Surface Finish and Final Processes

Surface Finish and Final Processes

Overview

Once the solder mask covers the traces, the copper at the pads remains exposed — unprotected, it would oxidize and undermine soldering. The surface finish (G stage) dresses this copper in an anti-oxidation “protective coat”, while the final processes (H stage) complete profiling, electrical testing, final quality inspection, and packing.

This article concludes the series, ending with a recap of the full 19-step route.

Surface Finish (G Stage)

Every conventional PCB has copper layers; unprotected copper oxidizes and degrades, directly affecting soldering. There are seven common protective finishes:

Finish	Full name	Key point	Advantages
HASL	Hot Air Solder Leveling	The board is fully coated with solder, then high-pressure hot air blows off the excess on the surface and in the holes and levels the rest; leaded and lead-free versions	Low cost; stays solderable throughout the process
OSP	Organic Solderability Preservative	Forms a thin, uniform protective layer on the copper	Cost comparable to HASL; good coplanarity; lead-free process
Plating Gold	Electroplated Nickel Gold	Electroplates nickel and a protective gold layer onto copper	Good solderability; flat surface; long shelf life; withstands multiple reflows
ENIG	Electroless Nickel Immersion Gold	Chemical displacement deposits a nickel-phosphorus layer, then a gold layer on top	Good solderability; flat surface; long shelf life; withstands multiple reflows
Gold Finger	—	Electroplated nickel-gold with a different gold composition (hard gold, wear-resistant)	Wear-resistant, low contact resistance; used for edge connectors
Immersion Silver (IS)	—	Immerses a 0.1–0.6 μm silver layer onto the copper	Good solderability; flat surface; a natural HASL replacement
Immersion Tin (IT)	—	Immerses a 0.8–1.2 μm tin layer onto the copper	Good solderability; flat surface; relatively low cost

Selection usually depends on: soldering process (lead-free/leaded), shelf life, cost, and appearance requirements (ENIG has become a common choice for high-end products).

Final Processes (H Stage)

01 Profiling

• Purpose: cut the board to the customer-specified dimensions
• Principle: mechanical cutting by CNC machines
• Main material: router bits
• Common forms: CNC routing, and V-cut (V-shaped scoring) — used for panel pre-scoring so finished boards snap apart along the groove; requires controlling the cut depth and remaining web thickness

02 Electrical Test

• Purpose: bare-board testing of PCB electrical performance (opens and shorts) to meet customer requirements
• Trade-offs among test methods:

Method	Principle	Pros	Cons	Best for
Dedicated	Custom bed-of-nails fixture	Fast throughput	Probes cannot be reused; high fixture cost	High volume
Universal on Grid	Universal grid fixture	Lower fixture cost	High equipment cost	Medium-high volume
Moving Probe (flying probe)	Two probes move in X/Y/Z to test each net’s endpoints in turn	No fixture; low cost	Low throughput	Samples, small batches, rush samples

03 Final Inspection and Laboratory

Final inspection/lab is the last quality review in the process, in two categories:

• Inspection items (appearance and dimensions): outline dimension, hole-to-edge distance, board thickness, hole diameter, line width/space, annular ring, and more
• Laboratory items (reliability): solderability, peel strength, micro section, thermal shock, ionic contamination, moisture and insulation resistance, impedance, and more

04 Packing and Shipping

The board is packed as the customer requires and shipped — completing the full journey of a PCB.

The Full 19-Step Recap

Expanding the eight stages into one line gives the complete PCB manufacturing route:

1. Inner layer   2. Lamination   3. Exposure   4. Developing   5. Etching
6. Strip         7. Lay-up       8. Pressing   9. Drilling     10. PTH
11. Lamination   12. Exposure    13. Developing 14. Cu+Sn plate 15. Strip
16. Etching      17. Tin strip   18. Silkscreen 19. Surface finish → final processes → shipping

Notice: the photoimage transfer and DES logic — “laminate → expose → develop → etch → strip” — appears three times (inner layer, outer layer, solder mask, in different forms). That is the process main thread emphasized in the first article.

Summary (Series Wrap-up)

• The seven surface finishes each have trade-offs; the ENIG/OSP/HASL choice directly affects solderability and cost
• The final processes handle three things: cut the profile (routing + V-cut), test opens/shorts (three test methods), and inspect before shipping (appearance + reliability checklists)
• Full recap: board cut → inner layer → lamination → drilling → metallization → outer layer → silkscreen → surface finish → final processes — 19 steps across eight stages

You have now walked the complete professional PCB manufacturing process. Recommended next reads:

• Chapter 24 (PCBA Manufacturing and Soldering) — assembling the bare board into a PCBA

Every step from “design file to manufactured part” deserves to be seen with your own eyes (or in a video). Understand the process, and you will make better designs.

Building a commercial IoT product?

We provide ESP32 ODM design-to-manufacturing services. From prototype to production — the team behind this tutorial can build it with you.

Talk to us →