✅ SMT Assembly Process Inspection Checkpoints

1. Solder Paste Printing Inspection

Objective: Ensure proper solder paste application on the PCB pads.

Checkpoints:

• Paste Coverage: Ensure the paste is uniformly applied on all pads (no missing or excessive paste).

• Paste Volume: Check if the volume of paste is appropriate for the component to be placed.

• Stencil Cleanliness: Confirm that the stencil is clean and free from any blockages.

• Print Definition: Verify sharp, well-defined print edges to avoid bridging.

• Alignment: Ensure that the paste is aligned correctly with the pads.

Inspection Tools:

• SPI (Solder Paste Inspection) machine, visual inspection

2. Component Placement Inspection

Objective: Ensure all components are placed in the correct positions and orientations.

Checkpoints:

• Component Placement Accuracy: Check component position against the design (component should be aligned with pads).

• Component Orientation: Ensure correct polarity for polarized components like diodes, capacitors, and ICs.

• Missing Components: Verify that no components are missing.

• Placement on Non-SMD Pads: Ensure SMD components are placed only on SMD pads.

• Component Placement on PCB: Confirm that components are firmly seated and not shifted.

Inspection Tools:

• AOI (Automated Optical Inspection), visual inspection

3. Reflow Soldering Inspection

Objective: Ensure that all components are properly soldered to the PCB.

Checkpoints:

• Solder Joints: Inspect for adequate solder joint formation (shiny, smooth, and concave).

• Solder Bridges: Check for unwanted connections between adjacent pins or pads (bridging).

• Tombstoning: Look for components that may have lifted on one side due to uneven soldering.

• Cold Solder Joints: Check for weak, dull joints that may have poor electrical conductivity.

• Solder Voids: Look for any air pockets or voids under the component that can impact reliability.

Inspection Tools:

• AOI, X-ray inspection, visual inspection

4. Post-Reflow Inspection

Objective: Ensure that the reflow process did not create any defects.

Checkpoints:

• Visual Quality: Inspect solder joints for consistency and neatness.

• Component Integrity: Ensure that no components are misplaced or damaged due to the reflow process.

• Flux Residue: Confirm that excess flux is removed and the PCB surface is clean.

• Lead-to-Pad Connection: Check that the leads are connected to the PCB pads properly.

Inspection Tools:

• Visual inspection, AOI, X-ray for BGA or hidden joints

5. Final Inspection Before Testing

Objective: Ensure that all components and solder joints meet the quality standards before moving to testing.

Checkpoints:

• Component Alignment: Ensure that all components are properly aligned, especially fine-pitch ICs.

• Component Damage: Check for any physical damage to components such as cracks, chips, or burns.

• Excessive Flux Residue: Ensure that there is no leftover flux that could cause future corrosion.

• Overall Appearance: PCB must have a clean, neat, and uniform appearance, with no misalignments or visible defects.

Inspection Tools:

• Visual inspection, AOI

✅ THT Assembly Process Inspection Checkpoints

1. Component Insertion Inspection

Objective: Ensure proper placement of through-hole components into the PCB holes.

Checkpoints:

• Correct Component Placement: Ensure components are placed in the correct holes, aligned with the PCB design.

• Orientation: Check that polarized components (e.g., diodes, electrolytic capacitors) are correctly oriented.

• Insertion Depth: Ensure that leads are properly inserted into the PCB holes.

• Lead Bending: Verify that the leads are bent to secure the component in place for soldering.

• Component Integrity: Ensure there are no bent, damaged, or defective components.

Inspection Tools:

• Visual inspection, manual checks

2. Soldering Inspection

Objective: Ensure that all inserted components are soldered properly to the PCB.

Checkpoints:

• Solder Joint Quality: Verify that solder joints are clean, shiny, and concave.

• Cold Solder Joints: Ensure that no joints are cold or cracked, which could lead to failure.

• Excess Solder or Solder Bridges: Check for excess solder or solder bridges between adjacent leads and pads.

• Solder Coverage: Ensure the entire lead is covered, making a solid connection to the PCB pad.

• Proper Pad Wetting: Check for proper wetting of the PCB pad and component lead.

Inspection Tools:

• Visual inspection, magnifying glass, microscope

3. Manual Soldering Inspection (Post-Soldering)

Objective: Ensure quality solder joints after manual soldering.

Checkpoints:

• Solder Joint Continuity: Check the consistency and smoothness of the solder joints.

• Excess Solder: Check for any excess solder that could cause shorts or defects.

• Component Positioning: Ensure that no components are displaced after soldering.

• Lead Clipping and Bending: Verify that the leads are clipped to a safe length and bent properly to secure the components.

Inspection Tools:

• Visual inspection, magnifying tools

4. Wave Soldering Inspection

Objective: Ensure that all through-hole components are soldered properly using the wave soldering method.

Checkpoints:

• Wave Solder Coverage: Ensure that all component leads are covered in the molten solder.

• No Cold Joints: Check that the solder joint is smooth, shiny, and void-free.

• No Solder Bridges: Look for excess solder between adjacent leads and pads.

• Component Integrity: Ensure components are not lifted or damaged due to excessive soldering heat.

Inspection Tools:

• AOI, visual inspection

5. Final Inspection Before Functional Testing

Objective: Verify that the PCB meets all visual and functional standards before moving to functional testing.

Checkpoints:

• Component Placement and Orientation: Ensure proper placement and orientation of all components.

• Defective or Damaged Components: Check for any physical damage or defects in components.

• Solder Joint Quality: Inspect all solder joints for completeness and reliability.

• Excess Flux: Ensure that all flux residues are cleaned off the PCB.

• Mechanical Integrity: Check for any bending, distortion, or cracking in the PCB or components.

Inspection Tools:

• Visual inspection, AOI, and functional checks

Summary of Inspection Tools Used: