PCB reverse engineering entails getting the internal structure and all layers connections by either non-destructive process or destructive process of delayering.
The non-destructive process involves imaging tomography, which you can apply to image the entire PCB without delayering.
On the other hand, the destructive process entails delayering, which you follow with imaging of each layer before you embark on the following round of material removal.
In either scenario, you can do the analysis manually or automatically whose outcome is a netlist that you can use to reproduce the PCB.
PCB reverse engineering technique
a)Non-destructive PCB Reverse Engineering Technique
The sector has expressed interest in switching to reverse engineering practices grounded in non-destructive techniques.
The industry shift is because of the method’s reduced costs, the shorter duration it takes to conduct PCB reverse engineering. And, the possibility of developing a test for detecting trust issues or faults.
The non-destructive nature of this technique of reverse engineering PCB gives more margins for error in the course of the operation.
PCB Reverse engineering – Photo source: Semantic Scholar
Besides, you can put the PCB into other uses afterward.
Non-destructive PCB reverse engineering commonly uses X-ray tomography.
Tomography is a non-invasive imaging method which enables you to observe the interior structure of a substance without interfering with the under- and over-layer structures.
X-ray tomography enables you to extract the geometrical information of connections, via holes and traces on PCB layers.
Scanning PCB – Image source: SMTNet
The technique allows you to capture all the printed circuit board layers (front, interior, and back) in a single imaging session.
The concept of tomography is to obtain a pile of two dimensional (2D) images.
Then apply mathematical algorithms like center slice theory and direct Fourier transform and to regenerate the three dimensional (3D) image.
You collect the 2D projections from many varying angles based on the quality you require for the final image.
The PCB features such as material density and dimension are vital to factor in when selecting the tomography parameters which comprise of:
- Source power: relates to the amount of penetration and X-ray energy
- Detector objective: dictates the resolution range and the field of view
- Filtering: regulates the dose which permits higher energy X–rays to pass through
- The distance of the detector and source to the sample: has inverse proportionality to the number of counts
- Number of X-ray projections: determines the angular increment for every rotation for the sample in the process of tomography
- Exposure Time: linearly correlated to counts and establishes the total time and, ultimately, the cost of scanning.
These parameters can impact on the signal-to-noise ratio and pixel size, which you must optimize depending on the region-of-interest.
Analysis of the interior and exterior structure is possible after reconstructing the 3D image, which requires beam hardening and center shift tuning.
The pixel size is the most essential parameter for determining the quality of the regenerated 3D images.
Based on it, you can tune many other parameters including detector objective (same as optical magnification and distance of detector and source from the sample (the geometric magnification.
b)Destructive PCB Reverse Engineering Techniques
The printed circuit board might be single, double or multilayered depending on how complex the system.
In destructive reverse engineering of PCB, you first analyze the external layer of the board to identify the components mounted on it, its ports, and its traces.
Consequently, you then delayer the multilayered circuit board to expose the via, connectivity, and traces within its interior layers.
Reverse engineering PCB
Often, destructive PCB reverse engineering entails three procedures: solder mask removal, delayering, and imaging.
·Solder Mask Removal
The aim of this step is to take out the solder mask from the PCB and reveal the copper traces on the bottom and/or top layers with minimal destruction.
Even though it is at times possible to recognize the copper traces via the existing solder mask, extracting the solder mask will facilitate a more clear view.
You should carry out the procedure after detaching all the components from the PCB.
You can apply the following techniques to remove the solder mask on the printed circuit board:
- Sandpaper
- Abrasive blasting
- Fiberglass scratch brush
- Chemical
- Laser
·Delayering
The aim of this step is to access the internal copper layers of a multilayer PCB by means of physical, destructive delayering.
You should also carry out the process after removing all the components on the PCB. Below are some methods of PCB delayering you can apply:
- X-ray
- Sandpaper
- Dremel Tool
- Surface Grinding
- CNC Milling
·Imaging
The aim of this step is to get individual images of each layer of a multilayer PCB, employing non-destructive imaging methods.
Such techniques may be effective even against populated or fully assembled PCB.
You can complete imaging during PCB reverse engineering by using either X-ray (2D) or Computerized tomography (3D X-ray).