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.

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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).

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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.

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