In 2016, copper was used in printed circuit boards (PCBs) to interconnect components on the substrate. Although it is a good conductor for forming the conductive paths and patterns on the PCB, it is easily damaged by oxidation and corrosion if exposed to air for extended periods. Therefore, various techniques must be used to protect copper traces, vias, and plated vias, including organic coatings, oxide films, and electroplating.
Organic coatings are very easy to apply, but due to variations in concentration, composition, and curing time, they are unsuitable for long-term use and can even lead to unpredictable deviations in solderability. Oxide films can protect circuits from corrosion, but they do not maintain solderability. Electroplating or metallization processes are standard practices for ensuring solderability and protecting circuits from corrosion, playing a crucial role in the manufacture of single-sided, double-sided, and multilayer printed circuit boards. In particular, plating a solderable metal layer onto printed lines has become a standard practice for providing a solderable protective layer for copper printed lines.
Printed circuit board
In electronic devices, the interconnection of various modules often requires printed circuit board (PCB) connectors with spring contacts and matching PCBs with interconnecting contacts. These contacts must have high abrasion resistance and very low contact resistance, which necessitates plating them with a rare metal, the most commonly used being gold. Other metal plating methods can also be used on the printed lines, such as tin plating, ballast plating, and sometimes copper plating in certain areas.
Another type of coating on copper printed circuit boards is an organic material, typically a solder resist film. A thin epoxy resin film is applied using screen printing technology to areas where soldering is not required. This process of applying an organic solder resist does not require electron exchange; when the circuit board is immersed in a chemical plating solution, a nitrogen-resistant compound adheres to the exposed metal surface without being absorbed by the substrate.
The precision technology and stringent environmental and safety requirements of electronic products have spurred significant advancements in electroplating practices, most notably in the manufacture of highly complex, high-resolution multi-substrate technologies. In electroplating, the development of automated, computer-controlled equipment, sophisticated instrumentation for chemical analysis of organic and metallic additives, and techniques for precisely controlling chemical reaction processes have propelled electroplating technology to new heights.
There are two standard methods for growing metal add-ins in circuit board conductors and vias, as follows :
1. Circuit plating
In this process, copper layer formation and etching resist metal plating are only performed on areas with designed circuit patterns and vias. During the circuit plating process, the increased width on each side of the circuit and solder pads is roughly equivalent to the increased thickness of the plated surface; therefore, allowance must be left on the original film.
In circuit plating, most of the copper surface is masked with resist, and plating is only performed on areas with circuit patterns such as traces and solder pads. Because the surface area to be plated is reduced, the required power supply current is typically significantly lower. Furthermore, when using contrast-reversing photosensitive polymer dry film plating resists (the most common type), the negative film can be made using relatively inexpensive laser printers or drawing pens. Less copper is consumed at the anode in circuit plating, and less copper needs to be removed during etching, thus reducing the analysis and maintenance costs of the electrolytic cell. The disadvantage of this technique is that the circuit pattern needs to be plated with tin/lead or an electrophoretic resist material before etching, and then removed before applying solder resist. This adds complexity and an additional wet chemical solution treatment process.
2. Full board copper plated
In this process, all surface areas and drilled holes are copper-plated. A resist is then applied to the unwanted copper surfaces, followed by etching resist metal plating. Even for a medium-sized printed circuit board, this requires a drilling process capable of providing a considerable current to create an easy-to-clean, smooth, and bright copper surface for subsequent processes. Without a photoplotter, a negative film is used to expose the circuit pattern, making it more commonly used in contrast-reversal dry film photoresist.
Etching a copper-plated circuit board will remove most of the plated material again. Due to the increased copper carrier liquid in the etchant, the anode is subjected to additional corrosion, which is greatly aggravated.
