A common myth about the printed circuit board (PCB) manufacturing process claims that all bare boards and components are clean and uncontaminated when they exit the assembly line. Many even imagine that flux, used during the PCB soldering process will not interfere with its operation. Reality has a way of complicating such misconceptions.
A PCB with residual flux contamination may initially pass quality control and work properly. Yet, when exposed to temperature fluctuations, high humidity or other harsh environmental factors, such seemingly inconsequential issues can lead to failure.
Industrial PCB cleaning is an essential part of the manufacturing process. Removing exposed adhesive, soldering residues, dust or other debris helps to ensure that the equipment or machinery for which a PCB is manufactured will operate effectively throughout its lifetime. For manufacturers, industrial PCB cleaning during assembly provides a way to achieve better performance and build trust with end users.
Miniaturization & Problematic Contaminants
Smartphones we carry in our pockets can outperform the giant supercomputers that once helped astronauts land on the moon. Over the years, circuit boards and their component parts have become miniscule—as small as one-tenth of a millimeter in some cases. Because of their small size, though, a specks of dust, flux residue or other minute contaminants can cause machinery, or even whole systems, to fail. Manufacturers can employ industrial PCB cleaning to remove common contaminants and ensure their boards operate reliably.
Common PCBA Contaminants
Common contaminants, which includes the following, are often inadvertently introduced but should never remain on boards.
- Board particles
- Natural and synthetic resins used in adhesives, inks and varnishes
- Solder balls
PCB cleaning during the manufacturing process helps ensure that miniature components are free of dust and debris. For example, by implementing a PCB cleaning process, manufacturers can prevent soldering flux and other assembly process residues from being present on the final product. While this type of residue--in small quantities--remain without causing immediate concern, the potential compromise of the PCBA’s performance and reliability in the long term is justification for removal.
Common Residues on PCBA
- Flux activators
- Plating chemicals
Inadequate cleaning can cause additional long-term problems that affect switches and relays, prevent strong adhesion, and reduce contact on interconnecting cables, sockets and edge connector fingers. Likewise, moisture exposure on PCBAs can accelerate corrosion or dendritic growth in the alloys present on the circuit board, causing a net to inadvertently short and leading to inefficiencies or even system failure.
Implementing an Industrial PCB Cleaning Process
Since there is no shortage of potential PCB contaminants, PCB manufacturers should decide, based on their own processes, which cleaning methods and materials suit their needs. Below, we’ll examine a few approaches to the PCB cleaning process that a manufacturer may want to consider.
Industrial PCB Cleaning Process Stages
- Prewashing cleans off larger contaminants prior to washing.
- Washing removes the remaining contaminants, often using specialized equipment.
- Anti-drag-out measures between the washing and rinsing stages prevent any liquid drag-out from the wash.
- Rinsing normally occurs in a purpose-built rinse tank, with some methods implementing wet isolation to further rinse wash water from the board.
- Drying utilizes high temperatures and high-pressure air (or gasses such as nitrogen) to thoroughly remove moisture.
Three Industrial PCB Cleaning Methods to Use After Surface Mount Soldering
Manual PCB Cleaning Method
Manual cleaning is still an effective way of cleaning PCBAs. Following the stages listed above, isopropyl alcohol is a common cleaning agent for this method.
Batch or Inline PCB Cleaning with Water
In order to reduce the time required to clean boards, a batch quantity of boards is often processed. An automated in-line process can increase efficiency. Both of these techniques may be performed using water or a chemical cleaning agent to remove no-clean flux residue.
Gas Phase PCB Cleaning Method
Gas or steam is also used to clean circuit boards. This method, also known as vapor phase cleaning, requires boiling a chemical solvent to produce steam which in turn separates contaminants from the board.
While all of these methods reduce board contaminants, residue can persist when using the manual industrial PCB cleaning method. Individual manufacturers will need to determine their preferred cleaning method that conforms to budget requirements.
|Tempo‘s Custom Demo and Evaluation Board PCBA Manufacturing Service
Tempo Automation specializes in low volume production and custom turnkey PCBA prototype development. We build the highest quality boards faster than anyone in the industry and clean every board that leaves our smart factory.
To help you decide the best way forward, we provide information for your DFM checks, enabling you to view and download DRC files. For Altium designers or Cadence Allegro users, just add these files to your PCB design software. We also furnish DRC information in other CAD formats and Excel for Mentor Pads or other design packages.