The advantages and disadvantages of common PCB surface treatment

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Copper is prone to oxidation in the air, which can heavily impact the soldering of printed circuit boards (PCBs). This can lead to the formation of false and weak solder joints, resulting in poorly soldered components. To address these issues, a process called PCB surface finish is used during production. This involves applying a special material, such as plating, to the pads to protect them from oxidation.

There are various types of PCB surface finishes available, including HASL with lead or lead-free, OSP, Immersion Gold (ENIG), Immersion Tin, Immersion Silver, Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG), Hard Gold, and more. Additionally, there are specific surface finishes designed for particular application scenarios.

Those involved in the printed circuit board (PCB) industry understand that PCBs have copper finishes on their surface. If left unprotected, the copper will oxidize and deteriorate, rendering the circuit board useless. The surface finish plays a crucial role in connecting the component and the PCB. The finish serves two vital functions: protecting the exposed copper circuitry and providing a solderable surface for component assembly (soldering) to the printed circuit board.

Bare copper board:

Advantages: low cost, smooth surface, good weldability (in the absence of oxidation).

Disadvantages: It is easy to be affected by acid and humidity, and cannot be stored for a long time. It must be used up within 2 hours after unpacking, because copper is easily oxidized when exposed to the air;

HASL board:

Advantages: the plating itself is tin, the price is lower, and the welding performance is good.

Disadvantages: Not suitable for welding fine gap feet and too small parts, because the surface flatness of the spray tin plate is poor. Solder bead is prone to be generated during PCB manufacturing process, and it is more prone to cause short circuit to fine pitch parts.

Gold plate (ENIG, Electroless Nickel Immersion Gold, electroless nickel immersion gold):

Advantages: It is not easy to oxidize, can be stored for a long time, and the surface is flat, suitable for welding fine gap feet and parts with small solder joints. The first choice for circuit boards with button circuits (such as mobile phone boards). Reflow soldering can be repeated many times without reducing its solderability. It can be used as a substrate for COB (Chip On Board) wire bonding.

Disadvantages: higher cost and poor welding strength.

OSP board (Organic Soldering Preservative, organic protective film):

Advantages: It has all the advantages of bare copper welding. The expired (three months) board can also be resurfaced, but usually only once.

Disadvantages: easily affected by acid and humidity. When used in the secondary reflow soldering, it needs to be completed within a certain period of time. Usually the effect of the second reflow soldering will be relatively poor. If the storage time exceeds three months, it must be resurfaced. It must be used up within 24 hours after opening the package. OSP is an insulating layer, so the test point must be printed with solder paste to remove the original OSP layer to contact the pin point for electrical testing.