Formfactor, Inc. · NASDAQ:FORM
Formfactor — Technical Presentation (June 2015)
14 slides from Formfactor's technical presentation, June 2015
Slide 1: Determining Probe's Maximum Allowable Current
Determining Probe’s Maximum Allowable Current Amer Cassier, Richard Folwarski (Qualcomm Technologies Inc.) Jarek Kister, Amy Leong (FormFactor) Qualcomm is a trademark of Qualcomm Incorporated, registered in the United States and other countries, used with permission. Other product and brand names m
Slide 2: Overview
Overview • ISMI CCC Spec vs. what wafer test engineer needs to know • Introducing Maximum Allowable Current (MAC) concept • Method for finding singular MAC value • Confirmation of MAC performance in repeatable loading • Relationship between MAC and CCC • MAC vs. current pulse width • Ways to minimiz
Slide 3: Cassier, Folwarski Kister, Leong
Cassier, Folwarski 3 Kister, Leong
Slide 4: CCC-level Current Damages Probes
CCC-level Current Damages Probes Test 1 Test 2 Test 3 CCC #3 CCC #2 CCC #1 Test 1 Test 2 Test 3 • The same probe tested for CCC three times shows diminishing actual CCC and Tip planarity, ~150mA reduction per test • Probes cannot sustain CCC-level current due to loss of planarity and contact force •
Slide 5: Probe ISMI-CCC Spec Does not Define Current that Probe Could Carry After Multiple Exposure
Probe ISMI-CCC Spec Does not Define Current that Probe Could Carry After Multiple Exposure in Production • Disparity between what test engineer needs to know about the probe and what ISMI-CCC spec defines: – Test engineer asks for maximum current that can be carried by the probe thousands of times w
Slide 6: Maximum Allowable Current Measurement Setup
Maximum Allowable Current Measurement Setup Deflection, Contact Force, Planarity Program mable Power Supply • Use probe tip’s planarity change in response to current pulses as a proxy for defining probe’s Maximum Allowable Current (MAC) • Each probe is tested at a unique current level in increasing
Slide 7: Calculation of MAC value
Maximum Allowable Current Calculation of MAC value No change to tip’s planarity Calculated MAC (0.1um) (742mA) • Plotting Log of planarity change vs. Log of current (use linear scale) allows for linearization of otherwise asymptotic curve • Finding best-fit line equation to the data is easy and used
Slide 8: Confirmation of MAC concept, Stable Probe Tip Planarity after 35k MAC pulses
Confirmation of MAC concept, Stable Probe Tip Planarity after 35k MAC pulses • No change to probe tip’s planarity during the performed 35k MAC (742mA) pulses • Each pulse 1min-on/1sec- off • 75um probe deflection (742mA) Cassier, Folwarski 8 Kister, Leong
Slide 9: MAC vs. CCC for a Range of Probes
MAC vs. CCC for a Range of Probes 1 2 10 pulses 50 pulses 3 4 • MAC/CCC Ratio is not a constant, is probe architecture dependent Probe ISMI CCC, mA MAC, mA MAC/CCC 1 450 278 ~0.6 2 800 478 ~0.6 3 800 637 ~0.8 4 900 742 ~0.8 Cassier, Folwarski, 9 Kister, Leong
Slide 10: MAC vs. Current Pulse Width for a 900mA CCC/742mA MAC probe
MAC vs. Current Pulse Width for a 900mA CCC/742mA MAC probe • For current pulse >=70mS the MAC value does not change • Practical current pulses used in wafer tests exceed 70mS, therefore, shorter pulses cannot be used to “increase” MAC • Ultra short pulses (<1 msec) can help “transient current” mana
Slide 11: Impact of Test and Power Supply on Probes
Impact of Test and Power Supply on Probes • Significant static and transient currents can happen during wafer test due to electric shorts in faulty chips • >2A current have been experienced • Faulty devices must be screened out at lower voltage setting with current clamp limits set <=MAC at the begi
Slide 12: Example 1: Current Profile and Clamp Response Time
Example 1: Current Profile and Clamp Response Time • Test Case: Clamp response time for the same Higher Current Range power supply under 100mV step into a shorted Transient Current > 10A device (Vdd shorted to Vss) at different current > 1mS Clamp Response Time range S Current F Bad PWR C Die Supply
Slide 13: Example 2: Slew Rate Effect on Transient Currents
Example 2: Slew Rate Effect on Transient Currents • Test Case: Transient current response versus Voltage slew rate. Same power supply. Case 1: 50x slew rate No current clamp FS 1V Transient Current > 3A Good PWR C Die Supply Current G • Case 1 : GS • Fast Slew Rate 50 x Voltage • > 3A peak current w
Slide 14: Conclusions
Conclusions • The Maximum Allowable Current (MAC) represents actual current that probe can safely deliver, a more reliable specification than CCC • MAC is defined as current level at which probe will not change its planarity or cause permanent damage in repeated use – Duty cycle representative of te