1. PCB Board Short Circuit
Short circuits are a frequent issue that directly impedes PCB functionality. Various factors contribute to this problem, each of which requires careful examination. One primary cause is improper welding pad design. Rectifying this involves changing round pads to oval shapes and increasing point-to-point distances to prevent short circuits. Incorrect orientation of PCB components can also lead to shorts and operational failures. For instance, aligning SOIC pins parallel to the solder wave increases the risk of shorts; adjusting the component orientation perpendicular to the wave can mitigate this issue. Another potential cause is the bending of leads during automatic insertion. IPC guidelines specify lead lengths should be less than 2mm to prevent parts from detaching due to excessive bending, which can cause shorts. Moreover, solder spots must be at least 2mm away from traces to avoid shorts. Additionally, other factors contributing to PCB short circuit faults include excessively large base plate holes, insufficient tin furnace temperatures, poor board surface solderability, solder mask defects, and surface contamination. Engineers should systematically address and verify each of these potential causes and fault conditions.
2. Dark and granular contacts appear on PCB
Dark or small granular contacts on PCBs typically result from solder contamination and excessive oxide mixed in dissolved tin, leading to a brittle solder joint structure. Care should be taken not to confuse this with the dark color caused by low tin content in solder. Another contributing factor is changes in the composition of solder used during processing and manufacturing, often due to high impurity content. Addressing this may require adding pure tin or replacing the solder entirely. Physical changes in the fibrous layers of speckled glass, such as layer separation, can also cause similar appearances, though not indicative of poor solder joints. Excessive substrate heat is another culprit, necessitating adjustments like reducing preheating and soldering temperatures or increasing substrate travel speed.
3. PCB solder joints turn golden yellow
While PCB solder is typically silver-gray, occasional golden solder joints indicate excessive temperatures. Lowering the tin furnace temperature resolves this issue.
4. Environmental impact on faulty boards
The structure of PCBs makes them vulnerable to damage under adverse conditions. Factors like extreme or fluctuating temperatures, high humidity, intense vibrations, and other environmental stresses can impair board performance or render it unusable. Temperature changes, for instance, may cause board deformation, leading to damaged solder joints or bent shapes, and exposed copper traces may corrode due to airborne moisture. Additionally, accumulation of dirt, dust, or debris on components and circuit boards can impede airflow, causing overheating and performance degradation. Physical stress from vibration, drops, impacts, or bending can result in cracks, while excessive current or voltage can hasten component and channel aging or cause outright failure.
5. PCB open circuit
An open circuit occurs when a trace breaks or when solder only adheres to the pad and not the component lead, resulting in no electrical connection. Such issues can arise during production, welding, or other operations, exacerbated by mechanical deformation from vibration or stretching. Chemical exposure or moisture can also contribute to solder or metal fatigue, leading to component lead breakage.
6. Loose or misaligned components
During reflow soldering, components may float on molten solder and deviate from intended solder joints. Causes of displacement or tilt include inadequate PCB support, furnace settings, solder paste issues, or human error during assembly.
7. Soldering issues
Poor soldering practices can lead to various defects:
– Disturbed solder joints: Movement before solidification due to external disturbances. Reheating can often correct this issue.
– Cold welding: Inadequate melting of solder resulting in rough surfaces and unreliable connections. Reheating and removing excess solder can rectify cold spots.
– Solder bridge: Unintended connection of solder between leads, potentially causing short circuits.
– Pad issues: Insufficient wetting of pins or leads, or problems arising from excessive or inadequate solder application. Overheating or rough soldering may also cause pad elevation.
8. Human error
The majority of PCB defects stem from human error, accounting for up to 64% of avoidable product issues. Errors in production processes, component placement, or non-compliance with manufacturing specifications are common causes. Factors such as densely packed components, multi-layer circuits, fine routing, surface-mounted components, and power/ground issues further increase the likelihood of defects. Despite efforts to minimize issues, design and production complexities contribute to various PCB problems, including short circuits, poor contact due to board misalignment, trace insulation issues leading to arcs, and susceptibility to short circuits from closely spaced copper traces or inadequate PCB thickness causing bending and fractures.
