Technetters,

I am interested in any comments about the following abstract of a report
presented
Oct. '99 at the Electrochemical Society meeting in Honolulu by Bell
Labs.

D. A. Douthit

--------------------

Corrosion Induced Electrostatic Damage Potential

John P. Franey
Lucent Technologies Bell Labs

Room 1B301
600 Mountain Ave.
Murray Hill, NJ 07974

Historically, the corrosion of electronic materials has been concerned
with
the aspects of solderability, loss of low resistance surfaces, and
galvanic
corrosion of plated /layered metal structures. This paper describes a
degradation of electronic functionality that takes place prior to the
traditional corrosion initialization levels. Electrostatic damage (ESD)
occurs when a static charge, which is generated on a material raises
it's
potential high enough to breach the insulation resistance of a nearby
grounded conductor. These conductors can be for example, connected to an

input line on a sensitive integrated circuit, or a more robust print or
feed
through on a circuit board. The potentials can range from 20 to 30,000
volts.

The component damage occurs when the discharge of this charged material
creates a current flow (in amperes of electrons) through a conductor
interface to ground. The energy of this discharge can cause complete or
partial evaporation of a conductor. When the complete evaporation of a
pathway occurs a failure is noted in initial testing. If the evaporation

of an electron path is partial the component may pass testing and be
incorporated in apparatus. Failure may occur prematurely at a future
date.

The measure of energy dissipated in a path is calculated by the formula
I 2
R (where I is electron current flow density in Amperes and R is
resistance
of the pathway in Ohms) the predominant factor in total energy (heat)
dissipated by the pathway is the current density. A corrosion product on
a
conductors surface elevates the Electro Static damage potential in two
distinct modes.

Increasing the surface resistance of a metal increases the surface
insulation capacity. Corrosion products interrupt the low resistance
skin of
the metallic conductor. The surface resistance of a metal approaches or
is
equal to the bulk resistance of that material. As corrosion products
form on
the surface of this metal the surface resistance increases. Typically
the
measurement to indicate a corrosion process has initiated are in the
range
of micro ohms. Some advanced techniques indicate pico ohms. However,
prior
to the increase in surface resistance an increase in insulation capacity

takes place. Taking copper as an example. Copper oxide and copper
sulfide
have dielectric constant s many times that of air. As a charged object
increases
it's potential an arc will occur through a grounded part of the
sensitive
circuit. As the corrosion product increases so does the insulation
capacity
of the metal surface, and the arc over potential. If a discharge occurs
at a
lower potential less damage is done. A corroded surface arcs at a higher

potential, the potential for damage increases with corrosion product.

Another aspect of Ohms law shows that w=E/I where E is the arc
potential.
Given that watts dissipated is the square of I as E increases with R the

damage increases by the square of I. This formula indicates that if the
corrosion growth is linear the damage will follow an exponential curve.

The second mode of failure is from a discontinuous surface skin.
Electrostatic damage radiates a signature wave in the range of 1 to 2
gigahertz. These microwaves of energy travel on the surface of
conductors due to the skin effect of AC waves. Corrosion products
disrupt these waves from
traveling to ground . When this occurs the disruption site will
retransmit
the energy on a different plain and will cause spurious noise emissions.

These emissions cause functional failures of digital electronic systems.

Lock ups are common and difficult to find because of the transient
nature
of the discharge phenomena.

Corrosion products can amplify the ESD noise problem by changing the
impedance of a properly ESD protected circuit. In many cases
electrostatic
damage will change the impedance (Q) of a circuit. This detuning may
force
an ESD generated wave to take a different path to ground than originally

engineered. This aberration in performance can be directly attributed to

corrosion.

In summary: As electronic components use less material, become more
sensitive to voltage and current variations, and increase their
operational
speed, corrosion can take on a myriad of new consequences. These new
phenomena can be caused by fractions of what have in the noise type
measurements in the past.

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