Presentation - RoHS Exemptions

Transcription

Pressure-Induced Whisker Growth in Press-in
Connections of PCB Through-Holes
Dr. Hans-Peter Tranitz
Project Manager–Advanced Technologies
Continental Automotive GmbH
About the Author
University career:
Diploma in Physics in 1998 at the Regensburg
University, Germany
PhD in Physics end of 2001 at the Chemnitz
Technical University in the field of
Ultrashorttimespectroscopy on Semiconductor
Nanostructures
Postdoctoral Fellow at the University of
Cincinnati, Ohio in 2002 for 6 month, build-up a
lab and train PhD students
Project Manager–Advanced Technologies
Continental Automotive GmbH
Postdoctoral Fellow at the Regensburg
University for 18 month in the field of
spectroscopy of GaAs nanostructures, MBE
growth and characterisation of highest mobility
2 dimensional electron gases
About 40 publications in peer reviewed
scientific journals (1 Science, 9 Phys. Rev.
Lett., 10 Phys. Rev. B, …)
Company career:
Technology Project Manager at SiemensVDO
since 2004 in Plant Regensburg for Press-fit
Technology, Thermal Conductivity, Laser
Marking, Laser Welding of Plastics
Since 2007 involved with Tin Whiskers at
Press-in Connections
Merge with Continental mid of 2007
Since 2009 Cluster Manager and Coordinator
of two global teams and Senior Expert for
Advanced Technologies Press-fit and Welding
of Plastics at the Central Electronic Plant
organization of Continental
Technology Project Manager of Whiskers at
Press-fit Technology and Alternative Surfaces
on Press-fit Zones
Pressure-induced Whisker Growth in Press-in
Connections of PCB Through-Holes
Agenda
Introduction to Continental Automotive
Press-fit Technology: Why this connection is so reliable?
Whisker mitigation strategy within Continental
History of legislation and surface finishes on press-fit zones
Whiskers on Press-fit connections: Set-up of Investigation and Evaluation
Classification of whisker growth modes on different press-fit geometries
Alternative Surface finishes
Summary
Central Electronic Plants – Manufacturing Technology – Advanced Technologies
2 © Continental AG
Introduction to Continental AG: Divisions and Business Units
Continental Corporation
Automotive Group
Rubber Group
Passenger and
Light Truck Tires
Commercial
Vehicle Tires
Chassis & Safety
Powertrain
Interior
Electronic
Brake Systems
Engine Systems
Transmissions
Instrumentation
& Driver HMI
Original
Equipment
Truck Tires
Europe
Air Spring
Systems
Hydraulic
Brake Systems
Hybrid & Electric
Vehicle
Infotainment &
Connectivity
Truck Tires
The Americas
Benecke-Kaliko
Group
Sensorics
Sensors &
Actuators
Body & Security
Replacement
Business
Europe
Commercial
Vehicles &
Aftermarket
Replacement
Business
The Americas
Truck Tires
Asia Pacific
Conveyor Belt
Group
Industrial Tires
Elastomer
Coatings
Passive Safety
& ADAS
Fuel Supply
Chassis
Components
Replacement
Business
Asia Pacific
Central Electronic Plants
Two-Wheel
ContiTech
Fluid Technology
Power Transmission Group
Vibration Control
Other Operations
3 © Continental AG
Automotive Group: Key Figures
in € millions
2009
2008
Sales
4,373.6
5,134.0
EBIT
-102.5
303.1
353.4
512.0
27,148
26,680
Chassis & Safety
Adjusted EBIT*
Number of employees
Automotive Group
in € millions
Powertrain
2009
2008
Sales
12,042.4
14,900.0
EBIT
-1,561.6
-1,205.8
192.0
824.6
78,030
82,737
Sales
3,399.2
4,040.0
EBIT
-943.2
-1,046.2
Adjusted EBIT*
-218.0
-188.9
Number of employees
24,172
25,244
Adjusted EBIT*
Number of
employees
Interior
Sales
4,362.7
5,856.7
EBIT
-516.0
-462.6
56.4
501.6
26,710
30,813
Adjusted EBIT*
Number of employees
* Before amortization on intangible assets from purchase price allocation,
changes in the scope of consolidation, and special effects.
4 © Continental AG
Central Electronic Plants: Locations
Karben, Germany
Ingolstadt, Germany
Nuremberg, Germany
Regensburg, Germany
Villingen, Germany
(Huntsville, USA)
Seguin, USA
Kaluga, Russland
Sibiu & Timisoara, Romania
Budapest, Hungary
Foix, France
(Rambouillet, France)
Toulouse, France
Rubi, Spain
Bangalore, India
Brandys, Czech Republic
Frenstat, Czech Republic
Cuautla, Mexico
Guadalajara, Mexico
Nogales, Mexico
Changchun, China
Tianjin, China
Huizhou, China
Cheongwon, S. Korea
Icheon, S. Korea
Manila, Philippines
Calamba, Philipines
Penang, Malaysia
Guarulhos, Brazil
Manaus, Brazil
5 © Continental AG
Bundoora, Australia
CEP Manufacturing Technology: Responsibilities and Scope
Locations: Nuremberg/Regensburg (Germany), Deer Park (USA), Manila (Philippines), Sibiu (Romania)
Manufacturing Technology
Manufacturing Technology Roadmap
Design For Manufacturing - Methods and Tools
Worldwide Technology Expert Network – TECH.net
Standardization of Processes and Equipment
Life Cycle Management (phase-in/phase-out) for Manufacturing Technologies
Technology and Material Evaluations and Generic Automotive Qualifications
6 © Continental AG
Press-fit Technology: Introduction
ept T-com press®
Compliant (flexible) press-fit zone is inserted to a specially designed PCB through hole
With friendly approbation of the author
7 © Continental AG
Mechanical Properties: Insertion and Retention forces (examples)
Insertion Force
Retention Force
100
180
90
160
force[N]
140
120
force [N]
Adhesion Peak
80
100
80
70
60
50
40
60
30
40
20
20
10
0
0
0
0.5
1
1.5
2
2.5
3
0
0,1
0,2
displacement [mm]
0,3
0,4
0,5
0,6
diplacement [mm]
The remarkable reliability is based on the pronounced adhesion peak: evidence for material diffusion and
cold welding
Reason for large mechanical and thermal stability of the connection/transition
Mandatory for common application with all different environmental conditions in the car
8 © Continental AG
0,7
Press-fit Technology: Applications in Automotive Electronics
Almost all PCB (FR4) based Electronics contains press-fit technology
Chassis and Safety examples: ABS-electronics, Airbag Satellites and Control Units, Sensors, Electronic
Parking Breaks and Electric Power Steering
Powertrain examples: Engine- and Transmission Control Units, Sensors
Interior examples: Body Controller, Fuse Boxes, Immobilizers, Door Control Units and many more
In summary billions of press-fit connections in all possible environments in the car and truck (0 dpb)
Press-fit into housing, connectors, component carriers, board interconnections, single standing pins, ….
9 © Continental AG
Continental Material Requirements – General Whisker Mitigation
Solder:
 Pb-free alloys selected by Continental Automotive show no risk for tin whisker growth.
 SAC305 and SAC387 solders contain silver and copper alloying additions which
reduce propensity for tin whisker nucleation and growth.
Printed Circuit Boards:
 Primary tin whisker growth mitigation methods are considered
 Storage life limit is 6 months at ambient conditions, with whisker length < 50 microns.
 Immersion tin thickness is controlled between 1.0 to 1.2 microns.
Components:
 no use of lead frames without barrier layer (like e.g. Nickel), alloy 42 is not recommended
 no use of galvanic bright tin as finish layer
 annealing of components to relax the stress
Summary:
 Qualification and testing for whisker prevention according to IEC 60068-2-82
 Continental Automotive takes all necessary precaution to avoid returns caused by
whisker growth.
 The behavior of whiskers induced by external stress is different and content of the
following presentation.
10 © Continental AG
Supplier is strictly
required to supply
materials without
whiskers
These requirements
are checked by basic
qualifications and
reviewed by
Continental Supplier
Quality Management
History and Legislation and Surface Finishes (on Press-fit Zones)
Increased effort for lead-free solutions
Surface finish
SnPb  pure Sn
Pin:
SnPb
PCB:
HAL (SnPb)
1995
imm. Sn
2000
2005
Press-fit whisker lead to band / field returns
in some special cases at different
automotive electronic manufacturers
imm. Sn
2010
2nd edition Annex II:
no exemptions in
electronics after 2010
1st edition of ELV
Annex II: lead-free
exemption for
electronics
Sn, SnPb in some cases and alternatives?
alternatives?
2015
next revision of
the exemption
3rd edition of Annex II: lead-free
exemption for press-fit +
official interpretation by the
Automotive Associations
Occurrence of short circuits
Whiskers potentially create short circuits or parasitary current paths. Fast growth of whiskers can be
observed in press-fit connections due to high mechanical stress at pure tin surfaces.
Some 0-km and field returns identified at a body controller 2007
Whiskers create direct parasitary signal path at sensor exits (very low current flow)
Whisker length > 2 mm within 2-6 weeks after insertion in this case
Direct bridging of low signal electrical contacts
Comparative Study: Set-up of Investigation and Evaluation
Using series production PCBs of one product
PCB pretreatment: series production reflow process (1x lead-containing reflow profile)
Numerous types of series production press-fit pins with the same thickness of pure tin surface
300 pins of each type inspected: representative sample size
1000 h storage at 23°C and 40% rel. humidity (cabinet)
Whisker inspection with standardized method: see next slide
Categorization
Category Length [µm]
Description
Risk
Weight
1
0
no whisker observed
no risk
0
2
< 50
customer accepted whisker length
no risk
0
3
50 - 100
low risk
1
4
101 - 200 electrical clearance may be affected medium risk
3
5
> 200
direct and indirect bridging
high risk
9
 representative test set-up
Set-up of Investigation and Evaluation
Metallurgical microscope
Incident light geometry (bottom-up)
Adjustable light intensity and aperture of pin hole
Camera system and software
adjustabel x-y table
To the right: Micrograph of a
press-fit pin in a press-fit via. A
whisker can be observed in the
bottom left corner.
Tips of press-fit pins show in the direction of the objective
To be able to inspect the complete press-fit via, a magnification
of at least 50x is required
Scroll focus through complete via
Whisker Growth on different press-fit geometries (10 variants)
Results:
• One cracking zone shows better performance (4) than the other pins
• All press-fit zones show whiskers > 200 µm
Whisker Behavior of Cracking Zones (example)
Some fillet or similar mechanism is cracking fully or partially during insertion
pin removed
cracking during
insertion
entrance area: large inelastic deformation
pin cracking in entrance area
surface stress is a well known mechanism
Cracking zones: Long whiskers grow
in entrance area of the PCB
SEM (press-fit pin removed)
Area of greater plastic deformation in the PCB
Expansion of the copper material in the area where
the pin enters
Surface tension is a known mechanism for whisker
formation
The tin layer of the pin peels off "upward or
laterally" against the press-fit direction and
adheres to the PCB in the upper area of the
through-hole
Observed whiskers originate in areas of great
deformation where the press-fit pin enters.
The point of origin is the copper bushing of PCB
Details in the Area of Deformation
Area of "stripped" cold welding
Tin/copper material interlocking due to the
contact pressure of the press-fit pin
Top right: Expansion steps in copper, arise
from pressing-in in the area of greater
material stress. Here, the initially closed
layer of the inter-metallic phase is probably
also damaged.
Bottom right: In the area of deformation,
seed crystals grow using the excess tin, socalled nodules and whiskers, to relieve the
surface tension.
Whisker Behaviour of Eye of the Needle Zones
pin removed
Eye of the needle pins
rim of via: tin abrasion of the pin
tin of pin almost lost for whisker growth
vertical cross-section
horizontal cross-section
inset shows tin abrasion in detail of vertical
cross-section
Tin agglomerations coming predominantly from the
PCB occurs at the side pockets and at the bottom
EON: Tin abrasion of the pin at edge of via (explanation for less whisker growth),
tin of the PCB moved to the side and to the bottom of the PCB.
Whisker Behavior of Spring Shapes
Additional bars (springs) connect the two legs of the press-fit zone
pin removed
deformation line along the insertion direction
tin agglomeration over the complete length of the bushing
horizontal cross-section
whiskers are observed in SEM
detail
Spring shapes: whiskers along the deformation lines
within the PTH, almost no tin abrasion at the rim
Types of Press-fit Geometries: Summary and Evaluation
Cracking zones: some fillet or similar mechanism is cracking fully or partially during insertion
characteristics: high insertion and retention forces, relatively high deformations
large whiskers in entrance area with a tendency to grow out of the hole
These pin types have shown direct bridging in the past
SnPb finish was applied as solution for the most critical cases, worst pin removed from portfolio
Eye of the needle (EON): a needle-eye is stamped to the sheet metal
characteristics: relatively low insertion and retention forces, usually lower deformations
tin abrasion on the rim of plated through hole, lower whisker-rate, whiskers inside the through hole
SnPb avoids whiskers, Sn surface has got a very low potential for bridging between pins
Spring shape: additional springs between the two legs of the pin
characteristics: medium to high insertion and retention forces, medium deformations
whisker growth along the deformation lines inside the through holes
SnPb avoids whiskers, Sn surface has got a low potential for bridging between pins
Additional remarks
There may be observed a mixture of some of these mechanisms e.g. at cracking zones
In case of incorrect galvanic treatment (pollution, bright surface, …) also EON pins may show many and long whiskers
In case pure tin finish is used, additional design rules need to be respected
Whiskers on Cross-Sections
Black flaws are observed on cross-sections in the intersection of pin and PCB’s copper bushing
SEM pictures show that these are whiskers that grow within days perpendicular to section plane
This demonstrates the three necessary pre-conditions for tin whisker growth:
1) bare tin exposed
2) tension at the surface
3) free space (at least in the range of whisker diameter)
Development of Alternative Surface Finishes on Pin and PCB
Pure Tin Containing Alternatives
Pure Sn finish (over Ni)
Analyses of alternative finishes:
Same PCB and pre-treatment (see slide 16)
Same PCB-supplier for alternative PCB finishes
300 Pins for each variant
50
First four variants of Pin finish using imm. Sn PCB
Last two variants of PCB finish using Pin 1 as a
reference (Sn 1 µm galv.1)
frequency of whiskers
Using Pin Type Nr.1 (most whiskers)
5
4
0
3
2
Results
sureface finish
No significant dependence on tin thickness in the specified range (0,3-1,5 µm)
PCB finish chem. Ag shows less whiskers than PCB finish OSP  pure Ag surface seems to have a mitigation effect
Sn finishes with temperature storage of the pins
Used press-fit zone: Pin type 9 (variants 1-3), Pin type 3 (4)
Sn finish with temperature
Imm. Tin PCB
50
5
4
3
0
2
Results
temperature pretreatment improves whisker frequency and risk for bridging
50 µm requirement of whisker length is exceeded within this investigation
SnXy finishes
Used press-fit zone: Pin Type 1 (variants 1- 3 + 7); PinType 9 ( variants 4 – 6)
Imm. TIn PCB
frequenzy of whiskers
SnXy - finish (over Ni)
50
5
0
4
3
2
Results
SnPb shows no whisker
surface finish
All SnAg variants show whiskers, sometimes more than pure tin finish
SnBi shows whiskers in all categories, tendency: less whiskers with high Bi content
For SnAg and SnBi: lower press-in/push-out performance than SnPb
Tin free alternatives
Used press-fit zone: Pin Type 1 (variants 1-4), Pintype 9 (5)
Sn ‐ free
Imm. Tin PCB
Results
50
Tin free finishes show less whisker
5
4
0
3
2
OctaDecaThiol as protection for oxidation and as lubricant
Ag-flash shows 2nd best whisker result
Worse press-in/press-out performance
Not usable for all pin types and all automotive applications
Indium substitutes Sn/SnPb: widely reduced whiskers
reduced length (max 125µm)
Very good press-in/press-out performance: lower
insertion forces and pronounced adhesion peak
surface finish
Summary
The press-in connection containing free tin on pin and/or PCB results in whiskers larger than 50 µm
on a large variety of press-fit zones.
Some cracking zones with pure tin surface are candidates for whiskers growing out of the through
hole and resulting in a risk for direct bridging.
Some plating alternatives reduce the risk of direct bridging but only SnPb seems to fulfill the
requirement of whiskers < 50 µm.
For automotive industry, the cold welding is necessary in harsh environmental reliability conditions.
From today‘s technical point of view, SnPb is the only surface that efficiently mitigates whiskers and
ensures a good cold welding.
A very good long-term alternative that is whisker- and Pb-free, works for a large variety of press-fit
geometries, and fulfills all requirements for automotive electronics is required.
Promising candidates Ag and In are under investigation
Acknowledgement
Many thanks to my former diploma student
Sebastian Dunker
Many thanks
to our main development partners:
Schempp & Decker
FCI Connectors
EPT
Interplex
Trainalytics
and for many useful discussions with
Atotech
Tyco Electronics
Fraunhofer IWM (Institute for Material Mechanics)
Thank you for your attention!

Presentation - RoHS Exemptions

Transcription

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