How to choose surface treatment processes for HASL, ENIG, and OSP circuit boards?

After designing the PCB board, we need to choose the surface treatment process for the circuit board. The commonly used surface treatment processes for circuit boards now include HASL (surface tin spraying process), ENIG (gold deposition process), and OSP (anti oxidation process). How should we choose the commonly used surface treatment processes? Different PCB surface treatment processes result in different fees and ultimately different effects. You can choose according to your actual situation. Below, I will explain the advantages and disadvantages of three different surface treatment processes: HASL, ENIG, and OSP.

1. HASL (surface tin spraying process)

Tin spraying process can be divided into lead-based and lead-free tin spraying. Tin spraying was once the most important surface treatment process in the 1980s, but nowadays, fewer and fewer circuit boards choose tin spraying process because circuit boards are developing towards "small and fine" direction. Tin spraying process can cause tin beads and spherical tin points during the soldering of fine components, leading to poor production. PCBA processing plants often choose ENIG and SOP surface treatment processes in pursuit of higher process standards and production quality.

Advantages of lead spray tin: lower price, excellent welding performance, better mechanical strength, glossiness, etc. compared to lead spray tin.

Disadvantages of lead spray tin: Lead spray tin contains lead heavy metals, which is not environmentally friendly and cannot pass environmental evaluation such as ROHS.

Advantages of lead-free tin spraying: low price, excellent welding performance, and relatively environmentally friendly, able to pass environmental evaluation such as ROHS.

Disadvantages of lead-free tin spraying: mechanical strength, glossiness, etc. are not as good as lead-free tin spraying.

The common drawback of HASL is that it is not suitable for welding pins with fine gaps and components that are too small, as the surface flatness of the tin spray plate is poor. In PCBA processing, it is easy to produce tin beads, which can cause short circuits in fine gap pin components.

2. ENIG (Gold Deposition Process)

Sinking gold technology is a relatively advanced surface treatment process, mainly used on circuit boards with connection functional requirements and long storage life on the surface.

The advantages of ENIG: it is not easy to oxidize, can be stored for a long time, has a flat surface, and is suitable for welding fine gap pins and components with small solder joints. Repeated reflow soldering is not likely to reduce its solderability. Can be used as a substrate for COB wiring.

The disadvantages of ENIG are high cost and poor welding strength, as the use of non electroplated nickel process can easily lead to black disc problems. The nickel layer will oxidize over time, and long-term reliability is a concern.

3. OSP (Anti oxidation Process)

OSP is an organic film formed chemically on a bare copper surface. This layer of film has anti oxidation, heat shock resistance, and moisture resistance to protect the copper surface from further rusting (oxidation or vulcanization, etc.) in a normal environment; Equivalent to an anti oxidation treatment, but in the subsequent welding high temperature, the protective film must be easily removed by the flux quickly, and the exposed clean copper surface can immediately combine with the molten solder to form a solid solder joint in a very short time. At present, the proportion of circuit boards using OSP surface treatment technology has significantly increased, because this process is suitable for low process circuit boards as well as high process circuit boards. If there are no surface connection functional requirements or storage period limitations, OSP process will be the most ideal surface treatment process.

Advantages of OSP: It has all the advantages of bare copper plate welding, and expired (three-month) boards can also undergo surface treatment again, but usually only once.

The disadvantage of OSP is that it is easily affected by acid and humidity. When used for secondary reflow soldering, it needs to be completed within a certain period of time, and usually the effect of the second reflow soldering will be relatively poor. If the storage time exceeds three months, it must be resurfaced. Please use it within 24 hours after opening the packaging. OSP is an insulation layer, so the test points must be printed with solder paste to remove the original OSP layer before they can contact the needle points for electrical testing. The assembly process requires significant changes. If the unprocessed copper surface is detected, it will be detrimental to ICT. Over pointed ICT probes may damage the PCB, requiring manual precautions to limit ICT testing and reduce test repeatability.

The above is an analysis of the surface treatment processes for HASL, ENIG, and OSP circuit boards. You can choose which surface treatment process based on the actual usage of the circuit board.