1. Electro-Chemical Migration Definition Stage Project
Wallace Ables - Dell
HDP User Group Member Meeting
Host: Ericsson
Stockholm Sweden
May 28, 2013
Presented by: Bob Smith
© HDP User Group International, Inc.

2. © HDP User Group International, Inc.
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.
© HDP User Group International, Inc.

3. Background
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.
The failure mechanisms occur on products assembled for all segments of the electronics industry.
The current industry standard testing does not take into consideration various acceleration factors associated with no clean flux and product design features.
© HDP User Group International, Inc

4. © HDP User Group International, Inc.
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
© HDP User Group International, Inc.

5. Not in immediate scope
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:
Conformal coating over no-clean fluxes. This may allow ECM under the conformal coating.
Solder mask test standards for ECM controls.
ImAg creep corrosion (covered by multiple current projects)
© HDP User Group International, Inc

6. © HDP User Group International, Inc.
Project Objectives
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:
Characterize failures escaping current test methods
Test flux residue levels: SMT, Wave Solder, Rework
Test flux application methods: controls, acceptable application levels, measurement methods and test methods
Enhance test board and test coupon designs
Identify acceptable flux residue levels by product class
© HDP User Group International, Inc.

7. © HDP User Group International, Inc.
Project Objectives
Identify the influence of PCB manufacturing defects and design properties on the development of ECM and corrosion failures.
Primary areas of investigation:
Exposed Cu from solder mask openings (pin holes, undercut, damage, etc.)
Moisture and chemical absorption properties
Minimum cure level
Voltage bias on a trace
Minimum spacing between positive and negative features to prevent ECM
© HDP User Group International, Inc.

8. 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

9. Current Project Activities
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.
Started a study of how to recreate the failure mechanism on the Test Vehicle.

10. Test Plan / DOE
First step is to reproduce the failure modes on test coupons.
Develop a Screening DOE / test plan to reproduce failure modes on test coupons
Select or design test coupons
Determine features that must be added to test coupons to reproduce failure modes
Select Flux materials
Flux application methods to use
Mixing of fluxes
Applied flux and flux residue characterization procedure
Test procedures to use
Build / testing
Inspection
Entrapment of fluxes under components (QFN’s, chip capacitors, etc) High voltage is worse for high resistance shorts.
Develop DOE matrix for full selection of fluxes

11. First Phase initial build on real product samples
DOE #1 Plan – Reproduce the open trace failure mode in a test environment
First Phase initial build on real product samples
OSP finish
10 pieces with solder mask openings created prior to assembly. Multiple locations, multiple sizes. (Done)
10 pieces with solder mask openings created after wave solder. Multiple locations, multiple sizes. (Done)
Characterize flux amount applied, and flux residue remaining on the boards (in process)
weigh coupons
C3 / IC analysis of residue
T&H chamber test: (Not started)
40 C
90% RH
Boards powered during test
Test to failure

12. DOE #1 Test board prep
Solder mask openings were created on test samples before the SMT process, and after the wave solder process
Loc 1 Before SMT
Loc 1 After Wave
Loc 2 Before SMT
Loc 2 After Wave
Sample 1
Sample 2
Sample 3

13. DOE #1 Plan Second Phase:
Reproduce first phase parameters on a trace test coupon boards.
Develop a repeatable method to reproduce the failure mode on a small, inexpensive test coupon board
Multiple trace widths and spacing
Multiple solder mask openings
Pads and vias
Multiple voltages
Acceleration test parameters (Temp, Humidity, time, etc)

14. DOE #1 Plan
Third Phase:
Evaluate different process settings to identify threshold for failures:
Flux amount applied
Flux type used
Flux residue
Amount of residue after wave solder
Activity level of residue
Presence of solder mask opening prior to or after wave solder
Impact of voltage level
Impact of moisture level
Process parameters
Impact of preheat and wave contact time on residue levels

15. DOE #2 Plan
Determine how to apply the information learned in DOE #1 to identify weakness or changes to the current industry standard test protocols and coupon designs

16. Industry Standard Test Methods to consider

17. No clean flux failure modes
Open Trace Corrosion Failure
Corrosion Mechanism:
A form of crevice or pitting corrosion at the small solder mask opening and the trace.
Failure mode dependencies:
Openings or defects in solder mask
Voltage bias
Activity level, type, and quantity of flux residue
Humidity levels
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
© HDP User Group International, Inc.

18. No clean flux failure modes
+ 3V
GND
+ 3V
Non soldered OSP
Corrosion Mechanism:
Surface corrosion
Surface Corrosion Failure
Failure mode dependencies:
Voltage bias
Activity level, type, and quantity of flux residue
Humidity levels
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
© HDP User Group International, Inc.

19. No clean flux failure modes
+ 3V
anode
GND
Corrosion Mechanism:
Electrochemical Migration – metal dendrite growth
ECM
Corrosion Failure
Failure mode dependencies:
Openings or defects in solder mask (exposed anode / + voltage)
Voltage bias
Activity level and quantity of flux residue
Humidity levels
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)
© HDP User Group International, Inc.

20. Proposed Execution Plan
Definition Stage
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
Implementation Stage
Complete
In-Process
Not Started

21. © HDP User Group International, Inc.
Team Members –To Date
Agilent
Fujitsu
Plexus
Alcatel-Lucent
H3C
Rockwell
Arlon
Huawei
Suntak
ASE
IBM
Shengyi
Celestica
Isola
TTM Tech
Ciena
IST Group
Ventec
Cisco
Kyzen
Zestron
Cobar
Medtronic
ZTE
Dell
Nihon-Superior
Emerson
Oracle
Ericsson
Panasonic
Flextronics
Phillips
© HDP User Group International, Inc.