The surface finish on a PCB protects the copper and provides a solderable surface for component attachment. The choice affects cost, shelf life, flatness, and reliability. Understanding the trade-offs helps you specify the right finish for your design.
HASL: The Budget Workhorse
Hot air solder leveling (HASL) is inexpensive and solderable, making it the default for many boards. Lead-free HASL meets RoHS requirements. Its main drawback is uneven surface flatness, which can be a problem for fine-pitch components and BGAs.
ENIG: Flat and Reliable
Electroless nickel immersion gold (ENIG) offers a flat surface, good shelf life, and excellent solderability for fine-pitch and BGA packages. It costs more than HASL, and the gold layer adds a premium that is justified for complex, high-reliability designs.
- HASL: lowest cost, fine for standard SMT and THT
- ENIG: flat surface, best for BGAs and fine pitch
- OSP: low cost and flat, but shorter shelf life
- Immersion silver: flat, good for high-frequency designs
OSP: Flat and Cost-Effective
Organic solderability preservative (OSP) is a flat, low-cost finish with good coplanarity. Its shelf life is shorter, and the protective layer is consumed during soldering, so assembly must be scheduled carefully. OSP suits boards assembled quickly after fabrication.
Match the finish to your assembly process, component density, and shelf-life needs. When in doubt, ask your assembler which finish they handle most reliably.
