PCBA Tech - SMT soldering components and PCBA solder joints fail

Precautions for SMT chip processing when soldering components

In SMT chip processing, there are many types of components, of which chip components are the key to SMT assembly and welding technology, which affects product quality and reliability. Chip components are miniature electronic components, and there are many types of them, with different shapes and physical properties. The following matters need to be paid attention to when mounting and soldering:

1. Before welding, it is necessary to understand whether there are special requirements for components, such as welding temperature conditions, assembly methods, etc. Some components cannot be immersed in tin, but can only be soldered with an electric soldering iron, such as chip potentiometers and aluminum electrolytic capacitors, so you need to choose the correct soldering method according to the situation.

2. For the components that need immersion tin soldering, it is best to dip them only once. Repeated tin immersion will cause the printed board to bend and the components to crack.

3. In the process of SMT patch welding, in order to prevent electrostatic damage to the components, the electric soldering iron and soldering furnace used should have a good grounding device.

4. For the selection of printed boards, the thermal deformation should be small and the copper foil coating should be strong. Due to the narrow traces of the copper foil for surface assembly and the small pads, if the anti-stripping ability is insufficient, the pads are easy to peel off. Generally, epoxy glass fiber substrates are used.

5. For rectangular chip capacitors, use larger-looking capacitors, such as type 1206, which is easy to weld, but cracks and other thermal damage are likely to occur due to uneven welding temperature; use smaller-looking capacitors, such as type 0805, although Welding is more difficult, but cracks and thermal damage are less likely to occur, and the reliability is high.

6. If the PCB board needs to be repaired, the number of disassembly and assembly of components should be reduced as much as possible, because multiple disassembly and assembly will result in the complete scrap of the printed board. In addition, for mixed printed boards, if interposing components hinder the disassembly and assembly of chip components, they can be removed first.

The welding of chip components in SMT chip processing is very complicated. The operator should learn the welding skills and understand the precautions clearly, and operate carefully to avoid errors and affect the quality of welding.

Cause analysis and avoidance of PCBA solder joint failure

With the development of science and technology, electronic products are developing towards miniaturization and precision. The PCBA processing assembly density used by SMT chip processing plants is getting higher and higher, and the solder joints in the circuit board are getting smaller and smaller. The mechanical, electrical, and thermodynamic loads that are carried are getting heavier and heavier, and the requirements for reliability are increasing day by day. However, PCBA solder joint failure may also be encountered in the actual processing process, and it is necessary to analyze and find out the reason to avoid solder joint failure again. The failure of solder joints may cause a series of problems. In severe cases, it may damage the PCB board or cause unknown problems to the product.

The main reasons for the failure of PCBA processing solder joints:

1. Poor component pins: plating, pollution, oxidation, coplanarity;

2. Bad PCB pads: plating, pollution, oxidation, warpage;

3. Solder quality defects: composition, impurity exceeding standard, oxidation;

4. Flux quality defects: low solderability, high corrosion, low SIR;

5. Process parameter control defects: design, control, equipment;

6. Defects of other auxiliary materials: adhesives, cleaning agents.

How to improve the reliability of PCBA solder joints:

For PCBA solder joint reliability experiment work, including reliability experiment and analysis, its purpose is to evaluate and appraise the reliability level of PCBA integrated circuit devices on the one hand, and to provide parameters for the reliability design of the whole machine; on the other hand, it is to Improve the reliability of solder joints during PCBA processing. This requires the necessary analysis of failed products to find out the failure mode and analyze the cause of the failure. The purpose is to correct and improve the design process, structural parameters, welding process and increase the yield rate of PCBA processing. The failure mode of PCBA solder joints The prediction of cycle life is very important and is the basis for establishing its mathematical model.