Printed circuit boards are the brains and hearts of any simple to complex device invented by man. They are also known as printed wiring cards or printed wiring boards.
Before their advent, manufacturing companies used the laborious point-to-point method which was not very reliable because of frequent wire malfunctions at their junctions. Pcbnet.com is also one of the manufacturing company which provides best reliable PCB product. There were also cases of short circuits when the insulation cracked because of long usage. Other methods also used before were turret board or wire wrap for small productions. In wire-wrap, small wires were tightly-wrapped in each connection point. This method was more durable and changeable.
The structure of printed circuit boards can be likened to that of a layered cake. Each layer contains different components. They are laminated together with solder – a strong metal that serves as adhesive that connects the electronic components to the surface of the circuit board.
Printed circuit boards are essentially composed of the following:
1. Substrate or FR4
It is the base material or the board which is usually a fiberglass or high-temperature plastic like Kapton. It is a solid, thick and durable core that gives PCB firmness and stability. Other materials which are cheaper are phenolics and epoxies. These materials are not durable enough to last for long and used in low-end electronic devices or household products.
Phenolics in particular are easily delaminated or burned because of its low thermal decomposition temperature. It also emits a bad smell during the soldering process.
2. Copper foil
It is a thin layer of copper laminated to the board. It can be one-sided, two-sided or multi-layered. One-sided board contains all the electronic components on one side only. Double-sided ones have copper foils on each side of the substrate. These are used when the product contains more chips and components. Holes are drilled through the substrate to make electrical connection. These holes are plated with conducting materials to avoid short circuits. The multi-layered board contains layers of printed circuits which are separated by insulation. These layers are also electrically connected by plated holes from the surface to the last layer. To make a strong and inseparable board, the materials are pressed through pressure and heat for a longer period.
The layer above the copper foil is the soldermask. It is the colored layer of the board which is usually green. It is put on top of the copper layer to protect the copper etchings and to avoid accidental contact with conductive materials, metals and solder. It also prevents solder jumpers. Areas that are not used for soldering are covered with soldermask. The plate covering can be gold, tin, nickel or solder to etch away the excess copper.
It is important to prevent the quick oxidation process of bare copper. Oxidation diminishes the ability of the copper to be solderable. The traditional way is to coat the unneeded copper with tin-lead alloy. But in order to comply with Restriction of Hazardous Substances Directive (RoHS) that restricts the usage of lead in United States and European Union countries, new solder compounds are used. One example is SN100CL which is composed of 99.3 percent tin, 0.05% nickel, 0.7% copper, and 60ppm of germanium.
4. Legend printing
It is the layer placed above the soldermask where symbols, letters and numbers can be found to indicate the individual function of the board LED or pins. The printable layer contains important component designators, settings, test points, and other helpful instructions for the user. The popular printing methods are silkscreen printing, ink-jet printing, and liquid photo imaging. In silkscreen, white is the common color, but other ink colors can be used like red, black, yellow and gray. The inkjet printing method is becoming more popular because of its capacity to print bar codes with serial numbers.
By now, one thing should finally be clear to you – printed circuit boards vary in complexity, which can be seen from their structure.