Solder balls after SMT reflow soldering are almost a common defect in the printed circuit board (PCB) assembly process. Several tinny balls surrounded along with the peripheral edge of the flux residue after reflowing are known as solder balls. In this section, we will discuss how to prevent solder balls.
Solder Balls can be present in wave and reflow soldering and hand soldering. Solder balls can cause failure or adversely affect the reliability of PCB Assembly products.
Acceptance criteria of solder balls
The presence of solder balls on PCBA indicates that something is going wrong in the fabrication process and needs to take the necessary action to eliminate solder balls’ defects and implement inspection checkpoints to be filtered.
Global standards define the acceptance criteria of solder balling defects in surface mount assembly. According to the IPC inspection document IPC- A 610, the solder balling can be defined as
“Solder balls can consider as a nonconforming defect for various class 1, 2, and 3 that violate min electrical design clearances or are not encapsulated in an everlasting coating or attached to a metal joint”.
Solder balls defect SMT reflow soldering can also consider as process indicators when they are within 0.13 mm of lands or tracks, and defective it exceeds a diameter of 0.13 mm, or solder balls are found in clusters of more than five solder balls (<= 0.13mm) 600 mm square area.
The question is what causes solder ball formation in surface mount technology and how to prevent solder ball formation in the SMT process.
What solder balls cause & how to prevent solder balls during reflow
The causes of solder ball formation could be random or Non-random in various process steps. Solder ball defects can result from poor solder paste handling, improper paste printing or cleaning, poor reflow temperature settings, rough PCB Pad Designing, or usage of oxidized electronics components during an assembly process.
Several factors can be responsible for solder ball generation. So, it becomes crucial to analyze each step carefully to find out the leading cause of the defect and solutions to eliminate it from the process.
Data analysis and information gathering to prevent the solder balls formation recommended some actions to avoid such Solder ball defects.
Tackling with Solder Ball Problem
To Tackling with Solder Ball Problem with solder balling, it is required to map the whole process and take appropriate corrective actions to avoid solder balls and inspection to detect the defect.
More focus is required on solder paste printing quality requires proper Analysis of received inspection results from the solder paste inspection machine. Few sample printed boards can be periodically inspected on a magnifier as a visual inspection.
Several other solder ball causes must be considered to make the process solder ball-free. A misprinted board must be adequately cleaned and dried before use. Component placement will be done accurately, and bulky components must be placed slowly.
Due to delay, the printed board must be reflowed quickly after component placement to avoid oxidation. The reflow profile must be set precisely as the solder paste supplier reminded. Monitoring and controlling shop floor humidity and temperature per electronic manufacturing requirements