Tin Whisker Mitigation – Corfin Industries Provides the Solution

February 29, 2008

Corfin Industries has been providing lead-free to tin-lead (SnPb) conversion services for several years for L-3, Raytheon, Lockheed, Northrop, BAE, Boeing and other defense, aerospace, medical, and similar high reliability users. For most defense contractors, Corfin Industries is the sole approved source for this service. Their Robotic Hot Solder Dip (RHSD) process has been qualified in a US Navy ManTech project to effectively remove all of the lead-free finish and replace it with Sn63Pb37 alloy to mitigate pure tin whisker risk and inferior solder joint reliability. The TMTI's extensive testing and destructive analysis confirms that damage is not induced by the RHSD process.

Tin Whisker Growth

Tin whiskers erupting from pure tin plated components can and do cause catastrophic failures. A tin whisker is a single crystal that emerges from tin-finished surfaces. It can take hours or years for them to grow, and they can grow up to 9 millimeters in length. Tin whiskers have been blamed for dangerous failures in heart pace makers, satellites, and nuclear power plants. The NASA Tin Whisker Site provides a wealth of information regarding the nature of the tin whiskers.

Generally speaking, the problems caused by tin whiskers fall into three categories:

• Short circuits
• Low pressure arcing
• Debris and contamination

Any of these issues could be a showstopper in electronic assembly. Unfortunately, much of the available electronic component supply is assembled with some degree of pure tin finish, especially on component leads. These leads are extremely vulnerable to tin whiskers and their associated failure mechanisms.

The Solution

What can be done to eliminate the risk of tin whiskering?

Right now, the simplest, most cost effective way to mitigate the danger of tin whiskering is to remove the tin finish; all of it. It has been clearly demonstrated that partial removal of pure tin during the soldering process is not enough. Though, new plating processes have been developed that appear to reduce the risk of tin whisker growth, there is currently no industry-accepted test for determining the propensity of tin whiskers to grow on a tin finished surface. Conformal coating may have future promise, but has not definitively proven effective in preventing whisker growth.

Removal of tin and replacement with tin-lead.

Sounds simple, but can it be done reliably and repeatably?

In 2005, The United States Navy, Raytheon, The University of Maryland, and Corfin Industries teamed up for the year-long, million dollar, Transformational Manufacturing Technology Initiative (TMTI) project to determine if tin mitigation (the removal of pure tin and replacement with tin-lead solder) could be reliably accomplished using Corfin’s precisely controlled, robotic hot solder dipping process.

The team designed an exacting process of computer controlled times and temperatures and precise robotic component positioning to accomplish this task. In short, Corfin’s hot solder dip process successfully removed the problematic tin finish from a wide variety of components and replaced that finish with non-whiskering tin-lead. Reliably and repeatably. All of this was accomplished without damaging sensitive components. To read more about the process, the draft report of that study can be found here TMTI Report

Tight Parameter Controls are the Key

It's important to note that the tight parameter controls provided by the robotic equipment ensure that the tin is fully removed and that the part isn't damaged. Many of Corfin’s current customers have discovered this fact after in-house experiments failed or after experiencing low yields from contract services employing traditional tinning methods. The twenty-three different part types in the TMTI study represent a wide variety of package construction styles: leaded and leadless, plastic, metal, ceramic, glass-sealed, etc. Many other devices, including connectors, axials, and chip components have also been successfully processed through

For more information about Corfin’s Tin Mitigation process or the other component services provided by Corfin, you can contact Liberty ASG or Corfin directly.

Corfin Industries LLC

7B Raymond Avenue

Salem, NH 03079

Tel: 603-893-9900

Fax: 603-893-6800

www.corfin.com

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