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1、GEIA ENGINEERING BULLETIN Reducing the Risk of Tin Whisker- Induced Failures in Electronic Equipment GEIA-GEB-0002 NOVEMBER 2003 GOVERNMENT ELECTRONICS AND INFORMATION TECHNOLOGY ASSOCIATION A Sector of the Electronic Industries Allianc Copyright Government Electronics & Information Technology Assoc
2、iation Provided by IHS under license with GEIA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without license from IHS -,-,- NOTICE GEIA Engineering Standards and Publications are designed to serve the public intere
3、st by eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchasers in selecting and obtaining with minimum delay the proper product for their particular needs. Existence of such Standards and Publication
4、s shall not in any respect preclude any member or nonmember of GEIA from manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of such Standards and Publications preclude their voluntary use by those other than GEIA members, whether the standard
5、 is to be used either domestically or internationally. Standards and Publications are adopted by GEIA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, GEIA does not assume any liability to any patent owner, nor does it assume any obligation whatever
6、to parties adopting the Standard or Publication. Technical Publications are distinguished from GEIA Standards in that they contain a compilation of engineering data or information useful to the technical community and represent approaches to good engineering practices that are suggested by the formu
7、lating committee. This Bulletin is not intended to preclude or discourage other approaches that similarly represent good engineering practice, or that may be acceptable to, or have been accepted by, appropriate bodies. Parties who wish to bring other approaches to the attention of the formulating co
8、mmittee to be considered for inclusion in future revisions of this publication are encouraged to do so. It is the intention of the formulating committee to revise and update this publication from time to time as may be occasioned by changes in technology, industry practice, or government regulations
9、, or for other appropriate reasons. (From Project Number PINS-GEB2, formulated under the cognizance of the GEIA G-12 Solid State Devices Committee) Published by O 2003 Government Electronics and Information Technology Association Standards & Technology Department 2500 Wilson Boulevard Arlington, VA
10、2220 1 All rights reserved Printed in U.S.A. Copyright Government Electronics & Information Technology Association Provided by IHS under license with GEIA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without licen
11、se from IHS -,-,- Copyright Government Electronics & Information Technology Association Provided by IHS under license with GEIA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without license from IHS -,-,- Governmen
12、t Revision I Description of change Elect ron i cs an d I n fo rma t io n Tech no logy (GEIA) Date Asso ci at i on Manual of Organization and Procedure G EIA-OP-0001 Copyright Government Electronics & Information Technology Association Provided by IHS under license with GEIA Licensee=IHS Employees/11
13、11111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without license from IHS -,-,- GEIA-GEB-0002 ACKNOWLEDGMENT The GEIA G-12 Solid State Devices Committee acknowledges the significant contributions of the authors and organizations whose publish
14、ed works, cited in the bibliography, provided the foundation for this document. Members of Task Group GO202 of the GEIA G-12 Solid State Devices Committee developed this document. The Task Group and Committee would like to recognize the principle contributors shown below and to extend gratitude to t
15、he many others who assisted in the evolution of this Bulletin. Mr. Gary Ewell Mr. Henry Livingston Mr. William Dieffenbacher Ms. Anduin Touw Mr. Jan Bunting Mr. Michael Cooper Ms. Dottie Fields Mr. Kent Walters Mr. James Moffett Mr. Jay Brusse Mr. Michael Sampson Mr. David Hillman Mr. John Nirschl M
16、r. Jeff Jarvis Aerospace Corporation BAE SYSTEMS BAE SYSTEMS Boeing Satellite Systems General Dynamics General Dynamics Microsemi Corp. Microsemi Corp. Northrop Grumman Mission Systems QSS Group, Inc. NASA Goddard Space Flight Center Rockwell Collins Rockwell Collins US Army Aviation and Missile Com
17、mand We wish to express our sincere appreciation to the NASA Goddard Space Flight Center Tin Whisker Investigation Team for their significant contributions to this Bulletin. I Copyright Government Electronics & Information Technology Association Provided by IHS under license with GEIA Licensee=IHS E
18、mployees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without license from IHS -,-,- GEIA-GEB-0002 Introduction As a result of world-wide consumer electronics demand for lead-free products, component manufacturers are increasingly conve
19、rting to lead-free materials. A popular choice for these finishes is tin. Tin finishes can be susceptible to the spontaneous growth of single crystal structures known as “tin whiskers”which can cause electrical failures, ranging from parametric deviations to catastrophic short circuits, and may inte
20、rfere with sensitive optical surfaces or the movement of micro-electromechanical systems (MEMS). Though studied and reported for decades, tin whiskers remain a potential reliability hazard, particularly for space applications and for equipment subjected to long term dormant storage and use (e.9. mis
21、siles and expendables). There is no pending US legislation mandating lead-free electronic products, and should such legislation arise, military, aerospace and medical equipment manufacturers would likely be exempt. Nevertheless, Department of Defense and NASA believe that the use, and therefore the
22、risk, of tin finish on electronic components will increase because: 1) commercial industry have stated initiatives to eliminate lead (Pb) from electronics, 2) defense and aerospace industry trends show increasing usage of commercial components, and 3) continuing reductions in circuit geometry and po
23、wer means that even small whiskers may cause catastrophic failures. Many factors can contribute to whisker formation, and their relative importance have not been determined. The quantitative risks of whiskers under various sets of material, manufacturing, and application conditions have not been det
24、ermined. Historically, whiskers have been of greatest risk to space and missile applications. This may be explained in part by: the longer lifetimes, the more destructive effects in low-pressure environments, and higher reliability requirements. However, it is felt by this committee that a wider com
25、munity may have concerns about whiskers as pure tin plating becomes more common and circuit geometries become smaller. This Bulletin includes various findings of government and industry experts regarding characteristics of tin whiskers and methods to mitigate future risks associated with them. It is
26、 meant to summarize the literature on tin whisker growths, not mandate a particular risk mitigation strategy. The appropriate actions will depend on the specific application, lifetime, and reliability requirements. II Copyright Government Electronics & Information Technology Association Provided by
27、IHS under license with GEIA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without license from IHS -,-,- GEIA-GEB-0002 Reducing the Risk of Tin Whisker-Induced Failures in Electronic Equipment CONTENTS . 1 2 Tin Wh
28、isker Formation . 1 2.1 2.2 Tin Whisker Growth Mechanisms 2.3 Environmental Factors . 4 Common Tin Whisker Attributes . 3 Methods to Reduce the Risk of Tin Whisker-Induced Failures 5 . 5 3.1 3.2 Parts and Material Selection Application Specific Risk Assessment 3.2.1 Avoid Using Components with Pure
29、Tin Finishes If Possible 5 3.2.2 Physical Barriers 6 Choice of Underplating or Substrate Material Select a Matte or Low Stress Tin Finish . . 7 3.2.3 3.2.4 3.2.5 Plating Process Considerations. . 7 3.3 Material and Assembly Processing . 8 . 8 3.3.1 3.3.2 Avoid Applying Compressive Loads on Plated Su
30、rfaces Conformal Coat or Foam Encapsulation Over Whisker Prone Surfaces 3.3.3 Heat treatments 9 3.3.4 Solder Dip Tin-finished Surfaces . 9 3.3.5 Replate Whisker Prone Areas . . 9 Bibliography 11 4 Conclusions iii Copyright Government Electronics & Information Technology Association Provided by IHS u
31、nder license with GEIA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without license from IHS -,-,- GEIA-GEB-0002 iv Copyright Government Electronics & Information Technology Association Provided by IHS under licen
32、se with GEIA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without license from IHS -,-,- GEIA-GEB-0002 1 Scope This Bulletin provides a brief description of tin whisker formation and describes various methods reco
33、mmended by government and industry to reduce the risk of tin whisker-induced failures in electronic hardware. It is not a mandate nor does it contain any requirements. A tin whisker is a single crystal that emerges from tin-finished surfaces. Tin whiskers can pose a serious reliability risk to elect
34、ronic assemblies that have pure tin finish. The general risks fall into several categories: I, 2, 3, 8, 161 Short Circuits: The whisker can create a short circuit, either by 1) growing from an area at one potential to an area at another or 2) breaking free and later bridging these areas. In some cas
35、es, these shorts may be permanent and cause catastrophic system failures. A transient short may result if the available current exceeds the fusing current of the whisker, and the whisker can fuse open. The amount of current needed to fuse open the whisker depends on the atmospheric pressure and the
36、diameter of the whisker. Low-pressure-lnduced Mefa/ Vapor Arcing (Plasma): In low-pressure environments, even a transient short can result in a catastrophic failure. Under certain current and voltage conditions (current more than a few amps and supply voltage over 12 V), when a tin whisker fuses ope
37、n, the vaporized tin may initiate arcing or a plasma. The plasma can conduct over 200 A and may continue until all the available exposed tin is consumed or the supply current is interrupted. I, 81 DebrislConfaminafion: The tin whiskers small diameter may allow it break free under handling or other v
38、ibration. A free floating whisker may cause the same problems typically associated with free floating particles, .e., interfering with the movement of mechanical parts or contaminating optical surfaces. I, 81 Tin Whisker Formation 2.1 Common Tin Whisker Attributes The following paragraphs provide an
39、 overview of some of the observed characteristics of tin whiskers. These features are discussed in more detail in the following references:l, 2, 3, 8, 9, 16, 19, 20, 23, 25, 27, 28, 30, 33, 351 Shapes & Surface Features: True whiskers are cylindrical, needle-like crystals that can grow either straig
40、ht or kinked. The surface is usually striated longitudinally. Whiskers may grow directly out of the surface or from pyramid-shaped nodules on the surface. Nodules, which may grow tens of microns in length, may also appear without whiskers. Because of their shorter length and larger diameter, they do
41、 not usually pose a reliability risk in and of themselves. (See Figure 1 for examples) Incubation (Dormancy) Period: Experimenters report an incubation period ranging from days to years before whiskers appear. This period is likely related to the amount of compressive stress. 27 This period is of pa
42、rticular concern because experiments to determine the propensity for a particular process to form whiskers may need to span very long periods of time. This property also complicates decisions about whether applications with short storage and usage lives are at risk for tin whiskers. Growth Rate: Gro
43、wth rate of tin whiskers is also variable: rates from 0.03 to 9 mm/yr have been reported. Some experiments also document non-linear growth rates and times when the growth has stopped all together. 27, 30, 331 Interrelated factors such as substrate materials, grain structure, plating chemistry, and p
44、lating thickness may influence growth rate. 1 Copyright Government Electronics & Information Technology Association Provided by IHS under license with GEIA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without lice
45、nse from IHS -,-,- GEIA-GEB-0002 Classic “needle-like“ whisker Kinks and striations Pyramidal shaped whiskers Nodules Nodules originating along a Whisker growing from a nodule (note how it appears to originate from amechanically induced surface scratch very fine surface scratch) Irregular shaped whi
46、sker tip Focused Ion Beam “cross section“ of a tin whisker conformal coat (note the solid, not hollow, structure and stnations) Whisker nodules beneath (growing preferentially along the line of a surface defect) Figure 1 -Whisker Shapes SI (Photographic images courtesy of NASA Goddard and The Aerosp
47、ace Corporation) 2 Copyright Government Electronics & Information Technology Association Provided by IHS under license with GEIA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/31/2007 00:05:39 MDTNo reproduction or networking permitted without license from IHS -,-,- GEIA-GEB
48、-0002 Whisker Length: Tin whisker length obviously depends on growth rate and sustained periods of growth. However, in experimental results, most measure between 0.5 mm and 5.0 mm. The longest reported length is 10 mm. 8, 231 Whisker Diameter: Whiskers are typically very thin with diameters between 1 and 5 microns 8, 301, yet diameters between 0.006 pm and 7 pm have been recorded. 33 Whiskers are not always the same diameter througho