🔌 PCB & Circuit Design Software: KiCad, Altium Designer, LTspice & PSpice

Electronic Design Automation (EDA) is not one activity, it is two, and confusing them is a common mistake for people new to electronics. Circuit simulators like LTspice and PSpice predict how a circuit will behave — voltages, currents, waveforms, frequency response — before any physical hardware exists. PCB design tools like KiCad and Altium Designer let you capture a schematic and then draw the physical copper artwork (traces, pads, layers) that a fabrication house etches onto a real board. A simulator never produces a manufacturable board, and a PCB tool does not model transistor behavior over time. Understanding this split is the first step to picking the right tool for the job.

SPICE Circuit Simulation Fundamentals

SPICE (Simulation Program with Integrated Circuit Emphasis) originated at the University of California, Berkeley in the early 1970s as a way to simulate integrated circuits mathematically instead of prototyping every variant on a breadboard. A SPICE simulation is built from a netlist: a text description of components (resistors, capacitors, transistors, sources) and the nodes connecting them, along with device models that describe how each component actually behaves (a real diode model, a specific MOSFET's characteristics, and so on).

Three analysis types cover most day-to-day simulation work:

• DC operating point analysis — solves the circuit at a fixed instant to find bias voltages and currents, useful for checking that transistors sit in the intended operating region.
• Transient analysis — simulates the circuit's response over time, showing waveforms such as a switching regulator's output ripple or a filter's step response.
• AC / frequency sweep analysis — linearizes the circuit around its operating point and sweeps frequency to produce Bode plots of gain and phase, essential for amplifier and filter design.

LTspice

LTspice is a free SPICE simulator originally developed by Linear Technology and now maintained by Analog Devices after its acquisition of Linear Technology. It is extremely popular in power electronics and general analog design because it is fast, has no cost or seat limitations, and ships with an enormous library of real op-amp, regulator, and power-management device models from the Analog Devices/Linear Technology catalog. Its schematic-driven interface lets engineers wire up a circuit visually and get simulation results without hand-writing a netlist, though the underlying netlist is always accessible.

PSpice

PSpice is a commercial SPICE variant owned by Cadence, historically bundled with the OrCAD schematic capture and PCB suite. It remains common in university electrical engineering curricula and in legacy industrial workflows that were built around OrCAD/PSpice decades ago. Cadence offers a free, capability-limited PSpice for TI or student edition, but full commercial licenses (larger circuit size, full model libraries, advanced analyses like Monte Carlo and worst-case) require a paid subscription. Where LTspice wins on being free and universally available, PSpice's advantage is tighter integration with OrCAD's schematic-to-PCB flow and continued use in industries that never migrated off it.

PCB Design Fundamentals

Laying out a printed circuit board starts with schematic capture: drawing the circuit's logical connections using symbols tied to real component footprints (the physical pad pattern a part needs on the board) drawn from a library. From the schematic, the tool generates a netlist that drives the physical layout, where parts are placed and connected with copper traces across one or more layers. Simple designs use 2-layer boards (top and bottom copper); denser or higher-speed designs use 4, 6, 8 or more layers, often with dedicated internal power and ground planes to control impedance and reduce noise.

Trace geometry is not arbitrary. Copper weight (commonly 1oz or 2oz per square foot, meaning roughly 1.4 mil or 2.8 mil of copper thickness) combined with trace width determines how much current a trace can carry without excessive heating; designers typically size traces using IPC-2221 current-capacity charts or calculators rather than guessing. Vias connect copper between layers: standard through-hole vias run the full board thickness, blind vias connect an outer layer to an inner layer, buried vias connect only inner layers, and microvias (used in HDI designs) are laser-drilled and much smaller than mechanically drilled vias.

Before a design is sent to manufacturing, design rule checking (DRC) automatically verifies clearances, minimum trace widths, annular ring sizes, and other fabrication constraints so that errors are caught in software rather than discovered on an unusable physical board. The final output is a set of Gerber files (one per copper, silkscreen, solder mask, and mechanical layer, in the RS-274X format) plus an Excellon drill file describing hole locations and sizes — together these are what a fab house actually manufactures from.

KiCad

KiCad is a free, open-source PCB design suite that has improved dramatically since its version 6 and 7 releases, adding a modern push-and-shove router, real-time DRC, better library management, and 3D board visualization. It was originally sponsored by CERN, which needed an open tool for its own hardware projects, and that lineage helped drive serious engineering investment into the project. KiCad is now credible for professional and commercial work, not just hobbyist boards, though very high-layer-count or extreme high-speed designs still lean toward commercial tools with deeper signal-integrity analysis.

Altium Designer

Altium Designer is a paid, commercial PCB design tool and the de facto industry standard for professional electronics design, particularly for high-speed and high-layer-count boards. Its strengths include mature signal-integrity analysis (controlled impedance, differential pairs, length matching), a polished unified schematic-to-layout environment, strong library and component management (including cloud-based supply-chain data through Altium 365), and broad compatibility with contract manufacturers' workflows. Its cost is a real consideration: Altium is sold as an annual subscription running into the low thousands of dollars per seat per year, positioning it as an enterprise tool rather than a hobbyist one.

Tool Comparison

How These Tools Fit Together in a Real Project

In practice, these two categories of tool are used sequentially rather than as alternatives to each other. A typical workflow looks like this:

• Model and simulate the circuit in LTspice or PSpice first, checking DC bias points, transient behavior, and frequency response until the design meets its electrical requirements on paper.
• Recreate the validated circuit as a schematic in KiCad or Altium Designer, attaching real component footprints from the library.
• Lay out the physical board: place parts, route copper on the appropriate number of layers, size traces for the expected current, and place vias where layer transitions are needed.
• Run design rule checking (DRC) to catch clearance, trace-width, and connectivity errors before committing to manufacturing.
• Generate Gerber and Excellon drill files and send them to a fabrication house such as JLCPCB or PCBWay for manufacturing, along with a bill of materials and pick-and-place file if the boards will also be assembled.

Skipping the simulation step is common for simple, low-risk circuits, but for anything involving tight tolerances, feedback loops, or power conversion, simulating first in LTspice or PSpice catches design mistakes while they still cost nothing to fix, long before copper is committed in KiCad or Altium.