Metal fusion bonding – Process – Applying or distributing fused filler
Reexamination Certificate
2002-07-08
2004-03-23
Stoner, Kiley (Department: 1725)
Metal fusion bonding
Process
Applying or distributing fused filler
C228S033000, C228S248100, C228S260000, C118S050000, C118S213000, C222S591000, C427S097100
Reexamination Certificate
active
06708873
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for filling holes in a substrate and more particularly, relates to an apparatus and a method for filling holes in electronic substrates that have high aspect ratios of at least 5:1 in a process for forming vias and interconnects.
BACKGROUND OF THE INVENTION
In the electronics packaging industry, there is often a need to fill holes in various substrates for forming vias and interconnects. The hole filling process is affected by a number of processing and material parameters, for instance, the diameter of the via hole, the depth of the hole and the type of the substrate material, etc. Typically, via holes are through holes and are used to electrically connect a top surface and a bottom surface of a substrate, the filler material utilized in forming the vias must be electrically conductive. A number of techniques have been used to perform the via hole filling process. Depending on the type of the substrate, the techniques may include electroplating, electroless plating, solder paste screen printing and conductive paste screen printing.
A fundamental processing problem arises when the depth-to-width ratio, or the aspect ratio grows. The problem gets more complex when the hole diameter is made aggressively small, i.e., 125 &mgr;m or less. For instance, for holes having depth-to-width aspect ratios of 5:1 or larger, it is no longer possible to use a conventional technique such as paste screening to fill the holes. Even the more advanced plating techniques cannot be used when diameters further decrease and aspect ratios further increase.
An attempt to fill via holes that have 17:1 aspect ratio with conductive epoxies by a screen printing method was found ineffective, even when the screening process is conducted from both the top and the bottom side of the substrate. One other attempt to fill a glass substrate that has via holes of 17:1 aspect ratio was carried out by utilizing a conductive material that has extremely low viscosity, i.e., an eutectic solder that has a viscosity of only 2 centipoise in its molten state, approaching that of water. Even at such low viscosity, known techniques for filling the high aspect ratio via holes were found ineffective. For instance, the conventional techniques tried include an injection molded solder technique with only pressure utilized. The injection molded solder technique was not able to fill deep vias holes that have very small diameters, i.e., smaller than 25 &mgr;m.
A second technique of vacuum injection molding was also tried. A graphic illustration of the vacuum injection molding process is shown in FIGS.
1
A~
1
D. The vacuum injection molding process was disclosed in a co-pending application that was assigned to the common assignee of the present invention under Ser. No. 08/518,874. The vacuum injection molding method utilizes a pressure differential formed between either ambient and vacuum or positive pressure and vacuum. The pressure and the vacuum are both supplied on the same surface of a substrate
10
, as shown in FIG.
1
A. The process is carried out by utilizing a shallow vacuum link
12
that allows a continual evacuation of air from via holes
20
that have a large aspect ratio such as 5:1. The vacuum link
12
must be sufficiently shallow such that the surface tension of molten solder prevents cross-leaking during the operation. Such a shallow link
12
effectively choke a significant part of the full pressure differential and thus producing only partial filling of via holes
20
that have high aspect ratios.
As shown in
FIG. 1A
, an injection head
14
which includes spaced apart vacuum slot
16
and injection slot
22
is positioned on top of a mold plate, or substrate
10
in fluid communication with the mold cavities, or via holes
20
contained therein. Relative axial sliding is effected between the injection head
14
and the mold plate
10
for sequentially evacuating gas from the mold cavities
20
using a continuous vacuum and injecting into the evacuated mold cavities
20
a liquid fed from a continuous source (not shown). The sliding of the injection head
14
over the mold plate
10
, as shown in
FIGS. 1B and 1C
, automatically provides self valving for sequentially evacuating and filling the mold cavities
20
from the same side, i.e., the top side
18
of the mold plate
10
. In a preferred embodiment, the vacuum slot
16
and the injection slot
22
are linked together at the mold plate
10
so that surface tension of the liquid restrains flow of the liquid (not shown) from the injection slot
22
to the vacuum slot
16
while allowing gas flow thereinbetween for effecting vacuum in the mold cavities
20
.
As shown in
FIG. 1A
, at the start of the process, i.e., before scanning begins, the mold cavities
20
are empty. As the scanning process begins, as shown in
FIG. 1B
, some cavities
24
are evacuated. As the scanning of the injection head
14
continues, some cavities
26
are filled with the liquid. In the final step of the process, as shown in
FIG. 1D
, the vacuum supply to the vacuum slot
16
is turned off while the scanning of the injection head
14
is completed, i.e., all the cavities
20
,
24
and
26
are filled with liquid.
The vacuum injection molding method illustrated in FIGS.
1
A~
1
D applies a vacuum and a liquid injection on the same surface of the substrate. To enable the operation, a shallow vacuum link must be used to allow the continual evacuation of air from mold cavities that have a larger aspect ratio such as 5:1. The drawback of the process is that the vacuum link must be sufficiently shallow such that the surface tension of molten solder prevents cross-leaking during the operation. The shallow link chokes off a significant part of the full pressure differential and thus only produces partial filling of the mold cavities, or the via holes that have high aspect ratios.
It is therefore an object of the present invention to provide an apparatus for filling a liquid in high aspect ratio holes that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for filling a liquid in high aspect ratio holes in a substrate that applies a vacuum and a liquid injection on the opposite sides of a substrate.
It is a further object of the present invention to provide an apparatus for filling a liquid in high aspect ratio holes in a substrate by utilizing a filler plate and a vacuum plate sandwiching a substrate thereinbetween such that vacuum and liquid injection are applied on the opposite sides of the substrate.
It is another further object of the present invention to provide an apparatus for filling a molten solder in high aspect ratio via holes in an electronic substrate which is effective in filling holes that have aspect ratios of at least 5:1.
It is still another object of the present invention to provide an apparatus for filling a molten solder in high aspect ratio via holes in an electronic substrate wherein a filler plate and a vacuum plate are connected together and are further equipped with a veneer adjustment means such that a relative position of the two plates can be adjusted corresponding to the viscosity of the liquid injected.
It is yet another object of the present invention to provide an apparatus for filling a liquid in high aspect ratio holes in an electronic substrate by pulling vacuum and injecting molten solder simultaneously from and into the same holes when the liquid injected has high viscosity.
It is still another further object of the present invention to provide a method for filling high aspect ratio via holes in an electronic substrate by pulling a vacuum from via holes on a first side of the substrate and injecting liquid on the opposite side of the substrate into the via holes.
It is yet another further object of the present invention to provide a method for forming interconnects in a substrate for a display panel such that a voltage potential can be placed on pixel display elements
Gruber Peter A.
Maurer Frederic
Romankiw Lubomyr Taras
International Business Machines - Corporation
Stoner Kiley
Trepp Robert M.
Tung Randy W.
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