Irregular Plating (Plating Folds/ Nodules)

Defect Description

Irregular plating results in folds/nodules that increases local stress concentrations and crack initiation upon the exposure to environmental stresses such as temperature cycling and vibration

Defect Formation Process(s)

Rough drilling can be a result of poor laminate material, worn drill bits, or an out-of-control drilling process

Improper hole preparation can occur due to excessive removal of epoxy resin caused by an incomplete cure of the resin system or due to a preparation process, like desmear or etchback, that is not optimized [1].

List of Tests to Precipitate this Defect

Failure Acceleration

Likelihood to Precipitate this Defect (condition)

Failure Mechanism(s)

Thermal Shock

• Cyclic thermal mechanical stress accelerates crack initiation or crack growth at the folds/ nodules where local stress concentration is high

• Thermal mechanical stress causes fracture of the copper plating at the folds/nodules where local stress concentration is high

Thermal Fatigue

Thermal Mechanical Overstress

Random Vibration (RS/ED)

• Random Vibration accelerates crack initiation or crack growth at the folds/ nodules where local stress concentration is high

• Vibration causes fracture of the copper plating at the folds/nodules where local stress concentration is high

✔/✇
(Defect orientation is sensitive to the vibration axes)

Mechanical Fatigue

Mechanical Overstress

Combined Environment

• Combination of Thermal Shock and Random Vibration

Combination of Thermal Shock and Random Vibration

Bend Test

• Bending can cause fracture of the copper plating at the folds/ nodules where local stress concentration is high

(Defect at a location with significant strain due to bending)

Mechanical Overstress


[3]

References

[1] Tulkoff C., Hillman C., “Reliable plated through via design and fabrication.” DFR Solutions

[2] Tukloff C., Caswell G., Hillman C., “ Best Practices for Improving the PCB Supply Chain: Performing the Process Audit”, DFR Solutions

Permission for pictures

[3] Tukloff C., Caswell G., Hillman C., “ Best Practices for Improving the PCB Supply Chain: Performing the Process Audit”, DFR Solutions


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