Underfill process for flip-chip device

Details Underfill process for flip-chip device Underfill process for flip-chip device

2001-12-21

2004-03-09

Lee, Eddie (Department: 2811)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S108000, C438S118000, C438S127000

Reexamination Certificate

active

06703299

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to microelectronic device packaging. More particularly, the present invention relates to underfill packaging of a flip-chip package. In particular, the present invention relates to a vacuum-assisted underfill process.
2. Description of Related Art
As the process of miniaturization progresses, chip packaging is also required to be miniaturized. This requirement has resulted in chip-scale packaging, wherein the ultimate goal is to have the chip and the chip package be virtually the same size.
A chip package usually includes a mounting substrate and a semiconductor chip or die that is located on or in the mounting substrate. One class of chip packaging includes semiconductor chips that are produced with C4 (controlled collapse chip connect) solder connections, on an active surface thereof, for purposes of electrically contacting the integrated circuit on the active surface of the chip to contact pads on the mounting substrate. The term active surface of a semiconductor chip or die, as used herein, means the surface of the chip or die which carries integrated circuitry. The term back surface, as used herein, means a side of the semiconductor chip or die that is opposite and parallel planar with the active surface.
During chip packaging, an epoxy is introduced under capillary action into a space between the die and the mounting substrate and is cured thereafter. The epoxy acts to bond the die to the mounting substrate and to protect the C4 solder connections during the temperature cycling it will experience during the product's lifetime.
As depicted in FIG.
1
A and
FIG. 1B
, a chip package
10
includes a die
12
, a mounting substrate
14
, an electrical connection
16
such as a C4 bump, and an underfill material
18
that has been inserted between the die
12
and the mounting substrate
14
by capillary action.
FIG. 1A
depicts a nonuniform profile
20
and
21
of the underfill material
18
including a fillet portion
22
and
23
, and an interstitial portion
24
that is sandwiched between the die
12
and the mounting substrate
14
. It is noted in
FIG. 1B
that there is a tongue
25
of epoxy underfill material
18
on one side thereof. Accordingly, the fillet portion
22
and
23
that is depicted at profiles
20
and
21
in
FIG. 1A
exhibits an asymmetrical footprint upon the mounting substrate
14
as depicted in FIG.
1
B. Although this tongue
25
of epoxy underfill material
18
may be of no consequence in some prior art embodiments, the pressure to miniaturize and to get even tighter bump pitch and chip-to-package gap height causes the presence of the tongue
25
to be undesirable.
One possible solution that is used in production is depicted in FIG.
2
A and FIG.
2
B. Processing is accomplished by directing a mold press
26
against a die
12
and a mounting substrate
14
. Between the mold press
26
and the die
12
and mounting substrate
14
, an adhesion-resistant film
28
is placed that is stretched and held while an underfill material feed tube
30
and a vent or vacuum tube
32
are used to flow underfill material
18
between die
12
and mounting substrate
14
. After the underfill material
18
has been properly flowed therebetween to form uniform fillet portions
22
and the interstitial portion
24
, the adhesion resistant film
28
and the mold press
26
are removed as depicted in FIG.
2
B. As the adhesion resistant film
28
and the mold press
26
are removed, some wicking action between the adhesion resistant film
28
and the underfill material
18
forms an uneven surface
34
(depicted in an arbitrary shape and surface roughness) that often must be smoothed after curing. Additionally, and more serious to process yield, some wick spillage
36
forms on the back surface
38
of die
12
that must be removed.


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