover, is advantageously capable of connecting a number of ball-like solder electrodes to the wiring board simultaneously, thus tending to be employed preferably in manufacturing of LSIs having an ever increasing number of pins with increasing integration densities and functions required.
The following will describe the above-mentioned method of manufacturing semiconductor devices with reference to
FIGS. 7A
,
7
B,
7
C,
8
A,
8
B,
9
A and
9
B.
First, as shown in
FIG. 7A
, a semiconductor chip
51
is prepared in which a number of ball-like solder electrodes
52
made of high-melting-point solder are connected onto a right face of the semiconductor chip
51
. Next, as shown in
FIG. 7B
, flux
53
is coated, to improve solderability, to the right face of the semiconductor chip
51
on which the ball-like solder electrodes
52
are formed. This flux
53
coating is performed by immersing that right face of the semiconductor chip
51
in for example a flux tub filled with flux
53
. Next, as shown in
FIG. 7C
, a wiring board
55
is prepared which includes a multi-layer wiring board and a number of eutectic solder bumps
54
connected thereto, so that on this wiring board
55
is mounted the semiconductor chip
51
in such a manner that its ball-like solder electrodes
52
may be aligned with corresponding eutectic solder bumps
54
and then, as shown in
FIG. 8A
, the eutectic solder bumps
54
are melted, thus packaging the semiconductor chip
51
to the wiring board
55
(primary packaging). This semiconductor-chip packaging process is performed by moving the wiring board
55
mounted with the semiconductor chip
51
as mentioned above, into a solder reflow furnace.
Next, to remove residual flux remaining on the right face of the semiconductor chip
51
or that of the wiring board
55
, it is washed to remove the flux. This flux removal by washing has been conventionally performed specifically by immersing the wiring board
55
as mounted with the semiconductor chip
51
thereon into a washing tub and by applying supersonic waves to a washing solution. Next, as shown in
FIG. 8B
, a resin is injected to an under-fill portion
56
sandwiched between the semiconductor chip
51
and the wiring board
55
, which is followed by a cure process to harden the resin, thus forming an under-fill resin
57
. By the above steps, a main portion of the semiconductor device is manufactured.
Next, as shown in
FIG. 9A
, a radiation plate
58
is attached to a back face of the semiconductor chip
51
and then, as shown in
FIG. 9B
, ball-like solder electrodes
59
for use in secondary packaging are connected onto a back face of the wiring board
55
, thus completing the semiconductor device.
The conventional method for manufacturing semiconductor devices, however, has a problem in that a process of flux removal by washing performed after a semiconductor chip
51
is mounted onto a wiring board
55
is not capable of completely removing the flux, thus leaving residual flux.
That is, as mentioned above, even when the wiring board
55
mounted with the semiconductor chip
51
thereon is immersed into the washing tub and washed therein, the flux cannot completely be removed, to leave part of its organic film on the right face of the semiconductor chip
51
or that of the wiring board
55
, thus generating flux residue. This may be because a distance between the ball-like solder electrodes
52
of the semiconductor chip
51
is extremely small and, at a same time, distance between the semiconductor chip
51
and the wiring board
55
is also small, thus suppressing full exertion of stirring effects by the supersonic wave in the washing solution. Such flux residue may be formed increasingly, taking into account that the distance between the ball-like solder electrodes
52
will be smaller with an ever increasing number of pins of a future LSI.
Although such a conventional method has been worked out that employs, instead of the supersonic-wave approach, a shower approach for spraying a washing solution to the under-fill portion
56
to wash off the flux, this shower approach cannot avoid the above-mentioned disadvantage either because it also finds it difficult to permit the washing solution to go sufficiently around an extremely small area between the ball-like solder electrodes
52
as well as narrow under-fill portion
56
sandwiched between the semiconductor chip
51
and the wiring board
55
.
As mentioned above, if the flux residue is generated, the following process of injecting a resin to the under-fill portion
56
suffers from a poor flowability of the resin. That is, the flowability of the resin degrades because flow of the resin is inhibited by action of the organic film of the flux left on the right face of the semiconductor chip
51
or that of the wiring board
55
. Therefore, the resin cannot completely be injected to the under-fill portion
56
, thus always giving rise to a void in the under-fill resin
57
when it is being injected. The void thus generated in the under-fill resin
57
may contribute to a poor continuity between the semiconductor chip
51
and the ball-like solder electrodes
52
when a completed semiconductor device is packaged onto a mother board of an electronic apparatus (secondary packaging).
As shown in
FIG. 10A
, a void
60
, if generated in the under-fill resin
57
when the resin is injected, may expand over melted ball-like solder electrodes
52
, as shown in
FIG. 10B
, because of heat treatment conducted when the semiconductor device is secondary-packaged to the mother board, to deform mutually adjacent ball-like solder electrodes
52
, thus resulting in short-circuiting therebetween.
Also, poor flowability, due to occurrence of the flux residue, of the resin during a process of injecting the resin to the under-fill portion
56
brings about longer time required for resin injection, thus affecting manufacturing costs.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide such a method for manufacturing a semiconductor device that improves flowability of a resin when it is injected to an under-fill portion, thus preventing a void from occurring in an under-fill resin during a resin injection process and also shortening a time required for that process.
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