Determining Critical Cleaning Process Parameters for QFNs

Transcription

1 Determining Critical Cleaning Process Parameters for QFNs Speaker: Kalyan Nukala, M.S.Chem.Eng. Application Engineer

2 Determining Critical Cleaning Process Parameters for QFNs Introduction Core Objectives Phase 1 Methodology Phase 1 Results Phase 2 Methodology Phase 2 Results Conclusion

3 Introduction Quad Flat No Leads (QFN) or Micro Lead Frame (MLF) packages are the fastest growing types within the electronics industry

4 Introduction QFN package is similar to the Quad Flat Package except that the leads do not extend out from the package sides Leads are located underneath the component body posing challenges to clean flux residues after soldering Low standoff (1-2 mil) and the large thermal pad at the center of the component body present barriers to the complete removal of flux residues

5 Introduction Partially removed or untouched residues can lead to component failure resulting from: Electrochemical migration resulting in dendritic growth Electrical leakage currents

6 Determining Critical Cleaning Process Parameters for QFNs Introduction Core Objectives Phase 1 Methodology Phase 1 Results Phase 2 Methodology Phase 2 Results Conclusion

7 Core Objectives Design of Experiment (DOE) developed to determine the critical cleaning process parameters for complete cleanliness underneath leadless devices or QFNs Study designed in two phases

8 Core Objectives Phase 1: Determine critical wash parameters and cleaning equipment settings for the MLF-68 component Cleanliness assessment through visual analysis Phase 2: Utilizing process parameters from Phase 1, verify cleaning results underneath various QFN configurations Cleanliness assessment through visual analysis and Ion Chromatography

9 Determining Critical Cleaning Process Parameters for QFNs Introduction Core Objectives Phase 1 Methodology Phase 1 Results Phase 2 Methodology Phase 2 Results Conclusion

10 Phase 1 Methodology Substrate: ZESTRON low standoff test board: MLF-68 component 10 mm x 10 mm body / 0.5 mm pitch MLF-68

11 Phase 1 Methodology Paste types used: A: Water soluble lead free (w/s l/f) B: No-clean lead free (n/c l/f) Cleaning equipment: Spray-in-air inline cleaner Cleaning agent: Dynamic surfactant

12 Phase 1 Methodology Cleaning equipment parameters evaluated: Factors Levels Paste Type w/s l/f n/c l/f Spray configuration 4 V-jet 8 Intermix Concentration (%) 5% 10% 15% Belt Speed (ft/min) Wash pressures obtained: Top Spray bars: Bottom Spray bars: Top Hurricane: 4 Spray bar V-jet design 8 Spray bar intermix design 85 psi 70 psi 40 psi 40 psi 40 psi 40 psi Full factorial analysis

13 Phase 1 Methodology Water soluble lead free trial matrix: Trial # Paste Concentration (%) Spray Configuration Belt Speed (ft/min) 1 w/s l/f 5 4 V-jet w/s l/f 5 4 V-jet 1 3 w/s l/f 5 4 V-jet w/s l/f 5 8 intermix w/s l/f 5 8 intermix 1 6 w/s l/f 5 8 intermix w/s l/f 10 4 V-jet w/s l/f 10 4 V-jet 1 9 w/s l/f 10 4 V-jet w/s l/f 10 8 intermix w/s l/f 10 8 intermix 1 12 w/s l/f 10 8 intermix w/s l/f 15 4 V-jet w/s l/f 15 4 V-jet 1 15 w/s l/f 15 4 V-jet w/s l/f 15 8 intermix w/s l/f 15 8 intermix 1 18 w/s l/f 15 8 intermix 1.5

14 Phase 1 Methodology No-clean lead free trial matrix: Trial # Paste Concentration (%) Spray Configuration Belt Speed (ft/min) 19 n/c l/f 5 4 V-jet n/c l/f 5 4 V-jet 1 21 n/c l/f 5 4 V-jet n/c l/f 5 8 intermix n/c l/f 5 8 intermix 1 24 n/c l/f 5 8 intermix n/c l/f 10 4 V-jet n/c l/f 10 4 V-jet 1 27 n/c l/f 10 4 V-jet n/c l/f 10 8 intermix n/c l/f 10 8 intermix 1 30 n/c l/f 10 8 intermix n/c l/f 15 4 V-jet n/c l/f 15 4 V-jet 1 33 n/c l/f 15 4 V-jet n/c l/f 15 8 intermix n/c l/f 15 8 intermix 1 36 n/c l/f 15 8 intermix 1.5

15 Phase 1 Methodology Lead free Reflow Profile: Belt Speed: 89.0 cm/min (266.4 seconds to peak temperature) Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Zone 8 Zone 9 Zone 10 Top: 100 C 120 C 150 C 180 C 190 C 210 C 225 C 235 C 245 C 225 C Bottom: 100 C 120 C 150 C 180 C 190 C 210 C 225 C 235 C 245 C 225 C

16 Phase 1 Methodology Standoff under MLF-68 component: 2 mil

17 Determining Critical Cleaning Process Parameters for QFNs Introduction Core Objectives Phase 1 Methodology Phase 1 Results Phase 2 Methodology Phase 2 Results Conclusion

18 Phase 1 Results Cleaning results were evaluated on the surface and underneath all components Percentage (%) area completely cleaned on all quadrants of the MLF were assessed Average of these values was taken as the % cleanliness for the trial

19 Phase 1 Results Overall cleanliness assessment underneath MLF-68 basis: 60% Clean 100% Clean 40% Clean 50% Clean 100% Clean 100% Clean 20% Clean 100% Clean % cleanliness = 42.5% % cleanliness = 100%

20 Phase 1 Results Water soluble lead free cleaning results: Trial # Paste Concentration (%) Spray Belt Speed Results (% clean) Configuration (ft/min) Underneath Surface V-jet % intermix V-jet w/s l/f 10% intermix V-jet % intermix

21 Phase 1 Results No-clean lead free cleaning results: Trial # Paste Concentration (%) Spray Belt Speed Results (% clean) Configuration (ft/min) Underneath Surface V-jet % intermix V-jet n/c l/f 10% intermix V-jet % intermix

22 Phase 1 Results Water soluble and no-clean fluxes easily cleaned from MLF-68 board surface in all scenarios

23 Phase 1 Results Water soluble flux averaged 96.94% cleanliness underneath all components

24 Phase 1 Results No-clean flux averaged 45.4% cleanliness underneath all components

25 Phase 1 Results

26 Phase 1 Results

27 Phase 1 Results

28 Phase 1 Results

29 Phase 1 Results The flux type is the most significant factor that determined cleanliness underneath the QFN component Improved cleaning results are achieved with: Higher concentration Slower belt speed Eight (8) spray bar intermix nozzle configuration

30 Phase 1 Results

31 Phase 1 Results Concentration, belt speed and spray configuration are not critical factors in cleaning water soluble fluxes from underneath the QFN component For no-clean fluxes, improved cleaning results are achieved with: Higher concentration Slower belt speed Eight (8) spray bar intermix nozzle configuration

32 Determining Critical Cleaning Process Parameters for QFNs Introduction Core Objectives Phase 1 Methodology Phase 1 Results Phase 2 Methodology Phase 2 Results Conclusion

33 Phase 2 Methodology Substrate used: Practical Component PCB007 test board MLF-20: 5 mm x 5 mm and 0.65 mm pitch MLF-44: 7 mm x 7 mm and 0.5 mm pitch MLF-68:10 mm x 10 mm and 0.5 mm pitch Dual Row MLF-156: 12 mm x 12 mm and 0.5 mm pitch

34 Phase 2 Methodology PCB007 test boards:

35 Phase 2 Methodology PCB007 test boards built at Rochester Institute of Technology Screened in automatic printer Components placed using pick and place machine Reflowed in a six (6) zone industrial reflow oven Boards returned to ZESTRON Technical Center for cleaning Fluxes were at least 24 hours old

36 Phase 2 Methodology Paste types used: Water Soluble Pastes Paste A Paste B Paste C Paste D No-clean Pastes Paste E Paste F Paste G Paste H

37 Phase 2 Methodology Belt Speed: 35.0 cm/min (287.5 seconds to peak temperature) Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Top: 110 C 125 C 165 C 200 C 240 C 260 C Bottom: 110 C 125 C 165 C 200 C 240 C 260 C

38 Phase 2 Methodology Standoff under MLF-20 component: 2 mil

39 Phase 2 Methodology Cleaning process settings (based on Phase 1 results): Cleaning Agent: Dynamic Surfactant Water Soluble Pastes: Cleaning Agent Concentration: 10% Inline Cleaner: Belt Speed: Spray Bar Configuration: 0.5 ft/min 8 bar intermix No-clean Pastes: Cleaning Agent Concentration: 15% Inline Cleaner: Belt Speed: Spray Bar Configuration: 0.5 ft/min 8 bar intermix

40 Determining Critical Cleaning Process Parameters for QFNs Introduction Core Objectives Phase 1 Methodology Phase 1 Results Phase 2 Methodology Phase 2 Results Conclusion

41 Phase 2 Results Wash Temperature Required for Complete Cleanliness Pastes MLF-20 MLF-44 MLF-68 Dualrow MLF-156 A 145 F 145 F 145 F 145 F W/S Pastes B 145 F 145 F 145 F 145 F C 145 F 145 F 145 F 145 F D 145 F 145 F 145 F 145 F N/C Pastes E 145 F 145 F 145 F 155 F F 145 F 145 F 155 F Residues under one component at 155 F G 145 F 145 F 145 F 155 F H 145 F 145 F 155 F 155 F

42 Phase 2 Results Paste F exhibited residues under one Dual Row MLF-156 component, although the other two on the same board were fully clean All no-clean pastes required 155 F to clean under the Dual Row MLF-156 Pastes F and H required 155 F to clean under the MLF-68 component

43 Phase 2 Results Underneath MLF-20 inspection after cleaning: Visual Analysis: Fully clean

44 Phase 2 Results Underneath MLF-44 inspection after cleaning: Visual Analysis: Fully clean

45 Phase 2 Results Underneath MLF-68 inspection after cleaning: Visual Analysis: Fully clean

46 Phase 2 Results Underneath Dual Row MLF-156 inspection after cleaning: Visual Analysis: Fully clean

47 Phase 2 Results Water Soluble Pastes: Anions and Weak Organic Acids Maximum (µg/in 2 ) Ionic Species Contamination Levels Paste A Paste B Paste C Paste D Fluoride (F - ) Acetate (C 2 H 2 O 2 ) 3 Formate (CH 2 O 2 ) 3 Chloride (Cl ( ) Nitrite (NO - 2 ) 3 Bromide (Br - ) Nitrate (NO - 3 ) 3 Phosphate (PO 2-4 ) Sulfate (SO 2-4 ) 3 WOA (Weak Organic Acid)(MSA) = Not Detected

48 Phase 2 Results Water Soluble Pastes: Cations Maximum (µg/in 2 ) Ionic Species Contamination Levels Paste A Paste B Paste C Paste D Lithium (Li) 3 Sodium (Na) Ammonium (NH 4 ) Potassium (K) Magnesium (Mg) 1 Calcium (Ca ( Ca) = Not Detected

49 Phase 2 Results No-clean Pastes: Anions and Weak Organic Acids Maximum (µg/in 2 ) Ionic Species Contamination Levels Paste E Paste F Paste G Paste H Fluoride (F - ) Acetate (C 2 H 2 O 2 ) 3 Formate (CH 2 O 2 ) 3 Chloride (Cl ( ) Nitrite (NO - 2 ) 3 Bromide (Br - ) Nitrate (NO - 3 ) Phosphate (PO 2-4 ) Sulfate (SO 2-4 ) 3 WOA (Weak Organic Acid)(MSA) = Not Detected

50 Phase 2 Results No-clean Pastes: Cations Maximum (µg/in 2 ) Ionic Species Contamination Levels Paste E Paste F Paste G Paste H Lithium (Li) 3 Sodium (Na) Ammonium (NH 4 ) Potassium (K) Magnesium (Mg) 1 Calcium (Ca ( Ca) = Not Detected

51 Determining Critical Cleaning Process Parameters for QFNs Introduction Core Objectives Phase 1 Methodology Phase 1 Results Phase 2 Methodology Phase 2 Results Conclusion

52 Conclusion Phase 1: Flux type is the most important factor to consider for achieving cleanliness underneath QFN components Water soluble flux residues were more easily cleaned as compared to the no-clean flux residues Cleaning agent concentration, wash exposure time and spray configuration are not as critical for achieving cleanliness of water soluble fluxes

53 Conclusion Phase 1: No-clean fluxes: Higher cleaning agent concentration, wash exposure time and the eight (8) spray bar manifold with the intermix nozzle technology resulted in better cleaning results underneath all QFN components Based on the DOE results, optimized cleaning process parameters are: Water soluble fluxes: 10%, 145 F, 0.5 ft/min, 8 spray bars No-clean fluxes: 15%, 145 F, 0.5 ft/min, 8 spray bars

54 Conclusion Phase 2: Water soluble fluxes: All four pastes were completely cleaned All the QFN types were completely cleaned

55 Conclusion Phase 2: No-clean Pastes E and G: Completely cleaned underneath MLF-20, MLF-44 and MLF-68 components using the process parameters determined in Phase 1 Dual Row MLF-156 were completely cleaned underneath at 155 F wash temperature No-clean Paste H: Completely cleaned underneath MLF-20 and MLF-44 components using the process parameters determined in Phase 1 Completely cleaned underneath MLF-68 and Dual Row MLF-156 at 155 F wash temperature

56 Conclusion Phase 2: No-clean Pastes F: Completely cleaned underneath MLF-20, MLF-44 components using the process parameters determined in Phase 1 Completely cleaned underneath MLF-68 components at 155 F wash temperature Slight residues remained under one of three Dual Row MLF-156 using 155 F wash temperature

57 Conclusion Phase 2: Specific no-clean paste types as well as the MLF size determine the process parameters required to clean underneath Cleanliness verified using Ion Chromatography IPC TM

58 Conclusion Visual inspection underneath all QFN component types used in this study as well as the Ion Chromatography results confirmed that a dynamic surfactant cleaning agent and an optimized inline cleaning process can fully clean the surface underneath low standoff MLF components!

59 Determining Critical Cleaning Process Parameters for QFNs Thank you! Questions? Speaker: Kalyan Nukala, M.S.Chem.Eng. Application Engineer