Influence of pick & place machines on product quality. The impact of placement quality on SMT manufacturing costs

Transcription

1 Influence of pick & place machines on product quality The impact of placement quality on SMT manufacturing costs

2 Introduction ABOUT ASSEMBLEON

3 Assembléon Headquarters in Veldhoven (Netherlands) A-series AX- Hybrid iflex Assembléon s focus is to provide competitive solutions for the electronics manufacturing industry based upon our core strength in Pick and Place machines 3

4 SMT process quality influencing factors SMT PROCESS Q CRITERIA 4

5 Typical SMT process flow Solder paste printing Component placement Reflow soldering 5

6 SMT process requirements Solder paste printing Component placement Reflow soldering Process requirements Right amount Right place Right component Right place Right temperature profile Good reflow 6

7 Assessment criteria for stencil printing process. Solder paste pattern resolution (paste transfer) 2. Bridging ( smearing ) 3. Misalignment Stencil printing 7

8 Solder paste pattern resolution OK! no paste irregular shape (few balls) 2 pyramid lower than stencil thickness 3 pyramid equal to stencil thickness 4 beginning flat top with "dog ears" 5 flat top side 6 scooped-out Stencil printing 8

9 Solder paste smearing Criterion: Neighboring pads May not have contact Smearing OK! Stencil printing Flux with incidental balls Perfect 9

10 Solder paste pattern misalignment 00% of paste centered on pad < 25% of paste off-pad > 25% of paste off-pad Perfect Acceptable Not acceptable 00% of paste on pad < 25% of paste off-pad > 25% of paste off-pad Remedy: Board to stencil alignment correction Acceptable Acceptable Not acceptable Stencil printing 0

11 Placement defect analysis Part misaligned Incorrect part Part damaged Wrong polarity Mis read fiducials Machine needs calibration Placement error Alignment error Part slid off pads Incorrect part reel loading Tape splice error Part damaged at supplier Placement force too high Programming error Tray rotated Misalignment Solder bridging Tombstoning Incorrect part Opens Component cracking Tilted part Wrong polarity Extra / missing part Symptom (before reflow) Part lost during pick & place Cause Extra / missing part Defect (end of process) Pick & place

12 Reflow solder process requirements Temperature deg. C 235 deg. C 27 deg. C 205 deg. C 80 deg. C 60 deg. C Maximum soldering temperature Minimum soldering temperature Soack Soak Reflow Reflow zone for Lead-free Reflow zone for PbSn Pre-heat < 70 sec < 60 sec < 70 sec Time < 3 C / sec < 6 C / sec Reflow soldering 2

13 Reflow process defect analysis Peak temperature too high: Charring Delamination Intermetallics Leaching Dewetting Voiding Ramp-up rate too high Hot Slump Bridging Tombstoning Skewing Wicking Opens Solder beading Solder balling Components cracking. Reflow soldering Soaking Zone too long Voiding Poor Wetting Solder Balling Opens Cooling rate too fast Solder detachment Pad Detachment Cooling rate too slow Intermetalllics Charring Leaching Dewetting Grain Size too large 3

14 Acceptable part to pad misalignment (IPC-A-60D) Self alignment: solder to pad Self alignment: part to solder Before reflow After reflow Reflow soldering 4

15 Relationship placement machine concept and placement quality control PICK & PLACE RELATED ERRORS 5

16 Possible defects in SMT: defect opportunities. Component opportunities (O C ) All parts that need to be assembled on board (incl. PCB) Every part counts for one defect opportunity Defect example: damaged parts 2. Placement opportunity (O P ) All parts that need to be placed on board, based on bill of materials (excl. PCB) Every part counts for one defect opportunity Defect examples: misaligned parts, missing parts 3. Termination opportunity (O T ) Any hole, pad or land or other surface to which a component is electrically terminated Every termination counts for one defect opportunity (example: QFP48 48 leads 48 termination opportunities) 4. Assembly opportunity (O A ) An overall defect opportunity that is not captured within component, placement or termination opportunity defect classes Defect examples: conformal coating, cleaning 6

17 IPC-926A Defect classification overview Base material damage Part lead stressed 2 Wire connected wrong Bent lead Plating or other finish problem 2 Wire routing wrong Birdcaged wire Sleeving problem 3 Blow holes Blisters, mealing, peeling Solderability problem 3 Cold solder joint Board warped or bowed Spliced where not permitted 3 Disturbed solder joint Cable made wrong Unprepped part 3 Fractured solder joint Circuitry damaged Wire damage 3 Icicles Connector damaged Wire not tinned where required 3 Insufficient solder Gold not removed 2 Cable connected wrong 3 Lead protrusion wrong Improper stress relief 2 Parts / loose / missing / wrong 3 Part coating meniscus in joint Incorrect terminal flange 2 Crimping wrong 3 Solder bridge Insulation or wire damage 2 Improper mounting 3 Solder wetting unacceptable Lead bend problem 2 Lead / cable routing wrong 3 Unsoldered connection Lead coplanarity out of spec 2 Min. electrical clearance violated 4 Assembly not clean Lead forming wrong 2 Part height wrong 4 Conformal coating absent Lead / cable length wrong 2 Part misaligned 4 Conformal coating peeling Leads bent under 2 Part extra 4 Conform. coat. present unwanted Leads not tinned 2 Part mounted wrong 4 Solder balls / splash Marking incorrect 2 Tilted part Part damaged 2 Tombstone ) Component defects 2) Placement defects 3) Termination defects 4) Assembly defects 7

18 Estimated Yield Yield vs. number of defect opportunities Mobile phone application Defect opportunities DPMO = Lower DPMO will increase Yield and thus reduce repair costs 8

19 Most pick & place machines are sequential PLACEMENT HEAD Pick Place High accelerations / decelerations High forces acting on components risk of component shift or loss No component position monitoring between component alignment and placement position In most cases: no placement force control / no presence check 9

20 Acceleration forces acting on pipettes D i D o m.a [N] m.g [N] H g F friction a [m/s 2 ] Risk of components shift: Acceleration force (= m.a) > friction force Risk of components break loose: m.a.h g > F vacuum.(d o /2) Revolver & turret heads add extra acceleration forces 20

21 Parallel pick & place principle PLACEMENT HEAD TRANSFER PLACE COMPONENT SUPPLY PCBs PICK Multiple parallel placement robots Indexing board transport Single placement head per robot 2

22 Total pick & place process control Component presence check Component force control Component pick correction Place Component presence check Component inspection Component alignment On-edge detection Pick height control Pick Component presence check 22

23 Placement head with integrated P&P process feedback Phi-Z module BA-camera module Laser Align module PCB Auto calibration Short accuracy loops Component pick correction 23

24 Force control No force control: Risk of component cracking Placement head PCB Contact stiffness Impact force is determined by : Velocity High velocity high impact force Contact stiffness High stiffness high impact force Impact mass High mass high impact force F F placement F v impact F m static impact k contact 24

25 Impact force control height force Impact detection Static force PCB / Substrate 25

26 Placement defect prevention Auto calibration Short accuracy loops Part misaligned Setup verification Incorrect part Part damaged Force control Wrong polarity Mis read fiducials Machine needs calibration Placement error Alignment error Part slid off pads Incorrect part reel loading Tape splice error Part damaged at supplier Placement force too high Programming error Tray rotated Low accelerations Misalignment Servo Z movement Solder On edge bridging detection Tombstoning Pick correction Splice detection Incorrect part Opens Component cracking Tilted part Wrong Presence polaritycheck Extra / missing part Pick & place Symptom (before reflow) Part lost during pick & place Cause Extra / missing part Defect (end of process) 26

27 Relationship DPMO and rework costs RESULTS 27

28 DPMO results for parallel placement machines WORK MONTH INSPECTION(output) PASS FAILED TOTAL DEFECT DPU DPMO DPU control level DPMO control level WORK MONTH INSPECTION(output) PASS FAILED TOTAL DEFECT DPU DPMO DPU control level DPMO control level DEFECT BREAKDOWN QTY QTY QTY QTY QTY COMPONENT RELATED Bend lead PROCESS RELATED DEFECT Wrong Direction Wrong Component Missing Component Extra Component 3 2 Damaged Component Misalignment Tombstone Component reversal 4 Component incline Component high total defect DPM DEFECT BREAKDOWN QTY QTY QTY QTY QTY COMPONENT RELATED Bend lead PROCESS RELATED DEFECT Wrong Direction Wrong Component Missing Component Extra Component Damaged Component Misalignment 6 3 Tombstone Component reversal Component incline Component high total defect DPM Product: LCD television (Shenzhen, China) (790 parts / board) Line A: Parallel placement DPU total (5 days) = Y = 96.% Line B: Sequential placement DPU total (5 days) = Y = 75% Difference in first pass yield: 2.% 28

29 Example: Rework cost savings for LCD television Item Parallel line Sequential line # Productive hours per year Real output per line [cph] # Components per board # Defect opportunities per board DPMO 7 50 DPU First pass yield [%] 96% 75% Average BOM cost per part [ ] Line cycle time [s] # Repairs per hour (board level) 5 3 Average rework per hour [s] # Rework operators (3 shifts) 2 4 Annual labor cost per operator [k ] 3 3 Total annual labor cost [k ] 7 45 # Rework stations needed 5 Annual station costs (excl. labor) [k ] Annual BOM rework costs [k ] 3 7 Total repairs per line per year [-] Total repair costs per line (per year) [k ] Average defect coverage [%] # Boards needing second order rework (per year) Average second order rework per hour [s] # Rework operators (3 shifts) 0 2 Total annual labor cost [k ] 5 # Rework stations needed Annual station costs (excl. labor) [k ] Annual BOM rework costs [k ] Second order repair costs (per year) [k ] Total repair costs per line (incl. defect recov. per year) [k ]

30 Quality inspection methods AXI Automatic X-ray Inspection ICT In-Circuit Test AOI Automatic Optical Inspection 30

31 Defect coverage estimates Source: Nokia & University of Oulu, Finland, 2005 HVI: Human Visual Inspection ICT: In Circuit Testing AOI: Automatic Optical Inspection AXI: Automatic X-ray Inspection BSCAN: Boundary Scan A combination of different test methods is needed for optimal test coverage Approximate test coverage: 90% ( 0% of all defects is not detected) 3

32 Conclusion Prevention is better than cure Solder paste printing Selection of optimal stencil & aperture definition Selection of optimal printing parameters Process monitoring (stencil cleaning, paste replenishment, etc.) Component placement Monitoring of every pick & place process step Selection of optimal P&P parameters ( Take it easy ) Reflow soldering Selection of optimal reflow temperature profile Reflow process control Parallel placement principle gives intrinsically better placement quality Continuous process monitoring More time available per process step less risks Result: Typical DPMO 0 Considerable savings on rework cost! 32

33 Sjef van Gastel October 3 rd 202