1、JEDEC STANDARD Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes JESD201A (Revision of JESD201, March 2006) SEPTEMBER 2008 JEDEC SOLID STATE TECHNOLOGY ASSOCIATION NOTICE JEDEC standards and publications contain material that has been prepared
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10、22201-2107 or call (703) 907-7559 JEDEC Standard No. 201A -i- ENVIRONMENTAL ACCEPTANCE REQUIREMENTS FOR TIN WHISKER SUSCEPTIBILITY OF TIN AND TIN ALLOY SURFACE FINISHES Foreword This standard was generated under the auspices of the JEDEC JC14.3 Subcommittee on Silicon Device Reliability Qualificatio
11、n and Monitoring and the iNEMI Tin Whisker User Group. It is intended to provide a uniform environmental acceptance testing and reporting methodology for tin whisker susceptibility of tin and tin alloy surface finishes used in the Electronics Industry. Introduction Many companies in the electronics
12、industry have adopted tin-based surface finishes as one of the methods to comply with various legislative lead-free (Pb-free) initiatives, e.g., the European Unions RoHS directive. However, tin (Sn) and tin alloy surface finishes may be prone to tin whisker formation with associated possible reliabi
13、lity degradation. Appropriate mitigation practices, as described in JEDEC guidance document JP002, may be incorporated to reduce tin whisker propensity to an acceptable level. Test conditions per JESD22-A121. Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes, and qualifi
14、cation limits presented in this document are based on known Sn-whisker data from around the globe. These test conditions have not been correlated with longer environmental exposures of components in service. Thus, there is at present no way to quantitatively predict whisker lengths over long time pe
15、riods 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 are not fully understood and acceleration factors have not been established. Therefore, the testing described in this document does not gua
16、rantee that whiskers will or will not grow under field life conditions. JEDEC Standard No. 201A Page 1 ENVIRONMENTAL ACCEPTANCE REQUIREMENTS FOR TIN WHISKER SUSCEPTIBILITY OF TIN AND TIN ALLOY SURFACE FINISHES (From JEDEC Board ballot JCB-08-43, formulated under the cognizance of the JC-14.3 Subcomm
17、ittee on Silicon Devices Reliability Qualification and Monitoring.) 1 Scope The methodology described in this document is applicable for environmental acceptance testing of tin based surface finishes and mitigation practices for tin whiskers. This methodology may not be sufficient for applications w
18、ith special requirements, (i.e. military, aerospace, etc.). Additional requirements may be specified in the appropriate requirements (procurement) documentation. This specification is intended for use in conjunction with JESD22A121, This specification does not apply to components with bottom-only te
19、rminations where the full plated surface is wetted during assembly (for example: QFN and BGA components, Flip Chip bump terminations). Adherence to this standard shall include meeting the reporting requirements described in clause 7. 2 Normative reference JESD22-A121 Test Method for Measuring Whiske
20、r Growth on Tin and Tin Alloy Surface Finishes JESD22A104 Temperature Cycling JP002 Current Tin Whisker Theory and Mitigation Practices Guideline 3 Terms and definitions Figure 1 Cross-sectional View of Component Surface Finishes Surface Finish Underplate (if applicable) Base Metal JEDEC Standard No
21、. 201A Page 2 3 Terms and definitions (contd) base metal: Metal alloy residing beneath all surface finish(es) and/or underplate. manufacturing process change acceptance, surface finish: Acceptance testing of a change to a surface finish manufacturing process already accepted by technology acceptance
22、 (q.v.) tests. minimum lead-to-lead gap: The minimum gap between leads (terminals) as shown in Figure 2. Figure 2 Minimum lead-to-lead gap similarity acceptance, surface finish: Acceptance of a change to a surface finish manufacturing process based upon similarity and data available from previous ti
23、n whisker technology and manufacturing process change acceptance (q.v.) tests. surface corrosion: A localized corrosion of the silver-colored tin surface finish appearing in an optical microscope as nonreflective dark spots ranging in size from about 25 micrometers on the longest dimension to the en
24、tire terminal. NOTE While tin oxide is ubiquitous on tin surface finishes, surface corrosion creates a locally thick layer of tin oxide that may span from the substrate to the surface of the deposit at the black spot. Typical photos of termination corrosion are shown in Annex A. technology acceptanc
25、e, surface finish: Acceptance testing of surface finish material set and manufacturing processes that includes a defined set of base metals, underplating metals, surface finish alloy, surface finish bath chemistry, and process flow steps. tin and tin alloy surface finish: Tin-based outer surface fin
26、ish for external component terminations and other exposed metal. tin whisker mitigation practice: The process(es) performed during the manufacture of a component to reduce the propensity for tin whisker growth by minimizing the surface finish internal compressive stress. underplate: Plated layers be
27、tween the base metal and the outer surface finish. whisker: A spontaneous columnar or cylindrical filament, usually of monocrystalline metal, emanating from the surface of a finish. (See JESD22-A121) JEDEC Standard No. 201A Page 3 3 Terms and definitions (contd) whisker length: The straight line dis
28、tance 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 3. Figure 3 Whisker length measurement 4 Test Method for Measuring Tin Whisker Growth Except
29、as specifically noted in this document, the procedures for conducting stress testing and inspections for tin whisker growth in JESD22A121, shall be used as applicable to satisfy this acceptance specification. Where differences with JESD22A121 exist this acceptance document takes precedence. 4.1 Test
30、 Samples In most cases, individual production components shall be used for the acceptance test. However, for some assembled components with internal tin plated surfaces that cannot be inspected optically, e.g., internal surfaces of cans and hybrid component lids, testing and inspection of piece part
31、s may be necessary. In addition, components with tin or tin alloy surface finishes used in press-fit, socketed applications, or with other compressive mechanical connections, should be qualified in their end use configuration. Additional testing and/or specifications may be needed for testing mechan
32、ically loaded components. 4.2 Handling Precaution Careful test sample handling is important in order to avoid possible damage or detachment of whiskers from the test samples. Excessive vibration, impact, or physical contact with the termination finish should be avoided because whiskers may be dislod
33、ged. Test sample contamination as a result of improper handling or as a result of the application of a conductive material for SEM inspection should be avoided if the samples are to be returned to the test condition for further exposure, because such material may impact whisker growth behavior. The
34、procedures outlined in JESD22A121 to limit condensation on the samples should also be followed during elevated temperature-humidity testing since condensation increases the likelihood of surface corrosion. SurfaceWhisker Whisker Length JEDEC Standard No. 201A Page 4 5 Acceptance procedure for Tin an
35、d Tin Alloy surface finishes 5.1 Determination of whether a Technology, Manufacturing Process, or Similarity Acceptance test is required The acceptance requirements for tin and tin alloy finishes depend on the acceptance testing history of the surface finish. For a surface finish without any accepta
36、nce testing history, a rigorous technology acceptance test shall be completed as described in 5.3. If the tin or tin alloy finish has already passed a technology acceptance test, then any change to the manufacturing process or the metallurgy shall be categorized as either a technology change, a manu
37、facturing process change, or a negligible change based on similarity. Table 1 may be used as guidance to differentiate between a technology and a manufacturing process acceptance change. Table 2 shall be used to categorize a change as either a technology change, a manufacturing process change, or a
38、negligible change based on similarity. In addition, Table 2 indicates required testing that is described in detail in Tables 3 and 4 in clause 5. The acceptance procedure for tin and tin alloy surface finishes shall follow the procedural flow outlined in Figure 4. A specific Surface Finish / Mitigat
39、ion process or change will necessitate a Technology or Manufacturing Process Change Acceptance unless the change is covered by Similarity. Annex B shows the typical Technology Acceptance test flow, using minimum sample size, for multi-leaded components using copper alloy leadframe with post bake mit
40、igation technology. JEDEC Standard No. 201A Page 5 5 Acceptance procedure for Tin and Tin Alloy surface finishes (contd) 5.1 Determination of whether a Technology, Manufacturing Process, or Similarity Acceptance test is required (contd) Figure 4 Flowchart to determine whether a Technology Acceptance
41、 Test, a Manufacturing Process Acceptance Test, or no testing is required on the basis of Similarity The acceptance requirements described in this document apply to a specific tin or tin alloy surface finish. The same surface finish may originate from multiple plating lines and be used on multiple c
42、omponent types, as long as the parameters described in Table 1 are the same. For the purposes of this document, a surface finish is defined by the base metal, surface finish composition, surface finish chemistry and manufacturing process, assembly process and component type, and factory or plating p
43、rocess. These categories are listed in the left column of Table 1. Within these categories, there are major parameters called Technology Parameters and minor parameters called Manufacturing Process Parameters that define the tin or tin alloy surface finish. Any new surface finish must be submitted f
44、or a Technology Acceptance Test. In addition, changes to Technology Parameters require a new Technology Acceptance test, and changes to a Manufacturing Process Parameter require a new Manufacturing Process Acceptance test, according to the flowchart in Figure 4. Surface Finish Acceptance/Change Proc
45、edure Acceptance by Similarity Re-evaluate Process / Re-Qual Change Lead Finish / Re-Qual Test Completed / Write Report Test Completed / Write Report Perform Manufacturing Process Acceptance TestingChange to a Manufacturing Process Parameter according to Table 2 Perform Technology Acceptance Testing
46、 New/Change to a Technology Parameter according to Table 2 Yes Yes No No Fail Fail Pass PassJEDEC Standard No. 201A Page 6 5 Acceptance procedure for Tin and Tin Alloy surface finishes (contd) 5.1 Determination of whether a Technology, Manufacturing Process, or Similarity Acceptance test is required
47、 (contd) Table 1 Surface Finish Technology and Manufacturing Process Change Acceptance Parameters Parameter Technology Parameters Manufacturing Process Parameters Base Metal Base Metal Composition Type, e.g., Etched or Stamped Surface Finish Composition Surface Finish Alloy Composition Surface Finis
48、h Thickness Underplate Composition Underplate Thickness Surface Finish Chemistry or Manufacturing Process Surface Finish Plating Process Process Chemistry Underplate Process Underplate Process Chemistry Dip Process Dip Process Chemistry Post Bake Process Parameters Plating Bath Vendor Major Plating
49、Process Control Parameters Minor Plating Process Control Parameters Dip Process Control Parameters Assembly Process and Component Type Lead Forming Process Factory or Plating Process Startup New Factory New Plating Equipment Table 2 lists the Technology and Manufacturing Process Change Acceptance tests required for parameter changes. The details of the tests are described in Table 3 and Tables 4 a-c. Table 2 also defines those changes that are considered negligible and do not require additional testing, according to the flowchart
