six sigma: systematic approach in probe damage...
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36th
International Electronic Manufacturing Technology Conference, 2014
Six Sigma: Systematic Approach In Probe Damage Reduction
Glenn T. Placido, Carl Olalia, Rhal Alolod
ON Semiconductor Philippines
ON semiconductor, Golden Mile Business Park, SEZ,
Governor’s Drive Bo. Maduya,
Carmona, Cavite Philippines 4116
Glenn.placido@onsemi.com, +632-8594000 loc .2472
Abstract
This paper describes how probe damage, the major
defect at sort process, was toppled down nearly to ground
level using the systematic approach of Six Sigma.
A thorough study on the characteristic of the probe
damage was made. Using root cause analysis tools, such as
process mapping, cause and effect matrix, significance
testing, and other useful quality tools, the sources of probe
damage were identified , validated and solutions were
developed .
The PPM level of probe damage was significantly
reduced resulting to less wafer scrappage, high yield and
improvement on sort process efficiency.
1. Introduction
Probe damage is the number one visual defect
contributor at wafer sort process having a direct impact on
yield and cycle time. This situation led the team to launch an
initiative to reduce, if not eliminate probe damage. This
initiative is aimed ultimately in improving wafer quality,
increasing productivity and as part of ON Semiconductor’s
“Road to Zero Defect” quality program.
Table 1 describes the probe damage that was studied.
Table 1: Probe damage
N
o
Defect visual aid Remarks
1
Probe marks
touching the seal
ring of the bond
pad
2
Expose oxide
on the bonding
pad
2. Section 2 Header
Before proceeding to root cause analysis, measurement
system analysis (MSA) was performed on outgoing optical
inspection system to ensure that results of inspection are
effective and consistent.
A detailed process mapping was done to identify all
possible root causes of the probe damage. This was
supplemented by fishbone diagram (refer to Figure 1) and
SIPOC diagram. Using the cause and effect matrix (refer to
Figure 2), a total of 144 key process input variables (KPIV)
were identified [1]. A prioritization based on impact of key
process input variables to key process output variables
(KPOV), 78/144 were short listed. Fifteen validation plans
were developed after combining similar KPIVs (see Table
2).
Figure 1: Fishbone diagram
Figure 2: Cause and Effect Matrix
36th
International Electronic Manufacturing Technology Conference, 2014
Table 2: Validation Plans
No. Hypothesis
1 Prober XY shift will increase if prober was
relocated
2 Using defective prober footings will cause
planarity problem and can induce probe
damage
3 Card relative Z height and overdrive does
affect probe mark size.
4 “Model not found" and "auto focus error"
will induce probe damage if not properly
corrected.
5 /6 Incorrect soak time will have effect on
probe mark size
7 Procedures is not yet robust or is not yet
define
8 Using out of spec screws in PC stiffener
(ELTESO PC) can induce probe damage.
9 Loading an wrong/not updated BOP disk
can cause smash the probe card and eventually
causes probe damage
10 Use of Sodium Hydroxide can cause
weakening of probe needle which can lead to
needle misalignment and eventually probe
damage.
11/12 Replacing the cleaning material incorrectly
and worn out cleaning materials will eventually
mis-align the needle during needle cleaning.
13 Accumulation of debris on the probe needle
can cause probe damage.
14 Leaning on the test head and removal of
cable on cable setup will induce probe damage.
15 Probe card with planarity issue can cause
probe damage.
3. Section 3 Header
The following are the results of validation experiments.
Corrective actions were defined for valid KPIV.
#1 Prober XY shift will increase if prober was
relocated
Result: During the first relocation, there was no
significant difference between XY measurements. However,
during the second relocation, X measurement showed
significant change. The same is true with the third
replication. Y measurement showed that there was no
significant difference during the three trials (see Figure 3).
Therefore the identified KPIV is VALID. Use of brackets
and quantitative measurement were the corrective actions
identified (refer to Table 3).
Figure 3: KPIV # 1 Hypothesis Testing
Table 3: Implement bracket and quantitative
measurement
# 2 Using defective prober footings will cause planarity
problem and can induce probe damage
Result: There is a significant difference between the XY
shift using good footings versus defective footings.
Therefore the identified KPIV is VALID. Figure 4 shows
the ANOVA for defective footings. As a corrective action,
checking of prober footings was implemented (Refer to
Table 4).
Figure 4: ANOVA for defective footings
36th
International Electronic Manufacturing Technology Conference, 2014
Table 4: Include footing check
# 3 Card relative Z height and overdrive does affect
probe mark size.
Result: Setting of card relative is critical as this will
dictate the needle cleaning height. As Z height increases
needle cleaning height also increases causing probe card to
smash and eventually probe damage will occur. Therefore
the identified KPIV is VALID. Table 5 lists the corrective
actions for this issue.
Table 5: Action implemented for KPIV # 3,4, 7
# 4 “Model not found" and "auto focus error" will
induce probe damage if not properly corrected.
Although “Model not found” error was not duplicated,
the team still consider this as valid since “Model not found”
error is due to probe card versus prober theta alignment and
corrective action to address this has to be defined. Therefore
the identified KPIV is VALID. Please refer to Table 5 for
the corrective action.
# 5 /# 6 Incorrect soak time will have an effect on probe
mark size
(Prober soak – 2hrs; PC soak- 10min)
Result: The results show that prober soak and PC soaking
are required as these affect the probe mark size and position
which can lead to probe damage. Probe mark size will
increase as PC soak time increases whereas probe mark
position shifts as prober soak time increases (see Figure 5).
Therefore the identified KPIV is VALID. The corrective
action was to implement automate soaking (See Table 5).
Figure 5: XY Shift
Table 5: Automate soaking
# 7 Procedure is not yet robust or is not yet defined
Result: There are no procedures defined on some of the
critical activities as listed on Table 6. As for the procedures
that exist, there is a need to enhance them to increase
detection of the problem. Each operator/technician has
his/her own procedure which may result to poor detection of
probe damage. Therefore the identified KPIV is VALID.
Process documentation for the identified processes were now
completed.
Table 6: Processes that needs documentation
No Processes without documents/ Procedure
needs enhancement
1 Prober relocation
2 PC/LB installation
3 Test head docking
4 Inspection methodology to detect theta
alignment problem
5 Setting z-ht and overdrive
6 Detect prober XY shift problem
7 Correct prober XY shift problem
8 Methodology after equipment repair
9 Probemark inspection criteria
10 Different criteria PCB vs prodn
11 Inspection of probecard needle prior use
– Has procedure
36th
International Electronic Manufacturing Technology Conference, 2014
As corrective action we have created procedure on all the
processes identified.
# 8 Using out of specifications screws in probe card
(PC) stiffener (ELTESO “Elevated temp sort” - PC) can
induce probe damage
Result: Special screws provide leeway for the board to
expand during high temp probing. On the other hand,
standard screws suppress the thermal expansion resulting to
probe damage (refer to Figure 6). Therefore the identified
KPIV is VALID. Table 7 list the corrective actions made.
Figure 6: Result of correct screw and not correct screw
Table 7: Use of specified/correct screws
#9 Loading a wrong/not updated BOP disk can smash
the probe card and eventually cause probe damage
Figure 7: Result of BOP disk simulation no damaged
Result: Incorrectly loading a BOP disk causes smashed
probe card. However, during validation, probe damage was
not induced. This however does not mean that this type of
probe damage will not happen, as previous data suggested
otherwise. Thus the KPIV is VALID. A more robust
system replaced the BOP disk (see Table 8).
Table 8: Remove BOP disk and replaced with auto
loading.
#10 Use of Sodium Hydroxide can cause weakening of
probe needle which can lead to needle misalignment and
eventually probe damage
Result: Sodium Hydroxide is the chemical used during
needle etching. Application of this chemical is subjective
and operator dependent while use of Duralco epoxy does not
effectively hold the needle of the probecard. This eventually
weakens the needle and will cause premature needle
misalignment (see Figure 8). The KPIV is therefore VALID.
The corrective action was to stop the use of sodium
hydroxide.
Figure 8: Needle misalignment
# 11 / # 12 Replacing the cleaning material incorrectly
and worn out cleaning materials will eventually mis-align
the needle during needle cleaning
Correct
screw NOT Correct
screw
36th
International Electronic Manufacturing Technology Conference, 2014
Table 9: Procedure on cleaning material
Table 10: Online needle cleaning
# 13 Accumulation of debris on the probe needle can
cause probe damage
Result shows that probe damage will occur if there is an
accumulated dirt/debris on the probe card needle. The size
and location of the probe damage coincide with that of the
debris on the probe card needle (see Figure 10). The KPIV
therefore is VALID. Tables 9 and 10 define the corrective
actions made.
Figure 10: Need tip dirt accumulation
# 14 Leaning on the test head and removal of cable on
cable setup will induce probe damage
Result: Result shows that after reseating the cable, probe
damage occurred (see Figure 11). Therefore the identified
KPIV is VALID. Table 11 shows the corrective actions.
Figure 11: Leaning on test head result
Table 11: Set-up on cable and hardware set-up
# 15 Probecard with planarity issue can cause probe
damage
Result: The result in the summary table (see Table 12) is
so convincing that even without the Chi-squared test one can
confidently state that non-planar probe card is conclusively
inducing probe damage. The KPIV therefore is VALID. As
a corrective action, ensure that probe card was planarized
using automated equipment that checks planarity before
running production.
36th
International Electronic Manufacturing Technology Conference, 2014
Table 12: Non planer PC result and Chi-square test
4. Conclusions
The team confirmed that the probe damage can be
reduced by thoroughly looking on all possible sources using
the right tools and prioritizing it using the cause effect
matrix. Below is the before and after performance of probe
damage.
Acknowledgments
The author would like to thank OSPI management for the
support that they provided over the course of this endeavor.
Peter Awayan for six sigma mentoring. The team for the
time spent during weekly meeting and technical expertise.
References
1. Pyzdek Thomas, The Six Sigma Handbook.
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