Electrostatic discharge protection package and method

Details Electrostatic discharge protection package and method Electrostatic discharge protection package and method

1999-02-08

2001-06-12

Leja, Ronald W. (Department: 2836)

Electricity: electrical systems and devices

Discharging or preventing accumulation of electric charge

Specific conduction means or dissipator

C206S710000, C206S719000

Reexamination Certificate

active

06246566

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to packaging technology, and more specifically, to an electrostatic discharge protection package and method.
BACKGROUND OF THE INVENTION
Electrostatic discharge (“ESD”) is the flow of electrostatic charge from a charged object. For example, a capacitor experiences ESD from one capacitor terminal to the other if the accumulated charge, and thus the voltage, across capacitor terminals is sufficiently large.
One source of ESD is, for example, the finger of a human being. As human beings engage in every day activities, electrostatic charge often accumulates in their bodies. This electrostatic charge is discharged from, for example, the finger when the finger contacts another object capable of receiving the charge. ESD can be damaging if the receiving object is circuitry containing minute wires, such as in, for example, VLSI and ULSI circuits. Fortunately, most circuits are protected by packaging and/or computer cases to avoid direct human contact. However, other circuits are not isolated from direct human contact or contact with other objects capable of accumulating electrostatic charge.
Therefore, what is desired is a package and packaging method for ESD protection in circuits that are not isolated from objects capable of accumulating electrostatic charge.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a package includes a substrate. Circuitry sensitive to electrostatic discharge is formed on a device mounted to the substrate. The circuitry may be, for example, VLSI or ULSI circuitry having minute wires that are damaged by even very low currents.
A conductive cover is positioned over the circuitry so that the circuitry is exposed below an opening of the conductive cover. The conductive cover may be, for example, a rectangular metal sheet having a rectangular hole in its center, the rectangular hole positioned above the circuitry. A portion of the conductive cover, such as a bent down corner of the conductive cover, is inserted into a conductive via. In one embodiment, each of the four corners of the rectangular conductive cover is bent down and the tips of the four corners are inserted within a corresponding conductive via.
In a method of fabricating a package, the conductive via is formed by inserting the portion (e.g., the bent down corner prong) of the conductive cover into the upper portion of a hole formed through the substrate. A conductive ball (e.g., a metal solder ball) is formed on the lower portion of the hole. During a subsequent heating step, the conductive material of the conductive ball is drawn up into the hole due to capillary forces, thereby forming the conductive via. The conductive material molds around the bent down corner prong. When the conductive via cools, the conductive material grasps the corner prong, thereby establishing a reliable electrical and mechanical connection between the conductive cover and the conductive via.
As a finger, or other object capable of accumulating electrostatic charge, approaches the circuitry, the finger first contacts the conductive cover, thereby draining the electrostatic charge in the finger. When the finger contacts the circuitry, electrostatic charge does not discharge from the finger into the circuit. Thus, the circuit is protected from electrostatic discharge.
In accordance with another embodiment of the invention, a package includes a substrate. Circuitry is formed on a device which is mounted to the substrate. A cover is positioned with respect to the substrate such that an opening of the cover lies over the circuitry. The cover is composed of a highly resistive material which dissipates (i.e., slowly conducts) the electrical charge it receives through a conductive via and into a charge drain. The cover may be, for example, a dissipative ring deposited around the circuitry and may be composed of an epoxy resin with conductive fillers.
The resistance between the charge drain and a contact surface of the cover for contact with a finger is relatively high (e.g., approximately 1000 ohms). Since the electrostatic charge drains relatively slowly from the cover, induced parasitic currents within the circuitry are relatively low and thus the circuitry is less likely to be damaged by induced parasitic currents.


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