Testing the Cleanliness of Board Inner Layers
Foresite has primarily specialized in preventing and solving product reliability issues associated with detrimental residues on the surface of electronics. But what if that affected surface is buried between layers of a multi-layer board?
Researchers at Foresite have developed an analytical technique to investigate board inner layer issues: we can separate multi-layer boards to expose the layer(s) of interest. Conventional failure analysis techniques, such as x-ray and cross-sectioning, can be utilized to investigate inner layer issues. But at times, we have to go farther to answer the how and why, after we know the what of a failure mechanism.
What Was Happening?
Recently a client presented us with an electronic assembly experiencing performance issues. We identified the what – a short circuit within the inner layers of the circuit board. The short was not direct/hard and no electrical components were found to be defective. Cross-sectioning, SEM, and optical imagery plus EDX clarified the failure location but not the source of the contamination. Copper was found in the failure area between board layers, connecting the vias, along with high levels of plating contamination - an area intended to be insulating.
Foresite has primarily specialized in preventing and solving product reliability issues associated with detrimental residues on the surface of electronics. But what if that affected surface is buried between layers of a multi-layer board?
Researchers at Foresite have developed an analytical technique to investigate board inner layer issues: we can separate multi-layer boards to expose the layer(s) of interest. Conventional failure analysis techniques, such as x-ray and cross-sectioning, can be utilized to investigate inner layer issues. But at times, we have to go farther to answer the how and why, after we know the what of a failure mechanism.
What Was Happening?
Recently a client presented us with an electronic assembly experiencing performance issues. We identified the what – a short circuit within the inner layers of the circuit board. The short was not direct/hard and no electrical components were found to be defective. Cross-sectioning, SEM, and optical imagery plus EDX clarified the failure location but not the source of the contamination. Copper was found in the failure area between board layers, connecting the vias, along with high levels of plating contamination - an area intended to be insulating.
Residues from the PCB fabrication process (primarily plating residues for the copper barrels, chloride and sulfate) had been able to penetrate the exposed weave around the barrel of the vias, down through the layers due to the poor resin melt. These detrimental residues resulted in electrochemical migration or CAF pathways for current leakage. In addition to the parasitic leakage, thermal damage subsequently occurred.
Process certification and control has to be in place all along your supply chain, including PCB fabrication.