I have not come across a wait time from soldering to cleaning under normal circumstances. Most solders appear to be amenable to functional testing of circuits almost immediately, assuming the temperature of the board is ok.

With regards to conformal coating. PCB materials soak up moisture very quickly. You can test this by taking a board and baking it overnight at 120Deg C. Weigh the board and weight it again each hour and plot the weight gain over time. You will see that within a couple of hours the boards will soak up the ambient moisture.

There are a number of factors that can impact the adhesion of the coating to the board. I happen to believe moisture is one of them. My preference is to coat a dry board. Over time moisture will ingress through a conformal coating but the better the adhesion to the board the less chance you will have delamination of the coating.

Steven Adamson Market Specialist, Nordson ASYMTEK Market Specialist for Nordson ASYMTEK. Mr. Adamson worked for Kodak, Motorola and Plessey, ICL in the UK with 5 US and 2 UK patents. He was awarded a HNC in electrical engineering and was 2008 President of IMAPS. Mr. Adamson was a respected mentor in the electronics industry. He passed away October, 2011. Learn about the Steve Adamson Memorial Annual Scholarship Fund.

As a rule, the sooner after reflow you clean a PCB, the easier it is to remove flux and other residues. After cleaning, the PCBs should be allowed to dry completely before any power is applied.

After heat testing, they just need to cool to room temperature before functional test. Unless a second round of cleaning is required after all that testing, there is no reason to wait before conformal coat.

John Vivari Application Engineering Supervisor, Nordson EFD Mr. Vivari has more than ten years of electronic engineering design and assembly experience. His expertise in fluid dispensing and solder paste technology assists others in identifying the most cost effective method for assembling products.

Typically the only two that are critical are reflow to clean and clean to coating and it depends on what are you cleaning off and how.

Terry Munson President/Senior Technical Consultant, Foresite Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.