PCB Assembly Services - Screaming Circuits: Law of Conservation of Parts


Law of Conservation of Parts

Reels of parts are the way to go when you need a lot of boards built. It's just not practical to deal with a bunch of cut strips when building hundreds or thousands of boards. It's even easier to use reels with small quantities, because the pick-and-place machines are designed for quick loading of reels.

However, reels can be a bit wasteful when you just need a few boards. But there is no need to waste those extra parts. You can send us cut strips for your small quantity builds and we can still machine assemble from those strips.

Sometimes buying in strips is more about conservation of cash too. Say, for example, you need 20 2.2K Ohm, 5% 0805 resistors. You could buy a small strip of 25 from Digikey for $0.32. That gives the 20 you need, plus a few spares just in case.

Alternately, you could buy a digi-reel ( a custom quantity reel). On the reel, you'll probably want more parts to keep the strip long enough for the feeder. Let's go with 250 parts for $1.39. Digikey charges $7.00 extra to create a custom reel, so that's a total of $8.39. Still peanuts.

For a third choice, you could just buy a full reel of 5,000 for $10.64. Still peanuts. If you're gong to need the same part for a lot of designs, this might make sense. But, there's more than just cost to consider. You need to store and ship it. Shipping two dozen reels gets pretty expense. Storing and inventorying several dozen reels can become a hassle too.

Cut strips on plateThe beauty of Digikey, Mouser, and other places that sell cut strips is that they essentially become your parts warehouse. You pay the $0.32 cents and never have to worry about whether the part is in your inventory, how many are in your inventory, digging it out of wherever you stuffed the reel when you last needed it...

If you do buy and store the whole reel, you don't need to ship the entire reel to us. Just cut a strip with the number you need, plus about 10% for that "just in case" (50% extra for tiny 0201 parts). In disrupted supply chain times like these, every little component is a potentially valuable resource, so keep the trimmings and feel free to use them for your small quantity builds.

Of course, if you need a few thousand of the parts, go ahead and send us the reel. It would make sense then.

Duane Benson
The law states that if a reel of 1,000 parts is cut into ten equal strips of 100 parts, you still have 1,000 parts
Unless you cut through a part. Then you will have less.

And don't forget, conservation of parts or not, Screaming Circuits is always here to build your prototypes and on-demand electronics manufacturing. Visit www.screamingcircuits.com and get a quote.


Yes, pretty much everyone can machine place from cut strips these days. We have a plate system. We do still like a few extras because the machines sometimes spit parts out, but the strips are good parts to us, not waste or just hand-add fodder.

If the parts are cheap, I try to order extra so there is some header for the machines. But even in cases where there is no header, Screaming Circuits and other CMs have a way to work magic and use them.

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