How to remove the IC block from the PCB?

Integrated circuits (ICs) are complex microchips mounted on printed circuit boards (PCBs) that contain digital logic gates, analog circuits, microprocessors and other components.

Sometimes ICs need removal from the PCB for:

• Upgrades and replacements
• Fault diagnosis testing
• Salvaging working ICs from discarded boards

However, safely extracting these delicate components requires meticulous desoldering techniques. Missteps risk permanent IC, PCB or pad damage.

This guide covers professional desoldering methods, tools and precautions when removing multi-pin IC components from boards.

Reasons for Removing SMT ICs from Circuit Boards

Typical reasons for removing soldered surface mount technology (SMT) integrated circuit blocks include:

- Replace defective or obsolete ICs
- Upgrade functionality with new ICs  
- Diagnostic failure analysis testing
- Reuse working ICs from discarded boards
- Solder mask repair around pads 
- Board rework and modifications        

Ideally, de-soldering only occurs for prototype engineering changes. Production boards favor full replacement over field removal. But for QA testing, salvage and repair, ICs require safe extraction.

Challenges of Removing Soldered Integrated Circuits

High density chip-scale packages with small delicate pins pose desoldering difficulties:

IC Desoldering Challenges:

- Small 0.3mm pitch leads  
- High 600+ I/O pin counts
- Leadless and hidden BGA pads  
- Interior pins with limited access
- Thermal shock and ESD sensitivity
- Avoiding pad lift-off or barrel cracks        

Precision tools, temperature control and proper techniques prevent damage to ICs and boards when removing components.

Desoldering Methods for Surface-Mount ICs

SMT integrated circuits connect to PCBs through an array of precisely soldered contact pins and pads. Powerful heating is necessary to thoroughly melt this solder to detach components without damage.

Common desoldering methods include:

Hot Air Rework Station

Dedicated SMT removal tools direct temperature-regulated forced air to locally heat the IC area. The device heats the entire component and board lands to ~250°C to liquefy solder, allowing air suction of molten metal while gently lifting the chip.

Soldering Iron with Solder Wick

Solder wicks help draw molten solder away from each pin individually. But dual-wielded fine-tip irons better heat multiples pins simultaneously. This prevents shock cooling adjacent pins.

Vacuum Desoldering Irons

Specialized "solder sucking" irons rely on hollow heated tips with integrated vacuum pump hoses. These vacuum nozzles melt solder while sucking it in for highly controlled results.

Comparison of IC Desoldering Methods

 | Hot Air Station | Solder Wick | Vacuum Desolder 
---|-------------|--------|---------------
Control | Moderate | Low | High
Speed | Very Fast | Slow | Moderate
Lead Access | Excellent | Limited | Very Good  
Cost | High | Low | Moderate        

Step-By-Step Guide to Removing ICs with a Hot Air Rework Station

Hot air stations offer the best combination of control, efficiency and convenience when removing chips. Follow these steps when using automated rework tools:

1. Prepare and Disassemble

• Power off all electrical supplies to the board
• Remove conformal coatings around the IC if present
• Disassemble any covers or shields surrounding the component site

2. Clean and Inspect

• Clear any obstacles or debris around workspace
• Probe check for hidden vias or planes under the chip
• Carefully clean flux residue from the pads and leads

3. Setup and Position

• Mount board securely in anchored holder clamps
• Optically align hot air nozzle 5-10 mm over center of the IC
• Set the lowest airflow to gently start heating

4. Reflow Desoldering

• Gradually increase temperature up to ~250°C
• Slowly ramp airflow to evenly spread heat
• Keep heating until all solder liquefies freely across pads
• Avoid directing harsh blasts directly at the IC

5. Chip Extraction

• When all solder flows clear, use vacuum pickup tool aligned on top to lift chip
• Slowly slide IC laterally while maintaining even vacuum suction
• Do not pry or bend the IC but continue lifting vertically
• If resistance, reapply heat until component releases

6. Final Cleaning

• Inspect pads for excess solder and barrel cracks under microscope
• Clear any solder bridges between neighboring pads
• Carefully trim excess pin lengths if needed
• Flux residues may assist tinning pads and require removal after

Caution and patience during thermal transfer and mechanical lift-off prevents ripping pads off the board or IC damage.

Hot Air Desoldering Specifications

- Rework Nozzle Size: 1-2 mm 
- Temperature: 380±10°C
- Ramp Rate: < 3°C / sec
- Airflow: 1-5 L/min        

Preventing Board and Component Damage

Mishandling during hot desoldering risks permanent PCB damage:

Potential Desoldering Hazards:

- Excessive heat warp boards or delaminate plating   
- Rapid changes cause thermal shock cracks
- ESD pulses through fast temperature spikes
- Side shear can rip copper pads off board  
- Pads lift during uneven mechanical stress 
- Leads tear or detach from IC if bent or twisted        

Careful heat ramping, ample flux usage and slow stead lift-off helps mitigate risks when removing ICs.

Rework After Integrated Circuit Removal

Once de-soldered, various steps complete the IC removal process:

Post Desoldering To-Dos:  

- Thoroughly clean board and reflow any leftover solder
- Inspect and repair pad lifting or thermal damage  
- Test continuity between emptied pads 
- Remove corrosion or tarnish from pad barrels
- Apply liquid flux preparatory to soldering new IC        

The open solder pads should re-tin easily during rework to install the replacement component.

For prototype engineering changes, the updated programmable IC gets soldered using techniques identical to the initial board assembly.

Production run repairs may utilize specialized conductive epoxy glues to attach replacement chips. Epoxy methods help prevent high thermal stress from repeated solder melting.

Key Takeaways on IC Removal from PCBs

• Modern surface mount ICs allow complex electronics but challenge removal and rework
• Thermal hot air stations reflow solder for clean desoldering from delicate boards
• Precautions against ESD damage and pad lifting are critical
• Careful mechanical lift technique preserves both chip and substrate lands
• Post-processing ensures good contacts for the replacement component

With responsible handling, even high density thinned ICs safely detach for necessary diagnostics, upgrades or reconfigurations.

Frequently Asked Questions about Removing ICs from Circuit Boards

Q: Can I use a heat gun instead of a specialized rework station?

No. Hardware store heat guns lack the precision airflow, temperature regulation and measured ramping vital not to damage boards, pads or ICs.

Q: Is leaded solder or lead-free solder easier to desolder from chips?

Leaded solder requires slightly lower temperatures which makes it somewhat more rework friendly. But proper desoldering technique works for both alloy types.

Q: Should I remove conformal coating before attempting IC removal?

Yes, any acrylic, silicone or other protective layers coating the PCB should get removed around the component to allow full heat transfer.

Q: Can I reuse an IC after removing it from a used PCB?

Sometimes, if the chip avoids damage during extraction. But performance testing before reuse is vital, since longevity is reduced through stressed removal and aging.

Q: Is a microscope required for inspecting pads post desoldering?

Strongly recommended. Subtle pad lifting not clearly visible necessitates magnification to catch. An X-ray scanner also further confirms all is sound.