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During PCB manufacturing, the PCB surface needs to be treated so that the metal parts of the board are protected from oxidation and corrosion. One common method of PCB surface finish is called Organic Solderability Preservative (OSP). Think about it like an unmistakable safeguard that keeps the metal parts perfect and glossy so they don’t get corroded or filthy. When electronic components are soldered or joined together, the OSP layer helps ensure they stick correctly and function properly. It’s similar to ensuring the puzzle pieces fit perfectly by keeping them clean and smooth.
In this blog, ELEPCB will learn more about the Organic Solderability Preservation (OSP) method of using it, and its advantages and challenges.
What is Organic Solderability Preservative?
Organic Solderability Preservative(OSP) is a PCB surface finish that conforms to RoHS compliance. OSP is a special protective layer for the copper parts on a circuit board used in electronics. It is a thin and clear shield that sticks to the copper. OSP coating shields copper from tarnishing upon exposure to air and moisture. It ensures cleanliness, maintaining copper’s readiness for soldering processes. This way, when the electronic device is put together, all the parts connect perfectly, and the device works just right.
However, during subsequent high-temperature soldering, this protective film must be easily and quickly removed by the flux so that the bare, clean copper surface can immediately bond with the molten solder, forming a strong solder joint in a very short time. In other words, OSP acts as a barrier between copper and air.
How does OSP Work?
The main function of the OSP layer is to form a protective film on the surface of the copper, preventing it from oxidizing when it comes into contact with oxygen and moisture in the air. This film will decompose rapidly during soldering, allowing direct contact between the solder and the copper surface to form a solder joint. Since the OSP layer is an organic material, it does not leave residue during the soldering process, thus ensuring the quality and reliability of the solder.
The process of OSP working in PCBs involves several key steps to ensure that the copper surface is effectively protected before soldering and provides good solderability during soldering. The following is the basic process of how OSP works in the PCB Fabrication of ELEPCB :
Step 1: Cleaning
Before the OSP process begins, the copper surface of the PCB needs to be thoroughly cleaned to remove oil, fingerprints, or other contaminants. This step is essential to ensure that the OSP layer can be uniformly and firmly adhered to the copper surface.
Step 2: Acid Rinse
After micro-etching, the PCB will go through an acid rinse step to remove any micro-etching agent and other impurities that may remain on the copper surface, ensuring that the copper surface is clean and laying the foundation for the uniform formation of the OSP coating.
Step 3: OSP Coating
After cleaning and preparation, the PCB is immersed in a tank containing OSP solution, which is usually composed of organic compounds that form a uniform organic film on the copper surface. The thickness of this film is generally between 0.15-0.35 microns, and its role is to prevent copper surface oxidation during storage and transportation.
Step 4: Washing and Drying
After the OSP coating is completed, the PCB will be washed to remove the unreacted OSP solution and then dried. This step ensures the stability and uniformity of the OSP layer.
Step 5: Post-treatment
After drying, the PCB may undergo some post-treatment steps, such as checking the thickness and uniformity of the OSP layer to ensure that it meets quality standards.
Step 6: Soldering
In the PCB assembly process, when it is necessary to solder components, the OSP layer will be decomposed under the action of soldering heat and flux, exposing a clean copper surface, and solder to form a good intermetallic compound, to achieve stable soldering.
Advantages of Using OSP
The OSP process for PCBs is widely used because of its many advantages. The following are some of the main advantages of the OSP process:
1.Keeps Copper Clean and Shiny
Copper on a circuit board can get dirty or rusty if it’s not protected.OSP acts like a protective layer that keeps the copper clean and shiny until we need to use it. Imagine you have a shiny new toy, and you cover it with a clear plastic wrap to keep it from getting dirty. That’s what OSP does for copper!
2.Easy to Use
Applying OSP is simple. Because OSP protects copper without any fuss, you don’t need complicated machines or steps.
3.Environmentally Friendly
OSP is better for the environment compared to some other protective coatings. The Organic Solder Protectant (OSP) process is based on three key materials – rosin-based, reactive resin-based and azole-based compounds, with azole-based compounds being the most widely used.
- The imidazole compounds used in the OSP process eliminate the use of lead, tin and other hazardous heavy metals compared to the traditional hot air leveling (HASL) process, significantly reducing the environmental impact of electronic products during manufacture, use and even disposal.
- The OSP process uses pure water for cleaning before and after film formation to avoid chemical residues, which not only guarantees product quality but also reduces the generation of hazardous waste, in line with the concept of green manufacturing.
- OSP is a process that meets the stringent requirements of the Restriction of Hazardous Substances Directive (RoHS) and has the advantages of low consumable consumption, high process efficiency and reduced downstream processing costs.
4.Helps with Soldering
When it’s time to attach the electronic parts to the circuit board, the clean copper makes it easy for the solder (the metal glue) to stick properly. Clean copper ensures strong, reliable connections.
5.Cost-Effective
Using OSP is an affordable way to protect copper without spending too much. Compared to other surface treatments, the OSP process is easy to operate, has short processes, is not harmful to solder paste (easy to solder), and is suitable for multiple reflow soldering (mostly used for applications with fewer soldering cycles).
6.Compatible with Modern Electronics
OSP works well with many different kinds of electronics, including modern gadgets that use lead-free solder. This makes OSP a versatile choice for protecting circuit boards in various devices.
Limitations and Challenges of OSP
Despite the numerous advantages of the OSP process, it has some limitations that may affect its performance in certain application scenarios.
1.Not Very Durable
OSP is not very strong. If the circuit board is handled a lot or gets scratched, the OSP layer can wear off. If you keep touching it or dragging it, the OSP layers might start to peel off and stop protecting the PCB.
2.Near 6 months' Shelf Life
OSP coatings can’t protect the copper forever. Over time, the protective layer can break down, especially if the circuit board isn’t used quickly. So, circuit boards with OSP need to be used sooner rather than later.
3.Sensitive to Heat
When the circuit board gets too hot, the OSP layer can start to break down. This is a problem because soldering, the process of attaching electronic parts, involves a lot of heat. If the OSP layer melts or breaks down too early, it might not protect the copper properly.
4.Rework Challenges
Sometimes, after parts are soldered onto the circuit board, we need to fix or change something. With OSP, reworking (fixing) the board can be tricky because the protective layer might already be gone or damaged.
Circuit boards with OSP need to be stored and handled carefully to keep the protective layer intact. If they are stored in a humid or dirty place, the OSP layer might not work well.
5.Handling and Storage Issues
Circuit boards with OSP need to be stored and handled carefully to keep the protective layer intact. If they are stored in a humid or dirty place, the OSP layer might not work well.
6.Not Suitable for All Environments
OSP might not be the best choice for circuit boards that will be used in harsh environments, like very hot, cold, or humid places.
Application of OSP
Organic Solderability Preservative (OSP) is used in many different types of electronic devices to protect the tiny copper paths on circuit boards.
- Gadgets: OSP helps keep the circuit boards in smartphones, tablets, and laptops working well.
- Cars: It’s used in the electronic parts of cars, like in the control systems and screens.
- Medical Devices: OSP is used in medical tools, like heart monitors and health trackers, to keep them reliable.
- Phones and Internet: OSP-coated circuit boards are used in devices like routers and network equipment that help us communicate.
- Factories: In big machines and robots used in factories, OSP helps the circuit boards handle tough conditions.
- LED Lights: It’s used in LED lights to make sure they work properly.
- Airplanes and Defense: OSP is used in the electronic parts of airplanes and defense systems to keep them reliable.
Conclusion
Organic Solder Shield (OSP) technology is an integral part of modern PCB manufacturing, with key benefits including: clean copper surfaces, ease of use, environmental friendliness, improved soldering performance and cost effectiveness, while being compatible with current technology limitations; drawbacks include limited durability, heat sensitivity, rework difficulties and not suitable for all environmental conditions.
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