PCB factory circuit board welding defects may be caused by these reasons
PCB manufacturer, PCB designer and PCBA manufacturer explain that PCB welding defects may be caused by these reasons
Solderability of PCB holes affects welding quality
Poor solderability of PCB holes in PCB plants will lead to faulty soldering defects, whICh will affect the parameters of components in the circuit, lead to unstable conduction of Multilayer board components and inner wires, and cause the failure of the entire circuit function.
Solderability is the property that the metal surface is wetted by molten solder, that is, a relatively uniform, continuous and smooth adhesive film is formed on the metal surface where the solder is located. The factors affecting the solderability of PCB mainly include:
Solder is an important part of welding chEMIcal treatment process. It is composed of chemical materials containing flux. The commonly used low melting point eutectic metal is Sn Pb or Sn Pb Ag. The impurity content shall be controlLED in proportion to prevent the oxide produced by impurities from being dissolved by the flux. The function of the flux is to help the solder wet the surface of the soldered board circuit by transferring heat and removing rust. - White rosin and isopropanol solvent are generally used.
The weldability is also affected by the welding temperature and the cleanliness of the metal plate surface. If the temperature is too high, the solder diffusion speed will be accelerated. At this time, the solder has high activity, which will cause rapid oxidation of the circuit board and solder melting surface, resulting in welding defects. The PCB factory's circuit board surface will be polluted, which will also affect the solderability and thus produce defects, including tin beads, tin balls, open circuit, poor gloss, etc.
2. Welding defects caused by warping
The circuit board and components are warped during welding, and defects such as false soldering and short circuit are caused due to stress deformation. Warpage is often caused by the temperature imbalance between the upper and lower parts of the circuit board. For large PCBs, warping will also occur due to the weight of the board itself.
Ordinary PBGA devices are about 0.5mm away from the printed circuit board. If the components on the circuit board are large, the solder joints will be under stress for a long time as the circuit board returns to its normal shape after cooling down. If the components are raised by 0.1mm, it will be enough to cause open circuit due to faulty soldering.
3. The design of circuit board affects the welding quality
In the layout, when the size of the circuit board is too large, although the welding is easier to control, the printing line is long, the impedance increases, the noise resistance decreases, and the cost increases; If it is too SMAll, the heat dissipation will drop, the welding is not easy to control, and the adjacent lines will easily interfere with each other, such as the electromagnetic interference of the circuit board. Therefore, the PCB design of the Pcb factory must be optimized:
Shorten the connection between high-frequency components and reduce EMI interference.
Components with large weight (such as more than 20g) shall be fixed with supports and then welded.
Heat dissipation shall be considered for heating elements to prevent defects and rework caused by large △ T on the surface of the element. The thermal sensor shall be far away from the heat source.
The arrangement of elements shall be as parallel as possible, which is not only beautiful but also easy to weld, and it is suitable for mass production. The circuit board is designed as a 4:3 rectangle. The wire width shall not be abrupt to avoid the discontinuity of wiring. When the circuit board is heated for a long time, the copper foil is easy to expand and fall off. Therefore, large area copper foil should be avoided.
To sum up, in order to ensure the overall quality of PCB board, in the production process, we should use excellent solder, improve the solderability of PCB board, and prevent warping to prevent defects. PCB manufacturers, PCB designers and PCBA manufacturers explain that PCB welding defects may be caused by these reasons.