Transcript
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 N.L. "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
First of all, don't put it in the ultrasonic cleaner. Okay, that was kind of trite. I think ultrasonic cleaning for a long time got a bad rap. This would be one for Myth Busters but it's a little too esoteric. The theory was you put components into the ultrasonic cleaner and the ultrasonics would cause wire bonds to break on IC's and sometimes it would crack capacitors.
Probably the most informative study was done at least 15 years ago, by John Maxwell, known in certain circles as Mr. Capacitor. John was doing a study for one of his clients at the time. He tested 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 regardless of the medium.
Jim
It really doesn't matter because this is an answer that you'll never prove 100 percent. The basic physics is that ultrasonics operate typically a certain frequency and if you have something in any particular component that resonates at that frequency, the potential for damage is there.
The potential internal construction of components is infinite 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 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
There's another possibility. You may be uncovering a latent defect in that component itself. One of the other things Maxwell discovered was that in many cases where the dielectric was not fired properly, ultimately there would be cracks induced in that component. All the ultrasonics did was to accelerate the development of that crack. So think of it almost like extremely accelerated life testing.
Jim
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 brakes. But if you're seeing this consistently, it's probably a system-level problem.
Phil
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.
Phil
On that note, 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.
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