Printed circuit boards are relatively small boards that house electronic components such as diodes and capacitors. These relatively small boards can perform complex functions at a rapid pace. PCBs have many applications ranging from household electronic appliances such as coffee makers to military-grade, high-performance, sensitive equipment such as missile guidance systems and satellite systems—all these in one small board.
To perform all these functions, a proper PCB assembly process has to be followed. This will minimize errors and defects that can compromise the sensitive functions of the electronic product. The different processes involved include the following:
The through-hole method is the most commonly used PCB assembly technique. The leads of the components are placed on the surface of the circuit board, then soldered using the wave soldering process.
The circuit components are equipped with long leads. These leads are inserted into plated through holes on the printed circuit board surface. Once through, the component is pulled further to flush it onto the surface of the PCB. Then, a soldering iron and a solder wire or bar is used to solder the component in place. Soldering is done on the connection pads located at the bottom surface of the printed circuit board.
Most hobbyists and manually-manufactured PCBs use this technology. Reworking is much easier with the through-hole process. This process is removing and replacing defective or errant components. The solder is removed from the connection joint. The component is then pulled out of the board and replaced with another one.
SMT (Surface Mounting Technology)
In the surface mount technology, circuit components are placed on connection pads found on the surface of the printed board circuit. Solder paste is placed on the connection pads before the components are mounted. This way, a good and stable connection is established. Next, the circuit board is placed in a reflow furnace. This step is necessary to melt the solder within the solder paste. The melting process creates the mechanical bond, as well as the electrical connection between the pads on the circuit board and the leads of the circuit components.
After this, the test process follows. The PCB assembly is placed into a fixture, where electrical power is passed through the entire circuit. This will turn the assembly into a live board. This live board is placed into an ESS chamber, or environmental stress system. The chamber subjects the circuit board to several cycles of high and low temperatures. The aim of this step is to test if any failures will arise in the board. That is, to determine if the assembly is able to withstand varying temperatures that may occur during actual use of the end-use product. Should any failures occur, analysis procedures will be initiated.
Most of the steps involved in SMT is performed by machines. The PCB design is loaded into the computer and the machine is left to follow the instructions in the design.
The defective board will be analyzed, looking for the source of the failure, such as inadequate or too much solder, inaccurately placed components, incorrect components specifications, etc.
Whatever process is utilized in PCB assembly, careful attention to detail and proper execution of the steps involved are important. PCBs perform critical function, whether in low-end consumer type of electronics or for sensitive instruments used in military and critical laboratory and medical applications. It is important that each component is able to withstand the rigors of function of the end use products. That is, the components should be able to withstand temperature changes, length of use and other stresses. These boards should also be fire retardant to reduce the incidence of electrical fires which can spell disaster to users.