BFK-Services has already reconstructed some multilayer boards from sample boards, therefore special processes and methods have been developed and special equipment has been acquired and constructed. Today we can determine that - at a complete or partly loss of data - multilayer boards can be roconstructed by BFK-services from sample boards and left information very reliable as a matter of routine.
A Case Example:
togehter with the well-known PCB producer ALWA PRINT AG from Switzerland (already in 2013) a 5layer Backpanel PCB, dimension 171 x 352 could be reconstructed from the last remaining sample (assembled with components).
In some steps the PCB was analysed at BFK-Services, whereby before any step a documentation of the actual state was created (pictures, scans).
In the first step the components (here press-fit connectors, THT and SMT components) had to be removed very carefully to avoid any damage of the Board.
To guarantee the geometric exactness special methods are available at BFK, among others the raster-foil-method, here additionally contour measures, connector positions and their grid measures provided a frame for a good exactness of the whole digitizing work.
in the second step the outer-layers, soldermasks and the legend printing have been scanned from the disassembled PCB (resolution 1/1280 inch) and by aid of the software system RECAD - exclusively available at BFK - digitized. Therefore some scans have been created, these modified using an image processing application (here PHOTOSHOP from ADOBE) to more contrasty grey-value pictures, which were used as background in RECAD.
In the following steps the inner electrical layers have been exposed and scanned and digitized in the same way. Exposure of those layers was only possible by milling off with a special developed device, caused by the wide layer gaps in this 3,5 mm thick board. Particularly we have to make mention of the enormous risk at this process to damage the conductor layers partly while exposing by milling or grinding and to loose information forever.
Using a sophisticated procedure those problems could be avoided.
In a last step the RECAD raw data have been put together, checked and transfered to GERBER-data (RS275X) in the CAM system CAM350 from Downsstream Technologies, then a mechanical drawing and GERBER output was created.
Of course, creating GERBER data from a sample board is much more expensive than from films - specially for reaching the same safety preserving the original conductor structure. At multilayers this is again much more expensive than for 2layers.
We sometimes work therefore with 2 screens: one is used for the RECAD-System (with a grey-value image of the original layer as background) and on the other one an original coulour scan will be stepped image section by image section to compare.
Another way to ensure the correct conductor structure from the original sample we did not use in this case because it is very cost expensive: in another case first outer layers have been digitized, than a test fixture was built and the sample was tested with an e-tester. The acquired conductor structure (electrical nets and terminal points from "golden board") can be compared with the net structure of the finally completed GERBER data of the digitizing work.
Despite an actually 100% success at all multilayers digitized form samples so far it would be, of course, grossly negligent to start serial production without sampling and testing before.