Phil
And welcome to Board Talk. This is Jim Hall and Phil Zarrow, the Assembly Brothers who by night work for ITM Consulting, on Board Talk, and we're here to talk about processing questions and problems and issues of the day. Jim, what's today's question?

Jim
Okay, today's question comes from NL. "Currently, we are using ultrasonic cleaning to remove no clean solder paste and it works fine. However, the use of ultrasonic system causes damage to one ultra sensitive SMT component. Can you recommend a method we could use to prevent damage to this component caused by the ultrasonic cleaning process?"

Phil
Okay. Well, first of all, yeah, don't put it in the ultrasonic cleaner. Okay, that was kind of trite. I think for the first point, I think ultrasonics and ultrasonic cleaning for a long time got a very bad rap. This would be one for myth busters but it's a little too esoteric. But the theory was you put components into the ultrasonic cleaner and the ultrasonics would cause wire bonds to break and things like that on IC's and sometimes it would crack capacitors, things like that.

Probably the most informative study was done, oh, many, many years ago, I would say at least 15 years ago, by John Maxwell, known in certain circles as Mr. Capacitor, Mr. Big Capacitor. And John was doing a study for one of his clients at the time and he found – and he tested this at various frequencies through the spectrum that ultrasonic cleaners might operate that indeed there was no damage promoted by the immersion of these components on boards into the ultrasonic cleaner and whatever the medium was in there. So that was one thing.

Now the other thing was, of course – and again, we don't know what this particular ultra sensitive SMT component is, NL.

Jim
Phil, it really doesn't matter because this is an answer that you'll never prove 100 percent. The basic physics is that ultrasonics operate at typically a certain frequency and if you have something in any particular component that resonates at that frequency, the potential for damage is there. Well, the potential internal construction of components is infinite in variety so you could never test every possible component so it's very possible that for your system, particularly if you don't have the chance to vary – to use different frequencies or if your system doesn't vary the frequency by itself, that you just happened to hit a component that has something in it that's resonating at the frequency of your cleaner.

Phil
Right, but there's another possibility, also. You may be uncovering a latent defect in that component itself. One of the other things Maxwell discovered was that in many cases, particularly these little capacitors – I did say he was Mr. Capacitor – was that in many cases where the dielectric was not fired properly, this would basically ultimately there would be cracks induced in that component. All the ultrasonics did, it would accelerate the development of that crack. So think of it almost like extremely accelerated life testing. It will show that defect on earlier mortality being in your facility rather than in the customer's facility. So what Jim says is exactly true, but again, sometimes it could be a good thing as a heads up.

Jim
Right. If you think about wire bonding, if your wire bonds aren't completely encapsulated when they do the over molding, maybe it's good that it gets broken in there. But if you're seeing this consistently, it's probably a system-level problem.

Phil
Yeah, and be sure it actually is the ultrasonics that's causing this problem.

Jim
But there are still many people who say don't use ultrasonics. There's just a certain amount of risk that you'll never be able to mitigate. All right, I think we've beat that one to death..

Phil
I think we cracked it up, yes –

Jim
We cracked it.

Phil
And again, we appreciate your hitting the little button and sending us your questions, comments, and preferably non-derogatory remarks. And on that note, I will say this is Phil Zarrow and Jim Hall, the Assembly Brothers, and whatever you do –

Jim
Don't solder like my brother.

Phil
And don't solder like my brother but feel free to put him in the ultrasonic cleaner.