White Residues on Assemblies: What’s Behind Them?

Understanding White Residues on PCBs: Causes and Solutions from Origin to Resolution.

Anyone who has ever dealt with assembly cleaning will probably have encountered the phenomenon of "white residues". But what is it all about? Why residues at all, why white? Where do they come from? And what can be done about them? Questions upon questions - the answers are here:

WHITE residues?Multiple Causes, Pragmatic Solutions

 

White spots can be seen on an electronic assembly due to material changes or process adjustments. | © Zestron

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 absolute 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 favorable 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 optimization.

The picture shows the ROSE test for measuring ionic contamination on electronic assemblies. | © @The Sour Cherry Fotografie - Michaela Curtis

TRIGGERSolder Resist Mask Not Completely Cured

Another 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 soldermask 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.

TRIGGERSolder Paste Change

A change of solder paste is also often responsible for white residues on the plantine. 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.

Two employees in the laboratory carry out a purity determination on an electronic assembly. | © @The Sour Cherry Fotografie - Michaela Curtis
Stephen Coburn - adobe.stock.com

zestron xpertiseWith Expertise and Analysis to Solve the Problem

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.

YOU CAN RELY ON ITZESTRON: Individual Solutions for Every Case

In general, it can be stated that in most cases where complications with white residues occur, good results can be achieved by optimizing the process. If a solution to the problem cannot be found in this way, the Application Engineering department is always available to our customers. We analyze each case individually and together go in search of the cause. A change of cleaner is usually only necessary in the rarest of cases.

The picture shows a consultation, both the customer and the engineer looking at a circuit board and discussing cleaning processes for electronic assemblies. | © @The Sour Cherry Fotografie - Michaela Curtis
The picture shows a white paper that deals with the causes and remedial measures for residues on electronic assemblies. | © Zestron

whitepaper-collection Residues on PCBs - Cuases and Remedial Measures

Surface contamination, such as white spots, streaks, or solder balls on electronic assemblies, can range from harmless to critical. In our whitepaper, we explore the causes and provide optimization suggestions.

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OPEN QUESTIONS?Do You Have Individual Questions?

Our ZESTRON application technology is available to advise you on your problem.

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