What is PCBA virtual soldering? Methods to solve PCBA virtual soldering
2026-02-25
PCBA virtual soldering is a common and hidden soldering defect that refers to the fact that the component pins and pads are connected on the surface, but there is actually no solid intermetallic compound (IMC) formed inside, resulting in unreliable electrical connections and on-to-and off. It is different from "cold welding" (insufficient heating), and the essence of virtual welding is that the welding interface does not undergo a real metallurgical reaction due to contamination or oxidation.
The solution to virtual welding can start from three links: prevention, detection and repair:
Prevention of false welding (source control)
Prevention is the most effective means to solve false welding. First of all, the materials should be strictly controlled, and the components and PCB boards should be stored in moisture-proof cabinets to prevent oxidation of the solder ends, and the oxidized pins should be tinned before soldering. Secondly, it is necessary to optimize the process, select the solder paste with appropriate activity, and accurately set the reflow soldering temperature curve to ensure that the preheating zone can fully activate the flux to remove oxides, and the soldering zone can reach a sufficient peak temperature. Finally, ensure the printing quality, adjust the squeegee pressure and stencil opening to ensure that the amount of solder paste is sufficient and uniform.
Detect false solders (find problems)
Due to the concealment of virtual welding, it needs to be discovered with the help of professional means. In appearance, the surface of the virtual solder joint is rough, concave or has a clear black boundary with the pad, which can be determined by gently plucking the pin with tweezers if it is loose. In terms of equipment inspection, AOI (Automatic Optical Inspection) can detect abnormalities through image comparison, X-Ray can see through the connection status inside hidden solder joints such as BGA, and multimeter can measure the on/off or oscilloscope signal stability can also be effectively troubleshooted.
Repair false welds (remedial measures)
Once a false soldering is found, a thermostatic soldering iron can be used for manual re-soldering. First, apply an appropriate amount of flux to clean the oxide layer, then touch the soldering tip (300°C-350°C) to the solder joint to melt the solder again, and add new solder wire to form a full solder joint if necessary, and stabilize the pins until the solder solidifies. For multi-pin precision devices, a professional rework table should be used to set precise temperature profiles for hot air soldering to avoid damage to peripheral components.
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