There's a component so useful, it's in every single piece of electronics. It's so ingenious,
it's been almost unchanged since World War II. It's so important that every electrical
engineer learns to design them. You won't find this component anywhere on a board, because...
it IS the board! I'm Zack Freedman, welcome to Voidstar Lab, and today we're asking a
big question about something that everyone takes for granted - why are circuits on boards anyways?
Every modern electronic device, whether it's a nuclear-powered space probe from 1977
or a self-balancing rideable beer cooler from 2020, has at least one
printed circuit board at the center. It's the most ubiquitous electronic component of all.
It's the technology that literally holds the world of electronics together,
the printed circuit board. You might have noticed that electronic components have become
a liiiiittle more advanced over the last century. This is a capacitor from the 1940s - it's made
of foil and paper soaked in electrolytes. This is the modern version - it's made of metallized
film and a gel electrolyte. Electrolytes - they're what electrons crave. This is Intel's cutting-edge
1971 processor that features a whopping 2,250 transistors. Here's their 2020 model with about
three and a half BILLION transistors. This is a printed circuit board from the 1950s - it's
made of copper on fiberglass. This is a 2020 circuit board, made of... fiberglass and copper.
Once upon a time, there were no boards at all. Manufacturers glued or screwed components directly
to the device's chassis, and then soldered the wires to each other. Point-to-point soldering
made early appliances possible, but it was crude. That web of twisted leads was not a good use of
space. It took a lot of manual labor to assemble, it made complex circuits diabolically snarly, and
it gave fork-wielding toddlers a buffet of options to zap themselves into the shadow realm.
Gosh!
As time passed, devices grew more complicated and wire wrapping was invented to cram more parts
into the same amount of space. Technicians stuck the components through a perforated
wiring board - literally just a board with holes - and they used a power drill to wrap little
wires around each of the leads. They routed the wire where it had to go, wrapped the other end,
and bam! Connection made. It looks nice and tight on top, but on the bottom...
[Cliche screechy horror string music]
This brings us to World War II. America had to shove a ton of electronics into a bomb THIIIIIS
big. Wire wrapping and point-to-point soldering were not only too bulky, they were far too
labor-intensive for wartime production. Instead, the Army screen-printed metallic paint onto a pair
of ceramic discs and soldered parts in between them. This didn't just speed up production - this
new so-called printed wiring board was more compact, more durable, it was easier to repair,
and it was harder to short, and these are all features that you want in a warhead. By 1943,
in the thick of World War II, the U. S. of A. had covered the country in an entire industry
of board fabricators just to make more of these fuzes. Anyways, a couple years passed,
America stuck 32 electronic detonators in a different kind of bomb, and we ended World War II.
As the war machine unwound, the birthplace of the stuffed-crust pizza found itself dotted with a
network of large-scale circuit board manufacturers who had just lost their biggest client. Soon,
cheap printed circuit boards were making their way into industrial, and then consumer products, and
a lot of former professional wire wrappers were... were checking the help-wanted ads. PCB's really
electrified the electronics industry. Before, you needed an entire factory full of artisan
wire wrappers and professional solderers just to manufacture a piece of electronics, but now,
all you needed was a stack of boards and a river of solder. Companies could suddenly produce a
wider variety of products, pack them with even more components, and sell them at even more
affordable prices. Parts manufacturing absolutely exploded to keep up with this demand, which
enabled even more consumer products, and that in turn begat even more demand and even cheaper
parts. The next thing you know, you're watching YouTube in the bathroom and you forgot to wipe.
Since 1943, electronics production has become way cheaper, safer, easier, and sexier,
but at the end of the day, circuit boards are basically the same today as they were back then.
They might be more angular and more green, but a printed circuit board is still
a thin stiff board with copper printing... for your circuits. Let's snoop around!
These are the traces, which carry electric current just like flat wires. This is a via,
a little tube-shaped wire that connects a trace on top of the board with a trace on the bottom.
This is a through-hole pad and this is a surface mount pad; components get soldered onto these
pads to connect them to the circuit. But the board also physically carries the components,
too - soldering a component onto the board makes a mechanical connection
as well as an electrical one. The board itself is made of an insulating high-dielectric material.
That means it doesn't conduct current or allow high-voltage arcs to punch holes through it. The
first commercial circuit boards were made of cardboard hardened with phenolic resin;
it turns out that running electricity over paper soaked in tree sap is actually a really
bad idea. Nowadays, we usually use fiberglass because it's tougher and it's heat resistant.
In fact the most common material is called FR4 - that's flame retar[REDACTED] type 4,
which actually extinguishes itself if it catches fire. Fun fact: Nearly every modern circuit board
actually fluoresces green under a blacklight. The manufacturer mixes a glow-in-the-dark dye
into the fiberglass so that assembly robots called pick-and-place machines can easily see
the board. Pick-and-place machines are really cool and they're going to get their own video,
and if you want to see that video - call to action - subscribe and hit notifications.
[Bling!]
The board begins life as a sheet of copper clad - that's a stiff backside with copper foil glued
to it that covers the entire board edge to edge. The PCB fabricator, AKA the fab house, draws the
circuit onto the board using a chemical-proof paint called resist. Then, the board is dunked
into etchant, which dissolves the exposed copper. Only areas covered by resist stay on the board. A
technician washes the board off, drills holes for the components, and bam! Printed circuit board.
Back in the day, an engineer would literally paint the traces, by hand, with a brush,
onto the screen used for printing. This is why old-school circuit boards have those whimsical
curvy traces and those teardrop-shaped pads - because those organic shapes are easier to paint.
Artwork for modern boards, with all the angles, is generated by an EDA program - that's electrical
design assistance - instead of by a steady-handed engineer. A photolithographic printer applies the
resist, and a computer controlled CNC mill, not a grizzled chain-smoking machinist, drills holes and
mills slots. But what's really neat is that even though the manufacturing has become a lot fancier,
modern PCB's are still like old school PCB's - they're still thin, stiff cards,
they got copper printed on them, they got holes drilled in them, and we stick stuff to the copper.
Since World War II, we have made some improvements. The most important is solder mask,
which is this enamel-like paint that protects copper traces from corrosion and prevents stray
solder from shorting circuits. That was a tongue twister! Most circuit boards are green because
they have green solder mask. It's... it's just... it's just green paint. Isn't that a letdown?
On top of the solder mask, there's markings, part numbers, etc. called an overlay; it's
screen-printed on to make life easier for jabronis like us to hack stuff. One set of wires is nice,
but what if we need even more wires? Let's double the fun by putting another set of traces,
mask, and overlay on the bottom side too! Now we got ourselves a dual-layer board.
Need even moooore wires? Just laminate a bunch of extra-thin boards together into
a Scooby-Doo sandwich and you got yourself a multi-layer board!
[Cartoonish munching noises]
Most modern devices actually still use double-layer boards because they're cheap,
but some PCB's, like the ones in computer motherboards, can have more than 20 layers!
So now we need to connect these layers of traces together. Solder a wire from the top
to the bottom nah? Drill a hole and electroplate it? Yeah. The same way that steel rusts, exposed
copper will corrode in air; we might as well gold plate the entire board while we're at it!
I love goooooold!
Finally, those big through-hole components with those wires that have to be jammed
through holes? Yeah, they gotta go. We replaced them with teeny-tiny surface-mount components
that use conductive pads on the ends. This is called surface mount technology because
they're soldered directly to the surface of the board as if the solder were glue.
They don't have wires that punch through the board and get soldered on the other side.
Manufacturers continued to make chips smaller even as they crammed in more and more features.
Some parts now have so many signals and need so many wires, they can't physically fit the pins, so
we've changed the connecting pins from metal tabs around the edge of the chip into a grid of metal
balls on the bottom of the chip. These ball grid array parts can expose hundreds of electrical
signals in only a few square millimeters, so modern boards need ultra-thin traces that
run in three dimensions just to spread those signals out far enough to wire up the part!
But what about those fancy flexible circuit boards the kids keep talking about? Will we ever be able
to roll up our iPads and smash a mosquito with Reddit? Flexible circuit boards are actually
really common nowadays. The only difference between a flex board and a rigid board is that the
flex board replaces that fiberglass with layers of a thin heatproof rugged plastic called Kapton.
Flex PCB's are way thinner than fiberglass and you can integrate cables into the board itself. Flex
PCB's are great for bending around obstacles and for tucking electronics into nooks and crannies.
What they're not very good at... is flexing. The first problem is that the board can bend
but the components can't. The second problem is that flexible PCB's take damage every time they
wiggle. Eventually the layers of plastic and metal will delaminate and the board will peel apart.
The thicker the board is, the more it strains when it flexes,
so we can't pile up multi-layer flex boards the same way we can stack up rigid boards.
[Canine ingestion]
Modern devices combine a stiff main board that has the most intricate circuitry
with flex PCB cables and modules wherever the engineer can tuck them. Flex PCB's are
really designed to flex just a single time, and that's when the device is assembled.
But can't we just go back to sticking components right to each other, or even integrate every
single component into one giant mega-chip? That way, we could trim off most of the board
and make the device that much smaller. Well, not really. The ability to put off-the-shelf
parts on custom boards, even though it makes the part a bit bulkier, is actually a good thing.
Modern devices have a lot of parts - you got processors, memory, modems, transceivers, sensors,
secret government espionage chips, security chips to protect you from secret government espionage
chips, and blinky blinky lights. Getting all those manufacturers to combine all their parts together
would be an absolute nightmare, and even if you managed to pull it off, you'd never be able to
make any design changes because everything's fused together into one chip! Integration is risky - the
more stuff you cram into a single package, the higher the odds that a single defect breaks the
entire thing. Stuff breaks - if everything is in one place, the device is impossible to repair.
This is still a big deal. Like, some hardware is always dead on arrival and it's cheaper to
repair it than to replace it. Manufacturers have also stopped making super-low-end devices because
they can refurbish last year's model and sell it at a discount.
If everything was integrated into a single part, that wouldn't be possible.
On top of that, integrating everything makes you your suppliers' bitch because all it
takes is a single supplier to threaten to revoke their license and your entire product is trashed.
Some components need to maintain social distance from other components. Antennae, for instance,
pick up interference unless they've got breathing room, and in a high-voltage board like this power
supply, arcs will jump between traces and blow [REDACTED] up unless they're a certain distance apart.
Some parts also need special packaging; this is a pressure sensor that needs a little breathing
hole to allow the air to flow in. This is a pulse oximeter that's in a special
glass capsule so that it can see the skin clearly. There's just no getting around it;
you need a bunch of parts to make electronics, the best way to put a bunch of parts together
is on a board, and the best way to make a board is to print it. No matter how many parts are in
your design, no matter how exotic they are and which suppliers are involved,
pretty much anyone can put anything into any project as long as they can mount it on a PCB.
Any parts can be combined in any configuration, and you'll always know you'll have this thin,
sturdy board, keeping everything together, with convenient mounting holes.
Integration is kind of happening in a way, but instead of putting every component into one chip,
manufacturers are integrating many components into one module. For instance,
the camera module compresses images. The fingerprint reader handles your security.
The display has the drivers embedded right into the glass. The wireless modem, processor, RAM,
graphics chips, are all integrated into a single part. This is really the best of both worlds,
because the manufacturer has already done a bunch of your engineering, and if something breaks
you just replace the module. This is great for the user because, like,
anybody with a screwdriver can replace a broken camera if the new one just pops into place.
So what's the future of the PCB? Are we still going to be using copper and fiberglass when
Brooklyn is under eight feet of water? Yeah, I think we probably will. The PCB production
process is just so well-established and so cheap that, like, boards are already as accessible as
they ever need to be. There have been some nitty-gritty technical advancements; like,
you can have a sheet of aluminum laminated onto your board to help spread heat;
you can add plugged vias, which are sort of vertical wires,
to route super duper dense components; oh, and now you can get FULL COLOR SILKSCREEN!
[Wolf whistle]
Electronics are becoming cheap enough that we can actually embed them straight into
some devices - this is a bunch of RFID tags, which are a tiny foil antenna and a teeny-weeny
microcontroller built directly into a sticker. These things don't need a circuit board because
the sticker holds the thing together. Your bank might have also given you a special bank card
that displays a security code, and that is also an electronic device with no circuit board. The
electronics are embedded directly into the plastic of the card.
There are some interesting rumblings in the hackersphere, where toxic chemicals
and electroplating tubs are kinda impractical. 3D-printed circuits are
this idea that just won't die; the idea is, you print the circuit board out of regular plastic,
and then you print the traces on top of it using a special conductive material. There's also the
inkjet circuit maker, which uses basically a modified inkjet printer to draw the circuits
on a sheet of paper using conductive ink made of silver. Finally, you have the desktop board mill,
which is like a tiny cute little CNC machine that you put on your desk and it mills you
circuit boards out of copper clad. CNC board mills have recently become affordable and practical,
and if you're okay with the lack of solder mask, you can make simple boards
right there on your workbench. Give me $2500 and I'll do it on video!
But what about the super-sci-fi future? Well, there's vitrionics, or embedding electronic
components into panes of glass. This is already used to make capacitive touchscreens for cell
phones and those super-thin OLED televisions. If you want to make transparent electronics,
this is how you'll do it... after you invent a transparent battery, of course. There's
also optronics, which replaces traces carrying electricity with fiber optics carrying light.
These could run way faster and way cooler ( temperature and awesomeness) but there
are severe practical problems that have to be overcome. The main one is that even though
you can easily send data through a fiber optic line, you can't send much power, so ironically,
you'll have to run wires in addition to your fiber optic traces to feed power to the chips.
[Geordi getting pwned noises]
Data? Yes?
What happened? Any answer would be mere speculation.
Decades of experience have proven that the best shape for a circuit is a board,
and the best kind of board is a printed circuit board. Printed circuit boards are still the most
common electrical component, even though they're basically unchanged since we used them to blow
up the Wehrmacht. I think they'll maintain their position as the literal foundation of electronics
deep into the future. Hopefully you've learned something about how they work
and why we use them. Thanks so much for watching, and I hope I've inspired you to bust open your
electronics and dig into the PCB's around you. Are you interested in exactly how engineers design
these things? Maybe you're really interested in those part-placing pick-and-place machines we
talked about earlier? Well, I make videos about all of those, and if you like the sound of them
apples, why don't you... uh... why don't you give me a little subscription? Thank you
so much for watching! Voidstar Lab is still a new channel, and every single view and
comment gives me the warm and fuzzies. May your boards not catch fire unless you want them to.
I'm Zack Freedman, this is Voidstar Lab, and I'll see you in the future.