Everybody has a few loose PCB components lying around. Sometimes it's a few chip caps left over from a hand-rework task. Sometimes it's a tiny QFN or big old BGA. These days, every good engineer has a little box or two full of loose parts, ones that are taken from a cut strip, fiddle with, and then just never put back together.
And it's not always easy to put them back in the strip anyway, which isn’t a big deal for passives and inexpensive parts, because when you need something assembled, you just buy another strip of ten for $0.29.
From time to time, PCB assemblers are asked if we can take in and assemble loose parts. While the answer differs from company to company, the response is often “maybe.” PCB assemblers can sometimes assemble from loose parts, but it's never a good idea. They can be dirty, damaged or of mixed value. It takes assemblers extra labor time, which will probably be charged back to you.
Because we're using robots to assemble, we'll have to put all of those loose parts into an empty strip — which is a pain. And we’re not the only ones that feel this way. Components manufacturers don't want you to store your parts loose either. They know that having the things rattle around can cause damage or contamination.
When it comes to the bigger, more expensive parts like BGAs, fine pitch ICs and QFPs, it’s a serious issue. The leads on the fine pitch parts tend to bend when jumbled up. If the QFP ends up with some pins bent or the BGA has some balls drop off, you've probably lost your prototype — which just might ruin your day. So keep those expensive parts in their original packaging.
When you look at the total system cost, a new part or two probably isn’t expensive anyway. A Freescale MCIMX31LVKN5B processor in a 457 ball BGA is around $26.00. Getting a new one of those is pretty cheap compared to the risk of spending a week trying to diagnose a problem caused by a BGA ball that cracked because of poor storage.
There are some processors, FPGAs and other specialized components that can cost hundreds or even thousands of dollars each. Those parts are probably worth repair if pins are bent or balls are knocked loose, but the best bet is to keep them in their original, not extra crispy, packaging.
So the long and short answer to “should you send your PCB assembler loose parts” is no. If you have loose parts, you’re probably best off just buying new ones. If you don't have a choice, go ahead and give your assembly house a call.
Duane Benson is Chief Technology Champion at Screaming Circuits.