Insights
PCB Cleaning: Why Excessive Foaming Occurs
Which factors influence foaming behavior during the cleaning and rinsing process, and how the underlying cause can be systematically identified.
Foaming During the Cleaning Process When Foam Becomes a Process Issue
Foaming can occur to varying degrees during the cleaning of electronic assemblies. It becomes critical when stable foam builds up in the cleaning bath or rinsing stage, causes parts of the equipment to overflow, or prevents the process from operating reproducibly.
The cause does not necessarily lie in the cleaning agent itself. Concentration, water ingress, flux, equipment parameters, air input or carryover into subsequent process steps can also influence foaming behavior. To resolve the issue effectively, it is therefore essential to determine where the foam is forming and which process parameter has changed.
Abstract
Excessive foaming during PCB cleaning often indicates that the cleaning medium, introduced residues, or process conditions are not interacting as intended. Possible causes range from changes in cleaner concentration and water ingress to interactions between the cleaner and flux, air input, cleaner carryover, or the use of a cleaning medium that is not suitable for the equipment process. A systematic root-cause analysis helps identify the relevant influencing factor and enables targeted process adjustments.
Foaming During the Cleaning Process What Can Cause Excessive Foaming?
For root-cause analysis, the first step is to determine when and where in the process the foaming occurs. It is equally important to establish whether the process had previously been stable or whether materials, process parameters, or equipment conditions have changed. This helps narrow down the potential sources of the problem. In practice, four areas are particularly relevant.
01 | Dosage Error and Water Ingress
The cleaner concentration affects not only cleaning performance but, depending on the formulation of the cleaning medium, also its foaming behavior. Deviations from the intended concentration range can result, for example, from incorrect dosing, additional water ingress, or equipment-related water entering the cleaning tank.
This changes the composition of the cleaning bath. If excessive foaming occurs, the current cleaner concentration, dosing, and any possible uncontrolled water ingress should therefore be checked.
02 | Improper Combination and Air Bubbling
The interaction between the cleaning medium and introduced flux residues can also affect foaming behavior. Particularly after a change in flux, it should be verified whether the existing cleaner-flux combination is still suitable under the current process conditions.
In addition, air input during air bubbling can mechanically intensify existing foaming. The extent of this effect depends on the cleaning medium, bath loading, and the equipment parameters used. If the foaming behavior changes, both modifications to the process materials and the mechanical action within the cleaning bath should therefore be considered.
03 | Foam Formation in Rinse Water
Foam can also occur only during the rinsing stage. When the assembly moves from cleaning to rinsing, small amounts of cleaning medium can be carried over with the assembly or through the equipment system. Depending on the amount of cleaner, its composition, and foam stability, this can lead to foaming in the rinse water.
Sufficient water exchange reduces the concentration of carried-over cleaner in the rinsing stage. If cleaning and rinsing are performed in the same chamber, however, cleaner carryover can become more significant, particularly at high equipment utilization. In this case, the rinsing concept and water exchange should be reviewed in addition to the cleaning bath.
04 | Incorrect Cleaner for the Process
Not every cleaning medium is designed for every equipment process. Different methods, such as spray cleaning, immersion cleaning, or air bubbling, introduce different levels and types of mechanical action into the cleaning bath and therefore place different requirements on the cleaner’s foaming behavior.
The cleaning medium, equipment principle, and process parameters must therefore be considered together when selecting the process. What matters is not only effective removal of the residues present, but also stable behavior of the cleaning medium under the actual process conditions.
from practiceNew Flux Causes Foam Formation
A fully utilized cleaning system developed pronounced foaming despite previously stable process conditions. Completely replacing the process bath did not improve the situation. This shifted the focus from the condition of the cleaning bath to potential changes in the upstream manufacturing process.
For root-cause analysis, a bath sample was sent to ZESTRON and evaluated together with the relevant process conditions. One key change became apparent: a new flux had recently been introduced. In combination with the existing cleaning medium, the new flux significantly altered the foaming behavior of the process.
Based on the analysis, ZESTRON recommended a cleaner matched to the new flux and the existing process conditions. After the changeover, the excessive foaming was eliminated and the cleaning system could once again be operated stably at high utilization.
This case demonstrates that changes in foaming behavior should not be assessed solely by looking at cleaner concentration and equipment parameters. Evaluating the cleaning bath together with the process materials and preceding process changes made it possible to narrow down the cause and adjust the cleaning process accordingly.
Ensuring Process Stability Analyze and Stabilize the Cleaning Process
Whether excessive foaming occurs during an existing process or a new cleaning process is being developed, the relevant influencing factors need to be evaluated in combination. ZESTRON supports you in narrowing down the causes, reviewing process conditions, and deriving suitable corrective measures.
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