PCBA Tech - Application of Thermal Analysis Technology in PCBA Failure Analysis

Application of Thermal Analysis Technology in PCBA Failure Analysis
Shenzhen PCBA processing PCBA, as the carrier of various components and the hub of circuit signal transmission, has become the most important and key part of electronic information products. Its quality and reliability determine the quality and reliability of the whole equipment. With the miniaturization of electronic information products and the environmental protection requirements of lead-free and halogen-free, PCBA processing is also developing in the direction of high density, high Tg and environmental protection. However, due to cost and material changes, PCBA has a large number of failure problems in the production and application process, many of which are related to the thermal performance or stability of the material itself, which has caused many quality disputes. In order to clarify the cause of the failure in order to find a solution to the problem and distinguish the responsibilities, it is necessary to conduct a failure analysis on the failure cases that have occurred. This article will discuss and introduce some commonly used thermal analysis techniques, as well as some typical cases.
1 Shenzhen PCBA processing thermal analysis technology
PCBA processing differential scanning calorimeter (DSC)

Differential Scanning Calorimetry (Differential Scanning Calorimetry) is a method of measuring the relationship between the power difference between the input material and the reference material and the temperature (or time) under the temperature control of the program. DSC is equipped with two sets of compensation heating wires under the sample and reference container. When the temperature difference ΔT between the sample and the reference occurs due to the thermal effect during the heating process, the differential thermal amplification circuit and the differential heat compensation amplifier can be used, Make the current flowing into the compensation heating wire change, balance the heat on both sides, the temperature difference ΔT disappears, and record the relationship between the temperature (or time) change of the difference between the heating power of the two electric heating compensation under the sample and the reference, and According to this change relationship, the physical, chemical and thermodynamic properties of materials can be studied and analyzed. DSC has a wide range of applications, but in the analysis of PCBA, it is mainly used to measure the degree of curing of various polymer materials used on PCBA (such as Figure 2) and glass transition temperature. These two parameters determine the PCBA in the subsequent process. Reliability.
Analysis of the curing situation of the epoxy resin in PCBA processing PCBA in Shenzhen
PCBA processing thermomechanical analyzer (TMA)
Thermal Mechanical Analysis technology is used to measure the deformation properties of solids, liquids and gels under thermal or mechanical force under program temperature control. Commonly used load methods include compression, penetration, tension, bending, etc. The test probe is supported by a cantilever beam and a coil spring fixed on it, and a load is applied to the sample through a motor. When the sample is deformed, the differential transformer detects this change and processes it together with data such as temperature, stress and strain. The relationship between the deformation of the material and the temperature (or time) under negligible load can be obtained. According to the relationship between deformation and temperature (or time), the physical, chemical and thermodynamic properties of materials can be studied and analyzed. TMA has a wide range of applications. It is mainly used in PCBA analysis for the two most critical parameters of PCBA: measuring its linear expansion coefficient and glass transition temperature. PCBA with a base material with too large expansion coefficient will often lead to fracture failure of the metallized hole after soldering and assembly.
PCBA processing thermogravimetric analyzer (TGA)
Thermogravimetry Analysis is a method of measuring the relationship between the mass of a substance and the temperature (or time) under program temperature control. TGA can monitor the subtle mass changes of substances in the process of program-controlled temperature change through a sophisticated electronic balance. According to the relationship of material quality with temperature (or time), the physical, chemical and thermodynamic properties of materials can be studied and analyzed. TGA has a wide range of applications in the study of chemical reactions or qualitative and quantitative analysis of substances; in the analysis of PCBA, it is mainly used to measure the thermal stability or thermal decomposition temperature of PCBA materials. If the thermal decomposition temperature of the substrate is too low, PCBA is undergoing Plate bursting or delamination failure will occur at the high temperature of the welding process.
Typical failure cases of PCBA processing in Shenzhen
Due to the many types and reasons of PCBA failure, and the length of this article is limited, the following will select a few typical cases of plate failure to introduce, focusing on the application of the above thermal analysis technology and the basic ideas for solving the problem. The analysis process is omitted. PCBA local blasting analysis
The samples of this batch are CEM1 type plates. The plate failure will occur after lead-free reflow soldering. The probability is about 3%. The samples are elongated, and there is a row of large electromagnetic relays (see Figure 1). The area of the blasting plate is concentrated in the part with few components, and the color of this part and the corresponding back surface is yellower, and the color is obviously darker than other parts (Figure 2). Through slice analysis, it is found that the PCBA base material is layered on the paper layer in the area where the board burst occurs. The thermal stress test was carried out with a similar batch of samples, and no similar burst failure was found at 260°C for 10 to 30 seconds, and the color of the sample after the test was not as deep as the actual failed sample. At the same time, thermal analysis methods (TGA and DSC) were used to analyze the material in the explosion area, and it was found that the thermal decomposition temperature and glass transition temperature of the material were in line with the technical specifications of the material. Based on the above analysis, it can be inferred that the conditions of the lead-free reflow soldering assembly process exceed the technical requirements of this type of PCB. In order to ensure that the solder joints of the large heat-absorbing devices are qualified or good during reflow, the set process parameters are mainly the soldering temperature and The time is too high and too long, resulting in the local temperature of the area with few components or blanks exceeding the technical specifications of this type of sheet material, and finally resulting in the product