!"#$%&'()'*"+,+$&#'

'

'

- ."%#&/01'%&2#-3/&&'- 4/&&+'&%&56/"+750'- 8'2+#'91'6$6"/72%'0&007"+'''

*":;"+&+6'900&:<%=>':26&/72%0'3"/'200&:<%='2+#'?"7+7+@':&6A"#0'7+'&%&56/"+750'

Most lead free Solder alloys melt at temperature higher then Sn-Pb

- To lower the melting point, use Indium or Bismuth

- Possess better rework/repair characteristics

INDIUM Alloys :- 52% In and 48% Sn 118°C MP

•  Useful for temperature sensitive components

•  Cost and Availability is a problem

BISMUTH Alloys :- 42 % Sn and 58% Bi 138°C MP

•  Cost comparative to TIN

•  Creates brittleness.

•  Poor fatigue Resistance Disadvantages : 1) Reduction in wetting 2) Special Flux required

Lower Melting Point lead-free alloys

TIN-SILVER-COPPER Based Alternatives These exhibits good wettability, fatigue resistance and good overall joint

Antimony Based Lead Free Solder :-

Stops gray tin (!-tin and "–tin formation) transformation at low temperature but is toxic, so this is a problem.

Lower Intermetallic Growth Desired

High Melting point lead-free alloys

Ternary Eutectic Composition

Sn-3.5 Ag- 0.9 Cu at 217°C

SOLDERNAME

SUPPLIER

COMPOSITION

MELTING POINT

COMMENTS

Indalloy™ 227

Arconium Specialty Alloy

77.2 Sn/20 In/2.8 Ag

187°C

Potential In-Pb incompatibility. Will require lead-free plating on PCB lands and component leads

Alloy H™

Alpha Metals

84.5 Sn/7.5 Bi/5 Cu/2 Ag

212°C

Liquidus temperature too high. Over 260°C wave temperature will be required

Tin-Zinc Indium

AT&T

81 Sn/9 Zn/10 In

178°C

Potential In-Pb incompatibility. Will require lead-free plating on PCB lands and component leads

Castin™

AIM Products

96.2 Sn/2.5 Ag 0.8 Cu/0.5 Sb

215°C

Liquidus temperature too high. Over 260°C wave temperature will be required

Tin-Silver –Copper

U.S. Dept. of Energy (DOE)

93.6 Sn/4.7 Ag/1.7 Cu

217°C

Liquidus temperature too high. Over 260°C wave temperature will be required

Commercially available Lead-free solders

LFS Materials for Bare PCB PCB

•  Consider benefits of reduced use of

brominated flame retardants

•  Avoid use of low-grade laminate

•  Change to pure tin as an etch resist

•  Use thermally-stable solder masks

Alternative finishes •  Organic solderability preservatives (OSP)

•  Palladium, silver and tin alloys

•  Lead-free hot air solder leveling

•  Nickel-gold

Thermal stability

•  Consider component stability at soldering at different temperatures, e.g. ‘popcorning effect’

•  Consider component suitability at soldering temperatures, e.g. electrolytic capacitors

Alternative finishes

Tin-copper, tin-bismuth, tin- Silver

Nickel-palladium (may not be cost-effective)

Silver and silver-palladium (may not be cost-effective)

LFS Material for Components

Fluxes •  Ensure flux compatibility with alloy used

•  Use a resin or water-based flux

•  Use ‘no-clean’ flux where possible

Solder alternatives

•  Tin-silver-copper alloys for all techniques (215 - 220°C)

•  Tin-copper possible for wave operations (227°C)

•  Bismuth-based solders for low-temperature

•  Other alloys specific to the application

•  Tin-bismuth-silver for reflow

Solder Alternatives

Reflow profiles

•  Optimize reflow profiles for selected alloy

•  Allow for narrower process windows

•  Optimize conditions according to the combination of assembly type, paste type, other materials and equipment for a particular application

Equipment

•  Maintain good temperature control

•  Consider energy consumption

•  Check temperature range of equipment

•  Consider using inert gas atmosphere

Reflow considerations

Reliability of LFS

!  Depends on material selection.

!  Fatigue performance of Sn-Ag-Cu solder is better than Sn-Pb.

!  Tin-Bismuth provides reliable joints for low temperature service.

!  Lead-free board finishes exhibit better solderability.

!  Fewer defects with lead-free solder.

!  Reliability of Sn/Ag/Cu BGAs are greater than Sn-Pb BGA based on thermal cycling

Environmental •  Lead-free solders are less toxic

•  Reduced risk of lead entering and polluting the

environment

•  Compliance with forthcoming legislation of hazardous substances

Economic •  Initial costs may be high

•  Converting to lead-free assembly may involve other costs

•  Recycling and disposal costs may fall

•  Profit margins may be higher for ‘green’ product

Benefits and Concerns

Technical •  Improved reliability possible

•  Lead-free board finishes exhibit better solderability and have a longer shelf-life

•  Fewer defects with lead-free solder than with tin-lead solder in well-designed process

Marketing •  Consumer willingness to support products with less environmental impact

•  Opportunity to demonstrate a company’s commitment to the environment

Benefits and Concerns

!"##$%#&#'(")$*'+',-.(%*+%(-#%*++/#%.+%0."%.+%#&#'(")$*'+%1.'2.!*$!%*+%')$'#"$#34%

+)5#%6.+*'+%()%/$3#"+(.$37%

089:;<=>%<?;%@:%@AB?9:;CAB%;D?%<8E?%F=F<?%GE%CA%?<?F;9GA8F%H9GB@F;I'

' %

'

• #<?F;98FC<>%J?FDCA8FC<%CAB%FD?J8FC<%B?:8KA%%

• "CL%JC;?98C<:>%H9GB@F;8GA%GE%*'%CAB%HC::8M?%FGJHGA?A;:>%G9KCA8F%NGC9B%

ECN98FC;8GA>%8AMG<M8AK%C%MC98?;=%GE%

FD?J8FC<:'

• .::?JN<=%GE%FGJHGA?A;:%@:8AK%C%MC98?;=%GE%DC9JE@<%JC;?98C<:%:@FD%C:%

&?CBO'

• .::?JN<=%GE%;D?%9?:@<;8AK%?<?F;9GA8F%NGC9B:%8A;G%?AB%H9GB@F;:%:@FD%C:%

F?<<@<C9%HDGA?:>%<CH;GH:%G9%

FCJFG9B?9:%?;FO'

• (9CA:HG9;C;8GA%GE%;D?:?%H9GB@F;:%;G%;D?%F@:;GJ?9:'

• /:CK?%CAB%FGA:@JH;8GA%GE%H9GB@F;:'• 38:HG:C<%CAB%9?F=F<8AK' !"#$%&'()*“+#,-./&,%.0'*"1*234$"'('%&/'*5.46.73,7”)*8."*9#//.0.*

B70C'0$<062+5&0'$0&#'7+'!75/"0=06&:0'

!"#$%&&% '()*"#(+%(,-./0#($%"(&% !#,%(,*-./1#.2,*#(&%

3-4%"/-(5/60/4-7"*$-,*#(% •  +G<M?A;:%

•  'D?J8FC<:%

•  $GAPDC9JE@<%:G<M?A;:%CAB%

FD?J8FC<:%

60/!-$8-9*(9/-(5/:&&%+7.;% •  &?CB%Q+G<B?9R%

•  '<?CA8AK%S<@T%

•  &?CBPE9??%:G<B?9%

•  'GAB@F;8M?%.BD?:8M?%

C;;CFDJ?A;%

•  58A8J8U?%:G<B?9%@:CK?%

1;&,%+<.%)%./!3=/-(5/:&&%+7.;%

•  &?CBPNC:?B%:G<B?9:%

•  '<?CA8AK%S<@T%

•  -C<GK?A%Q69R%C:%S<CJ?%

9?;C9BCA;%8A%1'6:%

•  +G<M?A;%?J8::8GA%8A%1,6%

JCA@ECF;@98AK%H9GF?::?:%

•  &?CBPE9??%:G<B?9%

•  'GAB@F;8M?%.BD?:8M?%

•  $GAPDC<GK?AC;?B%S<CJ?%

9?;C9BCA;%Q<8V?%1R%

•  +G<M?A;PE9??%1,6%H9GF?::%

1;&,%+/:&&%+7.;% •  'CBJ8@J%8A%NC;;?9=%

•  -C<GK?A%S<CJ?%9?;C9BCA;%8A%

DG@:8AK%

•  .<;?9AC;?%NC;;?9=%

•  $GAPDC<GK?AC;?B%S<CJ?%

9?;C9BCA;%

B70C'0$<062+5&0'$0&#'7+':2+$3256$/7+@';/"5&00'

<$6'+"6'7+'6A&'D+2%';/"#$56'

•  1#.)%(,/2&%5/*(/!3=/+-(24-$,2"*(9/>"#$%&&%

•  0?%+*$-.&/2&%5/4#"/@.2A/$.%-(*(9/52"*(9/&#.5%"*(9/>"#$%&&%

•  0?%+*$-.&/2&%5/*(/,?%/%,$?*(9/>"#$%&&/,#/9%(%"-,%/$#>>%"/.*(%&/#(/!3=/&27&,"-,%&%

•  3-&,%/B-,%"%

•  C#.-,*.%/#"9-(*$/$#+>#2(5&/2&%5/*(/@.2A/-(5/&#.5%"/>-&,%/%,$D%

EA&'&F&560'"3'6A&0&'/70C'0$<062+5&0'G7%%'%&2#'6"'

6A&'3"%%"G7+@'5"+5&/+0'

•  E%-.,?/?-F-"5&/,#/,?%/>%"&#((%./5*"%$,.;/%A>#&%5/,#/,?%/"*&8/&27&,-($%&%

•  G.#7-./B-"+*(9%

•  =-5/#5#"/-(5/>##"/B#"8*(9/%()*"#(+%(,%

•  H%&,"2$,*#(/#4/#F#(%/.-;%"/*(/,?%/&,"-,#&>?%"%%

•  :$*5*@*$-,*#(/#4/"-*(/7;/9%(%"-,*#(/#4/>?#,#$?%+*$-./#A*5-(,&%

•  0#(,-+*(-,*#(/#4/.-(5@*..&%

•  I#"%/%(%"9;/,#/7%/&>%(,/,#/"%$;$.%/"*&8/&27&,-($%&/4"#+/&>%(,/%<B-&,%%

6#((#"%#$#"!W%/(*&*+.(*)$%*$%#&#'(")$*'%1")3/'(+%*+%.&+)%.$%*51)"(.$(%

.+1#'(%)0%!"##$%#&#'(")$*'+%3#+*!$%.$3%5.$/0.'(/"*$!X'

'

'

'

'

H%&56/"+75'G206&>'&-G206&>'&-05/2;>'"/'I206&'H%&56/752%'2+#'

H%&56/"+75'HJ$7;:&+6'KIHHHL''

M#&05/7<&0'%""0&%='#7052/#&#>'0$/;%$0>'"<0"%&6&>'</"C&+>'

&%&56/752%'"/'&%&56/"+75'#&N75&0O'

B"P.-'B&06/75,"+'"3'P2Q2/#"$0'.$<062+5&0'

MR&2#>'*2#:7$:>'!&/5$/=>'*A/":7$:'KA&S2N2%&+6L>'

</":7+26&#'T2:&'/&62/#2+60'K$0&#'7+'UBV'%2:7+26&0L'

'

MM'W+"/@2+7Q&#'/&5=5%7+@'2+#'#70;"02%'"3'&-G206&'7+N"%N&0'

07@+7D52+6'/70C'3"/'&S2:;%&0'6"'G"/C&/0'2+#'5"::$+7,&0'

2+#'@/&26'52/&':$06'<&'62C&+'6"'2N"7#'$+023&'&S;"0$/&'7+'

/&5=5%7+@'";&/2,"+0'2+#'%&25A7+@'"3':26&/72%0'0$5A'20'

A&2N=':&62%0'3/":'%2+#D%%0'2+#'7+57+&/26"/'20A&0O'

'

MM'X200'"+'="$/'&-G206&'6"'2'%75&+0&#'K/&5"@+7Q&#'<='

X"%%$,"+'*"+6/"%'Y"2/#0L'&-G206&'/&5=5%7+@'"/@2+7Q2,"+O''

'

'

What is ROHS? What is WEEE? What are the restricted materials mandated under RoHS? Why is RoHS compliance important? How are products tested for ROHS compliance? Which companies are affected by the ROHS directive? Why is there a push for lead-free solders in electronics soldering applications? Why should some lead-free alloys be approached cautiously? Are lead-free alloys as durable as tin-lead alloys? How do lead-free alloys compare to tin-lead alloys for application temperature requirements? Are lead-free alloys compatible with all flux types? In what solder forms can lead-free alloys be produced? What are the attributes that one should look for while searching for a lead-free solder alloy?

low-cost, easily repaired, compatibility with existing parts and processes, no toxic or exotic constituents

!"#$%&'()*:;<)==&>.'%&7#3-&?3,1"*

Centre for Electronics Design and Technology, Indian Institute of Science, Bangalore 560012 Page 1 of 4 gvm/-

TUTORIAL CLASS- ELECTRONICS SYSTEMS PACKAGING TECHNOLOGIES

NPTEL VIDEO LECTURES AUTHOR: G V MAHESH, CEDT, IISC, BANGALORE 560012

THIS COVERS SMD ASSEMBLY, ASSEMBLY MATERIALS, LEAD-FREE

SOLDERS AND GREEN TECHNOLOGIES

1. Some SMD RESISTORS have a case form of 0402. What are the dimensions of this

resistor?

2. What is the melting point of 63/37 Sn/Pb solder material?

3. List different methods of machine soldering.

a. b. c.

4. What is flux? What are its functions during soldering?

5. Why are adhesives printed on PWBs before SMD mounting?

6. What is the function performed during IR/thermal reflow soldering?

Centre for Electronics Design and Technology, Indian Institute of Science, Bangalore 560012 Page 2 of 4 gvm/-

7. Can SMDs be repaired on board? How do you go about it?

8. Metal stencils are preferred to silkscreens during screen printing process in SMT

manufacturing. Justify this statement.

9. RMA in flux types stand for what?

10. 2-3% Ag is usually added to tin/lead solders. Why?

11. What is the function of pre-heating in machine soldering process when using rosin

fluxes? Is it to activate the flux?

12. What is dross? How do you dispose it?

13. Give two reasons for tombstoning and skewing in SMD assembly.

Centre for Electronics Design and Technology, Indian Institute of Science, Bangalore 560012 Page 3 of 4 gvm/-

14. What is the machine soldering process in Type I assembly process?

15. What causes ceramic capacitor cracking? What are the associated problems?

16. What are the options for selective soldering of SMD components?

17. Give two examples of lead-free solders being considered by large-scale industry?

18. How do you prevent solder bead formation during soldering?

19. What are the different reflow processes? Which is most popular?

20. What is a thermal profile? Is it important in machine soldering?

Centre for Electronics Design and Technology, Indian Institute of Science, Bangalore 560012 Page 4 of 4 gvm/-

21. Name the test options for SMT assembly.

22. Is nitrogen atmosphere soldering always recommended?

23. What are the causes of bridging in SOIC/QFPs during wave soldering?

Do you recommend this process for fine-pitch components?

24. What is the impact of BGA on board design and manufacturing?

25. What is popcorning in BGA?