Okay, so let's just unpack this. Look around
you right now. Literally anywhere. Yeah, right.
Whether you're listening to this on a phone or
maybe a laptop or you're in your car, inside
every single one of those devices is a hidden
city. The literal city. You've got your highways,
your power plants, your residential districts.
Exactly. And we usually just ignore it. I mean,
we treat our devices like these magic black boxes.
You press a button and a thing happens. Right.
But if you were to crack that box open, which...
Honestly, most of us are way too scared to do
because of the warranty. And the glue. So much
glue these days. Right. So much glue. But if
you did, you'd find the fundamental infrastructure
of the modern world. Today for our deep dive,
we were talking about the printed circuit board
or the PCB. It really is the nervous system of
everything we own. But you're right. I mean,
most people just see a green square with some
black chips on it and they don't think twice.
And that's our mission today. We are pulling
from a massive stack of source material covering
the history, the composition manufacturing, and
even future tech of PCBs. We want to move beyond
that whole green square with chips idea. Definitely.
I want to understand how we went from literally
hand wiring radios to these insane microscopic
metropolises. Because when you look at the research,
the PCB isn't just a holder for parts. It's a
map of engineering history. It is. And what's
fascinating here is that the evolution of the
PCB dictates the evolution of the device itself.
You literally cannot have a smartphone without
the specific manufacturing breakthroughs we're
going to talk about today. It's really a story
about density. So let's start with the before
picture. Yeah. Because I think... To appreciate
the sleek green board, you kind of have to understand
the absolute nightmare that came before it. Nightmare
is definitely the correct term. If you go back
to the early 20th century, so say the 1920s or
30s, electronics were built using what's called
point -to -point wiring. The rat's nest. Precisely.
The rat's nest. Imagine a heavy metal chassis,
so basically just a steel frame. You'd screw
these big... bulky vacuum tubes and transformers
onto it. And then to connect them, you'd have
a human being sitting there with a soldering
iron and a spool of copper wire, physically soldering
a connection from point A to point B. I've actually
seen photos of the insides of old guitar amplifiers
from the 50s that still use this. It looks like
a copper spaghetti explosion. It does. It's beautiful
in a chaotic way, but from an engineering standpoint,
it was terrible. First off, it was heavy, wood
bottoms, metal frames. Second, it was incredibly
labor intensive. You needed highly skilled craftsmen
to build a single radio. But the absolute biggest
problem was reliability. Well, yeah, because
if you shake a box full of loose wires, something's
going to touch something it definitely shouldn't
touch. Exactly. It was fragile. A short circuit
wasn't just a metaphor back then. It was a constant
daily risk. If two wires vibrated against each
other and the insulation wore off, the device
died. Or, you know, caught fire. So was the move
to the circuit board just about making things
tidier? Or was there a specific catalyst that
pushed it? Well, there were some early pioneers
playing with the idea. A German inventor named
Albert Hansen actually had a patent way back
in 1903 for flat foil conductors on a board.
1903? Yeah, very early. And then around 1936,
there was Paul Eisler, an Austrian engineer working
in the UK, who actually put a printed circuit
into a radio set. But the manufacturing tech
just wasn't there to make it cheap at scale.
The real force multiplier, the thing that forced
the... entire industry to change was World War
II. It always seems to come back to the war effort
in these tech deep dives. It usually does, yeah.
Specifically, the U .S. Army had a massive problem.
They needed something called the proximity fuse.
Okay. I was reading about this in the source
material. This is for anti -aircraft shells,
right? Yes. The goal was to shoot down planes.
But hitting a moving plane with a dumb bullet
in the sky is really, really hard. So they needed
a shell that had a tiny radar set inside it so
it would detonate when it just got near the plane.
But think about the physics of that. You are
taking a delicate radio, putting it inside a
bullet, and then literally firing it out of a
cannon. The g -forces are immense. We're talking
thousands of g's of acceleration in a fraction
of a second. Right. So if you use the old rat's
nest wiring inside a cannon shell. the shock
of the launch would just snap every single connection
instantly. It would be debris before it even
left the barrel. Exactly. So the Army worked
with the Central Lab Division of Globe Union
to find a way to make electronics that were completely
solid. And they came up with a ceramic plate.
Instead of copper wires floating in the air,
they screen printed metallic paint directly onto
the ceramic. So they were literally printing
the wires. Yes, printing them. They used a silver
paste for the conductors and a carbon ink for
the resistors. was effectively the first mass
-produced printed circuit. It was rugged. It
was solid state. And it could actually survive
being fired from a gun. And this wasn't just
some cool new gadget. It was classified top secret.
Highly classified military survival tech. The
U .S. didn't release this technology for commercial
use until 1948. But once they did, it triggered
an absolute revolution. By the mid -50s, companies
like Motorola were dumping millions into these
plated circuits for consumer radios. They realized
they could make them lighter, cheaper, and way
more reliable. Okay, so that gets us the concept.
But let's talk about the reality of the board
itself today. Because when I look at a motherboard
now, or even just the board in my toaster, I'm
not seeing ceramic and silver paint. I'm seeing
that iconic green stuff. Right, the modern PCB.
It's quite a bit different from the ceramic fuse.
Not as a single object, but as a laminate. It's
a sandwich. I always appreciate a good food analogy.
Walk us through the layers of this sandwich.
Okay, so the bread of the sandwich is the substrate.
The industry standard is a material called FR4.
Which the notes say is woven glass epoxy. Correct.
The FR actually stands for flame retardant. It's
basically fiberglass mixed with a really tough
resin. It provides a mechanical spine of the
board. It's stiff. It doesn't conduct electricity.
And crucially, it doesn't... melt when you get
it extremely hot okay so that's the rigid structure
then you have the copper the meat of the sandwich
you laminate a thin sheet of copper foil onto
that fiberglass but here is the part that people
often misunderstand and it's really the core
of the whole manufacturing magic we don't add
the wires to the board We use subtractive manufacturing.
Right. I really wanted to clarify this point.
All right. Because the sources emphasize this.
It's like a sculptor chipping away stone to reveal
a statue rather than a painter adding paint to
a blank canvas. That is the perfect analogy.
You start with a board that is completely covered
in a solid sheet of copper. Then you use a process
called photolithography. Which sounds a lot like
photography. It's chemically very, very similar.
You cover the copper with a light -sensitive
chemical called photoresist. Then you take a
mask, which is basically a negative image of
your circuit traces, and you blast the whole
thing with UV light. The light hardens the chemical
over the parts of the copper you want to keep.
So the artwork or the blueprint protects the
copper lines you need, and the rest of it remains
soft. Exactly. Then you dunk the whole board
into an acid bath. The chemical etching dissolves
all the exposed copper, the stuff you didn't
protect. When you wash it all off, the only thing
left is that intricate web of copper highways.
That perfectly explains why the lines on a circuit
board are so incredibly crisp. It's chemical
esching. It's not someone trying to draw with
a tiny pen. Right. It allows for precision down
to the micrometer level. But then you have a
new problem. Copper oxidizes. If you leave it
exposed to the air, it turns green and corrodes.
Plus, if you try to solder components to it later,
the hot solder might just flow everywhere across
the copper and connect things that definitely
shouldn't connect. Solder shorts. Exactly. So
you need a protective condiment. on your sandwich
that's the solder mask and that is the green
color yes it's a layer of polymer or epoxy that
covers the entire board insulating all those
tiny copper traces and leaving holes only where
you explicitly need to solder a component is
there a scientific reason it's green or is that
just a tradition thing mostly historical actually
the original two -part epoxy resins they developed
were just naturally a brownish green color But
it's stuck around because green happens to be
very easy for human eyes to inspect. Our eyes
are most sensitive to green light, so quality
control workers could spot tiny defects way easier
on a green board than, say, a red or blue one.
Though I have seen other colors lately. Yeah.
Like you see black boards in gaming PCs or purple
boards from those custom prototype manufacturers.
Oh, yeah. You can add any pigment you want now.
But green is still by far the cheapest and the
global standard. Got it. Then the final layer
on the very top is the writing. The R1, the C3,
the little brand logo. The silkscreen, it's literally
just ink printed on top. It's the legend for
the map telling the humans and the machines where
each specific part is supposed to go. So we've
got the complete sandwich. FR4, copper, solder,
mask, silkscreen. But a bare board is just a
board. It doesn't actually do anything yet. You
have to populate it. And looking at the history
we pulled, this seems to be where the second
massive revolution happened. The shift from through
hole to surface mount. Oh, this is the shift
that truly gave us the modern digital age. For
decades, through -hole was king. And it's exactly
what it sounds like. You drill a physical hole
all the way through the FR -4. The components
say a standard resistor looks like a little pill
with two long wire legs. I remember these from
shop class back in the day. You stick the wire
legs through the holes, you flip the board over
and you solder them to the metal pad on the back.
Then you take clippers and snip off the excess
wire. Right. And it's mechanically very strong.
If you're building a heavy guitar amp or a power
supply that might get kicked around a stage,
the Ruhold is fantastic. But think about the
manufacturing constraints of that. You have to
drill thousands of tiny holes. That eats up expensive
drill bits. It creates a ton of fiberglass dust.
It's just slow. And you're wasting so much space.
If I have to poke a leg completely through the
board, I can't put another chip on the backside
of that exact same spot. I've used up that real
estate on both sides of the board for one component.
Exactly. You're completely blocked. Enter the
1980s and surface mount technology or SMT. The
legs are gone. Completely gone. Instead of long
wires, SMT components just have tiny little metal
tabs or caps on the ends. You don't drill any
holes for them. You apply a precise paste of
solder to the pads on the surface. A machine
places the component right on top, kind of like
laying down a tile on a floor. And then you run
the whole board through a giant baking oven to
melt the solder. This sounds like it completely
changes the physical scale of everything. Drastically.
SMT components are a fraction of the size, sometimes
one -tenth the weight of their through -hole
counterparts. And because you don't need to drill
holes, you can suddenly populate both sides of
the board independently. And this is the great
enabler for mass automation, isn't it? Yeah.
I've watched videos of those pick -and -place
machines. They move so incredibly fast, they're
just a blur. That's the real key to SMT. A human
with a soldering iron. can maybe do a few hundred
joints an hour if they're highly caffeinated
and super fast. A modern pick -and -place line
can handle tens of thousands of components per
hour. The machine grabs a resistor, which is
literally the size of a grain of sand, now checks
its orientation with a high -speed camera and
slaps it onto the board with perfect precision.
Which is exactly why you can buy a smartphone
for a few hundred dollars today. If we were still
using through -hole technology, an iPhone would
probably be the size of a briefcase. Oh, at least.
And it would cost $10 ,000 to assemble by hand.
SMT is what allowed us to make complex electronics
cheap enough to be almost disposable. Speaking
of smartphones, though, the boards inside them
don't really look like the standard green rigid
squares anymore. I opened up an old broken phone
recently, and the board was, first of all, it
was incredibly dense. But there were also these
thin orange ribbon cables everywhere connecting
things. It's the next evolution. We are moving
beyond the rigid board. Those orange ribbons
you saw are flexible PCBs or FPCBs. I've heard
of Kapton tape before. Is that related to this?
Yes. Captain is a brand name for polymide. That's
the substrate they use. Instead of rigid FR4
fiberglass, they use this high -performance plastic
film. It's highly heat -resistant, so it can
handle the soldering ovens, but it's completely
flexible. Which allows you to essentially do
origami with the electronics. Exactly. If you
look at a modern folding phone, or even just
how the tiny camera module connects to the main
motherboard in a regular phone, you need that
circuit to bend and fold. FPCBs allow the electronics
to fold. flow into whatever complex 3D shape
the enclosure demands. That makes sense. And
what about the density aspect? Because you mentioned
microovias in the research notes. This is HDI
or high density interconnect. Remember how we
said drilling holes mechanically was slow and
took up too much space? Well, mechanical drill
bits can only get so small before they just snap
under the pressure. For modern processes like
the core brain of your phone, we need connections
between layers that are microscopic to handle
the sheer number of signals and the raw speed.
So how do you drill a hole that... that small
if the bits keep breaking. Lasers. Lasers, of
course. We use lasers to blast microscopic holes
called microvias to connect the different layers
of copper. And that's another thing. Your phone's
motherboard isn't just one layer of copper on
top and one on the bottom. It might be 10 or
12 independent layers of copper stacked up inside
that thin board like a lasagna, all connected
by these microscopic laser tunnels. It's just
incredible engineering. The level of precision
required to align 12 layers of copper at a micro...
Microscopic scale is mind -boggling. And the
sources also briefly mentioned metal core boards,
too. Yes, specialty boards. For things like those
super bright LED lights, we use metal core boards
with an aluminum or copper backing instead of
fiberglass. FR4 is a terrible conductor of heat,
so if you put a high -power LED on it, it would
burn itself out. The metal core acts as a giant
heat sink to pull the heat away. Ah, okay. So
we've got all these amazing advancements, HDI
flex boards, metal cores. But and here is where
the conversation kind of takes a turn and the
source is this incredible complexity comes with
the cost. And I don't just mean the literal price
tag. You're talking about the environmental and
repairability issues. Right. When I had that
old rat's nest guitar amp, if a capacitor blew,
I could actually see it. It would be physically
leaking or charred black. I could grab a soldering
iron, snip it out and put a brand new one in
for 50 cents. Correct. It was totally serviceable
by an end user. But with an HDI multilayered
surface mount board, if one single microscopic
component fails out of thousands, what happens?
The map is simply too complex for a human to
read. Troubleshooting which of the 5000 micro
components failed is incredibly time consuming.
And physically trying to replace a chip the size
of a dust moat without accidentally melting the
plastic connector right next to it. That requires
high -level skill microscopes and very expensive
rework stations. So the manufacturer just says,
we can't efficiently fix this. Just swap out
the entire board. Or even worse, they just say,
buy a new phone. The entire industry shifted
from component -level repair to board -level
replacement. And it is highly economically efficient
for the factory. They don't want to pay a skilled
technician $50 an hour to hunt down a $0 .10
broken resistor. But the downside is it creates
a massive mountain of e -waste. Which brings
up an interesting point from the sources. They
extensively cover this acronym ROHS. I actually
see this printed on electronics boxes sometimes.
ROH. That's related to the materials in the e
-waste, right? It is. It stands for the Restriction
of Hazardous Substances. It's a major piece of
legislation that started in the European Union
back in the early 2000s. And what exactly were
they trying to ban from the boards? The big target
for PCBs was lead. For decades, the standard
solder used to attach components was a specific
alloy of tin and lead. And lead is actually amazing
for manufacturing. It melts at a nice low temperature,
it flows beautifully across the pads, and the
resulting joints aren't brittle. It's a joy to
work with on an assembly line. But it's also
a known neurotoxin. Right. And when you start
throwing billions of discarded circuit boards
into global landfills that eventually leaches
out into the groundwater. The EU stepped in and
banned lead in consumer electronics. And we're
just impartially reporting on the legislation
from the sources here. But it's a fascinating
case study in how a regulation in one specific
region can inadvertently set a global standard
because. a massive company like Apple or Samsung
isn't going to set up two different factories
to make a clean phone for Europe and a leaded
phone for the U .S. Exactly. It's way too expensive
to run two entirely separate global supply chains.
So even though the U .S. didn't have a sweeping
federal ban at the time, manufacturers just unilaterally
switched to lead free solder globally to comply
with the EU. It definitely makes manufacturing
slightly harder because lead free solder needs
higher oven temperatures and the joints can be
a bit more brittle over time, but it removed
a massive amount of toxic heavy metal from the
global waste stream. Wow. So pulling this all
together for you listening, we've gone from the
rat's nest of bulky, fragile, hand -soldered
wires to classified military ceramic fuses to
the mass -produced green FR -4 sandwiches we
all recognize, and now to these laser -drilled,
flexible, high -density marvels in our pockets.
It's a relentless trajectory of integration.
Every single step has been about packing more
functionality into less space, removing the slow
human hands from the assembly process, and drastically
increasing the reliability. But looking at the
cutting -edge research you brought into the sources,
it seems like we aren't even close to done shrinking
things. We are now seeing things called embedded
components. Yes, this is the absolute bleeding
-edge frontier of PCB design right now. So usually
components sit on the surface of the board. But
you're saying we are starting to put them inside
the board itself. Correct. To save even more
precious surface area and to actually improve
electrical performance by shortening the signal
paths, manufacturers are figuring out how to
bury tiny capacitors and resistors directly inside
the inner layers of the fiberglass substrate
itself. We are quite literally merging the component
with the infrastructure. We are. The physical
distinction between what is the board and what
is the chip is starting to completely blur. So
here is the provocative. get a final thought
I want to leave you with today. As we move rapidly
toward this future, where the electronics aren't
just attached to a board, but functionally, are
the board what happens to the whole concept of
ownership and repair? It's a deeply valid philosophical
and economic question. When the battery, the
processor, and the memory are all fused into
a single indivisible block of material repairability,
it doesn't just get difficult. It becomes basically
physically impossible. Are we just moving to
a world where we don't really own our physical
devices anymore? We're just essentially leasing
the functionality until the internal glue finally
fails? It certainly seems to be trending that
way. When you can't access or fix the map, you
just have to replace the whole world. The PCB
is transforming from an open city into a sealed
vault. That is definitely something to chew on
the next time you're forced to upgrade your device.
Indeed it is. So do us a favor. The next time
you happen to see a bare circuit board, maybe
inside a broken TV remote, or if you walk past
an e -waste bin, don't just see a boring piece
of green plastic. Look closely at the traces.
Look at the complex layers and the tiny vias.
It's literally a history book written in microscopic
copper. Thank you so much for joining us on this
deep dive. See you next time.