Prototype pcb failure cause analysis (2)

5, Microscopic infrared analysis

spectra, analyzes the compound composition of the material, and combines the microscope to make visible light and infrared light share the same light path, as long as it is visible in the field of view, can be found to analyze trace amounts of organic pollutants.

If there is no microscope combination, usually the infrared spectrum can only analyze samples with a large amount of sample. In many cases in electronic processes, even trace contamination can lead to poor solderability of prototype PCB pads or lead pins. It is conceivable that it is difficult to solve the process problem without the infrared spectrum of the microscope. The main purpose of microscopic infrared analysis is to analyze the organic contaminants on the surface of the soldered surface or solder joints and analyze the causes of poor corrosion or solderability.

6. Scanning electron microscopy analysis (SEM)

Scanning Electron Microscopy (SEM) is one of the most useful large-scale electron microscopy imaging systems for failure analysis. It is most commonly used for morphological observation. The current scanning electron microscope is very powerful, and any fine structure or surface features can be amplified to observe and analyze hundreds of thousands of times.

In the failure analysis of prototype PCB or solder joints, SEM is mainly used for the analysis of failure mechanism, specifically to observe the surface structure of the pad surface, the metallographic structure of the solder joint, the measurement of intermetallic compounds, and the solderability coating analysis and make tin whisker analysis and measurement.

Unlike an optical microscope, a scanning electron microscope is an electronic image, so it is only black and white, and the sample of the scanning electron microscope requires conduction. The non-conductor and part of the semiconductor need to be sprayed with gold or carbon, otherwise the charge will accumulate on the surface of the sample which affect the Observation of the sample. In addition, the depth of field of the SEM image is much larger than that of the optical microscope, which is an important analytical method for irregular samples such as metallographic structure, micro-fracture and tin whiskers.

7, Thermal analysis

Differential Scanning Calorimeter (DSC)

Differential Scanning Calorimography is a method of measuring the relationship between the power difference between a substance and a reference substance and temperature (or time) at program temperature control. It is an analytical method for studying the relationship between heat and temperature. According to this relationship, the physical and chemical properties of the material can be studied.

DSC is widely used, but in the analysis of prototype PCB , it is mainly used to measure the curing degree of various polymer materials used on prototype PCB , and the glass state transition temperature. These two parameters determine the reliability of the PCB in the subsequent process.

8. Thermomechanical Analyzer (TMA)

Thermal Mechanical Analysis is used to measure the deformation properties of solids, liquids and gels under thermal or mechanical forces under programmed temperature control. It is a method to study the relationship between heat and mechanical properties. The physicochemical and thermodynamic properties of materials can be studied according to the relationship between deformation and temperature (or time).

TMA is widely used in prototype PCB  analysis. It is mainly used for the two most critical parameters of PCB : measuring its linear expansion coefficient and glass state transition temperature. PCBs substrates with excessive expansion coefficients often cause fracture failure of metallized holes after solder and assembly.

9, Thermogravimetric analyzer (TGA)

Thermogravimetry analysis is a method of measuring substance quality changes alone with temperature under program temperature control. TGA monitors the subtle quality changes that occur during the programmed temperature change process through a sophisticated electronic balance.

Physicochemical and thermodynamic properties of materials can be studied based on the relationship which substance quality changes along with temperature(or time). In the analysis of prototype PCB , it is mainly used to measure the thermal stability or thermal decomposition temperature of PCB materials. If the thermal decomposition temperature of the substrate is too low, the prototype PCB  will explode or delainate when it passes through the high temperature of the soldering process.