1. Material examination and preparation
The first step involves examining the PCB and the electronic components. We look for the flaws and then prepare the PCB and components accordingly. Usually, the PCB is very flat. On top of that, it includes lead-, gold-, silver, or copper-plated pads. These pads don’t have any holes and we refer to them as solder pads.
2. Stencil preparation
We use a stencil in PCB SMT assembly so that we can perform solder paste printing at a fixed position. So, we prepare the stencil as per our placements of solder pads.
3. Solder paste printing
Solder paste is basically a mixture of tin and flux. We use it for connecting the solder pads and the electronic components on the PCB. We use the stencil for applying the solder paste to the PCB. Hence, the positioning can vary between angles of 45° and 60°.
4. SMT placement
We then use automated machines for picking and placing the PCB. So, these machines then carry the PCB boards over to a conveyor belt. After that, we can place the electronic components on them.
5. Reflow soldering
After placing the components on the PCB, we place them in a reflow soldering oven. The heating is done in various stages. And each stage refers to a specific heating zone. So, these stages are as follows:
If the PCB is double-sided then we might have to repeat all of these processes for the other side as well.
6. Cleaning and Inspecting
Then we clean the PCBs and look for any inherent defects. If no defects are found then the PCB is good to go. Otherwise, we will have to perform repair or rework. Therefore, we use various equipment for performing the inspection. These include AOI, X-ray machine, Automated Optical Inspection, etc.