Lead-free soldering materials, some considerations. Presented at FHI conference, Gorinchem November 2005

Transcription

1 Lead-free soldering materials, some considerations Presented at FHI conference, Gorinchem November 2005

2 Outline Present situation in Europe towards RoHS Industry status Lead-free soldering materials Getting started... and continue 2

3 1st July 2006 Is only 199 days away This excludes weekends, public holidays, illness,.., so really 99 working days Act NOW 3

4 RoHS in Europe The smaller the company, the less forward going The more south in Europe, the less forward going A lot are waiting till the last moment Lets see what the neighbors are doing! 4

5 Industry status: Several industries to consider PCB manufacturers Components Solder and chemistry Equipment Assemblers 5

6 PCB manufacturers Metallization: OSP, Ni/Au, Sn, Ag, Substrate: warpage, discoloration, cost Tg: warpage Layout: help wetting They are ready! 6

7 Component Manufacturers Theoretically no problems Practically lots of problems - lead-free tracability???? - component identification!!!! - availability??? - thermal stress??? -cost??? Are they really ready? 7

8 RoHS components Component Identification Other RFID Technology New RoHS partnumber Info on component Differentiation via date code Info on packaging New Lead-free partnumber Percentage of suppliers 8

9 RoHS components How is RoHS compatibility communicated? Other Entrance code required Rosetta Net PIP's Info available other materials Info available hard copy Info available upon request Info available on line Percentage of suppliers 9

10 Solder and related chemistry Alloys are specified Alloys are available Pb-free compatible chemistry is there Excellent performances of solder materials Knowledge is still being gathered Support available We are ready!! 10

11 Equipment Printers: no change Pick and Place: no change Reflow ovens: higher temperatures, longer profiles: no problems Wave soldering: technically no problems, in general bigger and newer machines Hand soldering: higher usage of tips 11

12 Assemblers Very big variety of companies - size - activity - structure - knowledge - awareness 12

13 Assemblers activity European Electronics Production 2003 Computer/Communications 61% Military/Aero 9% Industrial/Medical/Control 11% Consumer 9% Automotive 10% 13

14 Lead-Free Alloy Selection for SMT, Wave and Rework

15 Alloy Selection Overview Alloy selection is the first step to identifying a lead-free process Must consider MP, alloy strength, ductility, reliability data, availability, patents, etc. Current trends are toward SAC system for SMT Current trends are toward SAC or Sn/Cu system for wave soldering 15

16 Most Common LF Alloys SnAgCu (or SAC ) family (MP = ~217C) Many available varieties with different proportions of Sn, Ag & Cu Sn96.5 Ag3.5 (MP = 221C) Sn/Ag Eutectic alloy Sn99.3 Cu0.7 (MP = 227C) Sn/Cu Eutectic alloy Sn99 Ag0.3 Cu0.7X (MP = C) Lower cost SAC alloy due to lower Silver content 16

17 SMT Alloy Selection SAC family of alloys are the default choice Debatable differentiation between SAC alloys SnAg have some history in SMT as a high temp alloy SnCu not used in SMT SnZn, SnBi for low cost applications where reliability is secondary 17

18 Major differences: Pb-free SnPb Higher melting point Slower wetting More sensitive to oxidation Different operating window Higher pre-heat requirements Different visual aspect Different behavior 18

19 Pb-free alloys In general higher mechanical strength Worse elongation Worse creep Fatigue resistance - SnAg3.5Cu0.7 Nf Sn96.5Ag3.5 Nf Sn63Pb37 Nf Sn99.3Cu0.7 Nf

20 Pb-free alloys: demands 20 Adequate Electrical conductivity Eutectic (small pasty range) Good thermal conductivity Good solderability - alloy oxidation - flux stability Good physical properties Compatibility with other materials Intermetallics Non toxic Price

21 SAC Alloy Variations Sn96.5 Ag3.0 Cu0.5 (SAC305) Sn95.5 Ag3.9 Cu0.6, inemi alloy Sn95.5 Ag4.0 Cu 0.5, fading away Sn95.5 Ag3.8 Cu 0.7, European favorite Argument over SAC alloys becomes a debate about high Silver ( %) versus low Silver (3.0%) and the effects on reliability, defects, etc. 21

22 Patents for Sn Ag Cu Cu% ISURF Senju 22 Sn96.5 Ag3.0 Cu0.5 is outside patents Ag%

23 SAC305 Benefits Proven track record as Japan s alloy of choice for SAC Less costly than higher-ag alloys No patent issues Less Ag 3 Sn, reduction of crack initiation and brittle fracture* Equal to or better than other SAC alloys in terms of reliability, strength, etc. (IPC report) 23 * Effects of Intermetallic Compounds on Properties of Sn-Ag-Cu Lead-free Soldered Joints, K.S.Kim and S.H. Huh, K.Suganuma, University of Osaka, Japan 2002.

24 Reflow Solder Selection on a Global Basis 60 SAC 67% SAC alloy more popular in SMT than wave. 10 Source: 24 Vitronics U.S.A. 1/2005 SnAg 13% SnAgBi 10% SnAgCuBi 6% SnZnBi 3% SnCu 1%

25 Wave Alloy Selection SAC family of alloys are the most popular Some concern about cost of SAC305 3% silver adds ~$3/pound to bar solder cost Low-Silver (0.3%) version being considered SAC0307 = Sn99 Ag0.3 Cu0.7 Lower cost, but lower reliability as well SnCu is the most popular low cost alternative to SAC305 SnCu may be available with additives such as Gallium, Nickel or Cobalt SnZn, SnBi, others generally not used in wave 25

26 Wave Solder Solder Selection on a 40 Global Basis 30 SAC 42% 20 Don t Know 29% 10 SnCu 17% SnAg 8% SnBi 4% Other Source: 26 Vitronics U.S.A. 1/2005

27 SAC305 for Wave Sn96.5 Ag3.0 Cu0.5 (MP ~217C) Most popular wave soldering alloy Highest cost, best for reliability 27

28 SACX for Wave Sn98.3 Ag0.3 Cu0.7Bi0.7 (MP C) Lower-Silver version of traditional SAC alloys for lower cost Originally used as a plumbing solder, little data for electronics applications Could be worth considering in some applications as a replacement for SAC305 with lower cost however with lower reliability 28

29 Sn/Cu for Wave Sn99.3 Cu0.7 eutectic point of this binary system (MP 227C) Low cost alternative to SAC305 for wave SnCu with additives, Nickel, Gallium, Cobalt SnCuNi may be an option, but single-sourced (patented) material may cause higher costs These materials are lower in cost and reliability than SAC materials 29

30 Wave Soldering Alloy Spectrum SAC305 SAC0307 SnCu Higher cost, better reliability Lower cost, poorer reliability 30

31 Rework / Hand Soldering Alloy Selection Rework alloy should match original alloy used for production process (SMT or wave) For general hand soldering alloy applications, be consistent alloy used on elsewhere on the board 31

32 SMT: Alloy Selection Summary SAC305 or other SAC alloys (MP ~217) Optimizes reliability, wetting, thermal issues Only real decision is to select level of Tin, Silver and Copper IPC SPVC Report indicates that there are no significant differences between SAC305, SAC396, others Most go for the lower Silver (SAC305) to reduce cost, avoid patents 32

33 Alloy Selection Summary Wave: SAC305, SAC0307 or SnCu SAC305 for best reliability SnCu for lowest cost SAC0307 in the middle for cost and reliability Actual selection dependent on user s product mix and reliability requirements 33

34 Alloy Selection Summary Rework: Match rework alloy to alloy used to produce original joint Other Hand Soldering: Match alloy to whatever is already used on the board 34

35 New Chemistries for Lead-free New activators New resins New gelling agents Better surfactants Oxidation inhibitors Alloy specific fluxes 35

36 Flux Selection Many fluxes designed for SnPb are not suitable for lead-free wave soldering Requires higher activity to drive a more sluggish alloy up the barrel Requires higher heat stability to survive a higher temperature wave End users are generally changing fluxes during transition to lead-free 36

37 Flux Selection Trade-off between how aggressive a flux is at removing oxides vs. the need for post-solder flux cleaning (removal). The more active a flux, the more effective it is during soldering but the greater the chance of post-solder corrosion and the need for stringent cleaning. Post-solder corrosion can lead to long-term reliability problems. Long-term Reliability FLUX ACTIVITY Efficiency of Soldering 37

38 VOC-Free Flux with Lead-Free VOC-Free = No Volatile Organic Compounds used as flux solvents Water used as solvent instead of alcohol Higher heat stability No-clean or Organic Acid versions available Spray application most common Some VOC-Free fluxes are not foamable Application Less is Best VOC-Free and Lead-Free is completely environmentally conscious 38

39 No-Clean Flux with Lead-Free Requirements for Lead-Free Compatibility Heat stable High activity Must be water based (VOC-Free) or Rosin-bearing in order to obtain the above attributes Reliable residue No corrosion, dendrites, etc. No issues with penetrating flux residues 39

40 Lead-Free Flux Compatibility No-Clean, Low Solids, No Rosin No-Clean, Low Solids, With Rosin Organic Acid (Water washable residues) Rosin-based VOC-Free (water is solvent) Best for LF * N/A Best for LF * N/A Alcohol-based Not suitable for LF Suitable for LF Suitable for LF Suitable for LF * Best selections for lead-free wave soldering 40

41 Getting started.

42 In which fase are you? Fully aware and ready Fully aware but not ready Still lots of things to do Convinced you will be exempt Convinced you have time Convinced RoHS will be delayed/cancelled RoHS/Pb-free will not happen 42

43 Road map Do you have a road map? About 50% do not have any plan yet* It is time to start now! Soldering materials are key to success * Soldertec 43

44 Alloy For reflow soldering: SnAgCu / SnAg For wave soldering: SnCu / SnAg / SnAgCu, SnCu+ For rework: SnCu / SnAg/ SnAgCu 44

45 Test vehicle Complexity Reality towards current/future process Functionality Cost Production board 45

46 Acceptance criteria Define before you start Use existing criteria Do not forget the differences! Test procedures 46

47 Training Roughness Dull - Shiny Different spread Heel-toe 47

48 Wave soldering Machine New pot? Solder pot compatibility? Pre-heat configuration Flux application Solder pot temperature Output capability Wave flexibility (contact time) Nitrogen? Change from SnPb Pb-free 48

49 Printing Same equipment Different stencil design - less aperture reduction - more paste Different behaviour 49

50 Reflow Change reflow profiles Higher peak temperature Different soak Different time above reflow Oven compatibility Nitrogen? 50

51 AOI Shiny/Dull Grainy/ smooth Heel/ toe Pad/ lead coverage AOI compatible Data base build up 51

52 Testing Training Soldering material Equipment Board Component Energy Budget Management involvement 52

53 Communication Listen to your customer Do not forget internal communication; get everybody involved Collect as much data as possible Get professional help Listen to your suppliers Re-evaluate Get into partnerships: customer you suppliers 53

54 and continue

55 Monitoring the Wave Soldering Pot Pot composition and purity analysis required monthly at first Copper content may increase Add Tin-Silver bar if using SAC Add Pure Tin bar if using SnCu Pot calculator on Kester website Lead impurities may also appear Hold Lead impurity below 0.1% 55

56 Melt Point of SnCu & SAC Alloys Research indicates a maximum of 0.5% add-on of copper or less is acceptable Same applies for Sn-Ag-Cu alloy in wave soldering Careful monitoring of the Copper level is required! 56

57 Pb contamination Lead-Free Solders are very sensitive to Lead contamination Low melting phases can be formed 1% Pb can lower solidus temperature by 40-50C SnCu: 227 C to 183 C SnAg: 221 C to 179 C Board & component finishes must be Lead-free before the pot is converted to lead-free to minimize this risk 57

58 Conclusion Think ahead Collect data Evaluate and choose carefully Ask for help Communicate Get everybody involved 58

59 Kester GmbH Ganghoferstrasse 45 D Gernlinden Deutschland Serge Tuerlings 59