IEEE Circuits and Systems Magazine - Q3 2020 - 35

Initial Design
- Components
- Schematic
- Ergonomics
- Layers
- Frequency/Current
- Materials
- Mechanical Specs
- etc.

Manufacturer Specs
- Feature Dimensions
- Layers
- Materials
- Schematic
- Frequency/Current
- Materials
- etc.

Placement
- Mechanical Requirements
- Area Optimization
- Feature Dimensions
- Testing Compatibility
- Thermal Considerations
- etc.

Routing/Simulation
- Critical Paths
- Feature Dimensions
- etc.

Fabrication/
Verification

Figure 1. Generic design process of PCBs. Less decisions are taken in advanced stages of the design. The process can also
include several iterations before fabrication.

II. Background
A. History
While it is difficult to identify one beginning of PCBs, the
first copper laminate etching in [9] resembles PCBs in
their current form. Single layer etched copper eliminated the majority of jumper wires, which made mass-production achievable. The increasing density of circuits,
due to the emergence of transistors at that time, in addition to needing a more mechanically reliable circuits
for space applications, lead to the invention of plated
through holes and multi-layered structures [10].
The next breakthrough in PCB design occurred in the
1980s when the Gerber file format was standardized and
adopted by several Computer Aided Design (CAD) tools
[11]. The rise of the PC business also increased the density of electronics packages, which resulted in a finer
featured fabrications.
In recent years, developments such as embedded
components, open cavity designs, and advanced materials, are available to PCB designers. Those features can
reduce the size and cost of the design, and improve the
overall performance.
Modern CAD tools also have extended simulation
capabilities that can reduce the PCB development time
by shortening the prototyping phase. Such capabilities
include signal integrity, thermal distribution, current
density, and radiation.
B. PCB Design Process
The process of designing a PCB requires taking numerous decisions concerning size, testability, ergonomics,
and manufacturability, among others. Deciding on each of
these requirements needs to be done at an adequate stage
of the design.

Fig. 1 summarizes a generic PCB design process. While
details might differ between projects, two major information can be inferred. First, the further the design
stage is, the less decisions the designer needs to make.
Second, PCB design is a cyclic and an iterative process.
For example, the number of layers in a PCB should be
decided at an early stage of the design and before any
routing takes place. If the number of layers is found necessary to change after the routing started, decisions
such as component placement and thermal dissipation
should be revised.
For PCBs with fine features or sensitive dimensions
(compared to the fabrication tolerances), additional verification steps might be necessary. These rely on multiobjective optimization and stochastic processes to ensure the circuit has low sensitivity to potential process
variations [12], [13].
After fabrication, assembly, and testing, further changes might be necessary. While a second (or more) iteration
of PCB design is costly, time consuming, and undesirable, it is common in PCB design.
C. Diagnosis
There are numerous sources for problems in a PCB.
This includes fabrication, assembly, components, and
signal integrity errors. The focus of this writing is on
the last one.
Narrowing an erroneous behavior of a circuit to signal integrity problems, however, can require extensive
tests and experience. Below are few symptoms which
are correlated to signal integrity errors [1]: 1) Design
fails intermittently for no obvious reasons (not a systematic error). 2) Some boards work, while others, from
the same batch, fail. 3) Design is sensitive to small variations on supply or temperature.

M. Abu Khater is with the School of Electrical and Computer Engineering, Purdue University, West Lafayette, (e-mail: mabukhater@ieee.org).
THIRD QUARTER 2020

IEEE CIRCUITS AND SYSTEMS MAGAZINE

IEEE Circuits and Systems Magazine - Q3 2020

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