Meaning
Systematic investigation of fractured or degraded solder connections in electronic assemblies identifies the physical and chemical root causes of electrical open circuits. This joint failure analysis utilizes microscopy, cross-sectional polishing, and mechanical testing to isolate the point of rupture. It is limited to the physical boundary of the solder connection and the immediate copper pads on the printed circuit board.
Diagnostic Methodology
Non-destructive testing represents the first step in the investigation, with x-ray imaging being used to locate internal cracks and voiding. If the imaging reveals anomalies, the next phase of joint failure analysis involves destructive cross-sectioning and scanning electron microscopy to study the microstructure of the solder. This detailed examination reveals the thickness of the intermetallic compound layer and the path of the crack propagation.
Stress Classification
Cracks usually originate from either thermal cycling or mechanical shock. Thermal fatigue produces characteristic intergranular cracks that follow the grain boundaries of the alloy, while drop testing or mechanical bending results in sudden brittle fractures along the interface between the solder and the copper pad.
Remedial Strategy
Identifying the fracture mode allows the engineering team to adjust the manufacturing process to prevent further occurrences. If the joint failure analysis points to inadequate wetting, the thermal profile of the reflow oven is adjusted to increase the time above liquidus or the flux chemistry is changed to improve surface cleaning. These corrective actions are vital for stabilizing the production line and maintaining the long-term reliability of the finished product.
