PCB Fabrication and Assembly process overview:
After receiving the bare PCB, the assembly of PCB components takes place.
Step by step procedure:
- Applying Solder Paste: Using a STENCIL, solder paste is applied to the precise locations on the pads where the components will fit. The stencil and PCB are held together with a mechanical fixture and then paste is evenly spread across the designated areas.
2. Pick and Place of Components: SMT components are placed on the board by robots. The designer creates an X,Y coordinates file for each component, enabling robot to identify the location of ecah component exactly. In the past, technicians used to manually place the components using tweezers.
Image by boarditto
3. Reflow Soldering: After the components are placed, the reflow soldering process takes place. This process involves passing the pcb through a conveyer belt, which moves into an oven (temperature 250° C). In oven, solder paste melts and bonding the components firmly into the PCB. After being exposed to high temperature, the PCB is the transferred to a cooling area to solidify the solder joints and complete the soldering process.
Image by gfycat
4. Inspection:
After reflow soldering, there is a possibility of errors such as short circuits, open connections and misalignments. To identify these flaws, the following steps are taken,
Manual inspection:
This method is feasible for boards with fewer components and (through hole)THT components.
Optical inspection:
The automated optical inspection (AOI) machines are equipped with cameras that can verify components from multiple angles in short time.
Image by raymig pcb
X-ray inspection:
This method allows for detection of inner- layer defects in PCB, providing visibility into hidden solder joints and other concealed issues.
5. THT component fixation and soldering:
THT components have leads that pass through holes on PCB. There are 2 methoda for soldering,
Manual soldering :
Technicians manually place the components on PCB and solder them in place using soldering irons.
Wave soldeirng:
Wave soldeirng is applicable mainly for single sided PCBs. After components placed on the PCB, it is moved to oven and then wave of molten solder is splashed on bottom layer where components leads present, creating strong joint.
6. Final Inspection:
After THT assembly, a Final Inspection and basic Functional test are performed. The inspection includes checking for Impedance issues, power line shorts and overall correctness of PCB. If everything is proper, the PCB is powered on and voltage levels are checked. Follow-up tests and other basic test cases are conducted to ensure proper functionality of the assembled PCB.
7. Final cleaning and shipment:
At this stage, the pcb is tested the working condition and declared “Ok”. It is cleaned to removes finger prints,residues,unwanted flux etc. Once cleaning is done, PCB is packed in a ESD protected cover and ready for shipment.
Image by pcb
Be connected!!
Sathya Priya N
