The electronics manufacturing industry needs clean, assembled PCBs to avoid any interference in how the final product works. Picking the right PCB cleaning machine ensures a clean, non-contaminated, standards-compliant PCB. This article helps you in selecting the right cleaning machine
By Sneha Ambastha
Assembled PCBs may have a lot of contaminants such as residues of solder, adhesives, flux, dust and debris from the manufacturing processes undergone. PCB cleaning is the most important process after the actual assembly. It’s not just a matter of aesthetics but requires dealing with ionic contamination too. The complete process is dependent on a combination of PCB cleaning machinery and the chemistry behind the solvents and resins used. There are various other factors that influence the PCB cleaning process such as contaminants on circuit boards, which are mainly composed of organic or synthetic resins, ions, acids, solder balls, fingerprints and to some extent, particulates of PCBs. The cleaning is done in several stages. It is done before stencilling and soldering to remove contaminants from previous production stages, and after the stencilling and soldering process to remove excess adhesives, corrosive flux residues and solder paste.
A PCB cleaning machine comes in various sizes, starting from a small brush based hand tool to a big assembly in-line cleaner for batch operations. The cost may range from about ₹ 6000 to ₹ 9 million. The variation in price is due to the different cleaning processes the machine is used for. Every cleaning process requires a special tool or equipment, so it is essential to comprehend this process to understand the tools and their usage.
Manual and benchtop cleaning. Manual (sometimes referred to as benchtop) cleaning is a common practice, requiring the least control in electronics manufacturing. It is not recommended for high reliability applications, as it may result in dispersing flux residue over a wide area. This does not mean that the process is not good; in fact, many a time it results in cosmetic improvements. Soft bristle brushes are used in manual cleaning, which if not cleaned or maintained properly, can transfer contaminants from one area to another. Poorly removed residues usually result in corrosion related failures.
Ultrasonic and batch immersion cleaning. In this process, the assembled boards are completely immersed in the cleaning agent so that the board’s surface can be fully in contact with the agent. This technique involves spray-under immersion (SUI) forces or ultrasonic energy, so as to circulate the fluid and to apply mechanical energy to the surface of the substrate in order to easily remove the contaminants. Now, as the name suggests, the batch immersion process involves cleaning in groups or in batches. There are many types of cleaning capabilities available in in-line cleaners, but they also cost more. Currently, the users of batch type cleaners are looking forward to non-inline cleaners with higher cleaning capabilities.
Vapour de-greasing and duo-solvent cleaning. The process involves passing a solvent over the assembled board, on to the contaminants. In this process, a combination of two solvents is generally used at a specific temperature. Nowadays, ultrasonic vapour degreasers are used to carry out this process.
In-line aqueous spray-in-air cleaning. Conveyorised machines are used in this process to enable high-flow and deflective forces, so that the solvent can get into the low-gap areas on the board, especially for the QFN packaged components present on it.
Batch aqueous spray-in-air cleaning. This process takes place in small areas. All the assembled PCBs are sealed inside a chamber of the batch cleaning machine, where the washing, rinsing and drying takes place together. The process has been so named because the complete process for a group of boards takes place in a single chamber.
Factors driving the market
Ongoing environmental concerns are forcing electronics manufacturers to move away from the traditional PCB cleaners that use ozone depleting chemicals or contain highly volatile organic compounds (VOC). The manufacturers are now replacing these chemicals with safer alternatives; and the industry has realised that the best alternatives are the water-based cleaning chemicals, which have several advantages including non-flammable properties, low odour, low or non-VOC and very low toxicity.
Equipment that combine the functions of a PCB cleaner as well as a testing device have been introduced to enable various functions in a compact footprint. Besides that, a new cleaning process with semi-aqueous chemistry called Aqua ROSE has been introduced. It can operate with aquous solutions with low chemical content ranging between 2-4 per cent. Such cleaning processes are used in batch cleaning and support high temperatures of up to 176°F.
One can also find cleaners with an inbuilt user interface for operators to select the duration and the type of wash, the duration of the forced-air dry cycle and the number of rinse cycles. Then there are universal cleaners suitable for PCBs, sub-assemblies, semiconductors and process tooling at the same time. The cleaners don’t even need an external de-ionised (DI) water source.
Points to tick off before making a purchase
Technically, there are plenty of points that need to be evaluated before purchasing a PCB cleaning machine. Based on the situation, let’s take them up, one by one.
According to the cleaning requirements, ultrasonic, spray under immersion or dishwasher type machines can be selected. Identifying the correct water-based cleaning chemical for the specific job is essential too. Water-based flux removers work by saponification, neutralising the flux acids. The only major disadvantage of water-based cleaners is that they require multiple stages to complete the cleaning process, including a two-stage rinse process and a final drying stage.
The chemical composition of the contaminants is based on the type of solder paste used, the type of PCBs, the number of flux cycles the PCB has gone through before cleaning, the green and white mask on the PCB and the type of components (aluminium, plastic, etc). So evaluation of the PCB cleaning machine is always done keeping in mind the cleaning chemical required for the respective PCBs.
As the size of the components decreases day by day, it’s also essential to identify the new technologies in use before selecting any cleaning machine so that the components do not get washed away in the process.
Other important factors that must be kept in mind are:
- The machine must be automatic to avoid any operator intervention during the cleaning process.
- The machine could be either single or multi-chambered.
- It should be capable of four processes at the minimum, such as chemical cleaning, rinsing, final rinsing and drying.
- The chemical cleaning tank must have a close loop filtration system to reduce consumption of chemicals and, hence, lower cleaning costs.
- Effectiveness of cleaning is a very important factor to check because the whole cleaning process is quite costly. Even the discharge from the machine involves an additional cost in treating the water before releasing it to the drain, as per pollution control regulations.
- The pre–rinse could be done with either tap water or DI water, but both the options should be available with closed loop filtration and zero discharge after every cycle.
- The final rinse should be done with DI water with closed loop filtration. This will help to check the ionic contamination in order to determine the cleanliness levels on the PCB.
- It should have an effective drying section that can reduce the heating temperature, which results in lower heating stress on the PCB.
- Suitable chemistries must also be considered when finalising the PCB cleaning machine. They should have very good solvency power, low surface tension properties to dissolve and remove contaminants, and good drying capabilities. The chemistries must be REACH/RoHS compliant.
- It is important to avoid excess power and water consumption as well as the requirement for a separate DI water source in order to keep process costs down.
- Apart from all this, other features like a barcode scanner, traceability, statistical process control (SPC), etc, can be considered.
Few newly launched products
Model: Super Swash III, Brand: PBT Works, Manufacturer: PBT Works s.r.o.
PBT-Works from the Czech Republic has recently introduced the Super Swash III, which uses a direct spray against surface technology. As the name suggests, the machine is a spray-in-air cleaning system for water-based cleaning processes. It can be used by multinational companies for high throughput stencil cleaning (up to 150 cycles/day) as well as small- and mid-sized OEM manufacturers to clean their sophisticated assemblies with BGAs, CSPs and LGAs. It is compatible with many cleaning agents from different manufacturers and can be used for other processes, like pallet cleaning, cleaning with two different cleaners and other customised tasks. It’s process chamber and manifold system have been optimised against liquid drag-out.
- Common piping system between valves and nozzles, which is drained after each cleaning cycle
- Part of the chamber has glass walls (which is a non-wettable material) to minimise the transfer of liquid between the processes
- Inner surface of chamber is minimised and smooth, and there are no horizontal surfaces
- Has an integrated DI water reclaim plant
- Drying process is concentrated only on the programmed area
USP: A unique hot air knife drying system for maximum efficiency
Indian distributor: Mectronics Marketing Services, Ph: 011-42208256/43041581, [email protected], www.mectronics.in
Model: Aqua ROSE PCB Cleaner, Brand: AAT, Manufacturer: Austin American Technology Inc. (AAT), USA
AAT from USA recently launched the Aqua ROSE PCB cleaner with inbuilt testing capabilities. It uses water and aqueous cleaning chemistries, and saves a lot of time and money. It is a batch cleaner with automatic IPC ROSE cleanliness testing technology built into the cycle to assure proper cleaning in every cycle. It can be configured for a closed loop wash-and-rinse process without any external DI source or any connection to the drainage system, while cleaning and rinsing. It comes in a small footprint with a choice to use either water or a commercial aqueous based defluxing agent.
- Enabled with an automatic ROSE cleanliness tester
- Has a fast cycle time for washing, rinsing, testing and drying
- Has coherent and efficient washing and rinsing jets with three spray wands
- Comes with easy programming and password protection
- Programmable ROSE limits 0.01 to 10.00 ug NaCl Eq./cm²
USP: Saves time and money by combining cleaning and testing in one step
Contact: Ph: +1- 512-756-4150, www.aat-corp.com
Indian distributor: Leaptech Corporation, [email protected], www.leaptech.in