PCB Technology has advanced so much that even the board cleaning process literally takes on new meanings. In short, this means if proper cleaning agents aren’t applied, a board may still have flux and solder paste residues trapped inside the small cavities. In turn, this hinders the board’s optimal performance since transmission and return signals are not 100% clean, especially with high-speed designs.
Cleaning PCBs has been relatively traditional with the use of water-soluble flux. However, today, the industry is switching to no-clean flux due to greater usage of QFN and flip chip devices on the PCB, which are better assembled using no clean flux. In those cases, special chemistries and aqueous batch cleaning take on a more important role compared to de-ionized water.
There is considerable information on this subject and its best to read our article appearing in Modern Printed Circuits Magazines. Click here to get more details. Meanwhile, here are some tips and hints that’ll help you get a better understanding:
- A second clean cycle is applied and then an ionograph machine (Fig. 1) is used to assure proper cleanliness when improper cleaning agents are used during the initial clean cycle.
- When residues and contaminants get stuck on a board, performance issues either emerge right away or remain latent, subsequently causing major system flaws in the field.
- No-clean flux residues left on a PCB create voids with a conformal coating. These result in air gaps or pockets creating major problems especially when these boards are subjected to harsh and rugged environments.
- Flux residues in high-voltage PCBs have a high probability of creating a spark between two points and short the circuit.
- The higher the frequency, the cleaner the PCB surface has to be. The slightest speed transfer change in a return path compared to the transmit path can have major consequences on performance.
- Flux residues can have a damaging effect on image processing-based applications for medical electronics leading to distorted results being read from such instruments.
It’s also important to know vendors add or delete certain chemical properties from their cleaning agents. When this occurs and changes go unannounced, it leaves the EMS Provider and CM guessing as to the proper PCB cleaning mix to avoid damaging boards.
Therefore, it’s highly important for the EMS Provider and CM to be at the top of his game and have up-to-date knowledge, expertise, and experience about today’s cleaning agents and their characteristics.
This includes expertly matching the right cleaning agents with the right PCB applications, fully understanding certain chemical properties in cleaning agents produced by specific vendors, having full knowledge of how to read and understand technical specification sheets, and making the right decisions based on precise know how.