HDI Microvia Cracking | Failure Analysis Steps

As a leading PCB manufacturer serving global customers since 2008, KnownPCB would like to share real-world insight: a classic HDI failure analysis, it is a logical method with clear steps for checking the root cause of HDI microvia cracking:

Where is the break in PCB?
What does the crack look like?
Find the PCB quality killer.

One of the most prevalent failure case in PCB failure analysis(FA): Microvia Cracking Post-Reflow

Post-reflow functional failures in a batch of HDI boards were traced to electrical opens in the HDI BGA area via flying probe inspection.

Analysis steps:

X-RAY inspection: A potential cracking in stacked via area
Cross-section analysis: confirmed the micro-cracks within the base plating layer
EDS Test: Chloride Concentration in the affected area was out of specification

Root Cause:

Inadequate post-plating rinsing led to the chemical attack and pitting on the copper layer
The copper was too brittle to handle the heat, causing it to crack during reflow.
Non-compliant with RoHS due to chlorinated solvent usage.

Solutions & Improvements for the PCB processing and quality control:

•Process Optimization: Added ultrasonic DI water rinse stages for a deeper cleaning.

•Upgrade Plating: Used pulse plating for tougher, more flexible copper.

•Stricter Compliance: Enforced a strict ban on all chlorinated substances at the source.

•Data-Driven QC: Introduced MSA to ensure consistent cleaning results. Outcome: No failures recorded after 1,000 thermal shock cycles (-55°C/+125°C).

Understanding the PCB manufacturing process is more than just building a functional board. It empowers you to design within fabrication limits during early design, sidestep risks during component selection, and lock in the optimal process window before mass production.