SMT & THT

SMT (Surface Mount Technology) Process

This is the core of PCBA production. The process is as follows:

1. Solder Paste Printing: A squeegee pushes solder paste through a stencil, accurately depositing it onto the PCB's pads.

2. SPI (Solder Paste Inspection): A 3D optical inspection system checks the quality of the printed solder paste, looking for defects in volume, area, height, and alignment.

3. Component Placement: A pick-and-place machine uses a vacuum nozzle to pick up surface mount devices (SMDs) from a feeder and precisely place them onto the solder paste on the PCB pads.

4. Reflow Soldering: The board, now populated with components, moves through a reflow oven. The oven follows a predefined temperature profile (preheat, soak, reflow, cool-down) to melt, flow, and solidify the solder paste, forming a reliable electrical and mechanical connection.

5. AOI (Automated Optical Inspection): After soldering, a high-resolution camera system inspects the PCBA for common defects like missing, incorrect, misaligned, or tombstoning components, as well as solder bridges.

THT (Through-Hole Technology) Process

1. Component Insertion: THT components are either manually or automatically inserted into the designated holes on the PCB.

2. Wave Soldering: The board with inserted components passes over a molten solder wave. The wave, created by a pump, wets the component leads and pads, completing the soldering process. Note: When a board that has already undergone reflow soldering is being wave soldered, a fixture is needed to protect the previously soldered SMD components.

3. Manual Soldering/Rework: For components unsuitable for wave soldering or for repairs, a technician uses a soldering iron to manually solder the joints.

Post-Soldering Processes

1. Cleaning: A cleaning agent is used to remove flux residue and other contaminants from the board, enhancing its reliability (especially crucial for high-reliability products in the military, medical, and automotive industries).

2. Program Programming: Firmware is written to microcontrollers, memory chips, and other programmable components on the PCBA.

3. Testing

   • ICT (In-Circuit Test): A bed-of-nails fixture is used to contact test points on the board to check for correct component values and identify open or short circuits.

   • FCT (Functional Test): The PCBA is powered up and given signal inputs in a simulated working environment to verify its overall function.

   • Burn-In Test: The PCBA is operated under high-temperature and high-load conditions for an extended period to screen for early-life failures.

4. Conformal Coating: A protective film is sprayed onto the surface of the PCBA to provide moisture, corrosion, dust, and insulation resistance, thereby increasing its reliability in harsh environments.