OSP is the abbreviation for Organic Solderability Preservatives, which translates to 有机钎焊保护剂 in Chinese. It is also known as Copper Protector or Preflux in English. Its primary function is to block moisture, prevent oxidation of the pad, and maintain good solderability on the copper surface during soldering. Due to OSP’s excellent surface flatness, high reliability of solder joints, relatively simple PCB manufacturing process, and low cost, it offers significant advantages over other surface treatments, making it increasingly popular in the industry.
In normal circumstances, PCBs treated with OSP exhibit good soldering properties. However, improper control of the PCB production process or incorrect SMT usage can lead to soldering issues. This article focuses on analyzing the factors that affect PCB solderability, specifically addressing OSP film thickness control, PCB storage conditions, and the correct use of SMT techniques. Based on the characteristics of OSP-treated PCBs and analysis of soldering issues, this article proposes corresponding improvement measures.
PCB is an indispensable material for modern electronic products. With the rapid development of surface mount technology (SMT) and integrated circuit (IC) technology, PCBs need to meet requirements such as high density, flatness, reliability, smaller apertures, and pads. Consequently, demands for PCB surface treatment and manufacturing environments are escalating. One prevalent PCB surface treatment technology is OSP (Organic Solderability Preservatives). OSP involves chemically growing a 0.2~0.5um organic film on a clean bare copper surface. This film provides anti-oxidation properties and withstands room temperature, thermal shock, and moisture, protecting the copper surface from oxidation or sulfidation. During subsequent high-temperature soldering, the protective film must swiftly dissolve under flux, exposing a pristine copper surface that rapidly combines with molten solder to form robust joints.
OSP offers several advantages and disadvantages:
a. OSP surfaces are flat, uniform, and maintain a film thickness of 0.2~0.5um, ideal for PCBs with closely spaced SMT components.
b. OSP films exhibit excellent thermal shock resistance, suitable for lead-free technologies and single/double panel processing, compatible with all types of solder.
c. Water-soluble process, operating below 80 degrees Celsius, prevents substrate bending and deformation.
d. Clean production environment, minimal pollution, and adaptable to automated production lines.
e. Relatively simple process, high yield, and cost-effective.
f. Drawbacks include vulnerability to scratching due to the extremely thin protective film.
g. Repeated high-temperature soldering can cause OSP film discoloration, cracking, thinning, and oxidation, affecting solderability and reliability, especially on unsoldered pads.
h. Variability in syrup formulas leads to differing performance and inconsistent quality.
2. Problem Description:
In practical production, OSP boards often encounter issues like surface discoloration, uneven film thickness, and excessive film (either too thick or too thin). Improper storage or usage after production may lead to soldering problems such as pad oxidation, poor tin adherence, weak solder joints, virtual soldering, and insufficient soldering. Double-sided PCBs in SMT production, particularly during second-side reflow soldering, are prone to issues like reflow soldering defects, solder joint leakage, and failure to meet IPC3 standards, resulting in a high tin furnace soldering failure rate.
In normal circumstances, PCBs treated with OSP exhibit good soldering properties. However, improper control of the PCB production process or incorrect SMT usage can lead to soldering issues. This article focuses on analyzing the factors that affect PCB solderability, specifically addressing OSP film thickness control, PCB storage conditions, and the correct use of SMT techniques. Based on the characteristics of OSP-treated PCBs and analysis of soldering issues, this article proposes corresponding improvement measures.
PCB is an indispensable material for modern electronic products. With the rapid development of surface mount technology (SMT) and integrated circuit (IC) technology, PCBs need to meet requirements such as high density, flatness, reliability, smaller apertures, and pads. Consequently, demands for PCB surface treatment and manufacturing environments are escalating. One prevalent PCB surface treatment technology is OSP (Organic Solderability Preservatives). OSP involves chemically growing a 0.2~0.5um organic film on a clean bare copper surface. This film provides anti-oxidation properties and withstands room temperature, thermal shock, and moisture, protecting the copper surface from oxidation or sulfidation. During subsequent high-temperature soldering, the protective film must swiftly dissolve under flux, exposing a pristine copper surface that rapidly combines with molten solder to form robust joints.
OSP offers several advantages and disadvantages:
a. OSP surfaces are flat, uniform, and maintain a film thickness of 0.2~0.5um, ideal for PCBs with closely spaced SMT components.
b. OSP films exhibit excellent thermal shock resistance, suitable for lead-free technologies and single/double panel processing, compatible with all types of solder.
c. Water-soluble process, operating below 80 degrees Celsius, prevents substrate bending and deformation.
d. Clean production environment, minimal pollution, and adaptable to automated production lines.
e. Relatively simple process, high yield, and cost-effective.
f. Drawbacks include vulnerability to scratching due to the extremely thin protective film.
g. Repeated high-temperature soldering can cause OSP film discoloration, cracking, thinning, and oxidation, affecting solderability and reliability, especially on unsoldered pads.
h. Variability in syrup formulas leads to differing performance and inconsistent quality.
2. Problem Description:
In practical production, OSP boards often encounter issues like surface discoloration, uneven film thickness, and excessive film (either too thick or too thin). Improper storage or usage after production may lead to soldering problems such as pad oxidation, poor tin adherence, weak solder joints, virtual soldering, and insufficient soldering. Double-sided PCBs in SMT production, particularly during second-side reflow soldering, are prone to issues like reflow soldering defects, solder joint leakage, and failure to meet IPC3 standards, resulting in a high tin furnace soldering failure rate.
