When white residues suddenly appear on assemblies for unknown reasons, the customer is often confused – and the first idea is often the same: something must be wrong with the cleaner. However, this is only the cause in extremely rare cases. In the majority of cases, there are other causes – but these can be manifold.
In many cases, changes in the assemblies are responsible. Cheaper materials, less development time, or simply a change of supplier can be the cause. A supposedly more favourable offer can also have disadvantages. If the new parts are not compatible with the previous cleaning process, problems arise – not infrequently in the form of white residues. If it is not possible to switch back to the old components, the only option is often process optimisation.
Reasons for white residues
Solder resist mask not completely cured: One reason that often causes white residues is that the solder mask is not completely cured. In this case, water from the cleaning process can accumulate in the material of the solder mask and condense there at room temperature. This can also lead to staining. A solution that is as practical as it is pragmatic: a hot hair dryer, held over the assembly for some time, quickly makes the milky, white residues disappear.
Solder paste change: A change of solder paste is also often responsible for white residues. If the change is made without first consulting the manufacturer of the cleaning media, the cleaner may not be able to optimally remove the new solder paste with the same system settings. Again, if the cleaner is not to be changed, in most cases other parameters will have to be changed.
In principle, however, there are a whole host of reasons why white residues can occur. Other causes include the quality or temperature of the rinse water. However, these problems can also be eliminated by adjusting the parameters or preparing the rinsing medium. If a cleaner has already been used too often, it is sometimes possible to achieve the desired result again by increasing the concentration.
In general, it can be stated that in most cases where complications with white residues occur, good results can be achieved by optimising the process. If a solution to the problem cannot be found in this way, consultation with an experienced solution provider who can analyse each case individually should be the next port of call. A change of cleaner is usually only necessary in the rarest of cases.
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