I've seen that many (if not all of them) MEMS, like accelerometers, they are only available in QFN packages.
Why is that?
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2 Answers
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Simply because: what else would you want to use?
- Chip-scale packages are typically out: MEMS devices typically need reliable enclosure; a layer of lacquer typically doesn't work.
- flip-chip BGA plastic packages minimize area of contacting (if you can't do chip-scale), but that's often not technically viable due to the MEMS structures being exactly where the balls would end up
- QFN is small enough for most applications, and cheap.
- Anything larger is undesirable because a) larger than necessary without being any easier to work with and b) more expensive, even if only for economics of scale: the very vast majority of MEMS applications will prefer the QFN package, so the other packaging option induce a higher per-device packaging cost.
- EEs will prefer packages they're used to work with – QFN is among these, and one of the, if not the, easiest to solder correctly IC package.
- Leaded packages are unattractive for applications that are subject to vibrations and the like, which is exactly where a lot of accelerometers are used.
answered Jul 24, 2019 at 12:04
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3\$\begingroup\$ QFN being one of the easiest packages to solder doesn't line up with my experience, but that experience is entirely soldering by hand, so perhaps they're just easy to reflow. \$\endgroup\$– HearthJul 24, 2019 at 14:18
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2\$\begingroup\$ I found them pretty easy to solder with paste & heat gun, given you get your pads separated – solder mask in between pads works surprisingly well, if you don't have a stencil. \$\endgroup\$ Jul 24, 2019 at 15:00
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1\$\begingroup\$ try with a really small amount of paste! \$\endgroup\$ Jul 24, 2019 at 15:18
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1\$\begingroup\$ I've not used paste before, just solder wire, which may explain why I've found QFNs so difficult! \$\endgroup\$– HearthJul 24, 2019 at 15:18
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1\$\begingroup\$ Oh, it's absolutely a non-starter these days, but DIP was really easy to manage by hand. I've done QFN, but I'll definitely say that QFP is easier to do by hand, at least without professional-level equipment. \$\endgroup\$ Jul 25, 2019 at 9:49
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It is not true that they are only in QFN enclosures. Look, for example, to the Farnell website and see how many types of package there are: https://pl.farnell.com/c/polprzewodniki-uklady-scalone/czujnikowe-uklady-scalone/moduly-mems
