Lead Free Soldering - SMTA

DFX FOR LEAD FREE PROCESSING
AND RELIABILITY
Presented By: Dale Lee
E-mail: Dale.Lee@Plexus.Com
1

WHAT DOES LEAD FREE MEAN TO YOU
Original RoHS Directive - Originally 8
Categories
RoHS2 Directive:
Categories 8 (Medical Devices) & 9
(Monitoring and Control
Instrumentation) Are Now In Scope
22-July 2014 – General Medical Devices
22 July 2016 – In Vitro Medical Devices
Active Implantable Devices
• Out Of Scope At This Time
• Review For Inclusion In 2020
Defense Excluded From
Specification
2

TECHNOLOGY DRIVEN DESIGNS
Component packaging technology trends:
• Decrease in size (length, width, thickness)
• Increase in functionality (electrical, optical, electrical mechanical and
mechanical)
• Interconnection density per unit area is increasing (increased number of
layers, smaller lines and spaces)
• Assembly functional performance is increasing (thermal, mechanical,
electrical)
Assembly process complexities continue to increase and LEAD FREE Soldered
3

LEAD FREE SOLDER ADVANTAGES
Material Costs
• NO
– More Expensive
Reflow Temperature
• NO
– Higher Temperatures For Reflow & Rework
– Increased Component & PCB TCE Mismatch (Warp, Crack)
– Increased Z-axis Expansion
Through Hole Soldering
• NO
– Higher Hand and Rework Solder Temperature
– Greater Lead to Hole Clearance
– Increased Copper Dissolution
Assembly Process Physics
• Yes
– Tighter SMT Lead Pitch Packages
– Increased Secondary Side SMT Package Mass
– Decreased Tombstone Components
– Increased Off Pad Printing Compatibility (Pin-in-Paste)
Reliability
• Maybe
– Dependant Upon Environmental Conditions.

MEET FUNCTIONAL AND LEGISLATIVE REQUIREMENTS
RoHS/non-RoHS compatible analysis ensures compliance with regulatory and
product reliability and assembly requirements
Not all RoHS compliant components are lead free soldering process compatible
Not All RoHS compliant components are backward compatible with tin/lead
solder process
RoHS & Green Information
Part #
Supplier
Lead-
Free
RoHS
RoHS
Exemption
RoHS
Exemption
Type
Component
Engineer
Comment
Terminal
Plating
MSL
Max
Temp
C of C/
Datasheet
C0402C102K3RACTU
RK73H1ETTP1002F
NACE221M
10V8X6.5TR13F
Kemet
Electronics
KOA Speer
Electronics
Compliant Compliant No Matte Sn 1 260°C Link
Not
Compliant
Compliant Yes 7.c-1 Matte Sn 1 260°C Link
NIC Compliant Compliant Matte Sn 1 235°C Link
0402YA331JATAT2A AVX/Kyocera Compliant Compliant Sn/Bi 1 260°C Link
5

LEAD FREE ASSEMBLY IMPACTS TO PCB LAMINATE
Traditional G10 and FR4 printed circuit board laminates cannot survive multiple
elevated lead free soldering process exposure or sustain impact to reliability
IPC Material Specifications (IPC-4101) For Epoxy Glass Lead Free Laminates are:
IPC-4101 /126 or /129 – Halide Flame Retardant (FR4), 170 Tg
IPC-4101 /130 or /131 – Low Halide Flame Retardant, 170 Tg
Severity of reliability impacts are influenced by:
• Assembly process thermal exposure conditions
• Board design – number of layers, conductor routing
• Component package types
• Conductor / component placement density
• Operational environment
Photos courtesy of Cookson and
Universal Instruments
6

MICRO-VIA DESIGN – RELIABILITY IMPACTS
Different Via Hole
Structures
Impact
Resistance To
Assembly,
Rework or
Handling
Damage
Design and Construction Affects on PWB Reliability, Paul Reid,
IPC Apex Proceedings 2012.

PRINTED CIRCUIT BOARD FINISHES
Final printed circuit board finish impacts
the ability to solder surface mount and
through holes components reliably and
cost effectively.
Assembly Characteristics
Lead
Free
HASL
OSP
Immer
Silver ENIG ENEPIG
Fine Pitch Leaded SMT Components Neutral Plus Plus Plus Plus
Chip Components (Passives)* Plus Plus Plus Plus Plus
Area Array (BGA/CGA) Plus Plus Plus Plus Plus
Reflow & Wave Soldered (SMT & PTH) Plus Neutral Plus Plus Minus
Wave Soldered PCB (SMT and PTH Components) Plus Neutral Neutral Plus Minus
Wave Soldered PCB (PTH Components Only) Plus Neutral Neutral Plus Minus
8

LEAD TO HOLE CLEARANCE
Lead Angle In Hole Combined With
Lead Clearance, Lead Shape And
Flux Quantity Can Impact Void
Creation In Plated Through Hole.
• Lead Type Can Impact Void Creation
– Round Versus Flat Ribbon
• Lead / Hole Metallization Can Impact
Void Creation
– Faster Wetting Rate = Greater Risk
Of Void Creation *
K. Seelig, et al, “Lead-Free Solder Assembly For Mixed
Technology Circuit Boards”, SMTA-I 2006

LEAD TO HOLE CLEARANCE
Lead Free Soldering
• Lead Clearance Minimum May
Increase
• Increasing Board Thickness May
Further Increase Lead To Hole
Clearance (Aspect Ratio)
• Larger Holes Create Less Voids
Smaller Lead To Hole Clearance
Decreases Shrinkage Holes /
Hot Tear Joints
IPC-A-610D, Fig. 5.67

INTERNAL PCB IMPACTS
Number of layer connections to plated
through-hole
• Increased number of layer
connections increases thermal
mass of plated through-hole
• Increased number of plane layer
connections greatly increases
thermal mass of plated throughhole
• Increase thermal pad isolation to
improve solder flow to topside
Higher solder temperatures or
increased solder dwell times create
problems with pads on solder side
11

WAVE SOLDER & REWORK ISSUES
Limit Effects Of Copper Dissolution
Use Lower Dissolution Rate
Solder Alloy
• Modified SAC Alloy
(Sb, Ni, Zn, Ge, In, Etc)
• Non-SAC Alloy
(Sn/Cu/Ni, Etc)
Original
SnPb
0.005” Trace Dissolution in 30 Seconds
Pad Trace Connection
– Tear Drop
– Snow Man Connection
– Wide Trace
– Greater Than 0.010”
SAC 305
SN100C
After wave soldering, 265 o C
solder temperature, 12 seconds
contact time
PCB Photo Courtesy of Cookson – Alpha Metals
Byle, Jean & Lee, “Copper Dissolution Rate in Pb-Free Soldering Fountain Systems”,
SMTA-I 2006

THROUGH HOLE PAD DESIGN
Square Pads Should Not Be Used On Solder Side
Increased Pad Lifting*
Increased Solder Defect – Bridge/Flag/Web
Decrease Component / Top Side Pad Size**
Reduced Fillet Lifting
* Dr. S. Zweiger, Solectron GMBH, Productronica Green Day, November 2005
** K Puttlitz, K Stalter, “Handbook of Lead-Free Solder Technology For Microelectronic Assembly”, pp 628, Fig 48

THROUGH HOLE PAD DESIGN
All Pads Should Be Same Shape
• Oval or Round
• Pin 1 square pad should not be used on solder
side
• In some situation legend ink in between pads
can help to minimize solder bridges
High Density Components (< 2mm Pitch)
• Pads Should Be Oval In Shape
• Staggered Pad Designs Should Be Used To
Enhance Solder Joint Formation On Exit Side Of
Component

SOLDER MASK SELECTION IMPACT
A Low Surface Energy “Glossy” Finish Can Generate
Solder Defects Similar In Appearance Of No Flux Or
Too Little Flux On The Board.
Resulting in Whiskers, Strings, Peaks, Bridges, Icicles,
Solder Balls, Solder Web, Solder Flags

DEFECTS CAUSED BY IMPROPER THERMAL BALANCE
Wave Solder Process
Thermal Shock
Damage
LED lead
LED
Increase Thermal Pad
Isolation
Balance Number
Connections For
Component Per Each
Plated Through Hole
Uniformity Of Trace
Size Connection To
Component Plated
Through Hole

THROUGH-HOLE COMPONENT MOUNTING
Leads Should Extend Below
Bottom of Board
Lead Protrusion: Shorter is
Better
• Decreased Solder Bridging
• Decreased Component Tilting
Lead Free Solder:
• Lead Length Should Be Even Shorter
Than Tin-Lead Solder.

EFFECT OF BOARD THICKNESS ON TOPSIDE FILLET
FORMATION
Board thickness increase thermal
mass of plated through-hole
Increase thermal pad isolation to
improve solder flow to the top
side
Increase lead hole clearance
(aspect ratio) to improve solder
flow to top side
0.062”
0.100”
0.150”
Board Thickness

Are You Confused
About Design For
Manufacturing
Requirements In
Today’s Lead Free
Soldering World
QUESTIONS SO FAR

COMPONENT PACKAGING AND DESIGN IMPACTS
0.2 mm
0.4 mm
0.8 mm
1.0 mm
Increased use of leadless component packaging technology
• Ball Grid Array (BGA)
• Quad Flatpack No-lead (QFN)
Increased sensitivity component/printed circuit board flatness
• Internal split plane or partial plane
• Nonfunctional pad removal
Increased use of component packaging with finer lead pitches
• 0.65mm > 0.5mm > 0.4mm > 0.35mm > 0.3mm >
1.27 mm
20

SOLDER MASK DESIGN AND FABRICATOR INCONSISTENCY
Non-solder mask defined (NSMD)
• Size of pad defined by copper pad and interconnections
(variable size)
• Solder encapsulates pad
• Limited to components with lead pitch greater than 0.4mm
Solder mask defined (SMD)
• Size of pad defined by solder mask opening (uniform size)
• Solder covers exposed pad (fills opening)
• Required for components with lead pitch 0.4mm or less
• Preferred for leadless array devices like land grid arrays,
multi-row quad flatpack no-leads, etc
Solder mask fabrication consistency
• Fabrication note interpretation “No solder mask permissible
on pads unless provided this way on supplied artwork”
• Selective solder mask opening changes between PCB
suppliers
21

ETCH IMPACTS OF SMALLER COMPONENT PACKAGES
Increased PCB supplier control/capability understanding may be required to
ensure proper etch compensation values are applied to other surface features and
not to conductor patterns.
Supplier A
Percentage reduction by pad size
Supplier B
22

IMPACTS OF INTERCONNECT DESIGN
Placement and types of vias in pad can affect assembly solder joint formation
More of an impact on smaller components and/or lower number
of electrical connections
Design and Construction Affects on PWB Reliability,
Paul Reid, IPC Apex Proceedings 2012.
23

STACKED VIA IN PAD FAILURE MODE
Lead free laminate is less ductile
Lead free solder is less ductile
Increased stress transmission to
internal connections
• Test fixture
• Assembly fixtures
• System integration
• Environmental
24

BOTTOM TERMINATE COMPONENT SENSITIVITY
Components without leads are more sensitive to minor design and assembly
process changes
• Land pattern design
– Exposed pad size uniformity
• Component /printed circuit board flatness/warping
– Copper distribution under package
• Paste volume control
– Pad to pad volume
– Pad to design defined volume
25

COMPONENT ISSUES - WARPAGE
Higher Lead Free Solder Solidification and Process Temperatures,
Increases The Amount Of Thermal Expansion Mismatch Of
Components Which Can Increase Amount Of Component Warping
During Assembly Process
May Require Redesign Of Package (Material Selection) For Thermal Mass And
Expansion Balance.

COMPONENT ISSUES – WARPAGE & THERMAL SHOCK
May Require Change In Production
Process
Tooling To Bridge Warpage Gap.
(Increased Solder Paste Volume Application, etc.)
Reflow Profile To Bridge Warpage Gap.
(Decreased Thermal Change Rate – Reduce Surface To
Cooler Location Temperature Delta - TCE Induced
Warpage)
Reflow Profile To Reduce Micro Cracks In
Multilayer Ceramic Capacitor Chips & Arrays.
(Decreased Thermal Change Rate – Reduce Surface To
Cooler Location Temperature Delta For Chip > 1210)

COMPONENT PAD - THERMAL IMBALANCE
Multiple trace connections
• Trace connections per pad
• Uniformity across all pads on
single component
Solder mask defined pad
increased soldering defects
• Delayed reflow across surface
mount technology components
– Tombstone components
– “Ball in socket” area array
component
28

COMPONENT PAD - THERMAL IMBALANCE
Small Passive Component Pad Design
• Mixed Solder Mask Defined
– Multiple/Large Trace
– Exposed Plane
• Smaller Component Package, The Greater The Impact

COMPONENT PAD - THERMAL IMBALANCE
“Via in pad” placement may
create mounting pad height
differences
• More of an impact on smaller
and/or lower lead count or
leadless (no solder ball/solder
bump) component packages
30

STENCIL TO PCB ALIGNMENT
Smaller components decrease total PCB and assembly process tolerance
Minor misalignment can impact process yields
3 mil
6 mil
31

TIN-LEAD AND LEAD FREE SOLDER DIFFERENCES
Stencil alignment of solder
paste to pad tolerance may be
critical to good manufacturing
yields
(Dependant upon PCB surface
finish)
Tin-lead paste
Lead free paste
Alpha Metals, SMT Mag Webcast
January 2006
32

TIN-LEAD VS LEAD FREE WICKING
Depending upon the pairing of PCB surface finish and component lead finish, the
amount of solder wicking/spread can induce or reduce solder defect formation
with lead free soldering process
Copper, tin, silver and gold Lead free Tin-lead
33

TO CLEAN OR NOT TO CLEAN
Ability to remove soldering process residues from PCBs may change due to
• Component package type
• Component size
• Solder mask design
34

TEST POINT AND SUPPORT DISTRIBUTION
Determines probe accessibility to the various components/nets for
the purpose of in-circuit testing and concentrate test probe stress
into localized area.
• Fixture induced printed circuit board bending during test
• Fixture induced bending during functional test from connector
mating/unmating.
35

MECHANICAL STRESS/STRAIN IMPACTS
Mechanical stress/strain impact analysis to identify test-initiated potential latent
field failure modes
• Solder joint crack initiation or fracture
• Micro/buried via design impacts
– Surface copper cracking/separation
– Internal copper cracking/separation
• Mechanical strain concentration
– Test point concentration
– Final assembly/disassembly
36

EXAMPLE OF EXCESSIVE STRESS
BGA Connection Near J5
• Bottom 3 Solder
Connections
• Two (2) Rows Of Solder
Balls
K
L
M
1
2
37

THANK YOU!
Dale Lee
Dale.Lee@Plexus.Com

QUESTIONS
39