Start-to-end PCB cleaning solutions: The Clean Path to Reliable Electronic Products

Electronic devices that consumers use every day depend on printed circuit boards (PCBs). We expect the electronics in our cars, homes, industry, and personal lives to be reliable. Diagnostic or instrument failure can be catastrophic in the medical and aerospace sectors. Developing electronic products is a complex process from concept to design to manufacture, and the PCB plays a vital role in making the product functional.

Many issues can contribute to PCB failure. These include design flaws which result in EMC problems, bad soldering, missing solder paste between pads and dirty PCBs. Among these issues, PCB cleaning is the most undervalued process during assembly.  This article examines the importance of clean PCBs in mitigating device malfunction.  We look consider challenges in today’s sophisticated manufacturing environment and assess start-to-end PCB cleaning solutions.

Clean PCBs matter

The PCB cleaning process begins at the start of the production line with bare board cleaning and ends with assembled board cleaning. Clean bare boards provide the best possible surface for the next stage of assembly which is component placement. Assembled boards that are clean or defluxed reduce major problems during testing and ensure the functionality of the finished electronic device. Here are the main reasons why this cleaning is essential:

Removing contaminants:  During the manufacturing and handling processes, PCBs can accumulate ionic contaminants. These include water-loving polar salts, dust and flux residues plus water-hating, non-polar fingerprints, oils, and fats which can interfere with the soldering process, leading to poor solder joints or even soldering failures.

Prevention of Electrical Failures: Flux residues can be corrosive and conductive risking electrochemical migration (ECM) which may significantly decrease the insulation between conductors and cause failures. Cleaning eliminates the possibility of ECM events such as shorts caused by dendritic growth leakage from ionic residues, current leakage, chemical leakage from components, and changes in impedance.  Similarly, non-conductive contaminants can create insulation resistance failures.

Avoiding Component Damage: During the soldering process, not only flux but also other contaminants such as solder balls and excess solder can accumulate on the PCB. Cleaning helps remove these potential threats, thereby preventing damage to the components.

Adhesion: For PCBs that undergo further processing, such as the application of conformal coatings, cleaning is essential to ensure good adhesion of the coatings. Non-polar contaminants can prevent the coating from properly adhering, compromising its protective qualities.

 

Challenges around cleaning boards

Today’s sophisticated SMT technology allows for greater flexibility and is suitable for high-density compact designs. Miniature components, multi-layer boards and developments in lead-free solder and no-clean flux add another layer of complexity to the cleanliness required for reliable functionality. Here are some of the key challenges:

Miniaturization of Components: Surface mount components are getting smaller allowing for dense placement and fine-line technology.  Mounted on the surface of the PCB they have metalised ends attached by solder where the flux residue can gather.  The tighter the spacing between components the more likely dendritic growth leakage from ionic residues will occur. Some components are so small they are like dust and are difficult to clean around.

No-Clean Flux: Some fluxes are designed to be no-clean to speed up the manufacturing process by eliminating the need to clean PCBs after reflow. The flux is made with chemicals that almost evaporate during soldering. However, salt activators in the no-clean flux may react with heat or other chemicals and leave a residue that can corrode circuits. Increasingly, for device reliability and longevity, it is better to clean than not to clean. No-clean fluxes are proving to be stubborn to remove as they are baked on after the reflow process.

Lead-Free Solder:  Many countries are banning the use of lead solder due to environmental and health concerns.  Lead-free solder can cause tin whiskers or filament structures that stick out from the PCB surfaces which can create short circuits. Tin whiskers also produce the growth of dendritic-shaped deposits made of metal oxide, another short circuit hazard.

Drying and Rinsing: The PCB must be completely dried after cleaning to prevent moisture-related failures. Inadequate rinsing can leave residues from the cleaning agents, affecting the board’s performance. If you use the wrong type of water like soft water which has too much salt instead of deionised water the results will not be satisfactory.  Blowers remove moisture from the surface of the PCB however multi-layer boards can store moisture between layers. Consider baking multi-layer boards before conformal coating.

Compatibility with Cleaning Agents: Selecting a cleaning agent that is effective at removing flux and other contaminants without damaging the PCB or components (e.g., causing corrosion or material compatibility issues) is critical. The cleaning agent must also be compatible with environmental regulations.

 

Start-to-End PCB Cleaning Solutions

There are several methods for cleaning PCBs, each suitable for different types of contaminants and manufacturing processes. Start-of-line cleaners include blowers and adhesive rollers, and end-of-line options are solvent, vapour phase and aqueous cleaning.

Most large-scale SMT manufacturers use in-line systems where assemblies are processed continuously on a conveyor system and cleaning cycle times are controlled by the conveyor speed. Batch-cleaning solutions are available for mid to small manufacturers where groups of PCBs are cleaned in a controlled time process. These machines can be bench-top for a small footprint or free-standing, depending on the capacity required.

Start of Line – Bare board cleaners

Typically, bare boards should arrive from the supplier “clean”. However, this is often not the case. Suppose the fabricator uses a LASER marker to add serial numbers/barcodes. In this instance, you are burning the top layer of PCB with the potential to create contaminants (even though the laser marker has a powerful vacuum system for extracting particles). Other common contaminants include plating/etch salt, flux residues, grease finger salts, and process oils, hence, the need to clean before printing.

The best way to start the assembly process is to add an inline PCB cleaning conveyor at the beginning of the line. A bare board cleaner eliminates particle pollution on bare boards to prepare a clean surface for screen printing and better bonding of components to the PCB.  This foundational step affects the quality, long-term reliability, and longevity of the finished electronic products.

Bare board cleaners work by blowing contaminants from the PCB or models like the Nutek NTM5000-L In-Line PCB Cleaning Machine use elastomer rollers to remove dust, particles, and glass fibres.

End of Line – Assembled board cleaners

The assembly process involves stencil printing, component placement and reflow during which PCBs accumulate no-clean flux residues, grease finger salts, and wave and silicone oils.

When manufacturers embraced PCB cleaning in the 70s and 80s, vapour and solvent degreasing were popular for cleaning assembled PCBs. In the 90s some chemicals were discontinued because of new CFC protocols and ozone layer environmental concerns.

Aqueous cleaning solutions came to the forefront and are popular with electronic manufacturers as they are eco-friendly and use water or a combination of water and chemicals. Some manufacturers use water-based flux in their paste, which as the name suggests is water soluble, so the boards can go through the PCB cleaner without surfactant added – just straight water.

Machines like the Aqueous Technologies Trident ZDO are available in zero discharge where chemistries are closed, mixed and re-used and the rinse water is recycled. Closed loop machines mean there is no waste discharge and no need for a waste disposal permit. Aqueous is committed to finding new ways of conserving water and reducing environmental impact through our equipment designs. It is a win for the environment and the manufacturer’s bottom line. Read more about green PCB cleaning machinery here.

Another important consideration when scoping for an aqueous machine is the spray technology. Some machines use non-diffused (coherent) sprays that create a high-pressure stream with a narrow target and are suitable for less complex boards like through-hole designs. Other machines have diffused nozzles that widely distribute smaller water particles that overlap. Smaller water particles are especially important in the rinse cycle where the water surface tension is higher than the wash cycle.

The IMO ECO 2000 is a cost-effective option for small manufacturers offering full recipe control for cleaning, washing, dosing and drying. Able to remove rosin-based, low-residue and water-soluble flux it caters for Euro-card style PCBs with a rack for odd-sized boards. Flux residues are completely removed. The solder joints and components are not attacked and the cleaning agent is completely removed again after the cleaning process.  See the IMO ECO cleaner in action here.

What cleaning system should you use?

Choosing the best cleaning system depends on the type of flux and solder paste used, the components on the PCB, the required level of cleanliness for conformal coating, and environmental considerations. Properly cleaned PCBs from start to end exhibit enhanced performance, reliability, and longevity, making the cleaning/de-fluxing process an integral part of PCB manufacturing and assembly.

At Hawker Richardson, we have a wealth of experience – over one hundred years and our personalised service includes helping you find the right cleaning product for your manufacturing requirements. Whether you are an OEM, a CEM or a smaller manufacturer we can help you navigate the challenges of cleaning PCBs.  Our full-service team maintains all products including cleaning solutions and our support is unparalleled with coverage anywhere in Australasia.