JEDEC JESD22-A121A-2008 Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes.pdf

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1、JEDEC STANDARD Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes JESD22-A121A (Revision of JESD22-A121.01, December 2005) JULY 2008 (Reaffirmed: MAY 2014) JEDEC SOLID STATE TECHNOLOGY ASSOCIATION NOTICE JEDEC standards and publications contain material that has been prep

2、ared, reviewed, and approved through the JEDEC Board of Directors level and subsequently reviewed and approved by the JEDEC legal counsel. JEDEC standards and publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitati

3、ng interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for use by those other than JEDEC members, whether the standard is to be used either domestically or internationally. JEDEC standards and publications are a

4、dopted without regard to whether or not their adoption may involve patents or articles, materials, or processes. By such action JEDEC does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the JEDEC standards or publications. The information

5、 included in JEDEC standards and publications represents a sound approach to product specification and application, principally from the solid state device manufacturer viewpoint. Within the JEDEC organization there are procedures whereby a JEDEC standard or publication may be further processed and

6、ultimately become an ANSI standard. No claims to be in conformance with this standard may be made unless all requirements stated in the standard are met. Inquiries, comments, and suggestions relative to the content of this JEDEC standard or publication should be addressed to JEDEC at the address bel

7、ow, or refer to www.jedec.org under Standards and Documents for alternative contact information. Published by JEDEC Solid State Technology Association 2012 3103 North 10th Street Suite 240 South Arlington, VA 22201-2107 This document may be downloaded free of charge; however JEDEC retains the copyri

8、ght on this material. By downloading this file the individual agrees not to charge for or resell the resulting material. PRICE: Contact JEDEC Printed in the U.S.A. All rights reserved PLEASE! DONT VIOLATE THE LAW! This document is copyrighted by JEDEC and may not be reproduced without permission. Fo

9、r information, contact: JEDEC Solid State Technology Association 3103 North 10th Street Suite 240 South Arlington, VA 22201-2107 or refer to www.jedec.org under Standards-Documents/Copyright Information. JEDEC Standard No. 22-A121A -i- Test method A121A (Revision of A121.01) TEST METHOD A121 Test Me

10、thod For Measuring Whisker Growth On Tin And Tin Alloy Surface Finishes Disclaimer This document is not a qualification standard. It contains a suite of recommended tin whisker growth tests. If these common tests are adopted, then the industry can collect common and comparable data that may improve

11、the understanding of the fundamentals of whisker growth and allows comparisons between technologies. Tests in this document may be changed in the future as a better understanding of the mechanisms causing tin whisker growth is developed. Based on a variety of testing and data review from around the

12、globe, three test conditions have been identified that appear to be suitable for monitoring tin whisker growth. The three test conditions include two isothermal conditions with controlled humidity and a thermal cycling condition. However, these test conditions have not been correlated with longer en

13、vironmental exposures of components in service. Thus, there is at present no way to quantitatively predict whisker lengths over long time periods based on the lengths measured in the short-term tests described in this document. At the time of writing, the fundamental mechanisms of tin whisker growth

14、 are not fully understood and acceleration factors have not been established. However until such time that acceleration factors are determined all acceptance requirements for commercial tin finishes are provided in JEDEC standard JESD201. Certain applications, e.g., military or aerospace, may requir

15、e additional and/or different tin whisker tests or evaluations. Introduction The predominant terminal finishes on electronic components have been Sn-Pb alloys. As the industry moves toward Pb-free components and assembly processes, the predominant terminal finish materials will be pure Sn and alloys

16、 of Sn, including Sn-Bi and Sn-Ag. Pure Sn and Sn-based alloy electrodeposits and solder-dipped finishes may grow tin whiskers, which could electrically short across component terminals or break off the component and degrade the performance of electrical or mechanical parts. JEDEC Standard No. 22-A1

17、21A Test method A121A -ii- (Revision of A121.01) JEDEC Standard No. 22-A121A Page 1 Test method A121A (Revision of A121.01) TEST METHOD A121 Test Method For Measuring Whisker Growth On Tin And Tin Alloy Surface Finishes (From JEDEC Board ballot JCB-08-42, formulated under the cognizance of the JC-14

18、.1 Subcommittee on Reliability Test Methods for Packaged Devices.) 1 Scope The methodology presented in this document, see Annex A for process flow, is applicable for studying tin whisker growth from finishes containing a predominance of tin (Sn). This test method may not be sufficient for applicati

19、ons with special requirements, e.g., military or aerospace. Additional requirements may be specified in the appropriate requirements document. The purpose of this standard is to: Provide an industry-standardized suite of tests for measurement and comparison of whisker propensity for different platin

20、g or finish chemistries and processes. Provide a consistent inspection protocol for tin whisker examination. Provide a standard reporting format. 2 Normative references JESD22-A104, Standard for Temperature Cycling IPC 7530, Guidelines for Temperature Profiling for Mass Soldering (Reflow they can be

21、 kinked, bent, or twisted; they usually have a uniform cross-sectional shape; they typically consist of a single columnar filament that rarely branches; they may have striations along the length of the column and/or rings around the circumference of the column; they have lengths of 10 micrometers or

22、 greater; features shorter than 10 micrometers may be deemed important for research but are not considered significant in JESD22-A121A. NOTE 2 Whiskers are not to be confused with dendrites: fern-like growths on the surface of a material, which can be formed as a result of electrochemical migration

23、of an ionic species or produced during solidification. 3.3 whisker density: The number of whiskers per unit area on a single lead or coupon area. 3.4 whisker growth: Measurable changes in whisker length and/or whisker density after exposure to a whisker test condition for a certain duration or numbe

24、r of cycles. 3.5 whisker length: The straight line distance from the point of emergence of the whisker to the most distant point on the whisker (i.e., the radius of a sphere containing the whisker with its center located at the point of emergence), see Figure 5 3.6 whisker test coupon: A piece of me

25、tal of specified size and shape that is plated or dipped with a tin finish for the purpose of measuring the propensity for whisker formation and growth. 4 Apparatus 4.1 Temperature cycling chambers Air to air temperature cycling chamber(s), capable of cycling from -55(+0/-10) C to +85(+10/-0) C or f

26、rom -40(+0/-10) C to +85(+10/-0) C. The temperature cycling chamber(s) must be able to satisfy the cycle conditions defined in Table 4. JEDEC Standard No. 22-A121A Page 3 Test method A121A (Revision of A121.01) 4 Apparatus (contd) 4.2 Temperature humidity chambers Temperaturehumidity (T therefore, i

27、t is recommended that the test samples be sufficiently shielded from any condensed water that may drip from the chamber ceiling and/or walls onto the samples. NOTE 3 When loading the test samples into the T refer to B.2, Note 1. Preferably, at least one sample will have a high density of whiskers an

28、d at least one sample will have a low density of whiskers, according to Table 5. The six samples can be six separate terminations on one electronic component, six separate terminations from multiple different electronic components, or can be six different areas on one or more coupons. The samples us

29、ed for validating whisker density measurement capability can be the same as those used for the whisker length measurement capability, B.2. For each sample, the number of whiskers greater than 10 microns in length shall be measured with both systems within the same viewing area. The optical system pa

30、sses if the following criterion is met: 1) The whisker density measured with the optical system is within 20% of that measured with an SEM. The measurements taken to validate the optical system and the results of the validation process should be documented for reference. JEDEC Standard No. 22-A121A

31、Page 18 Test method A121A (Revision of A121.01) Annex C Tin Whisker Images A collection of scanning electron microscope images are presented in the annex that exemplifies the appearance of tin whiskers. Tin whisker filaments. Whisker with a consistent cross section. Whisker initiating from a hillock

32、. Branched tin whiskers on bright tin (rare). Kinked whisker. Kinked whiskers growing from a nodule.JEDEC Standard No. 22-A121A Page 19 Test method A121A (Revision of A121.01) Annex C Tin Whisker Images (contd) Tin whisker filament with striations. Tin whisker filament with striations. Kinked whiske

33、r on odd-shaped eruptions. Tin whisker with rings. JEDEC Standard No. 22-A121A Page 20 Test method A121A (Revision of A121.01) Annex D Non-Whisker Surface Formations A collection of images is presented, exemplifying formations that may occur on a tin plated surface that are not considered whiskers f

34、or the purpose of this test method. These surface formations include dendrites, hillocks, and flowers. Dendrites are fern-like growths formed for example as a result of solidification. They are not whiskers. Hillocks may be precursors to whiskers in some cases, but are not considered whiskers for th

35、e purpose of this test method. Dendrites formed on a tin surface during plating. These are not tin whiskers. “Flower” created on a tin plating exposed to the test condition of high-temperature humidity storage and is most likely a result of a combination of surface contamination and condensation. JE

36、DEC Standard No. 22-A121A Page 21 Test method A121A (Revision of A121.01) Annex E Tin Whisker Test Standard Report Formats Table E.1 General Information (Add columns as needed) Basic Information: Sample ID Sample ID Date of Inspection Test Condition Cumulative exposure time (hours) or # of cycles at

37、 read point Observations: Type of whisker (kinked, straight, branched) Length of longest whisker (microns) Whisker density (Low, Medium, High per inspected area) Additional Comments / Exceptions Substrate: Type (e.g., package, coupon, chip) Substrate material (e.g., Cu, CuFe2, Alloy 42) Forming oper

38、ation (e.g., etched, stamped) Post finish treatment (none, reflow C, anneal time & temp, etc.) Time between pre and post-finish treatment (anneal, reflow, etc.) Time between finish application and initiation of environmental aging Underplating: Underplate date Underplate material (e.g., Ni, Ag, etc.

39、) Bath type (e.g., sulfamate) Underplate type (bright, matte, satin) Underplate thickness (microns) Tin Finish: Finish application date Alloy Type (e.g., tin, tin-bismuth) If an alloy of tin is used, alloy content range (e.g., 1-3%) Bath type (Methane sulfonic acid, mixed acid, etc) Finish type (bri

40、ght, matte, satin) Finish thickness (microns) Finish grain size (microns) 1Current density (Amps/ dm) Carbon content in the deposit 2* Impurity content in the plating bath, Cu * Impurity content in the plating bath, Zn * Impurity content in the plating bath, Fe * Impurity content in the plating bath

41、, Ag * Impurity content in the plating bath, Pb * Impurity content in the plating bath, Ni * Impurity content should be measured in the plating bath. These fields are not required, but are recommended to be reported. 1 Can be measured on the surface of the deposit. The test method should be disclose

42、d. The ASTM method E112 is recommended. 2 Carbon content may be measured on a separate coupon sample provided that the plating conditions are similar to the conditions used for creating whisker test samples. The test method should be disclosed.JEDEC Standard No. 22-A121A Page 22 Test method A121A (R

43、evision of A121.01) Annex E Tin Whisker Test Standard Report Formats (contd) Table E.2 Detailed Whisker Information Screening observations: Sample Info Features (e.g., corrosion, scratches, clamp marks, etc.) Number of samples inspected Number of terminations or coupon areas inspected per sample Tot

44、al number of terminations or coupon areas inspected Total area inspected Number of terminations or coupon areas with whiskers Detailed observations: Number of samples inspected Total number of terminations or coupon areas inspected Whisker density (Low, Medium, High per inspected area) Length of lon

45、gest whisker (microns) termination or coupon area 1 Length of longest whisker (microns) termination or coupon area 2 Length of longest whisker (microns) termination or coupon area 3 Length of longest whisker (microns) termination or coupon area 4 Length of longest whisker (microns) termination or co

46、upon area 5 Length of longest whisker (microns) termination or coupon area 6 Length of longest whisker (microns) termination or coupon area 7 Length of longest whisker (microns) termination or coupon area 8 Length of longest whisker (microns) termination or coupon area 9 Length of longest whisker (m

47、icrons) termination or coupon area 10 Length of longest whisker (microns) termination or coupon area 11 Length of longest whisker (microns) termination or coupon area 12 Length of longest whisker (microns) termination or coupon area 13 Length of longest whisker (microns) termination or coupon area 1

48、4 Length of longest whisker (microns) termination or coupon area 15 Length of longest whisker (microns) termination or coupon area 16 Length of longest whisker (microns) termination or coupon area 17 Length of longest whisker (microns) termination or coupon area 18 Additional Comments: Additional Co

49、mments / Exceptions: JEDEC Standard No. 22-A121A Page 23 Test method A121A (Revision of A121.01) Annex F Examples of Whiskers in Areas of Corrosion Corroded Area Whisker Corroded Area Whisker JEDEC Standard No. 22-A121A Page 24 Test method A121A (Revision of A121.01) Annex G (informative) Differences between JESD22-A121A and JESD22-A121.01 The following list briefly describes most of the changes made to the entries that appear in this publication, JESD22-A121A, compared