r o h s

7/30/2019 r o h s

1/6

Notes:

This paper has been downloaded from SMART Group or Nepcon web siThis paper has been downloaded from SMART Group or Nepcon web sitestes

www.nepcon.co.ukwww.nepcon.co.uk www.smartgroup.orgwww.smartgroup.org

Email SMART Group atEmail SMART Group [email protected]@smartgroup.org

The SMART Group A guiding Influence in the Electronics IndustThe SMART Group A guiding Influence in the Electronics Industryry

Notes:

NEPCON Brighton 2 0 0 4

Smart GROUP

Lead-free Experience 2

Components in a lead-free environment

Angus Westwater

2. Restriction of use of certain Hazardous Substances

- RoHS Directive.

1. Waste Electrical and Electronic Equipment

- WEEE Directive.

Cadmium Mercury Hexavalent Chromium

Lead Polybrominated Biphenyls (PBBs)

& - Polybrominated Diphenyl Ethers (PBDEs)

Legislative Directives

Components in a Lead-Free Environment

Termination plating Lead-free

Solderability

Increased process temperature.

- Thermo mechanical fatigue (TMF)

- Moisture sensitivity level (MSL)

Placement accuracy Self alignment

Lead contamination Transition period

Tin whiskers

Lead Free Component

1. No change to functionality specification.

2. Qualified to 260 C- 265C soldering temperatures

3. One or Two passes through the soldering process.

Typical Termination

Lead-Free Solder Plating

Tin, Silver, Copper SnAgCu

Tin, Silver - SnAg

Tin, Copper - SnCu

Nickel, Gold (on Copper) - CuNiAu

Tin (on Nickel) - Sn

Palladium, Gold - PdAu

Tin, Bismuth - SnBi*

* Will become more viable when lead has been removed

from the soldering process (PbBi low melting phase)

Reflow Process Temperature Profiles

- 183C (eutectic)

- 215HHHHC

- 235HHHHCSMD reflow

- 250HHHHC

flow/wave

67HHHHC

Leaded (SnPb) process

Component durability

re-qualification increase 10C

flow/wave

- 217HHHHC (Sn3Ag0.5Cu)

- 235HHHHC

- 240HHHHC

SMD reflow

- 260HHHHC

33HHHHC

Note: Sn2Cu for wave

melting point = 227HHHHC)

Lead-free process

+10HHHHC

Possibility to reduce

the superheat zone to 12HHHHC

(229C)

Superheat zone

32HHHHCSuperheat zone

18HHHHC

7/30/2019 r o h s

2/6

Notes:





Notes:

Reflow Soldering Profiles for Leadfree Solder

Time

a) High peak soldering temperature -Pb free

b) Longer a bove process temp. Pb

free

150HHHHC

260 HHHHC

230 HHHHC

Temperature

Typi cal SnPb soldering

temperature profile

SnPb melting point

183 HHHHC

SnAgCu melting point

217 HHHHC

C) Higher and longer preheating - Pb free

Ramp Soak Spike Cool

Increased heat Longer duration

Solder print area

Solder Bath

Fluxsprayer

Lead-frame

Die attach

Bond wires

Epoxy Molding

Termination Solder Plating Processes

Solder Dipping

Barrel Electroplating

+

-Electroplating anode

material (tin)

Marking Cropping

Final tes t Tape& Reel

Electroplating

solution

Hopper/feeder

approx.

10,000 pcs/lot

PrinterStrain gauge

& Controller

Sample

Heated block

Molten

Solder pellet

Component Termination SolderabilityForce +

Force -

TimeA

Downward Force

Solder

wetting

B

Point B

Point C

C Max wetting force

Key parameter

Wetting time

A D seconds

D

Upward Force

Immersion depth

0.1 mm

Solder surface

(meniscus)

IPC/EIA J-STD-002A

PCB solder pad wetting - SnPb versus Pb free

SnPb solder paste

Total pad coverage

with SnPb solder

Leadfree solder paste

Pb free higher surface tension produces slower wetting

(Improvements in nitrogen gas environment)

Copper hallow

REFLOW

HEAT

REFLOW

HEAT

The lead-free Solder Joint

Copper hallow

Sn10Pb plating

Sn37Pb solder

Sn plating SnAgCu

Not a solderability iss ue: Inspection & training

Solder paste 70%

PCB platting 25%

Component plating 5% (SnPb)

Solder joint material

by volume

Pb diffusion into so lder

Pb free solder

paste SnAgCu

SnPb platting 10 thick

Lead collects in l ast area to cool.

Pb rich region with poor thermal cycling

fatigue characteristics

Lead Contamination of Solder Joint.

(Thermal cycling - Increase in mechanical fatigue.)

SnAgCu+Pb Meltingpoint and solidification can be

7/30/2019 r o h s

3/6

Notes:





Notes:

Reflow /Flow Process(Lead contamination of PCB top side leadfree solder)

Lead bearing terminations (SnPb)

Leadfree solder SnAgCu (MP 217HHHHC)

Courtesy Seiko Epson

Top si de >170 HHHHC

(high risk of lifting)

Top side max 150 HHHHC

Lifting prevented

Top side solder alloy SnAgCu +Pb (MP < 180 HHHHC)

Flow process

Lead-free Introduced Tombstone Failures

Lead-Free solders Increased su rface tension

Increased solidification temperature range

Com ponent miniaturisation

PCB component pad dimensions/tracking

and heat transfer route become critical

Further reduction in the PCB assembly process window

Heat

transfer

Heat

transfer

Faster solidification

Solder shrink force

Tin (Sn) plating has many desirable qualities.

Easily applied, non toxic

Good corrosion protection (shelf life)

Excellent solderability.

Tin Plating

Down Side

Under certain circumstances, spontaneous growths of

metallic filaments will grow on the tin termination surfaces.

Tin Whiskers

Sn Sn

SMT Capacitors & Resistors

Alumina substrate

Chip Resistor Construction

Glass under coatingInner termination Ag/Pd

Top, side & bottom (10 - 30m)

Glass middle coating

Glass* over coating

Marking

Resistor element RuOxLaser trim

Nickel plating Ni (2 - 12m)

Lead-Free outer termination Sn/Pb replaced with Sn (5 -12m)

*Pb Glass replaced with resin 1206 and smaller

Tin Whiskers

Whiskers also grow on cadmium, zinc, aluminium & lead.

Growth is encouraged in tin layers under stress,

i.e. electroplated layers ?

Electroplated stress, is linked to high plating currents & rapid

electroplating process.

Electroplating processes can therefore be optimised by

component manufacturers to minimise plating stress

Sn

Critical Parameters Encouraging

Whisker Growth in Component Tin Plating

1. Stress in the tin coating

2. Tin purity

3. Plating thickness

1000 cyc 8.2 m

* 70 minutes @ 55 C - 30 minutes @ 125 C

All controllable during the

component plating process Note: human h airapproximately 50m

7/30/2019 r o h s

4/6

Notes:





Notes:

Tin Whisker Growth Prevention

Optimise electroplating current & plating time.

Electroplate Tin (Sn) on nickel (Ni). Similar CTE.

During PCB reflow or flow soldering processes.

1. Diffusion of alloys (%%%% 1%) from bulk solder.

2. Action of heating and cooling tin plating

relaxes lattice structure.

NOTE: Sn plated component terminations utilising low temperature

conductive adhesive, remain a risk f or whisker growth

Tin plating alloys with base SnAgCu solder

Solder heat

Lead-free BGA Placement, in SnPb Process

(Placement Tolerance)

215C Reflow temperature

SnAgCu Solder balls

MP 217C

SnPb Solder paste

MP 183 C

SnAgCu solder ball will not melt, flow and

create surface tension at < 217C

SnPb

50% placement

error tolerance.

Self alignment

SnPb paste

SnAgCu

Placement error

tolerance reduced

Self alignment

reduced

SnPb paste

Lead-free BGA

SnAgCu

SnAgCu Solder balls

MP 217 C

SnPb Solder paste

(reflow 215 C)Solder ball Coplanarity tolerances cause open

solder ball connections if SnAgCu balls do notcollapse during SnPb process reflow.

Coplanarity tolerance

Lead-free BGA Placement in SnPb Process

(Coplanarity Tolerance)

Component Durability to Lead-Free

Soldering Temperatures

Higher Temperature

Longer Duration

Moisture Sensitive Device (MSD)

Electronic devices encapsulated with plastic compounds

and organic packaging materials, absorb moisture.

Humidity enters the package by diffusion, collecting

at dissimilar material interfaces.

Device sensitivity to moisture is classified* by

Moisture Sensitivity Level (MSL)

* IPC/JEDEC J-STD-020B

Impact of Moisture Ingression

Rapid heating during soldering, creates internal vapour pressure

and accelerated expansion within the device.

Important - Catastrophic failure or LONG TERMRELIABILITY compromised.

7/30/2019 r o h s

5/6

Notes:





Notes:

Component Moisture

Ingression Induced Failures

Popcorn effect

Distortion / cracking

Bond wire damage

Vapour Delamination

Impact of Lead-free Temperatures on MSL

Existing Component MSL classification

Existing storage & handling procedures

Increased soldering heat

Longer heat duration

New potential for moisture ingression / solder heat failures

Particularly where existing procedures are marginal

Actions

1. Re-qualify component MSL. - Component manufacturer

2. Review component storage conditions. Component user

Industry Standard

IPC/JEDEC J-STD - 033A

Handling, Packing, Shipping and Use of

Moisture / Reflow Sens itive Surface

Mount Devices

Component Moisture Sensitivity Classification

MSL Time Conditions

1 Unlimited 30C/85%RH

2 1 Year 30C/60%RH

2a 4 weeks 30C/60%RH

3 168 hrs 30C/60%RH

4 72 hrs 30C/60%RH

5 48 hrs 30C/60%RH

5a 24 hrs 30C/60%RH

6 Tim e on label 30C/60%RH

(TOL)

Component floor life

* IPC/JEDEC J-S TD-020B

Infinite floor life

One year

One month

One week

Three days

Two days

One day

Dry before use

MSD Component Storage

MSL 3

Remove from packing at production line

Return components to hermetically sealed

packing during further storage

Humidity ingression is cumulative.

If MSL violated, bake and dry as per

IPC/JEDEC J-STD - 033A

Sealing Zip

MSL 6

Dry Pack

Dry Pack

Maintain Reliability

Lead-Free Soldering Process

Moisture Ingression

Electrostatic Discharge ESD*

* Nepcon 13.00 - 27th May. ESD and ho w components are damaged

7/30/2019 r o h s

6/6

Notes:





Notes:

Safe Handling and Storage

Very likely to be less

than the cost of component

final test and field failure.

IPC/JEDEC J-STD - 033A (MSL)

BS EN61340-5-1: 2001 (ESD)

Compliance Training - Education & Audit

r o h s

Documents

Transcript of r o h s