Alloys or metallic compositions – Tin base
Reexamination Certificate
1999-11-30
2003-12-02
King, Roy (Department: 1742)
Alloys or metallic compositions
Tin base
Reexamination Certificate
active
06656422
ABSTRACT:
1. TECHNICAL FIELD
The present invention includes to die-bonding solder materials used in die bond for fixing silicon chips or the like onto a base.
2. BACKGROUND ART
As pressure sensors to detect the pressure or the differential pressure, semiconductor pressure transducers using a semiconductor pressure sensor are known (example: Japanese Utility Model Laid-Open No. 59-135654 or the like).
FIG. 9
shows one conventional example of semiconductor pressure transducers
900
equipped with such a semiconductor pressure sensor.
This semiconductor pressure transducer is constructed by installing a base
902
on a carrier
901
and further installing a semiconductor pressure sensor
903
on the base
902
.
The carrier
901
is made of an about 0.5 to 3 mm thick metal plate or ceramic plate. A pressure inlet hole
904
is provided at the center, while a conductive pin
906
is inserted near the periphery and hermetically sealed with a seal material
905
such as glass.
The base
902
is formed of an insulating material closely resembling the semiconductor pressure sensor
903
in linear expansion coefficient into a 1 to 5 mm tall cylindrical body. Besides, this base
902
has an insert hole
908
communicating with the above pressure inlet hole
904
.
And, to enhance the solderability in joining the base
902
to the carrier
901
by soldering, the carrier
901
and the base
902
are jointed by using a solder material
907
in addition of a gilt simple substance or a nickel-plated simple substance or a product obtained after gilded on its nickel plated surface.
In joining the base
902
to the carrier
901
, for example, with ceramic employed for the base
902
, the solder material
907
(brazing material) placed between the junction surfaces
901
a
and
902
a
of the carrier
901
and the base
902
is heated with a joining jig to melt a solder material
907
for joining after the metallizing according to a conventional well-known method comprising baking Mo, Mn or the like to their joining surfaces
902
a
and overlapping a Ni or Au plated layer thereon. As a solder material
907
, a Sn—Ag series eutectic solder comprising Tin (Sn) and Gold (Au) is used and the thickness of the junction part is set generally to the order of 10 to 50 &mgr;m.
Besides, the semiconductor pressure sensor
903
is made of n-type monocrystal silicon (Si) or the like and has a semiconductor substrate
909
electrostatically joined to the top surface of the base
902
. On this semiconductor substrate
909
, a strain generating portion about 20 to 100 &mgr;m in thickness or a disk-shaped pressure receiving diaphragm
911
is formed. Besides, on the surface side of the diaphragm
911
, four gauges
912
acting as a piezoresistance region is formed by the technique of impurity diffusion or ion implantation. And, a Wheatstone bridge is constituted of these and connected to the conductive pin
906
through a lead wire
913
.
3. DISCLOSURE OF THE INVENTION
[Problem to be Solved by the Invention]
Because of being soft, however, the above solder materials
907
were apt to absorb a stress, but for some stationary chips, when the solder materials themselves solidify a stress was given to them to break the above sensor chips or to generate a drift in the measuring result of a sensor.
Besides, the above solder materials
907
were subject to oxidation, could not be preserved in air and therefore were inconvenient in handling.
[Means of Solution to the Problems]
Accordingly, it is the main object of the present invention to suppress the occurrence of a stress to a stationery chip and to enable the chip to be more easily fixed.
To attain such a object, a first invention in the present invention is so arranged that a die-bonding solder material comprises tin and gold and its substantial composition ratio is one which has the eutectic point with a more content of tin than that of gold.
As a result of such a composition, this die-bonding solder material increases in elongation percentage and tensile strength near room temperatures as compared with a solder material made of Sn—Ag eutectic.
Besides, a second invention is so arranged as to add an additive made of a higher metal in eutectic point with gold alone than with both tin and gold, having a higher eutectic point than tin and forming no eutectic with tin, to the die-bonding solder material mentioned in the first invention in addition to tin and gold.
This additive is deposited as a simple substance first in the cooling process of a melting die-bonding solder material.
Besides, a third invention is the second invention with the added amount of an additive ranging from 0.1 to 9% by weight.
Besides, a fourth invention is the second invention with any of antimony, germanium or silicon employed as the additive.
Besides, a fifth invention is the first invention with the eutectic of tin and gold comprising substantially 95% to 90% of tin and 5% to 10% of gold.
REFERENCES:
patent: 3493367 (1970-02-01), Onuma
patent: 5366692 (1994-11-01), Ogashiwa
patent: 5690890 (1997-11-01), Kawashima et al.
patent: 55-16525 (1980-02-01), None
patent: 55-127027 (1980-10-01), None
patent: 59-135654 (1984-09-01), None
patent: 61-125139 (1986-06-01), None
patent: 63178535 (1987-01-01), None
patent: 63-178535 (1988-07-01), None
patent: 5-259201 (1993-10-01), None
patent: 9-232340 (1997-09-01), None
“Metals Handbook, Desk Edition, 2nd ed.” ASM International: 1998, p 24.
Blakely & Sokoloff, Taylor & Zafman
Combs Morillo Janelle
King Roy
Yamatake Corporation
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