A FLOWERS OF SULFUR CORROSION CHAMBER FOR TESTING ELECTRONIC HARDWARE

Transcription

1 A FLOWERS OF SULFUR CORROSION CHAMBER FOR TESTING ELECTRONIC HARDWARE Prabjit (PJ) Singh IBM Corporation, Poughkeepsie, New York , 9 Feb

2 Prabjit Singh and Larry Palmer IBM Corporation, Poughkeepsie, NY, USA Simon Lee and Geoffrey Tong The Dow Chemical Company, Taipei and Hong Kong Dem Lee and Jeffrey Lee ist-integrated Service Technology, Inc., Taiwan Karlos Guo and Julie Liu Lenovo (Beijing) Limited Corporation, Beijing, China Chen Xu Nokia, Murray Hill, NJ, USA Haley Fu inemi, Shanghai, China 2

3 Agenda Flowers of sulfur (FoS) chamber design FoS chamber conditions (sulfur, chlorine and humidity) and their control Three examples of FoS chamber application Reproducing creep corrosion and the influence of humidity and chlorine gas Mapping corrosion rates on psychrometric chart Conformal coating characterization Summary 3

4 FoS chamber and Clorox TM setup 4

5 The moisture coming off the Clorox TM is throttled and forced to flow over the saturated salt. The saturated salt controls the relative humidity in the chamber to its deliquescence value. 5

6 FoS chamber conditions 200 g sulfur 100 ml 8.25% sodium hypochlorite Clorox TM 50 o C chamber temperature 20 rpm paddle wheel rotation %RH controlled by salt solution in the 11 to 90% range. 6

7 Influence of sulfur content Corrosion rate, Å/day Sulfur content, g Red dots are for Cu corrosion Blue dots are for Ag corrosion Open dots are from mass gain Solid dots are from coulometric reduction NH 4 NO 3 saturated salt solution, 100ml Clorox, 50 o C, 20 rpm. 7

8 Influence of sulfur content 200 AgCl growth rate, Å/day NH 4 NO 3 saturated salt solution, 100ml Clorox, 50 o C, 20 rpm Sulfur content, g 8

9 Chlorine gas content 13-18% RH 74-80% RH 9

10 Corrosion rate variation with time 100% Clorox TM 50% Clorox TM 50% CloroxTM 100% Clorox TM FOS with 200g sulfur, NaNO 2 saturated salt solution, 100ml Clorox, 50 o C, 20 rpm. 10

11 Influence of humidity FOS with 200g sulfur, 100ml Clorox, 50 o C, 20 rpm. 11

12 Influence of humidity FOS with 200g sulfur, 100ml Clorox, 50 o C, 20 rpm. 12

13 Influence of loading 13

14 Influence of pre-baking Pre-bake is necessary to avoid the VOCs coming off the PCBs from contaminating the limitedvolume FoS chamber. Not prebaked Baked Creep corrosion occurred only on pre-baked PCBs. 14

15 Reproducing corrosion in lab Creep corrosion and capacitor termination corrosion in FoS chamber at 50 o C and 81%RH. 15

16 Influence of humidity (ImAg) 16

17 Influence of humidity (ENIG) 17

18 Influence of humidity (OSP) 18

19 Corrosion rate measurements 19

20 Silver corrosion rate (nm/hr) %RH Ag corrosionrate, nm/hr Corrosion rate, nm/hr %RH Temperature, o C Temperature, o C 20

21 Silver corrosion rate (nm/hr) KCl (83% RH) NaNO 2 (62% RH) 0.38 Mg(NO 3 ) 2 (50% RH) K 2 CO 3 (44% RH) MgCl 2 (33% RH) ZnCl 2 (12% RH)

22 Conformal coating characterization 22

23 Summary FoS chamber has proven to be a convenient, low cost alternative to the MFG chamber. The relative humidity and sulfur concentration can be well controlled. The chlorine concentration released from the sodium hypochlorite containing Clorox TM rises over time in a relatively controlled manner. The creep corrosion tests done in the chamber have proven very successful in identifying PCB finishes prone to creep corrosion. 23

24 Summary (contd.) The FoS chamber test has revealed that ImAg finished PCBs have higher propensity to creep corrosion in the low humidity range; whereas ENIG finished boards suffer creep corrosion over a wider relative humidity range and OSP finished boards are quite immune to creep corrosion. The chamber has also been successfully used to measure silver corrosion rates across a range of temperature and humidity and to characterize conformal coatings. 24

25 Thank You! Prabjit (PJ) Singh, Senior Technical Staff Member, IBM Poughkeepsie Professor of power electronics, SUNY New Paltz, NY 39 years experience in the metallurgy, physics and philosophy of power, packaging and cooling of mainframe computers. 25