About the difference between various surface treatment processes of circuit boards
The main factor that determines the quality and positioning of a board is the surface treatment process. For example, OSP tin spraying, gold plating, and immersion gold. Relatively speaking, immersion gold is for high-end boards. Due to its good quality, immersion gold is also relatively costly. Therefore, many customers choose the most commonly used tin spraying process. Tin spraying is divided into lead tin spraying (i.e. hot air leveling) and lead-free tin spraying. You can see the difference between each process below;
After making circuit boards for a long time, you will always encounter various problems.
For example, some end users require lead-free spraying samples. When they are welded, processed and debugged, manual welding always feels that it is not as easy to tin as lead. At this time, it is not sure whether it is the problem of the circuit board factory or the problem of welding itself.
In fact, when manually welding samples, it is easier to tin with lead. The wettability of lead is much better than that of lead-free. Because lead will increase the activity of tin wire during welding. However, lead is toxic, and the melting point of lead-free tin is high, so the welding point is relatively much stronger.
Leaded and unleaded tin can also be distinguished visually: leaded tin is brighter, and lead-free tin (SAC) is darker.
Lead-free process: A basic concept of lead-free electronic assembly is that in the soldering process, whether it is manual soldering, dip soldering, wave soldering or reflow soldering, the solder used is lead-free solder (pb-feer soder). Lead-free solder does not mean that the solder is 100% lead-free. In lead solder, lead exists as a basic element. In lead-free solder, the basic element does not contain lead.
Lead process: In the traditional soldering process of printed circuit board assembly, tin-lead (sn-pb) solder is generally used, in which lead exists and plays a role as a basic element of the solder alloy. Leaded solder alloy has low melting point and low welding temperature, which causes less thermal damage to electronic products; leaded solder alloy has small wetting angle, good solderability, and less possibility of “false welding” of product solder joints; solder alloy has good toughness, and the formed solder joints have better vibration resistance than lead-free solder joints.
Compared with the three surface treatments of OSP, lead-free tin spraying and immersion gold process, although they are all relatively environmentally friendly,
but most ordinary conventional boards are more used for the first two. Because the cost is relatively low.
OSP is suitable for fine lines and fine SMT spacing. The operating temperature is low, there is no damage to the board, and it is easy to rework and repair.
However, the board made by OSP process is not acid-resistant, and the high humidity environment will affect its welding performance.
It needs to be welded in the shortest possible time. Although immersion gold and gold plating are both relatively wear-resistant, there is still a difference between the two: in the case of gold plating, gold is only plated on the surface, and there is only copper-nickel on the side. It is easy to oxidize over time. This is a defect of gold plating process and cannot be used in high-demand occasions.
If you do immersion gold, the entire pad, including the side, can be plated with nickel gold. It is currently the most stable and can be used in various occasions. However, immersion nickel gold has a more troublesome and difficult to detect problem, that is, the adhesion is not as good as gold plating, and it is easy to fall off after a period of use.