Introduction about OSP/ENTEK

Organic Surface Protectant (OSP) is a type of water based, organic surface finish that is typically applied to copper pads on a PCB. OSP is an organic chemical compound that will selectively bond to copper pads and provides an organometallic layer to protect that copper layer. However, OSP is not as robust as HASL and is very sensitive to small abrasions requiring gloves to avoid scratches. OSP is an environmentally-friendly compound, and extremely green in comparison with other lead-free finishes, which typically have more toxic substances or require substantially higher energy consumption. OSP is a good lead-free surface finish with very flat surfaces, but it has a very short shelf life. To apply this surface finish, you only need to dip the PCB into a chemical bath of the OSP compound, but you must note that this may only be done after all other processes are finished, including Electrical Test and Inspection. OSP is not a standard surface finish and incurs extra cost if chosen.See below figure 1:

Figure 1: Example of an OSP Surface Finish

Pros

• Lead-free
• Flat surface
• Simple process
• Repairable
• Cost-Effective

Cons 

• Not good for PTH (Plated Through-holes)
• No Way to Measure Thickness
• Short Shelf Life
• Can Cause ICT Issues
• Exposed Cu on Final Assembly
• Handling Sensitive

Konw more for different surface finish choices.