PCBmanufacturerChina talk Printed circuit boards (PCBs) form the backbone of electronics, providing mechanical support and electrical connections between components.  The pads and traces on PCBs are typically made from copper, which readily oxidizes when exposed to air.  This oxidation can impair solderability and electrical performance.  Therefore, surface finishes like gold, silver or organic coatings are applied to protect the copper from corrosion.

This article explores the rationale behind using expensive gold plating versus cheaper silver or copper in PCB fabrication.

Overview of Common PCB Surface Finishes

The exposed copper traces on PCBs are plated with metal coatings or organic films to prevent oxidation.  The popular metallic surface finishes include:

· Immersion silver – Chemical silver plating process
· Organic solderability preservatives (OSP) – Organic protective films
· Electrolytic nickel/gold – Electroplated nickel underlying gold
· Electroless nickel/immersion gold (ENIG) – Electroless nickel then immersion gold

FPCsupplier  talk， of these, ENIG and electrolytic nickel/gold utilize gold to maximize corrosion resistance and conductivity.  But gold is also the most expensive finish.

The Need for Surface Finishes on PCBs
PCBs act as the platform for mounting and interconnecting electronic components.  The copper traces etched on the PCBs provide the conductive paths for signals and power.

However, copper readily forms non-conductive copper oxide when exposed to oxygen and moisture.  This oxidation can already begin during PCB fabrication itself when copper is exposed.

The oxidation process continues as bare copper is left exposed to ambient environments.  This is especially true for the soldering pads which need to be soldered later to attach components.  Oxide formation on pads deteriorates solderability.

Furthermore, the oxidation increases resistivity, which impairs electrical connectivity.  Poor solder joints as a result can cause device failures or reduced reliability.

Therefore, PCB surface finishes serve multiple functions:

· Prevent copper oxidation prior to soldering
· Enable reliable solder joint formation
· Maintain low contact resistance at joints
· Protect copper from corrosion over product lifetime

Why Gold is Used in PCB Fabrication

Gold provides unique advantages that make it the metal of choice for PCB surface finishes in many applications:

Excellent Corrosion Resistance
Gold is highly inert and does not oxidize or corrode under typical use conditions or ambient environments.  This preserves the purity and conductivity of the gold-plated traces over decades of product lifetime.

High Electrical Conductivity
Gold has the highest electrical conductivity rating after silver and copper.  But both silver and copper are prone to surface corrosion.  Gold’s excellent conductivity combines with its corrosion resistance.

Flexible Deposition Options
Gold coatings can be easily applied on PCBs through processes like electroless or electrolytic plating.  Thickness can be controlled as needed.

Outstanding Solderability
Gold allows formation of highly reliable solder joints without any wetting issues.  The solderability remains intact over storage periods.

Long Shelf Life
Gold maintains its purity and properties indefinitely.  This enables exceptionally long shelf lives for gold-plated PCBs.

Ductile Deposits
Gold provides ductile coatings that are less prone to cracking or fracturing under thermal cycling stresses.

Wire Bonding Ability
The gold finish permits high yield wire bonding, important for microelectronics.

Reworkability
Gold coatings allow multiple rework and repair cycles without losing surface integrity or properties.

Lead-Free Compatibility
Gold is fully compatible with lead-free solders and soldering processes.