When companies are faced with the challenge of manufacturing an undocumented and partially obsolete printed circuit board assembly (PCBA) with only the PCBA as the starting point, the reverse engineering process can be a useful tool for reconstructing the design and production documentation, thus enabling its manufacturability using available and technically compatible components. There are many challenges for the manufacturer in the reverse engineering process, but following some standard process guidelines will increase the probability of manufacturing success and can indefinitely prolong the useful life of an aging PCBA.

Careful planning at the outset is critical to ensure that the necessary equipment, tools, software, expertise, and of course, the PCBAs are readily available. Having several boards on hand provides some flexibility and expediency to the process by allowing some parallel processing of the non-destructive re-engineering steps.

The first step should be the documentation of the components on the board. Access to the various electronic component vendors’ databases (current and previously published catalogues, specifications, cross references, etc.) is a good resource for component types and replacement component part numbers. This identification of components will lead to the development of the bill of materials (BOM) for the PCBA, an important documentation step in reconstructing the production materials needed. Coincident with the BOM development, color digital images of the PCBA should be taken. Detailed images are invaluable in the later reconstruction steps of the board layout.

Various methods and tools can be used to regenerate the electrical design of the circuit assembly. An in-circuit tester can be used to generate point to point connections, which include generating a net list, and determine some or all of the values for the components on the board. A system such as ScanCad can be used to regenerate the Gerber files for each layer of the board. X-ray imaging can also help clarify point to point connections. These tools are essential for efficient reverse engineering.

Conformal coating of the PCBA can complicate the task. The type of coating and how to remove it without damaging the board assembly will determine the overall level of difficulty for the reverse engineering process. If the type of conformal coating is not known, observation and testing will help identify the type of coating and the process required for removal. Several removal techniques are available, including using solvents, peeling, thermal, grinding and scraping, and micro-blasting. After removing any conformal coating, component removal can begin. Great care must be taken to insure that the underlying board remains sufficiently intact. Proper use of the right tools and equipment will save the board from damage and preserve it for any remaining analysis.

Up to this point, a list of components on the PCBA should be available from the BOM. Information gathered from an in-circuit tester and/or x-ray machine will be used to develop the design schematic. With this data and the BOM, one can use any of a number of computer aided design (CAD) software packages capable of circuit design and layout to generate the Gerber file, which is the machine code for circuit artwork. This may not replicate the same layout as the original PCBA and depending on the end application, further design work on the PCBA may be necessary to create the replacement design.

Many printed circuit board (PCB) fabricators and vendors claim that there is no easy way to take a PCB apart, layer by layer. Most boards are made of prepreg with an epoxy resin, a copper-clad surface etched for the circuitry design, patterned solder mask, a silkscreen print of the reference designators, and a finish plating on the exposed copper. These materials are designed to keep the PCB intact and to prevent separation, and to conform to strict commercial standards (designed to ensure PCB quality and reliability) but do make the task of separating the layers very difficult.

The board must be separated, layer by layer, which requires effort and patience. In some cases, a poorly constructed board can be separated mechanically using a knife and then pried apart (Figure 3-1).

A chemical application may be needed to help separate the layers without damaging the board. Methyl Ethyl Keytone (MEK) can soften the epoxy that bonds the layers together. This technique was developed through small sample testing on a modern, well-laminated board. The key process variable was to determine the quickest method to get the MEK soaked into the PCB. One sample was soaked in MEK for a set time period, another was soaked in MEK and then heated to 40°C, and the last was dipped in MEK for a few seconds. In this trial run, it was determined that heating of the MEK helped the PCB absorb it more rapidly. Caution should be taken when working with MEK. Please consult the MSDS. When the PCB is fully soaked, there is not much time before the MEK evaporates and the board re-hardens. This process of delaminating will take longer to work through a thicker board. Figure 3-2 shows the result of this technique.

After successfully separating each layer, the next step is to create the original Gerber file. There are commercially available systems that can replicate the artwork of the circuit layer by layer. This is done by scanning the board or each of its layers and capturing the image of the circuitry layout. One such system is ScanCad, which is currently used at the EMPF. With help from the software, the operator can begin tracing the image. After creating the PCB artwork, it can be verified with the original schematic that was previously generated. The BOM, schematic, and the Gerber file completes the supporting documentation to recreate the original PCBA.

Reverse engineering is not a straightforward process and requires technical expertise, patience, the proper tools and equipment, and the ability to make adjustments to fit the PCBA and the application. Successful results can extend the useful life of many PCBAs and, more importantly, the continuation of their end-use applications in systems and devices. It is important to know that existing PCBA designs may have proprietary restrictions on their use, so some prudent due diligence on design ownership is important prior to starting any reverse engineering process.