Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Making plural separate devices
Reexamination Certificate
1998-12-23
2001-05-22
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Making plural separate devices
C438S110000, C438S124000, C438S126000, C438S127000
Reexamination Certificate
active
06235555
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention generally relates to reel-deployed printed circuit boards for chip-on-board (COB) packages and a method for manufacturing IC packages using such circuit boards.
2. Description of the Related Art
In many applications, such as telephone cards, credit cards and identification cards, integrated circuit (IC) cards can advantageously replace conventional magnetic strip cards. The IC card typically includes a “chip-on-board” (COB) package in which a semiconductor integrated circuit chip is connected to a printed circuit board and is encapsulated with an encapsulant. COB packages are manufactured in several different ways, depending on the type of printed circuit board and the encapsulating methods used. Among these, a COB package using a reel-deployed printed circuit board is preferred due to lower production costs and higher assembly productivity.
FIG. 1
is an exploded perspective view of an IC card
10
which has a card body portion
11
with a COB package
20
assembled into it.
FIG. 2
is a cross-sectional view of the IC card
10
shown in FIG.
1
.
FIGS. 3 and 4
are top and bottom views, respectively, of a COB package
20
of the type shown in
FIGS. 1 and 2
. As shown in
FIG. 1
, the COB package
20
is inserted into a cavity in the body
11
of the card
10
. Thus, the card body
11
includes an adhesion area
12
to which the COB package
20
is attached, and a cavity
13
for receiving an encapsulated portion
24
of the COB package
20
.
Referring to
FIG. 2
, in manufacturing the COB package
20
, a semiconductor chip
21
is attached to a top surface of a printed circuit board
30
by an adhesive
22
, and bonding wires
23
electrically connect the semiconductor chip
21
to bonding pads
31
formed on the top surface of the printed circuit board
30
. The semiconductor chip
21
, bonding pads
31
, and bonding wires
23
are all then encapsulated with an encapsulant to seal and protect them from the environment. As shown in
FIG. 4
, the other side, that is, a bottom surface of the printed circuit board
30
, typically has a plurality of contacts
33
which are exposed on the card when the COB package
20
is assembled into the card body
11
in the orientation shown. The contacts
33
are electrically connected to the bonding pads
31
on the top surface by plated-through holes
32
, sometimes called “via holes.” Non-conductive gaps
34
on the bottom surface electrically isolate the contacts
33
from each other. As shown in
FIGS. 3 and 5
, a dam
35
prevents runoff of the liquid encapsulant and gives shape to the encapsulated portion
24
of the package.
FIG. 5
shows a conventional reel-deployed printed circuit board
40
which is used to manufacture a plurality of the COB packages
20
simultaneously in successive manufacturing steps, as depicted from left to right in the figure. In
FIG. 5
, reference numeral
37
indicates the outline of an individual COB package
20
.
To prepare the reel-deployed printed circuit board
40
for the encapsulation step, a dam
35
is formed on the top surface of the board. Among the various encapsulation methods available, a method that dispenses a liquid encapsulant onto the semiconductor chip and the wire bonding area and then cures the encapsulant in place, is preferred for COB packages that use a reel-deployed printed circuit board
40
. In such a process, the dam
35
prevents runoff of the liquid encapsulant and acts as a mold to shape the encapsulated portion outlined by the dam. The printed circuit board
40
further includes sprocket holes
41
, position holes
42
, assembly-reject holes
43
a
and test-reject holes
43
b
, the functions of which are described below.
An “in-line” system such as that described above can theoretically manufacture COB package
20
without any interruptions between consecutive assembly steps. However, as a practical matter, an unbalanced production capability among the steps can make operation of the in-line system difficult and inefficient. Further, an interruption of the line at any one point can halt the entire assembly line, and thereby reduce the productivity of the entire manufacturing process. In view of this, an alternative manufacturing method, one that performs each manufacturing process, or step, independently of the others, and which uses a reel hub
50
, such as the one shown in
FIG. 6
, for conveniently storing the reel-deployed printed circuit board
40
between manufacturing steps, and for transferring it from step to step, becomes more preferable.
In this alternative method, a reel-deployed printed circuit board
40
is initially provided in the form of a long strip wound onto a spool, as shown in FIG.
6
. At each independent step, or stage, in the manufacturing process, the printed circuit board
40
is wound off of the reel hub
50
, a process step is performed on it, and the board
40
is then wound onto another reel hub
50
for interim storage and conveyance to the next-succeeding manufacturing step.
The reel hub
50
thus may be seen as an almost indispensable tool for the practical mass-assembly of COB packages of the type that use a reel-deployed printed circuit board
40
. Without it, the assembly could, at best, be carried out using only a short, strip-type printed circuit board. COB assembly methods using reel-deployed printed circuit boards
40
usually result in a much higher productivity than assembly methods using a strip-type printed circuit board. For example, a reel hub having a diameter of 330 mm is typically capable of holding about 30,000 COB packages
20
simultaneously.
In
FIG. 6
, reference numeral
40
a
indicates the top surface of a reel-deployed printed circuit board
40
on which the encapsulated portion
24
is formed, and reference numeral
40
b
indicates the bottom surface of the circuit board
40
on which the contacts
33
are formed. Those skilled in the art will recognize that it may be desirable to temporarily insert an optional “interposer” (not shown) over the circuit board
40
after the die-is attached and wire-bonded but before it is encapsulated, to protect the fragile bonding wires
23
(see
FIG. 2
) until the encapsulant is in place. The interposer can then be removed after the encapsulation is complete.
Although the use of reel-deployed printed circuit boards
40
can enhance the productivity of COB packages
20
, their use can also result in an adverse effect. In particular, when the reel-deployed printed circuit board
40
is wound off of the reel hub
50
, the board
40
may not be desirably flat, but rather, curved to a certain extent. That is, the circuit board
40
may take an arcuate “set” while it is wound on the circular hub of the reel that remains in the board when it is removed from the reel.
FIG. 7
illustrates the undesirable curvature that a conventional reel-deployed printed circuit board
40
can assume after it is removed from a storage reel. Typically, the encapsulation and curing steps produce a slight warpage of the COB package
20
anyway, because of a mismatch of thermal expansion coefficients between the encapsulant and the semiconductor chip
21
. Thus, a warped printed circuit board
40
, such as that shown in
FIG. 7
, can then exacerbate the warpage of the COB package
20
. This warpage can cause an attachment failure between the card body
11
and the COB package
20
, as shown in FIG.
8
. Further, any protrusion of the COB package
20
from the surface of IC card
10
caused by this warpage of the COB package body will promote premature wear of the contacts
33
, and thereby decrease the usable life and reliability of the IC card
10
.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a reel-deployed printed circuit board includes a flexible base board and multiple unit boards formed in the base board for manufacturing COB packages. The unit boards include a die bonding area and multiple wire bonding pads on a top surface thereof, a plurality of contacts on a bottom surface thereof, and via holes which electrically
Lawrence Don C.
Picardat Kevin M.
Samsung Electronics Co,. Ltd.
Skjerven Morrill & MacPherson LLP
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