Mix Alloy Soldering. (Sn/Pb Soldering in a Pb Free World)

Transcription

1 Mix Aoy Sodering (Sn/Pb Sodering in a Pb Free Word) Dr. Nei Pooe January 2007

2 Why Backward Compatibiity? Some eectronics products have exemptions in EU RoHS directive Lead in soders in high reiabiity appications such as servers, medica equipment, teecommunication products unti 2010 or beyond. USA has no Pb free egisation (some states ooking CA) Some SnPb components wi be unavaiabe or command a high premium Component manufacturers do not want to carry both SnPb andead-free production ines due to the cost concern Voume of components for these high reiabiity products is ow

3 Intermetaic Bonding (Sodering). SOLDER INTERMETALLIC LAYER SUBSTRATE SUBSTRATE INTERMETALLIC (compound) Cu Cu 6 Sn Ag Ag 3 Sn Au Au Sn 4 (WEAK, BRITTLE) Ni Ni 3 Sn 4 - TIN IS THE ACTIVE INGREDIENT IN SOLDER -

4 The Intermetaic Layer Thickness of intermetaic ayer depends on: - Substrate composition Au > Ag > Cu > Pd > Ni Soder composition Temperature! Time!

5 Mixed Aoy Systems Pb free ead finishes with Pb soder Litte work done so far Possibe profie changes Pb ead finishes with Pb free soder Some work done Seen as a transitiona probem Even with exemptions fu Sn/Pb may not be possibe Mistakes wi happen

6 Mixed Aoy Systems Pb-free Component Finishes Pure Sn Most common Whiskers(?) Sn/Bi More popuar in Japan Reiabiity Questions Ni/Pd/Au Vendor Specific Questions about wettabiity Sn/Pb + Pure Sn Wetting issues Refow Profie Sn/Pb + Sn/Bi Sn/Bi/Pb ow met temp Sn/Pb + Ni/Pd/Au Least affected

7 Aoy Meting Points

8 Intermetaic Thickness Finish Treatment SAC 305 Aoy Sn62 Aoy Cu 6 Sn 3 Cu 3 Sn Cu 6 Sn 3 Cu 3 Sn Cu As Refowed Cu 125ºC for 1000 hr Im Ag As Refowed Im Ag 125ºC for 1000 hr ENIC As Refowed ENIC 125ºC for 1000 hr 3 1.5

9 Wetting Speed vs Temperature for Different Aoys time to 2/3 max wetting force, s /40 SnAg & SnAgCu base aoys SnCu base aoys Test temperature, C

10 Comparative Wetting Comparative Wetting Times for Pb Free Terminations For Sn62 and SAC 387 Aoys

11 Comparative Wetting

12 Comparative Wetting

13 Mixed Aoy Systems Pb-free Component Finishes Shear testing Pad Finish Peak Refow Temperature 215ºC Peak Refow Temperature 240ºC Copper ENIC Im Ag Im Sn 9.5 Kg 9.7 Kg N/A N/A 10.0Kg 10.3 Kg N/A N/A

14 Mixed Aoy Systems Pb-free Component Finishes Au 215 º C Cu 215 º C Au 240 º C

15 Mixed Aoy Systems Pb-free Component Finishes 215 º C 240 º C 0402

16 Mixed Aoy Systems Pb-free Leaded Component Finishes 215 º C 240 º C

17 Mixed Aoy Systems Pb-free Leaded Component Finishes Au 215 º C Au 240 º C

18 Concusions Leaded and Leadess Components Process temperature can infuence joint microstructure Higher peak temperature can increase Ag 3 Sn dendrites Higher peak temperature can increase Pb phase Higher peak temperature increase initia intermataic thickness Higher temperature reduces voiding Higher peak temperatures better wetting (eaded components) Initia joint strengths independent of the profie Effects on reiabiity sti to be determined!!!!

19 Mixed Aoy Systems Pb-free Bumped Component Finishes SAC Aoys SAC 305 SAC 405 SAC 387 A essentiay eutectic met point 217ºC SAC 105?? SACs 305, 387, 405 appear to be equa IPC Soder Vaue Counci Many, Many, Many Questions Underfi!!!

20 Mixed Aoy Systems Pb-free Bumped Component Finishes Pb-free BGA bumps / Sn/Pb Paste Metas in the soder joint: Sn (buk) Ag Cu Pb Ni Au Not eveny distributed not necessariy eutectic structure

21 Bumped Component Chaenge What refow profie??

22 Mixed Aoy Systems Pb-free Bumped Component Finishes Outer Appearance BGA bumps New BGA

23 Mixed Aoy Systems Pb-free Bumped Component Finishes Outer Appearance BGA bumps Ba did not met Lead paste 210 C

24 Mixed Aoy Systems Pb-free Bumped Component Finishes Outer Appearance BGA bumps Ba did not met Lead paste 210 C

25 Mixed Aoy Systems Pb-free Bumped Component Finishes Pb-free BGA bumps / Sn/Pb Paste & Profie Bump doesn t met/coapse Component at a higher standoff Stress distribution different Component tit Impact to reiabiity Segregated joint

26 Mixed Aoy Systems Pb-free Bumped Component Finishes Pb-free BGA bumps & Profie / Sn/Pb Paste Fux exhaustion of the Sn/Pb Paste Poor coaesance Increased voiding/bowhoes Insufficient activity Poorer wetting

27 Mixed Aoy Systems Pb-free Bumped Component Finishes

28 Mixed Aoy Refowed BGA Rockwe

29 Mixed Aoy Refowed BGA Therma Cycing -55 / C/min, 11 min dwe Norma Sn/Pb= Mixed Meta = 267 Rockwe

30 Mixed Aoy Refowed BGA Ag 3 Sn Pateet inside the void indicates that the void formed during the sodering process or during cooing.

31 Mixed Aoy Systems Pb-free Bumped Component Finishes Bump coapsed and part sef centered Fu mixing of aoys.

32 Micro Structure of Joints with Low Leves of Pb 0.2% Pb Forsten, Steen, & Widing, Sodering & Surface Mount Technoogy Pb-rich phase, 179 C meting temperature 4.0% Pb

33 Fina Joint Compositions & Liquidus for Sn3Ag0.5Cu Ba and Sn37Pb Paste Pitch (mm) Aperture Size (mi) Stenci Thickness (mi) Transfer Ratio (%) Ba Dia. (mi) % of Pb % of Ag % of Cu Liquidus temp. (C) (Ro) (Sq) (Sq) (Sq) (200*) (Sq) J. Pan, et a., IPC/JEDEC Pb-free Conference, San Jose, * Cacuated by Dr. Ursua R. Kattner of NIST from NIST thermodynamic database

34 Fina Joint Compositions & Liquidus for Sn4Ag0.5Cu Ba and Sn37Pb Paste Pitch (mm) Aperture Size (mi) Stenci Thickness (mi) Transfer Ratio (%) Ba Dia. (mi) % of Pb % of Ag % of Cu Liquidus temp. (C) (Ro) * (Sq) (Sq) (Sq) (197*) (Sq) J. Pan, et a., IPC/JEDEC Pb-free Conference, San Jose, * Cacuated by Dr. Ursua R. Kattner of NIST from NIST thermodynamic database

35 Mixed Aoy Reiabiity- Therma Cyce

36 Effect of Underfi on BGS/CSP CSP s ReiaSoft's Weibu Drop Testing.5mm CSP? (2900 Gs, 0.3 msec Puse) Underfi B 0.5 SAC Drop Underfi B0.5 SnPb Drop % Faiure ? Underfi A 0.5 SAC Drop Underfi A 0.5 SnPb Drop Tom White HENKEL /19/ : Drop Count

37 Concusions There are successes with mixed meta systems Reiabiity window is reduced (underfi?) Much work sti to be done inemi committee ooking into mixed meta BGA/CSP assemby Other companies aso investigating Avoid it if possibe, understand the risks if required

38 Sources Y. Kariya et a: J. Eectronic Materias, 1998, 27, p M. Harrison et a: Sodering & Surface Mount Technoogy, vo 13 no 3, p21-38 NCMS Report no 0096RE01, 2001 M. Bozack: Auburn University, 2002 G. Swan et a: Proceedings APEX, 2001, paper LF2-6 A. Syed: Proceedings APEX, 2001, paper LF2-7 D. R. Banks et a: Proc SMI conf, 1996, p

39 Acknowedgements Dr. Nei Pooe Sr. Appications Chemist Dr. Hector Steen Sr. Deveopment Scientist David Himan Rockwe Coins Pau Wood OK Industries Ramon Mendez Ecoteq Tom White Henke Pauine Chan Henke Dr. Jainbiao (John) Pan - Assistant Professor Ca Poy State University, San Luis Obispo.

40 Dr. Nei Pooe Any Questions