Based on years of production and application experience, FOSAN has sorted out the defective issues of SMD resistors caused by environmental, operational, material and other factors during production, storage or application. The core defect modes and their causes are as follows:

Electrical defects are a type of problem that directly impacts the service performance of SMD resistors, mainly characterized by excessive resistance, insufficient resistance or open circuit. Excessive resistance or open circuit is mostly caused by resistor body burnout (resulting from overcurrent, overvoltage or electrostatic discharge) and electrode sulfidation; insufficient resistance is associated with electrostatic shock, silver migration or moisture erosion. Among these, silver migration is a typical fault: in high-temperature and high-humidity environments, silver ions in electrodes migrate to the cathode under the drive of voltage, forming conductive dendrites and leading to abnormal resistance. Sulfidation refers to the reaction between sulfur-containing gases and silver electrodes to form insulating sulfides, which hinder current conduction and eventually cause excessive resistance or open circuit.

Mechanical structural defects mainly include resistor body fracture and electrode delamination. Resistor body fracture is mostly induced by mechanical stress (PCB warpage, external impact) or thermal stress (improper welding temperature profile); when the stress exceeds the tensile strength of the resistor, cracks or even complete fracture will occur. Electrode delamination also stems from mechanical or thermal stress, which causes separation between internal electrodes and intermediate electrodes and ultimately leads to circuit open circuit. Such problems are often related to improper installation operations (e.g., excessive solder volume) and PCB deformation in application scenarios.

Solderability defects directly affect the quality of circuit assembly, mainly manifested as cold solder, solder rejection and tombstoning. Cold solder and solder rejection are mostly caused by contamination of electrode plating, which prevents solder from effectively adhering to the electrode surface and results in unstable connections. Tombstoning occurs due to uneven solder volume or uneven heating, leading to uneven stress distribution on both ends of the resistor and its tilting, which impairs the stability of circuit connections. Such problems are mostly associated with improper control of welding process parameters.

Although appearance and packaging defects do not directly affect electrical performance, they may lead to potential risks in subsequent use. Appearance defects include faded marking (caused by surface wear of products) and damaged resistor body (resulting from mechanical external force). Packaging defects involve component pick-up failure due to moisture absorption of paper tape, as well as crushing damage to reels or cartons, which may cause product damage during transportation and storage and affect the convenience of use and product integrity.

Resistive layer breakdown is a common electrical overload fault. Due to the existence of trimming grooves, current concentration areas are susceptible to overvoltage, electrostatic discharge (ESD) or pulse impact, which damage the structural integrity of the resistive film material and result in resistance drift (excessive or insufficient) or even open circuit. To avoid such defects, it is necessary to select products matching circuit parameters, control the temperature, humidity and sulfur content of the service environment, and standardize welding and installation operations to reduce the risk of overload.