Note: Descriptions are shown in the official language in which they were submitted.
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Method for encapsulating semioonductor components mounted
on a carrier tape
The present invention concerns a method for encapsulating
semiconductor components on a carrier tape in accordance
with the preamble of claim 1.
Unpro-tected components are subject to environmental expo-
sure and ~echanical damage during the handling phases of the
components, or products incorporating these components.
Consequently,the components on the carrier tape must be
encapsulated so that the tape and the components on it beha-
ve in automated production machines in the same way as unen-
capsulated components.
In prior art methods for the protection of carrier tape com-
ponents, only the surface of the semiconductor component is
protected (cf. publication GB A 2,009 504), or only the com-
ponent and the leads extending therefrom are protected.Hence, the components are difficult to handle in automatic
encapsulatin~ machines. In the FI Published Application
840981, a method is disclosed in which the encapsulating po-
lymer is limited to a desired area of the carrier tape. In
the IMC-1984 Conference publication "Chip-size Plastic En-
capsulation on Tape Carrier Package", different encapsulat
ing methods are presented in which an encapsulating polymer is
applied on semiconductor components, or semiconductor compo
nents and their leads.
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Moreover, in the publication GB A 2,072,424 a method is pre-
( sented in which a formed metal cup is used for encapsulating
a semiconductor component. The metal cup is fastened from
its rims under the leads by meanq of a polyimide film coated
with epoxy inI~B st-ate or some other suitable cement layer.
Subsequently the component is covered with a metal film ha-
ving a hole through which the space around the component is
filled with encapsulating material. The filling of a metal
cup placed under the semiconductor element with encapsula~
ting polymer is presented as an alternative method
In accordance with this invention, a cup formed of a cement
layer coated film material, e.g., polyimide, is placed under
the annular lead support defining the hole on the carrier
tape where the component is to be located. This method gives
the encapsulated component an accurately defined form. The
polyi~ide film used as cup material, as well as the cement
layer coating thereon, efficiently protect the leads and the
component. The component is easy to handle, as situated in
the plane of the annular support, when using automatic
machinery.
By this method, the component is protected from all directi-
ons with a thin encapsulating material layer. No tensions
due to differences in the heat expansion coefficients of the
component and the encapsulating material occur, which are
typical if only one side of an element is protected, and
tend to damage the element.
The carrier tape components encapsulated from all directions
in accordance with the present invention are suitable for
use asdiscrete components. Differing from known methods, a
film material, preferably polyimide, coated with a cement
layer being activated when heated, as well as a carrier film
provided ~ith annular lead supports, is used. The cup formed
of the moldable film material is cemented onto the leads si-
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tuated under the annular lead support. The encapsulating
material is limited to the area defined by the inner rims
of the annular support, whereby the cup, the annular
support, and the encapsulating polymer together form a
micro-capsule around the semiconductor component.
More specifically, the method according to the invention
consists of a method for encapsulating components which
are mounted by their leads on a carrier tape, wherein each
component is supported under a hole in the tape with its
leads engaging an annular support portion of the tape,
characterized by the s-teps of~ providing a cup-shaped
structure formed of a film material which is coated with a
cement layer, wherein a polymer molding layer is placed on
the cement layer within the cup-shaped structure; placing
the cup-shaped structure under a said hole in the carrier
tape, wherein rim portions o~ the cup~shaped structure
engage the underside of the annular support portion of the
carrier tape, and wherein the molding layer in the cup-
shaped structure engages a said component to be
encapsulated; bonding the rim portions of the cup-shaped
structure to the annular support portion of the carrier
tape by using heating and pressing means; covering the
upper portion and sides of the component within the cup-
shaped structure with a protective layer of a polymer
encapsulating material, wherein -the encapsulating material
is dispensed from an applicator and wherein said covering
step is eEfected by conveying the applicator along a path
to cause the encapsulating material to extend over the
upper :Eace of the component, and to extend over the side
edges of the component into contact with the molding layer;
and subjecting the molding layer and the encapsulating
material to a heat curing treatment, wherein the entire
component is completely encapsulated by the molding layer
and the encapsulating material.
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Componen-ts protected by means of the method in accordance
with the invention can be advantageously used in component
bonding and placement machines. In -the placement phase,
the components with bent leads are bonded on a substrate
and the leads are soldered to the bonding pads on the
substrate.
The invention will be examined in the following in more
detail by means of the exemplifying embodiments in
accordance with the attached drawings.
Figure 1 shows a sectional view and Figure 2 a top view of
a TAB (Tape Automatic Bonding) component on the carrier
tape.
Figure 3 shows in schematic form the production of the cup
in accordance with the method of the invention.
Figure 4 shows a sectional view and Figure 5 a top view of
one protective cup.
Figure 6 shows in schematic form the dispensing of the
polymer on the bottom of the cup.
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Figure 7 shows in sectional view thè bonding of a cup to
the carrier tape.
Figure 8 shows in sectional view and Figure 9 in top view
the dispensing and application of the polymer on the
component.
Figure 10 shows in schematic form the~simultaneously
performed bonding, protection, and pre-curing phases.
Figure 11 shows in a sectional view and Figure 12 in a top
view a component with completed protection.
Figure 13 shows a sectional view of a component with
completed protection, detached from the carrier tape.
A chip TAB component 1 is supported as shown in Figure 1
by its lead electrodes 7 under a square hole 20 in a
polyimide tape 2 so that an annular area 4 remains between
the hole and the component 1. This area 4 is surrounded
as a part of the tape 2 by an annular support 5, which
additionally is surrounded by four elongated gaps 3. The
leads 7 attach the component 1 (by crossing the space 4
and the gaps 3) to test pad areas 6, outside the gaps.
The construction described above is the initial phase for
the five-phase protection method described below.
PHASE 1
A polyimide film 8 (thickness about 50 ~m), covered by a
pre-cured cement layer 21, is pressed with die tools 12,
13 with holding means 22 and cutting means 23 to form a
cup 9, 10, 11 with gently sloping sides 11. The cup 9,
10, 11 is cut from the film 8 so that it is provided with
a rim 9 of the desired width (Figure 4). The cup depth is
dimensioned so that a space of 100...200 ~m remains
between the semiconductor component chip 1 bottom side and
the cup bottom 10. The rim 9 of the cup 9, 10, 11 is
dimensioned according to the dimensions of the annular
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support 5. The outer dimensions of the rim in the cup
i 9, 10, 11 are 100... 200 ~m smaller than the outer dimensions
of the annular support 5. This~ and the exact alignment
of the cup 9, 10, 11 during the bonding phase, ensures
that the leads 7 on the ILB bonding area will not be cut
against the rim of the cup 9, 10, 11 during the bending
phase.
PHASE 2
The formed cup 9, 10, 11 is filled with polymer 15 on
its bottom 10 (Figure 6). This ensures the formation of
a voidless protective polymer layer under the component 1.
The polymer 15 is dispensed only by such an amount that
it fills the space between the component 1 and the cup
9, 10, 11 but does not lift the component 1 upwards.
PHASE 3
The cup 9, 10, 11 is bonded by the pre-cured cement layer21 on
the cup film material 8 under the component 1 (Figure 7,.
The pre-cured cement requires heat treatment (temperature
l00...20ooc) to make a bond to the carrier film 2.
The cup 9, 10, 11 is inserted in the press die 17 which
i~ formed so that it aligns the cup 9, 10, 11. The die
17 is heated and it compresses the cup 9, 10, 11 to the
carrier tape. The joint 5 is cooled before the compression
is released to ensure the permanent bonding of the cup
9, 10, 11. During the bonding phase, the ce~ent must
fill the space between the leads 7 and form an insulating
polymer layer between the leads 7. This ~ets a thickness
requirement of 25...35 ~m for the cement layer.
PHASE 4
The component 1 is covered with the protective polymer
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15' (Figure 8). The applicatorl~ is conveyed over the
component 1 in a spiral route so that its path totally
covers the entire coated area (Figure 9). Applicator
l~ and its tip movement are designed so that the polymer
15' is evenly spread over the entire tip path. The
quantity o~ polymer 15' is metered to fill the space
between the component 1 edge and the rim 9 of the cup
9, 10, 11, and to lift the sur~ace of the component 1
slightly above the surface of the carrier ~ilm 2. The
viscosities of the applied protective polymers are within
5,000...40,000 cPs. The choice of the protective polymer
is determined by its protective properties, cure time
and temperature, and wetting characteristics.
The wetting characteristics of the protective polymer
15' can be improved by heating the cup 9, 10, 11 because
the protective polymer viscosity decreases with increasing
temperature. In this case phases 3 and 4 are performed
simultaneously (Figure 10). The pre-curing o~ the protective
polymer can also be arranged at this phase when the protected
component is clamped and the pressing die temperature
ar4d appllcation time is adjusted for the polymer.
The pressing die 17 is provided with cooling channels
18, which allow the temperature of the pressing die 17
to decrease, and a release channel 19 to detach the encapsula-
ted component 1 from the pressing die 17. When the application
of the protective polymer 15' is done in vacuuml this,
together with the heating, accelerates the removal of
developing gases and voids in the encapsulation.
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PHASE 5
The carrier tape 2 with the encapsulated components 1
is routed via a pre-curing oven (not shown). The protective
polymer 15 is precured and the carrier film 2 is wound
with a spacer tape on a reel. Therea~ter, the reel is
transferred to the final curing o~ the protective polymer.
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The encapsulated component can now be cut off from the
carrier tape 2, e.g., at the outer rims of gaps 3, and the
leads 7 with which the component 1 is soldered on the
printed circuit board are bent (Figure 13). The components
can be placed and glued at their bottom on the PCB, and
all components can then be soldered either simultaneously
or individually.
The applied encapsulation polymers 15 and 15' can be of
an epoxy, silicone, or phenol type resin (e.g., CASTAL
341 FR or SUMITOMO CR 2000). A principal requirement
is that the resin mold leaves no voids between the component
1 and the cup 9, 10, 11.
The fil~ material 8 for the cups 9, 10, 11 can also be
a polyester film, instead of the polyimide film (e.g.,
NITTO JR 2250). Also other moldable films are applicable.
The cement layer covering the cup film material 8 surface
can be of any conventional silicone, acryl,or epoxy based
adhesive. The adhesive layer will not adhere when cold,
and it is easily formed.
The carrier tape 2 can be, e.g., a polyester film, instead
f the polyimide film. In this case, it is preferable
that the cup film material 8 is also a polyester film.
