Seriously, what sadist saw a flat PCB surface, flat pick and place machine heads, and said “lets create a round component”?
Joking aside I am genuinely curious what advantage the MELF design actually offers. I know they’re a pain to get a machine to place properly, they have more solder flow issues than components with flat leads, and they seem like they would be harder to manufacture too. So why a round component? Anyone here have any insight on why they even exist?
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I may be a simpleton, but I’ve always thought that MELF was just old school SMD, where the shape hadn’t evolved yet from the though hole package.
My thought was based on all the old junk I’ve repaired, where the older it was the more likely MELF seemed to be.
I haven’t designed with MELF before, but wouldn’t it make sense for assembly operations to add a MELF fee?
From what I’ve seen I am now inclined to believe the reason people use them is because they’re more durrable and stable environmentally speaking. I imagine the reason you see them less in newer electronics is just because chip resistors and such have gotten better to the point where MELFs usually aren’t required.
As far as the additional fee, I’m not on the pricing side of things but I sure hope we charge extra because the damn things are the bane of my existence.
Working at an OEM that designs their own boards I’ve often wondered the same thing. We only have one designer that used them but they were such a pain in the ass on the pick and place machines. Lots of drops
If you see that designer, you should ask them. There must be a reason they use them other than being a misanthrope.
I spent 3 hours fighting with a Fuzion tonight and even with the special MELF heads it drops enough to reliably jam up other component feeders. Unfortunately our customers pick what exact parts we use so we can’t just change them out for something equivalent but less hateful and I don’t communicate with them so I can’t ask why.
I’m starting to think MELFs are just pushed by big component to get people to buy more components (because the machines throw half of them on the ground.)
You guys made me curious, so I checked Wikipedia:
Despite their handling difficulties, and in the particular case of MELF resistors, they are still widely used in high-reliability and precision applications where their predictable characteristics (e.g., low failure rate with well-defined failure modes) as well as their higher performance in terms of accuracy, long-term stability, moisture resistance, high-temperature operation far outweigh their disadvantages.
I saw that earlier and at first I was thinking that must be outdated BS because none of our class 3 products use them. But, thinking about it now, almost all of our class 3 products are medical products. Meaning they are only ever going to be used in relatively clean and climate controlled environments.
The products we run that most frequently use MELFs are the class 2 products that are going to be used in more rugged environments (like ag products). So if they are more rugged environmentally speaking then that does make sense. It won’t stop me from complaining about them though.
I have never seen them in my short time working on space electronics.
I’m thinking about the products I’ve seen them on now and it’s always the more ruggedized boards but not the ones that are so ruggedized that they get potted or placed in hermitically sealed housings. Maybe if it’s potted or sealed well enough you don’t need the added environmental resistance and stability offered by a MELF.
I’ve never actually worked on anything that went into space to my knowledge but I imagine most electronics going into space you would want to be potted or sealed inside something just so the electronics have something to disapate heat into. That’s about the only situation I can imagine where potting would actually improve thermal characteristics. If that is the case then they would probably not use MELFs for the same reason the sealed electronics I work on probably don’t. Of course I’m still guessing on all of this though.
Fair points. Conformable coats are common in space applications.
Sorry for the slow response. I’ve seen the conversation has continued so this matters less now… But. Our guy that used them retired a few months back. And to your point, he was a misanthrope
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