Electro-Chemical Migration

Definition Stage Project Wallace Ables - Dell

HDP User Group Member MeetingHost: Oracle

Santa Clara, CA.

Feb. 26. 2013Presented by: Keith Howell

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Problem Statement

• The current industry standard test protocols were originally developed to identify highly ionic contaminant levels (halides) after a cleaning process.

• These test protocols are not completely effective at identifying ECM and corrosion exposures from no-clean flux residues.

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Background

1. Products assembled with no clean flux systems are experiencing various forms of corrosion and Electro Chemical Migration failures. These products and flux systems have passed the current industry standard cleanliness and corrosion resistance testing, demonstrating that these test procedures are not completely effective.

2. The failure mechanisms occur on products assembled for all segments of the electronics industry.

3. The current industry standard testing does not take into consideration various acceleration factors associated with no clean flux and product design features.

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Project Goal

Identify the required enhancements to current industry specifications, test methods, test boards and coupon design to increase detection of ECM and corrosion induced failures when no clean flux systems are used.

Areas to investigate: Cleanliness testing Corrosion resistance testing ECM testing Maximum acceptable residue levels Influence of PCB manufacturing defects Influence of PCBA design features

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Not in immediate scope

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Some closely aligned aspects of this project will be deferred to a follow-on project, or are already being investigated by other project teams. Therefore the following factors will not be in the scope of this project:

1. Conformal coating over no-clean fluxes. This may allow ECM under the conformal coating.

2. Solder mask test standards for ECM controls.

3. ImAg creep corrosion (covered by multiple current projects)

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Project Objectives

1. Identify modification to current industry standard specifications and test methods for cleanliness testing, corrosion resistance testing, and ECM testing to increase detection of failures when no clean flux systems are used.

Primary areas of investigation:a. Characterize failures escaping current test methodsb. Test flux residue levels: SMT, Wave Solder, Reworkc. Test flux application methods: controls, acceptable

application levels, measurement methods and test methods

d. Enhance test board and test coupon designse. Identify acceptable flux residue levels by product

class

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Project Objectives

2. Identify the influence of PCB manufacturing defects and design properties on the development of ECM and corrosion failures.

Primary areas of investigation:a. Exposed Cu from solder mask openings (pin holes,

undercut, damage, etc.)b. Moisture and chemical absorption propertiesc. Minimum cure leveld. Voltage bias on a tracee. Minimum spacing between positive and negative

features to prevent ECM

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Proposed Execution Plan

How the project will answer the Goal and Objectives

Compile list of current test methods /

standards / test vehicles

Compile list of failure modes from

team members

Correlate corrosion failures to gaps in current

test methods

Identify modifications

required to current test methods

Develop DOE’s to validate proposed

changes

Perform DOE’s. Collect and

evaluate test data

Draft proposed changes to test

methods / standards / test

vehicles

Provided proposed changes

and supporting data to test

standard owners.

Write final report

• Completed list of current test methods

• Completed identification of failure modes observed with no clean residues

• Started gathering existing possible Test Vehicles.

• Have met with IPC sub-committees on Coatings, Cleaning and Testing to discuss our activity.

• Established the basic project plan.

• Started to Identify the flux variables to be used in DOE.

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Current Project Activities

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Test Method

#

Method Type

Method Focus

Spec. Owner

Spec NumberBare

Board Rev Date

Title of Spec

1 ECM Material IPC TM650, 2.6.14.1 Sep-00 Electrochemical Migration Resistance Test

2 SIR Material IPC TM650 , 2.6.3.3B Jun-04 Surface Insulation Resistance, Fluxes

3 SIR Material IPC TM650 , 2.6.3.7 Surface Insulation Resistance,

7 Other Material IPC TM650, 2.6.15C Corrosion, Flux

9 CLN PCA IPC TM650,2.3.25CDetection and Measurement of Ionizable Surface

Contaminants by Resistivity of Solvent Extract (ROSE)11 CLN PCA IPC TM650,2.3.38C Surface Organic Contaminant Detection Test

12 Other PCA IPC TM650,2.3.39CSurface Organic Contaminant Detection Test (Infrared

Analytical Method)15 ECM PCA Bono

16 ECM Material HP EL-EN861-00 Flux Electrochemical Migration Test Method

18 CLN PCA IPC TM650,2.6.38 Bulk IC19 CLN PCA Foresite C3 Localized area IC

20 SIR PCA Foresite C3 Localized area Y pattern

26 CLN Material GR-78-CORE Silver Chromate Paper IPC-TM 650 2.3.33

27 Other Material GR-78-CORECopper Mirror Tests (Modified IPC / Bellcore Method) IPC-

TM 650 2.3.3228 Other Material GR-78-CORE Copper Corrosion Test IPC-TM 650 2.6.1529 Other Material GR-78-CORE Copper Corrosion Test JIS Z3197-1999 Test Method 8.4.1

30 ECM Material GR-78-CORE 13.1.4 Bellcore Electromigration

31 CLN PCA IPC TM650 IPC ROSE Test 32 SIR Material IPC IPC -920233 SIR Material JIS Z319734 ECM Material JIS Z3197

Industry Standard Test Methods to consider

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No clean flux failure modes

Failure mode dependencies:• Openings or defects in solder mask• Voltage bias • Activity level, type, and quantity of flux residue• Humidity levels

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Potential areas to investigate with current test methods:• Modify test coupon to detect crevice or pitting corrosion failure modes?

• Solder mask openings on test coupon (pitting corrosion)• Flux trapped under low stand off connections (crevice corrosion)

• Measure flux residue levels (identify threshold of acceptable residual flux contaminants)

• Multiple voltages to traces or nets on the test coupon (identify voltage level sensitivity)

• Multiple humidity levels

Corrosion Mechanism:A form of crevice or pitting corrosion at the small solder mask opening and the trace.

Open Trace Corrosion Failure

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No clean flux failure modes

Failure mode dependencies:• Voltage bias • Activity level, type, and quantity of flux residue• Humidity levels

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Potential areas to investigate with current test methods:• Measure flux residue levels (identify threshold of acceptable residual flux

contaminants)• Multiple voltages to traces or nets on the test coupon (identify voltage level

sensitivity)• Multiple test pad and hole sizes• Multiple surface finishes• Multiple humidity levels

Corrosion Mechanism:Surface corrosion

+ 3V

GND

Non soldered OSP+ 3V

Surface Corrosion Failure

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No clean flux failure modes

Failure mode dependencies:• Openings or defects in solder mask (exposed anode / + voltage)• Voltage bias • Activity level and quantity of flux residue• Humidity levels

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Potential areas to investigate with current test methods:• Modify test coupon to provide exposed anode adjacent to ground features (already

exists?)• Measure flux residue levels (identify threshold of acceptable residual flux

contaminants)• Multiple voltages to traces or nets on the test coupon (identify voltage level

sensitivity)

Corrosion Mechanism:Electrochemical Migration – metal dendrite growth

+ 3Vanode

GND

ECMCorrosion Failure

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1. Complete list of current test methods/standards/test vehicle. Complete

2. Compile list of failure modes from team members.Complete

3. Correlate corrosion failures to gaps in current test methods.

4. Identify modifications required to current test methods.

5. Develop DOE’s to validate proposed changes.

6. Perform DOE’s, collect and evaluate data.

7. Draft proposed changes to test methods/standards/test vehicle.

8. Provide proposed changes and support data to test standards owner.

9. Write final report

Proposed Execution Plan

CompleteIn-ProcessNot started

Team Members –To Date

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• Agilent • Alcatel-Lucent • Arlon • ASE• Celestica• Ciena• Cisco• Cobar• Dell• Emerson• Ericsson• Flextronics

• Fujitsu• H3C• Huawei• IBM• Intel• Isola• IST Group• Kyzen• Medtronic• Nihon-Superior• Oracle• Panasonic

• Phillips• Plexus • Rockwell • Suntak• Shengyi• TTM Tech• Ventec• Zestron• ZTE