Self alignment device for ball grid array devices

Details Self alignment device for ball grid array devices Self alignment device for ball grid array devices

1999-06-10

2001-11-06

Gaffin, Jeffrey (Department: 2841)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S783000, C361S808000, C361S809000, C361S820000, C439S078000, C439S083000, C439S526000, C439S876000, C174S13800J, C174S260000, C257S048000, C257S773000, C257S778000, C257S779000, C324S765010, C029S840000, C029S843000, C029S854000, C029S860000, C438S015000, C438S108000

Reexamination Certificate

active

06313999

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to electrical devices, and in particular to electrical devices for aligning the solder balls of a ball grid array semiconductor device.
DESCRIPTION OF THE RELATED ART
Semiconductor devices have been traditionally connected to other circuitry through the use of conductive metal pins. These metal pins provide input/output (I/O) terminals for transferring signals to and from the semiconductor device. The pins are typically arranged in rows or arrays on a surface of the semiconductor device, a configuration generally referred to as Pin Grid Array (PGA). Typically, the I/O pins of a PGA device are attached to other circuits and substrates through the use of wire bonds or solder. However, the drawbacks associated with PGA configurations have forced semiconductor manufacturers to develop new methods of attachment over the past decade. One such technology is referred to as Ball Grid Array (BGA) configuration.
In a BGA configuration, solder balls are formed on the I/O terminals of the semiconductor device. The solder balls are formed by depositing drops of solder on flat terminal pads formed on the surface of the semiconductor device. The semiconductor device is then attached to other devices by a process known as “flip-chip” mounting. Essentially, the semiconductor device is flipped upside down so that the solder balls face the surface of a substrate to which the semiconductor device is to be attached. The substrate typically includes flat pad terminals, much like the flat pad terminals on the semiconductor device, which correspond in position to the solder balls on the device. The semiconductor device is placed over the flat pad terminals of the substrate, so that the balls contact the flat pads on the substrate. The entire structure is then heated, causing the solder balls to reflow and form a stable connection between the semiconductor device and the substrate.
Many BGA semiconductor devices are subjected to testing at some point during the fabrication process. For testing applications, the semiconductor devices are removably mounted on a test fixture or substrate which provides electrical connections to the terminals of the semiconductor device. The test substrate is often similar to the bonding substrate described above, except that the solder balls are not allowed to reflow and become permanently connected to the substrate terminals. In order to test the semiconductor device, it is placed over the test substrate so that the solder balls contact the terminals formed on the test substrate. Typically, the device is held in place by a thumb screw or other similar means. Once the device is positioned on the substrate, control signals are supplied thereto through the test substrate terminals and measurements are made. These measurements are then used to determine whether the semiconductor device meets required design specifications.
FIG. 1
shows a conventional arrangement where a ball grid array (BGA) semiconductor device
10
is placed over a substrate
20
. The semiconductor device
10
includes a plurality of solder balls
15
. The substrate
20
includes a plurality of terminals
25
which correspond in position to the solder balls
15
. The substrate
20
also includes metal traces
30
formed on the surface of the substrate. The metal traces
30
provide a means of connecting the semiconductor device
10
to other circuit elements (not shown). In order to attach the semiconductor device
10
to the substrate
20
, the solder balls
15
of the device must be aligned with the terminals
25
of the substrate
20
. As mentioned above, this method of attachment is known as “flip chip” bonding since the semiconductor device
10
is flipped upside down (i.e. solder balls face down) and placed over the substrate
20
. In order to form a reliable bond between the semiconductor device
10
and the substrate
20
, the balls
15
of the device are placed on the terminals
25
of the substrate
20
. The entire device is then heated and then cooled, causing the solder balls
15
to melt and reform. The reflowing of the solder balls
15
forms a reliable electrical connection between the semiconductor device
10
and the substrate
20
. However, if the solder balls
15
are not perfectly aligned over the terminals
25
of the substrate, various problems can occur (e.g. short circuits between terminals).
FIG. 1
shows the solder balls
15
as being slightly off-center from the terminals
25
(by a distance d), as is often the case. Misalignment can occur from numerous causes, the most significant being improper placement of the semiconductor device over the substrate. The misalignment of the solder balls
15
can cause numerous problems which can result in the malfunction of the semiconductor device. If one of the solder balls flows into the space between terminals
25
, a short circuit may occur between two terminals
25
. Further, if a solder ball
15
is not properly aligned with the correct terminal
25
, a weakened electrical connection, or no connection may be caused to form.
Proper alignment is necessary not only when bonding semiconductor devices to substrates, but also during the testing of semiconductor devices. Semiconductor devices with BGA terminals are typically tested by placing them on a test substrate and supplying control signals thereto. The semiconductor devices are usually held to the substrate by a thumb screw or other similar means. The testing arrangement is very similar to the bonding arrangement described above, except that the device and substrate are not heated so that the solder balls melt. In this way, one substrate can be used to test multiple semiconductor devices. When testing, improper alignment of the semiconductor device can result in erroneous measurements.
As stated above, a major problem associated with BGA devices is obtaining the proper alignment of the solder balls of the semiconductor device over the flat pad terminals of the substrate. Often the semiconductor device is improperly placed over the substrate, or the device shifts during the heating process, causing the balls to become improperly aligned. In bonding applications, improper alignment can cause erroneous connections to be formed, and thus results in malfunction of the semiconductor device. In testing applications, misalignment can result in erroneous measurements. Various technologies have been developed to combat this problem. Most solutions are concerned with changing the topography of the substrate to better accommodate the balls of the semiconductor device. For example, U.S. Pat. Nos. 5,196,726 and 5,214,308, both to Nishiguchi et al., disclose substrates with depressions formed therein for receiving the balls of a BGA device. U.S. Pat. No. 5,810,609 to Faraci et al. shows a substrate with multiple spiral-like connectors formed thereon for receiving the balls of a BGA device. However, substrates like the ones described in the aforementioned patents are expensive and difficult to produce. Therefore, there currently exists a need for an alignment device for BGA devices which is both inexpensive and easy to manufacture.
SUMMARY OF THE INVENTION
The present invention is a alignment device for aligning the balls of a BGA device over a substrate. The alignment device includes a cup-shaped member which receives and aligns the balls of a BGA device. The alignment device is inserted between a BGA device and the substrate before bonding or testing. The alignment device of the present invention provides an efficient alignment tool for BGA devices which is both inexpensive and easy to produce.
The above and other advantages and features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention which is provided in connection with the accompanying drawings.


REFERENCES:
patent: 3745513 (1973-07-01), Gross
patent: 5076794 (1991-12-01), Ganthier
patent: 5196726 (1993-03-01), Nishiguchi et al.
patent: 5214308 (1993-05-01), Nishiguchi et al.
patent: 5348214 (1994-09-01),

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