Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With rotor
Reexamination Certificate
2000-11-28
2002-10-08
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With rotor
C324S754090, C324S758010, C324S537000, C324S755090
Reexamination Certificate
active
06462533
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an IC test system for testing IC packages such as BGA (ball grid array) packages.
(b) Description of the Related Art
BGA LSIs are increasingly used along with a higher integration of the LSI packages.
FIGS. 1A and 1B
are side view and a bottom view of a package of a BGA LSI. The BGA package
11
is substantially of a square having a 5×5 mm to 50×50 mm size with a thickness of 0.5 to 3 mm. A large number of solder balls
12
are mounted on the bottom surface of the package at the peripheral area thereof, and a LSI
13
is embedded at the central area of the package. A plurality of bonding wires extend within the BGA package between the LSI
13
and the solder balls
12
. The BOA package is mounted on a printed circuit board with the bottom surface mounting thereon the solder balls
12
being in contact with the top surface of a printed circuit board, and coupled thereto by thermally melting the solder balls for electric and mechanical connection between the solder balls and the terminals of the printed circuit board.
The solder balls
12
are arranged in an array on the outer periphery of the package. Each of the solder balls
12
is of a sphere having a diameter of around 0.3 mm and projects from the bottom surface. The number of the solder balls
12
in a LSI package may be as high as several hundreds to a thousand in a high-integrated LSI, wherein the pitch of the solder balls may be as low as 0.5 mm. In view of the higher integration of the next generation LSI together with demand for a smaller package size on the printed circuit board, a higher density for the arrangement of the solder balls
12
is desired in the BGA package.
For testing or measuring the electric characteristics of the BGA package, a test instrument (or test socket) is generally used which has an array of contact pins arranged in a pitch corresponding to the pitch of the solder balls
12
. The contact pins are attached to the test socket so that the contact pins advance and retract to/from the socket by a spring function. More specifically, the contact pin has a compression spring at the bottom thereof and the contraction of the spring provides a thrust force for a suitable electric contact between the contact pin and the solder ball. Thus, a tip of the contact pin exerts a thrust force to the solder ball during the abutment thereto.
FIGS. 2A
to
2
D show sectional views of a depression of a test socket, consecutively show the advancement of a BGA package
11
toward the contact pins
15
disposed in the depression. A suction head
16
holds the BOA package
11
at the top surface thereof by vacuum suction and moves in the horizontal direction for positioning of the BGA package
11
with respect to the test socket
14
. The suction tool
16
then moves downward or toward the depression
17
of the socket
14
, as shown in
FIG. 2A
, and allows the BGA package
11
to drop within the depression
17
by stopping the vacuum suction, as shown in FIG.
2
A. The depression
17
has a tapered wall portion at each side of the square and an additional straight wall portion at the bottom of the depression
17
.
The BGA package
11
slides along the tapered wall of the depression
17
, as shown in
FIG. 2B
, and stops at the straight wall portion, as shown in
FIG. 2C
, where the solder balls
12
are aligned with the contact pins
15
of the test socket
14
. The suction head
16
then further moves downward to thrust the BGA package
11
with a specific contact pressure, as shown in
FIG. 2D
, to obtain electric contacts between the solder balls
12
and the contact pins
15
. Thereafter, an electric test is conducted for the BGA package
11
,
FIG. 3
shows the structure of a conventional IC test system, which includes a base
10
, a carry-in tray
20
, a first carriage arm
21
, a positioning member
22
, a second carriage arm
23
, socket
14
, and a carry-out tray
24
. Both the carriage arms
21
and
23
have respective suction heads
16
for holding and releasing the BGA package
11
. In the drawing, a top cover is not shown which covers the top surface or table of the base
10
of the test system.
The first carriage arm
21
moves straight, then allows the suction head
16
to move in the vertical direction, thereby transferring the BGA packages
11
before testing one by one from the carry-in tray
20
to the positioning member
22
, which positions the BOA package
11
based on the external shape thereof.
The second carriage arm
23
turns horizontally about its vertical axis to allow the suction head
16
to move in the horizontal direction, thereby carrying the positioned BGA package
11
to the socket
14
. The BGA package
11
is dropped therein, as described before, and subjected to testing thereof. After the testing, the BGA package
11
is transferred to the carry-out tray
24
and temporarily stored thereon for waiting carry-out thereof.
In the conventional IC test system, as shown in
FIG. 4A
, it sometimes happens that the BGA package
11
is not smoothly dropped by the suction head
16
to the bottom of the depression along the taper wall, whereby an edge of the BGA package
11
is stopped by the taper wall. In this case, the suction head
16
which thrusts the BGA package
11
against the contact pins
15
may damage the BGA package
11
by an excessive thrust force exerted from above. This often happens when the second carriage arm
23
drops the BGA package
11
before the vibration of the second carriage arm
23
is stopped, or when the socket
14
receives a vibration (or waggle) from other members.
The excessive external force is also applied to the contact pins
15
in a horizontal direction as well as the vertical direction. The contact pins
15
are extendable in the vertical direction to some extent as described before. However, the contact pins
15
are susceptible to the horizontal thrust force and are bent thereby due to the fragility of the contact pins
15
having a diameter around 0.3 mm. Even if only one of the contact pins
15
is bent and cannot move in the vertical direction, the testing cannot be not carried out because the all the contact pins
15
are not likely in electrical contact with the solder balls
12
.
In addition, it may also happen that the contact pins
15
are not in a suitable abutment against the solder balls even if the BGA package
11
is dropped to the bottom of the depression
17
. This happens when the solder balls
12
are not correctly arranged with respect to the external shape of the BGA package
11
. For example, if the orientation of the solder ball array is deviated from the orientation of the BGA package
11
, the contact pins are not in a suitable abutment against the centers of the solder balls and are thus subjected to an undesirable external force in the horizontal direction upon the thrust by the suction head
16
. This may cause peeling-off of the solder balls
12
from the BGA package
11
or damage to the contact pins
15
.
In either case, a failed contact pin must be replaced by a new contact pin. The contact pin is fragile due to the extremely small diameter thereof and is difficult to settle on the socket without a skill. This necessitates the replacement of the whole socket on the user side of the test system, the cost of which is a heavy burden on the user.
The present inventors proposed in an earlier Japanese application No. 11-230237 for solving the above problems, wherein the positioning of the BGA package is carried out on the basis of the arrangement of the respective solder balls, the image of which is taken by a CCD camera and stored beforehand. This allows the solder balls to be in a suitable alignment with the contact pins In addition, the proposed technique uses a suction head which thrusts the BGA package so as to allow the solder balls to be in abutment against the contact pins while holding the BGA package without dropping.
The proposed technique achieved a significant solution for the above problems; however, it was
Hayes & Soloway P.C.
Le N.
NEC Machinery Corporation
Sundaram T. R.
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