KGD Probing of TSVs at 40 um Array Pitch

• 3D-TSV Probe Technology Goals

• MEMS probe tip evolution

• Contact performance

• TSV pad damage (or lack thereof)

• Conclusions

Ken Smith, Peter Hanaway, Mike Jolley, Reed Gleason, Chris Fournier, and Eric Strid

3D-TSV Probe Technology Development Goals

• Scale array pitch to 40 um

• Reduce pad damage to allow prebond probe

• Decrease cost of test– Simplified, high yield process

• Fundamental understanding and accurate

models of contact performance

Pyramid Probe Technology

• RF filters, switches

• Process monitors (including M1 copper)

• RFSOC Multi-DUT

3D Probing Requires a New Cost Structure

4

COGS/ pin ($)

in 2012

Array Pitch (um)

400200100502512 80063 1600

2

1

0.50

0.25

0.12

0.06

DRAM& Flash

Logic/SoCC

onst

ant c

ost p

er a

rea

Printed probe: n

early

constant cost

per area

Vertical probe: cost

increases with density

3D R

equi

res

cons

tant

cos

t per

chi

p

Technology must be printed, repairable, scalable, compliant

Scaling a Probe Card

100 um pitch~10 gm/tip

35 um pitch~1 gm/tip

• Decrease XYZ dimensions by K• Same materials• Decrease Z motions by K• Force per tip decreases by K2; tip pressure constant

• Pyramid Probe ST: Pads on membrane – Routing limitation ~3-4 rows deep from DUT

pad perimeter

• Replaceable contact layer

3D TSV Probe Card Architecture

Wafer

Plunger

PCB PCB

Replaceable Contact Layer

• Tips are 5 um

square and 20

um tall

• 35 um pitch

array

• 24 x 48 tips

Contact resistance versus probing force

• Single 12 um square tip

• Sn plated wafer 5 um thick

Contact resistance versus probing force

• 6 um tip

• Force required is similar to 12 um tip

Force (gm•f ) vs. Deflection (um)

• 1gm•f /um tip design

• High durometer elastomer

Force (gm•f ) vs. Deflection (um)

• 0.1 gm•f tip design

• Low durometer elastomer

Pyramid Probe ST Routing

• Unique fine-pitch routing

• High-frequency performance similar to Pyramid Probes

• Example is memory array

• – 50 um x 40 um pad pitch

• – 40 x 6 pad array

Fully routed 6x40 array with 40-50 um pitch

Optical photograph of probe mark array

• Marks are exceptionally

uniform

• ~1 gram / contact for

low pad damage

Profilometer scan of probe mark array

• Maximum depth 100 nm

• Maximum berm 500 nm

Probe marks on ENIG TSV pad

• Exaggerated conditions: 10 TDs at 2.5 gf

• Navigation grid (50 x 40 um) shows 3 probe

marks on the 100 um diameter pad

Probe mark depth less than surface roughness (~200 nm)

Probe mark on ENIG pad

• ~3 x 7 um

• Exposed Ni ~50%

• Depends on surface grains

Probe mark uniformity: Profilometer scans

• Depth: Mean 68, Stdev 11

• Berm: Mean 363, Stdev 76

TDR traces on open and short

• <40 ps rise / fall times (100 ps / div)

• Limited by routing density in ST

Conclusions

• Practical probe cards are capable of 40 um

pitch and tip forces below 1 gm

• Pad damage at these low forces is extremely

small with scrub marks less than 100 nm

deep

• Lithographically printed probe cards enable a

scalability path to lower cost and finer pitches

• Probing the TSVs is not out of the question