Chip Decapsulation Process in IC Packaging: Chemical and Mechanical Methods for QFN Packages

Chip Decapsulation Process in IC Packaging

Chip Decapsulation: A Key Step in IC Failure Analysis and Reverse Engineering

Chip decapsulation is a critical step in integrated circuit (IC) failure analysis (FA) and reverse engineering. Its purpose is to completely remove the encapsulating epoxy resin plastic (or other packaging materials) without damaging the internal chip structure, thereby exposing the die, bond wires, and pads for further inspection, electrical testing, or probing.

Based on packaging materials and decapsulation principles, the process is generally divided into two major categories:

  1. Mechanical Decapsulation – Suitable for ceramic and metal packages.
  2. Chemical Decapsulation – Applicable to most plastic encapsulations (epoxy resin), and the most widely used method.

This article focuses on chemical decapsulation, the most common technique.

1. Core Principle of Chemical Decapsulation

The key principle is to use strong acids such as Fuming Nitric Acid (HNO₃) or Fuming Sulfuric Acid (H₂SO₄), combined with heating or controlled reactions, to selectively dissolve plastic encapsulants without corroding the internal silicon die, metal wires, or pads.

2. Preparation Phase

Safety First:

  • Perform all operations inside a fume hood.
  • Operators must wear PPE: acid-resistant mask, gloves, apron, and protective goggles.
  • Emergency equipment (eye wash station, shower, neutralizing agents) must be available nearby.

Sample Information Confirmation:

  • Confirm chip model and package type (e.g., QFP, BGA, SOP, DIP, QFN packages).
  • Use X-ray imaging to evaluate die position, bond wire layout, or internal cavities to determine the optimal decapsulation site.

Sample Pretreatment:

  • Remove pins or solder balls (e.g., for BGA packages).
  • Clean surface using IPA to remove contaminants.
  • Fixation: Secure the chip in a ceramic or Teflon jig, ensuring only the top surface is exposed while protecting the sides and bottom from acid attack.

3. Chemical Decapsulation Execution

Method A: Acid Dropping (Most Common)

  • Equipment: Decapsulation machine (with heating stage, acid pump, exhaust system, and microscope).
  • Reagents: Fuming nitric acid (most common) or fuming sulfuric acid (for special resistant epoxy types).

Steps:

  1. Positioning: Place the sample on the heated stage, align the acid needle over the target area under a microscope.
  2. Heating: Typically set to 60–80°C to accelerate reactions.
  3. Acid Dropping: Acid is dripped slowly; bubbles form as resin dissolves, creating a pit. Stop once bond wires or die surface are visible.
  4. Monitoring: Carefully observe progress under microscope to avoid over-etching.
  5. Termination: Rinse immediately with deionized (DI) water, then ultrasonically clean in alcohol/acetone to neutralize and remove acid residues.

Method B: Jet Etching (High Precision)

  • Uses fine acid jet stream for localized, high-speed etching.
  • Better suited for small, high-density packages (e.g., UCSP, WLCSP, advanced QFN packages).

4. Post-processing and Inspection

  • Cleaning & Drying: After ultrasonic cleaning, dry the sample with N₂ gas to prevent water stains.
  • Microscopic Inspection: Use optical or SEM to check bond wire integrity, die surface condition, pad corrosion, and contamination.
  • Documentation: Capture high-resolution images to record findings for further FA or reverse engineering analysis.

5. Critical Notes

  • Endpoint Detection: Over-etching will damage bond wires or aluminum layers, leading to analysis failure.
  • Acid Selection: For chips with silicone gel protection, sulfuric acid is used first to remove gel, followed by nitric acid for epoxy.
  • Environment Control: Must operate inside a fume hood; manage acid vapors properly.
  • Waste Disposal: Acid waste must be collected and processed as hazardous chemical waste, not disposed into sewage.

6. Mechanical Decapsulation (Alternative for Ceramic/Metal Packages)

  • Use diamond saw or milling to cut grooves.
  • Carefully pry open the lid with a blade or wedge.

7. Conclusion

Chip decapsulation is a precise process integrating chemistry, mechanics, and microscopy. The workflow can be summarized as:

Safety preparation → Sample fixation → Heating & acid application → Real-time monitoring → Reaction termination & cleaning → Final inspection.

Successful decapsulation is the foundation for subsequent failure analysis, reverse engineering, and IC reliability assessment, including for modern QFN packages.

Disclaimer: All content is for reference only. Please use professional judgment before application.

Similar Posts