Wafer probe challenges for the automotive market Luc Van Cauwenberghe ON Semiconductor
Overview Automotive wafer probe requirements Results of experiments Summary Follow on Work Acknowledgements 2
Automotive wafer probe requirements Temperature 55ºC up to 200ºC Probed die deliveries: Full test coverage at probe Dual and tri temp probe Disturbed area on bond pad Multiple probe insertions Bond pad size reduction smaller Si area Bond wire diameter in Multi Chip Modules 3
Impact of temperature on probe card PCB temperature profile Z movement of probes X Y movement of probes 4
PCB temperature Radient heat transfer Thermal expansion of the PCB dominates the mechanical behavior of the complete probe card assembly CTE XY (ppm/ C) CTE Z (ppm/ C) FR4 `` 140 to 220 Rogers 11 to 16 46 to 50 N7000 10 to 12 2,5% N8000 11 to 13 70 to 375 Temperature limitation active and passive components Relays: typical maximum 85ºC or 125ºC Active components: typical maximum up to 125ºC Passive components: typical maximum 125ºC to 150ºC 5
PCB temperature evolution at hot PCB Temperature ( C) 100 90 80 70 60 50 40 30 20 10 0 start Left 1/4 wafer Top Bottom 1/2wafer Right Spider PCB Back Top PCB Back Bottom PCB Back Left PCB Back Right 3/4 wafer full wafer start Spider PCB Conclusion: Spider temp ½ Prober set temp PCB back side temp ⅓ Prober set temp Results independed cantilever vertical 1/4 wafer 1/2wafer 3/4 wafer full wafer start 1/4 wafer 1/2wafer 3/4 wafer full wafer 70 C 125 C 150 C Prober Set temperature / Test Time 6
PCB temperature evolution at cold 30 20 10 PCB Temperature ( C) 0-10 -20-30 -40-50 start 1/4 wafer 1/2wafer 3/4 wafer full wafer Findings & Conclusion @ cold: No major difference component side wafer side Less temperature variation over time vs hot probe Results independed cantilever vertical PCB Front PCB Back -50 C Prober Set temperature / Test Time 7
Z movement of probes Ambient Probe Head Probe PCB Space transformer High Temp T spider ⅓ T chuck T spider ½ T chuck Root cause Continuous moving heat source (chuck) Thermal behavior probe card assembly Build quality of the spider / probe head Independent of probe card type T chuck 8
Z deflection experiment: Initial conditions Soak prior to measurements Prober soak: 2hrs after reaching set temp Probe card soak: 10 min After prober soak Chuck centered under the probe card No contact Zero level = needle position after soak Process settings Test time per wafer: 1hr 10min Probe polish interval: every 100 die Probe polish recipe: 25 touch downs, 20µm overdrive 9
Z deflection: standard probe card at 175ºC 20 TESTER Start Probe Probe Polish Test Time 0 0:00 0:05 0:10 0:15 0:20 0:25 0:30 0:35 0:40 0:45 0:50 0:55 1:00 1:05 1:10 Z deflection (µm) -20-40 -60-80 -100-120 Chuck Independent of probe card type (cantilever or vertical) End Probe 10
Z deflection: standard probe card at 50ºC 80 70 60 TESTER Start Probe Z deflection (µm) 50 40 30 20 Probe Polish 10 Test Time 00 00:00 10:00 20:00 30:00 40:00 50:00 End Probe -10-20 Chuck Independent of probe card type (cantilever or vertical) 11
Z deflection: High Temp probe cards at 175ºC 60 TESTER 50 40 Start Probe Probe Card A: Spider Stiffener Heat shielded Z deflection (µm) 30 20 10 Probe Card B: Bridge Stiffener Test Time 0 0:00 0:05 0:10 0:15 0:20 0:25 0:30 0:35 0:40 0:45 0:50 0:55 1:00 1:05 1:10-10 -20-30 Chuck Probe Polish: limited impact on Z deflection Independent of probe card type (cantilever or vertical) End Probe 12
Z deflection: ON Semi High Temp probe cards at 175ºC 60 40 20 TESTER Start Probe Probe Card B: Bridge Stiffener Probe Card A: Spider Stiffener Heat shielded Z deflection (µm) -20-40 -60 Test Time 0 0:00 0:05 0:10 0:15 0:20 0:25 0:30 0:35 0:40 0:45 0:50 0:55 1:00 1:28 1:33 Probe Card D: ON Semi -80-100 -120 Chuck Probe Card C: Standard End Probe 13
Z deflection: ON Semi High Temp probe cards at 50ºC 80 TESTER 70 Start Probe 60 Z deflection (µm) 50 40 30 20 10 Probe Card C: Standard Probe Card D: ON Semi 00 00:00 10:00 20:00 30:00 40:00 50:00-10 -20 Test Time Chuck Independent of probe card type (cantilever or vertical) End Probe 14
ON Semi High Temp probe cards Patented design: US 7,816,930 Bridge stiffener concept Allows PCB expansion without Z deflection Implemented on: Teradyne uflex Teradyne Catalyst SZ M3650 & Falcon Credence ASL1000 15
X Y movement of probes 175ºC 100% 90% 80% 70% 60% 50% 40% 30% Probe movement vs temperature Cantilever: Swaying needles Vertical: Probe head drift 25ºC 20% 10% 00% Ambient Hot Root cause Build quality of the spider (cantilever) Build quality of entire probe card assembly Memory effect of the probes (cantilever) Thermal behavior probe card assembly 16
Experiment: X/Y movement Cantilever probe cards Swaying Probes Inspection limits 25 ºC: +/ 7.5µm Inspection limits High temp + Cold: +/ 12.5µm 17
Experiment: X/Y movement Vertical probe cards Inspection limits 25 ºC: +/ 7.5µm Inspection limits High temp + Cold: +/ 12.5µm 18
Bond pad damage Key for probed die deliveries Max disturbed area Diameter of entire probe mark area 28μm ( 615µm2) Probe depth Maximum half of the thickness of top layer (T) of pad metallization Maximum 500nm Number of probe marks Number of probe insertions + 1 19
Experiment: Bond pad disturbance Evaluation disturbed area and probe depth Test conditions Temperature: 25ºC Touch count: 1 Overdrive Cantilever: Typical production setting Overdrive Vertical: Max allowed overdrive 20
Max disturbed area ( 615µm2) Cantilever (25 µm tip) Cantilever Technoprobe No Scrub TM (25 µm tip) Vertical Technoprobe Route 60 (13 µm tip) 10 μm 10 μm Overdrive: 30µm Disturbed are: 610 µm 2 Vertical Buckling beam Vendor A (10 µm tip) Overdrive: 30µm Disturbed are: 200 µm 2 Vertical Buckling beam Vendor B (12 µm tip) Overdrive: 100µm Disturbed are: 295 µm 2 Vertical Buckling beam Vendor C (7 µm tip) 10 μm 10 μm 10 μm Overdrive: 100µm Disturbed are: 183µm 2 Overdrive: 100µm Disturbed are: 199 µm 2 Overdrive: 65µm Disturbed are: 76 µm 2 21
Probe depth ( 500nm or ½ top metal thickness) Cantilever (25 µm tip) Cantilever Technoprobe No Scrub TM (25 µm tip) Vertical Technoprobe Route 60 (25 µm tip) Probe depth: 527nm Probe depth: 270nm Probe depth: 360nm Vertical Buckling beam Vendor A (10 µm tip) Vertical Buckling beam Vendor B (12 µm tip) Vertical Buckling beam Vendor C (7 µm tip) Probe depth: 430nm Probe depth: 391nm Probe depth: 292nm
Overdrive vs disturbed area Cantilever (25µm tip diameter) Overdrive = 15 µm Overdrive = 30 µm Overdrive = 60 µm 10 μm 10 μm 10 μm 130µm 2 270µm 2 527µm 2 Vertical (10µm tip diameter) Overdrive = 25 µm Overdrive = 50 µm Overdrive = 75 µm Overdrive = 100 µm 10 μm 10 μm 10 μm 10 μm 174µm 2 182µm 2 183µm 2 183µm 2
Number of probe marks Probe mark Touch count Probe mark: Individual visible imprint of a probe Number of probe insertions + 1 Touch count: Number of touch downs on the bond pad Top metal thickness 5500Å: max touch count =3 Top metal thickness >5500Å: max touch count =5 Impact: Increased disturbed area Why multiple probe marks? Dual or tri temp probe Multi DUT probe and re probe Data retention bake pre and post bake probe 24
Probe card technology vs number of probe marks and disturbed area 1 Probe mark 2 Probe marks 3 Probe marks 4 Probe marks Cantilever probe cards (25µm tip) Vertical probe cards No Scrub TM (25µm tip) Vertical probe cards ( 25µm tip) No Scrub TM (25µm tip) Vertical probe cards (12µm tip) No Scrub TM (25µm tip) Vertical probe cards (<12µm tip) Multiple DUT probe with multiple probe insertions is only possible with advance probe card technologies The probe tip diameter selection is critical to comply with the max disturbed area requirement 25
Impact of touch count Experiment on cantilever touch count Overdrive = 75μm (worst case) Increment touch count 1 to 7 Thin top metal: thickness 5500Å Conclusion: Cantilever: Impact on probe depth and disurbed area (scrub) Aluminum build up at end of scrub Vertical: main impact on probe depth Touch count 5 : Exposed Metal Oxide (EMO) 10 μm 10 μm 10 μm 10 μm 10 μm 10 μm 10 μm Touch count = 1 Touch count = 2 Touch count = 3 Touch count = 4 Touch count = 5 Touch count = 6 Touch count = 7 26
Cantilever probe impacts bond process Aluminum build up at end of probe mark Build up amount driven by overdrive and touch count Random height Intermetallics only formed at part of the bond area Potential risk: Bond ball lift at temperature 27
Summary: Temperature impact Z deflection Dominated by PCB thermal behavior Best result at 175ºC: 15µm Best result at 50ºC: 10µm XY movement of probes Cantilever : Large differences depending on spider build quality Difference between individual probes Swaying probes Vertical : Determined by probe head design All probes show similar movement Probe head drift Best result at 175ºC: 6µm 28
Summary: Bond pad damage Automotive requirements and multi DUT probe require more advanced probe card technologies Standard Cantilever probe cards Disturbed area is very dependent on applied overdrive Difficult to comply with automotive requirements No Scrub TM (Technoprobe) is a potential alternative Vertical probe cards Probe tip diameter drives the disturbed area Disturbed area is less dependent on applied overdrive ON Semiconductor uses ROUTE 60 LL (Technoprobe) for high temp Combined with ON Semiconductor patented concept for high temp cards High current carrying capability: 850 ma Low pad damage Life time (tip length) ROUTE 60 LL 29
Future work Wafer probe at 200ºC Optimize Multi DUT probe recipes to reduce number of probe marks and touch count Ongoing evaluation on impact of the probe card configuration Ongoing evaluation of Multi DUT probe stepping pattern Analyze the influence of temperature on Contact Resistance (Cres) Analyze behavior of probe on Over Pad Metalization (OPM) 30
Frank De Ruyck Equipment Engineer, ON Semiconductor Wim Dobbelaere Director Test & Product Engineering Automotive Mixed Signal, ON Semiconductor Riccardo Vettori R&D and Process Engineer, Technoprobe Riccardo Liberini Mechanical Design Manager, Technoprobe Marco Di Egidio Acknowledgements Process Engineer, Technoprobe 31