Table of Contents
1. What Is Component Placement in PCB Design?
2.
How to Start PCB Component Placement
3.
Electrical and Thermal Factors in Component Placement
4.
PCB Component Placement for Manufacturing and Assembly
5.
Designing for Testing, Inspection, and Accessibility
6. Conclusion
7. FAQs
PCB component placement is not merely about putting all the
components into the board frame; it is a crucial step in PCB design. Good PCB
component placement will directly affect the trace length, signal paths, power
distribution, thermal performance, and manufacturability. If the related
components are placed too far apart, longer traces and more vias may be
required in the future; if the positions of high-speed devices, power
components, or heat-generating parts are arranged improperly, it will also
increase the difficulty in signal, thermal management, and manufacturing.
Therefore, a reasonable component placement needs to take into
account both electrical, mechanical, thermal, and manufacturing requirements.
The actual PCB layout rules should not only consider the spacing between
components, but also make the subsequent routing easier and leave appropriate room
for assembly, inspection, testing, and rework.
In this article, we will introduce the layout principles that need
to be focused on in actual PCB design from several aspects: the basic concept
of PCB component placement, the initial layout steps, electrical and thermal
design, manufacturing and assembly requirements, as well as testing and
accessibility.
What Is Component Placement in PCB Design?
The process
of deciding where and how to organize electronic components on a printed
circuit board is known as PCB component placement. It may be summed up as
converting the circuit connection relationships in the schematic into the
actual physical layout on the board for those who are looking for "what is
PCB place"?
A proper PCB component placement takes into account signal flow,
heat dissipation, available board space, routing, assembly, and mechanical
construction constraints all at once. Related components are often put as close
together as feasible, resulting in shorter and more direct traces; however,
components with high noise, high speed operation, or high heat generation may
necessitate particular spacing or separation considerations. Appropriate
component placement can reduce the number of needless vias and complex traces,
improve signal and thermal performance, and simplify PCB manufacturing and
assembly.
How to Start PCB Component
Placement
A good PCB component placement
process should start with the parts that have the least flexibility in
position. Instead of placing the components one by one, it is better to
determine the overall mechanical structure and functional divisions of the
circuit board first. A practical placement order is as follows:
1. Place the fixed mechanical
components first.
First, determine the board
outline, mounting holes, connectors, switches, antennas, prohibited areas, and
other mechanical restrictions. These positions are usually determined by the enclosure,
interface locations, or product structure, so they should be fixed before
arranging other components.
2. Divide the PCB into
different functional zones.
You can divide it according to
functions such as power, analog, digital, RF, sensors, communication, or
control sections. This is one of the very practical PCB layout rules, as it
helps to keep noisy circuits away from sensitive circuits. For example, if
conditions permit, high-current or high-frequency areas should be kept at a
certain distance from low-level analog circuits and sensor circuits.
3. Place the critical
components.
Processors, FPGAs, memory
devices, regulators, transformers, power devices, and other major ICs usually
have the greatest impact on subsequent routing and circuit performance.
Therefore, the positions of these components should be determined first before
smaller and more flexible parts.
4. Add supporting components.
According to the actual
electrical function, place the critical capacitors, resistors, filters, and
other supporting components near the devices they serve.
5. Place the general passive
components last.
General resistors, capacitors,
and other passive components with relatively flexible positions can be arranged
after the main layout structure of the circuit board is determined.
By following this sequence for
PCB component placement, the entire layout can be made clearer from the very
beginning, and it also helps to reduce subsequent routing conflicts, noise
coupling, and unnecessary layout modifications later in the design.
Electrical and Thermal Factors in Component Placement
When performing component placement, electrical performance and
thermal management usually need to be considered together. It is difficult to
focus only on one aspect because where the components are placed often
simultaneously affects the routing, signal quality, and heat dissipation.
If the distance between critical components is too far, the design
may require longer routing, more vias, and more complex signal paths later; if
the heat-generating components are concentrated in the same area, local
hotspots may form. Therefore, addressing these issues during the layout stage
is usually more effective than relying on routing or thermal measures for
remediation later.
Electrical
and Signal Considerations
When working on signal-related PCB component placement, we can first
look at the relationships between components along the signal flow. For
example, a signal enters the PCB from a connector, passes through protection
and filtering circuits, then enters the interface IC, and finally reaches the
processor. It is best to arrange the layout in this order as well. The benefits
are clear: shorter routing, no need for repeated loops, and easier handling of
subsequent routing.
In actual PCB design, you can focus on checking these PCB layout
rules:
• Place high-speed devices such as processors, memory, oscillators,
and other devices close to the components they are directly connected to.
• Clock lines, differential pairs, and other critical connections
should be kept short and direct.
• Try to minimize unnecessary signal backtracking, crossings, and
excessive vias.
• Sensitive analog signals and low-level signals should be kept away
from high-current and high-speed switching areas.
• Keep the high-speed signals below a continuous reference plane to
avoid crossing or splitting the plane at will.
• Decoupling capacitors should be placed as close as possible to the
corresponding power pins, rather than randomly placing them after leaving the
remaining empty space.
If you notice that a critical network needs to be routed over a long
distance or requires continuous increases in vias during the initial routing,
you may not necessarily rush to "optimize the routing". In many
cases, it is better to first check the PCB component placement and adjust the
positions of relevant components more reasonably, making the problem easier to
solve.
Thermal
Considerations
Thermal management is also a part of component placement that is
often underestimated. Devices such as processors, MOSFETs, voltage regulators,
and power resistors generate heat when they operate. If they are concentrated
in a small area, even if the temperature of a single device seems acceptable,
the entire area may gradually form a hot spot.
When planning the PCB component placement, we usually also consider
the following issues:
• Are high-power devices too concentrated and is it necessary to
appropriately disperse them?
• Is the position of the heat-generating devices convenient for using
air flow, heat sinks, thermal vias, or large copper foils?
• Are temperature-sensitive components such as sensors and precision
analog devices too close to the main heat source?
• Are tall components blocking fans or main air flow paths?
The focus here is not simply to separate all heat-generating devices.
What matters is where the heat ultimately goes. A reasonable component
placement for thermal management should leave a clear heat dissipation path for
the main heat source and keep temperature-sensitive devices away from obvious
heat-affected areas.
PCB Component Placement for Manufacturing and Assembly
Even if a PCB has no electrical design issues, if the component
placement does not align with the actual manufacturing process, problems may
still arise during the assembly stage. Therefore, before finalizing the layout,
we usually need to recheck it from a manufacturing perspective: how the board
will be soldered, inspected, and disassembled, and whether it is convenient for
rework in case of problems.
Some practical PCB layout rules include:
• Ensure there is an appropriate spacing between
components.
If they are placed too closely together, although it may save board
space, soldering, AOI inspection, and later rework will be more difficult. The
exact amount of space needed depends on the package size, assembly method,
detection method, and the manufacturing capabilities of the PCB assembly
factory.
• Pay attention to the board edges and the disassembly area.
If the components are too close to the routed edge, V-Cut, or breakaway
areas, mechanical stress generated during disassembly and handling may affect
the solder joints or the components themselves. Therefore, these areas usually
need to be reserved with safety space in advance.
• Arrange the component placement and orientation reasonably.
Direction-sensitive components such as diodes, LEDs, polarized
capacitors, and ICs should have their polarity or Pin 1 clearly marked for easy
identification. For the same type of components, if conditions permit, they can
be kept in the same orientation. However, if this affects routing or thermal
performance, it is not necessary to forcibly unify them for the sake of
"looking neat".
• The layout should be coordinated with the actual soldering
process.
The requirements for component positions and spacings vary for
different assembly methods such as SMT reflow soldering, wave soldering,
selective soldering, and manual assembly. For example, when using wave
soldering, we also need to pay attention to the component orientation, height,
and whether large components will block the subsequent welding area.
• Don't forget to leave space for repair.
During actual repair, technicians may need probes, tweezers,
soldering irons, or hot air guns. If the components are blocked by large
components or there is almost no operation space around, subsequent maintenance
and rework will become very troublesome.
In fact, there is no fixed set of spacing or component placement and
orientation rules that works for all PCBs. A more reliable approach is to review
the PCB component placement before production by combining actual DFM and
assembly requirements. This can help detect problems in soldering, testing, and
rework earlier and reduce the need to re-modify the layout for production
purposes later.
Designing for Testing, Inspection, and Accessibility
PCB component placement cannot only consider
whether the circuit board can be assembled. After the PCBA is produced and
rolled off the production line, it usually needs to undergo electrical testing,
inspection, programming, debugging, and sometimes even rework. All these
processes require actual operations on the relevant positions on the circuit
board.
Make the Test Points Easily Accessible
For ICT or flying probe
testing, the test points need to be placed at positions where the fixtures or
probes can actually come into contact. Even if a test point is correctly
connected in the CAD file, if it is located beneath a large-sized device or too
close to a tall connector, it may still be difficult to use during actual
testing.
The appropriate spacing between
test points, between test points and components, and between test points and
the edge of the board will vary depending on the testing method and the
equipment used by the manufacturer. Therefore, test accessibility should be
considered in advance during the PCB component placement stage, rather than
being added after the routing is completed.
Consider
inspection and rework
The arrangement of components also affects the inspection results.
If the components are placed too closely together, whether using AOI or manual
inspection, the difficulty will be much greater. For BGA packages where the
solder joints are hidden at the bottom of the components, X-ray inspection may
also be necessary.
Rework is the same. If certain components may need replacement,
debugging, or undergo engineering modifications in the future, it is best to
leave sufficient space around them so that probes, tweezers, soldering irons,
or hot air tools can operate normally. This is especially important for
prototype and NPI builds, as such projects are more prone to modification
requirements.
Check
Accessibility After Final Assembly
Judging the accessibility cannot only rely on the bare PCB. It
should also be considered in conjunction with the final assembly state of the
product. For example, parts like programming interfaces and connectors, which
seem to have ample operating space in the PCB design software, may be blocked
by heat sinks, enclosures, cables or another circuit board after installation,
making it impossible to operate normally.
Panelization also affects the component placement. If the components
are too close to V-Cuts, broken connection points or routed edges, they are
prone to mechanical stress during splitting. Leaving sufficient spacing in
these areas in advance can better protect the components and solder joints.
In simple terms, PCB component placement not only needs to make the
circuit board easy to assemble, but also needs to make subsequent testing,
inspection, debugging and maintenance more convenient.
Conclusion
A proper PCB component placement aims not to make the layout look
neater, but to facilitate the smooth progress of the design into the
manufacturing, assembly and testing stages. Many problems that only surface
later can actually be identified and adjusted during the placement stage.
This is why in actual projects, PCB layout rules should not only be
limited to the CAD design level, but also need to be checked in conjunction
with the actual production capacity. PCBasic can conduct DFM reviews for
component spacing, board edge areas, welding methods, test points and
manufacturability according to PCB manufacturing and PCBA assembly requirements
before the project goes into production, and provide services such as PCB manufacturing,
component procurement, SMT/DIP assembly, AOI, X-ray, flying probe testing and
functional testing.
If your design is ready complete, you can submit your Gerber files,
BOM and assembly files to PCBasic, allowing the PCBasic engineering team to
help check potential manufacturing and assembly issues before production.
FAQs
Q1: What does what is PCB place mean?
A1: The search phrase what is PCB place generally refers to what PCB
placement is. In PCB design, placement means arranging component footprints on
the board before detailed routing so that electrical, mechanical, and
manufacturing requirements can be met.
Q2: Which components should be placed first on a PCB?
A2: Start PCB component placement with mechanically constrained
parts such as connectors, switches, mounting holes, antennas, and external
interfaces. Then establish functional zones and position major ICs, power
devices, and other critical components before general passive parts.
Q3: How does component placement affect PCB routing?
A3: Good component placement can shorten critical connections,
reduce routing crossings and unnecessary vias, simplify differential-pair and
power routing, and provide more direct signal paths. Poor placement often
forces traces to take longer and more complicated routes.
