Residue on PCBA

Residues on PCBAs are unfortunately common place. SEM/EDS analysis helps to determine the nature of the residue.

residue on PCBA 1

The image above shows residue on the surface of the PCBA, but it is not clear what is the nature of the residue.

residue on PCBA 2

EDS analysis shows that the residue is likely tin bromide, suggesting corrosive bromide flux activator was left behind after assembly.

residue on PCBA 3

This is a BSE SEM image of some of the residue, which shows dendritic growth. The dendrites suggest that electrochemical migration (ECM) was a factor meaning ionic contamination, electric field, and moisture were likely at play. If the dendrites migrate between normally isolated signals (e.g. PWR & GND) then the circuit fails.

Check out SEM Lab, Inc.  to learn more.

MLCC Bending Fracture

A client provided two sensor assemblies for failure analysis of capacitor C4 on the internal PCBA.

MLCC Bending Fracture _1

This is an optical micrograph of the capacitor as mounted on the PCBA.

MLCC Bending Fracture _2

This is an optical image of an intermediate grinding stage during microsection preparation. A bending fracture was noted under one of the terminations.

MLCC Bending Fracture _3

This is a BSE SEM image of the capacitor microsection.

MLCC Bending Fracture _4

The fracture appeared to be due to flexure of the PCBA.

Check out SEM Lab, Inc.  to learn more.