By [Your Name], August 11, 2023

Reverse engineering of printed circuit boards (PCBs) is the process of understanding the design, components, and functionality of a PCB without access to the original design files or documentation. It is commonly done by hobbyists and engineers to repair, modify, or duplicate legacy electronics. This article provides an overview of PCB reverse engineering techniques, tools, and best practices.

Why Reverse Engineer a PCB?

There are several reasons why someone may want to reverse engineer a PCB:

• Repair – When the original designer is no longer around or unable to provide support, reverse engineering allows determining the root cause of failures and fixing problems.
• Improvements – Adding new features, upgrading components, or redesigning the board for manufacturability or reduced cost.
• Compatibility – Interfacing new electronics with legacy systems by understanding how they work.
• Education – Learning PCB and circuit design techniques used in existing boards.
• IP Theft – Extracting proprietary designs illegally (not recommended).

Steps for Reversing a PCB

Reverse engineering a PCB is essentially working backwards through the design process:

Visual Inspection

• Examine the board front and back under magnification
• Look for part numbers, board house markings, revision numbers
• Note number of layers and stackup (if multilayer)
• Scan both sides for high-resolution documentation

Schematic Capture

• Trace all copper connections, noting components in each net
• Draw a schematic showing all tracelines, vias, pads, and parts
• Identify components by package type and markings
• Consult datasheets to determine component pinouts

Netlist Extraction

• Enter schematic into PCB CAD software
• Run electrical rules check (ERC) to highlight errors
• Annotate components with part numbers
• Save netlist file defining connectivity

PCB Analysis

• Import netlist into PCB layout tool
• Compare to scanned PCB images
• Check for inconsistencies indicating errors
• Examine board for functional blocks and hierarchies

Validation

• Review schematic and PCB for errors
• Test with voltage probes, logic analyzer, etc.
• Compare observed operation with expected functions
• Iterate on schematic and netlist as needed

Helpful Tools and Techniques

Several tools and techniques can aid the PCB reverse engineering process:

• Multimeter – Measuring continuity helps tracing copper and determining net connectivity.
• Microscope – A stereo microscope or inspection camera allows clearly viewing fine traces and component markings.
• X-Ray Imaging – X-ray systems can reveal hidden components, internal layers, and blind/buried vias in multilayer boards.
• Acid Etching – Controlled etching with acid can remove solder mask to expose all copper features and traces.
• Scraping – Gentle abrasion using fiberglass brush or scalpel removes conformal coating to inspect traces and joints.
• Schematic Capture Software – EDAs like Eagle, KiCad, Pulsonix, etc. help recreating schematics from scratch.
• Gerber Viewers – Applications like Gerbv, ViewMate, GC-Prevue visualize bare board layouts from extracted Gerber files.

Challenges and Limitations

PCB reverse engineering has some challenges and limitations to be aware of:

• Recreating complex multilayer boards with blind/buried vias is very difficult and labor intensive. X-ray imaging helps.
• Determining functionality of custom ICs and BGA packages without detailed datasheets is often impossible.
• Errors can be introduced reconstructing schematics, especially for dense or illogical board layouts.
• Certain fabrication techniques like controlled-depth drilling and impedance matching are hard to back-engineer.
• Legal or ethical issues may exist around IP theft and copying of proprietary designs.

Best Practices

Follow these best practices when reverse engineering PCBs:

• Work methodically from simplest to most complex sections.
• Photograph and label key areas before using any destructive techniques.
• Triple check schematics, netlists, and layouts to avoid introducing errors.
• Seek help identifying unknown components and technologies.
• Use revision control and maintain thorough documentation of findings.
• Be mindful of IP rights and legal issues.

Case Study: Reverse Engineering an 80s Era Power Supply

To illustrate the PCB reverse process, let’s walk through an example of analyzing a vintage 1980s switching power supply:

Gather Information

• Externally labeled as Astec AA9212 ATX power supply
• Appears to be PC AT form factor
• Multilayer PCB in 4-layer stackup

Clean and Photograph

• Disassembled unit and cleaned boards
• Took high res photos of top and bottom
• Scanned boards on flatbed scanner

Trace Circuitry

• Visually traced all power train components and windings
• Identified likely switching and control ICs
• Mapped attrs to corresponding pins on schematic

Identify Components

• Located part