GEIA-GEB-0002-2003 Reducing the Risk of Tin Whisker-Induced Failures in Electronic Equipment《电子设备锡晶风险降低所引发的故障》.pdf

《GEIA-GEB-0002-2003 Reducing the Risk of Tin Whisker-Induced Failures in Electronic Equipment《电子设备锡晶风险降低所引发的故障》.pdf》由会员分享，可在线阅读，更多相关《GEIA-GEB-0002-2003 Reducing the Risk of Tin Whisker-Induced Failures in Electronic Equipment《电子设备锡晶风险降低所引发的故障》.pdf（22页珍藏版）》请在麦多课文档分享上搜索。

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 Reproduced by IHS under license with GEIA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-NOTICE GEIA Engineering Standards and Publications are designed to serve the public interest by eliminating misunderstandings between manufacturers and purchasers, faci

3、litating 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 Publications shall not in any respect preclude any member or nonmember of GEIA from manuf

4、acturing 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 is to be used either domestically or internationally. Standards and Publicati

5、ons 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 to parties adopting the Standard or Publication. Technical Publications are di

6、stinguished 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 formulating committee. This Bulletin is not intended to preclude or discourage othe

7、r 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 committee to be considered for inclusion in future revisions of this publication

8、 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, or for other appropriate reasons. (From Project Number PINS-GEB2, formulated

9、 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 2220 1 All rights reserved Printed in U.S.A. Copyright Government Electronics

10、& Information Technology Association Reproduced by IHS under license with GEIA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-Copyright Government Electronics & Information Technology Association Reproduced by IHS under license with GEIA Not for ResaleNo reproduct

11、ion or networking permitted without license from IHS-,-,-Government 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

12、 Reproduced by IHS under license with GEIA Not for ResaleNo 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 published works, ci

13、ted 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 the many othe

14、rs 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 Mr. Jeff Jarv

15、is 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 Command We wish

16、 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 Reproduced by IHS under license with GEIA Not for ResaleNo reprodu

17、ction 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 converting to lead-free materials. A popular choice for these finishes is tin. Tin finishes can

18、 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 interfere with sensitive optical surfaces or the movement of micro-electromechanical systems (

19、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. missiles and expendables). There is no pending US legislation mandating lead-free electronic

20、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 risk, of tin finish on electronic components will increase because: 1) commercial industry

21、 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 power means that even small whiskers may cause catastrophic failures. Many factors can contr

22、ibute 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 determined. Historically, whiskers have been of greatest risk to space and missile applicatio

23、ns. 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 community may have concerns about whiskers as pure tin plating becomes more common and circui

24、t 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 meant to summarize the literature on tin whisker growths, not mandate a particular risk m

25、itigation strategy. The appropriate actions will depend on the specific application, lifetime, and reliability requirements. II Copyright Government Electronics & Information Technology Association Reproduced by IHS under license with GEIA Not for ResaleNo reproduction or networking permitted withou

26、t license from IHS-,-,-GEIA-GEB-0002 Reducing the Risk of Tin Whisker-Induced Failures in Electronic Equipment CONTENTS . 1 2 Tin Whisker 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-Indu

27、ced Failures 5 . 5 3.1 3.2 Parts and Material Selection Application Specific Risk Assessment 3.2.1 Avoid Using Components with Pure 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 Platin

28、g Process Considerations. . 7 3.3 Material and Assembly Processing . 8 . 8 3.3.1 3.3.2 Avoid Applying Compressive Loads on Plated Surfaces 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 A

29、reas . . 9 Bibliography 11 4 Conclusions iii Copyright Government Electronics & Information Technology Association Reproduced by IHS under license with GEIA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-GEIA-GEB-0002 iv Copyright Government Electronics & Informat

30、ion Technology Association Reproduced by IHS under license with GEIA Not for ResaleNo 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 recommended by government an

31、d 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 electronic assemblies that ha

32、ve 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 cases, these shorts may be

33、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 diameter of the whisker.

34、 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 open, the vaporized tin may

35、 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 vibration. A free floatin

36、g 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 overview of some of the

37、 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 straight or kinked. The surfac

38、e 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 not usually pose a reli

39、ability 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 particular concern because

40、 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: Growth rate of tin whiskers

41、 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 plating thickness may inf

42、luence growth rate. 1 Copyright Government Electronics & Information Technology Association Reproduced by IHS under license with GEIA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-GEIA-GEB-0002 Classic “needle-like“ whisker Kinks and striations Pyramidal shaped w

43、hiskers 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 whisker tip Focused Ion Beam “cross section“ of a tin whisker conformal coat (note the solid, not hollow,

44、 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 Aerospace Corporation) 2 Copyright Government Electronics & Information Technology Association Reproduced by

45、 IHS under license with GEIA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-GEIA-GEB-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.

46、 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 throughout their entire length. 33 Despite some ear

47、ly hypotheses to the contrary, some whiskers have developed cross-sectional areas greater than either the grain size of the original tin or the thickness of the plating. 8 Density of Growths: Although whisker densities up to I 04/cm2 have been observed, this measurement also varies greatly in the li

48、terature. 8 Variation may be due to an inconsistent definition of what length should be counted 30 or to differences in the compressive stresses in the tin or substrate layers 8. Experiments also have recorded changes in whisker density from both radiation 34 and plating thickness 29. Current-Carryi

49、ng Capacity: Under normal atmospheric conditions, the capacity typically measures between 10 and 32 mA. 23,35 However, capacities as high as 75 mA have been observed. 8 The capacity depends on the thickness of the whisker and on the environment. Because air can provide cooling which might lead to higher current capacity, lower current capacity might be