Analysis of the causes of poor soldering of OSP surface treatment PCB

PCB is an indispensable material for modern electronic products. With the rapid development of surface mount technology (SMT) and integrated circuit (IC) technology, PCB needs to meet the development requirements of high density, high leveling, high reliability, smaller aperture, and smaller pads. The requirements for PCB surface treatment and production environment are getting higher and higher. OSP surface treatment is currently a common PCB surface treatment technology, which is to chemically grow a layer of 0.2~0.5um organic film on the clean bare copper surface. This layer of film has anti-oxidation, thermal shock resistance, and moisture resistance at room temperature, and can protect the copper surface from oxidation or sulfidation. In the subsequent high-temperature soldering, this protective film must be easily removed by the flux quickly. , The exposed clean copper surface is combined with molten solder to form a strong solder joint in a very short time.

Compared with other surface treatments, OSP surface treatment has the following advantages and disadvantages: OSP surface is flat and uniform, film thickness 0.2~0.5um is suitable for PCB with SMT close-pitch components; OSP film has good thermal shock resistance, suitable for lead-free process and single and double panel processing, and Compatible with any solder; water-soluble operation, the temperature can be controlled below 80 ℃, will not cause the problem of bending and deformation of the substrate; good operating environment, less pollution, easy to automate the production line; relatively simple process, high yield, low cost, etc.; The disadvantage is that the protective film formed is extremely thin, and the OSP film is easily scratched.

After the PCB is soldered at high temperature for many times, the OSP film (referring to the OSP film on the unsoldered pad) will be discolored, cracked, thinned, and oxidized, which will affect the solderability and reliability. There are many types of potions and different performances, the quality is uneven and so on.

In the actual production process, OSP boards are prone to problems such as surface discoloration, uneven film thickness, and excessive film thickness (too thick or too thin); in the later stages of pcb production, Improper storage and use of the formed PCB are prone to soldering problems such as oxidation of the pad, poor tin on the pad, inability to form a firm solder joint, virtual solder, and insufficient solder; The second side of SMT production double-sided board and solder furnace are prone to problems such as poor reflow soldering, solder joint leakage, appearance cannot meet IPC3 standards, and high solder furnace defect rate.

There are many factors that affect the poor soldering of the OSP surface treatment PCB, such as the composition and quality of the OSP syrup, the thickness and uniformity of the OSP film, the packaging and storage of the OSP board, the use and time control of the SMT section, and the process parameters of the production process (such as Steel mesh opening, furnace temperature, etc.) are closely related. Among them, the quality of the OSP syrup and the thickness and uniformity of the OSP film are the prerequisites for ensuring the quality of soldering. The soldering defects caused by these PCB Manufacturing problems are difficult or even impossible to solve through the process method in the SMT production process.

Therefore, to improve and ensure good soldering quality, the PCB factory needs to strictly control the key process parameters of PCB Manufacturing to ensure the quality of the OSP film and the production quality of the PCB; the PCB after production must be packaged and stored in strict accordance with the requirements of the OSP board; SMT When in use, it must be strictly controlled according to the time of use; the process parameters such as the opening of the steel mesh and the furnace temperature shall be controlled and optimized, and a complete OSP board production process shall be formulated.

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