PCB Friday: Microcontroller Packages 101

If you've been making custom microcontroller boards for any length of time, you're familiar with various chip packages and how they mount to a PCB. At the same time, if you're just starting out, package names like SOIC, PDIP, and BGA may seem like a foreign language – even if you're familiar with using an Arduino dev board.

In this PCB Friday article, I'll introduce some of the more common microcontroller formats, helping you go from blinking an Arduino to implementing your own custom boards... which may also blink.

Through-hole microcontroller packages

Through-hole technology (THT, AKA through-hole device, THD) microcontroller packages, as the name implies, consist of conductors that poke through holes in a PCB to be soldered. THT is older tech, replaced, in many cases, by smaller, and more easily machine-assembled surface-mount technology (SMT, AKA surface-mount device, SMD) chips, discussed later.

DIP: Dual in-line package

Dual in-line package chips feature two parallel rows of connector pins, typically sticking out of the two longer sides of the chip. Connector pins in each row are spaced at 2.54mm (.1") centerline-to-centerline, perfect for poking into a breadboard or perfboard. You might see these chips with modifiers before or after the DIP moniker, such as:

• DIPn: e.g., DIP14, DIP28, where n is the total number of pins. A DIP-format ATtiny85, with four pins on each side, is a DIP8 chip.
• DIPN or DIPW: N or W signifies narrow (.3") or wide (.6") chip formats. The wide/'W format isn't that common today, and brings to mind Sega's YM2612 sound chip of old.
• PDIP, CDIP: P or C indicate plastic or ceramic DIP, with the P version being more common. So a plastic DIP ATtiny85 could come in a PDIP8N format.

As seen above, multiple modifier characters can be used together. For example, a narrow plastic DIP chip with 8 total pins (i.e., an ATtiny85) is a PDIP8N chip. However, not every possible character is always used. A PDIP8N chip may simply be referenced as DIP8.

Other formats include the single in-line package (SIP), which sort of looks like the DIP format with one line of contacts cut off. Not to be confused with an SiP, or system-in-package, which is basically a bunch of chips shoved into a bigger chip. You also might also encounter the QIP, or quad in-line package, which is like a DIP, but with more closely spaced legs that alternate between long and short leads.

Surface-mount technology microcontroller formats

These days, if you're doing any sort of microcontroller development outside of the early prototyping or a one-off make, you're more than likely going to go with an SMT chip format. Being smaller and easier to machine-assemble, SMT has a lot of benefits. At the same time, placing them on a breadboard typically means using some sort of carrier PCB, so they are slightly harder to prototype with.

So, what kind of formats/acronyms will you run into in this realm? See below for a list of possibilities, roughly listed in order of hand-solderability.

SOIC: Small-outline integrated circuit

Shrink a DIP chip to half its size or so, push out the legs for surface-mount soldering, and you have a SOIC chip. The pin-to-pin pitch of a SOIC is 1.27mm (.5"), and SOIC chips may be defined by either JEDEC or JEITA, with slightly different characteristics.

While not the most compact SMT microcontroller format, SOIC is arguably the easiest to hand-solder, and if you are familiar with the pinout of a DIP chip, the equivalent SOIC chip will likely have the same pin arrangement. If you're a through-hole hacker and want to make the leap to SMT, SOIC is the format for you.

QFP: Quad flat package

Once you start using SOIC chips, you might logically consider why you're only using 2/4 sides for IO pins? As an answer to this question, QFP chips are (typically) square-shaped SMT chips that poke leads out of each of their four sides.

QFP chips often have an IO pin pitch smaller than the 1.27mm SOIC standard, allowing them to pack in many 10s or even 100s of pins on their perimeters. Variations include thinner versions like TQFP for thin quad flat package, or VTQFP for... very thin quad flat package, and several others.

While challenging, you can hand-solder these chips with enough flux and determination.

QFN: Quad flat no-lead

QFN microcontrollers get rid of external leads altogether, leaving only conductive nubs for connections. QFN devices can be challenging to solder, though even with my rudimentary skills, I've had success using a solder paste/stencil/hot plate setup. Supposedly, you can use a hot air gun or even a soldering iron with a fine tip. If you're assembling more than one or two, I say let your board house take care of it, saving you the hassle.

You might argue this format isn't particularly conducive to hacking/prototyping. However, these chips occupy less board space/IO than their external-lead counterparts, making them less expensive to implement en masse.

BGA: Ball-grid array

If you can solder to little pads on the perimeter of your QFN chip, then what is to stop you from soldering to pads in the middle of your chip with the proper heat application? This is indeed possible, using a grid of contacts connected via solder balls in an array on the underside of a chip. BGA tech represents another leap forward for IO/chip surface area.

Of course, hand-soldering BGA – in the traditional smell-chicken-you're-doing-it-wrong sense – is impossible, and using solder paste and a heat gun or rework station is apparently not easy either (I've yet to personally try it). Finally, beyond exotic tech like X-ray machines or CT scanners, there's no way to visually inspect that everything is properly soldered.

Of course, if you're getting someone(robot) else to precisely assemble your design, that becomes their/its problem. For purposes of this article, just know that BGA microcontrollers exist (here are 6000+), but if you're reading this 101 article, you probably want to start with something easier.

Standardized packages are awesome

While terms like BGA, QFP, and DIP might seem complicated and foreign at first, they do eventually become familiar. Given the number of parts floating around from the last 50 years, from a wide range of manufacturers, it's impressive things are as standardized as they are!

So when you're ready to take the leap from Arduino and other dev boards to a fully custom microcontroller implementation, you now have some sense of what's available. I suggest starting with something simple in a DIP or SOIC format. Leave the BGA, and QFN components until you have a bit more experience under your belt!

Thanks for reading!

Thanks for reading my biweekly PCB Friday column! I'm looking forward to sharing more PCB-related knowledge and insight here, and I hope you'll follow along for the journey. You can find my more semi-technical musings at TechAdjacent.io, or email me at hi@jeremyscook.com if you have any suggestions!