Solder balls, also known as ball soldering or solder balls, are a PCB defect or design error that causes small solder balls to form on the surface of the PCB during the soldering process.
Solder balls may be attached to pads or components on the PCB. It may also be freestanding - not attached to anything, but still sitting on the surface of the board.
What causes solder balls?
Solder balls are easy to identify because of their small shape, which often turns into a ball. But what exactly causes solder balls on a PCB?
Here are a few pointers:
Solder paste application
Solder balls are formed by the solder paste. Therefore, if you apply solder paste incorrectly, especially when working on the underside of the stencil during the printing process; the likelihood of a ball shape is high.
Flux activation failure
Failure of flux activation during preheating can lead to globular soldering. It is worth mentioning that activation failure can be caused by any of the following:
The preheating temperature is not high enough.
If there is no heating at all during the initial stages of soldering.
Too much solder paste
The presence of too much or more than required solder paste being expelled around the SMD pads leads to ball soldering. This concept is known as solder paste expulsion.
When this happens, it is due to any of the following factors:
Excessive pressure during placement
Misalignment can also lead to solder paste being expelled near the surface mount device (SMD) pads.
Printing misalignment
A misaligned or misplaced solder paste printing position may be the problem. In this case, printing the solder paste (e.g.) on the solder mask instead of on the SMD pads may lead to the creation of solder balls.
Excessive moisture
Excessive moisture may lead to so-called moisture contamination. This usually occurs during reflow when the initial preheating temperature is low; it often leads to solder paste migration.
Other possible causes of solder pilling are
Excessive placement pressure can potentially lead to pushing the solder paste out of the solder tray.
The possibility of solder balling after selective soldering, so insufficient cleaning and wiping after the reflow process is acceptable.
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