"GOLD WHISKERS:  Introducing a New Member to the Family"
Alexander Teverovsky, QSS Group, Inc. at NASA Goddard Space Flight Center
April 2003

During an evaluation of thermally actuated micro-machined relays, Dr. Alexander Teverovsky (QSS Group, Inc. at NASA Goddard) observed Gold Whiskers and micro-crystallites on various gold-plated nickel structures (e.g., contacts, springs, actuators) internal to the relay package. See Dr. Teverovsky's report "GOLD WHISKERS:  Introducing a New Member to the Family" for a discussion of his observations and additional images.

Summary:
During a NASA-sponsored evaluation of commercially available micro-machined relays, internal examination via Scanning Electron Microscopy (SEM) revealed Gold Whiskers on many of the gold-plated surfaces inside of the devices.  In the manufacture of the subject micro-relays, several internal elements were fabricated using a nickel surface micro-machining process, in which high aspect ratio structures (the thickness of nickel is 20 um) were manufactured by electroplating nickel onto lithographically defined copper plating stencils.  Gold was then electroplated over the nickel to a thickness of approximately 2 um.  The tips of the stationary and movable contacts were additionally plated with hard gold to a thickness of ~ 5 um.

Internal examination revealed Gold Whiskers of various size, shape, diameter, and density.  Typical whiskers had lengths of several micrometers and diameters of approximately 200 nm (see Figure 1).  Small, micrometer-sized whiskers with diameters from 100 nm to 400 nm were found in most of the inspected parts (see Figure 2).  Figure 3 illustrates needle-like whiskers with diameters of 100 nm to 200 nm and lengths from 2 um to 4 um.  Large, grass-root-like whiskers, of approximately 10 um in length and ~1 um in diameter, which were observed on several parts, are shown in Figure 4.  Giant, irregularly shaped, toothpaste-like whiskers of more than 20 um in length were observed in two out of 22 inspected parts (see Figure 5).

As is conventional with most kinds of metal whiskers, the reasons and conditions of their growth are NOT CLEAR.  In this specific example microanalysis of the gold plating found the presence of Rubidium (Rb) in areas with high whisker density.  It is possible that Rb may have played an important role in formation of the micro-crystallites and whiskers.  In any case, product designers, part engineers, failure analysts, and quality assurance specialists should be aware of the possibility of formation of whiskers on gold platings.

Additional References: For background information regarding the micro-relays discussed above, consult the following publications.  These references DO NOT discuss the observed gold whiskers since those observations are beyond the scope of the subject papers.

1. A. Teverovsky, A. Sharma, "Analysis of Failure Modes and Mechanisms in Thermally Actuated Micromachined Relays for Harsh Environments Space Applications", Symposium on Design, Test, Integration, and Packaging of MEMS and MOEMS, 2003, Napoule, France
2. A. Teverovsky, A. Sharma, "Reliability Evaluation of Thermally Actuated Micromachined Relays for Space Applications", SPIE: Micromachining and Microfabrication, 2003, San Jose, California USA, p. 12-21.

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