Experimenting with 7.5 Million Pastings: A Situation. Joe Voelkel CQAS, RIT 46 th Annual FTC

Transcription

1 Experimenting with 7.5 Million Pastings: A Situation Joe Voelkel, RIT 46 th Annual FTC Rev: 10/16/02 Paste Experiment 1 An Experiment? A knife? Rev: 10/16/02 Paste Experiment 2

2 Goal and Objective Goal Improve circuit-board assembly process Objective See how well solder paste can be deposited onto pads on circuit boards Rev: 10/16/02 Paste Experiment 3 Circuit Board 8" 10" Circuit Boards and Pads Where electronic components would be placed Pad 1/100" Want to put Solder Paste onto pads Rev: 10/16/02 Paste Experiment 4

3 Stencils Helps put paste onto the pads on the boards A set of holes for pushing paste through onto boards Stencil Board Rev: 10/16/02 Paste Experiment 5 Paste Squeegee Blade The material Screen Paste Stencil Board &Pads Rev: 10/16/02 Paste Experiment 6

4 Squeegee Blade Factors Considered Screen Paste Stencil Factors Board &Pads Rev: 10/16/02 Paste Experiment 7 Factors Considered Stencil 1. Technology 2. Manufacturer 3. Thickness 4. Solder-Paste Mfr 5. Board Finish 6. Component Type pad size Across-board factors Board factor Within-board factor Rev: 10/16/02 Paste Experiment 8

5 Factors 1. Stencil Technology 6 types Electroformed Chem Etch (CE) CE Eletropolished (CEE) Laser Cut (LC) LC Eletropolished (LCE) LCE Nickel plated (LCEN) Rev: 10/16/02 Paste Experiment 9 Factors 2. Stencil Manufacturer 5 manufacturers Manufacturers have only subset of technologies 19 Manufacturer/Technology combinations Stencil Manufacturer Electroform V X X X X 4 W X X X X 4 X X X XX X X 6 Y X X X 3 Z XX Stencil Technology Laser Laser Chem- Chem- Laser EP EP/NP Etch Etch EP Rev: 10/16/02 Paste Experiment 10

6 Factors 5 Mfr s 6 Tech s = 30 tc s 19 tc s Regard these 19 as a complex, unbalanced, fractional factorial design?? Stencil Technology Stencil Manufacturer Electroform Laser Laser EP Laser EP/NP Chem- Etch Chem- Etch EP V X X X X 4 W X X X X 4 X X X XX X X 6 Y X X X 3 Z XX No! Simply regard as one factor at 19 levels, and see what patterns develop Rev: 10/16/02 Paste Experiment 11 Factors 3. Stencil Thickness 4, 5, 6 mils 3 19 = 57 tc s So, a total of 19 3 = 57 (physical) stencils. A weakness of the design No replication of any stencils No direct ability to distinguish a stencil tech/mfr from stenciling variation Rev: 10/16/02 Paste Experiment 12

7 Factors 4. Solder-Paste Mfr Actually, a wide variety of solder pastes are available Only Type IV paste was used here Three manufacturers X Y Z 3 57 = 171 tc s Rev: 10/16/02 Paste Experiment Board Finishes Factors Two finishes HASL (Hot Air Solder Level) Ni/Au = 342 tc s For each finish, about 20 physical boards. Each of these 40 boards would wait in a queue get processed (paste applied to it) get measured get cleaned get placed back in the queue Board ID s tracked to look for bad ones Rev: 10/16/02 Paste Experiment 14

8 So Far Stencil 1. Technology 2. Manufacturer 3. Thickness 4. Solder-Paste Mfr 5. Board Finish 6. Component Type pad size Across-board factors Board factor Within-board factor Rev: 10/16/02 Paste Experiment 15 Now What? = 1368 boards For each of the 342 tc s may run 4 covered boards to have paste flow well process 4 physical boards Two processed front-to-back, two back-to-front Another (secondary-consideration) factor Rev: 10/16/02 Paste Experiment 16

9 Experimental Restrictions Changing Stencils (1 3) took a bit of time Pastes were hardest to change, but had to be changed after every 16 boards processed (4 tc s) Stencil 1. Technology 2. Manufacturer 3. Thickness 4. Solder-Paste Type 5. Board Finish 6. Component Type pad size Board finish was easy to change just put in different boards Across-board factors Board factor Within-board factor Rev: 10/16/02 Paste Experiment 17 Total of 342 runs Example of Processing Order Stencil Run St# Mfr Tech Thick Paste Board 9 11 Y Laser 5 X HASL Y Laser 5 X Ni/Au V Chem-Etch 5 X HASL V Chem-Etch 5 X Ni/Au Y Laser 1 6 Z HASL Y Laser 1 6 Z Ni/Au W CJ Laser EP 4 Z HASL W CJ Laser EP 4 Z Ni/Au 17 7 X Electroform 4 Y HASL 18 7 X Electroform 4 Y Ni/Au Z Laser EP/NP 6 Y HASL Z Laser EP/NP 6 Y Ni/Au 4 boards /run How was order created? 1. Non-random order in Excel. 2. Randomized, with restrictions, in MINITAB 3. Back into Excel Rev: 10/16/02 Paste Experiment 18

10 How to Reduce Errors in Processing? Overworked grad students Stencil Run St# Mfr Tech Thick Paste Board 9 11 Y Laser 5 X HASL Y Laser 5 X Ni/Au V Chem-Etch 5 X HASL V Chem Etch 5 X Ni/Au Stencils # d = 3 factors Rev: 10/16/02 Paste Experiment 19 How to Reduce Errors in Processing? Convert Stencil Run St# Mfr Tech Thick Paste Board 9 11 Y Laser 5 X HASL Y Laser 5 X Ni/Au V Chem-Etch 5 X HASL V Chem Etch 5 X Ni/Au 342 lines of run info from Excel To 342 pages in Word Use of Visual Basic in Excel to export information Use of Word macro to clean up, format, apply headers/footers Rev: 10/16/02 Paste Experiment 20

11 Result Stencil Run St# Mfr Tech Thick Paste Board 9 11 Y Laser 5 X HASL Y Laser 5 X Ni/Au V Chem-Etch 5 X HASL V Chem Etch 5 X Ni/Au Rev: 10/16/02 Paste Experiment 21 Results Rev: 10/16/02 Paste Experiment 22

12 How Bout Them Boards?? Each board was designed to accept components with different-sized pads 13 sets of Components Components themselves were not part of the experiment only the pad configurations associated with them A = 20 mil QFP B = 16 mil QFP C = BGA225 D = BGA352 E = CSP46 F = CSP208 G = FC48 H = 0201 I = 0402 J = 0603 K = 0805 L = CBGA256 M = CBGA196 All boards designed with same pattern Each component type was placed on two (or more) sections of the board, to try to balance out any frontback and left-right effects Rev: 10/16/02 Paste Experiment 23 Board Configuration Rev: 10/16/02 Paste Experiment 24

13 Board Configuration 1/5" 1/100" Rev: 10/16/02 Paste Experiment 25 Board Configuration Rev: 10/16/02 Paste Experiment 26

14 Board Configuration component diam 1/100" paste Rev: 10/16/02 Paste Experiment 27 # of Pads per Board, # Pads Design Component #pads/board A = 20 mil QFP 400 B = 16 mil QFP 480 C = BGA D = BGA E = CSP46 92 F = CSP G = FC48 96 H = I = J = K = L = CBGA M = CBGA Total 5, boards 5,462 = 7.5 million pads Each pad paste data point Rev: 10/16/02 Paste Experiment 28

15 How Many Conditions per Board? Condition Smallest unit for which we anticipate results should be similar diam 1/100" 1 Condition 5,462 pads/board 258 conditions/board 5 Conditions Rev: 10/16/02 Paste Experiment 29 Preprocessing Each run/board combination 5,462 pads The 5,462 pads were measured for area and height volume 5,462 rows exported to file Run#.for, e.g. 13.for Example of Preprocessing, in Excel 13.for (height 6 mil) Analyze via GSI_Summary5.xls FC48 and raw data plots vs row, and outliers Mostly % Transfer, later 5,462 rows 258 rows diam 1/100" Rev: 10/16/02 Paste Experiment 30

16 # of Pads per Board, # Pads Analysis In the design, certain pad conditions were not consistent with IPC standards. These were to be handled in a separate analysis. 3,222 of 5,462 were consistent with standards. 3,222 pads/board 66 conditions/board 66 conditions/board = 85,536 rows of data for IPC analysis In addition,18 tc s were not run poor stencils, so 324 of 342 were run, still with 4 boards per run So, # of pads for IPC analysis 3, = 4.2 millions pads. Rev: 10/16/02 Paste Experiment 31 Show Me the Money!!! OK, OK, show me some analysis!! Software Strategy Originally SPLUS. But too unnatural Do in SAS Better data integrity & speed Much nicer tabling features Analysis Strategy % Transfer (Actual/Theoretical Paste Volume) Separate analysis for each of 13 components (pad sizes). Informal analysis look for anomalies in data Formal analysis Rev: 10/16/02 Paste Experiment 32

17 Informal Analysis 66 conds/bd = 85,536 rows % Distribution of % Transfer Overall (Component-Condition Averages) by Component Name. 6 of 13 Components shown. Bad! No Paste Component Name BGA225 BGA > Total Bad! Flooding Rev: 10/16/02 Paste Experiment 33 Informal Analysis 0603 N=10,368 of 85,536 Rev: 10/16/02 Paste Experiment 34

18 Stencil Formal Analysis: Remember the Factors? N=324 tc s (runs) for each component ( components=4,212 observations) 1. Technology 2. Manufacturer 3. Thickness 4. Solder-Paste Type 5. Board Finish 6. Component Type pad size Across-board factors Board factor Within-board factor = Rev: 10/16/02 Paste Experiment 35 Formal Analysis 1 st, GLM for each component COMP_NAM=0603 Dependent Variable: PCT_TRA1 Source DF SS Model Error Corrected Total R-Sq CV RMSE Mean Source DF F Value Pr > F MTTF_C <.0001 THICK_C <.0001 PASTE <.0001 BOARD <.0001 MTTF_C*THICK_C <.0001 MTTF_C*PASTE <.0001 MTTF_C*BOARD THICK_C*PASTE <.0001 THICK_C*BOARD PASTE*BOARD Rev: 10/16/02 Paste Experiment 36

19 Formal Analysis Can t show and explain every statistically significant effect Too many confusion get lost in minutiae Want to show only practically significant effects Strategy. Use estimates, not hypothesis tests Estimates: fixed-effects variance components Basically, Φ(effect), adjusted by df/(# of levels) n µ µ n Estimates? ( ) 2 i= 1 i Rev: 10/16/02 Paste Experiment 37 Formal Analysis Now have 13 GLM s, one for each component 2 nd write SAS code to read in GLM o/p and return variance components, on % of total basis Source DF F Value Pr > F MTTF_C <.0001 THICK_C <.0001 PASTE <.0001 BOARD <.0001 MTTF_C*THICK_C <.0001 MTTF_C*PASTE <.0001 MTTF_C*BOARD THICK_C*PASTE <.0001 THICK_C*BOARD PASTE*BOARD Source StMT Thick 9 14 Paste 24 Board 4 StMT*Thick 6 StMT*Paste 5 StMT*Board 0 Thick*Paste 15 Thick*Board 0 Paste*Board 1 Error 23 Total 100 Rev: 10/16/02 Paste Experiment 38

20 Formal Analysis 3 rd Table results. Sort components in table by increasing pad area Rev: 10/16/02 Paste Experiment FC CSP CSP Component Pad Area and Name CBGA CBGA QFP BGA BGA QFP All Source StMT Thick 34 < mil Increasing Pad Area Paste Board >400 6 mil StMT* Thick StMT* Table tells us what First Graph, % Transfer vs Paste StMT* graphs to make Comp Size for each StMT Board Thick* Paste Thick* Board Paste* Board Error Total Rev: 10/16/02 Paste Experiment 40

21 80% 20% 19 lines= 19 St Mfr/Tech s Component Pad Area and Name CSP BGA CBGA CBGA QFP BGA QFP Increasing Pad Area FC CSP All Source StMT Rev: 10/16/02 Paste Experiment 41 Least Robust wrt Pad Size 19 6 lines= 6 St Technologies: CE, LC, Electroform, Increasing Pad Area Rev: 10/16/02 Paste Experiment 42

22 Least Robust wrt Pad Size 3 lines= 3 Paste Types Rev: 10/16/02 Paste Experiment 43 3 lines= 3 St Thicknesses 0080 FC CSP CSP Component Pad Area and Name CBGA CBGA QFP BGA BGA QFP All Source StMT Thick Rev: 10/16/02 Paste Experiment 44

23 Summary Design factorial, 4 boards 13 components (5,500 pads)=7.5m pads Protocol Randomized w/i practical constraints Error-Proofing Preprocessing 5,462 pads 258 rows %Transfer (Act/Theor Vol) Informal Analysis Look for anomalies Formal Analysis For each component Sorted by pad area % variance explained Key graphs Physical interpretation of results Rev: 10/16/02 Paste Experiment 45 Stencil 1. Technology Across-board 2. Manufacturer Stencil factors 3. Thickness Run St# Mfr Tech Thick Paste Board 4. Solder-Paste Type 9 11 Y Laser 5 Kester HASL 5. Board Finish Y Board Laser factor 5 Kester Ni/Au V Chem-Etch 5 Kester HASL 6. Component Type V Within-board Chem-Etch 5 Kester Ni/Au pad size YSource Laser factor 1 DF 6F Value IndiumPr HASL > F MTTF_C < Y Laser 1 6 Indium Ni/Au THICK_C < WPASTE CJ Laser EP Indium<.0001 HASL WBOARD CJ Laser EP 14 Least Indium<.0001 Ni/Au 17 7 XMTTF_C*THICK_C Electroform 33 Robust Alpha wrt <.0001 HASL 18 7 XMTTF_C*PASTE Electroform Alpha<.0001 Ni/Au Z MTTF_C*BOARD Laser EP/NP 18 Pad Size Alpha HASL THICK_C*PASTE < Z Laser EP/NP 6 Alpha Ni/Au THICK_C*BOARD PASTE*BOARD Source StMT Thick 9 14 Paste 24 Board 4 StMT*Thick 6 StMT*Paste 5 StMT*Board 0 Thick*Paste 15 Thick*Board 0 Paste*Board 1 Error 23 Total lines= 6 St Technologies Increasing Pad Area Rev: 10/16/02 Paste Experiment 46