Lead Free issues...IPC 7095 7.4.1.6 Primary Cause of Fillet Lifting Board holds heat longer, keeping...

Lead Free issuesCorné Hoppenbrouwers

Cookson Electronics

2005

Why is lead a problem for Society?Why is lead a problem for Society?Increasing use of PCBs in everything we use is leading to

more PCBs in our land fills.

Lead Consumption by ProductProduct

Storage batteriesOther oxides (paint, glass and ceramic products, pigments and chemicals)AmmunitionSheet leadCable coveringCasting metalsBrass and bronze billets and ingotsPipes, traps, other extruded productsSolder (non-electronic)Electronic solderMiscellaneous

Consumption (%)

80.814.78

4.691.791.401.130.72

0.72

0.700.492.77

Not very significantin the total picture.

When Lead Free ?1-july- 2006 to end userStocking time of the productsStocking of the components used

Time to implement LF technologyMakes the moment LF close by

Alloy choiceWhat is the basic building blockelement for a lead-free alloy ?

TINMelting Point 232 °C

Alloy choiceWhat are the potentialsubstitutes for lead ?

•Silver AG

•Indium In

•Zinc Zn

• Antimony Sb

• Copper Cu

• Bismuth Bi

Alloy choiceZinc, ZN

+ Inexpensive+ Readily Available+ Effective in Reducing melting Point

- Rapid Oxide Formation- Highly Stable Oxide- Corrosion Concerns- Significantly Reduces wettability !!

Alloy choice

Indium, In

+ Very good at reducing Melting point+ Very good wetting Properties+ Good physical Properties

- Too Expensive- Scare Supply- Concern About low Melt Point Phase at 114°C

Alloy choiceBismuth, Bi

+ Reduces Melting point+ Excellent Wetting+ Very Good Physical Properties

- Concern with Low Melting Point phase- Concern with Fillet Lift- Limited availability if lead is banned

Alloy Terminology

• No official standard for alloy terminology

• In the absence of a standard the followinghas evolved within the industry– SAC = Sn-Ag-Cu = Tin-Silver-Copper

• SAC405 = Sn 4.0%Ag 0.5%Cu• SAC387 = Sn 3.8%Ag 0.7%Cu• SAC305 = Sn 3.0%Ag 0.5%Cu• SAC0307 = Sn 0.3%Ag 0.7%Cu

Alloy SelectionPb Free alloy OVERVIEW

Name Notes Sn Ag Cu Sb Bi Zn Solidus LiquidusTin Silver Eutectic No Patent - prior art 96,5 3,5 221 221Tin Copper Eutectic No Patent - prior art 99,3 0,7 228 228Tin Zinc Eutectic No Patent - prior art 91 9 198 198SAB Bal 2-4 <5 205 210SZB 89 3 8 189 199SAC SAC - ALPHA Licence Bal 3-4 0.5-1 217 217

Constituents (Ranges NOT specifications)CELCIUS

FOR (+) AGAINST (-)No Patent Coverge Higher solidus/liquidus than SAC, w ill pick up Cu

from boards at a rate of around 0.03%Cu/1000 boards - w ill become a SAC alloy in use. Poorer w etting than SAC.Considered too high liquidus for reflow applications


Name Notes Sn Ag Cu Sb Bi Zn Solidus LiquidusTin Silver Eutectic No Patent - prior art 96.5 3.5 221 221Tin Copper Eutectic No Patent - prior art 99.3 0.7 228 228Tin Zinc Eutectic No Patent - prior art 91 9 198 198SAB Bal 2-4 <5 205 210SZB 89 3 8 189 199SAC SAC - ALPHA Licence Bal 3-4 0.5-1 217 217


FOR (+) AGAINST (-)No Patent Coverge. Low er Metal Cost than Silver Containing Alloys

Higher liquidus than SAC. Too High for reflow useage. High level of bridging in w ave Thermal fatigue concerns (cracked joints)


Name Notes Sn Ag Cu Sb Bi Zn Solidus LiquidusTin Silver Eutectic No Patent - prior art 96,5 3,5 221 221Tin Copper Eutectic No Patent - prior art 99,3 0,7 228 228Tin Zinc Eutectic No Patent - prior art 91 9 198 198SAB Bal 2-4 <5 205 210SZB 89 3 8 189 199SAC SAC - ALPHA Licence Bal 3-4 0.5-1 217 217


FOR (+) AGAINST (-)No Patent Coverge. Low er Metal Cost than Silver Containing Alloys Low liquidus temperature Could offer a similar reflow profile to SnPb

Zinc is highly corrosive, oxidises very readily Poor f luidity/drainage excludes from Wave Requires very active f lux/coated pow der/nitrogen atmosphere - question reliability




FOR (+) AGAINST (-)Low er liquidus than SA, SAC and SC alloys Increased f illet lif ting caused by SnBi phase

Reliability hazard w ith Lead on components (96C MP.phase)




FOR (+) AGAINST (-)Low er cost than SAC alloys. Low est solidus/liquidus temperatures

Zinc is highly corrosive, oxidises very readily Poor f luidity/drainage excludes from Wave




FOR (+) AGAINST (-)Low er liquidus than SnCu, SnAg - Reflow OK Good f luidity, low level of bridging. Low copper leaching compared to SnAg Rapidly becoming the "Standard" LF alloy

Patented in US and Japan - subject to licence fee

New SACX0307

Units Vaculoy SACX SAC305Leading competitor

Sn/Cu based product

Defect Rate (1) % +5% - +60%Wetting Speed (2) Time Sec 0.75 0.60 1.00

F Max mN/mm 0.21 0.26 0.10Copper Erosion (3 sec contact) Micron/s 10.7 11.0 11.7Drossing Rate Index 56 No Data 100Mechanical reliabililty Rank 1 1 3Pr

oces

s At

tribu

te

ALPHA Vaculoy SACX0307

Sn2.5Ag1Bi0.5Cu Sn3Ag0.5Cu Sn3Ag0.7Cu Sn3.5Ag0.5Cu Sn4Ag0.5Cu Sn37Pb Condition of measurementAl l oy Name Alloy T

Me l t i ng Range L/ S 217.1/216.3 219/218.6 219.3/218.4 217.5/215.7 218.5/216.4 183 Measured by cooling curveHar dne s s H V 16,6 14,1 15,5 15,5 14,9 12,8 Stress 50g/Keeping time 15s

De ns i t y g/cm3 7,4 7,39 7,39 7,40 7,41 8,41 Alchimedes methodSpe c i f i c he at J/gK 0,231 0,232 0,234 0,236 0,236 *0.15 20El e c t r i c al c onduc t i vi t y µΩ/ cm 13,4 12,6 11,4 11,8 11,7 *15 20

Young Modul e ×1010N/m2 5,7 5,49 5,74 5,2 6,03 4,1 20 Supersonic methodPoas on r at e 0,31 0,34 0,32 0,36 0,32 0,36 20 Supersonic Method

Li ne r e xpans i on c oe f f i . ×10-6/

Under measureme

nt

Under measurem

ent 21,1 22,1 21,4 24 20/100Te ns i l e s t r e ngt h 1s t MPa 51,4 40,1 40,80 38,61 39,48 45,57 25 Head speed 10mm/minSe c ond 51,7 39,2 39,78 53,86 39,22 44,59El ongat i on 1s t 35,8 43,4 42,88 38,61 18,74 32,3 25 Head speed 10mm/minSe c ond 38,7 48,7 41,10 53,86 22,60 36,60Cr e e p 100/6.9MPaLife h Re- measure Re- measure 91,4 82,9 43,9 4,5Initial warpage Re- measure Re- measure 0,019 0,022 0,044 0,074Static creep speed h Re- measure Re- measure 0,111 0,041 0,211 1,332Elongation 1st 42 19,8 38,09 30

Physical Properties of lead free alloys

What Does The Industry Want?Similar Alloy Properties to 63Sn/37Pb

• Same Price• Melting Point < 200 C

Reflow < 230 C• Eutectic or close• Low Toxicity• Low Drossing• Compatible With Existing

Fluxes

• Acceptable Wetting• Acceptable Physical

Properties (strength,fatigue properties)

• Adequate Electrical AndThermal Conductivity

• Compatible With PCBand component finishes

• Nortel - Sn/Cu ( 1998)• Ford - Sn/Ag (1999)• Nokia - Sn/Ag/Cu• Delco - Sn/Ag/Cu/Sb (1998-2000)• Philips – Sn/Ag/Cu• Matsushita - Sn/Ag/Bi, Sn/Ag/Cu, Sn/Cu• Toshiba - Sn/Ag/Cu• Siemens - Sn/Ag/Cu

Pulblished Alloy Selections by Company

Defect rate

PCB Finishes• SnPb HASL is out - it contains lead

– Pb-Free HASL finishes are possible (SnCu)• Most HASL users will move to one of4 common groups of finishes

– Copper (with OSP)

– Electroless Nickel Gold (ENiG)

– Electroless Silver

– Electroless Tin

PCB Finishes

Gold

OSP

Component Finishes• Many leaded devices have Tin-Lead finish

– This is moving towards pure Tin– SAC alloy solder will not cause catastrophic

failure when using SnPb components duringtransition

• Many fine pitch (<0.65mm pitch) IC’s have beenusing NiPd for some years (Texas Instruments)

• Grid Array comps (BGA, CSP) and connectorsalmost exclusively SnPb finishes– SAC alloy spheres are becoming commonplace

Failure at Pb contamination content

Joint Inspection

• Voiding :

63/36/2 Sn/Ag/Cu

Other Concerns, where are they ?

Exceeds IPC 7095 Class III requirements for solder joint area: 0 voids greater than 9%

The IPC criteria provide three classes of acceptance forboth the solder sphere and the sphere-pad interface.Where multiple voids exist, the dimensions will be addedto calculate total voiding in the joint.

d

0.25 d

Solder Outline

Void Outlines

0.1 d

Example:Total Void Diameter0.10d + 0.25d = 0.35d

Location of Void Class I Class II Class III

Void in Solder (Solder Sphere)

60% of diameter = 36% of Area

45% of diameter = 20.25% of Area


Void at Interface of Solder (Sphere)

and Substrate


35% of diameter = 12.25% of Area


Reflow CapabilitiesVoiding IPC Criteria for Voids in BGAs,IPC 7095 7.4.1.6

Primary Cause of Fillet LiftingBoard holds heat longer,keeping fillet/padinterfacehotter.

As fillet cools faster fillet padinterface under tension

Fillet LiftingBroken land

TerminalFailure

TearingFillet lifting

Benign Benign

Electrical Continuity can be maintained

Fillet Lifting• Caused by solder fillet cooling before the board; the

board contracts away from the fillet as some solder onthe board side is still pasty

• Cosmetic rather than a reliability issue• Made worse by tin-lead coatings, bismuth containing

alloys• Avoid by using lead-free components and rapid cooling

• IPC-610-D– Specifies pass fail criteria for shrinkage cracks.– “Crack must not touch the land or the lead”– “Bottom of the crack must be clearly visible”

SAC305

Pass

Fail

Shrinkage Cracks high silver SAC Alloys

• The Microstructure ofSAC alloys (3-4% Ag)forms step by step.

• This results in the alloydisplaying a surfaceroughness because ofthe shrinkage of theeutectic liquid betweenthe Sn dendrites. TheAg3Sn particlesimprove the reliabilityof the joints.

• Some Lead-Free alloys,such as SACX0307 donot display roughpatches.

Courtesy of Celestica International Inc.Snugovsky, Bagheri, Kelly, Romansky

SEM of rough patch on SAC387 soldersphere

Shrinkage Cracks high silver SAC Alloys

Rework

Rework Elevated Rework Temperature EffectsEmbrittlement,

Cold Solder joint Component andPoor Wetting Good Wetting PCB damage

183oC 223oC 263oC

Cold Solder joint Good WettingPoor Wetting

Tin-Lead 63/37

Lead Free SAC 305

Lead Free Rework Considerations:• Heat transfer to the component and board is less controlled than any other process

due to manual nature of repair work.• Soldering iron tips will corrode quicker using high tin alloys.

263oC223oC 303oC

Increasing Temperature

Use CEAM’s cored wire and target the optimum rework temperatures to deliver reliable joint

Higher Soldering Temperatures and LongerContact Times:• Increased chances of

– Printed circuit board damage– Component damage– Creating more intermetallics and hence brittle joints– Premature flux fuming yielding less flux on the joint during the

rework process

Rework recommendations for Successful Lead-Free Joint

Manual rework training will be required in the transition to Lead-Free

Rework Solder Iron Requirements

Solder Iron Settings:• Temperature of piece to be soldered (not the iron) should be about 250oC

(482oF), and a the solder iron tip should be a temperature of about 370oC(698oF). This should give an acceptable heat transfer time using the correcttip size.

• Aim for a contact time of 2 - 3 seconds. Overheating a joint damages theboard and may lead to board reliability issues over the lifetime of the product.

• Use a soldering iron bit that is suitable. A bit that is too small may preventthe formation of a joint or slow down the rework operation.

• Do not overheat as this can cause an increase in the depth of theintermetallic layer resulting in a weaker joint.

Planning the processing methods for the manual rework operation is critical to delivering a Lead-Free solution.

Solutions to Lead Free Rework Issues:• Minimize heat transfer to the board and component - more heat - more

potential damage• Use Lead-Free alloy with fastest wetting speed and lowest melting point• Use active solder flux with good post soldering reliability• Ensure that there is enough flux on the joint to make a bond in the shortest

time possible• Use an iron with suitable controller that minimizes its temperature variance.

Rework Barriers to a Successful Lead-Free Joint

Cookson Electronic Assembly Materials provides solutions for your Lead-Free processing issues.

Pb-Free Wire• Basically, not a major problem

• Most Alloys available

• Temp. up to tip of 400 °C

• Short life time of tips

• However, beware, some do not have sufficientductility to allow fine wire drawing (below 0.4mm)

PCB Labelling Specification

Contains leadNot “ROHS”CompliantNo Mark

e.g.: SnZn, SnZn-x,Pure-Sn, NiPd, NiPdAu,SnAu, SnSb

e.g.:SnZnBi, SnBi

e.g.: Sn3-4%Ag0.5-0.9%Cu

Material TypeProposedMark

Other lead freematerials

Contains Bismuth

SnAgCu Family

Categorization

e1

e2

e3

Reference Vivek Gupta Draft Specification IPC Lead-Free Conference 2003

• Proposed standard under review by IPC– Rework solder identification

PCB Labelling Specification

SMART Group Lead-Free Experience PCB with e1 markingReference Vivek Gupta Draft Specification IPC Lead-Free Conference 2003

Cost impactStandard Solder 63/37 in week 14

Tin cost 5,96 €/kg 0,63 x 5,96 €/kg 3,99 €/kgLead cost 0.73 €/kg 0,37 x 0.73 €/kg 0,27 €/kgTotal price 63/37 4,26 €/kg

Standard SAC Solder 96,5SN3,0Ag0,5Cu

Tin cost 0,965 x 5,96 €/kg 5,75 €/kgSilver cost 0,03 x 210 €/kg 6,30 €/kgCopper cost 0,005 x 1€/kg 0,005 €/kgTotal price SAC305 12,055 €/kg

Total price SAC405 14,155 €/kg

By density differences less product

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Lead Free issues...IPC 7095 7.4.1.6 Primary Cause of Fillet Lifting Board holds heat longer, keeping...

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