Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-06-06
2004-02-10
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S230000, C156S238000, C156S247000, C156S248000, C156S257000, C156S270000, C156S516000, C156S521000, C156S498000, C156S542000, C438S464000
Reexamination Certificate
active
06689245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a die bonding sheet sticking apparatus and relates to a method of sticking a die bonding sheet. In these die bonding sheet sticking apparatus and method of sticking a die bonding sheet, in the process for producing small electronic components, for example, semiconductor chips, a die bonding sheet capable of functioning as an adhesive material for die bonding is stuck to a back surface of wafer at the time of die bonding of semiconductor chips after dicing onto a lead frame.
2. Description of the Prior Art
In the conventional production of a wafer of semiconductor such as silicon (hereinafter simply referred to as “wafer”), the wafer is first produced in the form of a disk having a large diameter. A circuit pattern is formed on a surface of the wafer, and the surface of the circuit pattern is protected by a protective tape. The back side of the wafer is ground, and stuck onto a ring frame with a pressure sensitive adhesive sheet interposed therebetween. The protective tape is detached from the surface of the circuit pattern, and the wafer is cut apart into a multiplicity of dice formed chips by the use of a dicing cutter (dicing). In this state, the wafer chips are transferred to the subsequent steps such as cleaning, drying and die bonding steps.
In the conventional method of sticking a pressure sensitive adhesive sheet to a back surface of wafer, as shown in
FIG. 14
, wafer W is disposed on retention table
200
. Pressure sensitive adhesive sheet
202
consisting of base sheet
204
and pressure sensitive adhesive layer
206
is stuck to back surface W
3
of the wafer W. The pressure sensitive adhesive sheet
202
is cut by rotating upward arranged cutter
210
along the outline (circumference) W
4
of the wafer W.
However, recently, the reduction of the thickness of semiconductor chips such as IC cards is increasingly demanded. The demand for semiconductor chips whose thickness has been reduced to about 100-50 &mgr;m from the conventional about 300 &mgr;m is increasing in recent years. For obtaining such semiconductor chips, it is needed to produce extremely thin wafers having the above reduced thickness.
In the use of such extremely thin wafers, there is the danger of flawing of circumferential portion W
4
of the wafer W or cracking of the wafer W at the cutting of the pressure sensitive adhesive sheet
202
with the use of the cutter
210
. Moreover, there is the sheet stuck at V notch portion provided on the wafer, so that there would occur failure in the recognition of wafer alignment effected in a later step.
For the purpose of avoiding such wafer flawing or wafer cracking, it is also practiced in the prior art to cut a pressure sensitive adhesive sheet along the outline of wafer in a separate step in advance and stick the cut pressure sensitive adhesive sheet to a back surface of the wafer.
Further, in the prior art, die bonding is carried out by using an ultraviolet curable pressure sensitive adhesive sheet as the pressure sensitive adhesive sheet. In this die bonding, where semiconductor chips cut apart into a multiplicity of chips are die bonded (transfer mounted) to a lead frame, ultraviolet is applied to the ultraviolet curable pressure sensitive adhesive sheet. As a result, the adhesive strength of the ultraviolet curable pressure sensitive adhesive sheet is lowered so that die bonding is practiced by using suction collets.
Still further, at the time of die bonding, it is known to separately coat a lead frame with an adhesive and effect die bonding of semiconductor chips onto the coated lead frame.
However, the current situation is that, in any case, another step is needed to thereby cause the process to be complex, bringing about a cost increase.
The present invention provides a die bonding sheet sticking apparatus for wafer which, at the time of die bonding of semiconductor chips onto a lead frame, after dicing, a sequence of steps for sticking a die bonding sheet capable of functioning as an adhesive for die bonding to a back surface of wafer can be performed in a continuous and automatic manner without wafer damaging or cracking. The present invention also provides a method of sticking a die bonding sheet with the use of the die bonding sheet sticking apparatus.
SUMMARY OF THE INVENTION
The present invention has been made with a view toward solving the above problems of the prior art and attaining the above object. The die bonding sheet sticking apparatus of the present invention includes:
a wafer supply section for accommodating a plurality of wafers therein,
a wafer conveyance section including conveyance means for taking out a wafer from the wafer supply section and conveying the wafer,
an alignment section for positioning the wafer taken out from the wafer supply section via the wafer conveyance means of the wafer conveyance section,
a sheet sticking section for conveying the wafer arranged for given reference position at the alignment section via conveying means and for sticking a die bonding sheet to a back surface of the wafer by heating, said die bonding sheet comprising a release sheet and a base provided with heat-sensitive adhesive layer, and
a sheet peeling section including sheet peeling means for peeling the release sheet of the die bonding sheet from the wafer having the die bonding sheet stuck thereto at the sheet sticking section,
wherein the sheet sticking section comprises:
cutting means capable of, prior to the sticking of the die bonding sheet to the back surface of the wafer, cutting the base provided with heat-sensitive adhesive layer of the die bonding sheet in conformity with an outline of the wafer,
said cutting means capable of cutting the base provided with heat-sensitive adhesive layer in the direction of a width of the die bonding sheet with a spacing of given distance from a rear end portion of the wafer in the direction of conveyance of the wafer so as to form a leaf portion; and
leaf detaching means capable of, prior to the sticking of the die bonding sheet to the back surface of the wafer, detaching only the leaf portion, corresponding to portion outside the outline of the wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet after the cutting by said cutting means.
The above structuring of the apparatus enables continuously and automatically carrying out a series of operations including taking out a wafer from a wafer cassette wherein a plurality of wafers are accommodated, alignment for positioning the wafer, sticking a die bonding sheet comprising a release sheet and a base provided with heat-sensitive adhesive layer to the back of the wafer, detaching the release sheet of the die bonding sheet, and accommodating the wafer in a wafer cassette.
The die bonding sheet also functions not only as a protective tape at the time of dicing but also as an adhesive for die bonding at the time of die bonding of semiconductor chips to a lead frame after dicing, because the die bonding sheet comprises a release sheet and a base provided with heat-sensitive adhesive layer.
Therefore, as different from the prior art, it is not needed to apply an adhesive to a lead frame at the time of die bonding. In the present invention, only heating the die bonding sheet enables not only picking up, by suction, semiconductor chips with the use of suction collets but also direct thermocompression bonding because the heat-sensitive adhesive layer of the die bonding sheet also functions as an adhesive for a lead frame.
Also, the base provided with heat-sensitive adhesive layer of the die bonding sheet is cut in conformity with the outline of wafer before the sticking of the die bonding sheet to the back surface of the wafer. Therefore, there is no danger of flawing of a peripheral portion of wafer or wafer cracking as experienced at the cutting of die bonding sheet with a cutter in the prior art. Moreover, as different from the prior art, it is not needed to cut the die bonding sheet by a separate operation in advance.
Further, prior
Lintec Corporation
Mayes Curtis
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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