Unfortunately, today’s advanced PCB technologies can pose costly latent issues that ultimately surface when a product is in the field. That’s why cleaning methodologies, testing analysis, and special chemistries are being refined and taken to a new level. Doing so is crucial to assure OEMs and their end products of ultra clean boards to avoid those kinds of problems.
Board cleanliness is especially critical for mil/aero and medical applications. The right kind and amounts of cleaning agents need to remove flux residues to improve the integrity of the process such as bonding and conformal coating. During the coating process, if residues are left in poor wetting or de-lamination, they can cause assembly failures and ultimately lead to field failures.
For more details on PCB cleaning technologies, testing analysis, and special chemistries, read our article appearing in STM Magazine.
In the meantime, here are some tips and hints to help guide you in achieving ultra clean PCBs.
- Get your EMS provider to give you a basic 101 understanding of an ion chromatography meter and how it performs a high level of ionic contamination testing.
- Understand that even a tiny amount of flux trapped under a PCB can change the characteristics of impedance and resistivity. Ultra cleanliness is crucial if underfil or conformal coating is applied to a device.
- You, the OEM customer, can sometimes prescribe special washing techniques. But when they’re not prescribed, an assembly house uses special chemistries like batch cleaning, as shown in fig. 1.
- Sometimes special agents cannot be cleaned at a specific temperature, so cleaning agents need to be changed. Different permutations are required to achieve better results, making de-ionized (DI) water purer and cleaner.
- Special care must be taken for cleaning technologies used for certain PCB applications. The cleaning process can change when a cleaning solution’s conductivity is changed due to different residues left on a PCB.
- Keep in mind a vast array of either ionic or non-ionic residues and contaminants can be left on a PCB. Ionic residues can completely dissociate into negative or positive particles, changing overall conductivity of the solution.
Monitoring and qualifying the degree of cleanliness is absolutely important to make sure final assemblies are acceptable per IPC Class 3. There is some ambiguity in Class 3. However, there are a number of techniques deployed in terms of cleaning the PCBs, many are commonly used in electronics manufacturing in conventional ways.
Other cleaning techniques are in R&D, although newer cleaning products are coming on the market. But the point is cleanliness testing is critical. Ionograph testing and the other methods discussed above can best perform that testing.