To Clean or No Clean?

Estimated reading time: 19 minutes

Matties: And their own mindset.

Konrad: We have to educate our customers that cleaning may not be necessary. I wouldn't dare to say everyone needs to clean. I would like to be able to say that and have it be accurate, but it's not true. Not everyone needs to clean. The amount of products requiring cleaning today is greater than it was five years ago and I imagine it will be greater five years from now. It's like a shadow slowly enveloping a land, and if you're in that land and the shadow passes over you, you have to start cleaning. Not everyone is in the shadow. It has to do with the cost of failure. It has to do with the climatic environment that the assembly is going to be placed into. A board in a CISCO server in a server farm at Google or Amazon really doesn't have to be quite as clean as a board on the North Sea oil platforms.

Because the environment is much harsher and the environment plays a huge role in reacting with the residue to create ECM. We look at the climatic environment that the part is going to go in. We look at the cost of failure, airplane crash, defibrillator fails, itchy dog, etc. Then we also, when we get really geeky about it, start looking at the spacing between components. Because of the nature of the way we test for cleanliness, we look at the geographic diversity or differences between spaces of components on boards. That plays a role into how low of a number or high of a number we shoot for in terms of cleanliness. There are a lot of factors in there.

Matties: You just mentioned testing. Talk a little bit about testing and that process. When people use it, how they use it, and that sort of thing.

Konrad: The technology used today and for the last 30+ years for post re-flow circuit assemblies is ROSE testing (resistivity of solvent extract testing). There are four or five brands of testers on the market and they've been around forever. Thousands of them have sold. They express contamination in micrograms of sodium equivalent per square inch. Basically, how much salt would we have to add to the test solution to equal how dirty your boards are? We're not really measuring for salt, rather we're just measuring for how much salt we would have to add to this really sensitive solution to make it as dirty as your board made it dirty.

They're not perfect machines because they don't have the ability to test for every known contaminate. But their kind of like tracer bullets, that the military uses when firing bullets at night. They can't see every single bullet, but they don't need to. They need to see where the majority of them are going and then they can calibrate their aim. Same with these testers. They don't detect everything, but they detect enough stuff common in assembly residues that if they see something you know that there is probably more there. If they don't see anything, then there's really nothing else harmful left on the assembly.

The only thing that one has to know is that the pass-fail limit, which we still use today, of 10 micrograms of sodium per square inch, or 1.56 micrograms per centimeter square, was established many, many years ago before surface mount technology was even around. Although the pass-fail limit is 10, if I were testing boards and I received a 9.9 and my board was going in a medical device or on an airplane or something where failure is unacceptable, I would not go to sleep at night knowing it was a 9.9. because the nature of the test based on averages. So 9.9 could be 20 somewhere else on the board and zero on other places of the board and it's averaging a number over the entire surface area of an assembly.

I would drive that number down and I recommend in no case numbers greater than five. I recommend in most cases numbers lower than one. We like to see cleanliness values in the point range 0.1, 0.2, 0.3, etc. We don't like to see whole numbers. Because that mandates a person start determining the cost of failure and climatic environmental conditions. Rather than do that, just clean a little bit better. Drive a number so low that even if you round it up a little bit it doesn't really matter.

Matties: When people think of test and inspection, this probably isn't a test that usually comes to mind. Or is it?

Konrad: If you're a military contractor, or you're doing high-reliability jobs for flight, medical, etc., this is a common test.

Matties: It's required.

Konrad: Yeah. These testers have been sold by all four manufacturers in the thousands so they're very plentiful and they're very common. They're new to people who are new to cleaning. While not everyone is required to test, I would recommend people to test. The cleaners that we build and that other companies build all have testers built into them. They're not, however, the IPC approved ROSE test. Even if they say they are, there's not one cleaner on the market that has an approved ROSE tester built into it because IPC has a very strict standard of how ROSE testers operate. They have to operate with a very specific test solution. They have to have a very specific algorithm that they run. All of that is controlled through standards. The testing equipment built into cleaners doesn’t meet those standards, because that would actually make a rotten cleaner. It makes a good tester, but a rotten cleaner.

Not everyone needs to go to that extra effort and ROSE test their boards unless they're really concerned about cleanliness or if they're under a requirement to test. If you're under a requirement to test, pick your favorite tester and buy it and get on with it. If you're not under a requirement to test and the cost of failure is so high that you really want to cover your ass, it is a good idea to test. Because now you're meeting an accepted published industry standard.

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