PCBA Tech - Principle of PCBA water cleaning technology

PCBA water cleaning process uses water as the cleaning medium. A small amount (generally 2%~10%) of surfactant, corrosion inhibitor and other chemicals can be added to the water. Through cleaning, PCBA cleaning is completed through multi-source cleaning and drying with pure water or deionized water. Today, I would like to introduce the principle, advantages and disadvantages of PCBA water cleaning technology.

The advantage of water cleaning is that the cleaning medium for water cleaning is generally non-toxic, does not harm workers' health, is not flammable, does not explode, and has good safety. Water cleaning has good cleaning effect on particles, rosin flux, water-soluble pollutants and polar pollutants: water cleaning has good compatibility with the packaging materials of components and PCB material, will not cause rubber parts and coatings to expand, will not crack, and will keep the marks and symbols on the surface of components clear and complete, and will not be washed away. Therefore, water cleaning is one of the main processes of non ODS cleaning.

The disadvantage of water washing is that the investment in the whole equipment is large, and the investment in pure water or deionized water production equipment is also needed. In addition, it is not applicable to non airtight devices, such as adjustable potentiometers, inductors, switches, etc. Water vapor entering the device is not easy to discharge, or even damage the annular components. Water washing technology can be divided into pure water washing and water plus surfactant washing. The typical PCBA process flow is as follows: water+surfactant - water - purified water - ultrapure water - hot air washing - washing - drying. In general, ultrasonic devices are added in the cleaning stage. In addition to ultrasonic devices, air knife (nozzle) devices are also added in the cleaning stage. The water temperature should be controlled at 60-70 ℃, the water quality should be very high, and the resistivity should be 8-18mq? This alternative technology is suitable for SMT chip processing plants that have high requirements for mass production and product reliability. For small batch cleaning, small cleaning equipment can be selected.

With the development of miniaturization and precision of electronic products, the PCBA processing and assembly density adopted by electronic processing plants is getting higher and higher, and the solder joints in circuit boards are getting smaller and smaller, while the mechanical, electrical and thermodynamic loads they carry are getting heavier and heavier, and the requirements for stability are also getting higher and higher. However, PCBA solder joint failure will also be encountered in the actual processing. It is necessary to analyze and find out the cause to avoid the solder joint failure again. This article introduces the main causes of PCBA processing solder joint failure.

Main reasons for PCBA processing solder joint failure:

1) Poor component pins: coating, pollution, oxidation, coplanar.

2) Poor PCB pad: coating, pollution, oxidation, warping.

3) Solder quality defects: composition, impurities not up to standard, oxidation.

4) Flux quality defects: low flux, high corrosion, low SIR.

5) Process parameter control defects: design, control and equipment.

6) Defects of other auxiliary materials: adhesives and cleaning agents.

Methods for increasing the stability of PCBA solder joints:

The stability experiment of PCBA solder joint includes stability experiment and analysis. On the one hand, its purpose is to evaluate and identify the stability level of PCBA integrated circuit devices and provide parameters for the stability design of the whole machine. On the other hand, it is necessary to improve the stability of solder joints during PCBA processing. Therefore, it is necessary to analyze the failed products, find out the failure mode and analyze the failure cause. The purpose is to modify and improve the design process, structural parameters, welding process, and improve the finished product rate of PCBA. The failure mode of PCBA solder joint is the basis of predicting its cycle life and establishing its mathematical model. These are the main reasons for PCBA solder joint failure.