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Posted on 15 June 2019

Printed Circuit Boards (PCBs)

 

 

 

 

 

 

 

Printeed circuit boards (PCBs) are normally used to mechanically support and electrically connect electronic components using conductive pathways, tracks, or signal traces carved from copper sheets laminated onto a underlying nonconductive layer. Printed circuit boards are used in virtually all but the simplest commercially produced electronic devices. Some of the most important PCB details include the material used to make the board and the thickness of the board. Most PCBs are made of FR4, a fiberglass reinforced epoxy laminate. In Europe, most PCBs used in industrial applications have a standard thickness of 1.6 mm. Naturaly, multilayer PCBs are thicker. In North America, a thickness of 2.1 mm is also popular.

Types of PCBs

Conventional PCBs

Conventional printed circuit board (wave soldered)

Figure 1. Conventional PCB (wave soldered)

Conventional PCBs are attached to components using wave soldering or hand soldering. Wave soldering is a large scale soldering process by which electronic components are joined to a PCB to form an electronic assembly. The name is derived from the use of waves of molten solder in the soldering process. Wave soldering is ideal for boards which are manufactured with conventional leaded components and some surface mount boards that use larger components. Wave soldering is applied at temperatures as high as 200° C.

Using wave soldering, a first set of plated through holes in the PCB are covered by a protective solder mask on the solder side of the PCB while a second set of plated through holes are exposed. Electrical components are placed on the component side with leads inserted in the set of holes. The solder mask prevents solder from flowing into the first set of holes during wave soldering. Conductive pins designed for press fitting into the first set of holes are inserted to define connecting pins on each side of the PCB following wave soldering. This ensures the accomodation of both wave soldering and press fit operation.This is important if components are to be wave soldered to a PCB without interfering with the later mounting of a connector with pins which project through the PCB.

Wave soldering on a printed circuit board

Figure 3. Wave Soldering

Surface Mount Technology (SMT) PCBs

Another type of printed circuit board is the SMT PCB. For SMT PCBs, reflow soldering is applied at a temperature as high as 260°C. Unlike wave soldering, reflow soldering can be applied with or without pins. In the case of soldering without pins, components are simply mounted on the surface of the PCB. The most common use of reflow soldering is to connect or attach Surface Mount Devices (SMDs) to the PCBs. For application with pins, Through Hole Reflow (THR) technology is used to mount SMDs on to the desired surfaces.

Reflow Soldering on a printed circuit board

Figure 4. Reflow Soldering

Unlike wave soldering, reflow soldering applies a solder paste instead of 'waves' of solder. The sticky solder paste is made up of flux and solder in the form of minute solder balls. The heat applied during the process must never go beyond 260°C.

The main advantages of Through Hole Technology are

  • Effetive handling of high mechanical stress
  • Standard connector usage
  • Standard PCB usage

 

For more information, please read:

Connection Systems - Connectors and Terminals

 

 

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