Pb-free Plated
Component
Performance
& Production
Implementation
IPC, Beijing SMT & CBC
May 19, 2006
Tianjin, China
R. Schetty, Technic Inc.
Introduction
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In accordance with European WEEE RoHS
legislation, the plating on external leads of
electronic components must be Pb-free by
July 1, 2006
Matte tin is nearly universally accepted as the
standard Pb-free component plating finish to
replace Sn-Pb
Matte tin is plated on components in both
rack/barrel and high speed plating equipment
Technistan EP: high speed
0 Technistan EP-LS: rack/barrel
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Matte Tin Plating Equipment
High Speed
Plating
Barrel
Plating
Matte Tin Deposit Performance
Tin Whisker Standards
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Matte tin deposits used for Pb-free electronic component
plating must satisfy industry standards such as the new
JEDEC JESD201 tin whisker specification (March 2006)
JESD201 tin whisker test methods combine three accelerated
aging conditions with 3 levels of pre-conditioning prior to
accelerated aging:
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As plated & after Sn-Pb and Pb-free simulated reflow; followed by
Temp Cycling; Temp/Humidity; & High Temp/Humidity testing
Duration of specific test methods implemented and
acceptance criteria are dependent upon: (1) classification of
component (as determined by the end user); (2) Acceptance
test the component is being tested to:
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Technology Change Acceptance Test
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More rigorous
Applicable when major process parameters are changed
Manufacturing Process Change Acceptance Test
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Less rigorous
Applicable when minor process parameters are changed
JESD201 Determination of Component
Classification Level
• Class 3: Mission/Life critical applications such as
military, aerospace and medical devices
• Pure tin and high tin alloys are not acceptable
• Class 2: Business critical applications such as
Telecom Infrastructure equipment, High-end
Servers, Automotive
• Long product lifetimes with minimal downtime
• Class 1: Industrial / Consumer Products
• Medium Product lifetimes
• Class 1A: Consumer Products
• Short product lifetimes
• Minimal concern with tin whiskers
Test Requirements for Technology
Acceptance Test
JESD201
Test Requirements for Manufacturing
Acceptance Test
JESD201
Preconditioning Treatments
JESD201
JESD201 Technology
Acceptance Criteria
JESD201
JESD201 Manufacturing
Acceptance Criteria
MWL for Mfg. Acceptance criteria is lower
because test durations are shorter
Differences in JESD201 Test Methods
vs. previous JEDEC/NEMI methods
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(1) Change in High Temp & Humidity (HTH) test
conditions
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(2) Max. Whisker Length (MWL) measurement method
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Originally 60 deg C/ 93 % RH, then 60 deg C / 87% RH
Finally 55 deg C / 85 % RH in JESD201
Originally “segment” method was used
Now “radius” method is required in JESD 201
(3) MWL Acceptance Criteria
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Previously 50 microns MWL was acceptable
Now 40-45 microns
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WHY WERE THESE CHANGES MADE???
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(1) Tin Whisker Growth After HTH Testing
Observations
(1) HTH Testing Causes Corrosion and/or oxidation of the tin deposit surface
(2) Whiskers consistently grow in areas in/near corrosion sites after HTH testing
Many companies reported long tin whisker growth at/near
corrosion sites caused by former HTH test conditions, so HTH test
conditions were lessened in severity to minimize this effect
Source: E4 / ECTC June 2005
(2) Tin Whisker Measurement Method
•JESD201 Requires NEW “radius” measurement method for determining
whisker length :
•“The straight line distance from the point of emergence of the whisker to the
most distant point on the whisker (i.e. the radius of a sphere containing the
whisker with its center located at the point of emergence.).”
•Previous versions required “segment” measurement method
NOW (JEDEC Std 201):
BEFORE:
Whisker
R1
S2
S1
S3 S4
Whisker
Deposit Surface
Segment method:
Whisker length=S1+S2+S3+S4
Radius measurement may result in whiskers of
shorter length compared to segment method
Source: JESD201 March 2006
Deposit Surface
Radius method:
Whisker length=R1
(3) Acceptable MWL Change
MAWL requirement is more severe than
previous versions BUT measurement
technique is less severe
Matte Tin Deposit
Properties &
JESD 201
Tin Whisker
Performance
Process Data
Technistan EP
Technistan EP-LS
Sn = 70 g/l
Acid = 100 ml/l
EP Makeup = 80 ml/l
EP Additive = 30-40 ml/l
Additive C = 20 ml/l
Antioxidant = 10 ml/l
Temp = 40°C
Sn = 20 g/l
Acid = 100 ml/l
EP-LS Makeup = 60 ml/l
EP Additive = 15 ml/l
Additive C = 20 ml/l
Antioxidant = 10 ml/l
Temp = 22-25°C
Grain Structures of Matte Tin Processes
Used in this Study
SEM - 2000X Magnification
Technistan EP
15 ASD
Technistan EP-LS
1.5 ASD
These matte tin deposits are classified as fine-grained
with avg. grain diameter = 1-3 microns
Matte Tin Grain Structure Comparison
& Classification
SEM – 5000X Magnification
Large grain tin
Avg. grain diameter=5-8 µm
Fine-grained matte tin
Avg. grain diameter=1-3 µm
JESD 201 Tin Whisker Results
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High speed matte tin (Technistan EP / 15 ASD) and
rack/barrel matte tin (Technistan EP-LS / 1.5 ASD) were
plated on Olin C194 lead frame substrate, then subjected
to the test methods and acceptance criteria specified in
JEDEC JESD201 according to:
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Technology Acceptance Criteria
Class 2 components
JESD201 Whisker Results
Technistan EP-LS
Plating
Chemical
Base Material
Current Density
Sn Thickness
Technistan
EP-LS
C194
1.5 A/dm2
9.3 µm
Heat & Humidity (30°C,
no whisker
60% RH), 4000 hrs
Technistan
EP-LS
C194
1.5 A/dm2
9.5 µm
High Temp & Humidity
(85°C, 85% RH), 4000
hrs
Technistan
EP-LS
C194
1.5 A/dm2
9.7 µm
TC (-40°C to +85°C,
7 min dwell time)
1500 cycles
Whisker Test condition
Result MWL
(µm)
Magnification
Comments
100X
Pass
(MWL<40 µm)
< 10 µm
2000X
Pass
(MWL<45 µm)
< 5 µm
1500X
Pass
(MWL<45 µm)
SEM photo
JESD201 Whisker Results
Technistan EP: Heat & Humidity / High Temp & Humidity
Package Type
/ Base Material
Deposit
Thickness
Whisker Test condition
Pre-conditioning
Time Zero
Inspection
Results
Result MWL
(µm)
C194
Sn = 10.3 µm
Heat & Humidity
(30°C, 60% RH),
4000 hrs
None
no whisker
C194
Sn = 10.3 µm
Heat & Humidity
(30°C, 60% RH),
4000 hrs
Reflow @ 215°C
C194
Sn = 10.3 µm
Heat & Humidity
(30°C, 60% RH),
4000 hrs
C194
Sn = 10.3 µm
C194
C194
Magnification
Conclusion
< 5 µm
500X
Pass
(MWL<40 µm)
no whisker
< 5 µm
500X
Pass
(MWL<40 µm)
Reflow @ 260°C
no whisker
< 5 µm
200X
Pass
(MWL<40 µm)
High Temp & Humidity
(55°C, 85% RH),
4000 hrs
None
no whisker
22 µm
2000X
Pass
(MWL<40 µm)
Sn = 10.3 µm
High Temp & Humidity
(55°C, 85% RH),
4000 hrs
Reflow @ 215°C
no whisker
15 µm
150X
Pass
(MWL<40 µm)
Sn = 10.3 µm
High Temp & Humidity
(55°C, 85% RH),
4000 hrs
Reflow @ 260°C
no whisker
< 10 µm
500X
Pass
(MWL<40 µm)
SEM photo
JESD201 Whisker Results
Technistan EP – Thermal Cycling
C194
Sn = 10.3 µm
TC (-40°C to +85°C,
7 min dwell time)
1500 cycles
None
no whisker
5 µm
3500X
Pass
(MWL<45 µm)
C194
Sn = 10.3 µm
TC (-40°C to +85°C,
7 min dwell time)
1500 cycles
Reflow @ 215°C
no whisker
5 µm
3500X
Pass
(MWL<45 µm)
Sn = 10.3 µm
TC (-40°C to +85°C,
7 min dwell time)
1500 cycles
Reflow @ 260°C
no whisker
< 5 µm
3500X
Pass
(MWL<45 µm)
A42
Sn = 12 µm
TC (-40°C to +85°C,
7 min dwell time)
1500 cycles
None
no whisker
37.2 µm
3000X
Pass
(MWL<45 µm)
A42
Sn = 12 µm
TC (-40°C to +85°C,
7 min dwell time)
1500 cycles
Reflow @ 215°C
no whisker
30.7 µm
3000X
Pass
(MWL<45 µm)
Sn = 12 µm
TC (-40°C to +85°C,
7 min dwell time)
1500 cycles
Reflow @ 260°C
no whisker
19.3 µm
3000X
Pass
(MWL<45 µm)
C194
A42
Matte Tin Deposit
Solderability
& IR Reflow
Performance
Solderability Performance
260°C / Sn-Ag-Cu solder / Non-active flux
Figures 8 and 9 are wetting balance scan results of SOIC 24L before optimization with & without SRB .
Technistan EP-LS
Figure 8.0 Mixed Acid Tin Deposit (without SRB)
ZCT (1.2 sec), Fmax ( 300µN/mm)
Technistan EP
Figure 9.0 Mixed Acid Tin Deposit (with SRB)
ZCT (1.23 sec), Fmax ( 250µN/mm)
24 hr steam aging
ZCT 1.23 sec
ZCT 1.20 sec
Figures 10 and 11 are wetting balance scan results of SOIC 28L after optimization with & without SRB .
Figure 10. Mixed Acid Tin Deposit (without SRB)
ZCT (0.7 sec), Fmax ( 300µN/mm)
Figure 11. Mixed Acid Tin Deposit (with SRB)
ZCT (0.6 sec), Fmax ( 250µN/mm)
8 hr steam aging
ZCT 0.7 sec
ZCT 0.6 sec
The above matte tin deposits possess good solderability as demonstrated by
ZCT<1.0 sec and high/stable wetting forces > 200 mN/mm after steam aging
IR Reflow Performance Testing
Cu194 substrate plated with matte tin (EP & EP-LS) to 10 µm thickness
were subjected to 3X IR reflow in an Argus conveyorized IR reflow oven
with ~325 °C actual peak reflow temp
400
350
Temperature (degrees C)
300
250
200
150
100
50
0
0
20
40
60
80
100
120
140
160
180
200
tim e (sec.) for discoloration/dewetting
After reflow, parts are evaluated
IR Reflow Discoloration Testing
Results
Technistan EP
15 ASD
No Discoloration / No Dewetting
Technistan EP-LS
1.5 ASD
No Discoloration / No Dewetting
The above matte tin deposits possess good reflow characteristics as demonstrated
by no discoloration & no dewetting after passing through 3X IR reflow at 320°C
Tin Deposit Oxide Formation
Sn + O2 Æ SnO & SnO2
Tin Oxide Formation is the root cause of tin deposit
discoloration & poor solderability performance
Discoloration after IR reflow
due to tin oxide formation
Solderability failure (de-wetting)
due to tin oxide formation
Matte Tin Oxide Thickness Measurements
after 8 hr steam age + 16 hr bake @ 155 deg C
100
90
80
70
Total
60
Oxide
Thickness
(Angstroms) 50
40
30
20
10
0
Lg Grain
Fine grain
Fine-grained matte tin has better oxide resistance vs. large grained matte tin
Tin Oxides and Tin Whisker Formation
It has been demonstrated that tin oxides formed on tin deposit surface penetrate at the
deposit grain boundaries adding a “lifting” force which contributes to tin whisker growth
SnO, SnO2
Lifting force
Source: Alcatel
CuSn IMC
This in turn leads to long tin whisker
growth during High Temp & Humidity
(HTH) Tin Whisker Testing
Source: Tyco
Lower Oxide on Tin Deposit Surface Leads to
Less Tin Whisker Growth by High Temp &
Humidity Tin Whisker Testing
Lower surface oxide thickness
= less SnO2/SnOH transformation
= less driving force for tin whisker growth during HTH
X
Source: Philips
X
Source: Tyco
Conclusions
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The following correlation has clearly been established:
↓ Tin Deposit Grain Size
= ↑ Oxidation Resistance
= Improved Solderability & Reflow Performance
= Improved Tin Whisker Performance
The fine-grained matte tin deposits studied in this
report satisfy all industry requirements for Pb-free
electronic component plating, including new JEDEC
tin whisker specification JESD201
Pb-free Plated Component
Performance& Production
Implementation
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