Printed Circuit Board Products and Its types of Finishes

PCB stands for Printed Circuit Board which is responsible for physically supporting the circuits and wiring of any electronic goodies. It has a print of circuits embedded on it which are done by a conducting material, so it seems that it is printed but the board is highly conductive and helps in making an electronic gadget work.

The sole purpose of PCB’s are to provide a solid base so that the wiring can sit on it perfectly and in the same manner it can be put inside a machine. Every electronic device from parts of a computer like graphic cards, mother boards, to home appliances like washing machines, microwaves, fridges and television are wired on a printed circuit board.

These are called “printed” because they have circuit marks, conductive traces and vias on them. A “via” (Latin for path or way) is an electrical connection between layers in a physical electronic circuit that goes through the plane of one or more adjacent layers. A “via” is a small opening in an insulating oxide layer that allows a conductive connection between different layers.

There are different types of PCB factory which provides PCB on the basis of different conductive material used:
• Silver PCB: it is used as silver is highly conductive and the coats the copper from getting oxidized.

• Electroless Nickel immersion gold PCB: It has two layer of metallic coating over catalyzed copper. Gold protects the nickel from oxidation during storage and provides low contact resistance.

• Organic Solderability Preservative PCB: protects copper from oxidizing before assembly and is very thin at the range of (100-4000 Angstroms).

• Sn/Pb Hot Air Solder Level (HASL) with SN100CL alloy PCB: contains 63% tin and 37 % lead. The common thickness ranges from .00003” - .0015” (30-1500 µ”) and the melting temperature is 183 degrees C.

• Lead-Free HASL:  same process as the previous one, common alloys used are Sn/Cu/Co, Sn/Cu/Ni/Ge. It is slightly more uniform than the sn/pb one and has a higher melting temperature of 228 degrees C and thickness ranges from .0003”-.001” (300-1000 µ”).

• Immersion (White) Tin: it is formed with the intermetallic joint of copper/tin best used for backplane panels.

• Immersion Silver: it has the metallic solderability preservative with 8-15 micro inch of sheer silver and has an excellent solderability and can be easily bonded with aluminum wire.

• Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG):  layer from 120 – 240 µ” of nickel is deposited on copper and is the fastest growing surface finish as it forms solder joints with SAC solders.

Read also: Support of a Printed Circuit Board

Support of a printed circuit board

A printed circuit board (PCB) is the board base for physically supporting and wiring the surface-mounted and socket components in most electronics. It mechanically supports and electrically connects electronic components using conductive tracks, pads and other features etched from copper sheets laminated onto a non-conductive substrate. PCBs can be single-layer for simple electronic devices. Printed circuit boards for complex hardware, such as computer graphics cards and motherboards, may have up to twelve layers. PCBs are most often green but they can come in any color.

Purpose
Printed circuit board supports the wiring done in an electronic device. The sole purpose of PCB’s are to provide a rigid base so that the wires and connections can sit on it firmly and in the same fashion it can be put inside a machine. Every electronic device from computer parts like graphic cards, mother boards to home appliances like toasters, microwaves, fridges and television are wired on a printed circuit board.
These are called “printed” because they have circuit marks, conductive traces and vias on them. A “via” (Latin for path or way) is an electrical connection between layers in a physical electronic circuit that goes through the plane of one or more adjacent layers. A “via” is a small opening in an insulating oxide layer that allows a conductive connection between different layers.

Read Also: PCB and it`s connections!

History
Printed circuit boards evolved from electrical connection systems that were developed in the 1850s. Metal strips or rods were originally used to connect large electric components mounted on wooden bases. In time the metal strips were replaced by wires connected to screw terminals, and wooden bases were replaced by metal chassis. But smaller and more compact designs were needed due to the increased operating needs of the products that used circuit boards. In 1925, Charles Ducas of the United States submitted a patent application for a method of creating an electrical path directly on an insulated surface by printing through a stencil with electrically conductive inks. This method gave birth to the name "printed wiring" or "printed circuit”.

Method of production by PCB Manufacturer
Components on a printed circuit board are electrically connected to the circuits by PCB manufacturer using two different methods: the older "through hole technology" and the newer "surface mount technology." With through hole technology, each component has thin wires, or leads, which are pushed through small holes in the substrate and soldered to connection pads in the circuits on the opposite side. Gravity and friction between the leads and the sides of the holes keeps the components in place until they are soldered. With surface mount technology, stubby J-shaped or L-shaped legs on each component contact the printed circuits directly. A solder paste consisting of glue, flux, and solder are applied at the point of contact to hold the components in place until the solder is melted, or "reflowed," in an oven to make the final connection. Although surface mount technology requires greater care in the placement of the components, it eliminates the time-consuming drilling process and the space-consuming connection pads inherent with through hole technology. Both technologies are used today.

Two other types of circuit assemblies are related to the printed circuit board. An integrated circuit, sometimes called an IC or microchip, performs similar functions to a printed circuit board except the IC contains many more circuits and components that are electrochemically "grown" in place on the surface of a very small chip of silicon. A hybrid circuit, as the name implies, looks like a printed circuit board, but contains some components that are grown onto the surface of the substrate rather than being placed on the surface and soldered.