Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
2000-03-28
2001-09-18
Hoang, Tu Ba (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S553000, C228S110100
Reexamination Certificate
active
06291804
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The invention relates to a joined structure of a ceramic heater and an electrode terminal, and a joining method therefor.
With higher speed and higher pin counts of semiconductor devices, semiconductor implementation technology providing narrower pitch and higher accuracy has been becoming more and more important.
In particular, the flip chip bonding (FCB) technique shown in
FIG. 7
(
a
) has been used for the COG in liquid crystal panel package and MCM implementation in computers and portable telephones. In this technique, a Si chip
50
of a semiconductor device and an electrode
62
on a board
60
are directly bonded at a bonding terminal (bump)
52
of solder and Au solder by means of a thermocompression technique.
This flip chip bonding (FCB) technique provides more compact, smaller and faster devices than the wire bonding (WC) and tape carrier (TC) techniques in which conventional lead wires
54
(
FIG. 7
b
),
56
(
FIG. 7
c
) are used for bonding. Therefore, it is expected that the flip chip bonding technique will be mainstream instead of the wire bonding technique (WC) in the future.
FIG. 6
illustrates an example of apparatuses used for flip chip bonding.
When flip chip bonding is performed, a tool head
20
of the size corresponding to the Si chip
50
is selected and fixed to a heater
1
by vacuum absorption. Next, the Si chip
50
is attached to the tool head
20
, also by vacuum absorption.
Therein, the heater
1
is secured to a jacket
30
for forced-cooling of the Si chip
50
by screws
11
.
Then, a board
60
, on which an electrode
62
to be bonded to the Si chip
50
is disposed, is secured to a board stage
40
by vacuum absorption.
Then, the tool head
20
is lowered in the direction perpendicular to the board stage
40
, and positioned until the bonding terminal
52
on the Si chip
50
is brought into contact with the electrode
62
on the board
60
. Thereafter, the predetermined load (about maximum 50 kgf) is applied to the tool head
20
and at the same time the Si chip
50
is rapidly heated to a predetermined temperature (from 50° C. to approximately 450-500° C. about 5 seconds) which is then kept for a given time (about 3 to 5 sec) . Thus, the bonding terminal (bump)
52
on the Si chip
50
and the electrode
62
on the board
60
are thermo-compressed to each other.
And then, the power of the heater
1
is switched off without delay, and forced cooling (water-cooled or air-cooled) of the jacket
30
rapidly lowers the temperature of the Si chip
50
placed on the tool head
20
(from 450-500° C. to100° C. about 20 sec). Thereby, the bonding terminal (bump)
52
on the Si chip
50
and the electrode
62
on the board
60
are bonded together. Thus, the flip chip bonding (FCB) is completed.
In this case, in order to prevent the bonding terminal (bump)
52
on the Si chip
50
from being spread and at the same time to reduce thermal damage to the Si chip
50
, rapid temperature rise and drop (temperature rise: less than or equal to 5 sec., temperature drop: less than or equal to 20 sec.) are essential for ensuring flip chip bonding (FCB).
For meeting the conditions described above, recent bonding heaters
1
mainly used are made of ceramics such as aluminum nitride, silicon carbide, and silicon nitride which are excellent in the characteristics of thermal conductivity, heating uniformity, heat dissipation ability, and thermal shock resistance.
So, it is required in the method for joining an electrode terminal to the heater
1
described above that the joint portion is vacuum-tight such that a heating element embedded in the heater may be protected from high temperature air, in addition to high electric conductivity and having enough joining strength.
To this end, when a joining metal of the electrode terminal is joined to the heater, it is necessary to join the heating element and the ceramic base material surrounding it at the same time. Therefore, conventionally, active metal solder has been used for joining them.
However, as shown in
FIG. 3
, if the joining metal of a ceramic base material
2
and an electrode terminal
80
are joined directly to each other by a metal solder
90
, active metals in the metal solder
90
react with the joining metal of the electrode terminal
80
. So, this reaction causes a deficiency of active metals which can react with ceramic base material
2
, and so results in poor wettability between the ceramic base materia l
2
and the metal solder
90
. Consequently, there have been problems of a remarkable reduction in the joining strength between them and the short life of the heater.
In particular, these problems are outstanding in electrode terminals made of metals such as kovar and SUS, which include as main ingredients one or more kinds of the groups consisting of Fe, Ni, Co.
The present invention has been performed, considering such problems of the conventional joining technology. An object of the invention is to provide a joined structure and a joining method therefor which allow high reliability of the joining strength between a heater and an electrode terminal and also the longer life of the heater.
SUMMARY OF THE INVENTION
More specifically, the invention provides a joined structure comprising a ceramic heater and an electrode terminal, the ceramic heater comprising a heating element and a ceramic base material in which the heating element is embedded; wherein a metallized layer is made of an active metal solder on the surface of the ceramic base material to which the electrode terminal is joined; and a metal solder is interposed between said metallized layer and said electrode terminal to join the metallized layer and the electrode terminal.
Further, the invention provides a method for joining a ceramic heater comprising a ceramic base material in which a heating element is embedded and an electrode terminal, the method comprising; forming a metallized layer made of an active metal solder on the surface of the ceramic base material to which the electrode terminal is joined, placing a metal solder between said metallized layer and said electrode terminal, and then heat-treating them to join the ceramic heater and the electrode terminal.
According to the invention, the active metal solder is preferably Ag—Cu—Ti alloy, Cu—Ti alloy, or Au—Ti alloy, and also the metal solder is preferably Ag solder, Cu solder, Ni solder, or Au solder, which is used to join active metal solders and metals to each other.
Further, the electrode terminal is preferably a metal including as main ingredients one or more kinds of the groups consisting of Fe, Ni, and Co, and more preferably kovar having a low thermal expansion coefficient and good oxidation resistance.
Further, according to the invention, the ceramic heater is a bonding heater comprising a heater portion in which a heating element is embedded and a holder portion integrally combined to the heater portion for securing the heater portion.
Yet further, according to the invention, the ceramic base material is a single material, and preferably formed of silicon nitride, aluminum nitride, or silicon carbide, which may be either closely packed or porous.
REFERENCES:
patent: 4803345 (1989-02-01), Hoshizaki et al.
patent: 4804823 (1989-02-01), Okuda et al.
patent: 4883947 (1989-11-01), Murase et al.
patent: 5756971 (1998-05-01), Hipp
patent: 6039238 (2000-03-01), Panaghe
Burr & Brown
Hoang Tu Ba
NGK Insulators Ltd.
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