Tin Whisker Testing FAB

Transcription

1 Report Tin Whisker Testing FAB INHALTSVERZEICHNIS 1 INTRODUCTION INEMI TIN WHISKER USER GROUP TEST PROCEDURE INEMI TESTING ACCEPTANCE CRITERIA IMAGES CONCLUSION... 8 Page Created Created by: Released 1 of

2 1 Introduction The European Union s directive, the Reduction on Hazardous Substances (RoHS), sets phase-out dates for the use of lead (Pb) and several other materials used in electronic products in July The rapid transition away from tin lead terminations to materials such as 100% tin has caused concern about the phenomenon of tin whisker growth. Tin whiskers are crystalline structures that can grow from surfaces plated with pure tin. The whiskers are electrically conductive and hence can cause concern over circuits being re-wired from random whisker growth. While tin whiskers are hot topics in the general electronics industry more fundamental research is required to understand them. Today, much mystery enshrouds tin whiskers as it is unknown what mechanisms are required to form a whisker and what mechanisms cause the whiskers to grow. Without such definitive answers no universal solution has been found to guarantee prevention of tin whisker growth. Since no solution is in existence, tests have been designed to accelerate tin whisker growth and hence try and find electronic components that are susceptible to tin whisker growth. One such test procedure is the inemi Tin Whisker Acceptance Test Requirements (JEDEC STANDARD JESD201 and JESD22A121.01). The mentioned document address the requirements for tin whisker mitigation practices and tin whisker testing necessary for user acceptance of pure tin, or high tin content tin alloy finishes over base materials typically used in lead frame type applications. The following report details these tests as were performed on the FAB product family which uses pure tin over nickel plated base material. 2 inemi Tin Whisker User Group Test procedure The following table shows the tests performed on the Fuseholder FAB samples in order to accelerate the growth of tin whiskers. These test conditions represent a minimum set of conditions that shall be used to assess the propensity for tin whisker growth on any given tin finish under study: Flow Thermal Cycling Ambient storage High Temperature/Humidity storage Test Condition cycles, 3 cycles/hr, Min Temp -55 to -40 (+0/-10 ) C, Max Temp +85 (+10/-0 ) C, air to air; 5 to 10 minutes, Inspection intervals 500cycles/1000cycles/1500cycles ±2 C and 60±3% RH, Inspection intervals 1000hrs/2000hrs/3000hrs/4000hrs ±5 C and 87+3/-2% RH, Inspection intervals 1000hrs/2000hrs/3000hrs/4000hrs Preconditioning was used before each test. The preconditioning details were as follows: Item Details Preconditioning Storage at room temperature for 4 weeks Assembly SnPb Solder reflowed at 215 C Assembly Pb-free Solder reflowed at 255 C Once the samples were tested to the above procedure, they were inspected using an optical microscope Leica MZ 16A capable of detecting whiskers with a minimum axial length of 10 microns. Page Created Created by: Released 2 of

3 3 inemi Testing The inspection areas for tin whisker growth of the Fuseholder FAB are outlined below. Tin Surface Type Sn over Ni and brass Type FAB d c e a f b h g 4 Acceptance Criteria Page Created Created by: Released 3 of

4 Test results The following tables outline the results of tin whisker growth on the samples after the three testing conditions. Tin Whisker Inspection after Temperature Cycling Part number Preinspection 500 Temp. Cycling 1000 Temp. Cycling 1500 Temp. Cycling FAB No Whisker No Whisker No Whisker No Whisker Tin Whisker Inspection after Ambient Temperature Humidity Storage Part number Ambient Storage 1000hrs Ambient Storage 2000hrs Ambient Storage 3000hrs Ambient Storage 4000hrs FAB No Whisker No Whisker No Whisker No Whisker Tin Whisker Inspection after High Temperature Humidity Storage Part number FAB High Storage 1000hrs Whisker Area Where No Whisker - High Storage 2000hrs Whisker Area Where No Whisker - High Storage 3000hrs Whisker Area Where No Whisker - High Storage 4000hrs Whisker Area Where No Whisker - 5 Images New State Picture 1: FAB (section b) Picture 2: FAB (section g) Page Created Created by: Released 4 of

5 SCHURTER AG **After 1500 Temperature Cycling test** No Preconditioning Picture 1: FAB (section a) Picture 2: FAB (section b) Precondition: Sn/Pb Solder reflowed at 215 C Picture 3: FAB (section d) Picture 4: FAB (section e) Precondition: Pb-free Solder reflowed at 255 C Picture 5: FAB (section c) Page Created Created by: 5 of SKA Picture 6: FAB (section f) Released Released by: Document No. Index HRÜ _

6 SCHURTER AG ** After 4000hrs Ambient Temperature Humidity Storage** No Precondition Picture 7: FAB (section c) Picture 8: FAB (section h) Precondition: Sn/Pb Solder reflowed at 215 C Picture 9: FAB (section d) Picture 10: FAB (section e) Precondition: Pb-free Solder reflowed at 255 C Picture 11: FAB (section a) Page Created Created by: 6 of SKA Picture 12: FAB (section b) Released Released by: Document No. Index HRÜ _

7 No Precondition **After 4000hrs High Temperature Humidity Storage Test** Picture 13: FAB (section b) Picture 14: FAB (section g) Precondition: Sn/Pb Solder reflowed at 215 C Picture 15: FAB (section e) Picture 16: FAB (section f) Precondition: Pb-free Solder reflowed at 255 C Picture 17: FAB (section e) Picture 18: FAB (section f) Page Created Created by: Released 7 of

8 6 Conclusion The tests where performed on a total number of 81 pieces FAB. We could not find any whisker growth during and at the end of the three test conditions Peter Straub, Manager Circuit Protection Page Created Created by: Released 8 of