1 Best Practice Guide Use of XRF in Electronics Manufacture Christopher Hunt

2 XRF in Electronics Manufacture  XRF systems are excellent tools for screening electronics components  ROSH  Sn whisker mitigation  Compared to chemical analysis  Lower unit cost  Lower running cost  Faster results  Smaller sample size  Semi-skilled operation

3 Tin Whisker Mitigation  RoHS has resulted in many SnPb terminated components changing to pure Sn plated finishes  To inhibit Sn coatings from whiskering, they need to contain at least 3% Pb  As manufactured  After soldering

4 NPL Project Partners  Alcatel Alenia Space Italia  EADS Astrium  Fischer Instrumentation (GB) Ltd.  MBDA (UK) Ltd  Niton  Oxford Instruments Analytical  Research in Motion  RMD Instruments  Roentgenanalytik  Rolls Royce Marine  RS Components Ltd  Tin Technology

5 Instrumentation  PIN/SiLi systems suitable for  RoHS compliance  Sn whisker mitigation  Proportional counters  Some systems may be suitable for Sn whisker mitigation  For analysis of new components, systems require semi-skilled operator with knowledge of materials (typical compositions)

6 Instrument Types  Total of 15 XRF systems  11 Bench-tops  8xPIN  1xSiLi  3xProportional Counters)  4 Portables (PIN) (1xCo57 source)  12 Partners, 11 different systems

7 Instrument Types  Sources  Portable  Approx. 40kV, 10uA  Isotope  Benchtop  Approx. 50kV, 1000uA  Detectors  Proportional (resolution ~1000eV)  Pin diode (resolution ~250eV)  Si(Li) diode (resolution ~140eV)

8 Spectra

9 Typical Spot Sizes and Test Times

10 Round Robin Samples  9 Plastics samples with either Pb, Cd, Hg  Cr passivated Zn plated screw, poss Cr 6+  Sn contaminated with lead from 50 -> 20000ppm Pb  SOIC solder joints from NPL test boards  0,1,2,5,8% Pb in SAC joints from a manufactured PCB  BGA, SnPb and LF, looking thru component and PCB  Components in reels and sticks  Solder paste

11 Project Report  Full report available from NPL website  Individual system responses to all project samples (~40)  XRF system details

12 Pb in Sn Sample  19210ppm Pb  All systems failing for Pb (RoSH)  One system with high Cd

13 Preparation/Presentation of Test Samples  Ideally sample should be segregated to provide single material sample  Particularly if initial measurements of complete sample so any presence of RoHS restricted substances

14 Preparation Issues (i)  Knowledge of Pb in metals beneath coatings necessary  ROHS compliance and Sn whisker mitigation SnPbAgCu Cu SnPbAgCu Au Ni Cu Epoxy (Br) Pb in brass underneath Sn plating

15 Presentation Issues (ii)  Sample should fill detection window  Multiple samples in suitable container acceptable

16 Presentation Issues (iii)  Samples should be removed from tape/tubes/tubs for accurate analysis

17 Presentation Issues (iv)  Handheld systems without stand  Attention to background to sample  Generally  Attention to containers etc

18 Presentation Issues (v)  Accurate Pb content determination of assemblied area array joints difficult  Reflowed solder on unused pads, test points can be used for solder paste alloy determination  Test pad/aperture could be added to designs and stencil  Destructive analysis may be required for accurate BGA ball analysis

19 RoHS Compliance XRF Screening >2000ppm Non-compliance <500ppm Compliance Further analysis YES NO YES NO Pb, Hg Cr, Br >500ppm Non-compliance YES <50?ppm Compliance Further analysis YES NO Cd Cr/Br issues: speciation Cd issues: false detection low RoHS limit ppm values may differ for some systems

20 Sn Whisker Mitigation XRF Screening <30000ppm Unacceptable >30000ppm Acceptable YES NO YES Pb