PCB / PCBA failure analysis

Date：2022-03-09 14:00:00Views：969

PCBA is a system composed of PCB and various electronic components. The main material of PCB is the composite of glass fiber and epoxy resin, which is divided into single panel, double-sided board and multilayer board. As the carrier of various components and the hub of circuit signal transmission, it has become the most important and key part of electronic information products. Its quality and reliability level determine the quality and reliability of the whole equipment. Due to the development trend of PCB high density and the environmental requirements of lead-free and halogen-free, more and more PCBs have various failure problems, such as poor wetting, plate explosion, delamination, CAF and so on. The acquisition of PCB failure mechanism and causes will be conducive to the quality control of PCB in the future, so as to avoid the recurrence of similar problems.

Failure mode:

Plate explosion, delamination, short circuit, blistering, poor welding, corrosion migration, etc.

Common means

NDT:

Appearance inspection, X-ray fluoroscopy, three-dimensional CT, C-sam, infrared thermal imaging

Surface element analysis:

Scanning electron microscope and energy spectrum analysis (SEM / EDS)

Micro infrared analysis (FTIR)

Auger electron spectroscopy (AES)

X-ray photoelectron spectroscopy (XPS)

Secondary ion mass spectrometry (TOF-SIMS)

Thermal analysis:

Differential scanning calorimetry (DSC)

Thermomechanical analysis (TMA)

Thermogravimetric analysis (TGA)

Dynamic thermomechanical analysis (DMA)

Thermal conductivity (steady state heat flow method, laser scattering method)

Electrical performance test:

Breakdown voltage, withstand voltage, dielectric constant, electromigration

Destructive performance test:

Dyeing and penetrant testing

PCB / PCBA failure analysis steps:

1. Visual inspection

Cracks on the substrate indicate the existence of bending and other stresses. Overheated or discolored lines are a sign of overcurrent. Broken solder joints indicate solderability problems or solder contamination. Several solder joints have gray surfaces or too much or too little solder. These are characterized by poor welding technology, pollutants or signs of overheating. Any decolorization may mean overheating. Solder reflow produces pores, which means high temperature.

2. X-ray

Check for any disconnection / shorting or damage to wiring, through holes that are not fully filled, wiring or component pads that are misaligned.

3. Electrical measurement

For the electric leakage caused by pollutants in the solder joint used to confirm cracking and fracture, the voltage can be added to measure the current, but the voltage should be limited to a reasonable range. Applying some stress during the test may find some intermittent abnormalities.

4. Section analysis

The defects in solder joints and multilayer plates can be checked by preparing metallographic samples.

5. SEM and EDX

The pollutants on the surface of the substrate can be identified by SEM. The pollutants may appear on the surface of the plate or under the conformal coating. Sometimes the conformal coating must be removed without affecting the pollutants. Chlorine, fluorine, sulfur and bromine are concerned elements, and bromine is a flame retardant component in some materials. EDX can be used to check whether there are pollutants in the solder joint. Sulfur, oxygen, copper, aluminum and zinc are pollutants that may cause problems in the solder joint. Solder joint fracture caused by pollutants often occurs in intermetallic compounds at the interface between component pins and solder.