A Closer Look at Utilizing Tungsten Wire for Probes

August 20, 2015 Joshua Jablons Ph.D.

Why Tungsten Works for Probing Applications That Require Wire That Is Straight as an Arrow

Probing is a broad industry with many types of applications, but two that have proven to be ideal for tungsten wire are probes used for semiconductor wafer testing and neural activity testing. What properties of tungsten wire make it a great material for these probing applications?

For the purpose of probe blanks, straightness is a key property — and here, the mechanical properties of tungsten give it remarkable stiffness even at small diameters. That neatly sums up the benefits of tungsten wire for both semiconductor and neural testing probes — applications that seems almost counterintuitive for tungsten because it is not a highly conductive material. Yet, for these applications, tungsten wire simply works.

Cantilever Probes: A Chip Off the Old Integrated Circuit Wafer

In the process of fabricating semiconductor devices, there is no better time to test an integrated circuit than when it is on the sliced monocrystalline silicon wafer, before it is sliced, diced, and packaged — and before the costs associated with those activities are incurred. Here, the array of repeating chips on the wafer is aligned and exposed to electrical testing via contact pads and cantilever probes, to quickly identify any chips that are flawed. Non-passing circuits are typically marked with a small dot of ink in the middle of the die, and only the good, unmarked chips are sent on for further die preparation and dicing.

The use of cantilever probing has benefitted from the stiffness of both tungsten wire and rhenium tungsten wire. Newer methods, such as cobra probing and powder deposition, offer finer pitch than cantilever probes; however, the use of cantilever probing has never gone away and remains viable. Tungsten and rhenium tungsten wires still form the backbone of cantilever probing because the mechanical properties of these materials enable them to maintain their exact position even with remarkably densely pitched circuit arrays.

Additionally, other benefits of tungsten wire — including the ability to allow the shaping of the needle point on the cantilever, to take and hold a form, and to resist contact patch oxide buildup — make it a great material for checking the integrity of integrated circuits.

Neural Probes: Who Knew Tungsten Wire Could Be So Stimulating?

We talked previously about the value of tungsten wire in medical device applications where electric current is utilized and precision is critical. As the ability to go deeper into the human body has increased, so too has the ability to go deeper into the human brain — and it is here where another important application for tungsten wire is probes for testing neural activity.

Part of the success of tungsten wire in this application is due to the ability to go to exact spots within the brain tissue without causing collateral damage. This is very much a function of the fact that tungsten wire probes can be made so thin while maintaining their straightness and shape — characteristics that are vital for directional accuracy. For the purpose of probing to find causal areas for medical conditions, as well as for deep brain stimulation (DBS) treatment of conditions such as Parkinson’s disease, the ability to target a very specific area of the brain is crucial.

What’s Next?

With all of its interesting properties, it’s no wonder that tungsten wire is used in a growing range of applications in both electronics and medicine, as well as in general industry. Experienced providers of tungsten wire — such as Metal Cutting Corporation, which has been in the specialty tungsten products business since 1967 and is the exclusive North American distributor for Nippon Tungsten Co., Ltd. — can help you decide whether tungsten wire is right for your application.


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