Why is surface treatment necessary for PCB board?
2026-02-09
Surface treatment of PCB board is a key process to ensure their reliability and performance. The main reasons include the following aspects:
1. Prevent copper layer oxidation and ensure solderability
The core of PCB circuits is copper foil, but copper easily oxidizes in the air, forming insulating copper oxide, which can lead to cold solder joints or solder refusal. Surface treatment applies a dense protective layer on the copper, isolating it from the air and ensuring that the pads maintain good solderability within their effective period (usually several months to a year). This is the fundamental purpose of surface treatment.
2. Provide solderable surfaces suitable for different processes
Modern electronic assembly technologies are diverse, and surface treatments must match them. For example:
- Lead-free HASL: low cost, great process compatibility, suitable for through-hole components.
- ENIG (Electroless Nickel/Immersion Gold): flat surface, suitable for high-density pads and fine-pitch components, but may pose a 'black pad' risk.
- Immersion tin/silver: provides excellent coplanarity and solderability, but silver can migrate and tin can grow whiskers.
- OSP (Organic Solderability Preservative): environmentally friendly and low-cost, but the protective layer is thin and not resistant to multiple high-temperature exposures or long-term storage.
- ENEPIG (Electroless Nickel/Electroless Palladium/Immersion Gold): high performance, compatible with gold wire bonding and soldering, but expensive.
3. Meet specific electrical and mechanical performance requirements
Some treatments directly affect performance. For example, gold-plated surfaces have low and stable contact resistance, commonly used for gold fingers and key contacts that require frequent insertion or contact. Thick gold plating can also meet the low-loss transmission requirements for high-frequency wireless signals.
4. Adapt to environmental and lead-free trends
With the implementation of regulations like RoHS, traditional lead-containing HASL has been phased out, promoting the development of environmentally friendly processes such as lead-free HASL and OSP. Surface treatment has become an essential part of compliant production.
In summary, PCB surface treatment is a crucial bridge between PCB manufacturing and component assembly. It creates a 'compatible layer' between the copper traces and the external environment through physical and chemical methods. Choosing the appropriate surface treatment requires considering soldering processes, storage requirements, cost control, reliability, and end-use conditions. It is a decisive step in balancing performance, reliability, and economy. Without proper surface treatment, even the most precise PCB design cannot achieve stable electrical connections and long-term reliable operation.
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