FAQ: Electronic Assembly Cleaning
This page summarizes key questions on cleaning electronic assemblies. The focus is on typical residues, established cleaning processes, the selection of suitable cleaning technologies, analytical verification methods, and the robust design and optimization of cleaning processes.
Last updated: 27.01.2026
The Most Important Facts in Brief
-
Assembly cleaning describes the removal of production-related residues such as flux, particles, fibers, and ionic contamination on printed circuit boards (PCBAs), electronic assemblies, and power modules.
-
Cleaning is particularly relevant when reliability requirements, cleanliness certificates, or critical operating conditions are involved.
-
In practice , spray cleaning, spray under immersion, and ultrasonic cleaning are commonly used, depending on the geometry, contamination, and component sensitivity.
-
ROSE testing, ion chromatography, FTIR microscopy, and SEM/EDX analysis are among the methods used for verification and cause analysis.
-
It is not only the cleaner that is decisive, but also the interaction between the washing medium, system technology, parameters, rinsing, drying, and quality control.
-
(Failure) analysis supports cause clarification, process validation, and the reduction of follow-up costs due to rejects, rework, and field failures.
-
Process optimization and quality assurance ensure reproducible cleaning results throughout the entire washing process.
Further links:
SMT manufacturing
Power modules
Cleaning chemicals & process control/optimization
Analytical services
Failure remediation and risk assessment
FAQ Assembly cleaningQuick Access
AssemblycleaningWhat is assembly cleaning?
Assembly cleaning refers to the removal of production-related residues from printed circuit boards and electronic assemblies. Typical residues include flux, dust particles, fibers, and ionic contamination, which are often not visible to the naked eye
Depending on the task at hand, suitable cleaning media (cleaners/detergents) are used to achieve defined cleanliness targets. In quality-critical applications, cleaning can be an essential component in reducing the risk of failure
Definition: In many manufacturing processes, component cleaning is referred to as a washing process, sometimes also as a washing program or PCB washing. Internationally, the term PCBA cleaning is often used. Defluxing specifically refers to the removal of flux residues after reflow soldering.
Customer terms in context: The washing process typically includes washing medium, washing equipment, and washing parameters such as temperature, time, mechanics, and concentration, supplemented by rinsing and drying.
AssemblycleaningWhen is assembly cleaning necessary?
Assembly cleaning is advisable when residues or contamination could impair electrical function or reliability, or when technical cleanliness requirements must be met.
This is particularly relevant:
-
in applications where high reliability is required, such as in the automotive industry, medical technology, aerospace, or the military.
-
when particulate, ionic, or film contamination is present on surfaces
-
when specifications, audits, or customer requirements demand proof of cleanliness
Without cleaning, these contaminants can lead to corrosion, creep currents or even complete failure of the assembly
In such cases, the cleaning effect is not only evaluated visually, but is often verified using defined quality criteria in the washing process, for example, using test methods for ionic contamination or surface residues.
How do modern cleaning processes for assemblies work?
Modern cleaning processes for electronic assemblies are designed to reproducibly remove production-related residues such as flux, particulate contamination, film residues, and ionic contamination.
The key is the interaction of cleaning chemistry, plant technology, and process control, supplemented by rinsing, drying, and process monitoring, in order to consistently achieve defined cleanliness targets.
Three methods are particularly well established in electronics manufacturing:
- Spray cleaning
The cleaning effect is achieved by directed jets and defined mechanics. The process is particularly suitable for high quantities and easily accessible geometries when uniform cleanability is required. - Spray under immersion
This combines spraying and immersion. The process is often used when complex geometries are present and a combination of wetting and mechanical support is required. - Ultrasonic cleaning
Ultrasound can support cleaning in areas that are difficult to access. Suitability depends on the component, assembly structure, and process boundary conditions, and in practice is always evaluated in conjunction with material compatibility and risk requirements.
Which control variables determine the cleaning process?
The following are typically relevant for effectiveness and reproducibility:
-
Temperature, time, mechanics, and concentration
-
Rinsing strategy and drying
-
Monitoring of bath condition and process drift
-
Definition of quality criteria and verification methods to ensure cleaning results are not only visually apparent but also verifiable
Why is this crucial for reliability?
Residues are often visually inconspicuous, but can promote corrosion, leakage currents, or electrochemical migration. Modern cleaning processes reduce this risk when they are not designed in isolation as "cleaning," but as a stable washing process with clear parameters, monitoring, and verification logic.
In practice, different cleaning technologies are used:
- Water-based cleaning with neutral to alkaline systems, often in combination with rinsing and drying.
- Solvent-based cleaning with modern halogen-free solvents for demanding residues, depending on EHS and process requirements.
The appropriate technology depends on the material, residues, assembly structure, and required proof of cleanliness.
From the customer's point of view, this decision is often made based on the question of which cleaning medium and which cleaning system together reliably achieve the required cleanliness criteria, with reasonable process times and safe material compatibility.
Component cleaningWhat are the advantages of professional component cleaning?
Professional cleaning can support several goals at once:
-
Reduction of failure rates in the field through controlled residue minimization.
-
More stable electrical function, even under demanding voltage levels and environmental conditions.
-
Better reproducibility through defined process control and verification.
In the long term, this reduces follow-up costs from rework, rejects, and complaints.
It is crucial that the washing process is designed and monitored in a stable manner so that cleaning results do not depend on batches, bath condition, or parameter drift.
How can residue risks in power modules be controlled?
Power electronics, especially power modules, operate under high electrical and thermal loads. Even small residues or process residues on surfaces can affect reliability, for example through leakage currents, electrochemical migration, or corrosive effects.
An additional cleaning stage is therefore not a blanket "standard," but is evaluated on a risk basis. If it is used, it is not only the cleaning medium that is decisive, but above all the controlled process management in the cleaning process, so that critical geometries and material combinations can be reliably achieved and material compatibility and verifiability are guaranteed.
How is yield related to surface quality?
The quality of the surface along the entire process chain can directly influence the success of production. The more stable and cleaner the surface, the higher the yield is in most cases. Contaminants or uneven surfaces, on the other hand, can lead to bonding defects that cause rejects or field failures.
Targeted surface analysis , critical deviations can be identified at an early stage. If these are corrected in time, the manufacturing process can be stabilized and the yield significantly increased, while at the same time reducing rework and material costs.
In practice, washing parameters, rinsing strategy, and drying are often adjusted to ensure that the surface condition and residual contamination remain within the target range.
Failure analysis & analytical servicesWhat does a professional damage analysis involve?
A structured damage analysis helps to identify the causes of failures or anomalies, such as contamination, material issues, or process deviations.
The results can also help to provide assurance to customers or OEMs and serve as a basis for corrective measures.
The central question is often whether residues originate from the production process or the washing process, or whether environmental conditions and material interactions play a role.
What analytical methods are used in damage cases?
Depending on the issue at hand, various measurement methods are used individually or in combination for damage analysis:
-
ROSE test for indicative determination of ionic contamination
-
Ion chromatography (IC) for detailed chemical characterization
-
FTIR microscopy and spectroscopy for material and residue identification
-
Scanning electron microscopy (SEM/EDX analysis) for high-resolution surface analysis and elemental information
The choice of method often depends on whether ionic, film or particulate residues are to be evaluated and which quality criteria are to be verified in the washing process.
How can an assembly cleaning process be optimized?
A stable cleaning process (washing process) is based on the interaction of cleaning chemicals (washing medium), plant technology, and quality control.
Validation and standardized tests support reproducible results, while training reduces operating and interpretation errors.
Typical control variables are process parameters such as temperature, time, mechanics, and concentration, as well as rinsing, drying, and monitoring of bath condition and process drift.
Why can a neutral comparison of cleaning systems be worthwhile?
An objective comparison helps to adapt the combination of cleaner, system technology, and process monitoring to the specific use case. This shortens cost-intensive test phases and supports stable series processes.
When is it worthwhile to invest in external analytics?
External analytics is particularly helpful when internal measuring equipment or methods are lacking or when reliable evidence is required:
-
unclear causes of errors or recurring anomalies
-
product launches and process approvals
-
OEM and customer audits
-
Verification of the effectiveness of measures
In practice, this often includes verifying whether adjustments to the cleaning process (e.g., washing parameters, rinsing strategy, drying, or bath condition) achieve the desired effectiveness.
Support in the development, qualification, and stabilization of cleaning processes for electronic assemblies and printed circuit boards, including coordination of cleaning medium, cleaning system and process parameters (e.g., temperature, time, mechanics, concentration) as well as rinsing and drying.
Possibility of a neutral comparison of cleaning systems and process concepts in the technical center in order to determine the suitable combination of system concept, process control, and cleaner for the specific use case. The goal is a robust process window that reproducibly covers component geometries, contamination distribution, and series conditions.
Analytics for evaluating residues and contamination and for ensuring cleanliness targets, depending on the issue at hand, for example: ROSE test, ion chromatography (IC), FTIR microscopy and spectroscopy, SEM/EDX analysis and more.
This allows critical deviations to be identified at an early stage and process corrections to be derived in a targeted manner.
Support for recurring anomalies, complaints, and field failures through structured failure analysis and risk assessment, including the derivation of appropriate measures and verification of their effectiveness.
Who are ZESTRON training courses suitable for?
's training courses are aimed at anyone involved in the production, quality assurance, or development of electronic assemblies—from production staff and engineers to managers.
What topics do the seminars cover?
Typical content ranges from the basics of assembly cleaning, failure analysis, and process optimization to key topics such as power modules and testing technologies. Requirements, specifications, and their practical implementation can be integrated.
Here you can access our knowledge hub with current challenges from the industry and practical solutions.
Discover our analysis services, which reveal causes and secure processes.
Request our latest white papers for compact, expert knowledge on relevant topics.
Take advantage of our on-demand webinars to learn more about specialist topics in the electronics industry.
Discover our product page with powerful cleaning media and industrial detergents for your electronics manufacturing.
Learn how our solutions can sustainably improve the quality and reliability of your electronic assemblies.
Find out about our risk assessment and failure remediation procedures .
Learn how precise surface analysis and modification create the basis for robust connection processes and maximum yield in power modules.
ContactEnsuring Targeted Assembly Cleaning
Define the cleaning solution – from cleaning medium and process parameters to rinsing and drying to verification by analysis and, if appropriate, a neutral system comparison in the technical center.