In the production process of aluminum surface screen printing for PCBs, defects such as pinholes, bubbles, poor adhesion, and misalignment are prone to occur due to factors like materials, equipment, and operations. Relevant standards not only define the criteria for defect judgment but also provide systematic prevention and control solutions. By adhering to the principle of "prevention first, process control, and timely correction," these standards aim to minimize defect rates and ensure product quality.

The standard prevention and control for pinhole defects focus on source management. According to standard requirements, the judgment of pinholes should center on "whether functionality is affected," with pinholes in densely wired areas considered critical defects. Prevention measures include: thoroughly cleaning the screen and aluminum substrate surface before printing to remove dust, impurities, and other contaminants; fully stirring and allowing the ink to settle before use to eliminate air bubbles generated during stirring; controlling ink viscosity to avoid pinholes caused by improper viscosity during printing; optimizing the screen production process to ensure even coating of the photosensitive emulsion and promptly repairing screen pinholes. For minor pinholes that have already appeared, re-printing can be used for repair, while critical pinholes require rework.

The standard prevention and control for bubble defects emphasize process management. The judgment of bubble defects should consider their size, location, and quantity, with large bubbles in critical areas deemed unacceptable. Prevention measures include: thoroughly drying the aluminum substrate during pre-treatment to remove surface moisture and volatiles; selecting ink that complies with standards and avoiding expired or deteriorated ink; strictly following curing process parameters, adopting a stepwise heating method, and extending the dwell time at lower temperatures to promote the discharge of volatiles from the ink; controlling screen printing pressure and speed to prevent air entrapment in the ink layer. If bubble defects occur, it is necessary to analyze whether the issue stems from materials or process parameters and make targeted adjustments before resuming production.

The standard prevention and control for poor adhesion focus on optimizing interface bonding. Adhesion is judged using the tape test method, with peeling of the printed layer considered a critical defect. Prevention measures include: strictly implementing surface activation treatment standards for aluminum substrates to ensure the quality of the oxide film or surface roughness meets requirements; selecting ink types compatible with aluminum substrates, preferably using high-adhesion inks such as epoxy-based ones; controlling curing temperature and time to ensure thorough ink curing; avoiding prolonged delays between printing and curing to prevent secondary oxidation of the aluminum surface. Products with substandard adhesion must undergo surface treatment and re-printing.

The standard prevention and control for misalignment focus on precise positioning. Misalignment is judged based on "whether it affects assembly or identification," with printed identifiers misaligned onto pads or via holes considered non-conforming. Prevention measures include: using high-precision fixtures for screen positioning and regularly calibrating alignment accuracy; checking the placement of the aluminum substrate before printing to ensure precise alignment with the screen; controlling printing pressure and speed to avoid substrate shifting during printing; regularly maintaining equipment to ensure smooth squeegee movement and uniform screen tension. For minor misalignment that does not affect functionality, evaluation may permit acceptance, while severe misalignment requires rework.

Defect prevention and control require establishing a "standard implementation + continuous improvement" mechanism. This includes regularly conducting statistical analysis of defect data to identify high-frequency defects and root causes, then optimizing process parameters or material selection accordingly; enhancing employee training to improve standard implementation; and introducing automated inspection equipment such as AOI to increase defect detection efficiency and accuracy, ensuring that the aluminum surface screen printing process for PCBs meets standard requirements.