inemi lead-free alloy characterization program update...

iNEMI Lead-Free Alloy

Characterization Program Update:

Thermal Cycle Testing and Alloy

Test Standards Development

October 21, 2011

Chair: Greg Henshall, HP

Co-Chair: Stephen Tisdale, Intel

Authors

Julie Silk and Bill Jones; Agilent

Richard Coyle and Joe Smetana; Alcatel-Lucent

Ahmer Syed; Amkor

Jasbir Bath; Bath Technical Consultancy

Mike Osterman and Elviz George; CALCE

Tae-Kyu Lee; Cisco

Ranjit S. Pandher; Cookson

Richard Parker; Delphi

Joelle Arnold, Nathan Blattau; DfR Solutions

Jennifer Nguyen; Flextronics

Mark Currie and Srini Chada; Henkel

Gregory Henshall, Jian Miremadi, Aileen Allen; Hewlett-Packard

Fay Hua and Stephen Tisdale; Intel

Jeffrey Lee, Graver Chang, IST

Keith Sweatman and Keith Howell; Nihon Superior

Sze Pei Lim and Weiping Liu; Indium

Dave Godlewski and Haley Fu; iNEMI

Bill Barthel and Ursula Marqez de Tino; Plexus

Derek Daily; Senju

Project Team Members

20 companies; 55 individuals

Solder alloy suppliers, component suppliers, EMS providers, OEMs

Outline

• Background and Objectives

• Thermal Fatigue Reliability

• Alloy Test Requirements and

Standards

• Summary and Conclusions

Near-eutectic SAC allowed industry to meet

RoHS deadline of July 1, 2006

• Industry adopted SAC 305 & other “near eutectic” alloys as the standard Pb-free alloys during the RoHS transition

• Selected by industry consortia balancing many factors

• Major factors included:

– Relatively low melting point

– Reasonable thermal fatigue reliability

• Selected prior to understanding impact of composition on mechanical robustness and copper dissolution

• Further optimization anticipated

Typical Sn-Ag-Cu (SAC)

microstructure

Problems with SAC305/405 include:

• Poor drop/shock performance for

BGAs, especially on Ni/Au surfaces

• Expense of Ag is driving the desire to

reduce Ag content

– $660/lb – August 30, 2011

(Tin ~ $10.80/lb)

– Wave solder bar main concern

• Poor barrel fill on thick boards for

some surface finishes

• Copper dissolution

• Hot tearing and other surface

phenomena create inspection issues &

possibly unnecessary rework

Ni

Cu

Solder

IMC

Fracture surface showing intermetallic

layer left, no solder

Gregorich, et al., IPC/Soldertec Global 2nd International

Conference on Lead Free Electronics (2004).

SAC305/405 functional but not the optimal

Pb-free solution

Wide range of alloy choices is both

an opportunity and a risk

Addressing issues with alloy alternatives led to

expanding alloy choice

•SAC is Sn-Ag-Cu

• SAC305 is Sn-3.0Ag-0.5Cu

• SAC105 is Sn-1.0Ag-0.5Cu

• SACX is SAC with small quantities

of dopants added

•Partial list of Pb-free solder alloys used

commercially or being investigated for

BGA/CSP balls

•Most new alloys have low silver content

(or none at all)

AlloysSn1.0Ag0.5Cu (SAC105)

SAC205

Sn-3.5Ag

Sn0.3Ag0.7Cu+Bi (SACX)

Sn0.3Ag0.7Cu+Bi+Ni+Cr (SACX)

SAC 305+0.05Ni+0.5In

SAC255+0.5Co

SAC107+0.1Ge

SAC125+0.05-0.5Ni (LF35)

SAC101+0.02Ni+0.05In

Sn-3.5Ag + 0.05-0.25La

Sn-0.7Cu

Sn0-4Ag0.5Cu + Al + Ni

SAC305 + 0.019Ce

Sn-2.5Ag-0.8Cu-0.5Sb

Sn-0.7Cu-0.05Ni

Sn-0.7Cu-0.05Ni + GE (SN100C)

SAC105 + 0.02Ti

SAC105 + 0.05Mn

Sn-3.0Ag-1.0Cu

7

Concerns with alternative alloys

• There is no “perfect” alloy – there are

concerns with every alloy

• Concerns with alternative alloys

include:

– Technical issues

• Manufacturing and rework

• Reliability (thermal fatigue, drop/shock,

bending, etc.)

• Copper dissolution

• New alloys may or may not solve all

problems of SAC305

– Non-technical issues

• Supply chain management

• Cost of ownership

• Industry management (part number

changes, standards on dopants, etc.)

SAC305

SAC305

8

Pb-Free Alloy Characterization Project focused on

addressing high priority knowledge gaps

2008 iNEMI assessment of key areas where knowledge is lacking

High Priority Knowledge Gaps

Advantages and disadvantages of specific

alloys

Composition limits for microalloy additions;

ranges of effectiveness

Standard method to assess new alloys;

standard data requirements

Consistency of testing methods, including test

vehicles & assembly, test parameters, etc.

Establish the microstructural characteristics of

specific alloys

Long term reliability data for new alloys,

particularly low Ag & microalloyed

Lack of thermal cycle data for evaluating new

alloys; benchmark to Sn-Pb and SAC 305/405

iNEMI Alloy

Characterization

Project Focus Areas

Outline




Standards


Questions to answer about thermal fatigue

performance of new alloys

10

1. How does the performance of low-silver alloys

compare to that of eutectic Sn-Pb and

SAC305?

2. What is the quantitative impact of Ag

concentration?

3. What is the impact of dopants?

4. Does relative performance among alloys

depend on the package type?

5. How do the thermal fatigue conditions impact

acceleration behavior?

Impact of alloy

composition on thermal

fatigue life in the field

difficult to judge

Overview of industry efforts to generate thermal

fatigue data

11

Industry Working Group (complete)

Alcatel-Lucent Working Group

Jabil Working Group (ATCcomplete)

iNEMI Alloy Characterization

Impact of Ag concentration Impact of Ag concentration & dopants

Rapid results

through using

existing test

materials

Comparison to Sn-Pb

Mixed Sn-Pb/Pb-free jointsData for common commercial alloys

Effects of thermal cycle profileQuantitative acceleration

factors

Impact of package type

Alloys under test

12

• 12 Pb-free alloys plus

Sn-Pb control

• Systematically investigate

impact of Ag content

• Impact of common dopants,

such as Ni

• Alloys becoming fairly

common in practice

• Impact of aging

• Paste alloy is SAC305

except as noted in red

Cell

No. BGA Ball Alloy Trade Name

Solder

Paste Comments

1 Sn-37Pb Eutectic Sn-Pb Sn-37Pb Control

2 Sn-0.7Cu+0.05Ni+Ge SN100C SN100C 0% Ag joint

3 Sn-0.7Cu+0.05Ni+Ge SN100C SAC305 Impact of [Ag]

4 Sn-0.3Ag-0.7Cu SAC0307 SAC305 Impact of [Ag]




8 Sn-4.0Ag-0.5cu SAC405 SAC305 Impact of [Ag]

9 Sn-1.0Ag-0.5Cu+0.05Ni SAC105+Ni SAC305

Impact of

dopant

10 Sn-2.0Ag-0.5Cu+0.05Ni SAC205+Ni SAC305

Impact of

dopant

11 Sn-1.0Ag-0.5Cu+0.03Mn SAC105+Mn SAC305

Impact of

dopant

12 Sn-0.3Ag-0.7Cu + Bi + X SACX0307 SAC305

Doped

commercial

alloy

13 Sn-1.0Ag-0.5Cu SAC105 aged SAC305 Effect of aging

14 Sn-3.0Ag-0.5Cu SAC305 aged SAC305 Effect of aging

15 Sn-1.0Ag-0.7Cu SAC107 SAC305 Impact of [Cu]

16 TBA SACi SAC305

Doped

commercial

alloy

ATC test vehicle

13

192 CABGA84 CTBGA

• 0.8mm pitch 192 CABGA

– Large die 475x475 mils

– Ball size: 0.46mm

• 0.5mm pitch 84 CTBGA

– Large die 200x200 mils

– Ball size: 0.3mm

• Balling performed by

Premier Semiconductor

• 6-layer 0.093” board

• 16 parts of each type per bd.

• 16 parts per test “cell”

• One daisy-chain per part

• In-situ monitoring

• Over 3000 parts under test

ATC thermal profile definition for consistency

N

Nominal ThiActual Thi

Nominal Tlow Actual Tlow

Tem

per

atu

re

Time

Ramp Rate

Temperatures measured on parts!

(NOT air temperature)

Consistency is the critical issue

ATC thermal profile –

use of IPC-9701 standard

N

Nominal Thi

Actual Thi

max +5C

Dwell start

Dwell end

Tem

per

atu

re

Dwell time

Dwell

ends

here

Dwell starts here

IPC-9701A Table 4.1: = +5/-0 for peaks.

Time

Standardized solder joint failure definition

• First “event”: 1st occurrence of a resistance measurement 1000 ohms

• 9 or more additional “events” within 10% of the number of cycles for the

first event

• Follows IPC-9701 for event detectors; also use for data loggers

– 1st event at 1000

cycles

– 9 more events

within 100 cycles

of the 1st event

– Failure defined to

be at 1000 cycles

Example 9 events

Failure

1st event

Example

Thermal cycle test overview and status

17

Test Profiles and

Status as of 21 Sept ‘11

Began cycling: March 2011

Est. completion: Dec. 2012

• Full factorial structure for

determination of acceleration

factors

• Impact of Tmin, Tmax, T,

and dwell time

• Interactions among the

three main variables

(Tmax, T, dwell time )

• Two additional profiles

• Long dwell

• Test alloys for harsh

environment applications

– Auto, aerospace, military

Profile

No. Company

Cycle

(Min/Max/Dwell)

Date Started

Cycling

Current

Cycle #

1 ALU 0/100/10 3/21/2011 3633

2 IST 25/125/10 7/22/2011 520

3 Henkel -40/100/10 7/27/2011 865

4 Nihon -15/125/10 8/3/2011 300

5 ALU 0/100/60 2/10/1960 1769

6 HP 25/125/60 5/12/2011 855

7 HP -40/100/60 5/31/2011 624

8 CALCE -15/125/60 5/2/2011 606

9 CALCE -40/100/120 6/15/2011 246

10 Delphi -40/125/10 8/24/2011 850

Outline




Standards


Lack of test standards creates risk and slows

adoption of new alloys

• Risks of not having standard test data

– High melting point alloys will shrink an already small

process window; need data to establish practical process

limits

– Alloys formulated to meet specific goals not consistently

tested to determine general suitability

• Example: low-Ag alloys tested for improved

mechanical shock performance but thermal fatigue

reliability not evaluated

• Risks of not having standard test methods

– Data from one valid experiment may not be comparable

to another (data not “portable”)

– Test results may not directly correlate with OEM

concerns

• Data must enable alloy acceptability decisions

– Example: Bulk properties not sufficient to predict solder

joint thermal fatigue life

Incomplete solder joint

formation for a 1% Ag ball

alloy assembled at the low

end of typical Pb-free reflow

process window.

CSP Package

CSP Package

PCB

PCB

Efforts underway to develop solder alloy

test standards

• Key assumption: alloy acceptability may vary by industry sector,

product type, and company BUT testing methodology and data

requirements are largely the same

IS

Standardized

tests and reporting

IS NOT

Standardized

P/F criteria

Underlying data needed to evaluate new alloys are

similar even if acceptance criteria vary by industry, by

company, by product

21

Approach to developing alloy test standards

• Test methods divided into three

areas:

– Basic material properties

– Impact to PCA reliability

– Impact to PCA manufacturing

• Tests must focus on alloy

performance and results must not

be overwhelmed by other parts of

the assembly (laminate properties,

board design, etc.).

• Reliability tests should include at

least:

– Accelerated thermal cycling

– Mechanical shock (drop)

– Other tests still being discussed

Multi-step process for developing industry

standard alloy tests

HP Specifications

iNEMI Recommendations

Align with SPVC

Develop IPC standards

SPVC = Solder Products Value Council (solder suppliers)

Complete Some SPVC Members Critical

Stakeholders

Relevant

Standards

Body

Status of industry standards development for

testing of new alloys

* HP has specifications that include all three topic areas. One each for:

• Wave solder and mini-pot rework

• Surface mount reflow (paste)

• BGA spheres

Basic Material Properties

Board-LevelReliability

Impact on Mfg. Process

HP Acceptance Specifications*

Complete Complete Complete

iNEMI Recommendations

Complete Complete Started

Alignment of iNEMI and SPVC/IPC Recommendations

Nearly Complete Started Not Started

IPC Standards Development

Pending Early Draft Not Started

Outline




Standards


Summary and conclusions

25

• Pros and cons of second generation alloys

− Second generation Pb-free alloys provide an opportunity to address

issues with near-eutectic SAC

− Concerns about thermal fatigue performance and management of alloy

change identified as top priorities to address

• iNEMI investigating thermal fatigue performance

− Generating substantial data on new alloys

− Data will enable development of quantitative life prediction models

• Alloy test standards

− iNEMI is leading industry efforts to drive standardization of alloy testing

− Goal is to enable use of new alloys with minimal reliability risks

− Progress has been made in the development of standard testing methods,

but work remains before IPC standards are available

www.inemi.orgEmail contacts:

Bill Bader [email protected]

Bob [email protected]

inemi lead-free alloy characterization program update...

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