What are the types of PCB pad processes?

PCB pad process is critical to the reliability of components welding, etc., different processes are applicable to different scenarios, common classifications and descriptions are as follows:

Classification by surface treatment process

Hot air leveling (HASL)

Principle: PCB dipped in molten tin-lead or lead-free alloy, hot air blowing excess solder.

Characteristics: low cost, mature process, good solderability with thick layer of solder, but poor surface flatness, not suitable for fine pitch components, lead-free HASL solderability is slightly worse.

Application: low-end consumer electronics, simple industrial control boards.

Chemical Immersion Gold (ENIG)

Principle: Copper pads are first immersed in nickel and then gold.

Characteristics: flat surface, suitable for fine-pitch components, gold layer of antioxidant, low contact resistance, but the cost is high, the nickel layer has a "black disk" risk.

Applications: smart phones, high-end communication equipment, etc.

Immersion silver (ImAg)

Principle: Copper soldering disk surface replacement reaction sinking silver.

Characteristics: flat surface, good solderability, low cost, but the silver layer is easy to oxidize, "silver migration" risk.

Applications: medium precision digital circuits, some automotive electronics.

Immersion tin (ImSn)

Principle: copper surface replacement reaction of tin.

Characteristics: Flat surface, suitable for fine pitch components, good solderability, but the thin layer of tin is easy to scratch.

Application: Replace HASL's lead-free process for consumer electronics, etc.

Electrolytic Hard Gold Plating

Principle: Electrolytic plating of gold containing alloy elements.

Characteristics: High hardness, wear-resistant, suitable for frequent insertion and removal of connector pads, but high cost.

Applications: connectors, key pads, slot gold fingers, etc.

Organic solder-preserving flux (OSP)

Principle: copper pad surface to form an organic film against oxidation.

Characteristics: low cost, simple process, flat surface, but short storage time, not resistant to multiple reflow soldering.

Applications: low-cost consumer electronics, high-density PCBs.

Electroplating nickel gold (ENEPIG)

Principle: Electroplated nickel first, then electroplated thin gold, and finally immersed gold.

Features: strong corrosion resistance, suitable for high reliability scenarios, but high cost.

Applications: automotive electronics, aerospace equipment, etc.

Classification by pad form and function

Ordinary welding pads: used for component welding, various forms, surface treatment commonly used HASL, ENIG, OSP.

Through-hole pads: both conductive and welding functions, common process for HASL or immersion gold.

Heat dissipation pads: used for high-power components heat dissipation, mostly HASL or immersed gold, need to design heat dissipation holes.

Gold finger: used for plugging connection, surface treatment for electroplating hard gold.

Process Comparison Summary

HASL low cost, good solderability but poor flatness, applicable to ordinary PCB; ENIG high cost but excellent performance in all aspects, applicable to fine pitch, high reliability equipment; OSP low cost, good flatness but short storage time, applicable to high-density, low-cost PCB; immersion silver cost medium, good solderability but easy to oxidize, applicable to medium-precision circuits; plating of hard gold high cost, good wear resistance, applicable to connectors, gold fingers. connectors, gold fingers.

Suggestions for selection

Choose HASL or OSP for low cost and large pitch; choose ENIG for fine pitch and high reliability; choose hard gold plating for frequent plugging and unplugging or high abrasion resistance; choose ENIG or ENEPIG for high humidity or long term storage; choose ENIG or ENEPIG for comprehensive product cost, reliability requirements, and component type.