Plastic ball grid array assembly

Details Plastic ball grid array assembly Plastic ball grid array assembly

2000-03-17

2003-08-12

Chaudhuri, Olik (Department: 2823)

Semiconductor device manufacturing: process

Packaging or treatment of packaged semiconductor

Insulative housing or support

C438S108000, C438S127000, C257S704000, C257S730000, C257S778000, C257S787000

Reexamination Certificate

active

06605492

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a plastic ball grid array (“PBGA”) assembly, and more particularly, to an improved PBGA assembly including strengthened corner sections.
2. Description of the Related Art
A PBGA assembly is a package for enclosing semiconductor logic chips. PBGA assemblies are designed to increase the number of paths available for delivering signals to and from the logic chips. For example, conventional semiconductor packages commonly have a single row of pins disposed about their outside edge. Whereas PBGA assemblies employ the larger surface area under the PBGA assembly to connect signals to the internal logic chips, e.g., a plurality of solder balls spaced about the bottom surface area are used for the transfer of signals.
A PBGA assembly generally comprises two parts: a substrate and an overmold. During assembly of the package, the logic chip or die is glued, or otherwise attached, to the top of the substrate. The overmold is then molded on the substrate over the die to form a protective covering.
The substrate is a relatively thin member, commonly having a thickness of about 0.36 to about 0.65 millimeters thick. Further, the substrate can include printed circuit traces, dielectric material, and solder balls. Typically, the substrate is either square or rectangular in shape, and is relatively flexible. Substrates generally range in sizes from about 27 to about 50 millimeters in width and in length. Overall, substrates are relatively fragile devices, prone to damage if not protected.
A typical PBGA assembly
10
is shown in
FIGS. 1A and 1B
. The assembly
10
includes a mold cap
12
disposed upon a substrate
14
. The mold cap
12
includes chamfered side edges
16
and chamfered corners
18
. Disposed beneath the substrate
14
are a plurality of solder balls
20
for use in connecting the PBGA assembly
10
to a printed circuit board (not shown), and in transferring signals to and from a logic chip
22
mounted on the substrate
14
and covered by the mold cap
12
.
The solder balls
20
disposed along the bottom of the substrate
14
provide the connections between the PBGA assembly
10
and the printed circuit board. Installation of the PBGA assembly
10
onto the printed circuit board is relatively straight forward. The PBGA assembly
10
is heated during installation to a relatively high temperature so that the solder balls
20
melt and the PBGA assembly
10
in effect solders itself to the printed circuit board.
The mold cap
12
comprises a mold compound of sufficient thickness to form a protective covering over the die
22
(typically, about 0.8 millimeters thick). Typically, the mold compound is a thermoset plastic compound, and is used to protect the die
22
from environmental conditions. The mold cap
12
extends over all but the four side edges of the substrate
14
, so that the edges of the substrate
14
remain free for clamping during the. molding operation (e.g., to hold the substrate
14
in place proximate the mold during the overmolding process when plastic is injected into the mold), and during subsequent processing, handling and installation. The edges
16
of the mold cap
12
are chamfered to facilitate removal from the mold. The mold cap edges
16
define an acute angle and are designed to ease the separation of the mold cap
12
from the mold. The mold cap
12
also typically includes chamfered corners
18
. Thus, the corner sections
19
of prior PBGA assemblies
10
are unsupported, and generally consist of only the substrate
14
.
As a result of this construction, the corner sections
19
of prior PBGA assemblies
10
are susceptible to mechanical damage. The flexible corner sections
19
are easily damaged, for example, during processing associated with the assembly, test, and installation of the PBGA assemblies
10
, and during normal handling.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In one aspect of the present invention, an apparatus for enclosing a logic chip is provided. The apparatus includes a substrate, which has a surface adapted to receive the logic chip mounted thereon. Further, a mold cap is disposed upon the substrate, and the mold cap extends at least partially over the logic chip. The mold cap also includes at least one extension of a preselected size and shape that extends at least partially into a corner section of the substrate.
In another aspect of the present invention, a method is provided for enclosing a logic chip. The method includes mounting the logic chip on a polygon shaped substrate, and forming a mold cap on the substrate extending at least partially over the logic chip and into a corner section of the substrate.


REFERENCES:
patent: 4915607 (1990-04-01), Medders et al.
patent: 5708300 (1998-01-01), Woosley et al.
patent: 5732465 (1998-03-01), Tokita et al.
patent: 5886398 (1999-03-01), Low et al.
patent: 5933324 (1999-08-01), Barrett
patent: 6060777 (2000-05-01), Jamieson et al.
patent: 6064117 (2000-05-01), Barrett
patent: 6130383 (2000-10-01), Lamourelle
patent: 6310298 (2001-10-01), Barrett et al.
patent: 2002/0001874 (2002-01-01), Barrett

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