Bridge connection, also known as bridge, refers to the end of the components, between the components adjacent solder, and solder joints and adjacent wires, holes and other electrical should not be connected connect together by solder (bridge connection is not actually short circuit, but the circuit board short circuit problem must caused by bridges).
Causes and preventive measures for bridge connection or short circuit of solder joints:
The Pcb design is unreasonable, and the pad spacing of the pcb board is too narrow.
Preventive measures: Design according to PCB design specifications. The long axis of the two terminal Chip components should be as perpendicular as possible to the running direction of the PCB during soldering. The long axes of the SOT and SOP should be parallel to the running direction of the PCB. Widen the pad of the last pin of the SOP (design pad obtaining tin)
The pins of the plug-in components are irregular or the package is skewed. The pins are close to each other or have been touched before soldering.
Precautionary measures: Pins of the inserted components should be formed according to the pitch and assembly requirements of the printed board. If the short-insertion and single-welding process is adopted, the pins of the soldered surface components should be exposed to the surface of the printed board by 0.8~3mm. The components are required to be in correct position.
The preheating temperature of pcb is too low. Due to the lower temperature of the PCB and components, the components and the PCB absorb heat during soldering, which reduces the actual soldering temperature.
Preventive measures: Set the preheating temperature according to the size of the PCB, whether it is a multi-layer board, the number of components, and whether or not there are mounted components. The preheating temperature is 90-130 ° C, and the preheating temperature takes the upper limit when there are more components.
If the soldering temperature is too low or the belt speed is too fast, the viscosity of the molten solder is too large.
Preventive measures: Tin-wave temperature is 250 °C ± 5 °C, welding time is 3 ~ 5s; when the temperature is slightly lower, the conveyor temperature should be slowed down.
Poor flux activity
Preventive measures: replace the flux