Fritting: Experiences with Non-Ohmic Contact Resistance while ...

Fritting
Experiences with non-ohmic contact
resistance C RES while wafer test probing
Jan Martens
Philips Semiconductors Hamburg
Awarded “Best Overall Presentation at SWTW-2006”

Overview
• Fritting – What‘s that?
• Fritting – How to measure?
C RES measurements within production
environment
• Definition of the Fritting ratio Φ
• Why measuring Fritting and not only C RES?
• Measurement results
• Summary and Outlook
06/12/2006 SWTW2006 – Jan Martens 2

Fritting – What‘s that?
• The vertical Probe tip
touches the contact pad.
• Depending on the contact
pressure the oxide film is
broken partly and
electrical bridges arise.
• The number and size of
the bridges is equivalent
to the C RES quality
Probe Tip
Contact Pad
06/12/2006 SWTW2006 – Jan Martens 3

Fritting – What‘s that?
Probe tip
Oxide film
Contact pad
• What happens, if bridges
are only few and small?
Small bridge through oxide film.
Before high current flow.
06/12/2006 SWTW2006 – Jan Martens 4

Fritting – What‘s that?
• Current must flow through small bridge.
• Bridge and neighbourhood are heated up
• Contact Pad material migrates to the bridge.
Probe tip
Oxide film
Contact pad
High current flow situation:
Black Lines of current flow.
White Lines of equipotential surface.
06/12/2006 SWTW2006 – Jan Martens 5

Fritting – What‘s that?
• Bridge is widened C RES decreased
• Contact pad material migrated to the bridge and tip
surface
Probe tip
Oxide film
Contact pad
Wide bridge through oxide film.
After high current flow.
Tip surface is contaminated.
06/12/2006 SWTW2006 – Jan Martens 6

Fritting – What‘s that?
Probe Tip
Contact Pad
• Fritting is a kind of electrical breakdown at the
contact surface between the probe tip and the
contact pad of the IC.
• It improves the electrical contact by building or
stabilizing bridges through the oxide film, if the
film was not mechanically broken completely.
• After Fritting the probe tip is welded with the
contact pad. After removing the contact
residuals of the welding remain at the probe
tip and will oxidize.
06/12/2006 SWTW2006 – Jan Martens 7

Fritting – How to measure?
Needs:
• A C RES measurement is needed before and after fritting.
• The change of C RES is the indicator of occurence.
Implementation:
• C RES Monitor is installed twice within the production test
program flow of a smart card measuring C RES on the
power supply pin for every IC.
• First monitor at test program start, last monitor at the end.
• Hardware used is Teradyne J750, Accretech (TSK)
prober UF200A and 32-multisite vertical probe card
Viprobe from Feinmetall.
• Data of first and last C RES per touchdown is collected and
analyzed.
06/12/2006 SWTW2006 – Jan Martens 8

Fritting – How to measure?
Last CRES CRES / Ω
10
8
6
4
2
0
First C RES = Last C RES
Stable contact!
CRES CRES Scatter Plot
First C RES > Last C RES
Fritting contact!
0 2 4 6 8 10
First CRES CRES / Ω
06/12/2006 SWTW2006 – Jan Martens 9

Fritting – First data review
Number of TDs
5000 5000
4000 4000
3000
2000
1000
0
CRES CRES Distribution
Distribution
C RES Improvement
0 22 44 66 8 10 10
CRES CRES / / Ω
First Cres
First Cres
Last Cres
06/12/2006 SWTW2006 – Jan Martens 10

Definition of Fritting ratio Φ
Number of TDs
5000
4000
3000
2000
1000
0
CRES CRES CRES Distribution
Fritting Ratio Φ
=
0 2 4 666 8 10
CRES CRES CRES / Ω
NFrit
+ N
First Cres
First Cres
First First Cres Cres / Stable
First Cres / Stable
First Cres / Fritting
06/12/2006 SWTW2006 – Jan Martens 11
N
Frit
Stab

Fritting ratio Φ. Typical examples
Fritting ratio Φ
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Change of Fritting ratio Φ per time
Within 2k TDs
Φ80%
example 1
example 2
0 500 1000 1500 2000 2500
Touchdowns
06/12/2006 SWTW2006 – Jan Martens 12

Why measuring Fritting and not only C RES ?
• C RES measurement only indicates a problem in
the signal path but doesn‘t answer where.
Fritting measurement verifies a probe tip
contamination.
• In cases where an absolut C RES measurement is
impossible, a relative C RES decrease can still be
measured.
• The fritting analysis is more convenient and
simpler to analyze.
06/12/2006 SWTW2006 – Jan Martens 13

How influencing the fritting ratio?
• Changing overdrive
• Probing on gold bumps instead of
aluminum
• Using refurbishment methods
– Probe Polish (online cleaning)
– T.I.P.S. (offline cleaning)
06/12/2006 SWTW2006 – Jan Martens 14

Changing overdrive
Fritting ratio Φ
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Fritting ratio Φ
Overdrive improves Φ
(nonlinear probing force only small improvement)
2 Mil 3 Mil 4 Mil 5 Mil
Overdrive
06/12/2006 SWTW2006 – Jan Martens 15

Probing on gold bumps (instead of aluminum)
• Searched in many production lots
• Fritting ratio always Φ=0%
Gold is not oxidized.
No Fritting!
06/12/2006 SWTW2006 – Jan Martens 16

Probe tip refurbishment – How does it work?
Probe Tip
Highly cross-linked polymeric
material with spatially distributed
abrasive particles. (Probe Polish)
Flattened tip
Semiround tip
06/12/2006 SWTW2006 – Jan Martens 17
Pictures from T.I.P.S. Messtechnik GmbH

Online cleaning method: Probe Polish (ITS)
Fritting ratio Φ
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Fritting ratio Φ
Online using
Probe Polish
(1000 touchdowns)
Probe tip
Refurbishment
Fritting prevention and
Yield win 1%
0 200 400 600 800 1000 1200
Touchdowns
06/12/2006 SWTW2006 – Jan Martens 18

Fritting measurement and Probe Polish
Number of TDs
3000
2500
2000
1500
1000
500
0
CRES CRES Distribution
First Cres / before cleaning with Probe Polish
First Cres / before cleaning with Probe Polish
Last Cres / before cleaning with Probe Polish
First Cres / after cleaning with Probe Polish
Last Cres / before cleaning with Probe Polish
Last Cres / after cleaning with Probe Polish
Fritting prevention
with Probe Polish
0 2 4 6 8 10 10
CRES CRES / ΩΩ
06/12/2006 SWTW2006 – Jan Martens 19

Offline cleaning method: T.I.P.S.
Fritting ratio Φ
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Fritting ratio Φ
Offline using
T.I.P.S.
(24k touchdowns)
Probe tip
Refurbishment
Fritting prevention and
Yield win 3%
0 500 1000 1500 2000
Touchdowns
06/12/2006 SWTW2006 – Jan Martens 20

Fritting measurement with T.I.P.S.
Number of TDs
5000
4000
3000
2000
1000
0
CRES CRES Distribution
0 2 4 6 8 10
CRES CRES / Ω
First Cres w/o T.I.P.S.
First Cres w/o T.I.P.S.
Last Cres w/o T.I.P.S.
First Cres w/ T.I.P.S.
Last Cres w/o T.I.P.S.
Last Cres w/ T.I.P.S.
Fritting prevention
with T.I.P.S.
06/12/2006 SWTW2006 – Jan Martens 21

Summary
• Fritting was detected by comparing C RES values
during one touchdown.
• Fritting ratio Φ was defined and used as C RES
quality indicator.
• Fritting contaminates probe tips.
• Fritting was prevented and yield was increased by
using probe tip refurbishment techniques:
Probe Polish www.inttest.net
T.I.P.S. www.tips.co.at
06/12/2006 SWTW2006 – Jan Martens 22

Outlook
• Fritting ratio Φ can indicate preventive
maintenance of probe cards.
• Fritting ratio Φ can help to optimize
cleaning setups.
• Fritting can help to identify and engineer
(too) high current tests.
• Fritting could be an explanation for a fast
abrasion of probe tip material.
06/12/2006 SWTW2006 – Jan Martens 23

Thank You!
Questions?
06/12/2006 SWTW2006 – Jan Martens 24