Method of making ball grid array package

Details Method of making ball grid array package Method of making ball grid array package

2000-07-06

2002-03-12

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Packaging or treatment of packaged semiconductor

C438S051000

Reexamination Certificate

active

06355499

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to an encapsulating method for use in forming a ball grid array (BGA) package, and more particularly to a molding method for use in forming a BGA package having a cavity down configuration.
2. Description of the Related Art
BGA packages are roughly classified in two types, i.e. “cavity-up” type and “cavity-down” type in view of manner of incorporating a chip. The cavity-down BGA package typically comprises a chip disposed in a cavity formed in a upper surface of a substrate. Bonding pads formed on the active surface of the chip are connected to chip connection pads formed on the upper surface of the substrate around the cavity through a plurality of bonding wires. The upper surface of the substrate is provided with a plurality of solder pads arranged about the periphery of the chip connection pads. The solder pads are electrically connected to the chip connection pads, respectively. Each solder pad has a solder ball mounted thereon for making external electrical connection. The chip, the bonding wires and the cavity of the substrate are encapsulated in a package body. The package body is typically formed by a transfer molding process
FIG. 1
shows a conventional molding device
100
for use in forming a cavity down BGA package. As shown, the molding device
100
mainly comprises a molding die having a runner
110
, a gate
120
and a molding cavity
130
. The runner
110
extends from a pot (not shown) and connects to the molding cavity
130
through the gate
120
. After molding compound is positioned in the pot, the molding die is closed and clamped, and a transfer ram (not shown) is moved down in the pot to compress the molding compound. The molding die and molding compound are pre-heated so that when the transfer ram compresses the molding compound, the liquefied molding compound is forced through the runner
110
and the gate
120
to fill the cavity
130
so as to encapsulate the chip. When the molding compound fills the cavity
130
, the transfer ram stands still for a predetermined time until the molding compound cures. Then the transfer ram is raised, the molding die is opened, and the molded product is removed from the molding die. However, the molding compound not only fills the molding cavity
130
but also fills the gate
120
, the runner
110
and the pot. Typically, this resulted excess molding compound must be removed from the molded product. Therefore, the molding device
100
further comprises a metal shim
140
for separating the excess molding compound from the substrate thereby protecting the substrate from being twisted or damaged during “degating” process, i.e., the removal of the excess molding compound.
FIG. 2
shows another molding device
200
for use in forming a cavity down BGA package. The molding device
200
is characterized by comprising a side gate
150
for separating the excess molding compound from the substrate.
However, one shortcoming of the above conventional molding devices is apparent. Specifically, it is difficult—if not impossible—to automate a molding process using the conventional molding devices described above because the metal shim
140
or side gate
150
can not be simultaneously removed during the degating process. After the excess molding compound is removed, the metal shim
140
or side gate
150
will interfere with automatic ejection of the molded product by moveable pins built in the molding die. Therefore, the metal shim
140
or side gate
150
must be removed manually before ejection of the molded product. This will causes substantial molding down-time and increase the cycle time for the whole process.
Further, the metal shim
140
or side gate
150
may be deformed due to clamping pressure after long term use. This may cause “flash” (i.e. molding material that extends beyond the cavity) thereby adversely affecting the solder joint reliability of the solder pads.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of making a ball grid array package which utilizes a film to separate excess molding compound from the substrate wherein the film is allowed to be simultaneously removed during the degating process thereby automating the molding process.
It is another object of the present invention to provide a method of making a ball grid array package which utilizes a film to reduce the occurrence of flash during molding process.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of making a ball grid array package comprises the steps of: (a) providing a film having an opening defined therein; (b) placing the film on a substrate; (c) attaching a semiconductor chip onto the substrate such that the semiconductor chip is positioned in the opening of the film; (d) electrically coupling the semiconductor chip to the substrate; (e) providing a molding die having a runner, a gate and a molding cavity defined therein, wherein the runner is connected to the molding cavity through the gate; (f) closing and clamping the molding die in a manner that the semiconductor chip is positioned in the molding cavity wherein the edges of the molding cavity fit entirely within the opening of the film and the edges of the runners and the gates are entirely positioned against the film; (g) transferring a hardenable molding compound into the molding cavity; (h) hardening the molding compound; (i) unclamping and opening the molding die; and (j) simultaneously removing the film and degating.
The film in accordance with the present invention is characterized in that the adhesive force between the film and the molding compound is greater than the adhesive force between the film and the substrate. This makes the film tend to adhere to the excess molding compound; hence, the film will be removed along with the excess molding compound during the step (j) thereby automating the molding process. Further, the film can be a disposable film; hence, the deformation problem due to repeating use can be avoided. Therefore, the flash problem can be significantly reduced by using a new film for each molding operation.


REFERENCES:
patent: 5532513 (1996-07-01), Smith et al.
patent: 5796038 (1998-08-01), Manteghi
patent: 5961912 (1999-10-01), Huang et al.

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