PCB Technical - What is circuit board tin spraying and anti-oxidation?

In the circuit board industry, common surface treatment processes are: hot air leveling, oxidation resistance (OSP), electroless nickel/immersion gold, immersion silver, immersion tin, etc. Some friends are not very clear about what is tin spraying and anti-oxidation and the difference between them, the following editor will talk about it in detail.

Circuit board spray tin introduction
The so-called tin spraying is to immerse the circuit board in molten tin and lead. When enough tin and lead is attached to the surface of the circuit board, hot air pressure is used to scrape off the excess tin and lead. After the tin-lead is cooled, the soldered area of the circuit board will be stained with a layer of tin-lead of appropriate thickness. This is the general procedure of the tin-spraying process.
Circuit board spray tin introduction

PCB surface treatment technology, currently the most widely used is the spray tin process, also called hot air leveling technology, which sprays a layer of tin on the pad to enhance the conduction performance and solderability of the PCB pad.

Tin spraying SMOBC&HAL) is the most common form of surface coating for circuit board surface treatment. It is widely used in the production of circuit boards. The quality of spraying tin directly affects the quality of soldering during subsequent customer production. And solderability; therefore, the quality of spray tin has become a focus of quality control for circuit board manufacturers.

Circuit board anti-oxidation introduction
Anti-oxidation is also called OSP. OSP is a process for surface treatment of printed circuit board (PCB) copper foil that meets the requirements of the RoHS directive. OSP is translated as organic solder protection film, also known as copper protection agent. Simply put, OSP is to chemically grow a layer of organic film on the clean bare copper surface.

This layer of film has anti-oxidation, thermal shock resistance, and moisture resistance to protect the copper surface from rusting (oxidation or sulfidation, etc.) in a normal environment; but in the subsequent welding high temperature, this kind of protective film must be very It is easy to be quickly removed by the flux, so that the exposed clean copper surface can be immediately combined with the molten solder into a strong solder joint in a very short time.

With the development of electronic products that are light, thin, short, miniaturized, and multifunctional, printed circuit boards are developing in the direction of high precision, thinness, multilayer, and small holes, especially the rapid development of SMT As a result, high-density thin boards for SMT (such as printed boards such as IC cards, mobile phones, notebook computers, tuners, etc.) continue to develop, making the hot air leveling process less and less suitable for the above requirements.

The difference between tin spraying and anti-oxidation
Tin spraying has a layer of tin on the surface, and the oxidation-resistant surface is a layer of oxide film. The process of spraying tin is before molding, and the process of anti-oxidation is after molding. The oxidation resistance is flatter than spraying tin, which is more conducive to subsequent SMT.