Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With structure for mounting semiconductor chip to lead frame
Reexamination Certificate
1999-09-23
2001-02-27
Picardat, Kevin M. (Department: 2823)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With structure for mounting semiconductor chip to lead frame
C257S666000, C257S678000, C257S734000
Reexamination Certificate
active
06194780
ABSTRACT:
RELATED PATENT APPLICATIONS
(1) (E83-0002), Ser. No. 08/239,375, filed May 6, 1994, entitled “Composite Bump Bonding” assigned to the same assignee.
(2) (E83-0004), Ser. No. 08/239,380, filed May 6, 1994, entitled “Composite Bump Flip Chip Bonding” assigned to the same assignee.
(3) (E83-0003A), U.S. Pat. No. 5,393,697, to Chang et al, Feb. 28, 1995, entitled “Composite Bump Structure and Methods of Fabrication,” filed May 6, 1994.
(4) (E83-0003B), Ser. No. 08/387,095, filed Feb. 13, 1995 entitled “Composite Bump Structure and Methods of Fabrication,” assigned to the same assignee.
(5) (E84-0010), Ser. No. 08/494,582, filed Jun. 23, 1995 entitled “Connection Construction and Method of Manufacturing the Same,” assigned to the same assignee.
(6) (ERSO-84-0052), Ser. No. 08/579,511, filed Dec. 27, 1995, entitled “A New Tape Automated Bonding Method And Bonded Structure” assigned to the same assignee.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to the use of an anisotropic conductive film, having conductive particles in an insulating adhesive, with tape automated bonding to form interconnections between a lead array and an integrated circuit element. The use of an anisotropic conductive film provides a bonding process with reduced temperature and pressure and a reliable encapsulated bonded structure.
(2) Description of Related Art
In conventional tape automated bonding high temperatures are required to form the bond between the inner lead ends of a lead array and the bonding pads on an integrated circuit element. The difference in thermal expansion between the elements of the assembly can distort the lead array and make subsequent processing, such as bonding the outer lead ends, difficult. This invention provides a method to avoid this problem by using an anisotropic conductive film in combination with tape automated bonding. The anisotropic conductive film comprises conductive particles in an insulating adhesive.
U.S. Pat. No. 4,963,002 to Tagusa et al. describes a connection construction using conductive particles and both conductive and insulating adhesives. Japanese Patent 3-62927 to Fujimoto describes a composite conductive particle, an adhesive layer, and flip chip bonding.
U.S. Pat. No. 5,001,542 to Tsukagoshi et al. describes a board made of glass, synthetic resin, metal ceramic or their composite materials. One variation of the disclosed board has a center part removed for a film carrier or TAB structure. Tsukagoshi et al. use a combination of deformable conducting particles, rigid conducting particles, and an adhesive to form the electrical bond. The Tape Automated bonding structure and method of this Invention uses a different, and more flexible, lead frame. This Invention uses an anisotropic conducting film using an adhesive with a different type conducting particles than Tsukagoshi et al. The method used to form the bond are different from Tsukagoshi et al.
U.S. Pat. No. 4,470,657 to Tsukagoshi et al. describes the use of an anisotropic conductive film using an adhesive with conductive particles of multiple sizes. Tape Automated Bonding is not described in this patent.
U.S. Pat. No. 4,731,282 to Tsukagoshi et al. describes insulating adhesives.
SUMMARY OF THE INVENTION
A diagram of a conventional TAB, or tape automated bonding setup is shown in
FIG. 1. A
lead array having leads
22
of a metal such as copper are formed on a dielectric layer
23
such as polyimide. The inner end of the leads contact conductive bonding pads
21
, of a material such as gold, formed on an integrated circuit element
20
. Heat energy at a chosen temperature and pressure, for a chosen time is delivered by a thermode
10
which is brought into contact with the leads of the lead array and a bond is formed between the inner ends of the leads
22
and the conductive bonding pads
21
.
In conventional tape automated bonding high temperatures, often between 450° C. and 550° C., are required to form the bond between the inner lead end of the lead array and the bonding pad on the integrated circuit element. The difference in thermal expansion between the copper lead
22
and the dielectric layer
23
which will distort the lead array and make subsequent processing, such as bonding the outer lead ends, difficult. Frequently the hardness of the gold bump can transmit damaging forces from the thermode to the integrated circuit element. The planarity of the thermode with respect to the bonding pads becomes very important and increases the cost of the equipment used in the bonding process. In conventional tape automated bonding it is important to encapsulate the bond as soon as it has been formed to prevent damage due for example to moisture and corrosion.
It is an object of this invention to provide a low cost method of tape automated bonding which uses lower temperature and pressure in the bonding process and provides a bond which is automatically encapsulated after the bonding has been completed.
It is a further object of this invention to provide a bonded structure formed using a low cost method of tape automated bonding which uses lower temperature and pressure in the bonding process and which is automatically encapsulated after the bonding has been completed.
These objectives are achieved using an anisotropic conductive film in the bonding process. The anisotropic film comprises conductive particles in an insulating adhesive. Using the anisotropic conductive film conductive particles
31
are placed between the leads
22
of the lead array and the conductive bonding pads
21
formed on the integrated circuit element
20
, see
FIGS. 2A and 2B
. The conductive particles compensate for deviations in planarity between the thermode and the conductive bonding pads so the bonding pressure can be substantially reduced, between about 20 and 40 kilograms/cm
2
. When the bond is formed the insulating adhesive
32
forms an encapsulation of the bond which protects the bond from moisture, corrosion, and mechanical damage. The bonding temperatures required are between about 150° C. and 180° C. and the insulating adhesive forms an adhesive bond to keep the electrical bond in place.
The lead array can be of the window type such as that shown in
FIG. 2C. A
lead array having leads
22
formed of a material such as copper are formed on a dielectric layer
23
formed of a material such as polyimide. The dielectric layer has an inner perimeter
73
bounding a region
75
with no dielectric material. The inner lead ends
74
of the leads extend into the region of no dielectric material. In this type of lead array an isolation film comprising a metal foil layer
27
formed on a polyimide layer
25
is used in the bonding process, see FIG.
2
A.
The lead array can also be of the type shown in
FIG. 2D
where there is no window and the leads
22
of the lead array are formed entirely on the polyimide layer
23
. In this type of lead frame the isolation film is not required, as shown in FIG.
2
B.
The insulating adhesive in the anisotropic conductive film can be a thermoplastic material, a thermosetting material, or a type of material which is both thermoplastic and thermosetting. The conductive particles can be metal spheres, graphite particles, or composite particles having a polymer body covered by a conductive metal coating.
REFERENCES:
patent: 4731282 (1988-03-01), Tsukagoshi et al.
patent: 4740657 (1988-04-01), Tsukagoshi et al.
patent: 4963002 (1990-10-01), Tagusa et al.
patent: 5001542 (1991-03-01), Tsukagoshi et al.
patent: 5861661 (1999-01-01), Tang et al.
patent: 362927 (1991-03-01), None
Ackerman Stephen B.
Collins D. M.
Industrial Technology Research Institute
Picardat Kevin M.
Prescott Larry J.
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