Module 0 — Before You Touch a PCB: The Essential Primer
Ready for the full bootcamp?
12 modules · 84 quizzes · live calculators & design checklists.
Get full bootcamp

Before You Touch a PCB: The Essential Primer

Advanced PCB Design Skill Bootcamp

MODULE 0
Module 0 — The Prerequisite

You don't need to understand why the layout works.
Until the board fails.

Software can hide hardware for a while. But the first time a board oscillates unexpectedly, an IC gets hot, or the signal is noisy for "no reason" — you need the foundation. This module builds it before you need it.

What this module is
1

A vocabulary reference

Every technical term used across Modules 1–12, defined precisely with context. Stop Googling mid-session.

2

A concept ladder

The ten ideas that everything else builds on — in the correct order, with no assumed knowledge.

3

An electricity & components primer

Ohm's Law, current paths, return paths, and how every passive component behaves in a real layout.

4

A schematic reading guide

How a layout engineer reads a schematic — not symbol by symbol, but as functional blocks with signal flow.

5

A complete design-review preview

Follow one mixed-signal controller from requirements and stackup through placement, routing, EMI, thermal, DFM and release review.

Who this is for

This bootcamp assumes you have an interest in electronics. It does not assume you know PCB layout. If you've ever wondered:

— "Why do I need to put the capacitor right next to the IC pin?"

— "What does a ground plane actually do?"

— "Why does trace width matter if copper is copper?"

— this module answers those questions first, so every layout decision in Modules 1–12 makes immediate sense.

The single most important mental model

Once you hold this model, ground planes make sense. Decoupling capacitor placement makes sense. Return path routing makes sense. The entire bootcamp is elaborating on this one idea from different angles — getting closer and closer to why real boards fail.

How to read the level of this bootcamp
Foundation Track · Module 0

Entry point

Electricity, components, schematic reading, current loops and basic PCB construction. This removes assumed knowledge so beginners can enter the course without memorising rules they do not understand.

Engineering Track · Modules 1–12

Advanced outcome

Stackup decisions, placement priority, power and return paths, mixed-signal partitioning, EMI containment, thermal design, manufacturing review and release evidence on complete boards.

Advanced describes the outcome, not the prerequisite The bootcamp starts from first principles, then moves into engineering-level board decisions. Experienced learners can use Module 0 as a reference and move directly to the applied modules.
Where this leads
Module 0 is the prerequisite. Modules 1–11 take this mental model and apply it to real boards — placement decisions, routing strategy, EMI containment, debugging walkthroughs.
View bootcamp →
01

The Big Picture

What a PCB is, what it contains, and how copper becomes a working circuit

What a PCB actually is

A PCB (Printed Circuit Board) is a structured sandwich of materials that mechanically supports components and electrically connects them through patterned copper. It is not a wire mesh — it is an engineered system where every material choice, every layer, and every copper trace has a consequence.

Substrate (FR4)

The structural core. Glass-reinforced epoxy. Electrically insulating, mechanically rigid, thermally stable. Standard thickness: 1.6mm. Determines the board's dielectric properties.

Copper Layers

Your traces, pads, and planes. Etched from copper foil laminated to FR4. Typically 35µm (1oz) or 70µm (2oz). Width and thickness determine how much current a trace can carry.

Solder Mask & Silk

Solder mask (green/black/red coating) protects copper and prevents solder bridges. Silkscreen prints component labels. Neither conducts electricity.

The key insight A PCB is not passive wiring — it is an electromagnetic system. Every copper trace has resistance, inductance, and capacitance. Every layout decision changes these parasitics. Understanding this is what separates a real PCB engineer from someone who just draws lines.
The complete PCB cross-section
1.6mm VIA Silkscreen — labels, polarity marks Solder mask — exposes pads only Top copper — signals, power FR4 substrate — insulating core Bottom copper — often GND plane Solder mask
The via A drilled hole plated with copper connects top copper to bottom copper straight through the FR4 — adding roughly 1nH of inductance, which starts to matter once you're routing high-frequency signals.

Multilayer boards (4, 6, 8 layers) add internal copper layers laminated between FR4 prepreg sheets. Internal layers are usually dedicated power and ground planes — enabling cleaner signal routing on outer layers.

Single-layer vs Double-layer vs Multilayer — the decision framework
TypeCopper LayersWhen to useMain limitation
Single-layer1 (top only)Very simple circuits, cost-sensitive, basic LED boardsCannot cross traces — forces component placement constraints
Double-layer2 (top + bottom)Most hobby and medium-complexity designs. Default starting point.No dedicated plane layers — ground plane on bottom limits signal layers
4-layer4 (top + GND + PWR + bottom)Any design with high-speed signals, switching power, or EMI sensitivityHigher cost, more complex DFM rules
6+ layers6, 8, 10…Dense BGA routing, RF boards, complex mixed-signal designsCost, lead time, increased via complexity
Stackup goes deeper
This table introduces the framework. The bootcamp goes module-by-module on stackup choices — quantified EMI comparisons, plane pairing, dielectric trade-offs, and decision matrices for real product classes.
View bootcamp →
02

The Concept Ladder

Ten ideas in the right order — each one makes the next possible

Read these once before starting Module 1

These ten ideas are the prerequisite for everything else in the bootcamp. They appear in order — each concept uses the previous one. If one doesn't click, everything after it will feel like memorization instead of engineering.

From ladder to bench
These ten ideas open the door. The bootcamp walks you through applying each one to design decisions on real boards — with worked examples, scenario quizzes, and reusable checklists you keep.
View bootcamp →
03

Course Map

What each day covers and how they connect — click any day to expand

12 modules — one complete mental model of PCB design

The modules form a deliberate sequence: engineering thinking → layout fundamentals → advanced techniques → manufacturing readiness. Each module builds on all previous ones. Every technical term you'll encounter is defined in the glossary of this module.

This is what's inside
You've just seen the full curriculum. 12 modules. 84 scenario-based quizzes. Live calculators for IPC-2221, impedance, crosstalk. Reusable templates. Interactive reference modules and reusable design checklists.
View pricing →
04

Keyword Glossary

Every technical term used across Modules 1–12 — defined before you need them

Search and filter — 40+ terms across 5 categories
Vocabulary becomes fluency
This glossary has the words. The bootcamp turns them into design instinct — applied across 12 modules of layout decisions, with quiz scenarios that test understanding, not memorisation.
View bootcamp →
05

Electricity Basics

Voltage, current, resistance, and the return path — the four ideas every layout decision uses

The three quantities — and what they mean in a layout context
Voltage (V)

Electrical pressure. The force pushing electrons through a conductor. Always measured relative to a reference — on your PCB, that reference is ground. "3.3V rail" means 3.3V above the GND net.

Current (I)

The actual flow of electrons, measured in Amperes. This is what heats your traces. When you size a trace width for a power net, you are sizing it for current — not for voltage.

Resistance (R)

Opposition to current flow. Your copper traces have resistance — thinner and longer means more resistance. More resistance means more voltage drop and more heat generated in the trace itself.

Ohm's Law — memorize it V = I × R. If 1A flows through a trace with 0.5Ω resistance, you drop 0.5V across that trace. On a 3.3V rail that's 15% — an IC expecting 3.3V sees only 2.8V and may malfunction. Every trace width decision is an Ohm's Law calculation.
Try it — how wide does the trace need to be?

Same idea as the Ohm's Law box above, worked in reverse: given a current, what trace width keeps heating under control? This uses the actual IPC-2221 external/internal-layer formula — the same one professional trace-width calculators use.

Minimum trace width

IPC-2221: A = (I / (k·ΔT^0.44))^(1/0.725), k=0.048 external / 0.024 internal. Always add margin over the bare minimum and check your fab's DFM limits.

The return path — the most ignored concept in PCB design

Current always flows in a complete loop. Always. Kirchhoff's Current Law: what flows out of a source must return to it. For every milliamp going forward through a signal trace, there is exactly the same current returning through the ground network.

Why beginners get this wrong

Most beginners obsess over the forward path (the signal trace) and treat ground as passive. Ground is not passive — it carries identical current. The shape and quality of the return path determines noise, EMI, and stability equally to the forward trace.

What a ground plane does

A ground plane provides a low-impedance return path for all signals simultaneously. Return current flows directly beneath each signal trace through the plane — minimizing the current loop area and therefore EMI radiation.

/* CURRENT LOOP — the fundamental unit */ VCC ──[forward trace]──→ IC │ │ (current consumed) │ GND ←─[return path]────── IC /* The LOOP AREA between forward + return */ /* path determines electromagnetic radiation */ /* LARGE loop = large antenna = bad EMI */ VCC ──────────────────→ IC │ GND ←──────────────── ??? (random path) /* SMALL loop = controlled = good */ /* Ground plane return directly under trace: */ VCC ──[trace, top layer]──→ IC GND ←─[plane, bottom, DIRECTLY BENEATH]── IC ↑ minimum loop area achieved
DC vs AC — why digital signals are both

DC (Direct Current) flows in one direction steadily. Your power supply, your battery — these are DC. Most ICs consume DC power from their VCC pins.

AC (Alternating Current) reverses direction periodically. Mains power is AC at 50/60Hz.

The critical PCB insight A digital clock signal switching at 50MHz is AC at 50MHz. It creates electromagnetic radiation. It causes crosstalk with adjacent traces. It creates return path challenges. Every high-speed digital signal must be treated as an AC problem — not a DC wire.
/* DC power rail — relatively simple */ +3.3V ──────────────── VCC pin GND ──────────────── GND pin /* Concern: voltage drop, trace width */ /* 50MHz clock signal — AC problem */ CLK ──/\/\/\/\/\/\/──→ IC /* At 50MHz, harmonics at 100, 150, 200MHz */ /* Radiates from trace like an antenna */ /* Couples into nearby traces (crosstalk) */ /* Concerns: impedance, loop area, length */ Rule: if it switches, treat it as AC. The faster it switches, the more care needed.
From physics to layout
These four ideas explain why. The bootcamp shows you how to apply them at the layout level — return paths, current loops, switching noise containment, and the rules that protect them.
View bootcamp →
06

Core Components

What each component does — and its specific PCB layout implication

The layout engineer's view of every component

You will encounter these on every board. Understanding their physical behavior — not just their schematic symbol — is what makes a layout decision engineering rather than guesswork.

ComponentWhat it doesPCB layout implication
ResistorLimits current. Voltage dividers. Pull-up / pull-down on logic lines.Usually non-critical placement. Exception: high-frequency termination resistors must be within 1–2mm of the driver output.
CapacitorStores charge. Filters noise. Decouples power supply transients from IC pins.Decoupling caps must be as close as possible to IC VCC pins. Every mm of trace adds inductance that reduces effectiveness at high frequency.
InductorStores energy in a magnetic field. Filters. Core of switching regulators.Inductors in buck/boost circuits radiate magnetic fields. Keep away from sensitive analog or RF traces. Short, wide traces for current path.
DiodeOne-way current valve. Polarity protection. Rectification.Schottky diodes in power paths need wide copper for current. Fast-switching diodes radiate — short traces. Always check polarity in footprint.
MOSFET / BJTSwitching and amplification. Controls large currents with small signals.High-current MOSFETs need thermal management. Gate drive trace should be short — long traces add inductance that causes ringing and slow switching.
Voltage RegulatorConverts one DC voltage to another, stably. Linear (LDO) or switching.Input and output caps must be placed per datasheet — often within 2–5mm. Feedback resistors extremely sensitive to noise coupling from nearby traces.
Crystal / OscillatorProvides a precise clock frequency reference to an MCU or processor.Most sensitive component in most designs. Traces must be short. Keep away from RF, high-current, and switching traces. Surround with guard ring connected to GND.
Decoupling capacitors — the deep explanation

Every digital IC draws current in rapid bursts — millions of times per second as its internal logic switches. When it suddenly demands a burst of current, the power supply cannot respond instantly. The supply voltage at the IC's VCC pin dips.

A decoupling capacitor placed close to the IC acts as a local charge reservoir. It pre-charges from the supply, then instantly delivers charge when the IC demands it — preventing the voltage dip.

The distance problem Every millimeter of trace between the capacitor and the VCC pin adds roughly 1nH of inductance. Inductance limits how fast a capacitor can deliver charge. At 100MHz, even 5mm of trace makes the cap nearly useless. The capacitor must sit within 1–2mm of the pin — via directly on the cap pad if possible.
/* WRONG — cap too far from IC */ [VCC]───10mm trace───[CAP]───[IC VCC pin] ↑ ~10nH inductance Useless above ~15MHz /* RIGHT — cap immediately adjacent */ [VCC]──[CAP]──[IC VCC pin] ↑ ~0.5nH inductance Effective up to 300MHz+ /* Best practice: multiple values */ 100nF + 10µF per VCC pin /* 100nF handles high frequency (fast IC switching) */ /* 10µF handles lower frequency (longer bursts) */
Try it — place the decoupling cap

Your IC switches internally at 100MHz. You've got a 100nF cap. Pick how far it sits from the VCC pin and see whether it can actually keep up.

Through-hole vs SMD — why package type affects layout
Through-hole (THT)

Leads pass through drilled holes and are soldered on the opposite side. Mechanically strong. Used for connectors, large caps, inductors, and anything needing mechanical strength. Occupies space on both sides of the board. Harder to assemble automatically.

Surface Mount (SMD)

Soldered directly onto pads on one surface. Smaller. Suitable for reflow oven assembly. Enables higher density. Standard for all modern ICs, resistors, caps. Most of your board will be SMD.

Package naming you must know

SOIC — Small Outline IC. Gull-wing leads. Common for op-amps, drivers.
QFN — Quad Flat No-lead. Bottom pads only. Excellent thermal. Common for power ICs.
DIP — Dual In-line Package. Through-hole. Classic through-hole IC shape.
0402 / 0603 / 0805 — Resistor/cap sizes in inches (04×02 mil footprint).
BGA — Ball Grid Array. Pads under the chip. Requires multilayer + X-ray inspection.

Components in real layouts
You now know what each component does. The bootcamp shows you where to place them, how to route to them, and why every choice matters for signal integrity, EMI and manufacturability.
View bootcamp →
07

Reading Schematics

How a layout engineer reads a schematic — not symbol by symbol, but as a system

The layout engineer's 5-step schematic analysis

Module 2 of the bootcamp asks you to read schematics and identify critical signal paths. Without a systematic approach, you'll miss the layout-critical information buried in the schematic.

1

Identify power entry points

Where does power enter? What voltages? Regulated externally or internally? Trace the power section first — it determines where to place your power ICs, bulk caps, and power trace widths.

2

Identify the main ICs and their function

MCU, power management IC, sensor, radio — each has a different layout sensitivity. The MCU's crystal is highly sensitive. A power IC's switching node radiates. An RF module needs a keepout zone.

3

Trace signal paths and classify them

Which signals are high-frequency? Which are sensitive analog inputs? Which carry high current? Annotate the schematic before opening your PCB tool. High-frequency signals need short traces with reference planes.

4

Find datasheet layout recommendations

Every IC datasheet has a "PCB layout" or "application" section. These specify critical component placement distances, keep-out zones, and ground connection requirements. They are engineering specifications — not suggestions.

5

Understand net names and what they carry

Net names like CLK_48M, MOSI, SDA tell you the signal type and sensitivity. GND is your return path — understand every connection to it. VCC/VDD are power — understand which ICs share a rail and why isolation might be needed.

Common schematic symbols — the layout engineer's reference
/* PASSIVE COMPONENTS */ ─/\/\/─ Resistor ─┤├─ Capacitor (non-polarized) ─┤╠─ Capacitor (polarized — + side marked) ─UUUU─ Inductor ─◁── Diode (triangle points direction of current) ─◁◁─ Zener Diode (reverse breakdown) /* POWER SYMBOLS */ VCC ─── Positive supply (connects same-name nets) ⏚ GND — connects all GND symbols together +3V3 ─ Labeled rail (same rules as VCC) /* NET LABELS */ Same label = same wire, even not drawn connected CRITICAL: verify net names match across sheets A typo here creates an open circuit on the PCB
/* IC PINS */ ─□ Input pin (data flows in) □─ Output pin (data flows out) ─□─ Bidirectional ○─□ Active-Low (circle = inverted logic) /* VOLTAGE REGULATOR */ IN ──[LDO]── OUT │ GND (and ADJ for adjustable types) /* HOW TO READ A COMPLEX IC */ 1. Find VCC/VDD pins — need decoupling 2. Find GND pins — must all connect to plane 3. Find ENABLE/RESET — level-sensitive, check polarity 4. Find reference pins — most noise-sensitive 5. Find output pins — classify signal type
Before you open your PCB tool Spend 20 minutes with only the schematic open. Mark which signals are sensitive (highlight in red). Mark which components are thermally critical. Mark high-current paths. This annotation becomes your placement priority list — you place the most critical components first, everything else around them.
How to read a datasheet — the parts that matter for layout
Pin description table

What does each pin do? Which are analog inputs? Which are high-speed digital? Which carry high current? This table determines your placement strategy.

Recommended operating conditions

Decoupling cap values. Power supply noise limits (PSRR spec). Thermal ratings. Maximum junction temperature. These constrain your layout directly.

Application schematic

The reference circuit the manufacturer tested. Use this as your schematic starting point — every component value and connection has a reason.

PCB layout recommendations

Often a section literally titled "PCB Layout Considerations." Contains: critical component placement, keep-out zones, thermal pad connections, ground pour requirements. These are your highest-priority layout constraints.

Package drawing / land pattern

Exact mechanical dimensions for creating or verifying footprints. Pad sizes, pitch, land pattern recommendations. Incorrect footprints cause assembly defects or no-contact opens.

Datasheet = engineering contract When a datasheet specifies component placement, it is specifying it because deviation causes predictable failure. Regulators oscillate. Oscillators drift. RF ICs miss specifications. Treat datasheets as binding.
Quick check — did it actually land?

Seven real symptoms. Pick the root cause for each — this is exactly how Days 2–12 will test you, except with a real board in front of you instead of four options.

Score: 0 / 0 answered (7 total)
You've finished Module 0

If this was the prerequisite,
now comes the bootcamp.

Module 0 gave you the language and the mental model. The full bootcamp takes that foundation and applies it across 12 modules of real PCB design — placement, routing, stackup, return paths, EMI, debugging, and tape-out readiness — with 84 scenario-based quizzes and live calculators built into every module.

Self-paced bootcamp
Everything Module 0 gave you a taste of — full-length
12 modules, 84 scenario-based quizzes, live calculators in every module, and industry-practice examples and design-review checklists built in.
Self-Paced ₹9,999 One-time · 365-day access
08

Complete Board Review

One representative board reviewed from requirements to release evidence

Reference project — mixed-signal industrial controller

The project is a 4-layer controller with 24 V input, a 5 V buck converter, a 3.3 V LDO, an STM32-class MCU, an 8 MHz crystal, USB, isolated RS-485 and a low-level analogue sensor input. It is complex enough to expose the interactions that isolated layout rules hide.

POWER ENTRY 24 V protection 5 V buck + hot loop 3.3 V LDO MCU DOMAIN MCU XTAL local decoupling + stitching USB / DIGITAL I/O ESD at connector controlled return path ISOLATED RS-485 isolation boundary TVS + termination ANALOGUE SENSOR FRONT END connector filter → amplifier → ADC Illustrative placement zoning — not a fabrication drawing
Review principle The board is not reviewed one net at a time. It is reviewed as interacting current loops, functional domains, thermal sources, interfaces and manufacturing constraints.
The twelve-stage review sequence
1

Requirements and block diagram

Capture input range, load current, interfaces, isolation, environment, board outline, connector positions and compliance targets before selecting a stackup.

Deliverable: reviewed requirements sheet + functional block diagram
2

Schematic annotation

Classify high-current loops, clocks, reset, analogue inputs, differential pairs, protection components, thermal parts and layout-constrained components.

Deliverable: colour-coded schematic + net-class list
3

Stackup and fabrication capability

Choose a 4-layer stackup with uninterrupted ground beneath signal layers. Confirm minimum trace, spacing, drill, annular ring, copper weight and controlled-impedance capability with the fabricator.

Release gate: stackup approved before routing
4

Placement priority

Lock connectors and mechanical features, then place power loops, crystal, decoupling, analogue input chain and interface protection before non-critical passives.

Reject if: a critical loop cannot be drawn compactly after placement
5

Power routing and decoupling

Minimise the buck commutation loop, size high-current copper, connect decouplers with short pin-to-cap-to-ground paths and verify regulator feedback is sensed from a quiet point.

Evidence: marked current loops + voltage-drop estimate
6

Clocks and sensitive signals

Keep the crystal loop compact, prevent fast digital routes from entering the analogue region, route USB as a referenced differential pair and keep reset away from noisy edges.

Evidence: critical-net routing screenshots
7

Return-path review

Trace the return beneath every fast signal. Add stitching vias at layer transitions and connector boundaries. Do not allow high-speed routes to cross splits, voids or plane cut-outs.

Release gate: every critical signal has a continuous reference
8

EMI, ESD and interface containment

Place TVS and filters at the connector entry, provide a short discharge path, control common-mode current and keep external-cable currents away from the logic ground path.

Evidence: interface current-path sketch
9

Thermal review

Estimate dissipation, check copper-spreading area, thermal vias, airflow assumptions, nearby temperature-sensitive components and enclosure conditions.

Reject if: temperature margin depends only on room-ambient testing
10

DFM and assembly review

Verify footprints, courtyard clearance, solder-mask slivers, paste apertures, component orientation, test access, panelisation assumptions and hand-solder constraints.

Evidence: DFM report + assembly drawing
11

Gerber or ODB++ verification

Inspect the actual manufacturing output rather than trusting the PCB editor view. Check layer polarity, apertures, drills, slots, solder-mask openings, plane clearances and fabrication notes.

Release gate: independent output review completed
12

Final design-review report

Record assumptions, unresolved risks, simulations, calculations, rule waivers, review comments and sign-off status. A board is released with evidence, not because it “looks complete”.

PASS: evidence complete · HOLD: open risk without owner or verification plan
Minimum release package
Requirements and assumptionsElectrical, mechanical, environmental and compliance basis.
Reviewed schematic and BOMCritical nets and layout constraints explicitly marked.
Stackup and fab rulesConfirmed against the selected manufacturer.
Critical-layout evidencePower loops, clocks, return paths, isolation and interface protection.
Calculation and simulation setTrace current, voltage drop, impedance, thermal and other applicable checks.
Manufacturing outputsGerber/ODB++, drill, IPC-356 if used, pick-and-place, assembly and fab drawings.
Review logComments, dispositions, waivers, owners and closure evidence.
Bring-up checklistSafe power-up sequence and measurements for the first assembled board.
09

Bad Board Review Cases

Six layout defects that can pass DRC and still fail electrically or in manufacturing

Review the symptom, evidence and correction
CASE 01

Decoupling capacitor is close in millimetres but far electrically

The capacitor shares a long narrow neck and a distant ground via with other loads.

Likely symptom

Supply-pin droop, reset sensitivity or high-frequency noise despite the correct capacitor value.

Evidence

The pin-to-cap-to-ground current loop is long. The capacitor is visually nearby but trace and via inductance sit in series with it.

Correction

Route pin → capacitor pad → dedicated ground via with the smallest practical loop. Use multiple vias when current and frequency require them.

CASE 02

Crystal network is placed too far from the MCU

Long oscillator traces run beside a GPIO bus and over a plane discontinuity.

Likely symptom

Intermittent startup, excess clock radiation or frequency instability sensitive to touch and temperature.

Evidence

The oscillator loop area is large and the return path is discontinuous. Fast adjacent signals inject noise into a high-impedance network.

Correction

Place crystal and load capacitors beside the oscillator pins, keep the loop compact, avoid unrelated routing through the area and follow the MCU vendor's grounding guidance.

CASE 03

Switching node copper extends beneath the analogue section

The buck SW node is enlarged for “current capacity” and routed under the sensor amplifier.

Likely symptom

Switching-frequency spikes appear in the ADC data and radiated emissions increase.

Evidence

The high-dV/dt copper creates strong capacitive coupling. SW-node area, not only trace resistance, controls the field.

Correction

Keep the SW node only as large as needed, contain it within the power stage, keep sensitive copper away on every layer and preserve a compact commutation loop.

CASE 04

A fast signal crosses a split in its reference plane

The top-layer trace looks short and clean, but the ground plane beneath it has a slot.

Likely symptom

Ringing, crosstalk, elevated common-mode radiation or failures that depend on cable attachment.

Evidence

The return current must detour around the split, increasing loop area and shared inductance.

Correction

Reroute over continuous reference copper. Do not “repair” the path with a distant stitching capacitor unless the interface and current path justify it.

CASE 05

Connector pinout and net names are logically inconsistent

The schematic labels TX/RX from the MCU perspective, while the cable drawing labels them from the remote-device perspective.

Likely symptom

The assembled board is electrically intact but the interface is dead or requires a crossed cable.

Evidence

DRC and connectivity checks pass because each net is internally consistent. The system-level interface definition is wrong.

Correction

Review the connector against the interface-control document, mating view and cable orientation. Use explicit names such as MCU_TX_TO_REMOTE_RX.

CASE 06

BGA escape is routable in CAD but not manufacturable

Neck-down width, annular ring and via drill are below the selected fabricator's capability.

Likely symptom

Fabricator rejection, yield loss, open vias or an unexpected move to expensive HDI processing.

Evidence

The footprint and rules were created from generic online values rather than the chosen stackup and drill process.

Correction

Agree the escape strategy with the fabricator before layout. Verify pad diameter, drill, annular ring, solder mask, via type and impedance neck-down limits.

Why these cases matter Every case above can pass basic connectivity and clearance checks. DRC proves that the geometry obeys programmed rules; it does not prove electrical performance, system correctness or manufacturability with a specific supplier.
The review question to ask before approving any critical region