Use of SMT along with that of through-hole components give rise to different assembly methods. Here we have used the term primary side/ component side interchangeably and this represents the side where conventional through-hole components are placed. The term secondary side/ solder side are used interchangeably and this represents the side which gets soldered when using through-hole components alone. Assembly methods can be broadly classified into 2 groups as given below:
1. Type I A and IB : Single or double side surface mount component attachment.
2. Type II: Component side mixed components, i.e. both SMCs and through-hole components used. On the secondary side (also called solder side) only surface mount components are used.
1. Type IA assembly : Here the surface mount components are soldered only on the component side of the PCB. This is the simplest form of assembly. The process steps involved are given below.
Type IB assembly: Type IB consists of surface mount components on either side of the PCB and as expected the functional density is very high. Large space savings are attainable here. Here the components on the secondary side are placed first using adhesive and then reflowed. The components on the primary side are placed next without use of adhesive as shown in the figure. Though we have shown assembly method on the secondary side of the board by using adhesive for keeping the components in place during the reflow on the other side, it is possible to use low melting point solder on the other side of the board and thus avoiding the use of adhesive. Secondary side of the board generally loaded only with simple chip components such as caps, resistors, etc.