Screaming Circuits: Favorites


What's your favorite MCU package and why?

  • The DIP is big and easy to use. You can stick it in a breadboard (wireless or soldered), a socket or easily hand solder it. But, it tends to be more expensive and takes up more real estate.
  • SOIC is a good step down in size. It can be machine soldered. It's big enough that most people can hand solder in a pinch. But, as an SMT, I'm not sure it has much purpose anymore. If there's an SSOP available for the same part, why would you take the bigger SOIC package?
  • SSOP are nice and small so that, unless you are really tight on space, they'll do just fine. They aren't really any more difficult to layout than and SOIC. If you do need to hand-solder, this package is probably too small. Being smaller with everything else being equal, it might have more issues with heat dissipation than the bigger part or a smaller one with a heat slug under it.
  • QFP - these are just lie either an SOIC or SSOP, but with leads on four sides.
  • BGAs are really compact and and do a good job of keeping signals close to the PCB and to bypass caps. They can be a challenge to layout though. Many will require upping your layer count. The really fine pitch BGAs may require expensive PCB features such as blind or buried vias. CSP and WSP BGAs can be more difficult to handle because of their small size. Breathing on them wrong can toss them around like dust.
  • QFN and DFNs are somewhat newcomers to the scene. The package can lead to some very tiny components. It's great for signal cleanliness and the heat slug underneath can dissipate (with proper layout) a lot of heat. But, QFNs and DFNs seem to garner the most layout problems. Careful use of thermal vias is critical for maximum performance, but you either have to use expensive techniques, such as filled and plated vias, or you have to rationalize and get around some nearly mutually-exclusive requirements.

Yeah. They all have their pluses and minuses. Fortunately, with proper board design, our SMT machines can place all of the these types all day long without breaking a sweat. All the SMT designs, that is. We do hand place the DIPs. What's your preference?

Duane Benson
All we are is BGAs in the wind


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Hackcasual - thanks for pointing Chad in the right direction. I've been falling down on my blogging job lately. Here's another one to check out:

According to the folks at Ti, layout is one of the biggest factors in success with the part.

@Chad Here's a blog post from when Screaming Circuits assembled a beagleboard, it's specifically about PoP:

Recently we have done some designs with the T.I. OMAP processor family, which uses Package-on-Package (PoP) technology to attach the memory device.

Have you folks at Screaming Circuits encountered this assembly method yet?

Personally, I've come to prefer QFP for things with a medium to high pin-count (the larger-pitched versions are pretty easy to hand-solder), and SOIC for low-pin-count designs.

In my experience, you pick QFN/DFN for its thermal properties or for its smallness - it doesn't really have many other redeeming features over the other packages. Since most MCUs aren't very challenging to design with from a thermal perspective, that means I'll only be likely to use a DFN/QFN if I'm building something exceedingly small - and the ironic thing is that due to the inability to (reliably) put vias underneath a DFN/QFN, it sometimes requires *more* space than a similar SSOP/QFP.

BGAs are fine for what they are, but I've never seen the need for one yet in my designs - and there'd have to be a pretty good reason for it too.

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