7 different surface finish for PCB boards

A conventional printed circuit board (PCB) has a copper layer on the board. If the copper layer is not protected, it will be oxidized and damaged, directly affecting subsequent soldering. And surface finish is to enable protection of the surface and good solderability of the pcb. There are 7 different surface finish are available in PCBHERO: HASL, ENIG, OSP, Hard gold, IS, ENEPIG and IT. 

1. Hot Air Solder Levelling (HASL)

After the board is completely covered with solder, the excess solder on the surface and the hole is blown off by high-pressure hot air, and the solder attached to the pad and the hole wall is leveled; there are two types: lead spray tin and lead-free tin spray. It's generally the cheapest finish available and a great choice for general-purpose boards.

Advantages: low cost, maintain solderability throughout the manufacturing process etc.


2. Immersion gold(ENIG) 

A nickel-phosphorus layer is replaced on the copper surface through a chemical reaction, and then a layer of gold is replaced on the nickel layer.

Since the sulfur-containing compound from the solder mask is immersed in the plating bath, a non-conductive layer containing nickel and phosphorus may be formed on the coating, called a "black pad". And the problem like brittle nickel-phosphorus alloy may also appears.

Advantages: good solderability, flat surface, long storage life, can withstand multiple reflow soldering etc.

3. Organic Solderability Preservative (OSP )

OSP is to chemically grow a layer of organic film on the clean bare copper surface. This layer of film has anti-oxidation, thermal shock resistance, and moisture resistance to protect the copper surface from rusting (oxidation or sulfidation, etc.) in a normal environment; but in the subsequent soldering high temperature, this protective film must be very easy to be quickly removed by the flux, so that the exposed clean copper surface can be immediately combined with the molten solder into a strong solder joint in a very short time. But it is not suitable for multiple reflow soldering.

Advantages: Comparable with HASL in cost, good coplanarity, lead-free process etc.

4. Hard gold

Nickel and gold are electroplated on the same surface. It contains other metals so that to improve the wear resistance of the product. as well as increase the number of insertion and removal and electroplating of hard gold. The abrasion resistance of electric gold is relatively high. As the integration of IC becomes higher and higher, IC pins become more dense. The vertical spray tin process is difficult to flatten the thin pads, which brings difficulty to the SMT placement; in addition, the shelf life of the spray tin plate is very short. The gold-plated board just solves these problems, so the whole board gold plating is common in high-density and ultra-small surface mount processes.

Advantages: good solderability, flat surface, long storage life, can withstand multiple reflow soldering etc.


5.Immersion silver(IS) 

The silver is immersed in a metal layer of 0.1 to 0.6 microns on the copper layer to protect the copper surface.

Immersion silver process is between organic coating and electroless nickel/immersion gold. The process is relatively simple and fast; even if exposed to heat, humidity and pollution, silver can still maintain good solderability, but will lose its luster . Immersion silver does not have the good physical strength of electroless nickel/immersion gold because there is no nickel under the silver layer. As the immersion silver surface treatment with other unmatched good electrical properties, it can also be used in high-frequency signal board.

Advantages: good solderability, smooth surface, good replacement of HASL immersion etc.


Compared with immersion gold, chemical nickel palladium gold has an extra layer of palladium between nickel and gold. Palladium can prevent corrosion caused by substitution reaction and make full preparations for immersion gold. Gold is tightly covered on palladium, providing a good contact surface.

Advantages: long-term reliability of the coating, high reliability of soldering and wire bonding, avoid the risk of black pad etc.

7. Immersion Tin (IT)

Tin is immersed in the metal layer of 0.8 to 1.2um on the copper layer to protect the copper surface. Since all current solders are tin-based, the tin layer can match any type of solder. The tin-immersion process can form a flat copper-tin intermetallic compound. This feature makes tin-immersion have the same good solderability as hot-air leveling without the uneven problem of hot-air leveling, however, tin-immersion boards cannot be stored for too long.

Advantages: good solderability, smooth surface, relatively low cost etc.

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