2. DFMEA, Thermal Derating CAF, VIA Fatigue
Dr. Nathan Blattau

3. DFMEA – Design Failure Mode Effects Analysis
Potential failure modes of the components
The effect that a failure of the component will have on the circuit
Thermal Derating
Component temperature ratings for storage and operation
Comparison of those ratings to the applied thermal environments
CAF – Conductive Anodic Filament Formation
The potential for conductive filaments forming internal to the circuit board
Typically due to drill damage and hole spacing
VIA Fatigue
Thermal cycling fatigue of the plated through holes of the PCB
IMEC and IPC-TR-579 models

4. DFMEA
Analyzes potential reliability problems early in the development cycle of a product, when it is easier to fix problems and therefore enhance overall reliability. 
FMEA is used to
Identify potential failure modes
Determine their effect on the operation of the product
Identify actions to mitigate the failures 
Design Failure Modes and Effects Analysis (DFMEA) focuses on components and subsystems

5. What DFMEA is…. A systematic group of activities designed to:
Recognize and evaluate potential failures of systems, products, or processes
Identify the effects and outcomes of the failures
Identify actions that could eliminate or mitigate the failures
Provide a historical written record of the work performed

6. Why perform a DFMEA? Purpose of an DFMEA Study is to analyze:
What might go wrong?
How bad might the effect be?
How might it be prevented, mitigated or detected at the earliest possible moment?
With lowest cost, impact, safety risk….
Develop a DFMEA process for use in future designs

7. DFMEA Basics - Failure Mode And Effect Analysis
DFMEA is a widely used and powerful analysis & design review technique.
Extremely comprehensive element by element review of:
What can go wrong
What will happen
How the situation can be improved
For improving a design
For each design component or element:
List how failures can occur (Failure Mode, what can go wrong, how the failure manifests itself)
List what could happen (Failure Effect, consequences of the mode).
List how processes or the system itself can detect & prevent the problem
Generate Recommendations for Improvements.

8. Some Key DFMEA Terms
Failure: The loss of expected or intended function under stated conditions
Failure mode: The way in which a failure is observed; generally describes the way the failure occurs.
Failure effect: The immediate consequences of a failure on operation, function or functionality
Failure cause: Defects in design, system, process, quality, or part application, the underlying cause of the failure or things which initiate a process which leads to failure.
Severity: The consequences of a failure mode. Severity considers the worst case outcome of a failure as determined by the degree of injury, property damage, or harm that could ultimately occur.

9. DFMEA Basics - Failure Mode And Effect Analysis
Calculate a Risk Priority Number (RPN) for Each Line Item using 3 Criteria,
Severity of the Failure Effect “S” (Scale of 1 (Low) - 10 (High)).
Frequency of Failure Occurrence “O” (Scale of 1(Infrequent) -10 (Frequent)).
Detectability/Preventability/Warning “D” (Scale or 1(Very Detectable) - 10 (Not Detectable)).
RPN = S x O x D, range (1 (good) to 1000 High Risk).
An unacceptable range is defined.
Example: RPN’s > 150 are unacceptable and require a corrective action redesign.
Often a Pareto Ranking of the RPN is performed and used to prioritize corrective action efforts.

10. DFMEA – The Old Way

11. DFMEA - Sherlock
Ties the Netlist and the Sherlock Parts list automatically
Generates template based worksheets that can be imported and exported into Excel using a custom markup language
User configurable parameters to control failure modes, causes, effects
Can group components into subcircuits

12. The Netlist, Subcircuits
Sherlock will automatically extract it from the ODB++
For Gerbers a IPC netlist will need to be uploaded
Subcircuit information
PRP fields in the ODB++, need to specify this from your designers
Manual entry

13. DFMEA Sherlock Input Configuration

14. DFMEA Sherlock Default Failure Modes

15. Populate the DFMEA Using the Partlist
Multiple levels
Safety critical applications
Component and I/O level analysis
Specify how far away to check for adjacent pins
Ignore pins without connections, or adjacent pins on the same net
Component failure only

16. DFMEA Inputs Input subcircuit details
User should enter function and update the default information
0.5 mm pin to pin short distance

17. Formatting DFMEA Outputs

18. Generate DFMEA Output

19. Edit the Template

20. Output with New Template

21. Plated Through Hole Fatigue
IPC-TR-579
Standard model
IMEC PTH model – license enabled

22. IPC-TR-579 [Engelmaier Model for PTH fatigue]
Beam model formulation, main concern is the effective area assumption of the PCB

23. IMEC [Model for PTH fatigue]
Axisymmetric model formulation, better accounts for the area effect of the PCB around the PTH
The effective PCB area Equation

24. IMEC Model
Better captures the drop in strain as the hole size increases

25. PTH Fatigue Parameters
Drill size, extracted from the drill file
Z axis coefficient of thermal expansion (CTE) of the PCB computed in the stackup
Temperature ranges from the Life Cycle
Analysis Parameters
PTH Quality
Copper properties
Hole size filter
PTH wall thickness

26. Parameters There are two qualitative factors IST/HAT Qualification
This doesn’t change the probability of failure prediction
Limits the maximum score one can achieve based on qualification testing conducted
PTH Quality Factor
For the IMEC model this only changes the Weibull slope used to generate the prediction curve
For the IPC model it changes the stress concentration factor and the Weibull slope parameter

27. Conductive Anodic Filament Formation (CAF)
Conductive anodic filament formation (CAF), is a failure observed within the glass-reinforced epoxy printed wiring board (PWB) laminates
It is an electrochemical process involving the ionic transport of metal under the influence of an electric field

28. CAF Failures
Failures are typically the result of damage during drilling of the printed circuit board
Drilling causes fracture of the laminate in which plating chemicals get entrapped
Failures can occur very rapidly in the presence of humidity and electric bias
Sherlock does a spacing analysis coupled with fiber direction to generate a score based on distance and overlap
Qualitative analysis

29. Sherlock CAF Analysis
Sherlock uses the drill file for hole locations and sizes
Analysis user inputs
Holes size filter, removes holes from the analysis
Damage zone tells Sherlock how far out to look for intersections
Qualification changes the score based on the qualification tests done

30. Sherlock CAF Results Scoring is based on a 15 mil wall to wall spacing
Maximum score limited by qualification testing conducted (or not)

31. Thermal Derating
Data check to compare the part temperature ratings to the thermal cycles defined in the life cycle
Need to verify that parts have operating and storage parameters in the parts list

32. Thermal Parameters
Set the Life Cycle State in the Thermal Event Editor
Storage is assumed to be non-operating conditions
Therm tab in the Part Properties

33. Temperatures
Sherlock will look at temperature inputs from the Life Cycle or thermal inputs (images, csv files assigned to a temperature cycle) to compare against
Margin above the minimum operating/storage temperature and margin below the maximum operating/storage temperature used for scoring
Margin on the cold side is not as critical as the hot side