Highly advanced PCB technologies to include newer, smaller packaging, as well as ever shrinking board real estate demand the ultimate PCB cleaning solutions possible. Cleaning solutions, methodologies, testing, analysis and special chemistries are being taken to a new level these days. The goal is to assure OEMs of ultra clean boards to avoid costly latent issues that can ultimately surface once a product is in the field.
There is a vast array of residues and contaminants that can be left on a PCB, as shown in Fig. 1. Therefore, ultra PCB cleanliness is critical for all applications, but in particular for mil/aero and medical electronics ones. Flux residues need to be removed to improve the integrity of the process such as bonding and conformal coating.
Even the tiniest amounts of residue left in poor wetting or de-lamination can cause assembly failures and subsequently lead to field failures. Also, small amounts of flux remaining trapped under the board can change impedance and resistivity characteristics.
Take a few minutes to learn more about the issues poor PCB cleaning can create in our SMT Magazine’s “Zulki’s PCB Nuggets” column.
But, meanwhile, here are some tips and hints to get you better acquainted with the criticality of PCB cleanliness and how you can take the necessary steps to get a better handle on this subject.
- Overall, find out if PCB assembly personnel have taken all possible measures and steps to assure your devices and boards are ultra clean.
- Get familiar with ionic and non-ionic contaminants as the basis for discussions with your EMS Provider.
- Find out what special cleaning technology and care your PCB application requires.
- Understand cases where de-ionized (DI) water cannot be used for cleaning your PCBs. Find out why.
- Learn from your EMS Provider why your PCB project needs certain cleaning solutions to help maintain high reliability.
- Understand as much as possible about different contaminants and how to test for them.
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. Traditional Ionograph testing and other methods can best perform that testing.