What Causes Virtual Soldering in SMT Chip Processing

 Virtual soldering is one of the most common issues in SMT chip processing. Sometimes, after soldering, it appears that the front and rear steel strips are welded together, but in reality, they do not achieve complete fusion. The bonding surface has low strength, and the weld seam goes through various complex processes on the production line, especially high-temperature furnace zones and high-tension straightening zones. Therefore, virtual soldered welds are extremely prone to cause strip breakage accidents on the production line, significantly affecting the normal operation of the production line.

The essence of virtual soldering is that the temperature of the weld bonding surface is too low during soldering, the size of the fusion nucleus is too small, or it does not even reach the melting point—only reaching a plastic state. After rolling, the materials are barely bonded together, making it seem soldered, but they are not fully integrated.

Analysis of Causes and Steps for Virtual Soldering in Chip Processing:

  1. Check the weld bonding surface first for rust, oil stains, or other impurities, or unevenness and poor contact. These will increase the contact resistance, reduce the current, and result in insufficient temperature on the soldering bonding surface.
  2. Verify whether the current setting complies with process regulations. If the current setting does not increase correspondingly when the product thickness changes, insufficient current during soldering will cause poor soldering.
  3. Inspect the overlap amount of the weld seam for normalcy, as well as any reduction or cracking in the drive-side overlap. A reduced overlap amount decreases the bonding area between the front and rear steel strips, shrinking the total stress-bearing surface and making it unable to withstand high tension. In particular, drive-side cracking causes stress concentration, leading to increasingly larger cracks and eventual breakage.
  4. Check if the welding wheel pressure is reasonable. If the pressure is insufficient, the contact resistance will be too high, and the actual current will decrease. Although the welding controller has a constant current control mode, if the resistance increase exceeds a certain range (generally 15%), it will exceed the limit of current compensation, and the current cannot increase correspondingly to the set value, triggering an alarm during normal system operation.

Emergency Handling: If the exact cause of virtual soldering cannot be identified immediately during actual operation, clean the head and tail of the steel strip, increase the welding overlap amount, appropriately raise the welding current and welding wheel pressure, and re-solder while closely monitoring the weld formation. In most cases, this can address the issue temporarily.

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