Defect Description

Bonding of the Pad/ Via interface is poor which can leads to crack initiation or delamination upon the exposure to environmental stresses.

Defect Formation Process(s)

Possible causes to this defect include:

i. Under-ablation

Resins are not sufficiently removed due to incorrect energy levels or poor trepanning techniques, creating a non-conductive barrier between the target pad and subsequent metallization [1]

ii. Contamination

Insufficient desmear causing the by-product form ablation process to trap
at the interface between pad/via plating boundaries, results in crack initiation at the interfaces [1-2]

iii. Insufficient surface preparation

The copper plating bath process involves various chemistries that prepare the surfaces for a strong chemical bond. For example, electroless copper on the target pad creates a strong bond to copper foil interface for a strong chemical bond, without such, foundation for the base of a microvia is not established [1].

List of Tests to Precipitate this Defect

Failure Acceleration

Likihood to Precipitate Defect (condition)

Failure Mechanism(s)

Thermal Shock

• Thermal shock accelerates separation of copper-hole wall interface due to Coefficient of Thermal Expansion(CTE) mismatch

Thermal Fatigue/

Thermal Mechanical Overstress

Random Vibration (RS/ED)

• Random vibration can deteriorate of adhesion strength of the poorly bonded interface due to overstress or fatigue

(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 separate poorly bonded interface due to mechanical overstress

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

Mechanical Overstress


[1] Ghaffarian R. “Reliability of PWB Microvias for High Density Package Assembly”, NASA Electronic Parts and Packaging Program (NEPP), 2006.

[2] L. Ji and Z. Yang, “Analysis of Cracking Blind Vias of PCB for Mobile Phones,” International Conference on Electronic Packaging Technology & High Density Packaging, Shanghai, China, 2008