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What is FR-4 PCB? Surface Treatment & Plating

Views: 253 Author: Site Editor Publish Time: 2023-05-31 Origin: Site

Dielectric FR-4 generally has a dielectric constant of 4 to 5. FR-4 is a mixture of epoxy binder and fiber glass cloth. FR means Flame Retardant.

FR-4 stands for a specific glass fiber reinforced epoxy laminate material and were designated by the National Electrical Manufacturers Association.

Paper phenol board (FR-1, 2)

Mainly used for single-sided boards. A printed circuit board made of paper impregnated with phenolic resin. It is characterized by high workability and low cost, and is widely used in consumer equipment.

It is weak against heat and humidity, and it warps easily and has low mechanical strength. Also, it is not suitable for through holes.

Mold costs are cheaper than glass substrates.

Paper epoxy board (FR-3)

It is used for single-sided boards as well as paper phenolic boards.

Due to its excellent heat resistance, moisture absorption, insulation resistance, and high frequency characteristics, it is often used in high-voltage circuits and circuits that require moisture resistance.

It is possible to form through-holes that are unsuitable for paper phenol. This is an intermediate grade between paper phenol substrates and glass/epoxy substrates.

Paper-based substrates are currently on the decline. Mold costs are cheaper than glass substrates.

Glass composite substrate (CEM-3)

The base material is a mixture of glass cloth and glass non-woven fabric, and is impregnated with epoxy resin.

It has excellent tracking resistance and is cheaper than glass epoxy (FR-4), so it is used in a wide range of double-sided boards, including home appliances and industrial equipment that cannot be handled with single-sided boards.

Glass epoxy board (FR-4)

Epoxy resin is impregnated into a glass woven fabric made of glass fiber.

Although the price is more expensive than that of glass composite substrates (CEM-3), materials with various copper foil thicknesses are also available and are highly versatile, and are used for multilayer substrates as well as double-sided substrates.

Teflon substrate

Teflon is non-flammable and exhibits extremely high insulation and low dielectric constant, so it is mainly used in circuits that require high-frequency characteristics.

Due to the high price and the use of special chemicals for through-hole plating, the application area is not very wide.

Ceramic substrate

Ceramic substrates use ceramic as the base material. It is manufactured by mixing alumina or glass with ceramics and firing.

It has many excellent properties such as little dimensional change, insulation, high frequency properties, and thermal conductivity, but it is fragile and very expensive.

Flexible substrate

Its greatest features are its thinness and flexibility. Polyimide, polyester, etc. are used as the base, and are mostly used for three-dimensional circuits and moving parts such as printers.

Metal base substrate

Typical metal-based substrates use aluminum or copper as the base material.

Although it is more expensive than CEM-3 and FR-4, it is cheaper than ceramic substrates and has excellent thermal conductivity.


On the surface of the printed circuit board, there are exposed lands and pads, which are not coated with resist, where electronic components are soldered.

The lands and pads are made of copper, so they will oxidize and rust if left untreated. Due to the presence of rust, there are cases where solder does not stick well when mounting parts, resulting in defects.

In order to prevent oxidation of copper, it is necessary to apply plating (plating, plating) that is difficult to oxidize the surface of copper and coating with chemicals for the purpose of preventing oxidation, and these are called surface treatments.

There are various types of surface treatment methods such as pre-flux treatment (Tough Ace treatment), eutectic solder leveler, lead-free solder leveler, electroless gold plating, and electrolytic gold plating.

It is also necessary to select an appropriate surface treatment according to the component mounting conditions and product specifications (RoHs compliance, etc.), so if it is unclear which one is compatible, it is necessary to check.

Water-soluble preflux treatment

Prefluxing is the most commonly used surface treatment method in printed circuit board manufacturing.

It is often chosen because of its low cost and excellent connection reliability with solder during mounting.

However, the recommended storage period after preflux is applied is only guaranteed for about 3 months, so it is not suitable for long-term storage. Pre-flux treatment keeps the cost low, but the storage period is short.

Eutectic solder leveler

A eutectic solder leveler is a surface treatment method in which a printed circuit board is immersed in melted solder in a device called HAL, and the solder is applied to the copper of the land and pad. Excess solder is blown off with hot air from a device called an air knife. 

Solder is composed of an alloy of 63% Sn (tin) and 37% Pb (lead).In recent years, the use of lead-free solder levelers has increased due to concerns that the lead component of solder may affect the human body. I'm here.

The eutectic solder leveler has excellent solder wettability, although there are concerns that it may be harmful to the human body.

Lead free solder leveler

Lead-free solder is also called lead-free solder or Pb-free solder.

Lead-free solder is an alloy composed of 1000 ppm (0.1 wt %) lead content, which makes it a RoHS compliant solder leveler.

Since it has a higher melting point than eutectic solder and is inferior to solder wettability, it used to cause problems during mounting, but in recent years it seems to have improved considerably.

*Because lead is not used, there is little impact on the human body, but the characteristics of the lead-free solder leveler are that it has poor wettability and makes it difficult to control the temperature of the soldering iron. We support both eutectic solder leveler and lead-free solder leveler treatment.

Nickel plating

It is highly glossy and rust-resistant, and is used for decoration and anti-corrosion purposes.

Hardness (HV) is high, and Ni hardness (450-550HV) is higher than Ag hardness (90-110HV). For this reason, it is used for connector terminals or switch contacts (sliders). Nickel plating is also used to suppress galvanic corrosion.

Galvanic corrosion is a phenomenon in which metals with a high ionization tendency and metals with a low ionization tendency are corroded when they come into contact with each other.

When a potential difference occurs between dissimilar metals, it becomes a local battery, ionizing the metal and causing corrosion.

In order to suppress this galvanic corrosion, nickel plating is applied to prevent galvanic corrosion.

Electroless gold plating

Electroless gold plating and electrolytic gold plating have similar names and finishes, but their uses and costs are completely different.

Electroless gold plating is an alloy treatment of Ni and Au. Basically, the nickel plating layer is 3.0 μm and the gold plating layer is 0.03 μm, and most of the components are nickel.

It has excellent solder wettability and high surface smoothness, making it suitable for mounting small parts.

Electrolytic gold plating

Electrolytic gold plating has a thickness of 0.3 μm, which is thicker than electroless gold plating. The cost will be higher as well.

It is suitable for places where it will be inserted and removed many times. It is not suitable for component mounting because it has poor solder wettability.

Electroless bond

Mainly for COB applications, especially gold plating for wire bonding pads.

Due to miniaturization and high density, it became difficult to arrange lead wires, so it was put into practical use.

Soft gold plating is applied to the nickel base.

Electrolytic bond

This refers to the gold plating treatment of wire bonding pads. The current mainstream is electroless bonding. We outsource both electroless gold plating and electrolytic gold plating. Solder plating is compatible only with electrolytic solder plating method.

In the past, it was widely adopted in opposition to the Gold Register Law, and many were deployed in landless.

In recent years, due to environmental issues, there has been a change to a different method that does not use solder plating.

Why Victory PCB?

Victory PCB offers reliable and heat resistant FR4 PCB, so you can be sure to find one that meets your needs. They also offer competitive prices, so you can save money on your PCBs.

When selecting an FR4 PCB manufacturer in China, it is essential to consider the following decisive factors:

· Price

· Quality

· Turnaround time

· Customer service

By considering these factors, you can be sure to choose the best FR4 PCB manufacturer for your needs.

About The Author

I am the Engineering and Sales supervisor working in Victorypcb from 2015. During the past years, I have been reponsible for all oversea exhibitions like USA(IPC Apex Expo), Europe(Munich Electronica) and Japan(Nepcon) etc. Our factory founded in 2005, now have 1521 clients all over the world and occupied very good reputation among them.


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