PCB Plating


What is PCB plating?

PCB plating is a metal deposition process that ensures that these PCBs are protected from oxidation. PCB plating is not only to help assemble components, but also to increase the copper thickness of surface pads and conductors, as well as improve the strong copper connection between the layers in the vias. Electroless copper plating PCB is very convenient. In addition, in PCB design, PCB plating provides a clear surface finish and an accurate soldering surface for assembled components.
Through hole plating – The process of drilling holes with copper fill to provide a current path from the surface of the board to the inner layer, between two inner layers, or from one surface to another. These plated through-holes (PTH) are often referred to as through-holes.
Surface plating or finishing – The process of covering surface copper traces to prevent environment, oxidation, moisture, and contamination and to provide a more suitable surface for soldered components during printed circuit board assembly (PCBA).
Both of the processes listed above can be referred to as PCB electroplating. While the primary purpose of the two is to help facilitate good current flow along the circuit path of the board, there are differences in the materials used.
Simply put, PCB trace plating is an external trace that is also present on the PCB. In addition, they help protect the board. Therefore, if the PCB is not covered, the unfixed end of the circuit board may be oxidized. Also, this can lead to PCB damage. In addition, damage renders the ends of the board unusable. PCB plating options also have a lot of them.

What are the types of PCB plating process?

There are different types of production processes for circuit board plating. However, it is commonly divided into the following 5 main types of PCB plating:

Rare metals need to be plated on board edge connectors, board edge bumps or gold fingers to provide lower contact resistance and higher wear resistance. This technique is called pcb gold finger plating or protruding plating. In the PCB gold plating process, the operation requirements of selective gold plating PCB and electroless copper plating PCB are relatively high. Especially in the thickness of PCB copper plating and PCB gold plating and PCB hardness gold thickness, the requirements for high quality are higher. Gold plating is usually plated on the inside of the board-side connector, protruding from nickel. Manual or automatic plating of fingers or plate edges. Contact plug or gold finger gold plating is electroplating and plating. Replace the plated button. The steps involved in finger plated are:

  1. Choose prominent professional PCB assembly equipment that can meet your needs. Then, remove the coating. The purpose here is to remove the tin-lead coating.
  2. Rinse the protruding contact head thoroughly with water.
  3. Scrub with abrasives.
  4. Place the protruding contacts in activated immersion solution of 10% H2SO4 (sulfuric acid).
  5. Use a thickness of 4-5 microns. When you do, paint the protruding contacts with nickel.
  6. Take the time to clean the protruding contacts. The reason for this step is to remove mineral water.
  7. Treatment (gold infiltration).
  8. Continue with gold plating.
  9. Clean the protruding contacts correctly.

There are many ways to form an ideal coating on the borehole substrate wall. This is called pore wall activation in industrial applications. The commercial production process of printed circuits requires multiple intermediate tanks, each of which is stored. Storage tanks have their own control and maintenance requirements. Pcb through hole plating is an indispensable drilling process in the PCB manufacturing process.
As the drill bit passes through the copper foil and the substrate underneath, the heat generated will cause the insulating synthetic resin that makes up most of the substrate to melt, melting the resin and other drilling debris. It gathers around the hole and is applied to the newly exposed wall of the copper foil, which is actually harmful to the subsequent plating surface. The molten resin also leaves a thermal layer on the substrate wall that has poor adhesion to most activators. Plated through holes requires the development of a technique similar to decontamination and etching chemistry.
Prototyping of PCB Hole Plating. A suitable prototyping method is to use specially designed low-viscosity inks to form a film with high adhesion and high conductivity on the inner wall of each via. This eliminates the need for multiple chemical treatments. Only one application step is required, followed by thermal curing, forming a continuous film on the inside of all hole walls, which can be plated directly without further processing. This ink is a resin-based material with strong adhesion that can be easily bonded to most hot-polished holes, eliminating the need for etching steps. Learn more about other PCB inks.

The pins and pins of electronic components such as connectors, integrated circuits, transistors and flexible printed circuits are selectively plated for good contact and corrosion resistance.
This plating method can be manual or automatic, and the individual selection of each pin is very expensive, so batch soldering is necessary. The metal foil is usually flattened to the desired thickness end for die-cutting, chemical or mechanical cleaning, and then selectively used, such as nickel, gold, silver, iridium, button or tin-nickel alloy, copper-nickel alloy continuous plating nickel-lead alloy, etc. In the selective electroplating method, the part of the metal copper foil plate that does not require electroplating is first coated with an anti-corrosion film, and only the selected copper foil part is electroplated.

Another method of selective plating is called “brush plating”. This is an electrodeposition technique in which not all parts are immersed in an electrolyte. This electroplating technique only electroplates a limited area and has no effect on other areas.
Typically, rare metals are plated on selected parts of the printed circuit board, such as edge connectors and other areas. Brush plating is more commonly used for scrap board repair in electronics assembly shops. Special anodes (chemically reactive anodes such as graphite) are wrapped in an absorbent material (cotton swab) to bring the plating bath where it is needed.

Side plating is the metallization of the edge of the circuit board in a PCB. Edge plating, frame plating, plating profiles, side metal, these words can also be used to describe the same function.
Pcb side plating process: Drilling – Milling plating baths – cleaning – copper sinks.
Possible applications for side plating: Improve EMC performance by shielding multilayer internal areas such as HF boards.
The edges are used as a cooling function for additional cooling surfaces, and active heat dissipation can be used Cabinet connection, Board-to-board connection.
Design parameters: To ensure the productivity of side plating, overlapping copper (copper surfaces, pads, or traces) must be used to define metallized areas in the CAD layout. Minimum overlap: 500 m. On the connection layer, at least 300um of connecting copper must be defined. In the plated copper process, there should be a gap of at least 800m between the copper above the unconnected layer and the outer contour.
Since manufacturers need to secure the PCB to the production panel during this process, they cannot plate the entire edge. Therefore, some clearance is required when placing path labels. Manufacturing a circuit board using edge plating requires the layout of the board that requires edge plating before starting the through-hole plating process. This does not include the V-cut part of the plate that requires edge plating.

When The Working Temperature Of The Circuit is High, High TG FR4 Should Be Selected.


PCB plating process flow.

  • The first step is the chemical process, in which a thin copper layer is deposited on the surface area of the circuit board as well as inside the drilled hole. This is important in the PCB copper plating process.
  • Clean the holes drilled in the board to remove residues and contaminants generated during the drilling process. More PCB hole knowledge.
  • The interior of the wells is prepared using micro etching, which helps improve copper bonding.
  • Photoresist material is added to the bottom and top of the board and exposed to ultraviolet light. This UV exposure is limited to the free area without the pattern.
  • Next, wash off the photoresist and cover the board area with hardened photoresist.
  • The plate is connected to the cathode of the current and immersed in a chemical bath for plating. Dissolved copper is attracted to a negative charge and deposited on the exposed circuit.
  • Next, the board is immersed in a cleaning and plating bath to form a uniform copper layer.
  • After that, In the process of board manufacturing, the tin is plated on copper to protect the circuit.
  • Next, remove the non-circuit copper and photoresist.
  • In the last step, the tin is removed, and the copper circuit remains.

Read more detailed PCB manufacturing process.

PCB Plating Thickness Recommendations.

A typical PCB plating required thickness value is about 100 microinches. For sinking silver and OSP, typical thicknesses can be as low as about 10 microinches of thin laye.
Why is pcb copper plating thickness important? There are two reasons for this. First, the IPC-2221A standard specifies the minimum plating thickness for each IPC product category. If you want your product to meet any of the standard IPC product categories, then you need to make sure that your plating thickness meets its specifications. Generally, if you specify the product category as you usually do in manufacturing instructions, you imply a minimum plating thickness.

  • Another reason to worry about PCB plating thickness is its effect on losses. At low frequencies, you may not notice any effect on the frequency, so low-speed digital signals and sub-GHz radios don’t have to worry too much about PCB plating thickness.
  • Losses occur at millimeter-wave frequencies such as short-range radar (24GHz) and higher. At these frequencies, the roughness of copper becomes a very obvious loss factor. The thickness of the coating will determine the roughness as the signal propagates, which will be reflected in the skin effect resistance.

How to choose the right plating for your PCB?

If the contacts are not conductive or wear out easily, the lifespan of this electrical component will be greatly reduced, and your reputation for quality will be greatly reduced. This is why it is essential to choose the best contact plating to protect or even enhance the connections within the electrical components, depending on the environment in which the electrical components are used.
Here are three common PCB plating materials:

  • Gold-
    Although it is not as conductive as copper commonly used in wires today, gold is still extremely conductive. However, the real advantage of gold is that of all metal plating options, it is the least prone to oxidation, while copper is prone to corrosion. But the disadvantage is that it is expensive.
  • Tin-
    Compared to the high price of gold, tin is a very affordable plating option and common conductor. The tin market is much less volatile than the gold market, so PCB tin plating solutions are also plentiful, tin is also resistant to water corrosion, and the shipbuilding industry is famous for its use of tin in electrical components. PCB tin plating is also popular.
  • Nickel-
    Last but not least, if you need something really affordable to electroplate contact lenses, nickel is the way to go. It is highly resistant to corrosion – unless exposed to excessive moisture – and is even used to electroplate many other metals that are more susceptible to corrosion. In terms of electrical conductivity, nickel is also better than tin, but not as good as gold.

What are the types of PCB plating surface treatment?

Listed below are the surface preparation processes suggested for using different PCB plating materials.

This PCB surface treatment may be the cheapest option, but it is RoHS non-compliant due to the use of lead in plating. Immersion tin is a lead-free alternative that can be used on entry-level circuit boards.
Merit Shortcoming
Affordable It is easy to be damaged during transportation
Compatible with a wide range of solders Over time, tin filaments may form
The surface is very flat Multiple rework is inconvenient

HASL is popular among PCB plating types, but it is not as reliable as other plating materials. It is inexpensive and offers a lead-free option, so it can be used as an entry-level plating option. ENIG has excellent surface flatness, making it ideal for welding fine-pitched parts. It is Restriction of Hazardous Substances (RoHS) compliant and is durable and has a long shelf life. On the other hand, it is more expensive than other finishes like HASL.

Repairs can be carried outThe surface is relatively uneven
The price is cheaperIt is more difficult to weld in dry conditions
/May be damaged by thermal shock
Considering the disadvantages of SnPb and immersion tin, ENIG is now arguably the most popular surface treatment in the industry. In this electroplated material, nickel acts as a barrier between the copper and the thin gold surface layer of the part to be welded. Advantages and disadvantages of PCB Nickel Plating.
Merit Shortcoming
Welding is very easy Expensive
The surface is very flat Inconvenient rework
Sutures can be made with leads It is easy to lose signal at high frequencies

This electroplating material has a copper-nickel-palladium-gold layer structure that can be bonded directly to the plating layer through wires. The last layer of gold is very thin, as in the case of ENIG. The gold layer is soft, just like ENIG, so too much mechanical damage or deep scratches can expose the palladium layer.

The surface is very flatExpensive
It can also be used when the spacing is relatively smallMay make the material difficult to wet and weld
Sutures can be made with leadsProcessing lines require special configurations
This plating material is ENIG in nature, but has a very thick gold outer layer, so it is one of the most expensive pcb gold plating materials. The PCB Gold Plating Process is also important. The gold layer provides a hard surface that can be damaged, but pcb hard gold plating thickness makes it difficult for the nickel layer to be fully exposed. So, the pcb gold plating thickness needs to be tightly controlled.
Merit Shortcoming
The surface is very durable Expensive
Sutures can be made with leads Tremor occurs
/ The steps are cumbersome
This is the PCB plating material I chose for high-frequency applications. It forms a smooth interface with bare copper, so it does not increase conductor loss like other PCB surface treatments. The main disadvantage is tarnishing on the bare board, so it should be soldered and packaged as soon as possible after manufacturing. The disadvantage is that this surface treatment is sensitive to contaminants in the air or on the circuit board and must be kept in protective packaging to prevent their discoloration. Even with special packaging, its shelf life is around 12 months, and it must be used as soon as possible after exposure to air.
Merit Shortcoming
The surface is very flat Silver filaments may form
Sutures can be made with leads Small plating makes it difficult to form holes
It can also be used when the spacing is relatively small It is easy to change color after prolonged exposure

How to do PCB Plating Rework and Repair?

There are several different ways to perform PCB plating repair and restoration work, which will vary depending on the issue. However, for most repair and recovery jobs, there are some general steps you can follow.
First, you need to determine what the problem is. You can do this by visually inspecting the PCB for any damage or using a multimeter to test the continuity of the circuit. Once you’ve identified the problem, you need to decide on the best way to fix it.
Here are the steps to fix P CB Plating:

  • Gather the tools and other materials you need
  • Remove damaged pads or components
  • Clean the tracks and remove the solder
  • Place the copper strip on the track
  • Weld joints
  • Restore PCB boarded vias
  • Placing and welding components
  • Trim excess tape in the service area

After completing the above steps, most of the PCB boards can work. At the same time, you can also gain a deeper understanding of more comprehensive PCB rework knowledge.

Choose JHD to escort your PCB electroplating.

At JHD, we can make circuit and surface treatment decisions for your circuit board. Our engineers can provide you with PCB plating material suggestions and thickness selection suggestions. Not only that, but we can also help you select materials of high quality and the most suitable plating method. Choose us, JHD will strictly control the quality of your PCB manufacturing process. We have many years of experience in PCB plating to escort you.

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