Tin Whiskers Gerd Fischer and Bob Esser gfischerdfrsolutions

Tin Whiskers Gerd Fischer and Bob Esser gfischer@dfrsolutions. com besser@dfrsolutions. com © 2004 - 2007

Tin Whiskers n n Metallic crystal filaments that grow from tin-based materials Tin whisker come in lots of shapes Xu, Cookson Electronics, IPC 2002 q Pure tin platings show the highest propensity to whisker © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 2

Focused Ion Beam Etching on Sn plating on Cu underplate Xu, Cookson Electronics, IPC 2002 © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 3

Tin Whiskers Failure Modes Courtesy of P. Bush, SUNY Buffalo n Direct Contact q q n Requires growth of sufficient length and in the correct orientation Electromagnetic (EM) Radiation q q n Causes an electrical short Emits or receives EM signal and noise at higher frequencies Deterioration of signal for frequencies above 6 GHz independent of whisker length Df. R Solutions Debris q Whisker breaks off and shorts two leads (primarily during handling) © 2004 - 2007 Observation of tin whisker debris as reported to NASA from Sanmina-SC 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 4

Tin Whiskers – Root Cause n Whiskering behavior is speculated to be driven by stress gradients q n Stresses can be extrinsic or intrinsic q q n Results in preferential diffusion paths Extrinsic: pressure, bending, corrosion Intrinsic: plating, intermetallics The grains that whisker are supposedly based on orientation and oxide morphology © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 5

What Do We Know about Tin Whiskers? n n It can take days to years before tin whiskers start to grow Growth rates can vary by orders of magnitude q n Maximum lengths can vary by orders of magnitude q q n Usually 1 to 5 μm Current carrying capability q q n Highly dependent upon plating type and substrate material Bright (? ) tin on steel - 10 mm; Matte tin on copper - 0. 5 mm Diameters of 6 nm to 7 μm recorded q n 0. 1 to 200 microns per day Typically 10 - 35 m. A, up to 75 m. A observed Plasma arcing, up to 200 A possible Plating type plays a very important role Source GEB-0002 © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 6

Plating Differences n Bright tin can be “bad” plating and matte tin can be “better” plating, not necessarily “good” plating q n Problem: Quantitative definitions of bright tin and matte tin can vary What are the differences? q q Appearance Sulfate, Methanesulfonate (MSA) or Fluoroborate baths Carbon content in plating (organic brighteners and other agents) Grain size and grain orientation (lattice structure) Grain Size Carbon Content © 2004 - 2007 Bright Tin Matte Tin Tyco < 1 mm ~ 3 mm i. NEMI < 1 mm 1 – 5 mm Tyco < 0. 3% < 0. 05% i. NEMI 0. 05 – 1. 0% 0. 005 – 0. 05% 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 7

Grain Size n Pure tin will melt under Pb-free reflow conditions q n Melt point is 232ºC How will this influence grain size? q n As Plated Observations to date seem to suggest this melting phenomenon does not definitively mitigate whisker behavior Reflowed Note: Reflowed plating can exhibit a non-uniform thickness compared to as-plated sample Henshall, HP © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 8

What Else Do We Know? n Temperature cycling primarily accelerates whiskering when there is a large mismatch in thermal expansion q q n Temperature/Humidity q q n Tends to be more effective for tin-plated copper ‘Corrosion’ sites, areas of condensation, tend to accelerate whisker growth Electric Field q n Example: Tin-plated Alloy 42 (Ni-Fe alloy) Tends to be less effective for tin-plated copper No effect Barometric Pressure q No effect © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 9

Tin Whiskering and Alloy 42 n Industry seems to be unable to prevent whiskering of tin plating over discrete (‘loose’) Alloy 42 components q n Standard mitigation techniques are not available (Ni. Pd. Au) or have limited influence (nickel underplate, anneal) q n When exposed to JESD 22 A 121 temperature cycle, whiskers greater than 67 microns (Class 1 as per JESD 201) tend to be observed Exposure to Pb-free reflow (peak temp > 232 C) may provide mitigation (Micron) Maximum whisker length may saturate at values lower than tin over copper q Where is the graph? © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 10

i. NEMI DOE 3 Tests Part A started in 2003 Thermal cycling – 55 C to + 85 C 3000 cycles 20 minute cycle with 7 minute dwell / air to air inspect every 500 cycles 9000 hours (~ 1 year) inspect every 1000 hours 18000 (~2 years) inspect every 1000 hours combination of all above Samples Plating Sn, Sn. Bi, Sn. Cu and Sn. Ag Leadframe C 194 and C 7025 Treatment' As-is reflowed post-plate bake hot dipped Storage: 60 C / 93 RH Temperature and ambient temp. (~23 C) / humidity conditions ambient RH (~28%) © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 11

i. NEMI DOE 3 Samples thickness 2 64 LQFP C 194 Sn-10 wt% Pb 10 µm 3 64 LQFP C 194 Matte Sn 10 µm 4 64 LQFP C 194 Matte Sn 3 to 5 µm 5 32 LQFP Cu 7025 Matte Sn 10 µm 7 44 LQFP C 194 Matte Sn/ with 2 -3 wt% Bi 10 µm 8 16 SOIC C 194 Matte Sn/ with 2 -3 wt% Cu 10 µm 10 8 SOIC C 194 Hot dipped Sn 10 µm 11 64 LQFP C 194 Matte Sn, 245 C reflow 10 µm 12 64 LQFP C 194 Matte Sn, bake 150 C 1 hr 10 µm 14 64 TQFP C 194 Matte Sn/with 2 -4 wt% Ag 10 µm JEITA samples bright Sn C 1020 Bright Sn – finish B Alloy 42 Bright Sn – finish B C 194 Bright Sn – finish B Sn/Ni underlay/Be. Cu substrate Matte Sn Phase 2 DOE parts © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 12

i. NEMI DOE 3 whisker length (µm) Ambient Storage 6000 hrs whisker length (µm) average of 9 60°C/93%RH 5000 hrs -55°C/85°C 3000 cycles Ambient Storage 10000 hrs longest 60°C/93%R H 8000 hrs -55°C/85°C 3000 cycles Sn-10 wt% Pb 0 0 <10 (nodules) 0 0 0 Matte Sn 0 100 37 10 190 40 Matte Sn 30 110 14 40 115 20 Matte Sn 0 200 35 20 215 80 Matte Sn/ with 2 -3 wt% Bi 0 50 42 0 195 45 Matte Sn/ with 2 -3 wt% Cu 0 130 35 0 230 65 Hot dipped Sn 0 150 30 0 190 35 Matte Sn, 245 C reflow 0 110 30 0 75 45 Matte Sn, bake 150 C 1 hr 0 160 30 0 270 50 Matte Sn/with 2 -4 wt% Ag 0 20 10 0 75 15 JEITA samples bright Sn Bright Sn – finish B 45 30 0 Bright Sn – finish B 0 35 X Bright Sn – finish B 70 30 0 Sn/Ni underlay/Be. Cu substrate 0 80 X Matte Sn Phase 2 DOE parts © 2004 - 2007 0 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 80 0 13

i. NEMI DOE 3 whisker length (µm) Ambient Storage 6000 hrs whisker length (µm) average of 9 60°C/93%RH 5000 hrs -55°C/85°C 3000 cycles Ambient Storage 10000 hrs longest 60°C/93%R H 8000 hrs -55°C/85°C 3000 cycles Sn-10 wt% Pb 0 0 <10 (nodules) 0 0 0 Matte Sn 0 100 37 10 190 40 Matte Sn 30 110 14 40 115 20 Matte Sn 0 200 35 20 215 80 Matte Sn/ with 2 -3 wt% Bi 0 50 42 0 195 45 Matte Sn/ with 2 -3 wt% Cu 0 130 35 0 230 65 Hot dipped Sn 0 150 30 0 190 35 Matte Sn, 245 C reflow 0 110 30 0 75 45 Matte Sn, bake 150 C 1 hr 0 160 30 0 270 50 Matte Sn/with 2 -4 wt% Ag 0 20 10 0 75 15 JEITA samples bright Sn Bright Sn – finish B 45 30 0 Bright Sn – finish B 0 35 X Bright Sn – finish B 70 30 0 Sn/Ni underlay/Be. Cu substrate 0 80 X Matte Sn Phase 2 DOE parts © 2004 - 2007 0 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 80 0 14

i. NEMI DOE 4 – electric bias effects n No influence of electrical bias Tests Solder 32 LQFP C 7025 Bright tin None Whiskers 32 LQFP C 7025 Matte tin None Whiskers 64 LQFP O 194 Matte tin None 32 LQFP C 7025 Sn/Pb None N/A 64 LQFP O 194 Semi-bright tin None N/A Whiskers N/A 16 SOIC O 194 Matte tin None N/A Samples © 2004 - 2007 30°C / 60% RH Sn. Pb Bias No Bias 60°C / 85% RH Sn. Ag. Cu Bias No Bias Sn. Pb Bias 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com No Bias Sn. Ag. Cu Bias No Bias 15

What Don’t We Know? n n Tin whiskering is a complex problem Drivers are a combination of Materials and Environment q Materials: metals, intermetallics, organic inclusions, affect grain size, grain structure, grain boundary behavior n q Depends on: substrate materials, substrate thickness, substrate geometry, plating bath composition, plating thickness, plating material composition, plating microstructure Environment: temperature, humidity, corrosion, stress gradients n Compressive stress gradients play a very important role q Intermetallic formation, residual stresses in tin plating, external stress, mechanical loading, coefficient of thermal expansion (CTE) mismatches, corrosion or oxidation, damage to surface © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 16

What Don’t We Know: Hydrogen? n Pinsky of Raytheon (2007) speculates that insoluble hydrogen from the plating process may play a role q q n Function of cathode current efficiency Can range from tens to hundreds of ppm Initially proposed by A. Jafri in 1960 s q q q Modifications to tin plating bath (p. H increase, solution agitation, etc. ) designed to reduce hydrogen content also reduced whisker propensity Post-plate bake found to be most effective (hydrogen diffuses from bulk to grain boundaries to surface) Similar to hydrogen relief bake in high strength steels © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 17

Don’t Know (cont. ) Critical: No organization has identified a plating parameter or additive (other than Pb) that will consistently (under all conditions) prevent plated tin from whiskering n What’s left? n q Mitigation © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 18

How to Mitigate Tin Whiskers? n n The first step is to focus mitigation on critical components Critical components are based upon three pieces of knowledge q q q The overwhelming majority of tin plated electronic parts are matte tin over copper Matte tin over copper produces whiskers of a finite length Whiskers tend to only break off during handling © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 19

Maximum lengths – Matte Sn over Cu Reference Environment Time Period Maximum Length 60 C/93%RH 3000 hours 70 microns Hashemzadeh (Linköping)[2] -60 C/60 C 500 cycles 130 microns Okada (Murata)[3] -40 C/85 C 2200 cycles 85 microns Gedney (i. NEMI)[4] 60 C/95%RH 3000 hours 60 microns -55 C/85 C 3000 cycles 35 microns i. NEMI – DOE 3)[5] 60 C/93%RH 8000 hours 270 microns Brusse (NASA)[6] -40 C/90 C 500 cycles 250 microns 60 C/93%RH 5000 hours 450 microns Room Conditions 8500 hours 100 microns -55/85 C 3000 cycles 40 microns Romm (TI)[8] 51 C/85%RH 3634 hours 34 microns Dittes (E 4)[9] 30 C/60%RH 450 days 275 microns -55 C/85 C 3000 cycles 35 microns Peng (Freescale)[1] Hilty (Tyco)[7] [1] Peng Su, Min Ding, and Sheila Chopin, "Effects of Reflow on the Microstructure and Whisker Growth Propensity of Sn Finish", Proceedings of the 55 th ECTC [2] Study of Tin Whisker Growth and their Mechanical and Electrical Properties, Moheb Nayeri Hashemzadeh, Undergraduate Thesis, Linköping University, 2005 [3] S. Okada, et al, "Field Reliability Estimation of Tin Whiskers Generated by Thermal Cycling Stress", Capacitor and Resistor Technology Symposium (CARTS) Europe, October 2003 [4] R. Gedney, J. Smetana, N. Vo, G. Galyon, "NEMI Tin Whisker Projects", Second International Conference on Lead Free Electronics, June 21 -23, 2004 (Amsterdam) [5] “Tin Whisker Test Committee Results (Phase 3)", Presentation at ECTC NEMI workshop, June 1, 2005 [6] J. Brusse, "Tin Whisker Observations on Pure Tin-Plated Ceramic Chip Capacitors", Proceedings of the American Electroplaters and Surface Finishers (AESF) SUR/FIN Conference, June 24 -28, 2002, pp. 45 -61 [7] Tin Whiskers in Electronic Components, Bob Hilty, www. tycoelectronics. com/environment/ leadfree [8] D. Romm, D. Abbott, S. Grenney, M. Khan, "Whisker Evaluation of Tin-Plated Logic Component Leads", Texas Instruments Application Report SZZA 037 A, February 2003 [9] Standard for Whisker Acceptance Level in Pb-free Lead Finish. A Step towards Green Packaging for Consumer Products to Drive Future European Strength, Final Report. Contract No: IST-2001 -37826. 01. 06. 2002 - 30. 11. 2004, Marc Dittes, Infineon Technologies © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 20

Where are the Scary Whiskers? n When do really long whiskers occur? q Usually bright tin and/or tin plating over a substrate material other than copper (brass, bronze, steel, etc. ) NASA (Leidecker): 25 mm over +10 years Df. R (Fischer): +2 mm over 6 months Bright tin over Be. Cu(? ) or steel(? ) Tin (matte? ) over brass © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 21

Tin Whiskering – Effect of Substrates Sakuyama (FUJITSU Sci. Tech. J. , 2005) Sn-Cu over Cu © 2004 - 2007 Sn over Phosphor-Bronze 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 22

Mechanical Tests (Conditions) References Resonance Sweep Dunn Hashemzadeh Ando Type Sinusoidal Random Sinusoidal Frequency (Hz) 10 – 2000 10 – 4500 10 – 2000 Maximum Acceleration 20 G 3. 5 Grms 20 G Duration N/A 5 minutes N/A Sinusoidal Random 50, 100, 250 10 - 2000 6 G 18 Grms 60 sec / frequency 22 hours 2000 G 500 G 1000 G 3000 G Pulse Width (ms) 1 6 0. 3 Events 50 100 18 Type Frequency (Hz) Extended Duration Maximum Acceleration Mechanical Shock Ando, Toshihiro, Shibata, Masamitsu, Okada, Seiichi, and Namasuya, Yoshikazu, "Stress Analysis and Accelerated Evaluation of Tin Whisker under Thermal Shock Stress, " Murata (whisker length limited to 75 microns) B. D. Dunn, "Mechanical and Electrical Characteristics of Tin Whiskers with Special Reference to Spacecraft Systems, " European Space Agency (ESA) Journal, 12, pp. 1 -17, January 14, 1988. Mc. Dowell, M. E. , “Tin whiskers: a case study”, Aerospace Applications Conference, 1993. Page(s): 207 -215 © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 23

Tin Whiskering - Vibration Natural frequencies of tin whiskers calculated by Dunn (left) and Hashemzadeh (right). The formula for natural frequency is , where E is modulus, L is length, d is diameter and r is density. © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 24

Mechanical Tests (cont. ) n Experiments: no breaking observed n Theoretical Approach: q q q n Structure to model loads during vibration would be a uniform load on a simply supported beam Maximum stress within the beam (or whisker) σmax = L 2 p/2(d 3/6), L is the length, p is load, d is diameter Mass of a whisker 1 mm long x 2 microns in diameter: 2. 8 x 10 -8 grams (density 0. 007 g/mm 3) Acceleration: 3000 G force 8. 4 10 -7 N Resulting stress: 0. 3 MPa < 8 MPa (ultimate tensile strength determined by Dunn) Scenario of whiskers breaking off is unlikely, unless the part is handled (e. g. during rework or repair) © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 25

Critical Components JEDEC JESD 201 n Spacings of less than 500 microns q q q n n n Parts with 0. 8 mm lead pitch or less 0201 chip components Metal can housing Contact points (connector flex circuitry) q Stress gradients could change maximum length Welds (electrolytic capacitors) q Stress gradients could change maximum length Note: Some organizations specify the critical spacing as 350 microns (e. g. , EU) q 0. 65 mm pitch or less © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 26

How to Mitigate? n n n There are three basic approaches to mitigation Data Gathering and Monitoring Part Manufacturer Mitigation q n Steps offered by your suppliers Equipment Manufacturer (OEM) Mitigation q Steps you have to perform yourself © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 27

Data Gathering and Monitoring n n Driven by i. NEMI and JEDEC (JESD 22 A 121. 01, JESD 201, JP 002) Industry recommended qualification tests q q n Ambient (30 C/60%RH, 4000 hrs) Elevated (55 C/85%RH, 4000 hrs) Cyclic (-40 to 85 C, 1500 cycles) Shorter test times for consumer products Use manufacturer’s data, require thirdparty testing, or perform your own q q Visual inspection should be performed properly http: //nepp. nasa. gov/whisker/video/ inspection/index. html © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 28

JESD 201: Potential Issues n n Document allows for test coupons versus actual components (JESD 22 A 121 -01, sec. 5. 1) Document does not specify if components are discrete (‘loose’) or board-mounted q q n Temperature cycling and elevated humidity exposure of non-preconditioned discrete parts may not be representative of storage conditions Board-mounted parts may not be representative of hand assembly or repair conditions Test times are not based on a failure model q Unable to correlate to time in the field for various use environments © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 29

Part Manufacturer Mitigation n Nickel underplate between the tin plating and the copper leadframe q q Some question about effectiveness (IBM vs. TI) Some question about minimum thickness n n n q q n This is the approach for Freescale Fusing (melting of tin through dipping in a hot oil bath) q n What if the nickel underlayer cracks? Might not help for ceramic substrate due to CTE mismatch Anneal for 1 hour at 150ºC within 24 hours of plating q n i. NEMI article recommends minimum of 2 microns (Smetana, Global SMT, 6/07) PC manufacturer requires 1. 2 microns JP-002 requires 0. 5 microns Excellent field history; must be performed soon after plating Minimum plating thickness q Some question about minimum thickness n n © 2004 - 2007 Telecom manufacturer requires 10 microns JEP-002 recommends 7 microns 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 30

Mitigation (Sn-Bi and Sn-Ag) n Some component suppliers promoting bismuth and silver additives (1 – 3 wt%) q q n Not as accepted as other mitigation techniques However, increasing acceptance by some OEMs (e. g. , Rockwell Collins) Concerns q q q Low melting point Sn. Pb. Bi alloys Some claim test results demonstrating this behavior Others state thermodynamically impossible below 6 wt% Gordon, Northrop Grumman © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 31

Part Manufacturer Mitigation (cont. ) n Some component manufacturers claiming proprietary whisker-free plating formulation q n Be skeptical; require Statistical Process Control Request palladium (Pd) plating – Ni. Pd. Au q q Increasingly offered as an option, even to low volume customers (medical, industrial controls, etc. ) Most manufacturers have moved to Pd as a standard plating for fine-pitch components © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 32

Leadframe Platings Amkor Company Intel QFP / TSOP Samsung QFP / TSOP Ni. Pd. Au Texas Instruments QFP / TSOP Ni. Pd. Au TSOP (Discretes) Ni. Pd. Au TSOP (Memory) Sn. Ag or Sn. Cu TSOP (LSI) Ni. Pd. Au or Sn. Ag or Sn. Bi QFP / TSOP Ni. Pd. Au QFP Sn or Sn. Pb TSOP Ni. Pd. Au QFP Mostly Sn-Cu, Sn-Bi; some Ni. Pd. Au TSOP Mostly Ni. Pd. Au, with some Sn-Cu, Sn-Bi QFP / TSOP Pd or Sn. Pb QFP Sn TSOP Ni. Pd. Au Hynix TSOP Sn. Bi Freescale QFP / TSOP Sn NEC QFP / TSOP Sn, Sn. Bi, or Ni. Pd. Au Micron TSOP Sn, Sn. Pb QFP Pd TSOP Sn. Bi AMD QFP Sn, Sn. Cu, or Sn. Pb IBM QFP N/A Qualcomm N/A QFP Sn. Bi TSOP Sn. Bi QFP Sn. Bi, Ni. Pd. Au TSOP Sn. Bi STMicroelectronics Infineon Renesas Technology Sony Philips/NXP Palladium and Sn. Bi are seeing an increasing market share due to concerns with tin whiskering Matsushita/Panasonic Fujitsu Sharp © 2004 - 2007 Plating Sn[1] Toshiba Amkor Package 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 33

OEM Mitigation n Four Options q n Procurement / Design q q q n Procurement, Re-packaging, Post-plate or dip, Conformal coat Select only components with Sn. Pb or Pd plating May require complete change in circuit design if alternative component required Rarely performed (functionality trumps reliability) Subcontract packaging or Re-packaging q q Sn. Pb or Pd plated leadframes Rarely performed (cost, risk of damage) © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 34

Post-Plate or Dip Options n Reflowing solder q q n Replating (Passive Components / AEM) q q q n Needs bake for enhancing interdiffusion Hot-tin dipped coating q n Stripping and refinishing with whisker-free plating material $0. 10 - $0. 40 per part (4000 part minimum) Avnet considering stocking this option (Rollins / Minter) Lead (Pb) overplating q n Application of solder over the entire exposed lead Whiskers do not occur where solder is present Found not be to effective (i. NEMI) Hot solder dip with Sn. Pb © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 35

Sn. Pb Solder Dipping n Initially relevant only to products not covered by Ro. HS q n GEIA-STD-0006 (Draft) q n q q Gap at component body could still result in whiskers Risk of solder bridging and popcorning on fine pitch; thin components with large die areas will be problematic Some programs have erroneously assumed ‘qualification by similarity’, both process and part, and ended up with damaged parts (Rollins / Minter) Costing (Rollins / Minter) q n Requirements for Using Solder Dip to Replace the Finish on Electronic Components Problems may outweigh solution q n Fine-pitch components now exempt from Ro. HS $2. 00 -3. 50 per part for 100, plus $450 -$900 set-up fee; NASA Avnet considering stocking this option (Rollins / Minter) © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 36

Tin Whiskering – Conformal Coating n n n Potential to provide a dual barrier Prevention or delay of whiskering q Some indication of 2 - 6 year delay in whiskering (Rollins / Minter) q Short tin whiskers will eventually penetrate all current conformal coatings q No definitive trend in regards to coating properties Buckling q Based on calculations (Leidecker, NASA) Leadframe q Not experimentally proven Conformal Coating Limitations q Insufficient coverage at leads (gravity) Tin Whisker q Problems with conformal coat may outweigh possible risk avoidance q Fine pitch components may have no air gap! Conformal Coating Current status: Leadframe q Development of whisker-resistant coating q Assessment of single vs. double coating © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 37

Tin Whisker Mitigation Plan n Step 1: What does your customer want? q q q n Customer can be internal or external Make them an active participant May prevent conflicts in the future Step 2: Be aware of relevant GEIA documents q q GEIA STD-0005 -2: Standard for Mitigating the Effects of Tin Whiskers in Aerospace and High Performance Electronic Systems Why GEIA? n n © 2004 - 2007 Provides a useful template for all hi-rel industries Three control levels; Four whisker control activities 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 38

GEIA-STD-0005 -2 (Control Levels) n Simplest: Level I and III q q n Level I. No restrictions on tin finish use Level III. Use of tin finish is prohibited and measures must be taken to verify compliance Level II more nuanced q Tin finish is allowed under some circumstances © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 39

Level II Definitions n Level IIA. Use of tin finish without explicit controls is acceptable under most circumstances but the likelihood of whiskers and methods used to estimate their impact and mitigation strategies will be documented. Tin finish may be prohibited in some specific circumstances called out in contractual documents. n Level IIB. Tin finishes may be used but only with customer approved and specified control measures. These tin finish approvals may be blanket approvals for multiple components and applications within the system. Tin finish may be prohibited in some specific circumstances called out in contractual documents. n Level IIC. Restricted use of tin finish. Tin finish is prohibited unless an exception is made. Specific instruction on use of tin finish and required control measures to be provided and reviewed on a case-by-case basis. © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 40

Control Activities n Documentation q n Detecting and Controlling q n Do you have a process for identifying whisker-susceptible platings? Mitigation q n Where are whisker-susceptible platings? How will you prevent tin whiskers? Assessment of Risk and Mitigation q q What’s your risk? How do you know your mitigation will work? © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 41

Level IIA Requirements n Documentation q n Detect and Control q n No requirements Mitigation q n No requirements, but general information should be provided If specified by the customer Assessment of Risk and Mitigation q MUST be performed © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 42

Assessment of Risk and Mitigation n Analysis of Tolerance q q n Whisker Testing q n n Spacings, potential barriers (could whiskers induce failure? ) FMEA (if a whisker induces failure, what happens? ) JEDEC tests only acceptable for Level IIA Analysis of Field Data Other q q Qualitative discussions of mitigation techniques (nickel barrier, conformal coating, etc. ) Algorithms that predict risk © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 43

Level IIB n Documentation q n Detect and Control q q n Should be agreed upon between customer and supplier E. g. , XRF sampling on a periodic basis Mitigation q n A list of all parts with Pb-free tin platings At least two mitigation measures recommended Assessment of Risk and Mitigation q q More extensive than Level IIA Documentation of mitigation measures, tests or analyses for determining risk, potential callout for a risk algorithm © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 44

Accepted Mitigation Measures n Design q n Spacing requirements or barriers Lower Risk Pb-free Tin Platings q q q Refers to Appendices and JEDEC JP 002 Examples include matte tin w/ nickel underplate Some confusion over heat treatment n Is the standard reflow process acceptable? q n n “The heating should be done in an inert atmosphere and followed by a slow cooling to minimize stresses reforming” Replating or Solder-Dipping q n Tin does not have to melt (fusing / annealing) If coverage is not comprehensive Conformal Coating © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 45

Level IIC n Documentation q n Detect and Control q q q n Shall be agreed upon between customer and supplier How will Pb-free tin platings will prevented from being introduced Potentially sampling one part per lot (XRF) Mitigation q n How Pb-free tin platings will be avoided At least two mitigation measures required Assessment of Risk and Mitigation q MUST be performed © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 46

Mitigation - Summary n The appropriate mitigation technique will primarily be driven by risk sensitivity q n Our recommendation: q n GEIA-STD-0005 -2 provides general guidelines on identifying levels of risk Given recent trends in the component industry, the military/avionics community, in concert with telecom and industrial controls, should make a collaborative effort to drive all fine-pitch parts to Sn. Pb or palladium plating. This is the lowest cost, lowest risk approach. Example: q q Freescale has indicated an interest in serving the mil/avionics community, but have chosen tin plating. They should be clearly informed that they are the outliers and their stance places future purchases at risk. © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 47

Appropriate Finishes (i. NEMI) J. Smetana (Alcatel), Global SMT & Packaging - June 2007 © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 48

Risk Assessment and Prediction n n Due to the degree of uncertainty, risk assessment and prediction can be problematic Prediction based upon time in service can be suspect q q n Proposed by i. NEMI Growth rates can be highly variable Prediction based upon maximum whisker length is a more realistic approach q Proposed by Tyco © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 49

i. NEMI DOE 5 n Designed to capture incubation and growth behavior as a function of temperature and humidity q n n n Test time: 6000 to 15000 hours Incubation period proposed at ECTC (May 2007) Incubation period and growth behavior proposed in J. of Materials Science (March 2007) Only for matte tin over copper © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 50

Incubation Period n Incubation algorithm (empirical fit to test data) q n n Variations in model constants reported in JMat. Sci and ECTC 3 micron thickness (ECTC) q n A = 1. 15 hrs; Ea = 0. 31 e. V; C = -0. 031%RH 10 micron thickness (ECTC) q n A*exp(Ea/KT)*exp(C*%RH) A = 0. 002 hrs; Ea = 0. 47 e. V; C = -0. 015%RH Generic (JMat. Sci) q A = 0. 007 hrs; Ea = 0. 44 e. V; C = -0. 044%RH © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 51

Incubation Period (3 microns) © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 52

Incubation Period (10 microns) © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 53

Incubation Period (Generic) Most conservative A nominal data center environment could initiate whiskers in 3 -4 yrs © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 54

Whisker Growth Rate n Proposed growth model n Better used to develop acceleration factors then absolute times to failure If no whiskering at 55 C/85%RH for 4000 hrs, then equivalent to Southeast Asia (35 C/90%RH) 1 years USA** (30 C/85%RH) 2 years Data Center (22 C/45%RH) 40 years **Worst case Data Center © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 55

Risk Assessment Robert Hilty, Tyco Length measurements and Monte Carlo Simulation of the distribution of whisker length for mitigated (matte tin over nickel - left) and unmitigated (3 micron matte tin over brass - right) plating © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 56

Risk Assessment Probability of failure as a function of separation distance Robert Hilty, Tyco © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 57

Tin Whiskers – Applicable Publications n GEIA-GEB-0002 (November 2003) q n GEIA-STD-0005 -2 (June 2006) q n n Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes JEDEC/IPC JP 002: q n Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes JESD 22 A 121. 01: q n Standard for Mitigating the Effects of Tin Whiskers in Aerospace and High Performance Electronic Systems JESD 201: q n Reducing the Risk of Tin Whisker- Induced Failures in Electronic Equipment Current Tin Whiskers Theory and Mitigation Practices Guideline http: //nepp. nasa. gov/whisker/ http: //www. inemi. org http: //www. ipc. org Pb-free listserv on www. ipc. org © 2004 - 2007 5110 Roanoke Place, Suite 101, College Park, Maryland 20740 Phone (301) 474 -0607 Fax (240) 757 -0053 www. Df. RSolutions. com 58