Screaming Circuits: Bouncing BGAs


Bouncing BGAs

I dropped my cell phone on the pavement the other day. That's bad enough, but in my instinctive attempt to catch it, I actually hit it and increased it's downward velocity. Luckily, everything still works. The odd thing is that I just assumed that it would still work. No real questions or doubts on that thought.

That realization got me thinking. (it happens now and then) What other devices do I have that I automatically expect to survive a drop onto concrete? I have a carpenter's hammer. I expect that to survive a drop intact. I would not expect my camera to survive such a drop intact, and have empirically verified that fact. A little car GPS? Probably not. Laptop; uh... no.

I'm sure there are some other devices that would easily survive. I just can't think of any off the top of my head. I suspect that there are a lot of factors that go into making cell phones survivable. The case, the overall mass, the quality of solder joints.

Along those lines, some folks use an underfill glueish type substance to hold their BGAs more securely. Some designers use pick and placeable solid underfil. Some just rely on extra good soldering and some leave it to luck. Of course, not all BGA installations require much shock resistance. How do you secure your parts when shock or vibration are serious concerns?

Duane Benson
Quick, where's Henry? I need an inductor.


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I know that at most reputable consumer electronics companies (well, the two that I've worked for -- and some that my friends work for), there is quite a rigorous drop test. It's brutal seeing your product dropped from 3 feet directly onto a 1" thick steel plate. Then again and again on all sides and corners. That's a lot of energy with a 9 lb plastic audio product.

The amazing thing is that as long as the industrial/mechanical designer has done their work right amazingly little breaks. Then we take it apart and look at the PCBs. I've had a few cases where we needed to modify the pcb to move components out of the way of other bits to avoid them being crushed, but by and large the PCB survives. On our portable product, we used underfill on the BGAs, but Im not sure that it was ever verified to be mandatory to pass the drop test.


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