What is PCB Reverse Engineering?
Reverse engineering a PCB means analyzing the target board with the purpose of reproducing its likeness. According to Rush PCB Inc, reverse engineering can deduce and create a likeness of the design of the process flow, structure, functional characteristics, and technical specifications of a PCB to reproduce a similar board, but not its exact copy. The primary purpose here is to analyze the finished product directly and make a reproduction when the necessary production information is not readily available.
The Process of Reverse Engineering a Single-Sided Board
To reverse engineer a product, the operator begins by identifying all electronic components on the board, and creates a rough bill of material. They photograph the entire board very carefully, and create an enlarged photocopy. The operator then de-solders each component from the board, and glues it to its location on the photocopy. By measuring each resistor and capacitor, they proceed to update the bill of materials and procure the components. Then they scan the bare board to recreate the trace pattern and thereby generate a new board. Finally, they mount and solder all components on the new board, and send the assembly to the customer for confirmation.
Reverse Engineering a Double-Sided Board
The operator must note down the model number, and position of all components on the board, especially the direction of ICs, diodes, and transistors. It is also advisable to use a digital camera to photograph both sides of the board.
The operator can then remove all components from the board by de-soldering them carefully, and remove all solder from vias and pads. Cleaning the board with alcohol helps to remove any dirt and grease on the surface. If there is lettering on the surface of the layers, photographing/scanning them will help in creating the silkscreen layer. Lightly polishing the top and bottom layers with fine emery paper helps to remove the solder mask from the copper traces, making the copper traces shiny. The operator can then scan both surfaces separately with a scanner to generate two high-detail photographs.
By adjusting the brightness and contrast of the canvas, it is possible to generate photo images with strong contrast between the copper parts and the bare substrate. The operator can turn the images into black and white to check if all lines are clear and well-defined. If any track is not clear, the operator can either regenerate the image, or correct them using common software like photoshop or gimp. They may save the images in bmp format for easily converting them to PCB formats for use in PCB design software like Protel.
After converting the images of the two sides into the PCB design software format, the operator can place the two images one atop the other to make the pads and vias coincide. If they had carried out the previous steps properly, then the two images will overlap correctly. Else, the operator must regenerate the photo images. Adding the silkscreen layers will complete the basic reverse engineering. Reverse engineering is a process requiring huge amounts of patience, as each step can affect the quality and the degree of matching.
By combining all the layers in the PCB design software, it is possible to generate the remaining layers like solder mask. As a cross-check, the operator can print the top and bottom copper layers in 1:1 ratio on transparent film using a laser printer. By placing this film over the original PCB, they can confirm if the process is on the right track.
Once everything matches, the operator uses the output of the PCB design software to fabricate new boards.
Reverse Engineering a Multi-Layered Board
As with the previous two boards, the operator makes a detailed record of all the components on the board, their location numbers, their markings, component packages, and their orientation. It is advisable to keep a photographic record at this stage.
Now the operator can remove all the high components from the board, leaving only the SMDs and other smaller components. Preserving another photographic record is advisable at this stage. The operator must carefully remove and dust and dirt from the PCB surface to capture all the IC models and other characteristics on the board.
At this stage, the operator begins recording a bill of materials, starting with the items they have already removed from the board. Next, they can use a hot air gun to desolder all the resistors while recording each in the bill of materials. After removing all the resistors, they can remove all the capacitors. During the removal process, it helps to identify each resistor and capacitor value with an LCR bridge. The bill of materials must record the value, position number, package type, model number, etc. of each component.
After removing all other components, the operator carefully removes the ICs from the board. As with the other components, it is necessary to record the position number, type number, manufacturer, package type, and orientation of each IC in the bill of materials.
Once the operator has stripped the board of all components, they must use braided copper wire, flux, and a hot soldering iron to remove excess tin and solder. The tip of the soldering iron may need temperature adjustment according to the number of layers in the board. Typically, operators must use a hotter soldering iron for higher layer numbers to remove solder thoroughly from vias. Once cleaned of excess solder, the operator washes the board and dries it.
Next, the operator scans the top and bottom layers of the board for generating the silkscreen. They convert the images into a PCB design software format. They can adjust the font and size of characters in the silkscreen to a suitable size.
Using fine sandpaper, the operator then proceeds to remove the silkscreen and the soldermask layers from the top and bottom surfaces of the board. This exposes the copper features as shiny metal surfaces. Scanning these surfaces, the operator can generate clear and complete images for the top and bottom surfaces of the board.
For multi-layered boards, the operator proceeds for the rest of the layers from the outside to the inside. Once they have recorded the details of the top and bottom surfaces, the operator proceeds to remove the two outer surfaces using a grinding machine. Once they have exposed the next two layers, they scan them and record the images, numbering them appropriately. Likewise, they proceed to the next layers and so on, until they reach the core layers.
Once they have recorded all the layers and transformed them into the PCB design software layers, the operator aligns all the layers to form a complete package. The accuracy of the reverse engineering process depends entirely on the accuracy of the original scanned images and the accuracy of the PCB design software.
According to Rush PCB Inc, many industries require PCB reverse engineering services for maintaining electronic products that are now no longer available because of obsolescence or other reasons. For reverse engineering of PCBs, many make use of 3D scanning technology such as laser scanners, X-ray tomography, or structured light source converters for measuring dimensions and then construct 3D visual models.