13.9 PCB Assembly Process

The traditional method of the PCB assembly is to attach the leaded components through holes in the board. The bonding of the components with the board is by solder which provides both the electrical and mechanical connections. Subsequently, with the developments in micro-electronics, with the VLSI chip packages having large number of joints on small pin pitches, surface mount technology has evolved. However, not all components are available in surface mount form. Therefore, PC boards continue to have mixed technology components i.e. both leaded as well as surface mount type.

The PCB assembly can be done either manually or by using machines which make the assembly process automatic, fast and reliable. Since the final assembled PCB consists of lot of different types of components with various configurations, an assembly process must be carefully selected in order to make it both economical as well as reliable.

A typical PCB will have a number of dual-in-line packages (DIP), resistors, capacitors, transistors, connectors, etc. mounted on them. All these components have typical hole spacing required for their leads to be inserted. The assembly process, in general, involves the following steps:

• Component collection as per the specifications given in the bill of materials;

• Preparation of the components or component forming (cutting and bending the leads before insertion);

• PCB cleaning: washing with commercial cleaners or rinsing in water etc.;

• Inspection of boards and components for dimensions;

• Placing of components in respective trays in the assembly line;

• Component insertion;

• Soldering of component...